cxEPA
United States
Environmental Protection
Agency
EPA542-B-93-012
November 1993
Solid Waste and Emergency Response (5102W)
Innovative Site
Remediation
Technology
Soil Washing/Soil Flushirfg
Volume 3
"til Floor
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INNOVATIVE SITE
REMEDIATION TECHNOLOGY
SOIL WASHING/
SOIL FLUSHING
One of an Eight-Volume Series
Edited by
William C. Anderson, P.E., DEE
Executive Director, American Academy of Environmental Engineers
1993
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:
American Society of
Civil Engineers
345 East 47th Street
New York, NY 10017
Air & Waste Management
Association
P.O. Box 2861
Pittsburgh, PA 15230
American Academy of
Environmental Engineers®
130 Holiday Court, Suite 100
Annapolis, MD 21401
American Institute of
Chemical Engineers
345 East 47th Street
New York, NY 10017
Hazardous Waste Action
Coalition
1015 15th Street, N.W., Suite 802
Washington, D.C. 20005
'Water Environment
Federation
601 Wythe Street
Alexandria, VA 22314
Published under license from the American Academy of Environmental
Engineers®. © Copyright 1993 by the American Academy of Environmental
Engineers®.
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Library of Congress Cataloging-in-Publication Data
Innovative site remediation technology/ edited by William C. Anderson
p. cm.
Includes bibliographic references.
Contents: - [3] Soil washing/soil flushing
- [6] Themal desorption.
1. Soil remediation. I. Anderson, William, C., 1943-
II. American Academy of Environmental Engineers.
TD878.I55 1993 628.5'5--dc20 93-20786
ISBN 1-883767-03-2 (v. 3)
ISBN 1-883767-06-7 (v. 6)
Copyright 1993 by American Academy of Environmental Engineers. All Rights 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 information
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 Environ-
mental Engineers nor any such associated organization or author shall be responsible
for any errors, omissions, or damages arising out of use of this information
Book design by Lori Imhoff
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.
-------
f-
CONTRIBUTORS
This monograph was prepared under the supervision of the WASTECH® Steering
Committee. The manuscript for the monograph was written by a task group of experts
in soil washing/soil flushing and was, in turn, subjected to two peer reviews. One
review was conducted under the auspices of the Steering Committee and the second by
professional and technical organizations having substantial interest in the subject.
PRINCIPAL AUTHORS
Michael J. Mann P.E., Task Group Chair
President
Alternative Remedial Technologies, Inc.
Donald Dahlstrom, Ph.D. Greg Peterson, P.E.
Department of Chemical Engineering Director of Technology Transfer
University of Utah CH2M Hill
Patricia Esposito, M.S. Richard P. Traver, P.E.
General Manager, Environmental Health Program Director
and Safety BergmannUSA
PAK/TEEM,Inc.
Lome G. Everett, Ph.D.
Chief Research Hydrologist
Geraghty & Miller
In addition, the following made substantial contributions as authors and reviewers
of the material addressing soil flushing:
Sarah L. Kimball, Ph.D. Shao-Chih (Ted) Way, Ph.D.
Department of Civil Engineering President
The Water Quality Research Laboratory In-Situ, Inc.
Oklahoma State University
Chester R. McKee, Ph.D. David L. Whitman, Ph.D., P.E.
Chairman of the Board College of Engineering
In-Situ, Inc. University of Wyoming
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REVIEWERS
The panel that reviewed the monograph under the auspices of the Project Steering
Committee was composed of:
Timothy B. Holbrook, P.E., Chair Khalique Kahn
District Engineering Manager Sverdmp Corporation
Groundwater Technology, Inc.
Dale Pflug
Paul Becker Argonne National Laboratory
Exxon Research and Engineering
Company Mike Skriba, P.E.
Technical Director
Gwen Dukes Fluor Daniel Environmental
Exxon Research and Engineering Services, Inc.
Company
David Williams, Ph.D.
Stephen Fink CIBA-GEIGY
Sverdrup Corporation
Richard Griffiths
U.S. Environmental Protection Agency
iv
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STEERING COMMITTEE
Frederick G. Pohland, Ph.D., P.E., DEE
Chair
Weidlein Professor of Environmental
Engineering
University of Pittsburgh
William C. Anderson, P.E., DEE
Project Manager
Executive Director
American Academy of Environmental
Engineers
Paul L. Busch, Ph.D., P.E., DEE
President and CEO
Malcolm Pirnie, Inc.
Representing, American Academy of
Environmental Engineers
Richard A. Conway, P.E., DEE
Senior Corporate Fellow
Union Carbide Corporation
Chair, Environmental Engineering
Committee
EPA Science Advisory Board
Timothy B. Holbrook, P.E.
District Engineering Manager
Groundwater Technology
Representing, Air and Waste Management
Association
Walter W. Kovalick, Jr., Ph.D.
Director, Technology Innovation Office
Office of Solid Waste and Emergency
Response
U.S. Environmental Protection Agency
Joseph F. Lagnese, Jr., P.E., DEE
Private Consultant
Representing, Water Environment Federation
Peter B. Lederman, Ph.D., P.E., DEE, P.P.
Center for Env. Engineering & Science
New Jersey Institute of Technology
Representing, American Institute of
Chemical Engineers
Raymond C. Loehr, Ph.D., P.E., DEE
H.M. Alharthy Centennial Chair and
Professor
Civil Engineering Department
University of Texas
James A. Marsh
Office of Assistant Secretary of Defense
for Environmental Technology
Timothy Oppelt, Ph.D.
Director, Risk Reduction Engineering
Laboratory
U.S. Environmental Protection Agency
George Pierce, Ph.D.
Editor in Chief
Journal of Microbiology
Manager, Bioremediation Technology Dev.
American Cy anamid Company
Representing the Society of Industrial
Microbiology
H. Gerard Schwartz, Jr., Ph.D., P.E.
Senior Vice President
Sverdrup
Representing, American Society of Civil
Engineers
Claire H. Sink
Acting Director
Division of Technical Innovation
Office of Technical Integration
Environmental Education Development
U.S. Department of Energy
Peter W. Tunnicliffe, P.E., DEE
Senior Vice President
Camp Dresser & McKee, Incorporated
Representing, Hazardous Waste Action
Coalition
Charles O. Velzy, P.E., DEE
Private Consultant
Representing, American Society of
Mechanical Engineers
William A. Wallace
Vice President, Hazardous Waste
Management
CH2M Hill
Representing, Hazardous Waste Action
Coalition
Walter J. Weber, Jr., Ph.D., P.E., DEE
Earnest Boyce Distinguished Professor
University of Michigan
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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 organization 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 Associa-
tion provides a neutral forum where all
viewpoints of an environmental manage-
ment issue (technical, scientific, eco-
nomic, social, political, and public health)
receive equal consideration.
This worldwide network represents
many disciplines: physical and social
sciences, health and medicine, engineer-
ing, law, and management. The Associa-
tion serves its membership by promoting
environmental responsibility and
providing technical and managerial
leadership in the fields of air and waste
management. Dedication to these
objectives enables the Association to
work towards its goal: a cleaner environ-
ment.
Qualified reviewers were recruited
from the Technical Council Committee,
Waste Division. It was determined that
the monograph is technically sound and
publication is endorsed.
The reviewers were:
James R. Donnelly
Director of Environmental Services and
Technologies
Davy Environmental
Felix Flechas, P.E.
Environmental Engineer
U.S. Environmental Protection Agency
William Kemner*
Vice President of Corporate
Development
Environmental Quality Management
Jennifer Uhland, P.E.
Project Engineer
CH2MHill
* A&WMA lead reviewer
American Institute of Chemical
Engineers
The Environmental Division of the
American Institute of Chemical Engineers
has enlisted its members to review the
monograph. Based on that review the
Environmental Division endorses the
publication of the monograph.
American Society of Civil
Engineers
Qualified reviewers were recruited
from the Environmental Engineering
Division of ASCE and formed a Subcom-
mittee on WASTECH®. The members of
the Subcommittee have reviewed the
monograph and have determined that it is
acceptable for publication.
Hazardous Waste Action
Coalition
The Hazardous Waste Action Coali-
tion (HWAC) is an association dedicated
to promoting an understanding of the
vi
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state of the hazardous waste practice and
related business issues. Our member
firms are engineering and science firms
that employ nearly 75,000 of this
country's engineers, scientists, geologists,
hydrogeologists, lexicologists, chemists,
biologists, and others who solve hazard-
ous waste problems as a professional
service. HWAC is pleased to endorse the
monograph as technically sound.
The reviewers were:
James D. Knauss, Ph.D.*
Hatcher-Sayre, Incorporated
*HWAC lead reviewer
Water Environment
Federation
The Water Environment Federation is
a nonprofit, educational organization
composed of member and affiliated asso-
ciations throughout the world. Since
1928, the Federation has represented
water quality specialists including engi-
neers, scientists, government officials,
industrial and municipal treatment plant
operators, chemists, students, academics,
equipment manufacturers, and distribu-
tors.
Qualified reviewers were recruited
from the Federation's Industrial, Ground-
water, and Hazardous Wastes Commit-
tees as well as from the general member-
ship. It has been determined that the
document is technically sound and publi-
cation is endorsed.
The reviewers were:
Richard A. Bell, P.E.
Manager, Environmental Projects
TRW, Incorporated
Larry J.DeFluri*
Project Manager/Environmental
Engineer
R.E. Wright Associates, Inc.
Michael R. Foresman
Director, Remedial Projects
Monsanto Company
Walter F.Hansen
Project Manager/Air Quality Engineer
R.E. Wright Associates, Inc.
W. Michael Joyce
Director of Engineering Sales
R.E. Wright Associates, Inc.
Murali Kalavapudi
Senior Engironmental Engineer
ENERGETICS, Incorporated
Robert N. Kenney
Division Manager, Environmental &
Construction Administration
Jordan, Jones, & Goulding
Say Kee Ong
Professor
Polytechnic University
Charles D. Sweeny, Ph.D.
President
CDS Labs, Inc.
* WEF lead reviewer
VII
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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 professionals
and substantial effort in coordinating meetings, facilitating communications, and
editing and preparing multiple drafts was made possible by a dedicated staff
provided by the American Academy of Environmental Engineers® consisting of:
Paul F.Peters
Assistant Project Manager & Managing Editor
Susan C. Richards
Project Staff Assistant
J. Sammi Olmo
Project Administrative Manager
Yolanda Y. Moulden
Staff Assistant
I. Patricia Violette
Staff Assistant
viii
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TABLE OF CONTENTS
Contributors iii
Acknowledgments viii
List of Tables xiv
List of Figures xvi
1.0 INTRODUCTION 1.1
1.1 Soil Washing 1.1
1.2 Soil Flushing 1.2
1.3 Development of the Monograph 1.2
1.3.1 Background 1.2
1.3.2 Process 1.3
1.4 Purpose 1.4
1.5 Objectives 1.5
1.6 Scope 1.5
1.7 Limitations 1.6
1.8 Organization 1.6
2.0 PROCESS SUMMARY 2.1
2.1 Soil Washing 2.1
2.1.1 Process Identification and Description 2.1
2.1.2 Potential Applications 2.2
2.1.3 Process Evaluation 2.3
2.1.4 Limitations 2.5
ix
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Table of Contents
2.1.5 Comparative Cost Data 2.5
2.1.6 Technology Prognosis 2.6
2.2 Soil Hushing 2.6
2.2.1 Process Identification and Description 2.6
2.2.2 Potential Applications 2.7
2.2.3 Process Evaluation 2.8
2.2.4 Limitations 2.8
2.2.5 Comparative Cost Data 2.9
2.2.6 Technology Prognosis 2.10
3.0 PROCESS IDENTIFICATION AND DESCRIPTION 3.1
3.1 Soil Washing 3.1
3.1.1 Description 3.1
3.1.2 Soil Washing Systems 3.5
3.1.2.1 Pretreatment 3.6
3.1.2.2 Separation 3.6
3.1.2.3 Coarse-Grained Treatment 3.7
3.1.2.4 Fine-Grained Treatment 3.7
3.1.2.5 Process Water Treatment 3.8
3.1.2.6 Residuals Management 3.9
3.1.3 Scientific Basis 3.10
3.1.4 Design Data and Equipment Sizing 3.13
3.1.4.1 Bench-scale Treatability Data 3.14
3.1.4.2 Pilot-scale Treatability Data 3.16
3.1.4.3 Full-scale Plant Size or Capacity 3.17
3.1.5 Pre- and Posttreatment Requirements 3.18
3.1.5.1 Fugitive Dust and Volatile Organic Contaminant
Emission Control 3.19
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Table of Contents
3.1.5.2 Debris Washing 3.21
3.1.6 Operational Requirements 3.22
3.1.6.1 Site Infrastructure Requirements 3.22
3.1.6.2 Scale-up of the Soil Washing Process 3.22
3.1.6.3 Manpower Requirements 3.23
3.1.6.4 Materials Handling Requirements 3.23
3.1.7 Unique Planning and Management Needs 3.24
3.1.8 Comparative Cost Data 3.24
3.1.9 Special Health and Safety Requirements 3.25
3.1.10 Technology Variations 3.26
3.1.11 Status of Development 3.35
3.2 Soil Flushing 3.35
3.2.1 Process Description 3.40
3.2.1.1 Soil Rushing Solutions 3.40
3.2.1.2 Dissolution Reactions 3.40
3.2.1.3 Transport Mechanisms 3.42
3.2.1.4 Passive Hydraulic Methods 3.42
3.2.1.5 Soil Flushing Component Activities 3.44
3.2.1.5.1 Site Characterization 3.44
3.2.1.5.2 Injection 3.47
3.2.1.5.3 Contaminant Mobilization and
Recovery Techniques 3.47
3.2.1.6 Measuring Effectiveness 3.53
3.2.2 Status of Development 3.53
3.2.3 Design Data and Unit Sizing 3.54
3.2.4 Pre- and Posttreatment Requirements 3.55
3.2.5 Operational Requirements and Considerations 3.55
xi
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Table of Contents
3.2.6 Unique Planning and Management Needs 3.56
3.2.7 Cost Data 3.56
3.2.8 Special Health and Safety Requirements 3.57
3.2.9 Technology Variations 3.57
3.2.10 Summary of Good Practice 3.57
4.0 POTENTIAL APPLICATIONS 4.1
4.1 Soil Washing 4.1
4.1.1 Site Characterization 4.1
4.1.2 Bench- and Pilot-Scale Testing 4.2
4.1.3 Potential Applications 4.3
4.1.4 Application at Superfund and European Sites 4.7
4.2 Soil Flushing 4.13
4.2.1 General 4.13
4.2.2 Soil Flushing (Enhanced Oil Recovery (EOR)) 4.14
4.2.2.1 Gas Processes 4.15
4.2.2.2 Chemical Processes 4.15
4.2.2.3 Thermal Processes 4.16
5.0 PROCESS EVALUATION 5.1
5.1 Soil Washing 5.1
5.1.1 Process Performance 5.1
5.1.2 Range of Costs 5.4
5.1.3 Key Operational Considerations 5.4
5.2 Soil Flushing 5.5
5.2.1 Process Performance 5.5
5.2.2 Process Byproducts 5.6
5.2.3 Range of Costs 5.6
xii
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Table of Contents
6.0 LIMITATIONS 6.1
6.1 Soil Washing 6.1
6.1.1 Process Limitations 6.1
6.1.2 Reliability of Performance 6.2
6.1.3 Site Considerations 6.3
6.1.4 Waste Matrix 6.3
6.1.5 Risk Considerations 6.3
6.1.6 Process Needs 6.3
6.2 Soil Flushing 6.4
6.2.1 General 6.4
6.2.2 Reliability of Performance 6.5
6.2.3 Site Considerations 6.5
6.2.4 Waste Matrix 6.8
6.2.5 Risk Considerations 6.9
6.2.6 Process Needs 6.10
7.0 TECHNOLOGY PROGNOSIS 7.1
7.1 Soil Washing 7.1
7.1.1 Further Treatment of Fines 7.1
7.1.2 Fixed Plant Operations 7.2
7.2 Soil Flushing 7.2
Appendices
A. List Of Vendors and Contacts A. 1
B. Soil Washing Case Histories B. 1
C. Guide for Conducting Treatability Studies Under CERCLA:
Soil Washing C.I
D. List of References D.I
E. Suggested Reading List E.I
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LIST OF TABLES
Table Title Page
3.1 Treatment trains of innovative treatment technologies
selected for remedial/removal sites 3.20
3.2 Major cost components of a full-scale soil washing
operation 3.25
3.3 Worksheet for evaluating the feasibility of soil flushing 3.45
3.4 Summary of screening criteria for enhanced recovery
methods 3.52
3.5 Comparative summary 3.53
4.1 Applicability of soil washing to general contaminant
groups for various soils 4.5
4.2 Waste soil characterization parameters 4.6
4.3 Superfund project status summary, April, 1992 4.8
4.4 Remedial/removal Superfund sites using soil washing
as a part of a treatment train (April 1992) 4.8
4.5 Detailed site information on soil washing applications
at U.S. Superfund sites 4.9
4.6 Evaluation of existing soil washing technologies (1989) 4.12
4.7 In situ soil flushing target contamination table 4.14
5.1 Example of potential cost savings of soil washing 5.3
5.2 Typical cost comparison for a cleanup project 5.3
5.3 Soil washing comparative cost data 5.5
5.4 Optimum conditions for in situ surfactant-enhanced
soil flushing 5.7
xiv
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List of Tables
Table Title Page
5.5 Modeled example site parameters and values 5.8
5.6 Cost evaluation breakdown for in situ surfactant flushing
of one acre example site 5.9
B. 1 Treatment standards for the Bruni soil washing project B.9
B .2 Delivery sequence and volumes B. 14
B.3 Soil washing solutions B.15
xv
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LIST OF FIGURES
Figure Title Page
3.1 Soil washing diagram 3.3
3.2 Basic soil washing flow diagram 3.4
3.3 Aqueous soil washing process 3.5
3.4 Basic sample composite: particle size distribution 3.11
3.5 Basic sample composite: concentrations vs. particle size 3.12
3.6 Flow schematic of the Haubauer soil washing installation:
chemical extraction/soil washing 3.27
3.7 Schematic of the EPA mobile soil washing system: chemical
extraction/soil washing 3.28
3.8 Waste-Tech Services, Inc., soil washing plant flow sheet 3.30
3.9 Generalized flowsheet and material balance for 50 TPD soil
washing plant 3.31
3.10 Process scheme of the Heijmans Milieutechniek installation:
chemical extraction/soil washing 3.33
3.11 DeconterraR process flow sheet 3.34
3.12 Schematic of in situ flushing field test system 3.36
3.13 Soil flushing sprinkler system of the Poly-Carb Site, Wells,
Nevada 3.37
3.14 Site cross section and idealized conceptual model 3.38
3.15 Example of soil flushing injection scheme 3.39
3.16 Typical drain system 3.44
3.17 Site characterization soil flushing activities 3.46
3.18 Proposed groundwater flow model area: Union Pacific
Railroad Sludge Pit NPL site 3.48
xvi
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List of Figures
Figure Title Page
3.19 In situ flushing target contaminants through fiscal year 1991 3.54
4.1 Soil washing applicable particle size range 4.4
5.1 Processed materials distribution 5.2
6.1 Moisture retention curves — three soil types 6.7
6.2 Variation of porosity, specific yield, and specific retention
with grain size 6.8
6.3 Relationship of pressure potential to relative permeability to
water 6.9
6.4 Bench-scale flushing apparatus 6.10
6.5 Bench-scale soil flushing study: actual and simulated
trichloroethene vs. pore volume 6.11
7.1 Cross-sectional and three dimensional conceptualizations of
capture zone vs. cone of depression 7.4
7.2 Contaminant increases after remediation stops 7.5
7.3 Permeability variations limit remediations 7.5
xvii
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Chapter 1
1
"*
INTRODUCTION
This monograph on soil washing and soil flushing is one of a series of eight
on innovative site and waste remediation technologies that are the culmination
of a multiorganization effort involving more than 100 experts over a two-year
period. It provides the experienced, practicing professional guidance on the
application of innovative processes considered ready for full-scale application.
Other monographs in this series address bioremediation, chemical treatment,
solvent/chemical extraction, stabilization/solidification, thermal desorption,
thermal destruction, and vacuum vapor extraction.
7.7 Soil Washing
Soil washing is an ex situ, water-based process that employs chemical and
physical extraction and separation processes to remove organic, inorganic, and
radioactive contaminants from soil. It is usually employed as a pretreatment
process in the reduction of the volume of feedstock for other remediation pro-
cesses.
The contaminated soil is excavated and staged, pretreated to remove over-
sized material, and washed with water and, possibly, other cleaning agents to
separate and segregate the contaminants. The process recovers a clean soil
fraction and concentrates the contaminants in another soil portion.
The principal advantage of soil washing lies in its ability to concentrate con-
taminants in a residual soil as a pretreatment step, facilitating the application of
other remediation processes. In reducing the volume of soil that must be
treated, soil washing can reduce the overall cost. Soil washing performance is
highly sensitive to site conditions. The process is most effective when applied
to soils and sediments containing large proportions of sand and gravel and is
relatively ineffective when applied to soils having a high silt and clay content.
1.1
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Introduction
7.2 Soil Flushing
Soil flushing is the enhanced in situ mobilization of contaminants in a con-
taminated soil for the purpose of their recovery and treatment. Soil flushing
uses water, enhanced water, or gaseous mixtures to accelerate one or more of
the same geochemical dissolution reactions that alter contaminant concentra-
tions in groundwater systems. The process accelerates a number of subsurface
contaminant transport mechanisms that are found in conventional groundwater
pumping.
In general, soil flushing is most effective in homogeneous, permeable soils,
such as, sands or certain silty sands. The process may be effective also in the
recovery of mobile degradation products formed after soil treatment with
chemical oxidizing agents and in the enhancement of oil recovery operations.
Effective application of the process requires a sound understanding of the man-
ner in which target contaminants are bound to soils and of hydrogeologic trans-
port. Depending on the matrix, organic, inorganic, and radioactive contami-
nants are amenable to soil flushing.
7.3 Development of the Monograph
1.3.1 Background
Acting upon its commitment to develop innovative treatment technologies
for the remediation of hazardous waste sites and contaminated soils and ground
water, the U.S. Environmental Protection Agency (EPA) established the Tech-
nology 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 Advi-
sory Council on Environmental Policy and Technology (NACEPT), convened a
workshop for representatives of consulting engineering firms, professional
societies, research organizations, and state agencies involved in remediation.
The workshop focused on defining the barriers that were impeding the applica-
tion of innovative technologies in site remediation projects. One of the major
1.2
-------
Chapter 1
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 Acad-
emy of Environmental Engineers®. The Academy is a long-standing,
multidisciplinary environmental engineering professional society with wide-
ranging affiliations with the remediation and waste treatment professional com-
munities. By June 1991, an agreement in principle (later formalized as a Coop-
erative Agreement) was reached. The Academy would manage a project to
develop monographs describing the state of available innovative remediation
technologies. Financial support would be provided by the EPA, U.S. Depart-
ment of Defense (DOD), U.S. Department of Energy (DOE), and the Academy.
The goal of both TIO and the Academy was 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
multiorganization 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 Co-
alition, the Society for Industrial Microbiology, and the Water Environment
Federation, together with the Academy, 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 process 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 monograph began in earnest in January, 1992.
1.3.2 Process
The Steering Committee decided upon the technologies, or technological
areas, to be covered by each monograph, the monographs' general scope, and
the process for their development and appointed a task group composed of five
or more experts to write a manuscript for each monograph. The task groups
were appointed with a view to balancing the interests of the groups principally
concerned with the application of innovative site and waste remediation tech-
nologies — industry, consulting engineers, research, academe, and government
1.3
-------
Introduction
(see page iii for a listing of members of the Soil Washing/Soil Flushing Task
Group).
The Steering Committee called upon the task groups to examine and analyze
all pertinent information available, within the Project's financial and time con-
straints. This included, but was not limited to, the comprehensive data on
remediation technologies compiled by EPA, the store of information possessed
by the task groups' members, that of other experts willing to voluntarily contrib-
ute their knowledge, and information 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 conducted
by the Steering Committee itself, employing panels consisting of two members
of the Committee supplemented by at least four 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 organiza-
tions represented in the Project reviewed those monographs addressing tech-
nologies in which it has substantial interest and competence. Aided by a Sym-
posium sponsored by the Academy in October 1992, persons having interest in
the technologies were encouraged to participate in the organizations' review.
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 Purpose
The purpose of this monograph is to further the use of innovative soil wash-
ing/soil flushing site remediation and waste processing technologies, that is,
technologies 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 the art of soil washing and soil flushing
technologies.
1.4
-------
Chapter 1
7.5 Objectives
The monograph's principal objective is to furnish guidance for experienced,
practicing professionals and users' project managers. The monograph is in-
tended, 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 person-
nel and the public about the conditions under which the processes it addresses
are potentially applicable.
7.6 Scope
The monograph addresses soil washing and soil flushing, technologies that
are not yet conventional, that is, not commonly applied, but that have been
sufficiently developed so that they can be used in full-scale applications. It
addresses all aspects of the technologies for which sufficient data were avail-
able to the Soil Washing/Soil Flushing Task Group to describe and explain the
technologies and assess their effectiveness, limitations, and potential applica-
tions. Laboratory- and pilot-scale studies were addressed, as appropriate.
Application of site remediation and waste treatment technology is site spe-
cific and involves consideration of a number of matters besides alternative
technologies. Among them are the following that are addressed only to the
extent essential to understand the applications and limitations of the technolo-
gies described:
• site investigations and assessments;
• planning, management, specifications, and procurement;
• regulatory requirements; and
• community acceptance of the technology.
1.5
-------
Introduction
7.7 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 spe-
cific application.
Readers are cautioned that the information presented is that which was gen-
erally available during the period when the monograph was prepared. Develop-
ment of innovative site remediation and waste treatment technologies is ongo-
ing. Accordingly, postpublication 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 stan-
dard of any of the organizations associated with the WASTECH®Project; nor
does reference hi this publication to any specific method, product, process, or
service constitute or imply an endorsement, recommendation, or warranty
thereof.
1.8 Organization
This monograph and others in the series are organized under a uniform out-
line intended to facilitate cross reference among them and comparison of the
technologies they address. Chapter 2.0, Process Summary, provides an over-
view of all material presented. Chapter 3.0, Process Identification, provides
comprehensive information on the processes addressed. Each process is fully
analyzed in turn. The analysis includes a description of the process (what it does
and how it does it), its scientific basis, status of development, environmental
effects, pre- and posttreatment requirements, health and safety considerations,
design data, operational considerations; and comparative cost data to the extent
available. Also addressed are process unique planning and management re-
quirements and process variations.
Chapter 4.0, Potential Applications, Chapter 5.0, Process Evaluation, and
Chapter 6.0, Limitations, provide a synthesis of available information and in-
formed judgments on the processes. Each of these chapters addresses the pro-
1.6
-------
Chapter 1
cesses in the same order as they are described in Chapter 3.0. Chapter 7.0,
Technology Prognosis, identifies elements of the processes that require further
research and demonstration before full-scale application can be considered.
1.7
-------
-------
Chapter 2
PROCESS SUMMARY1
2.1 Soil Washing
2.1.1 Process Identification and Description
Soil washing is an ex situ process employing chemical and physical extrac-
tion and separation techniques to remove a broad range of organic, inorganic,
and radioactive contaminants from soils. The process entails excavation of the
contaminated soil, mechanical screening to remove various oversize materials,
separation processes to generate coarse- and fine-grained fractions, treatment of
those fractions (soil washing), and management of the generated residuals. It is
a separation and volume reduction process, typically used in conjunction with
other technologies. By concentrating the contaminants in a smaller volume for
further treatment, it enables more overall cost-effective treatment.
Surficial contaminants are removed through abrasive scouring and scrubbing
action in a step using a washwater that is sometimes augmented by surfactants
or other agents. The soil is then separated from the spent washing fluid, which
carries with it some of the contaminants. The recovered soils consist of a clean,
coarse fraction, sands and gravels (>230 mesh or >63 microns (urn)), a con-
taminated fine fraction, silts and clays (<230 mesh or <63 urn), and a contami-
nated organic/humic fraction. The contaminated fines typically carry the bulk
of the chemical contaminants and generally require further treatment using
another remediation process, such as, thermal destruction^.thermaLdesorption,
or bioremediation.
1. This chapter is a summary of Chapters 3.0 through 7.0. Sources are cited, where appro-
priate, in those chapters — Ed.
2.1
-------
Process Summary
2.1.2 Potential Applications
Soil washing may be used to treat soils containing a wide variety of organic,
inorganic, and radioactive contaminants, including:
• petroleum and fuel residues;
• radionuclides;
• heavy metals;
• polychlorinatedbiphenyls(PCBs);
• pentachlorophenol (PCP);
• pesticides;
• cyanides;
• creosote;
• semivolatiles; and
• volatiles.
Soil washing is most appropriate for treating noncomplex soils that contain
at least 50% sand and gravel, such as, coastal sandy soils and soils with glacial
deposits and is relatively ineffective in treating soils that are rich in clay and silt
sized particles. Further, soils with a relatively high cation exchange capacity
(the capacity to exchange cations for those in the polluting substance) tend to
bind pollutants more tightly, which can limit the ability of the soil washing
process to effectively separate the pollutant from the soil.
Studies have shown that soils contaminated with fuel oil, jet fuel, and waste
oil from underground tank system releases can be effectively treated by soil
washing. According to Superfund Innovative Technology Evaluation (SITE)
Program reports, removal efficiencies for residual metals and hydrocarbons of
90 to 98% have been achieved when heat and surfactants are added to the
washwater. Although studies have shown that soil washing can be effective in
removing gasoline and diesel fuels from soils, thermal desorption, biodegrada-
tion, vapor extraction, or other processes may be more effective and appropri-
ate.
Soil washing can be used to remove volatile organic compounds (VOCs) and
other materials having a relatively high vapor pressure or water solubility quo-
tient. Removals of 90 to 99% or more of VOCs can be achieved by simple
water washing. Removal rates for semivolatile organic materials tend to be
2.2
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Chapter 2
lower, on the order of 40 to 90%, and the addition of surfactants to the
washwater is often required to aid in the washing and/or separation.
Removal of metals and pesticides, which tend to be less soluble in water,
often requires the addition of acids or chelating agents. Table 4.1 (on page 4.5)
shows the general effectiveness of soil washing in removing various types of
chemical groups.
Site characterization is the first and most important step in determining
whether soil washing may be effectively applied. Removal efficiencies are
highly dependent on the specific blend of physical and chemical characteristics
of the soil and the contaminants and on the spatial distribution of pollutants
throughout the soil. Among the extensive data required for site characterization
are the site geology and hydrogeology, soil type and composition versus depth,
soil chemistry, and variability of contaminants in the soil. It is important to
know how soil type and contaminant concentrations change with latitude and
depth in order to develop an accurate profile of the feedstock soil and to guide
sampling efforts in collecting representative soils for further characterization
and for bench and pilot testing. Table 4.2 (on page 4.6) summarizes key soil
parameters that should be measured.
Bench- and pilot-scale tests should be conducted on representative contami-
nated soil samples to determine whether soil washing can be used to effectively
remove the contaminants and determine the requirements for soil feedstock
preparation. In addition, these tests provide the bases for gauging the perfor-
mance capabilities of commercially available systems at the particular site.
2.1.3 Process Evaluation
Full-scale projects are now being implemented in the U.S., primarily using
applications already proven in Europe. Several variations have been tested in
the SITE Program. The project reports are cited and the contractors are identi-
fied in this monograph. In 1989, the United States Environmental Protection
Agency (US EPA) funded an evaluation of existing soil washing configura-
tions. The summary of the report of the evaluation is included here as table 4.6
(on page 4.12).
Soil washing has been selected for remedial application at 23 Comprehen-
sive Environmental Response, Compensation, and Liability Act (CERCLA)
(Superfund) National Priorities List (NPL) sites and one other, lower priority
CERCLA site. None of these applications involve the separation and recovery
2.3
-------
Process Summary
of volatile contaminants, but, instead, will involve the treatment of soils for
semivolatile, polynuclear aromatic hydrocarbon (PAH), dioxin, pesticide, and
heavy metal contamination. The average amount of soil to be washed at these
sites is nearly 34,000 m3 (44,000 yd3), ranging from 1,400 to 150,000 m3 (1,800
to 200,000 yd3).
The selection of a soil washing system usually depends upon the quality of
the oversize materials, coarse-grained materials, fine-grained fraction contain-
ing the concentrated contaminants, and other residuals produced. In most ap-
plications, the principal objective is to meet treatment standards for the oversize
materials and coarse fraction so that they may be placed back on site. The ma-
jor measure of effectiveness, therefore, is the ability to meet specified standards
for the residuals that are targeted for placement back on site.
Soil washing performance is closely tied to two key physical soil characteris-
tics evaluated during site characterization — particle size distribution and cation
exchange capacity — which should be carefully evaluated in light of the overall
site geology and the vertical and horizontal extent of the chemical contamina-
tion. Many contaminants tend to bind to the fine particle (silts and clays) frac-
tion of the soil and will be separated from the clean soil during the washing
process to much the same extent as the fines are separated from the coarse
(sands and gravels) fraction.
When used as a pretreatment step for other remediation processes, soil wash-
ing presents two key advantages. The first is its ability to substantially contrib-
ute to waste minimization, that is, concentrating a large proportion of the non-
volatile and heavy metal contaminants into a residual soil product representing
less than half the original soil volume. The washed soil product may be suitable
for redepositing on site or other beneficial uses. The second advantage lies in
its potential cost-effectiveness. Lower remediation costs result for many sites
through the reduction of sheer volume of contaminated soil that must be treated
by more expensive methods.
Soil washing is a relatively low-cost alternative for separating wastes. The
soil washing system can be operated as a closed treatment system permitting
control of fugitive dusts and volatile emissions, an asset in securing public ac-
ceptance.
Compared with thermal processes, soil washing has a broad range of accept-
able influent concentrations. But the range can be exceeded by a broadly diver-
gent or heterogeneous feed stream, a risk that can be reduced through proper
attention to treatability studies and pilot tests.
2.4
-------
Chapter 2
2.1.4 Limitations
The waste matrix may pose the most significant limitation. Complex mix-
tures of contaminants make it difficult to formulate a single suitable washing
fluid and may require sequential washing steps with different additives. Fur-
ther, frequent changes in the contaminants and their concentrations in the feed
soil can disrupt the process requiring modification of the wash fluid formula-
tion and the operating settings.
Soil washing will usually not be cost-effective in treating soils having a high
percentage of clay and silt (e.g., more than 30 to 50%); high humic content in
the soil makes separation of contaminants very difficult. It may be relatively
ineffective in treating soils contaminated with a high concentration of mineral-
ized metals or hydrophobic organics. Hydrophobic contaminants can be diffi-
cult to separate from soil particles into the aqueous washing fluid.
Certain chelating agents, surfactants, and other additives may be hazardous
and are often difficult and expensive to recover from the spent washing fluid.
Further, some of these additives may be retained in the contaminated soil and
treatment sludge residuals and may cause added difficulty in residuals manage-
ment.
The main risk in soil washing operations is that of inaccurate site character-
ization. The material encountered during site remediation may not be like the
soils studied in treatability or pilot scale tests.
Also, site conditions may impose limitations. For example, a source of pro-
cess water is required, commercial electrical power is normally required (al-
though mobile generators may be used), permits for wastewater discharges
must be obtained, land use must be approved, and, in remote areas, a roadway
may have to be constructed to provide access.
2.1.5 Comparative Cost Data
A clear understanding of the site is essential to developing costs that may be
used in comparing soil washing with other technologies. Table 5.3 (on page
5.5) provides a detailed listing of components for use in estimating costs. Be-
cause no hazardous waste sites in the U.S. have been treated using soil washing,
cost information must be based upon the literature and information provided by
vendors. Based upon projects in the range of 23,000 to 180,000 tonne (25,000
to 200,000 ton), the estimated treatment price, including disposal of sludges and
2.5
-------
Process Summary
all known cost components, is in the range of $170 to $280/tonne ($150 to
$250/ton).
2.1.6 Technology Prognosis
Continuing process development will focus on additional treatment of the
fine-grained fractions, potentially decreasing the residual material that must be
disposed of off site and reducing unit treatment prices. Work is underway on
bioslurry reactors for use in further degrading the organic constituents in the
fines and on developing extraction and recovery techniques to remove
inorganics. Improved extraction and recovery may result in recovered contami-
nants with market value.
Although soil washing will undoubtedly continue to be offered in mobile
configurations, the European experience has clearly demonstrated that fixed-
based plants are more efficient. The key barrier that will need to be addressed
in order to realize effective fixed-based plants is the ultimate disposal of residu-
als that are generated from the fixed plant, particularly, the clean products.
22 Soil Flushing
2.2.1 Process Identification and Description
Soil flushing is an in situ process that uses water, enhanced water, or gaseous
mixtures to accelerate the mobilization of contaminants from a contaminated
soil for recovery and treatment. The process accelerates one or more of the
same geochemical dissolution reactions, such as, adsorption/desorption, acid/
base reactions, and biodegradation, that alter contaminant concentrations in
groundwater systems. In addition, soil flushing accelerates a number of subsur-
face contaminant transport mechanisms, such as, advection and molecular dif-
fusion, that are found in conventional groundwater pumping.
Soil flushing can be broken down into three separate activities — site char-
acterization, fluid injection, and contaminant mobilization and recovery tech-
niques. Site characterization requires a field understanding of hydrogeology,
geochemistry, and the relative permeability and lithology above, within, and
below the zone of contamination.
2.6
-------
Chapter 2
The fluids used can be applied or drawn from groundwater and can be intro-
duced to the soil through surface flooding or sprinklers, subsurface leach fields,
and other means. When the contaminants have been flushed, the contaminated
fluids can be removed either from a perched condition, from a groundwater
system, or, depending upon the contaminants and the fluids used, can be left in
place.
Soil flushing techniques used to mobilize contaminants are classified as
conventional and unconventional. Conventional techniques are further classi-
fied as:
• natural restoration;
• well and capture methods in the vadose zone; and
• pump-and-treat systems in the saturated zone.
Unconventional techniques consist of primary, secondary, and tertiary recov-
ery techniques. Primary recovery encompasses, among other methods, neutral
water drive and gravity drainage; secondary recovery involves waterflooding
and pressure maintenance methods; and tertiary recovery consists of gaseous
and chemical processes and thermal methods.
2.2.2 Potential Applications
In situ soil flushing should be considered for applications involving petro-
leum hydrocarbons, chlorinated hydrocarbons, metals, salts, pesticides, herbi-
cides, and radioisotopes. Many industrial sites throughout the U.S. have chlori-
nated hydrocarbons in the subsurface, and since excavation and other existing
remediation strategies require access, in situ soil flushing offers clear advan-
tages. Other advantages include no soil replacement and/or disposal costs,
minimal disruption of the ecosystem, cost advantages at greater depths, and
minimized worker exposure to contaminants.
In general, soil flushing is most effective in homogeneous permeable soils.
Soil flushing may also be appropriate for the recovery of mobile degradation
products formed after soil treatment with chemical oxidizing agents, and en-
hancement of oil recovery operations.
Adaptation of Enhanced Oil Recovery (EOR) and in situ mining techniques
provide the potential for substantially increasing the rate of waste extraction
and, thereby, lowering costs. In general, EOR techniques involve the injection
2.7
-------
Process Summary
of materials that are not normally found in the soil in order to facilitate the re-
moval of hydrocarbon type wastes.
2.2.3 Process Evaluation
Bench scale tests of soil flushing have been very successful, but field appli-
cation has not shown the same success, because of reduced permeability by
plugging and biofouling. Field operations may be subject also to flow instabili-
ties resulting in finger type flow of the flushing fluid and failing to reduce the
contamination between the fingers.
Large variations of removal efficiencies in the field are attributable more to
site hydrology than to the contaminants. The vadose zone is poorly understood
by most investigators, as is the relationship between capillary pressure, water
content, and permeability. Since the success rate under laboratory conditions is
high and that in the field is not, it appears that a better understanding of the
vadose zone is required to successfully implement soil flushing.
2.2.4 Limitations
The generation of large quantities of contaminated elutriate, the recovered
mixture of water, surfactants, and contaminants, can pose a limitation. On-site
treatment may have to be devised if access to compatible wastewater treatment
facilities is not available.
A variety of site conditions can limit the use of soil flushing:
• Soils with pockets of low hydraulic conductivity may limit effec-
tiveness;
• Pipes and underground utilities may limit effectiveness of flushing
underground storage tank sites;
• Soil flushing will be less effective where the contaminants are rela-
tively insoluble or tightly bound to the soil; and
• The lack of an adequate supply of process water.
There may be limitations in the use and effectiveness of surfactants. Hard
water may render a surfactant ineffective, soil of high clay content can cause
chemical adsorption of the surfactant to the soil, and, in some situations, a sur-
factant may biodegrade too quickly. High rates of surfactant consumption raise
the cost of soil flushing.
2.8
-------
Chapter 2
There is a limitation in treating contaminated soils located in the vadose
zone. Soil retention capacities must be satisfied before contaminants will be
transmitted through the vadose zone.
Nonhomogeneous subsurface conditions, nonuniform distribution of con-
taminants, or a nonaqueous phase liquid (NAPL), will cause channeling and
uneven treatment. It may be difficult to determine whether the flushing solution
has contacted the waste material and whether cleanup objectives can be
achieved within estimated flushing water volumes. Quite often, NAPLs accu-
mulate in layers in the form of either light nonaqueous phase liquids (LNAPLs)
or dense nonaqueous phase liquids (DNAPLs), and often must be removed
before appreciable soil flushing of soluble contaminants can be accomplished.
The solubilization of product into the groundwater will otherwise continue as a
source for quite some time. Heterogeneities in natural geological materials
make the prediction and detection of contaminant behavior in groundwater
difficult in practice.
Pump-and-treat programs have been unable to bring the concentration levels
down to required levels because of problems related to nonideal aquifer condi-
tions such as heterogeneity, anisotropy, and variable density. In addition,
pump-and-treat programs suffer from well construction effects, vandalism,
operational failures, and other problems.
State regulations may require vadose zone monitoring, contending that sol-
ute transport models in the vadose zone are not reliable. Site characterization in
the vadose zone is a complex problem, and only a few companies specialize in
vadose zone investigations. Little is known about predicting dispersion in frac-
tured media. The dispersion of solutes during transport through many types of
fractured rocks differs from that described for transport through homogeneous
granular materials.
2.2.5 Comparative Cost Data
Section 5.2.3 presents the results of two extensive cost comparisons covering
water flooding and subsurface injection techniques. The best-case scenario
study uses the equilibrium solubility model for surface flooding and results in a
cost estimate of $61.16/m3 ($80/yd3). The worst-case scenario study uses the
two component equilibrium model for subsurface injection and results in a cost
estimate of $126.15/m3($165/yd3).
2.9
-------
Process Summary
Capital and operating costs are similar for traditional pump-and-treat and
chemically-enhanced solubilization processes. Estimates are compared in Sec-
tion 5.2.3. The cost of in situ flushing is considerably less than that of other
remediation processes, which can range as high as $765 to $l,530/m3 ($1,000
to$2,000/yd3).
2.2.6 Technology Prognosis
Additional investigation is required of several factors, such as, soil or water
incompatibility, permeability reductions, and flushing chemical retention in the
subsurface, although recent development of a "supersurfactant" decreases the
concerns about soil or water incompatibility and permeability reductions to
some degree. The issues of chemical retention in the vadose and saturated
zones must be addressed. For pump-and-treat systems to be more effective, the
following areas need more study and improvement:
• hydraulically containing fluids as they are flushed from the system;
• treating the contamination at the surface; and
• eliminating the hydraulic isolation (dead spots) that occurs within
well fields.
Although soil flushing will remove the source of contamination in the va-
dose zone, it must also remove contaminants which have diffused into low
permeability sediments. In addition, it must be able to desorb contaminants
from sediment surfaces and cause liquid-liquid partitioning of immiscible con-
taminants in order to mobilize the pollutants of concern.
2.10
-------
Chapters
PROCESS IDENTIFICATION AND
DESCRIPTION
3.1 Soil Washing
3.1.1 Description
Soil washing is a relatively new, commercially proven (since 1982) method
for treating excavated soil and dredged sediments that are contaminated with
toxic or other hazardous pollutants. It involves the application of a set of estab-
lished engineering principles, unit processes, and equipment that have been
used for years in the mining, mineral processing and ore benefaction, and
wastewater treatment industries.
As considered here, soil washing is an ex situ, water-based process that relies
on traditional chemical and physical extraction and separation processes for
removing a broad range of organic, inorganic, and radioactive contaminants
from soil. Following are typical hazardous contaminant groups that can be
effectively removed by soil washing:
• petroleum and fuel residues;
• radionuclides;
• heavy metals;
• polychlorinatedbiphenyls(PCBs);
• pentachlorophenol (PCP);
• pesticides;
3.1
-------
Process Identification and Description
• cyanides;
• creosote;
• semivolatiles; and
• volatiles.
Whether soil washing should be applied depends upon three key, individual
site characteristics — the soil's mix of contaminants, particle size distribution,
and specific gravity. For example, it can generally be said that the higher the
percentage of sand and gravel in the soil or sediment, the more effective is soil
washing. Soil washing can be a very cost-effective, stand-alone soil treatment
process and, in addition, can be used as a volume reduction and feedstock
preparation step for other more complex soil-treatment technologies. In both
cases, residuals from the treatment process must be anticipated and properly
managed.
Most commercially available soil washing systems utilize mechanical
screening devices to remove oversize material, separation systems to generate
coarse- and fine-grained fractions, treatment units for washing, systems for
scrubbing the separated fractions, equipment for rinsing and dewatering, and
water treatment and recycling systems for water management. The specifica-
tions for each system are largely driven by individual site characteristics.
Soil washing involves the use of wet, mechanical scrubbing and screening
processes to separate particles that contain contaminants from those that do not.
In this sense, it is a volume reduction or pretreatment technology. It exploits
the tendency of contaminants to adhere to the organic matter (leaves, roots, and
twigs) and the fine-grained soil fraction (silt and clay), rather than the coarse-
grained mineral fraction (sand and gravel). In addition, or, in some cases, alter-
natively, contaminants may be removed from the soil as a result of being solu-
bilized in the washwater.
Simply stated, soil washing entails the following steps:
• excavation and staging of contaminated soil or sediment;
• pretreatment of the soil to remove large objects and oversized clods
and material;
• washing the soil with water to separate and segregate the contami-
nants; and
3.2
-------
Chapters
• recovering a clean soil fraction that can be redeposited on site or
otherwise beneficially used.
The process frees contaminants and concentrates them in a residual portion
of the soil (typically 5 to 40% of the original soil, by volume), where they can
be subsequently treated by other remediation techniques. The washwater is
treated by conventional wastewater treatment techniques and then recycled.
Figures 3.1 and 3.2 (on page 3.4) are basic soil washing flow diagrams.
Figure 3.1
Soil Washing Diagram
Soils containing organic?
and/or inorganics
\%ter and extraction agents
Clean soil
Sludge/contaminated fines
Wastewater
Possible fugitive air
emisions
i Separation and volume reduction
I Residuals require subsequent treatment
The soil washing process begins with the excavation and preparation of the
feedstock soil. Soil preparation can involve the mechanical screening of the
feedstock to remove rocks, debris, and other oversized material. Most soil
washing systems cannot accept feed materials that are larger than 50 mm (2 in.)
in diameter.
In the second stage, the contaminants are separated and concentrated. This is
accomplished primarily through active mixing of the soil with water or an
amended water-based washing fluid, separation of the soil from the spent fluid,
and recovery of the soil in two distinct fractions. One is a relatively high-vol-
ume, coarse sand and gravel fraction (>230 mesh or >63 micron (|am)) that is
clean and suitable for use as on-site fill, and the other is usually a smaller-vol-
ume, fine silt and clay fraction (<230 mesh or <63 um) that typically carries the
bulk of the chemical contaminants. A third fraction, contaminated, naturally
occuring organic material, may be separated from the coarse soil fraction by
specific gravity separation.
3.3
-------
Process Identification and Description
Figure 3.2
Basic Soil Washing Flow Diagram
Materials
Characterization handling^
V-
Excavat
>
)
t
Process
treatme
and rec]
Pretreatment
^^^ Excavated
^~ soil pile ^»w«
edarea j
Oven
mater
^ Return to excavated area ^
f
^
sized
al
1
— >
(
water
,-cle
* t
1 H Fii
S
E
P
A
R
A
T
I
O
N
1
Dff site
disposal as
olid waste
\ .
t
i
\es f
k
Froth
>
— >. Co
k
arse
1
Clean soil
fraction
>.
i
1
Contaminants
and sludge
1
Further treatment
& disposal
Soil returned to site of origin
v JJurfidaljcQiitamination that is attached to sand and gravel fractions through
forces of adhesion and compaction is removed from the coarse fraction by abra-
sive scouring or scrubbing action. This washing step is sometimes augmented
by adding to the washwater a basic leaching agent, surfactant, pH adjustment,
or chelating agent (such as ethylene diamine tetra-acetic acid (EDTA)) to help
remove organics or heavy metals. After washing, the coarse soil fraction may
be rewashed to further remove residual contaminants and washwater additives.
The spent washwater and rinsewater are treated to remove the contaminants
prior to recycling back to the treatment unit. Fines and wastewater treatment
solids are handled separately.
Figure 3.3 (on page 3.5) illustrates a very simplified soil washing process.
3.4
-------
Chapters
Figure 3.3
Aqueous Soil Washing Process
Source US EPA 1990
3.1.2 Soil Washing Systems
Soil washing systems usually consist of the following six distinct pi
its:
irocess
units:
1. pretreatment;
2. separation;
3. coarse-grained treatment;
4. fine-grained treatment;
5. process water treatment; and
6. residuals management.
3.5
-------
Process Identification and Description
The most commonly used equipment is discussed in the following subsec-
tions. Undoubtedly, other kinds of equipment may be employed in soil wash-
ing and new kinds of equipment will be developed as improvements over the
years.
3.1.2.1 Pretreatment
Pretreatment is performed to remove grossly oversized material and to pre-
pare a homogeneous feed stream of reasonable size for delivery to the soil
washing plant. Unit processes that may be employed are scalping, crushing and
grinding, mechanical screening, jigging and tabling (specific gravity separa-
tion), blending and mixing, and magnetic material removal.
Grossly oversized material can be anything from solid construction debris
and waste down to pea gravel-size material (approximately 50 mm (2 in.) in
diameter). It is usually material that is not grossly contaminated, does not re-
quire treatment by another method, or that can be reclaimed as a by-product
(metals, wood, etc.). Scalping, mechanical screening, and jigging and tabling
are examples of processes that can make the initial separation. Crushing and
grinding (reduction to natural grain size) may be necessary to liberate contami-
nated particle surfaces in order to successfully wash this fraction. Blending and
mixing can reduce large variations in the size and contaminant distribution in
the feed stream so as to provide products of more consistent quality.
3.1.2.2 Separation
Separation systems are designed to make a precise first cut at the selected
interface of coarse- and fine-grained solids. The most common cut point is
usually between 63 and 74 microns (230 and 200 mesh). The two fractions
above and below the cut point generally require different treatment methods for
final cleaning. In addition, the coarser solids will be separated through use of
conventional techniques (usually hydrocyclones), while the finer solids must be
settled by various methods. Thus, two streams will issue from this basic separa-
tion step and go on to separate processes. It is important that a relatively clear
break be made within the critical particle size range. Hydrocyclones are almost
always employed to make the first size separation, although mechanical screens
are sometimes used where contaminant-specific requirements apply. This is
screening primarily at a larger particle size, such as 500 microns (28 mesh
Tyler) or larger. There is difficulty screening at finer sizes.
3.6
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Chapters
There will be some fine-grained solids that carry over into the coarse fraction
with the washwater accompanying the coarse fraction. The fine-grained solids
accompanying the coarse fraction will be in the same proportion as the
washwater applied to the coarse fraction. Accordingly, the washwater from the
coarse fraction processing will have to be recycled to the fine-grained solids
treatment to recover the fine-grained solids.
Another separating device often employed is the upflow classifier, some-
times called a hydrosizer. It is used primarily to remove organic material, such
as, roots, leaves, twigs, wood chips, coal, and other light debris. Separation is
effected by forcing water upward through a relatively fluid bed, separating the
materials through specific gravity difference and upward velocity currents.
Spiral concentrators can be employed to separate either lighter or heavier mate-
rials from the sand grains.
3.1,2.3 Coarse-Grained Treatment
After the separation step, there will be a small amount of material finer than
63 to 74 microns (230 to 200 mesh), but it should constitute less than 5% of the
total solids by weight. In addition, some fine-size particles will probably be
found in the water removed in dewatering the coarse-grained fraction. Addi-
tional cycloning follows and then, this water should be sent to the fine-grained
treatment process for recovery of these solids.
The contaminants of interest will be found predominantly in the finer solids,
but the coarse fraction may also require treatment to remove any polluting ma-
terial that is adsorbed on or coats the solids. Several debris washing methods,
for example, surface attrition, acid or base treatment for solubilization, or spe-
cific solvents for dissolving the contaminants, can be employed to release the
pollutant from the solids into the liquid fraction. The solids can then be sepa-
rated further and sent either to the fine-grained treatment or to the water treat-
ment process for removal of the target contaminants.
The removal of contaminants from the sand-like particles can be effected by
two methods, attrition scrubbing or flotation. Sand dewatering methods are
important because they also remove contaminants trapped in the washwater.
This washwater must be appropriately processed for destruction of pollutants.
3.1.2.4 Fine-Grained Treatment
At the beginning of fine-grained treatment, this fraction is now finer than 63
and 74 microns (230 and 200 mesh) and typically consists of an appreciable
3.7
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Process Identification and Description
proportion of solids in the colloidal range 6 to 10 um. In addition, the solids
concentration, coming primarily from the cyclone overflow in the separation
step, will be relatively dilute, as low as 5 to 10% solids by weight. These solids
will settle slowly, and some will not settle at all because of their clay and colloi-
dal nature. The separation and concentration of the contaminated fines fraction
is necessary before the selection of an appropriate residuals management strat-
egy. Fine-grained treatment precedes the residuals management step, whose
strategy depends upon the nature and concentration of contaminants, cleanup
standards, economics, etc. Residuals management is discussed in Subsection
3.1.2.6.
3.1.2.5 Process Water Treatment
Contaminated washwater may result from the soil washing process. This
washwater will contain some or all of the following materials and contami-
nants:
• Some coarse-grained sands, particularly from 360 jam (40 mesh)
down to >63 um (230 mesh). There may be little or no contami-
nants attached to these solids.
• Fine-grained solids <63 |jm (<230 mesh) — these solids will still
contain attached contaminants and colloidal silt and clay material;
• Dissolved salts that are present in the original soil, probably mostly
sodium and chlorine-containing compounds. There must be enough
bleed-out of the water to prevent an excessive buildup. Depending
on the type of dissolved salts, this water may be discharged to a
municipal sewer in accordance with local requirements;
• Organic humic compounds (leaves, twigs, roots, etc.) that must be
removed to acceptable levels;
• A pH value that may have to be changed to a desirable range either
for recycle or disposal;
• Dissolved or solubilized heavy metals requiring treatment and re-
moval; and
• Other contaminants, such as, free-floating petroleum hydrocarbons
requiring removal.
The washwater must be treated either for recycling back to the process or for
disposal. Water to be recycled usually does not need to be of the quality that
3.8
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Chapters
must be produced for discharge to sewers or water courses. Therefore, it is
always cheaper to reuse the water as long as there is not a deleterious effect on
the soil washing treatment processes.
The washwater to be disposed of either in a city sewer or a water course
must meet regulatory discharge limits, such as:
• pH range, e.g., 6 to 9;
• total dissolved solids, in addition, there may be maximum limits for
particular ions or compounds;
• biochemical oxygen demand (BOD) and chemical oxygen demand
(COD);
• oil and grease content, both dissolved and undissolved;
• suspended solids content; and
• other hazardous or toxic waste limits.
If any of the above effluent discharge criteria cannot be met, the washwater
will have to be manifested as an industrial or hazardous waste and discharged at
an appropriate waste treatment and disposal center.
It is emphasized that the water can always be recycled back to the appropri-
ate processing step for additional treatment. Factors that caused inefficient
treatment may be correctable resulting in water of disposable quality.
Depending upon the washwater's composition, various steps are employed in
process water treatment. The more common are:
• neutralization;
• carbon treatment;
• ion exchange;
• flocculation;
• sedimentation and thickening;
• dewatering; and
• volatile organics stripping.
3.1.2.6 Residuals Management
The quantities of products and residual materials generated by a soil washing
plant will vary directly in proportion to the grain-size distribution of primary
3.9
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Process Identification and Description
feed material to be processed. The quantities of these streams can be rapidly
estimated by bench-scale wet sieve analysis and elutriation (upflow classifica-
tion).
^^Contaminated fines and sludges resulting from the process may be disposed
of in a regulated landfill and/or require further treatment through one or a com-
bination of the following treatment technologies in order to permit disposal in
an environmentally safe and acceptable manner: incineration; low temperature
thermal desorption; chemical extraction/dechlorination; bioremediation; solidi-
fication/stabilization; or vitrification.
There are a number of residual technology vendors that can provide informa-
tion and costs associated with the above systems. The JJS.EPA Vendor Infor-
mation System for Innovative Treatment Technologies (VISITT) data base
provides information about vendors (US EPA 1992c). See also the Soil Wash-
ing Vendors List in Appendix A.
The contaminated feed material usually will require removal of the organic
vegetative material (leaves, twigs, roots, grass, etc.), through specific gravity
separation. This material, although a relatively small portion of the contami-
nated feed material, will partition the greatest quantity of contaminants because
of its highly porous nature and carbon-based adsorptive characteristics.
3.1.3 Scientific Basis
A normally distributed soil consists of oversize material (gravels and
cobbles), coarse-grained particles (sands), and fine-grained particles (clays and
silts). The first step in soil washing is to acquire an understanding of the par-
ticle size distribution (see figure 3.4 on page 3.11) of the soil to be washed and,
by analyzing the retained fractions, characterize the soil matrix-contaminant
relationship. It is very common to find the majority of the contaminants "resid-
ing" in the fines, as indicated in figure 3.5 (on page 3.12). This often results
from the complex chemical and electrical forces in the lattice of fines. Addi-
tionally, contaminants tend to weather in soils and sediments. Weathering
occurs through physical degradation, oxidation or reduction, hydrolysis,
dehydrohalogenation, biological decay, and radioactive decay. Over time, they
become tightly bound through physical or chemical forces to the organic matter
(roots, leaves, peat, humus, and other naturally-occurring organic material) and
to the fine-grained mineral particles (i.e., fine sand, silt, and clay fractions) in
the soil. Such weathering has been observed repeatedly in soils contaminated
3.10
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Chapters
Figure 3.4
Basic Sample Composite: Particle Size Distribution
10000- 4000- 2000- 1000- 500- 250-
40000 10000 4000 2000 1000 500
Fraction size (microns)
with heavy metals, organic solvents, petroleum products, dioxins, PCBs, and
several pesticides.
Clay, silt, and colloidal particles, those having a size of less than 63 microns
(passing 230 mesh), tend to be loosely attached to the larger, coarse sand and
gravel particles by physical forces, primarily adhesion and compaction. Physi-
cal washing or attrition scrubbing of the contaminated soil with water will ef-
fectively break the physical forces of compaction and adhesion, separating the
organic material and fine sand, silt, and clay particles from the coarse sand and
3.11
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Process Identification and Description
Figure 3.5
Basic Sample Composite: Concentrations vs. Particle Size
10000-
9000-
8000-
N 7000-
Ł 6000-
:
> 5000-t-
! 4000-
I
3000-
2000 H-
1000- -
0-
il
I40000'l0000? 4000-' 200CK 1000-' 500-^^250- ' 125- 63- ' 38-63 20-381 <20^
40000 10000 4000 2000 1000 500 250 125
Fraction size (microns)
Cu, cone. D Ni, cone. D Cr, cone.
gravel particles. Separation techniques based on particle size and specific grav-
ity can be used to effectively collect and segregate the fine soil fractions from
the coarse fractions.
Soil contaminants will be collected and concentrated in the fine sand, silt,
colloidal, and organic material. They will be segregated from the coarse sand
and gravel to the same extent that the fine sand, silt, humus, and clay are sepa-
rated and segregated from the coarse material. Increasing the efficiency of the
washing process will directly increase the separation and segregation efficiency
for the majority of the contaminant mix.
Soil composition is a key factor governing the performance of soil washing.
Mineral silts and clays are the principal hosts for adsorption of hazardous con-
3.12
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Chapter 3
taminants because of their relatively high surface area-to-volume ratio and their
strong cohesive properties. Roots, leaves, peat, humus, and other naturally-
occurring organic matter also have a high affinity for many contaminants due to
their carbonaceous makeup and porous structure. Experience has shown that
the cost of soil washing is roughly inversely proportional to the overall silt,
clay, and organic content of the soil. Generally, soils that tend to be lower in
organic matter and clay or silt content tend to respond better to soil washing.
3.1.4 Design Data and Equipment Sizing
Each contaminated site presents unique characteristics. The quantity and
quality of the contaminants of interest and their relationship with the mineral-
ogy of the soil or sediment require each site to be evaluated individually for the
optimum combination of washwater additives necessary to solubilize, mobilize,
precipitate, and complex, the organic and/or inorganic chemical constituents.
In order to properly design a full-scale (>9 tonne/hr (>10 ton/hr)) soils and
sediment washing plant, information is required to assess the applicability of
this volumetric reduction technology. To determine initial data requirements
the following questions should be answered:
a. What quantity of material is to be processed on site ?
In general, a site should have a minimum of 4,500 tonne (5,000 ton)
of contaminated feed material to justify equipment mobilization and
demobilization, and site preparation costs;
b. Is the material to be processed by soils and sediment washing ap-
propriate for volumetric reduction and waste minimization?
Approximately 70% of the particle size matrix of the candidate soil
and sediment material should be >74 um (>200 mesh). This break
is at the fines/sand definition, at which point the washing technol-
ogy can effectively concentrate the contaminants of interest into the
fine silt, clay, and colloidal fractions;
c. What is the contaminant of interest (or generic group, that is, poly-
nuclear aromatic hydrocarbons (PNAs), reactive sulfides, cyanides,
PCBs, etc.) and what is the target and regulatory cleanup standard
(value) for the process for treatment of the cleanable coarse frac-
tion?
3.13
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Process Identification and Description
Target values vary widely, from EPA region-to-region and state-to-
state regulatory agency, even for the same target contaminant.
Many hazardous waste site remedial Record of Decisions (RODs)
are now being determined on a health risk analyses basis or on the
demonstrated removal efficiency of the best demonstrated available
technology (BOAT); and
d. What is the ultimate objective of the management of the concen-
trated fines that the soils and sediment washing technology will
produce?
The contaminants will generally partition to the silt, clay, and col-
loidal fractions of the contaminated matrix because of these par-
ticles' very high cation exchange capacities that will tend to com-
plex the contaminant into the fine material. The relatively high
surface areas of fine particles present excellent hosts for contami-
nant absorption. These fines must be subsequently managed by
another remediation process or processes, each of which has vary-
ing feedstock requirements as to, for example, maximum particle
size and, particularly, moisture content of the enriched fines. The
selection of the residual management technology, or technologies,
will affect the design and configuration of the front-end soils and
sediment plant. Dependent upon the specific residuals management
technology, fines are either thickened to approximately 35% solids
for heavy metal extraction or bioslurry operations or are dewatered
to approximately 50 to 60% solids by filter press operations.
3.} A. 1 Bench-scale Treatability Data
Bench-scale studies are performed to specifically evaluate and optimize each
of the system's unit operations. The studies also enable determination of where
the primary contaminants will partition according to soil grain-size distribution.
A bench-scale treatability study enables the initial identification of fugitive
emissions that could emanate from a full-scale operation from either volatile
organic contaminants, or unanticipated chemical reactions of washwater addi-
tives and unidentified contaminants within the waste material matrix, or the
mineralogy of the material itself.
Soil and sediment washing typically uses standardized modules that can be
incorporated in or deleted from a full-scale operation, depending upon material
3.14
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Chapters
and contaminant characteristics. Examples of modules that are interchangeable
within the basic system configuration and their functions are:
• Dual Step Grizzly Bar Screen — classification, separation and
removal of >50 mm (>2 in.) oversized debris from raw feed;
• Tramp Metal Separator — removal of ferrous tramp iron and steel
from >9.52 mm (>0.375 in.) feed material;
• Rotary Trommel Screen — system utilized for initial breakup and
deagglomeration of lumpy contaminated soil fractions. Primary
feed is approximately 50 mm (2 in.) with screened coarse product
fractions occurring at >9.52 mm (>0.375 in.);
• Oil and Grease Separation System — concentration and removal of
light and heavy hydrocarbon oil products from wastewater system
for separate concentration and disposal;
• Attrition Scrubbing Module — a high-energy unit processing sys-
tem that contacts <9.52 mm (<0.375 in.) contaminated material
with chemical wash additives to effectively solubilize appropriate
contaminants and to "deslime" or mobilize the highly contaminated
fines (<74 urn (<200 mesh)) material. The attrition cells function at
a 50 to 65% solids content;
• Dense Media Separator Module — separation and removal of veg-
etative and marine organic materials (leaves, twigs, roots, wood
chips, plants, shells, etc.) based upon specific gravities;
• Cyclone Separator Unit — a high efficiency, solids and liquid sepa-
ration device utilized for desliming <74 um (<200 mesh) clay silt
and colloidal material from coarse (sand and gravel) soils fractions.
The unit operates with no internal moving parts on the basis of the
differing specific gravities of light and heavy media. For a coarse
sand underflow, it delivers approximately 70 to 75% solids, regard-
less of influent solids loading concentrations;
• Reverse Slope Dewatering Module — a high-frequency mineral
screen assembly specifically designed for final rinsing, dewatering,
desliming, and removal of very fine material from mineral slurries.
Each unit utilizes snap-in, modular screen deck panels and replace-
able, bolt-in, side liner plates;
3.15
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Process Identification and Description
• Washwater Clarifier Treatment Module — a compact water-treat-
ment system specifically designed for flocculation and sedimenta-
tion and gravity separation of fine (<74 um (<200 mesh)) contami-
nated clay, silt, and colloidal materials. This system utilizes a qui-
escent settling zone for preliminary sludge densification prior to
removal by sludge pumps. The unit incorporates a pH adjustment
system and polymer mix tank and chemical feed pump for coagula-
tion operations;
• Dissolved Air Flotation Module — for the precipitation, floccula-
tion, and removal of dissolved heavy metal hydroxide and oil frac-
tions from wastewater;
• Sludge Densifier — gravity conditioner to bring residual fine solids
content within sludge to a maximum of 30% to 35% for subsequent
residual management technologies requiring a thickened slurry
feed, such as, biodegradation, chemical extraction, or stabilization/
solidification; and
• Continuous Belt Filter — module for continuous dewatering opera-
tion of mineral (<63 urn (<230 mesh)) sludges and intermittent
metal hydroxide Dissolved Air Flotation scum dewatering. Solids
content of filter cakes will range from 40 to 60% solids.
Bench-scale treatability evaluations are critical not only in identifying appli-
cable chemical additives for wash solutions, but also in identifying which criti-
cal unit process module needs to be included in a full-scale remedial system.
3.1.4.2 Pilot-scale Treatability Data
When a large (>18,000 tonne (>20,000 ton)) site requires additional
treatability evaluation in order to provide more complete engineering design
data because of significant variations in a site's soil matrix composition or con-
taminant partitioning, it may be desirable to employ a pilot treatability system.
This system could be taken to the client's site to evaluate the effect of changes
in soils and washing chemical additives (i.e., surfactants, chelants, etc.). Opera-
tion of such a plant is often permitted under the EPA's small quantity
treatability exemption.
It is estimated the system would enable effective treatment and evaluation of
several tons of material on site. Approximately 90 to 900 tonne (100 to 1,000
ton) of contaminated material should be processed for each heterogeneous soil
type or contaminant group. On-site operation of the pilot plant greatly simpli-
3.16
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Chapters
fies the logistics of securing representative samples of contaminated materials
for feasibility testing, manifesting, and transporting off site and for managing
residuals of treated material following the completion of a field test program.
3.1.4.3 Full-scale Plant Size or Capacity
The specification of plant size or capacity is based upon a combination of the
following factors:
• the physical characteristics of soils to be treated;
• amount of material to be processed;
• the desired separated cut point;
• client's decision whether to have plant operated on an 8,16, or 24
hr/day basis; and
• operational season (whether freezing temperatures are probable).
Whether the operation of the plant be on a one-, two-, or three-shift basis is
generally based upon the client's decision either to expedite the remedial project
or to extend operations over multiple fiscal years in order to have a longer
payout period.
Typical plant operations are based upon two eight-hour shifts accounting for
14 hr/day feed with an hour for start-up and an hour for shutdown each day.
Planned maintenance activities are generally scheduled for Saturdays with in-
terim emergency repairs and part replacements being accomplished as required.
Although there are commercial soil washing plants as small as 1.8 tonne/hr
(2 ton/hr) capacity, an economically and practically sized plant should have a
rated capacity of 23 tonne/hr (25 ton/hr). Soils and sediment washing equip-
ment vendors typically design plants at 23,45, and 90 tonne/hr (25,50, and 100
ton/hr) capacities. The largest commercial sediment washing plant is sized for
318 tonne/hr (350 ton/hr) operations.
A 23 tonne/hr (25 ton/hr) plant with a 14 hour day on-line feed factor will
have an anticipated capacity of 7,940 tonne/month (8,750 ton/month) based
upon a 25 day/month operational period. A 46,000 tonne (50,000 ton) site
would be processed in less than 6 months. A 23 tonne/hr (25 ton/hr) plant re-
quires 3 to 5 operational technicians/shift.
As to the power needed, the typical 23 tonne/hr plant will require 440V, 3
phase and an estimated 775 - 800 hp. A 45 tonne/hr (50 ton/hr) plant will re-
quire 1,000 -1,200 hp.
3.17
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Process Identification and Description
The "footprint" of a typical 23 tonne/hr soils washing plant is approximately
15 x 30 m (50 x 100 ft) for the operational modules; an area of 23 x 45 m (75 x
150 ft) is required for a 45 tonne/hr system. The area required for a complete
soils 23 tonne/hr washing plant encompassing a feeder module, oversized mate-
rial pile, clean soil product bins, and sludge cake lugger boxes is approximately
30 x 60 m (100 x 200 ft); a 45 tonne/hr plant will require approximately 38 x 76
m (125x250 ft).
In 1978, EPA designed and fabricated a Mobile Soil Washing System
(MSWS). This four trailer system consists of: (1) scalping screen and rotary
trommel washing screen, (2) four stage countercurrent froth flotation system,
(3) 120 cm (48 in.) wide plate and frame filter press for dewatering operations,
and (4) physical and chemical treatment system for the recycling of process
washwater. The MSWS has a rated capacity of approximately 3.6 tonne/hr (4
ton/hr), dependent upon the portion of fines in the contaminated feed material.
In order to more rapidly assess the applicability of soil washing at a potential
site while minimizing the expense of mobilization and operation of the 3.6
tonne/hr (4 ton/hr) MSWS, EPA designed and fabricated a 227 kg/hr (500 Ib/hr)
pilot soils washing system, which is self-contained upon two 14 m (45 ft) trail-
ers. This unit is referred to as a Mobile Volume Reduction Unit (MVRU). It is
available for field operational support for Superfund predesign site activities
through the EPA's Risk Reduction Engineering Laboratory (RREL), Edison,
New Jersey. It has been used on a creosote Superfund Site in Pensacola,
Florida.
3.1.5 Pre- and Posttreatment Requirements
Pretreatment requirements for soil washing are dependent upon the amount
and type of oversized debris and moisture in the material. If a site contains
large quantities of oversized (>15 cm (>6 in.)) material, such as, construction
rubble (chunks of concrete, reinforcing bars, asphalt slabs, brick, pipe, etc.) bulk
containers (drums, pails, buckets) or general trash and debris (paper, cardboard,
wire, metal, wood, plastic, tires, etc.) there should be a preprocessing step by
which this material is either screened or scalped out. There are a number of
commercial systems which readily accomplish this task. A major concern dur-
ing the preprocessing step is the control of fugitive dusts and volatile organic
contaminant emissions.
Oversized material may have small-to-significant quantities of contaminated
soils adhering to its surfaces through adhesion or compaction. Most large ob-
3.18
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Chapter 3
jects, such as boulders and refrigerators, can be adequately decontaminated
through high-pressure spraying using water or water with industrial detergents,
steam cleaning, or high-pressure washing, along with the introduction of an
abrasive sand through a process known as hydro-blasting.
Posttreatment requirements generally do not appertain because soil washing
is usually applied in combination with other treatment technologies, either as a
feedstock preparation step or as a subsequent separation technology in a treat-
ment train. Table 3.1 (on page 3.20) shows treatment trains of innovative tech-
nologies that have been selected for remedial sites.
3.1.5.1 Fugitive Dust and Volatile Organic Contaminant Emission
Control
The primary safety concerns in handling contaminated soils and sediments
are two-fold: (1) worker exposure, and (2) downwind, off-site community ex-
posure. Chemical constituents which exhibit moderate to high volatility are of
principal concern. Most of the release of these high-vapor pressure materials
will occur during excavation and removal of the contaminated matrix, prior to
preliminary screening and soil/sediment washing and processing. Volatile
organic compounds must be managed at this stage.
The U.S. EPA has issued a report evaluating numerous techniques for the
control and treatment of fugitive dusts and emissions in the handling and treat-
ment of contaminated soils from Superfund site^ Preliminary wetting or "fog-
ging" of dry contaminated soils during excavation will effectively suppress the
majority of volatile organic chemicals and virtually any associated dusting and
blowing of inorganic fine fractions. Obviously, during dredging operations, the
contaminated sediments are totally saturated, eliminating any possibility of
dusting.
The control, collection, and treatment of fugitive dusts and emissions has
readily been accomplished in full-scale soil and sediment washing through
application of covers and shroud assemblies incorporated into the conveyor,
hopper bin, and tank designs, along with large volume air handling systems,
such as a Calgon Vapor Pack 10 Absorbers containing 5,400 kg (12,000 Ib) of
activated carbon or biofilters. These subcomponents are negatively vented
through the application of explosion-proof, inducted-draft air fans. Any volatile
emissions or nuisance vapors are collected and drawn through granular, vapor
phase, activated carbon packs or canisters. Once the carbon has been exhausted
3.19
-------
Process Identification and Description
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3.20
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Chapters
or experiences "break through", it can be removed from the system for either
on-site or off-site regeneration and then placed back into service.
For extremely toxic or dusty materials (i.e., dioxin, radionuclides) high-
efficiency particulate air (HEPA) systems have been very successful in full-
scale remedial operations.
An alternative method for fugitive volatile emission and dust control is the
erection of a temporary structure over either the excavation site, treatment sys-
tem, or both. The structures can be of either sheet metal, (i.e., Butler Build-
ings), or supported fabric, internal frame design (i.e., Rubb or Sprung Struc-
tures). The structure can be negatively vented through a vapor collection and
treatment system.
Each site must be assessed for the possible deleterious effects of fugitive
vapor and dust emissions. This assessment may indicate the need for a long-
term ambient air monitoring program. This is accomplished through the posi-
tioning of long-term (24 hour) air sampling stations around the site and at the
face of the contaminated soil and sediment excavation. Once adequate data are
obtained, identifying primary volatile chemical constituents and their concentra-
tions, properly-sized vapor and dust emission collection and control systems
can be readily incorporated into the site-specific remedial technology design
and operating procedures.
Semivolatile and nonvolatile organic chemicals (i.e., oils, greases, diesel
fuels) pose little or no environmental or health threat to workers or the off-site
community at large. Because of their inherently low vapor pressure, little to no
volatilization is generally detected. All volatilization rates are temperature
dependent. The colder the ambient operational temperature, the less volatiliza-
tion will occur.
3.1.5.2 Debris Washing
Material between 45 and 15 cm (18 and 6 in.) diameter can be subjected to a
series of high pressure water knives or sprays while being processed upon a
vibratory screen deck. Oversized material, if appropriate, can be returned to a
crusher/shredder for resizing, and subsequent washing.
Debris and oversized material ranging from 5 to 15 cm (2 to 6 in.) diameter
can be processed through a log washer unit for desliming operations. This
heavy-duty equipment employs two counter rotating sets of paddles mounted
on a heavy shaft while the feed material is a submerged section of the unit. As
3.21
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Process Identification and Description
new make-up water is introduced into the unit, the contaminated fines are dis-
charged via an overflow weir assembly for subsequent treatment.
3.1.6 Operational Requirements
3.1.6.1 Site Infrastructure Requirements
Site infrastructure requirements for a soil washing plant operation include,
but are not limited to, all civil engineering works associated with roads, founda-
tions, water, power, and the storage of supplies. An area approximately 13x13
m (42 x 42 ft) is required for a 14 tonne/hr (15 ton/hr) soils washing plant ver-
sus 15 x 30 m (50 x 100 ft) for a 23 tonne/hr (25 ton/hr) plant. It is important to
consider also the staging, prescreening, and blending areas that will be required
for feeding the soils into the plant. These areas can be provided under a flexible
plan of soils management.
3.1.6.2 Scale-up of the Soil Washing Process
Factors such as: (1) waste feedstock preparation, (2) performance capabili-
ties, (3) analytical data, and (4) worker and community health and safety con-
siderations must be taken into consideration when predicting scale-up from the
bench-style testing to pilot-scale testing and to the full-scale soil washing treat-
ment systems.
In scaling up the cost and performance estimates from bench-scale testing to
the full-scale soil washing system, the parameters to be considered are:
a. Performance capabilities of the soil washing process, including
design parameters for:
• soil throughput in dry tons per hour;
• optimum washwater usage in gallons per dry ton of soil; and
• dosages of additives (if any) mixed with the washwater;
b. Nature and form of contaminant concentrations in the fines soil
fraction. Basically, the question is, where do the contaminants
partition within the soils gradation analysis? It is desirable to be
able to estimate the volume and physical and chemical characteris-
tics (i.e., sulfides/sulfates) of this fraction in order to design treat-
ment systems (e.g., dewatering, stabilization, etc.) and estimate
disposal costs;
3.22
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Chapters
c. Identification of contaminants and their concentrations in the spent
washwater. Generally, this water is treated for recycling back into
the washing process. Therefore, treatment will include separation
of the fine soil particles. In addition, other treatment steps may be
necessary to remove organics, inorganics, and additive chemicals.
Scale-up design requires estimates of the process water volume and
quality requirements;
d. Risk analysis evaluation for worker and community protection.
This entails characterizing and quantifying bulk excavated soil
contamination levels pertinent to worker and community protection
during excavation. (Health and Safety Plans (HASPs) and any risk
analysis evaluation being conducted require this information.); and
e. Cost of screening (removing debris, rocks, and other materials) for
bulk soil washing.
3.1.6.3 Manpower Requirements
Operational experience indicates that a 14 tonne/hr (15 ton/hr) and a 23
tonne/hr (25 ton/hr) plant each require three operators, and, therefore, operation
of the 23 tonne/hr plant should maximize revenues. The cost of labor will be
the same as that for a 14 tonne/hr plant, but the capital equipment cost per ton
of processed material will be reduced. Each team should include a supervising
engineer and, for projects of long duration, a part-time administrative assistant.
Depending upon the size and complexity of the soil washing plant operation,
a 45 tonne/hr (50 ton/hr) module designed plant can be erected with four work-
ers and a 20 ton crane in approximately 5 working days. Leak testing of tanks,
pumps and interconnect systems, adjustment of sump level controllers, scale
calibration, feed conveyors, flow balancing, etc., requires approximately 3 tech-
nicians working 5 days.
The design and operation of full-scale soil washing systems is based upon
practices traditionally found in the mining and ore processing industries and
systems utilized in sand and aggregate plants.
3.1.6.4 Materials Handling Requirements
The basic processing equipment is very similar to that of a small mining
operation. It is designed and manufactured for very heavy duty and long ser-
vice. Normal start-up procedures will include water and slurry testing before
3.23
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Process Identification and Description
introduction of contaminated soils. Normal plant start-up problems can be
expected. During steady operations, the crew will be directly involved in daily
controls.
Excavation is required for soil washing, and the wastes must be screened to
break up soil clods to remove rocks, branches, debris and the oversize foreign
material. Large soil clods must be reduced in size by crushing and grinding, if
necessary, to achieve a feed size required by the equipment, normally less than
5 cm (2 in.) top size. The waste material, washwater, and any additives that are
needed will require mixing to ensure adequate separation of the contaminants.
3.1.7 Unique Planning and Management Needs
The following are the three primary planning and management consider-
ations:
• Soils Management — A requisite for effective soil washing is the
proper excavation, preparation, and staging of material to be treated.
Success can depend mainly on whether only soils requiring treat-
ment are fed and whether they are fed in the most balanced quan-
tity;
• Flexibility of the Process — Soil washing is not a fixed process; it
is flexible and can be modified for each unique project. Bench-
scale testing is a good start, but may not clearly identify the actual
forces and capabilities of a continuous process system; and
• Permitting — Major projects will typically be conducted under the
Comprehensive Environmental Response, Compensation, and Li-
ability Act (CERCLA) or the Resource Conservation Recovery Act
(RCRA) regulations. Projects under CERCLA are exempt from
permitting when supported by approvable designs, while RCRA
Corrective Action Program responses may be exempt as a Correc-
tive Action Management Unit (CAMU) action.
3.1.8 Comparative Cost Data
Cost information presented here is based upon the literature and infor-
mation provided by vendors. It is essential to have a clear understanding of the
site in order to develop working cost estimates so that the technology may be
3.24
-------
Chapter 3
compared fairly with other alternatives. The development of the range of costs
should, therefore, include such considerations as:
• capitalized costs of equipment, depreciation, and interest;
• plant operations labor;
• variable costs of operations, including chemicals, safety equipment,
utilities, and process sampling;
• transportation and disposal of residuals requiring management; and
• management costs, including overhead and profit.
A detailed listing of cost components is set forth in table 3.2.
3.1.9 Special Health and Safety Requirements
Although control of fugitive dust and volatile organic contaminant emissions
is a major concern, the incorporation of specifically engineered control systems
Table 3.2
Major Cost Components of a Full-Scale Soil Washing Operation0
1. Soil excavation.
2. Transport of excavated soil to the processing unit.
3. Temporary stockpiling of excavated soil.
4. Prevention of contaminant releases to the environment during Steps 1 through 3 above due to ram,
wind, volatilization, accidental release, etc.
5. Bulk soil pretreatment steps, such as, screening, crushing, and physical/chemical characterization.
6. Management of the screened-out rocks, roots, debris, etc.
7. ^shwater supply facilities, e.g., storage tanks, pumps, piping, controls.
8. Additive (if any) supply facilities, e.g., storage tanks, pumps, piping, controls.
9. The soil washing process system, which may consist of a series of mixers, washers, screens, conveyors,
cyclones, and other units. It is assumed that generally this cost will be obtained from the manufacturer.
10. Temporary stockpiling, transport, and deposition of the adequately clean, washed soil product fraction.
11. The dirty washwater treatment process, which is usually a treatment train that may include clarif iers,
chemical reactors, filters, carbon contactors, dewatering presses, tanks, etc.
12. Recycle or disposal of the treated wastewater fraction.
13. Further treatment and disposal of the dirty soil fraction
14. Further treatment and disposal of the water treatment sludge.
15. Permitting and legal services.
16. Engineering design.
17. Services during construction.
18. Contingencies.
Where applicable, the engineer performing the cost estimate will usually break down the cost estimate
components listed above into:
construction (roads, foundations, buildings, etc);
process equipment (mixers, tanks, screens, pumps, danders, etc);
material handling equipment (power shovel, bulldozer, portable conveyor, trucks, etc.); and
labor (operators, supervisors, analytical, etc.); energy (electrical power, diesel fuel, etc.), utilities (water,
sewage, etc.), materials (chemical additives, spare parts, etc.), and various overhead administrative and
profit items.
3.25
-------
Process Identification and Description
usually is not necessary. This is due to the relatively small concentrations of
contaminants within the material utilized during typical full-scale operations
and the wet environment of a soil washing operation. For hazardous waste-site
operations, all operations personnel must be trained in accordance with Occupa-
tional Safety and Health Administration (OSHA) Instruction 1910.120 (series),
with the normal soil washing plant being operated under a "modified Level D"
protective equipment designation. This requires safety shoes, work coveralls,
possibly Ty vek Splash Coveralls or rainsuits, hard hats, impervious gloves, and
safety glasses or goggles. For dusty operations, or operations with radionu-
clides, such as the contaminated feed end of the plant, full-face, air-purifying
respirators or self-contained breathing apparatus (SCBA) should be employed.
If necessary, personnel must use air-purifying respirators for personal protec-
tion.
3.1.10 Technology Variations
The "soil washing system" is not limited to a fixed arrangement of equip-
ment. There are many variations in soil washing systems, many employing
process units other than those described in Section 3.1.2 above. The process
configuration employed is usually a function of the soil-contaminant relation-
ship and the flexibility desired in the process. Several actual process flow dia-
grams that have been used in the field will be employed here for illustration.
Figure 3.6 (on page 3.27) shows a system used by Harbauer GMBH of Ger-
many. The process involves chemical extraction of the process wastewater.
Blade washers (very high-pressure, wide streams of water), are employed to
blast off contaminants from the sand and gravel fractions. The <200 um (<70
mesh) solids and water are then sent to small diameter cyclones to provide a
0.200 x 0.020 mm fine sand fraction. The <200 um solids' overflow is floccu-
lated and dewatered on a continuous belt filter press. The filtrate or washwater
is subjected to several different steps as required by the contaminants in these
streams. Chemical additions are performed to enhance the precipitation, flota-
tion, or countercurrent stripping steps with an insoluble liquid. Thefjnal waste-
water effluent is passed through sand filtration for complete solids removal and
then through activated carbon for removal of trace organics and color agents.
The treated water is then directed to reuse to close the circuit.
Figure 3.7 (on page 3.28) presents a process flow diagram of a mobile sys-
tem installed on two trucks. The system was developed by the U.S. EPA in
order to test whether clean sand could be produced from contaminated soils
3.26
-------
Chapters
Figure 3.6
Flow Schematic of the Haubauer Soil Washing Installation:
Chemical Extraction/Soil Washing
Metallic
objects
Gravel
^- 10 mm to
60mm
Low frequency
vibration unit
Conditioning r^— NaOH
~T ^~ Surfactants
- -- TOiter addition
Sludge
LJlUUgV
Belt filter press h>-15 urn to
Air
stripping
i>
<-
Count
strippi
Sand
filtration
Solids/slurry
— — — — Liquid
Source: US EPA 1988a
3.27
-------
Process Identification and Description
a>
o
o
D
.o
UJ
0)
?
O
"B
0
3.28
-------
Chapters
through the use of screens and cyclones. Soil is metered to the first screen
where wet screening through spray water addition is performed, allowing un-
dersized solids to pass through the screen as a soil slurry. Oversize solids are
directed to a rotating drum to break any consolidated solids down to true grain
size. This stream is passed to a second screen where clean water is applied and
the oversize material goes as washed solids. The screen undersize, along with
the bulk of the water, is passed back to the first screen as the spray water. Thus,
fine solids are more likely to flow to the contaminated soil slurry.
The fine solids from the first screen underflow are conveyed to the final
stage of a four-stage countercurrent cyclone operation. Fresh water is used as a
repulp fluid for the second stage underflow, which is the feed to the first-stage
cyclone. From this first-stage unit, the resultant clean sand is produced from
the cyclone underflow, while the overflow is the repulp fluid for second stage
feed. Water is moving in a countercurrent fashion to the fine solids coarser than
the desired split size, for example, 63 um (230 mesh). Thus, the most contami-
nated (<63 um) solids and water result from the fourth-stage cyclone overflow.
Three products are produced: sand, fines, and spent washing fluids. The
spent washing fluids should contain the large majority of the very fine particles,
contaminants, and dissolved solids. This disposition permits analysis of the two
sand fractions to ascertain whether they can be disposed as clean products and
whether the spent washing fluids can be treated for contaminant removal. Tests
can be performed at varying water-to-soil ratios to determine optimum operat-
ing parameters.
Another countercurrent operation, conducted with flotation cells, is shown in
figure 3.8 (on page 3.30). Contaminated soil comes from the underflow of the
trash screen and is then contacted with the selected surfactant. The soil solids
move forward from the third (and last) flotation cell as froth product to the
second cell feed and finally as froth product to the first stage cell. All flotation
cells underflows flow in the opposite direction to the froth products. The third
stage underflow is passed to an oil and water separator where the bulk of the
contaminants and the collector reagent issues as an overflow and the underflow
water is returned back to the third stage feed. The fresh collector agent is added
to the first stage feed and flows countercurrent to the soil, the latter appearing as
froth product in each of the three stages.
The first stage froth product goes to a gravity thickener, and the underflow is
considered decontaminated soil. The overflow is then sent to a reverse osmosis
unit so that the resultant water product can be recycled.
3.29
-------
Process Identification and Description
(D
o
CL
D>
r.
o
> '
•g
3
o
B!
""
»*—
\
te\
i \
>«* /
•3 I
Ł
,'S
2S
~l
3.30
-------
Chapters
A countercurrent operation increases the opportunity for recovering clean
soil, while the contaminants are increased in relation to the waste stream. In
addition, water consumption is reduced.
Figure 3.9 is a flow diagram of a typical system using flotation cells to re-
move the contaminants as a froth product in a relatively simple operation. Wa-
ter and reagents are fed with the presized contaminated soil, freeing the target
contaminants, while collectors are added so the contaminants will be captured
in the froth product. The froth product is dewatered in a plate and frame filter
press for final disposal, and recyclable filtrate is produced for process water.
The flotation underflow is flocculated and then acts as feed to a gravity thick-
ener. The underflow is dewatered by a semicontinuous plate and frame filter.
The filter cycle time can range from approximately 5 to 15 minutes and can be
Figure 3.9
Generalized Flowsheet and Material Balance for
50 TPD Soil Washing Plant
Sized
contaminated soil
Reagents
Flocculant
Water bleed
when necessary
Thickner
Sized Contaminated
Soil
50TPD
80% solids
1% organics
40 TPD soil
9.5 TPD water
Overall Material Balance
Froth Solids Clean Dewatered Soil
8.5 TPD
47% solids
5-9% organics
4 TPD soil
4 TPD water
41.5 TPD
86.7% solids
nil organics
36 TPD soil
5.5 TPD water
Semicontinuous
plate and frame
filter
Clean'
dewatered soil
3.31
-------
Process Identification and Description
automatically controlled with a consistent feed. Washwater is used to keep the
filter cloth from binding. The filtrate, along with the thickener overflow, is
returned to the process water tank. A granular activated carbon column is em-
ployed to remove organics and other color agents from any bleed stream used to
control dissolved salts buildup.
This is a good example of a simple process for producing a clean dewatered
soil along with a concentrated contaminant stream. The key to the process is
the kind of reagents that are used in the initial reactor to produce a floatable
contaminant product.
An elaboration of the previous process is presented in figure 3.10 (on page
3.33). Both dry and wet screening are employed to remove the > 5 mm (>0.2
in.) solids. The undersize solids in slurry form are subjected to high-intensity
mixing with appropriate chemical reagents to clean the 5 mm (0.2 in.) by 63 um
(230 mesh) fraction sands. This sand fraction is then separated by
hydrocyclones with the underflow dewatered on screens.
Hydrocyclone overflow is also screened to remove unwanted material, such
as, grass, coke, and other light solids. The screen underflow is flocculated and
passed to a tillable plate separator, which is an adjustable angle lamella clarifier.
The settled solids are <63 um (<230 mesh), and can be treated either as clean
material or as contaminated solids, depending upon their quality.
The clarifier overflow is sent to an oil-contaminated water separator, which
is subjected to coagulation and flocculation and fed to a thickener. The over-
flow from this thickener is sent to a flotation cell. The flotation product and the
underflow from the thickener are sent to individual belt presses for dewatering.
All filtrates and flotation underflow are used as recycled process water for dilu-
tion before being fed to the hydrocyclones.
This kind of process yields a great deal more flexibility (as well as a more
complex operation), while producing a clean sand coarser than 63 um and de-
watered contaminants.
A final flow diagram, of a very complex process for treating highly contami-
nated soils, is presented in figure 3.11 (on page 3.34). After screening to re-
move gross solids, the undersize is sent to an attrition mill for scrubbing of the
solid surfaces. A single- or double-decked screen is applied to the attrition
scrubber discharge. Oversize is sent to a crusher to reduce the particle size and
is then returned to the scrubber.
3.32
-------
Chapters
Figure 3.10
Process Scheme of the Heijmans Milieutechniek Installation:
Chemical Extraction/Soil Washing
extracting chemical
agent , ,
1 i
V V
^ Dry and wet _w. (intensive _
^ sieving devices ^ mixing*
chemical
^ oxidation)
Contaminated Coarse ,
soil materials
Flocculants
Coagulants — ^
Flocculants
precipitants
pH(8.5)
Key
01 „, -urrj
- (Mainly) Liquids
s
. c >r^
; v ^1 H>
i
T
Tillable ~^
plate
separator — ;
i
y
Coagulation
flocculation
1
i
Flotation
drocyclones |— > siev
K Silt (<63um)
>^.
-^- Double Mil
wires
press
1
vatering I
1
Cleai
sand
Double
wires
press
1
1
icral sludge
Sludge
The undersize from the screen is sent to a spiral classifier with spiral product
passed to a second attrition scrubber. The overflow of the spiral classifier (now
the finer sizes) is sent to the hydrocyclones to make a 63 um split. The cyclone
overflow contains the <63 um solids which flow to a lamella clarifier.
The >63 um solids in the hydrocyclone underflow also pass to the second
attrition scrubber, and this product is subjected to flotation. The froth product
contains the contaminants while the flotation underflow contains clean sand
coarser than 63 um. The latter is concentrated in hydrocyclone underflows and
final dewatering is accomplished on a horizontal continuous belt filter. Filtrate
is also sent to the lamella clarifier.
3.33
-------
Process Identification and Description
Figure 3.11
Deconterra" Process Flow Sheet
Contaminated
soil feed
Ion Activated
exchange carbon filter
Contamination
Overflow from the clarifier is process water, while the underflow is further
thickened in a conventional gravity thickener. This overflow also returns to the
process water stream. The .thickened underflow, now containing the contami-
nants, is dewatered on a plate and frame filter press and disposed. The filtrate is
clarified by a sand filter and is then directed to a carbon column and an ion
exchange system for cleaning the process water for recycle.
The second-deck screen oversize is fed to a jig, where applicable, to separate
lesser specific gravity solids from the greater. The light solids jig product is
screened and dewatered and considered contaminated. The heavy solids are
also screen dewatered and are considered clean after confirmatory analysis.
The screened underflow is returned to the lamella clarifier.
The process, while very complex, can produce clean products and isolate the
contaminants into the volume-reduced sludge cake. A bleed stream to control
dissolved salts and contaminant build-up is also included to completely close
the water circuit.
3.34
-------
Chapters
It is emphasized that processes are designed for the specific soil matrix and
contaminant problem being addressed. The range of these technology varia-
tions demonstrates that soil washing is a flexible process incorporating a broad
range of process trains.
3.1.11 Status of Development
At this writing, soil washing had been selected as a remedial source control
technology at 23 Superfund sites, at which full-scale projects are in progress or
have been completed. They include eight wood preserving sites (polynuclear
aromatic hydrocarbons (PAHs)), PCP, and metals), one lead battery recycling
site, three pesticide sites, one site containing volatile organic compounds
(VOCs) and metals, and two containing metals only. Soil washing has been
selected for one emergency response action. It is widely used in Europe, espe-
cially in Germany, the Netherlands, and Belgium.
See also Subsection 3.1.4.3 for a discussion of the Mobile Soil Washing
System (MSWS) and Mobile Volume Reduction Unit (MVRU) designed by
U.S. EPA.
3.2 Soil Flushing
hi situ soil flushing accelerates the in situ mobilization of contaminants from
a contaminated soil for recovery and treatment (see figure 3.12 on page 3.36).
Depending on the matrix, organic, inorganic, and radioactive contaminants are
amenable to soil flushing.
The process uses water, enhanced water, or gaseous mixtures to accelerate
one or more of the same geochemical dissolution reactions that alter contami-
nant concentrations in groundwater systems, such as:
• adsorption/desorption;
• acid/base reactions;
• solution/precipitation reactions;
• oxidation/reduction reactions;
• ion pairing or complexation; and
• biodegradation.
3.35
-------
Process Identification and Description
33
0
•-. c
2
5
o
o
-------
Chapters
In addition, soil flushing accelerates a number of subsurface contaminant
transport mechanisms that are found in conventional groundwater pumping,
including:
• advection;
• dispersion, as expressed by the dispersivity coefficient;
• molecular diffusion; and
• depletion via volatilization or solubilization.
The fluids can be applied and/or drawn from the groundwater in the immedi-
ate area. They can be introduced to the soil either through spraying (see figures
3.13 and 3.14 on page 3.38), surface flooding, subsurface leach fields, or sub-
surface injection (figure 3.15 on page 3.39).
Figure 3.13
Soil Flushing Sprinkler System of the Poly-Carb Site,
Wells, Nevada
• SB
PI
I
i
Particula
Filters
Flov
L = \
SB = S
ST = S
PRC = F
^__ __ Granular ac
F carbon units
ic»y »PRC
oP-
^~O^ 1
e \^
tank/water '
reservoir
Vfell liquid sample
oil backround
oil treatment sample
recarbon water
(
1
I
POC = Postcarbon water
ivated
'ST ^
O
O
O
o
iST °
0
,ST \ S1°I«
° ST.
O
o -^
o
o
° ST I
0
>ya.
Tl
^ .._ ...*1
i
i
i
i
\
/"t^ Vitllno 1
Sprinkler
system
S fivA
Not to scale
•^ft- Wfell no. 2
70 feet
3.37
-------
Process Identification and Description
Figure 3.14
Site Cross Section and Idealized Conceptual Model
Union Pacific Railroad NPL Sludge Pit Pocatello, Idaho
Static Conditions
A EW1
Sludge Pit
4440
t
4420 •
.9
§ 4400-
i 4380-
• 4380 53
Conceptual Model
Extraction Well Excavated Sludge I*
G Sediment Drainage Blanket
y
N
${$& Soil Rushing ZoneT&4>?? >.?<'•. -V
Layer 1 U
^Upper Aquifer) j
aturated
/ / / /
7- •** *• / j
er Aquifer) /
/ / A
Approximate Scale in Feet
Vertical Exaggeration = Sx
Fill
Recent Alluvium
Older Alluvium
Michaud Gravel
American Falls
Lake Beds Clay
Pleistocene
Gravel
Flow Direction
Water Table
EW1 Boring number
Ground surface
^ — Screened interval
Bottom of boring
V T
Explanation:
This cross section is a diagrammatic interpretation of subsurface conditions based on interpolation and extrapolation of
data from bonngs.
Actual conditions are substantially more complex than depicted and will vary between borings.
Source: Applied Geotechnology, Inc. 1990
3.38
-------
Chapters
Figure 3.15
Example of Soil Flushing Injection Scheme
Produced fluids treatment
Reagent
delivery
system
Delivery drain line
Aquitard
Recovery drain lines
Reprinted by permission of the National Water Well Association from 'Chemically Enhanced In Situ Soil Washing* by
T.Sale and M. Pitts in the Proceedings of the Conference on Petroleum Hydrocarbons and Organic Chemcials in Ground
Water: Prevention, Detection and Restoration, Houston, Texas, 1989. Copyright 19B9 National Water Well Association.
Once the infiltrated or percolated mixture has flushed the contaminants to a
certain location, the contaminated fluids must be removed. They can be re-
moved either from a perched condition or from a groundwater system. With
some organics and inorganics, it is reasonable to conclude that with a large
depth-to-water ratio, and because of limited contaminant mobility, the contami-
nation may be left in place over a vertical profile. For example, where petro-
leum organic contamination has been flushed using surfactants and nutrients,
passive bioremediation might be selected and the contamination left in place.
Effective application of the process requires a sound understanding of the
manner in which target contaminants are bound to soils and of hydrogeologic
transport. In addition, since soil washing increases contaminant mobility, con-
sideration needs to be given to the potential consequences of deviations from
the assumed site condition that could spread contamination. This concern can
usually be addressed by employing conservative design parameters and the
3.39
-------
Process Identification and Description
observational approach. Brief discussions of these and other scientific bases for
soil flushing is integrated into the following subsections.
3.2.1 Process Description
3.2.1.1 Soil Flushing Solutions
Flushing solutions may include water, dilute acids and bases, complexing
and chelating agents, reducing agents, solvents, or surfactants. In many cases,
water can be used to flush water-soluble contaminants. Surfactants can be
added to increase the mobility of certain semivolatile and inorganic contami-
nants and chelating agents can be added to solubilize heavy metals. Acids or
bases can also be added to improve flushing efficiency.
Surfactants can be used to improve the solvent property of the recharge wa-
ter, emulsify nonsoluble organics, and enhance the removal of hydrophobic
organics sorbed onto soil particles. Surfactants improve the effectiveness of
contaminant removal by improving both the detergency of aqueous solutions
and the efficiency by which organics may be transported by aqueous solutions.
Surfactants were originally developed for the tertiary recovery of oil; however,
they have also been demonstrated to remove contaminants from soil.
Applicability of other flushing agents must be evaluated on a case-specific
basis. The effectiveness and rate of cleanup are site- and contaminant-specific,
with hydrogeological transport models or field tests used to assess performance.
Column studies can also be performed using site-specific soils, contaminants,
and flushing solutions.
3.2.1.2 Dissolution Reactions
If the input of contaminants in a groundwater system is discontinued, con-
taminants will be dissolved back to the liquid phase as lower concentration
groundwater flushes through the previously contaminated zone. In theory, after
contamination input is discontinued and if all partitioning reactions are com-
pletely reversible, all contamination should be eventually removed from the
system as complete desorption occurs. Many substances do not, however, react
sufficiently fast relative to the rate of groundwater movement to enable a suffi-
ciently rapid rate of dissolution. Therefore, dissolution of contaminants by
adsorption or other geochemical processes from the pore water to the solid
phase causes the advance rate of the contaminant mass moving from a point
3.40
-------
Chapters
source to be retarded relative to the ground water mass, and can be described by
the retardation factor Rf=v/vc, and by its inverse, the relative velocity, vc/v. The
solute or contaminant velocity, vc, can be calculated from the relationship vc=W
RP such that a larger retardation factor indicates a slower solute velocity.
Retardation can be expressed by the equation:
where v = groundwater velocity
v = contaminant velocity
... .. void volume
n = total porosity, or
total volume
p = soil relative density
Kd = distribution coefficient, or solute mass per solid phase unit mass
The partitioning of solutes between liquid and solid phases in a porous me-
dium is commonly expressed by the log-log Freundlich isotherm:
S = KdCb
where S = mass of solute species adsorbed or precipitated on the solids per
unit bulk dry mass of porous media
C = solute concentration
Kd= distribution coefficient
= solute mass per solid phase unit mass concentration of solute in
solution
b = slope of the log-relationship between S&C.
A reactive flushing solution can react with other target constituents. Com-
plex wastes containing a range of contaminants with different solubilities and
partitioning characteristics may make soil flushing infeasible. Reactive flushing
solutions may have toxic or other environmental effects on soil and groundwa-
ter and may also pose special problems in the treatment required to dispose or
reinject them into the aquifer.
In some situations, a portion of the contaminant mass transferred to the solid
part of the porous material by adsorption or precipitation is irreversibly fixed
3.41
-------
Process Identification and Description
within a reasonable time frame. This portion is not transferred back to the pore
water as new water passes through the system and is therefore isolated in the
subsurface environment.
When a mixture of reactive contaminants enters the groundwater zone, each
species has different dissolution reactions and will travel at a different rate,
depending on its relative velocity. After a given time, the concentration distri-
bution of the dissolved reactive species will be retarded at different rates rela-
tive to groundwater flow.
3.2.1.3 Transport Mechanisms
Soil flushing also involves the transport of dissolved constituents,
primarily by advection, whereby solutes are transported by the bulk mass of the
flowing fluid. Dispersion causes spreading of the solute and is caused by mo-
lecular diffusion (mixing caused by random molecular motions due to solute
thermal kinetic energy) and by mechanical mixing within the substrata. Disper-
sion is much stronger in the direction of flow (longitudinal dispersion) than in
the direction normal to the flow line (transverse dispersion). Longitudinal dis-
persion is proportional to groundwater velocity. Transverse dispersion remains
largely diffusion controlled until the flow velocity is quite high. See Domenico
and Schwartz 1990 and Freeze and Cherry 1979 for further discussion.
The dispersion of solutes during transport through many types of frac-
tured rocks cannot be described by the same relationships for homogeneous
granular materials. Fractured geologic materials, are notoriously anisotropic
with respect to the orientation and frequency of fractures. For example, distri-
bution coefficients are more commonly expressed on the basis of media surface
area than on the basis of mass. Little is known about predicting dispersion in
fractured media.
Vertical transverse dispersivity can be greater than horizontal, such
that if the transverse dispersivity is large, contaminants transported along rela-
tively horizontal flow paths can disperse more in depth than in breadth. Dis-
persivity can be established only by detailed field testing and experiments.
3.2.1.4 Passive Hydraulic Methods
Conveyance and transport systems include sumps, French drains, and other
equipment and designs that allow for passive removal of accumulated free
product from the unsaturated zone. (This subsection does not address caps,
3.42
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Chapters
slurry walls, or other physical barriers to flow or technologies, such as freez-
ing.)
Passive hydraulic methods for removing gross levels of contaminants from
unsaturated or saturated zones can be simple and relatively inexpensive, but do
nothing to remove contaminants to low levels. They are effective in the unsat-
urated zone only when perched zones are present or a positive head is intro-
duced by infiltrating waters. The collection system needs to be located down
gradient from and as close to the source as is practical. Passive hydraulic meth-
ods are unlikely to be selected as a primary cleanup method and might best
serve as an initial step in easily collecting gross contaminants before, or in con-
junction with, implementation of another technology. For example, when a
leaking underground storage tank (UST) is removed, the resulting excavated
area might begin to accumulate residual free product. The heavy machinery
already on site could be used to enlarge the excavated area to install a sump or
French drain to further promote accumulation with little added effort.
Groundwater drawdown will create a groundwater gradient and can also
increase permeability in the saturated zone, causing residual liquid contami-
nants to flow readily toward that zone. An impervious layer can be placed at
the base of the trench to prevent reinfiltration of free product. As the product
accumulates, it can be pumped out or removed manually. This maintains a
gradient that facilitates further seepage into the trench. Figure 3.16 (on page
3.44) shows a drain system for staging contaminated soil in below-grade
trenches.
Passive hydraulic methods collect and remove only the mobile liquid and
dissolved contaminants (and may also serve as a passive venting system). Con-
taminants sorbed to soil particles or held as residual saturation are little affected
by passive hydraulic methods and typically must be removed by other means.
The method is best used in situations where the mobile phase — residual liquid
and pore water — content is relatively high. Passive hydraulic methods are
most effective for recent releases of significant quantities of contaminants at
shallow depths.
Table 3.3 (on page 3.45) lists several critical success factors (CSF) for pas-
sive hydraulic methods. The single most important CSF is the amount of con-
taminant in the liquid phase. This method will not be effective unless signifi-
cant quantities of liquid contaminant are in the soil.
3.43
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Process Identification and Description
Figure 3.16
Typical Drain System
SDS recovery system process trailer
Purified SDS to surface distribution system
/ UQ
Staged
contaminated
Uresaturated zone
^Water table
Saturated zone
• Typical SDS flow lines
Aquitard
V-trench with plastic liner
and recovery pipe
3.2.1.5 Soil Flushing Component Activities
Soil flushing can be broken down into three activities — site characteriza-
tion, injection, and contaminant mobilization and recovery techniques — dis-
cussed in the following subsections. (See also figure 3.17 on page 3.46 for a
representation of these activities.)
3,2.1.5,1 Site Characterization Site characterization requires a full under-
standing of hydrogeology, geochemistry, and the relative permeability and
lithology above, within, and below the zone of contamination. In general, soil
flushing is most effective in homogeneous, permeable soils (e.g., sands, gravels,
and silty sand with permeabilities >10J* cm/sec). The relationship between
capillary processes, water content, and hydraulic conductivity must be under-
stood before a water-based flushing technique can be effectively used. For gas-
phase soil flushing, the intrinsic air permeability and the effect of soil moisture
must be measured.
Factors that affect the residual hydrocarbon concentration are:
• water solubility of the hydrocarbon contaminants;
• interfacial tension (IFT) between the hydrocarbon, water and soil,
and the contaminant; and
3.44
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Chapters
Table 3.3
Worksheet for Evaluating the Feasibility of Soil Flushing
Critical Success
Factor
SITE RELATED
• Dominant
Contaminant Phase
• Soil Hydraulic
Conductivity
• Soil Surface Area
• Carbon Content
• Fractures in Rock
Units Site of
Interest
Phase
cm/sec.
m2/kg
%
Wsight
....
Success Less
Likely
\&por
Low
(<10"5)
High
OD
High
Present
Success
Somewhat Likely
Liquid
Medium
(10-5-10'3)
Medium
(0.1- 1)
Medium
(1-10%)
....
Success More
Likely
Dissolved
High
oio-3)
Small
Small
(<1%)
Absent
CONTAMINANT RELATED
• Wfcter Solubility
• Sorption
Characteristics
Soil Sorption
Constant
• Vapor Pressure
• Liquid Viscosity
t Liquid Density
mg/L
Ukg
mmHg
cPoise
g/cm3
Low
«100)
High
(>10,000)
High
High
(>20)
Low
«D
Medium
(100-1,000)
Medium
(100-10,000)
Medium
(10-100)
Medium
(2-20)
Medium
(1-2)
High
(>1,000)
Low
(<100)
Low
(<10)
Low
(<2)
High
Other Considerations
• Cost is from $150 to $200 per cubic yard
• Using surfactants may increase effectiveness
• Effluent requires separation techniques such as distillation, evaporation, centrifugation.
• Most effective when used ex situ (above ground).
• relative permeability of the contaminant and water.
The low solubility of residual hydrocarbons limits the effectiveness of water-
based soil flushing methods because the amount of oil that dissolves into water
and is flushed from the subsurface is insignificant in comparison with the re-
sidual oil left in place.
3.45
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Process Identification and Description
Figure 3.17
Site Characterization Soil Flushing Activities
Interfacial tension can be described as the unbalanced forces acting on a
droplet of free-phase hydrocarbon contamination. The lower the IbT, the
greater the tendency of the droplet to be miscible in groundwater. The result of
high IFT is the retention of the hydrocarbon on soil particles as opposed to its
movement when groundwater is swept through the soil pores.
Relative permeability can be described as the tendency of a porous system to
selectively conduct one fluid when two or more fluids are present. The mobil-
ity ratio is the term used to describe the effects of relative permeability in the
enhanced oil recovery industry. The mobility ratio is defined as:
where: m = Mobility ratio
KD = Effective permeability with respect to the displacing fluid
KQ = Effective permeability with respect to the oil
UD = Viscosity of the displacing fluid
Uo = Viscosity of the oil
3.46
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Chapters
The higher the mobility ratio, the greater the tendency of the displacing fluid
to flow around, rather than push out the contaminant residual oil.
For homogeneous soils, the vertical and horizontal permeabilities must be
measured. Problems, however, begin to develop in layered soils where the
contamination is located in the finer-grained materials. For surface flooding
applications, the infiltration and percolation rates must be tied into the number
of pore volumes required to achieve the cleanup goal. For down-hole injection
applications, the vertical and volumetric sweep parameters must be understood.
3.2.1.5.2 Injection The in situ flushing process requires that the flushing fluids
be injected into the soil matrix. Injection can be by surface water flooding,
surface sprinklers, leach fields, septic systems, vertical and horizontal injection
wells, or a trench infiltration system (see figure 3.18 on page 3.48).
3.2.1.5.3 Contaminant Mobilization and Recovery Techniques Soil flushing
techniques for mobilizing contaminants can be classified as conventional and
unconventional. Conventional soil flushing can be broken down into the fol-
lowing activities:
• natural restoration;
• well-and-capture methods in the vadose zone; and
• pump-and-treat systems in the saturated zone.
Above ground treatment systems are conventional remedial wastewater
treatment applications that are familiar pump-and-treat operations. The treat-
ment system will be sized based upon the recovery volumes and the rates of
withdrawal from the collection system. The treatment system is designed to
remove and recover contaminants from the waste stream and to provide reinjec-
tion water at a certain contaminant concentration level.
The treatment system will be configured to remove specific contaminants of
concern. For organic contaminants, in most cases, the treatment system will
consist of air stripping, carbon adsorption, and/or biological treatment units.
For inorganic treatment, the systems will usually include standard precipitation
systems, electrochemical exchange, ion exchange, and/or ultrafiltration sys-
tems. For many sites, the contaminants of concern will include organics and
inorganics in the same waste stream. For these cases, process treatment trains
will be configured to provide appropriate removals. In all cases, the key con-
cern, and the primary contributor to long-term operation and maintenance, will
3.47
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Process Identification and Description
3.48
-------
Chapters
be the volume and quality of sludge generated from the process treatment sys-
tem.
Unconventional soil flushing can be broken down into:
• primary recovery;
• secondary recovery; and
• tertiary recovery —
• gaseous processes;
• chemical processes —
• polymers;
• surfactants;
• alkaline agents;
• in situ solvent extraction; and
• thermal methods —
• alkaline, surfactant, and polymer flooding.
Unconventional soil flushing methods can effect primary recovery of con-
taminants using the natural energy within the system. These methods include a
neutral water drive, gravity drainage, solution gas drive, or a gas cap drive.
The secondary recovery methods include waterflooding and pressure main-
tenance techniques. Tertiary recovery techniques remove the contaminants by
the injection of materials not normally found in the soil. Tertiary recovery
methods include gaseous processes such as carbon dioxide flooding, an En-
hanced Oil Recovery (EOR) technique that relies on achieving a decreased
mobility ratio. Carbon dioxide is injected under pressure into a hydrocarbon-
contaminated zone. The viscosity of the contaminant decreases as carbon
dioxide dissolves into the hydrocarbon. Because this method relies on high
pressures, it would be applicable only at relatively large depths in a confined
strata. The effectiveness of this technique in environmental applications is not
known.
Chemical recovery processes include polymer flooding and surfactant flood-
ing. Polymer flooding is a commonly-used EOR method that may have envi-
ronmental applications, although this application has not yet undergone exten-
sive evaluation. The contaminant removal effectiveness of the waterflood can
3.49
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Process Identification and Description
be increased by adding polymer to the water, which increases the viscosity of
the flood and thus lowers the mobility ratio.
Soil flushing with surfactant solutions to extract hydrophobic organic con-
taminants appears to be one of the most promising of in situ cleanup technolo-
gies. Aqueous surfactant solutions are superior to water alone in extracting
hydrophobic contaminants. Both the detergency of aqueous solutions and the
efficiency by which organics are transported by aqueous solutions are thought
by researchers to be improved by surfactant addition. The processes for im-
proving the detergency of aqueous solutions are preferential wetting, increased
contaminant solubilization, and enhanced contaminant emulsification
(Edwards, Luthy, and Liu 1991). The addition of surfactants is thought to in-
crease the efficiency by which organics are transported in aqueous solutions by
lowering the interfacial tension between the aqueous and contaminant phase,
which facilitates the distortion of spherical oil droplets as they pass through the
soil.
Another reason the use of surfactants for in situ soil flushing applications
appears promising is that numerous environmentally safe and relatively inex-
pensive surfactants are available commercially.
Enhanced Oil Recovery research has identified an IFi reduction method that
may be much more cost-effective than the use of surfactants. When in contact
with certain hydrocarbon mixtures, alkaline agents (e.g., sodium carbonate) can
react to form surfactants that are created at the aqueous-hydrocarbon interface,
and the surfactants can effectively reduce the IFT. The use of a combination of
alkaline agents and surfactants may be the most cost-effective way to reduce
IFT and to enhance hydrocarbon recovery (Sale and Pitts 1989).
As in surfactant flooding, IFT reduction through the use of alkaline agents is
not likely to be effective if unfavorable mobility ratios still exist. Other poten-
tial problems with the use of alkaline agents may result from the high pH and
reactive nature of these solutions. These problems include precipitation and
resultant aquifer plugging, dispersal and expansion of clays, and leaching of
trace metals.
In situ solvent extraction involves flooding the subsurface zone containing
the residual oil with an organic solvent or water containing an organic solvent.
This technique is based on increasing the solubility of the residual oil in the
3.50
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Chapters
fluid used for flushing the subsurface. This method is not generally considered
practicable for the following reasons:
• environmental concerns regarding injecting organics that are effec-
tive as solvent into the subsurface;
• residual solvents left in the subsurface;
• difficulties in treating fluid withdrawn from the subsurface that
contain miscible mixtures of water, solvent, and oil; and
• high project costs for implementation.
One combination of the techniques described above that has undergone
limited testing for environmental applications is alkaline, surfactant, and poly-
mer (ASP) flooding. The addition of an alkaline agent and a surfactant address
IFT; the addition of a polymer gives the flood a favorable mobility ratio. In
bench-scale tests, an ASP flood was highly effective in displacing residual
waste wood-preservatives oil from a subsurface sandy soil (Sale and Pitts
1989).
The most commonly considered thermal methods are hot water flooding and
steam flooding. These methods rely on decreasing the residual oil level by
increasing contaminant solubility and achieving a more favorable mobility
ratio. Contaminant solubility in the soil flushing solution is increased because
the water solubility of many organics increases at higher water temperature.
More importantly, the viscosity of free-phase hydrocarbon decreases with in-
creasing temperature because of the loss of volatiles, causing a decrease in the
mobility ratio.
A major limitation in the use of thermal methods is that at increased tem-
peratures, denser-than-water, free-phase oil may be converted to a floating oil.
The effect is that oil initially confined to a narrow lens may float through and
wet, previously uncontaminated portions of the subsurface. Costs may also be
high because of the heat loss that occurs as large volumes of subsurface materi-
als are heated.
The effectiveness of this technology in environmental applications is un-
known. A summary of screening criteria for EOR methods is given in table 3.4
(on page 3.52) and a comparative summary of recovery percentages is given in
table 3.5 (on page 3.53).
3.51
-------
Process Identification and Description
•o
o
It
l!
o:
0
a.
8
o
LLJ
02
B
.s:
u u
U
z
u
Z
u
Z'
o
7!
o
A
=3 P'-S A
0
A
u => s
Z A A
Is- Is-
's'l o s's i
o.ua. coo. co
s
"S "S
!„ --
ECO fiu KO 3.S-S Z
0
Z
O
v
-2
^- in so
tsmo
AAA
1
ZE
>n
cs
A
8-3
E&
Sco
3 I
<
3.52
-------
Chapters
Table 3.5
Comparative Summary
Process
Immiscible gas
Miscible gas
Polymer
Micellar/Polymer
Alkaline/Polymer
Steam (drive or
soak)
In situ
Recovery Mechanism
Reduces oil viscosity
Oil swelling
Solution gas drive
Same as immiscible plus development of miscible
displacement
Increase volumetric sweep efficiency by reducing
mobility ratio
Same as polymer plus reduction in IFT forces
Same as micellar/polymer plus wettabiltiy
alteration
Reduces oil viscosity
Vaporization of light ends
Same as steam plus cracking of heavy ends
Typical
Recovery %
5 to 10
5 to 15
5
15
5
50 to 65
10 to 15
Typical Agent
Utilization
lOMscfgas/
bbloil
lOMscfgas/
bbl oil
0.5 to 2 Ib
polymer/bbl oil
15 to 25 Ib
surfactant/bbl oil
35 to 45 Ib
chemical/bbl oil
produced
0.5 bbl oil
consumed/bbl oil
produced
5 to 10 bbl
steam/bbl oil
lOMscfair/bbloil
Source: McKee and Whitman 1991
3.2.1.6 Measuring Effectiveness
The measurement of the effectiveness of soil flushing requires the use of
field monitoring instrumentation to determine soil moisture flux, changes in
capillary pressure, and water content. Changes in capillary pressure can be
measured using transducerized transmitters; changes in water content can be
measured using neutron probes or frequency domain capacitance probes.
Change in contaminant concentration can be measured using field soil gas total-
izers, portable gas chromatographs, specific ion probes, and radiation monitor-
ing systems.
3.2.2 Status of Development
Soil flushing has been practiced on a commercial level for more than 50
years in the oil and gas industry to mobilize product material near the wellhead.
The process is now being modified for application in the treatment of hazardous
waste. Some difficulties arise because hazardous waste soil flushing systems
must perform in a finer mode to seek out, destabilize, and collect contaminants
in low concentrations from extremely difficult geological settings.
3.53
-------
Process Identification and Description
Nevertheless, conventional applications of soil flushing have been em-
ployed, in most cases, using the treated effluent from a pump-and-treat opera-
tion for reinjection and improved contaminant mobilization. Unconventional
methods are now being accepted and will be demonstrated soon on specific
Superfund sites. Some representative case histories are presented in Appendix
B.
In situ soil flushing is in the predesign and design stage at 21 Superfund sites
(see figure 3.19).
3.2.3 Design Data and Unit Sizing
The following data are required to select the flushing solvent and to predict
soil flushing effectiveness:
• site hydrogeology; permeability, geochemistry, direction and rate of
vertical and horizontal groundwater flow, vadose zone saturation,
bulk density, average particle size, thickness of receiving aquifer,
aquifer confinement, aquifer and adjacent aquifer use, porosity,
plume location and rate of travel;
Figure 3.19
In Situ Flushing Target Contaminants Through Fiscal Year 1991
30 -,
25 -
20 -
Number
of
Remedial
Sites
10 -
5 -
n -
'
/
*—
/
/
1
)
0
./
/ A
\
•
•
r
14
f f / / / A
I I I I •
1 1 1 1 P-
/ /
4
/
/
/ A
'-m
h
3
( f ( ( ( A
VOCs
Metals Other SVOCs PAHs
Contaminant
Note At some sites, treatment is far more than one contaminant. Treatment may be planned, ongoing, or completed
3,54
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Chapters
• soluble contaminant extent and concentration, Freundlich isotherm,
molecular diffusions, retardation factor, O2 concentration, water
table fluctuation, solubility, residual nonaqueous phase liquids and
their relative density; and
• nonaqueous phase liquid (NAPL) vertical and lateral distribution,
density, adsorption coefficient, seasonal relationship of water table
to contamination.
Actual field experience with in situ soil flushing for petroleum remediation is
very limited, and thus data on effectiveness, costs and limitations are generally
unavailable. The petroleum industry has experimented for several years with
enhanced oil recovery, which uses surfactants to increase the production of an
oil deposit.
3.2.4 Pre- and Posttreatment Requirements
Preflushing of the contaminated area may be required to demonstrate that the
monitoring system is working. In addition, prefiushing is required to adjust the
salinity for both the use of surfactants and the application of polymers.
Preflushing also results in a reduction of the adsorption of the surfactant.
As to posttreatment, once the recovery system (i.e., pump-and-treat) has
been shut down, infiltration may have to be controlled to prevent further mobili-
zation of residual contaminants. This posttreatment will allow the further
breakdown of contamination by microbial activity. In addition, it may be pos-
sible to effect posttreatment using bioventing once the permeability has been
increased through removal of the bulk of contaminants.
3.2.5 Operational Requirements and Considerations
Once the appropriate surfactant type and dosage are determined from shaker
table and column bench studies, the field conditions must be evaluated, con-
trolled and monitored. The field operations require that the surfactant mixing,
holding, and delivery systems be monitored. The surfactant application system
must be maintained. The recovery drains or the contaminant capture system
must be monitored. The recovered fluids treatment system must be maintained.
The pumping system for the surfactant delivery and contaminant capture needs
to be fully operational. And, finally, the use of any contaminant barriers must
be monitored.
3.55
-------
Process Identification and Description
In planning soil flushing operations, the likelihood that it may rain should be
considered. If the loading rates of waterflooding are scaled to the pump-and-
treat system and there is heavy rainfall, the recovery system may not remove all
of the contaminated fluids that could migrate downgradient.
3.2.6 Unique Planning and Management Needs
Several unique and extremely important matters must be considered when
implementing a soil flushing project. They are:
• A well designed and executed Remedial Investigation must charac-
terize the site to define key contaminants and occurrence within the
zone of contamination;
• The dynamics of the vadose zone are particularly complicated and
are very different than flow dynamics in the saturated zone. Solute
transport mathematical models are not applicable in the vadose
zone, and, in fact, limited models are currently available that can
describe the vadose zone phenomena. The plan for implementation,
therefore, must contain a special approach to the collection of re-
quired data in the vadose zone, including water content, capillary
pressure, hydraulic conductivity, relative permeabilities, and hori-
zontal and vertical distribution of fine-grained materials;
• The potential for retention of flushing enhancements (chemicals or
surfactants) will be very critical to obtaining approval for a soil
flushing application; and
• A substantial field test is recommended to confirm the applicability
of this technology.
3.2.7 Cost Data
Cost data are sparse. The Superfund site at Palmetto Wood, S.C. cited costs
of $3,710,000 (capital) and $300,000 (annual O&M). These figures, on a unit
basis, equal $240/m3 ($185/yd3) for capital costs, and $20/m3 ($15/yd3) annually
for O&M. At Palmetto Wood, soil flushing will be used to clean 15,400 m3
(20,000 yd3) of soil contaminated with metals (US EPA 1988).
3.56
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Chapters
3.2.8 Special Health and Safety Requirements
As in soil washing, workers are usually remote from the waste material.
Further, because soil flushing is an in situ remedy, the potential for exposure is
even more remote than those activities requiring excavation. Nevertheless, all
activities must be performed under an approved HASP, and all activities per-
formed in the field must be conducted by personnel qualified in conformance
with the requirements of OSHA directive 1910.120 (series). Operations will be
routinely conducted in Level "D" protection, consistent with the direct monitor-
ing requirements of the HASP.
3.2.9 Technology Variations
Soil flushing can be performed in two primary modes: conventional and
unconventional (see Subsection 3.2.1.5.3). Conventional applications employ
water only as the flushing agent. In the flooding variation, clean water is ap-
plied to the site through pumping, spraying, or the routine release from storage
areas. Conventional methods also include reinjection of the flushing water
through a series of injection wells, through horizontal distribution headers, or
through infiltration galleries.
Unconventional applications consist of the enhancement of the flushing
water with surfactants, chelants, or other chemicals to aid in the desorption/
dissolution of the target contaminants from the soil matrix to which they are
bound.
3.2.10 Summary of Good Practice
In situ soil flushing good practice requires that the appropriate shaker tests
and column studies be made in the laboratory to identify the correct surfactants,
dosage, and pore volumes for field trial. In the field, good practice requires
selection of an appropriate injection technique, based upon site characterization,
an appropriate mobilization and recovery technique, and a complete monitoring
system capable of demonstrating that the system is working.
3.57
-------
-------
Chapter 4
POTENTIAL APPLICATIONS
4. 7 Soil Washing
Soil washing may be used to treat soils containing a wide variety of organic,
inorganic, and radioactive contaminants. The technology is most appropriate
for noncomplex soils contaminated with either metals or organics.
Because the technology is primarily a separation and volume reduction pro-
cess, it is usually used in conjunction with other technologies. For example,
soil washing may be used to separate and concentrate the contamination into a
smaller volume of fine soil particles. Because only this smaller volume of soil
and contaminants needs treatment, the additional treatment technology is more
cost effective when applied after the soil washing step.
Soil washing is most effective when applied to soils and sediments contain-
ing high percentages of sand and gravel. It is most cost-effective when water
alone (without additives) is sufficient to achieve target cleanup levels.
4.1.1 Site Characterization
Site characterization is the first and most important step in determining
whether soil washing may be effectively applied. In addition, it can provide the
basis for informed decisions about the design and execution of bench- and pilot-
scale tests that yield the best possible data at the least cost.
Soil data that are necessary to characterize a candidate site include the fol-
lowing:
• site geology and hydrogeology;
• soil type and composition versus depth;
4.1
-------
Potential Applications
• soil chemistry;
• aerial extent of the soil contamination (vertical and horizontal pro-
files);
• total amount of contaminated soil to be treated;
• range, concentration, and variability of contaminants in the soil; and
•f;/history, process, and time frame of the conditions leading to the
f contamination.
Information from geological surveys, aerial photos, topographical surveys,
groundwater maps, and nearby soil borings and well logs can provide substan-
tial information about the subsurface conditions likely to be encountered during
excavation of the contaminated soil. It is important to know how soil type and
contaminant concentrations change with latitude and depth so that an accurate
profile of the feedstock soil can be developed. This information will be very
helpful also in guiding sampling efforts for collecting representative soils for
further characterization and for bench and pilot testing.
4.1.2 Bench- and Pilot-Scale Testing
Site characterization is followed by bench- and pilot- scale tests on represen-
tative samples to determine whether soil washing can be used to effectively
remove contaminants. Such tests can be used to determine also the require-
ments for soil feedstock preparation and to gauge the performance capabilities
of commercially available systems. If bench test results are promising, pilot test
demonstrations should be conducted before final commitment to a full-scale
soil washing system.
Guidelines and procedures for soil washing treatability studies are explained
in EPA's 37-page interim guidance document titled Guide to Conducting
Treatability Studies Under CERCLA: Soil Washing (EPA/540/2-91/020A,
September, 1991). A fact sheet by the same name, also published by EPA
(EPA/540/2-91/020B), highlights and summarizes the material contained in the
companion guidance document. Appendix C of this monograph is the Septem-
ber, 1991 issue of the fact sheet.
4.2
-------
Chapter 4
4.1.3 Potential Applications
The two most important aspects of soil type and composition that should be
evaluated during site characterization are:
• particle size distribution; and
• contaminant relationship to the soil matrix.
Soil washing performance is closely tied to these two key physical soil char-
acteristics. Because these characteristics can vary substantially with area and
with soil depth across a given site, care must be taken to evaluate them in light
of the overall site geology and the vertical and horizontal extent of the chemical
contamination.
[P Particle size distribution has a direct effect on the ability of a soil washing
system to separate contaminants from the major soil mass. Many soil contami-
nants tend to bind to the fine particle fraction of the soil (i.e., bind with the silt
and clay portion). These contaminants will be separated from the clean soil
during the washing process to much the same extent as the fines are separated
from the coarse sand and gravel fraction. If a soil is tested and found to have a
relatively small percentage of silt and clay (e.g., <25%), the probability will be
high that soil washing will be effective in reducing contamination in the bulk of
the soil. Therefore, knowledge of the typical particle size distribution (and
likely variations therein) that will be encountered throughout the contaminated
soil area can be particularly valuable as an early indicator (or screening tool) of
the potential effectiveness of soil washing in separating out the contaminants.
Soils containing a relatively high percentage of sand and gravel (curve #1,
figure 4.1 on page 4.4) will most likely respond favorably to the soil washing
treatment process, whereas soils that are rich in clay and silt sized particles
(curve #3) are likely to respond poorly. In general, soil washing is most appro-
priate for soils that contain at least 50% sand and gravel, such as coastal sandy
soils and soils with glacial deposits. Grain-size distribution tests should be
conducted under wet sieve conditions using American Society for Testing and
Materials (ASTM) Method D422.
3- - The contaminant relationship to the soil matrix is a very important consider-
ation. Depending upon site conditions, a wide variety of chemical contami-
nants and pollutants can be removed from soils through soil washing, as table
4.1 (on page 4.5) shows. But the exact removal efficiencies that can be
4.3
-------
Potential Applications
Figure 4.1
Soil Washing Applicable Particle Size Range
Soil Wash with
Specific Washing Fluid
(Regime fl)
Economic Wash
with Simple Particle
Size Separation
(Regime.1)
0.001 0.002 0.0060.01 0.02
0.063 0.1 0.2 0.6 1 2
Diameter of Particle in Millimeters
10 20
60 100
*S=Stone
achieved at a particular site will be highly dependent on the specific blend of
physical and chemical characteristics associated with the composition of the
soil and the contaminants.
) • In addition to particle size distribution and contaminant relationship to the
^sbil matrix, cation exchange capacity of the soil is another important consider-
ation. Cation exchange capacity measures the tendency of the soil to exchange
natural and weakly held cations in the soil for cations in the polluting substance.
Soils with a relatively high cation exchange capacity tend to bind pollutants
more tightly to the soil. This can limit the ability of the soil washing process to
effectively separate the pollutant from the soil. Cation exchange should be
measured using EPA Method 9080 (ammonium acetate test) or 9081 (sodium
acetate test).
Soil washing can be used to remove volatile organic compounds (VOCs)
from soil and other materials that have a relatively high vapor pressure or water
solubility quotient (water/octanol partition coefficient). Experience shows that
removals of 90 to 99% or more of VOCs can be achieved by simple water
4.4
-------
Chapter 4
washing. Care must be taken, however, to collect the volatile material in a
manner that prevents it from being released into the environment. Removals of
semivolatile organics tend to be lower, on the order of 40 to 90%, and often
require the addition of surfactants to the washwater to aid in the separation.
Successful removal of metals and pesticides, which tend to be less soluble in
water, may require the addition of acids or chelating agents.
Table 4.1
Applicability of Soil Washing To General Contaminant Groups
For Various Soils
Contaminant Groups Matrix
Sandy/
Gravelly Silty/Clay
Soils Soils
Organic
Inorganic
Halogenated Volatiles
Halogenated semivolatiles
Nonhalogenated volatiles
Nonhalogenated semivolatiles
PCBs
Pesticides (halogenated)
Dioxins/Furans
Organic cyanides
Organic corrosvies
Volatiles metals
Nonvolatile metals
T
T
T
T
T
T
T
T
T
T
T
Asbestos Q Q
Radioactive materials ^
Inorganic corrosives ^
Inorganic cyanides ^
Reactive
Oxidizer
Reducers
• Good to Excellent Applicability: High probability that technology will be successful
T Moderate to Marginal Applicability: Exercise care in choosing technology
Q Not Applicable: Expert opinion that technology will not work
Source: US EPA 1990
Soils contaminated with fuel oil, jet fuel, and waste oil from underground
tank system releases can be effectively treated by soil washing. Removal effi-
ciencies for residual metals and hydrocarbons of 90 to 98% have been achieved
when heat and surfactants have been added to the washwater. Although studies
have shown that soil washing can be effective in removing gasoline and diesel
4.5
-------
Potential Applications
Table 4.2
Waste Soil Characterization Parameters
Parameter
Purpose and Comment
Key Physical
Particle Size Distribution:
>2 mm
0.25 - 2 mm
0.063 - 0.25 mm
<0.063mm
Cation Exchange Capacity
Other Physical
Type, physical form, handling properties
Moisture content
Key Chemical
Organics
Concentration
Volatility
Partition coefficient
Metals
Humic acid
Other Chemical
pH, buffering
capacity
Oversize pretreatment requirements
Effective soil washing
Limited soil washing
Clay and silt fraction-difficult soil washing
A measure of soils ability to attract and bind pollutants in
exchange for naturally occurring ions or elements
Affects pretreatment and transfer requirements
Affects pretreatment and transfer requirements
Determine contaminants and assess separation and washing
efficiency, hydrophobic interaction, washing fluid
compatibility, changes in washing fluid with changes in
contaminants. May require preblending for consistent feed.
Use the jar test protocol to determine contaminant
partitioning
Concentration and species of constituents (specific jar test)
will determine washing fluid compatibility, mobility of
metals postreatment.
Organic content will affect adsorption characteristics of
contaminants on soil. Important in marine/wetland sites.
May affect pretreatment requirements, compatibility with
equipment materials of construction, wash fluid
compatibility.
Source: US EPA 1990
fuels from soils, thermal desorption, biodegradation, or vapor extraction may be
more effective and appropriate for treating the volatile components, since these
techniques will destroy or degrade the contaminant1.
Table 4.2 summarizes the key soil parameters that should be measured at a
site and factored into the bench- or pilot-scale performance test plan. This
information also will be useful to commercial system vendors as they begin
selecting and sizing the equipment for full-scale operations.
Table 4.1 (on page 4.5) shows the general effectiveness of soil washing for
removing various types of chemical groups from soils. Excellent to good appli-
cability ratings shown in this table mean the probability is high that soil wash-
1. See the monographs in this series, Innovative Site Remediation Technology: Thermal
Desorption, Innovative Site Remediation Technology: Bioremediation, and Innovative Site
Remediation Technology: Vacuum Vapor Extraction—Ed.
4.6
-------
Chapter 4
ing will be effective for removing chemicals in the group from the soil type
indicated. Moderate to marginal applicability indicates situations where care
must be exercised in choosing soil washing.
Because treatment performance is so closely linked to individual site charac-
teristics, broad indicators or guidelines cannot be used to accurately predict
whether soil washing will provide the desired degree of performance at any
given site. The specific chemical form of a contaminant when it is released into
the soil directly affects the mobility, fate, and removal of the chemical. For
example, metallic forms of lead scattered on the ground as a fine particulate or
dust can be much more difficult to remove from the soil than dissolved forms
that might have been spilled on the ground as a liquid. Also, the length of time
that a soil has been contaminated can also have a dramatic effect on the ability
of a soil washing system to achieve desirable contaminant separation efficien-
cies. For example, over time, lead and other metals can mineralize in the soil,
becoming very tightly bound to the soil matrix and virtually impossible to ex-
tract with water solutions, even with the aid of pH adjustments and chelants.
4.1.4 Application at Superfund and European Sites
Soil washing has been selected for remedial application at 23 Comprehen-
sive Environmental Response, Compensation, and Liability Act (CERCLA)
(Superfund) National Priorities List (NPL) sites and one other lower priority
CERCLA site. See tables 4.3 (on page 4.8), 4.4 (on page 4.8), and 4.5 (on page
4.9), for information about soil washing applications at Superfund sites. None
of these applications involves the separation and recovery of volatile contami-
nants. Instead, soil washing was selected to treat soils contaminated with
semivolatile organics (SVOCs), polynuclear aromatic hydrocarbons (PAHs),
dioxins, pesticides, and heavy metals. The average amount of soil to be washed
at these sites is nearly 34,000 m3 (44,000 yd3), ranging from 1,400 to 150,000
m3 (1,800 to 200,000 yd3). Some full-scale soil washing projects have been
completed at Superfund sites, while others are in various stages of planning,
design, or installation.
In developing soil washing processes several major environmental contrac-
tors in the Netherlands and in Germany progressively improved upon combina-
tions of mining and chemical processing approaches for removing contaminants
from sandy soils. In 1989, the US EPA funded an evaluation of existing soil
washing technologies. Table 4.6 (on page 4.12) presents a summary of the
evaluation.
4.7
-------
Potential Applications
Table 4.3
Superfund Project Status Summary, April, 1992
Region Soil Washing Status
02 Ewan Property, NJ PD
02 CE Wiring Devices, PR D
02 King of Prussia, NJ C (mid Oct. 1993)
02 Myers Property, NJ PD
02 Vmeland Chemical, OU1 and OU2, NJ D
04 American Creosote Works, FL D
04 Cabot Carbon/Koppers, FL D
04 Southeastern Wood Preserving, MS (Removal) O
04 Cape Fear Wxxl Preserving, NC D/I
05 United Scrap Lead/SIA, OH D
05 ZanesvilleWell Field, OH PD
05 Moss-American, WI D
06 Arkwood.AR PD
06 Koppers/Texarkana, TX PD
06 South Cavalcade Street, TX D
06 Sand Creek Industrial, OU 5, CO D
09 FMC (Fresno), CA PD
09 Koppers Company, Inc. (Oroville Plant), CA D
09 Poly-Carb, NV C
09 Sacramento Army Depot, CA PD
10 Gould Battery, OR I
10 Idaho Energy Lab D
10 Naval Sub Base, Bangor, WA PD
PD - Predesign phase
D - In Design and contractor onsite
D/I - Design completed awaiting installation
I - Being installed
O - Operational
C - Completed
Table 4.4
Remedial/Removal Superfund Sites Using Soil Washing
as Part of a Treatment Train, April, 1992
Site State Treatment Sequence
Myers Property
Zanesville Well Field
Ewan Property
American Creosote
Cabot Carbon/Koppers
Southeastern Wxxl
Preserving (Removal)
Moss-American
Koppers (Oroville)
Arkwood
South Cavalcade Street
Sand Creek OU 5
FMC (Fresno)
NJ
OH
NJ
FL
FL
NC
WI
CA
AR
TX
CO
CA
Dechlorination followed by Soil Washing
Soil Vapor Extraction followed by Soil Washing
Solvent Extraction followed by Soil Washing
Soil Washing followed by Bioremediation
Soil Washing followed by Bioremediation
Soil Washing followed by Bioremediation
Soil Washing followed by Bioremediation
Soil Washing followed by Bioremediation
Soil Washing followed by Bioremediation
Soil Washing followed by Bioremediation
Soil Washing followed by Bioremediation
Soil Washing followed by Bioremediation
Source: USEPA19923
4.8
-------
Chapter 4
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4.9
-------
Potential Applications
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-------
Chapter 4
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4.11
-------
Potential Applications
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4.12
-------
Chapter 4
4.2 Soil Flushing
4.2.1 General
In situ soil flushing should be considered for applications involving petro-
leum hydrocarbons, chlorinated hydrocarbons, metals, salts, pesticides, herbi-
cides, and radionuclides. Current interest seems to be focusing on the use of in
situ flushing for chlorinated hydrocarbons. A unique capability centers on
cleaning up contaminated soil beneath structures. Many industrial sites
throughout the U.S. have chlorinated hydrocarbons in the subsurface. Since
excavation and other existing remediation strategies require access, in situ soil
flushing offers clear advantages. Other advantages include: no soil replace-
ment and/or disposal costs, no disruption of the ecosystem, cost advantages at
greater depths, and minimized worker exposure to contaminants. Excavation
can also be cost prohibitive in complex hydrogeologic environments.
In general, soil flushing is most effective in homogeneous permeable soils
(e.g., sands or silty sands with greater than 10~4 cm/sec permeability) with low
recharge capacity for metals and low adsorptive capacity for organic contami-
nants. Soil flushing may also be appropriate for the following applications:
• Recovery of mobile degradation products formed after soil treat-
ment with chemical oxidizing agents. This application may be
particularly appropriate if excavation presents a high safety and
health hazard; and
• Enhancement of oil recovery operations. Water (sometimes con-
taining emulsifying chemicals) is pumped into the ground, forcing a
free oil phase towards recovery wells. Steam has also been used for
enhanced oil recovery.
Key contaminants that can be remediated by in situ flushing are listed in
table 4.7 (on page 4.14).
Organics amenable to water flushing can be identified by the magnitude of
their octanol/water partitioning coefficient. Soil flushing is generally applicable
to soluble organic compounds with octanol/water coefficients less than 1,000
(log Kow<3). Highly water soluble organics, such as low molecular weight
alcohols, phenols, carboxylic acids and other organics with a coefficient less
than 10 (log Kow10) that could be
4.13
-------
Potential Applications
Table 4.7
In Situ Soil Flushing Target Contamination Table
Target Groups Specific Contaminants
VOCs TCE, DCE, PCE, TCA, BTEX, Vinyl
Chloride, Carbon Tetrachloride,
Chloroform, Bis-2-chloroethylene, DCA,
Dichloromethane
S VOCs Benzo (a) Pyrene, Benzo (a) Anthracene,
Chrysene, Phenols, Methyl Ethyl Ketone,
Dichlorobenzene, Tnchlorobenzene
Inorganics Ferrous sulfate
Metals Chromium, Lead, Arsenic, Nickel,
Mercury
Petroleum Creosote, Cresol, Pesticides (PAHs)
Hydrocarbons
effectively removed from solids by water flushing include low to medium mo-
lecular weight ketones, aldehydes, aromatics, and lower molecular weight halo-
genated hydrocarbons such as TCE and perchloroethylene (PCE).
Soil flushing is generally applicable also to inorganic compounds with
solubility >1 ppm, with soluble salts, such as the carbonates of nickel, zinc,
copper, and chromates. Dilute acids, such as acetic acid or dihydrogen phos-
phate, or chelating agents, such as ethylene diamine triacetic acid (EDTA) or
diamene tricedic pyrrolidine acid (DTPA), may be necessary to enhance inor-
ganic solubilization and removal. Hexavalent chrome and nitrates are amenable
to soil flushing because of their negative charge (easier to remove from nega-
tively-charged clays and organic matter). Dilute acids or reducing agents could
change hexavalent chrome to the trivalent form and thereby reduce its solubility
and, thus, its amenability to soil flushing (but, since the chrome toxicity would
be reduced by three orders of magnitude, this would reduce the need for soil
flushing).
4.2.2 Soil Flushing (Enhanced Oil Recovery (EOR))
Transfer of technology from EOR and in situ mining (ISM) has the potential
to substantially increase the rate of waste extraction from the ground and there-
4.14
-------
Chapter 4
fore lower costs. The EOR technology results from years of research and de-
velopment. The oil and gas industry developed a number of alternative meth-
ods to recover oil that remains trapped in a particular reservoir after the conven-
tional means of production no longer allows the particular reservoir to produce
at economic rates. Many of these processes are also applicable as in situ waste
recovery schemes or what might be called "unconventional soil flushing".
In general, EOR techniques involve the injection of materials that are not
normally found in the soil in order to facilitate the removal of the hydrocarbon
waste. The EOR processes fall in the following categories:
• gas processes;
• chemical processes; and
• thermal processes.
4.2.2.1 Gas Processes
In gas processes, gases, such as, CO2, N2, and CH4, are injected at relatively
high pressures in order to create a miscible mixture with the hydrocarbon.
Once miscibility has been achieved, the interfacial tension (IFT) is reduced to
nearly zero and the resultant mixture flows more readily through the reservoir.
Because of the high pressures that are generally required, gas processes would
be applicable only at relatively large depths in a confined stratum.
4.2.2.2 Chemical Processes
Three chemical processes appear to have applicability to in situ soil flushing:
(1) polymer flooding, (2) surfactant flooding, and (3) alkaline flooding. Poly-
mer and alkaline flooding have not been evaluated extensively for use in envi-
ronmental applications. On the other hand, a good deal of research has been
conducted on the use of surfactants to assist in the cleanup of soils that contain
hydrocarbon waste.
In polymer flooding, a water-soluble polymer is added to the injected water
in order to increase its viscosity. The increase in injectant viscosity will de-
crease the mobility ratio. This, in turn, will increase the areal sweep efficiency,
Ea, and, to some small degree, the displacement efficiency, Ed, but will not
increase the capillary number significantly enough to reduce the final hydrocar-
bon saturation to a reasonably small value.
4.15
-------
Potential Applications
The use of surfactants as an additive to the injected water in order to extract
organic contaminants appears to be one of the most promising of in situ soil
flushing techniques. In this process, a surface-active agent, a surfactant or mi-
celle, is injected into the soil in order to reduce the IFT to nearly zero. Micelles
allow the injected water and the hydrocarbon to form an emulsion that flows
more readily through the soil. Once this emulsion moves to the surface, it can
be broken and the hydrocarbon can be recovered. While surfactants are envi-
ronmentally safe and relatively inexpensive, the proper design of an in situ
cleanup system using them is complicated by factors such as adsorption, salin-
ity of the injected water, concentration of the surfactant, and temperature.
The use of alkaline agents, instead of direct injection of surfactants is another
process that may be applicable to the in situ cleanup of hydrocarbons. When in
contact with certain hydrocarbons, alkaline agents, such as sodium hydroxide or
sodium carbonate, can react to form surfactants. These in situ generated surfac-
tants then act to reduce the EFT of the system. In most cases, the hydrocarbon
waste that is the target must exhibit an acidic-type behavior. That is, it must
contain a minimum amount of acid components.
4.2.2.3 Thermal Processes
In thermal EOR processes, heat is injected into the soil. The most common
methods of adding this thermal energy are through the injection of hot water or
steam. The most important mechanism in this process is the reduction of hy-
drocarbon viscosity because of the increased temperature. Lowering the viscos-
ity decreases the mobility ratio to a value where the efficiencies described ear-
lier are increased to reasonable values. The applicability of this process, there-
fore, is limited primarily to situations where a very heavy hydrocarbon is being
recovered. The effectiveness of the technology in environmental applications is
not known.
4.16
-------
Chapters
PROCESS EVALUATION
5.7 Soil Washing
5.1.1 Process Performance
The evaluation of a soil washing system usually turns upon the quality of the
residuals produced. The residuals of concern are:
• the oversize materials, typically everything >6.4 mm (>0.25 in.);
• the coarse-grained materials, the sands produced by treatment;
• the fine-grained fraction containing the concentrated contaminants;
and
• the process water.
In most soil washing applications, the principal objective is to meet the treat-
ment standards applicable to the oversize materials and the product sands so
that they may be placed back on the site without limitation. The major measure
of effectiveness, therefore, is the ability to meet specified standards for the
residuals that are targeted for placement back on site.
The fine-grained fraction may be either dewatered into a sludge cake for
disposal off site, or subjected to additional treatment. The process water is
recycled, and may or may not require treatment dependent upon the contami-
nants removed. At the conclusion of the project, the process water remaining in
tankage will require treatment for disposal off site.
When used as a pretreatment step to other remediation processes, soil wash-
ing presents two key advantages. The first is its ability to substantially contrib-
ute to waste minimization. The process can concentrate 70 to 90% or more of
5.1
-------
Process Evaluation
the nonvolatile and heavy metal contaminants in a residual soil product repre-
senting only 5 to 40% of the original soil volume. The washed soil product
(representing 60 to 95% of the original volume and containing from 0 to 30%
of the original contamination) may be suitable for redeposition on site or for
other beneficial uses (see figure 5.1). Even better removals have been achieved
with volatile organic compounds (VOCs).
FigureS.l
Processed Materials Distribution
Original volume of
contaminated soil or
sediment
>.
Soil (sediment)
washing process
70% to 90%
Washed (decontaminated)
product returned to source or
otherwise beneficially used
] 1
10% to 30%
Residual contaminated
concentrate requiring
ultimate destructive
treatment or disposal
The second advantage lies in its potential cost-effectiveness. For many sites,
substantial remediation savings can be realized by reducing the sheer volume of
contaminated soil that must be treated and disposed of by more complex and
expensive methods. Costs are estimated to be $170 to $280/tonne ($150 to
$250/ton) of soil for commercially-available soil washing systems, compared to
$390/tonne ($350/ton) for secure landfill and $l,100/tonne ($l,000/ton) for
incineration, including excavation, site support, gate rate disposal, transporta-
tion, and applicable taxes. Further savings are realized through reduced trans-
portation costs. Tables 5.1 and 5.2 (on page 5.3) present examples of potential
cost savings.
Because its treatment systems are closed and contain fugitive dusts and vola-
tile emissions, soil washing should be viewed favorably by the public when
compared with other remediation methods.
5.2
-------
Chapters
Table 5.1
Example of Potential Cost Savings of Soil Washing*
A. Site remediation costs without soil washing -100,000 yd3 (76,460 m3) soil excavated and transported to
off site facility 500 miles for incineration and disposal.
• Excavation, staging and site management $3,000,000
• Transportation (20 yd3 load, $3/mile) 7,500,000
• Incineration ($l,000/yd3) 100,000,000
• Disposal of Ash (80,000 yd3 @ $150/yd3) 12,000.000
$122,500,000
B. Site remediation costs using soil washing -100,000 yd3 (76,460 m3) soil excavated and soil washed,
25,000 yd (19,110 m3) transported off site for incineration and disposal.
Excavation and site management $3,000,000
Soil Wishing 15,000,000
Transportation of Sludge Cake 1,875,000
Incineration of Sludge Cake 25,000,000
Disposal of Ash 3,000,000
$47,875,000
•Assuming the soil requires incineration
Table 5.2
Typical Cost Comparison for a Cleanup Project
Involving 38,230 m3 (50,000 yd3) of soil contaminated with PCBs.
Assumes that residuals requiring further treatment or disposal are 15% of the
original volume processed.
Destruction by incineration only Soil pretreatment with incineration of residuals
$50,000,000 $12,250,000
Disposal in an RCRA designated Soil wash pretreatment with landfill
landfill (50,000 yd3)
$12,500,000 $6,625,000
Destruction by dechlorination Soil wash pretreatment with dechlorinization of
(50,000yd3) ttSftSn
$11,500,000 $6,475,000
Solidification/stabilization with Soil wash pretreatment with
landfill storage at a separate site solidification/stabilization of
(50 000 yd3) residuals, landfill storage at a
w'nnn nm separate site
$8,000,000 $5,950,000
Unit Costs Used For Comparisons
Per Cubic Yard
Incineration $1,000.00
Landfill $250.00
Dechlorination $230.00
Solidification/Stabilization $160.00
Soil Washing Pretreatment $95.00
5.3
-------
Process Evaluation
Soil washing is a low-cost alternative for separating wastes. Testing to date
indicates the technology can remove volatile organic contaminants with 90 to
99% effectiveness, and semivolatile organics and metals with 40 to 90% effec-
tiveness.
5.1.2 Range of Costs
The cost of soil washing is dependent upon several key variables:
• volume of the soil to be treated;
• nature of the contaminants to be removed;
• particle size distribution, particularly the volume of fines in the
process stream; and
• site preparation requirements.
Although there are presently no completed full-scale soil washing operations
in the U.S. from which to derive comparative cost data, estimates have been
made based upon the literature. Based upon projects in the range of 23,000 to
180,000 tonne (25,000 to 200,000 ton), the estimated treatment price, including
all known cost components, is in the range of $170 to $280/tonne ($150-$250/
ton). Details of these estimates are set forth in table 5.3 (on page 5.5). These
costs are consistent with current field pricing.
5.1.3 Key Operational Considerations
Key operational considerations for soil washing include the following:
• cleanliness or treatability of the oversize material;
• whether standard screening steps can be used to prepare soils for
treatment;
• whether materials can be effectively separated; and
• whether the generated sludge volume will be within disposal and
cost limitations.
5.4
-------
Chapters
5.2 Soil Flushing
5.2.1 Process Performance
Laboratory column and shaker studies have been very successful, demon-
strating removal efficiencies of petroleum hydrocarbons, chlorinated hydrocar-
bons, and metals at levels above 99%. Pilot studies are reporting highly suc-
cessful removals.
The removal efficiencies in the field have varied from site to site. This vari-
ability is related more to the site hydrogeology than to the contaminants of
concern. The vadose zone is generally poorly understood by most investiga-
foble 5.3
Soil Washing Comparative Cost Data
Capital Costs
Plant Capacity
Process Time
Plant Cost ($)
25,000
15 ton/hr
6 months
3,000,000
\61ume (Short tons)
50,000 100,000
25 ton/hr
9 months
4,500,000
25 ton/hr
12 months
4,500,000
200,000
50 ton/hr
12 months
7,500,000
Prices expressed in $/ton
Operating Costs
Depreciation
MOB and DEMOB
"Normal" Site Prep
Material handling
Labor
Chemicals
Maintenance
Safety Equipment
Utilities
Process Testing
Disposal of Residuals
10% assumption
Management/Engineering
Overhead and Profit
NET PRICE ($/short ton)
40
8
12
15
30
15
8
3
8
15
32
70
256
30
4
6
15
25
15
6
3
g
12
32
60
216
15
3
4
15
20
15
4
3
g
g
32
48
175
12
1
2
15
15
15
2
3
8
5
32
40
150
Assumptions: • The "Basic" Plant consists of mechanical screening, separation, flotation, and fines handling
• Site excavation is not included, materials exist at an influent feed pad.
• The soil is predominantly sand and gravel with 20% <63 microns
• Contaminants of concern are PNAs and metals, existing in fines and sands
• The plant throughput capacity is sized to spend 1 year processing
• Process time is 2 shifts per day, 5 days per week, one day of maintenance.
• Summary does not include RI/FS, treatability studies, or the RD package.
5.5
-------
Process Evaluation
tors. In addition, the State of California has taken the position that even for site-
specific conditions, there is no solute transport model that is reliable.
The relationship between capillary pressure, water content, and permeability
is not generally understood in the field. In addition, the complexity of some
hydrogeologic settings precludes a successful soil flushing operation. Since the
success rate under laboratory conditions is very high and that in the field is not,
it appears that a better understanding of unsaturated flow in the vadose zone is
required to successfully implement soil flushing. One study reported at the
Volk Field, Wisconsin, site (US EPA 1990), showed that the field tests did not
agree with the laboratory tests for the firefighter training pit soil. Heavy rains at
the site, however, may have contributed to the decreased percolation and pore
clogging.
Bench-scale soil flushing tests have proven to be very successful; however,
field applications have not shown the same success. The problems of reduced
permeability by plugging and biofouling must be overcome. In addition, soil
flushing in the field may be subject to flow instabilities which result in finger
flow that may not remove the contamination between the fingers. The use of
supersurfactants (REMSOL) may reduce this problem. No single in situ re-
moval or treatment technique is likely to be the most effective technique in all
situations. The most cost-effective in situ remediation approach may require
two or more different techniques in sequence.
5.2.2 Process Byproducts
The majority of the surfactants, polymers and gas additives are biodegrad-
able and, consequently, the byproducts are CO2 and water. Some alkaline/acid
wastes may require pH control, with minimal measurable byproduct. The ma-
jority of the byproducts are the contaminants that are removed by the treatment
process. The amount of these contaminants varies with the condition of the site.
5.2.3 Range of Costs
Because of the site specific nature of remedial techniques and the limited
field application of in situ flushing, it is difficult to obtain comprehensive, de-
tailed cost estimates of this technique at this time. The following preliminary
economic evaluation of the technique by Sara Kimball is based on a process
that is being developed by Eckenfelder Inc., Nashville, Tennessee (Oma, Wil-
5.6
-------
Chapters
son, and Mutch 1991). The estimates are based on the results of two math-
ematical models of hypothetical contaminated sites and represent the upper and
lower estimates of remediation of an area with the characteristics listed in table
5.4.
Table 5.4
Optimum Conditions for In Situ Surfactant-Enhanced Soil Flushing
Factor Optimum Conditions
Soil Characteristics
Particle Size Low Silt and Clay Content
TOC Low, <10%
Hydraulic Conductivity Medium to High, >10
Waste Characteristics Hydrophobic KOW = 3 or less
Nonvolatile
Organic
Surfactant Characteristics Non toxic, biodegradable
Soluble at Ground Witer Temps
Doesn't sorb to Soil
HLB # matches Contaminant HLB #
Effective at Low Cone., <3.0%
Low-Soil Dispersion
Low-Surface Tension
Low CMC
Rom Kimball, S.L, "Surfactant-Enhanced Soil Flushing: An Overview of an In Situ Remedial Technology
tor Soils Contaminated with Hydrophobic Hydrocarbons," in 'Hydrocarbon Contaminated Soils," \fol II,
Kostecki. FT, Calabrese, E.J., Bonazountas, M., Eds, Lewis Publishers 1992, a subsidiary of CRC
Press, Boca Raton, Florida. With permission
The best case model (Equilibrium Solubility Model) is a materials-balance
model based on the solubility limit of the organic contaminant(s) within the
sodium docyl sulfate (SDS) surfactant. This model calculates the volume of
surfactant needed to solubilize a given mass of contaminants within the soil.
The surfactant is distributed at the surface. The model predicts a cost of
$103.70/m3 ($79.30/yd3) of contaminated soil.
The worst case estimate is made with the Two Component Local Equilib-
rium Model created by Wilson and Clarke (1991). With this model, an injec-
tion and a recovery well flush a 2-dimensional aquifer with surfactant. With a
5.7
-------
Process Evaluation
surfactant flow rate of 1,950 L/min (516 gal/min), this model predicts recovery
of 95% of the polychlorinated biphenyls (PCBs) and all the trichloroethylene
(TCE) in 2 years. Cleanup times depend on site-specific soil and/or contami-
nant characteristics. This model gives an estimated remedial cost of $214.907
m3 ($164.30/yd3) of contaminated soil. Input parameters required by the model
are listed in table 5.5.
fable 5.5
Modeled Example Site Parameters and Values
Parameter Wue
Contaminants
Arochlor 1254 in heavy oil 2,000 mg/kg - V&dose Zone
200 mg/kg - Saturation Zone
TCE 200 mg/kg - \adose Zone
20 mg/kg - Saturation Zone
Site Area 4 QOO m2 (1 acre)
%dose Zone Depth 3 m (10 feet)
Aquifer Depth 3 m (10 feet)
Soil Density l,700kg/m3
Soil Porosity 0.3
Surfactant
Sodium Dodecylsulfate 2.5%
From Kimball, S.L., 'Surfactant-Enhanced Soil Flushing: An Overview of an In Situ Remedial "technology for Soils
Contaminated with Hydrophobic Hydrocarbons,* in "Hydrocarbon Contaminated Soils," Vol. II, Kostecki, PI", Calabrese,
E.J., Bonazountas, M., Eds., Lewis Publishers 1992, a subsidiary of CRC Press, Boca Raton, Florida. With permission.
The cost evaluation breakdown for both models is given in table 5.6 (on
page 5.9). The cost for in situ flushing is considerably less than other forms of
remediation. The Oma, Wilson, and Mutch (1991) study yields costs of $1,300
to $2,600/m3 ($1,000 to $2,000/yd3) for off-site disposal.
Direct capital costs included in the study are purchased equipment, equip-
ment installation, instrumentation and controls, piping, and electrical. A 12%
interest rate and a 7-year amortization apply to capital costs. Indirect capital
costs include engineering and supervision, construction expenses, fees, and
contingency.
5.8
-------
Chapters
Table 5.6
Cost Evaluation Breakdown for In Situ Surfactant Flushing
of One Acre Example Site
Cost Component
Amortized Cap. Equip.
Site Construction
Operations &
Maintenance
Labor
Materials
Electrical Power
Analytical
Wfeste Disposal
Total
Equilibrium Solubility
Model (78 gal/min SDS)
Total Cost
($1,000)
978
129
727
414
132
31
143
2,554
Unit Cost
($/cu yd)
30.40
4.00
22.60
12.60
4.10
1.00
4.40
79.30
Two Component Local Equilibrium
Model (5 16 gal/min SDS)
Total Cost
($1,000)
3039
129
915
414
622
31
143
5,293
Unit Cost
($/cu yd)
94.40
4.00
28.40
1280
19.30
1.00
440
164.30
• All costs are in 1990 dollars.
• Site construction cost includes labor and materials
• Site construction cost range is for excavation of PCB-contaminated soil without (lower cost) and
with (higher cost) the use of sheet piling.
Reprinted from "Surfactant Flushing/Washing. Economics of an Innovative Remedial Process Including Recovering and
Recycle" by K.H. Oma, D.J. Wilson, and R.D. Mutch, Jr in the Proceedings of the Fourth Annual Hazardous Material
Management Conference/Central, 1991. Published by Advanstar Expositions. Copyright 1991 by K.H Oma, DJ
Wilson, and R.D Mutch, Jr. By permission.
Included in the operation and maintenance (O&M) costs are labor, materials,
electrical power, analytical work, and waste disposal. The O&M costs com-
prise 56.6% of the estimated total remediation cost. The O&M cost assump-
tions are given in table 5.6.
The following costs were not included in the remediation evaluation because
they vary considerably from site-to-site:
• remedial investigation/feasibility study;
• permitting — local, state, and federal;
• administrative and legal project management;
• contractor profit; and
• contingency — usually 10 to 15% of total cost.
Capital costs for chemically enhanced solubilization (CES) are similar to
those for traditional pump-and-treat (P&T), except for the initial expense of
5.9
-------
Process Evaluation
surfactant handling equipment. Operating costs are similar also, except for
surfactant replacement and handling. Overall, on a life-cycle basis, CES is
significantly less expensive than P&T because of the much shorter time frames
and smaller volumes of water which have to be extracted and treated.
The following set of parameters can be used to compare cost and time esti-
mates for CES with those for pump-and-treat. Assume a 3 x 30 x 30 m con-
taminated aquifer with a hydraulic conductivity of 10"1 cm/sec and a porosity of
35% containing 135,000 L of TCE (a residual dense nonaqueous phase liquid
(DNAPL) saturation of 14%). For an injection-withdrawal system with 3 injec-
tion and 3 withdrawal wells, the groundwater level time across the system
would be on the order of 70 days at an injection rate of 10 L/min. Approxi-
mately 21 pore volumes of a 1% surfactant solution would be needed to solubi-
lize the TCE, based on interpretation of the data from the Borden test site. This
would require 21 x 70 days, or approximately 4 years.
The equivalent time for pump-and-treat with groundwater as the solvent
depends on the effective solubility of the groundwater. Normally, pumped
effluents contain less than 10% of the aqueous solubility of the halogenated
solvent being pumped. Thus, for TCE, the effective aqueous solubility would
be on the order of 100 mg/L. This would require over 2,000 pore volumes of
ground water and about 400 years to decontaminate the aquifer.
Capital costs for this example are estimated to be $200,000, including sur-
factants, air stripping, and carbon treatment of the offgas. Annual operating
costs are estimated at $150,000 per year, including $50,000 per year for surfac-
tants. The four-year cleanup is then estimated to cost a present value of
$697,000 at a cost of capital of 8%. A similar system for P&T would cost ap-
proximately $100,000 initial capital and $100,000 annual operating cost. After
9 years with less than 3% of the TCE removed, the present value cost of the
P&T system exceeds that of CES (Jackson, Fontaine, and Wunderlich 1992).
5.10
-------
Chapter 6
LIMITATIONS
6.1 Soil Washing
6.1.1 Process Limitations
Effectiveness of soil washing is highly dependent on site conditions. It is
relatively ineffective on soils with high silt and clay content (i.e., more than
40% of the soil has a particle size of <63 mm (230 mesh)). It may be relatively
ineffective also on soils contaminated with a high concentration of mineralized
metals or hydrophobic organics. Washing additives (e.g., chelating agents,
solvents, surfactants) may be tailored to the site, soil, and contaminant condi-
tions; however, these may be hazardous, difficult to recover, and interfere with
washwater treatment. If these conditions occur, process costs may be prohibi-
tive because of the cost of treating washing fluids and replenishing additives.
Hydrophobic contaminants can be difficult to separate from soil particles
into the aqueous washing fluid. Estimated aqueous distribution coefficients
(Kd), also known as partition coefficients (K ), indicate the fraction of the con-
taminant expected to remain on the soil particle versus the fraction of the con-
taminant dissolved in the water. Alternative methods can be used to estimate
these values when tabulated values cannot be located. A contaminant with a
high Kd (e.g., polychlorinated biphenyl (PCB) >10,000) is more difficult to
wash off the soil particles using water than a contaminant with a lower Kd (e.g.,
trichloroethylene (TCE) = 3). Additives, such as surfactants, may be required
to improve removal efficiencies. When additives are used, however, larger
volumes of washing fluid may be needed.
Complex mixtures of contaminants in the soil, such as a mixture of metals,
nonvolatile organics, semivolatile organics, etc., make it difficult to formulate a
6.1
-------
Limitations
single suitable washing fluid that will remove all the different types of contami-
nants from the soil. Sequential washing steps, using different additives, may be
needed. Frequent changes in the contaminant and its concentration in the feed
soil can disrupt the efficiency of the soil washing process. To accommodate
changes in the chemical or physical composition of the feed soil, modification
of the wash fluid formulation and the operating settings may be required. Alter-
natively, additional feedstock preparation steps, such as blending soils to pro-
vide a consistent feedstock, may be appropriate.
High humic content in the soil makes separation of contaminants very diffi-
cult. Humus consists of decomposed plant and animal residues and offers bind-
ing sites for accumulation of both organics and metals.
A high percentage of clay and silt (e.g., more than 30 to 50%) in the soil
usually indicates that soil washing will not be favored because of the amount of
time and money required to treat the soil. A volume reduction process like soil
washing is most cost-effective when the clean soil fraction is much larger than
the more contaminated soil fraction. Performance can be limited also by weath-
ering and aging. Mineralized or degraded contaminants cannot be easily re-
moved.
Chelating agents, surfactants, solvents, and other additives are often difficult
and expensive to recover from the spent washing fluid by conventional treat-
ment processes, such as, settling, chemical precipitation, or activated carbon, in
order to recycle it. The presence of additives in the contaminated soil and treat-
ment sludge residuals may cause added difficulty in disposing of these residu-
als.
6.1.2 Reliability of Performance
As opposed to thermal processes, where the heat transfer unit (the kiln or the
dryer) must be kept within limited operating ranges, soil washing is a particu-
larly forgiving process. This is because the moving force of the process, the
feed stream that is driving the soil through the system, has a broad range of
acceptable influent concentrations. This advantage can be significantly dimin-
ished, however, by a broadly divergent or heterogeneous feed stream. Proper
attention to treatability studies and pilot-scale tests can reduce this risk.
6.2
-------
Chapter 6
6.1.3 Site Considerations
Commercial power will normally be used, although in extreme circum-
stances, the plant can be operated with generators. Process water is required as
plant makeup, supplied from commercial sources or from a local well. In re-
mote sites, a roadway may have to be constructed before the plant can be in-
stalled. The plant itself will be placed on a properly designed operations area
providing protection of uncontarninated areas and normal run-on and run-off
controls.
6.1.4 Waste Matrix
The waste matrix may pose the most significant limitation on soil washing.
It is often reported that soil washing is not effective over a certain percentage of
fines (often cited as 30%). But this is not necessarily the case. Soil washing is
a separation and treatment system. Therefore, the ability to properly remove
and treat any portion of the contaminated soil should be evaluated in the context
of what other options are available. For example, a project where incineration
has been specified as the remedy may be substantially improved by using soil
washing as part of the process train to allow for incineration of only the material
really requiring that step.
6.1.5 Risk Considerations
The main risk in soil washing operations is that of inaccurate site character-
ization. The material encountered at the remedial site may not be like the soils
studied in treatability or pilot-scale tests. Additional contaminants may be
encountered, and the percentage of the fine-grained fraction may be signifi-
cantly different from that expected.
6.1.6 Process Needs
Every soil washing project requires a treatability study, and, possibly, a pilot-
scale study. The treatability study can be conducted in the laboratory on a batch
basis. It will characterize the soil/contaminant relationship and enable evalua-
tion of each of the unit operations considered for the full-scale process plant. In
addition, it will enable development of a mass balance and process diagram so
that the system can be adequately understood on an operations and cost basis.
In some cases, the bench-scale treatability study must be supported by a pilot-
scale study. The pilot plant studies will normally be performed in the field, on a
6.3
-------
Limitations
continuous process basis. The pilot-scale study is intended to confirm the find-
ings of the bench-scale study and provide adequate data to upgrade processes to
full-scale operations.
6,2 Soil Flushing
6.2.1 General
One principal drawback of soil flushing is the generation of large quantities
of contaminated elutriate, the mixture of water, surfactants, and contaminants
that is recovered in the soil flushing process, requiring treatment. In some
cases, the elutriate may be discharged to a local publicly-owned treatment
works (POTW), but often on-site treatment must be devised. As with many
other treatment methods, soil flushing requires that the groundwater flow pat-
tern be well defined to ensure complete recovery of the elutriate. If not, physi-
cal barriers such as slurry walls may be required. This technique also requires
access to a source of water for flushing. Typically, groundwater is extracted,
treated, and recycled as the flushing solution.
Soils with pockets of low hydraulic conductivity may limit the effectiveness
of flushing. This limits the ability to pass large quantities of water through the
contaminated soil. Many underground storage tank (UST) sites, especially
those in urban settings, do not lend themselves to flushing because of nearby
pipes and underground utilities. Soil flushing will be less effective at sites
where the contaminants are relatively insoluble or tightly bound to the soil. The
lack of an existing water supply may also be limiting.
The use of surfactants involves several considerations. The interactions of
the surfactant with the biological, physical, and chemical properties of the un-
saturated zone are typically uncertain, and must be determined at each site. For
example, the addition of a surfactant containing sodium may lower soil perme-
ability due to its reactive effect on the soil/sodium adsorption ratio (US EPA
1987b), which with time would decrease the effectiveness of this technique.
The groundwater geochemistry also should be assessed for troublesome, natu-
rally-occurring constituents prior to addition of any surfactant. For example,
hard water may render a surfactant ineffective. The soil may also reduce a
surfactant's effect. High clay content can cause chemical adsorption of the
6.4
-------
Chapter 6
surfactant to the soil, thereby reducing available surfactant concentrations and
limiting its effectiveness. Biological effects on the surfactant may also be im-
portant. In some cases, a surfactant may biodegrade too quickly, reducing its
exposure time to the contaminated soil. On the other hand, the surfactant
should be degradable by the soil microbes at a slow rate so that surfactant
buildup does not occur.
At the present, another limitation of soil flushing is the inability to separate
the surfactant from the water, so that the surfactant can be recycled. Until the
surfactant can be separated from the water, the high rates of surfactant con-
sumption will limit the cost-effectiveness of soil flushing.
6.2.2 Reliability of Performance
Since very few test sites have been evaluated, the reliability of soil flushing
is an open issue. Soil flushing as a remediation technology is in its infant stage.
While water flooding has been used at several sites, the enhanced oil recovery
(EOR) approaches have undergone very little testing at contamination sites.
The success of EOR techniques over the past fifty years, however, suggests
their probable success in soil flushing.
A limitation occurs with contaminated soils located in the vadose zone. As
contaminants are mobilized by soil flushing, the soil's capacity to retain oil must
be satisfied before the oil will flow through the materials. Residual adsorption
capacities of soils can be in the neighborhood of 1/3 of a pore space. This can
result in the loss of large volumes of free-phase oils and increases the volume of
soils at residual saturation that need to be remediated.
The limitation of water flooding or primary oil recovery lies in its capability
to remove only a portion of the total free-phase hydrocarbon contamination in
the subsurface, leaving a substantial residual oil level in the subsurface.
6.2.3 Site Considerations
While many theories are available to describe soluble contaminant transport
in ideal homogeneous media, many sites are far from ideal, involving
nonhomogeneous subsurface conditions, nonuniform distribution of contami-
nants, or a nonaqueous phase liquid (NAPL), any of which will cause channel-
ing and uneven treatment. In any of these conditions, it may be particularly
difficult to determine whether the flushing solution has sufficiently contacted all
6.5
-------
Limitations
waste material in the aquifer and whether the cleanup objectives can be
achieved within the estimated flushing water volumes.
Quite often, NAPLs accumulate in the form of a floating "free-product"
layer, or dense nonaqueous phase liquids (DNAPLs) may sink down to pool on
top of a lower confining layer. These concentrated products must often be
removed before appreciable soil flushing of soluble contaminants from the
groundwater can be accomplished. The solubilization of product into the
groundwater will otherwise continue as a source for quite some time. Removal
of this product is based on the basic premise that the physical forces that hold
large fractions of this residual product immobile can be overcome by the addi-
tion of chemical solutions to modify the pore-level environment or by the cre-
ation of sufficiently steep hydraulic gradients to recover the product in its free
form.
Heterogeneities in natural geological materials make the prediction and de-
tection of contaminant behavior in groundwater difficult in practice. Advection
is normally considered on the macroscopic scale in terms of the pattern of
groundwater flow. Flow patterns and flow nets in ideal uniform media are
described extensively in textbooks; however, heterogeneities, such as, horizon-
tal permeable lenses, often dominate the actual transport of contaminants and
groundwater. It is not unusual to encounter lenses of 2 to 3 orders of magnitude
higher permeability (K) or conductivities 100 to 1,000 times that of the sur-
rounding media. For example, a change of silt or clay content of only a few
percent in a sandy zone can have a large effect on hydraulic conductivity.
These lenses exert a very strong influence on the migration patterns,
dispersivity, and velocity distribution. Contaminants can move through the
flow system almost entirely in these thin layers at an overall reduced travel
time. Similarly, lower permeability aquatards can impair vertical groundwater
and contaminant migration, particularly that of NAPLs.
Pump-and-treat as a remediation strategy is coming under close scrutiny in
the U.S. because of its inability to bring the concentration levels down from
below required action levels. Problems associated with pump-and-treat ap-
proaches can be related to nonideal aquifer conditions such as heterogeneity,
anisotropy, and variable density. In addition, pump-and-treat programs suffer
from well construction effects, including partial penetration, partial screening,
and incomplete development. Anthropogenic influences such as property ac-
cess, vandalism, and unknown pumpage or injection can create further prob-
lems. Issues such as physiochemical attenuation, biological transformation, and
operational failures all lead to shortcomings in pump-and-treat.
6.6
-------
Chapter 6
Figure 6.1
Moisture Retention Curves — Three Soli Types
so r
Soil suction, bars
Source: Everett 1986
Site characterization requires an understanding of soil suction and percent
moisture in the soils under investigation (figure 6.1). In the field, soil suction
can be measured with tensiometers and then related to percent moisture through
the use of water characteristic curves (Everett 1992). In order to determine
when unsaturated flow takes place, the relationships between porosity, specific
yield, and specific retention (figure 6.2 on page 6.8) must be understood
(Everett, Wilson, and Hoylman 1984). For modeling purposes, it also must be
understood that the relative permeability in the vadose zone increases dramati-
cally over a narrow range of soil moisture pressure potentials (figure 6.3 on
page 6.9). For definitive treatment of vadose zone flow and monitoring see
Everett, Wilson, and Hoylman 1984 and Everett 1986 and 1992.
6.7
-------
Limitations
Figure 6.2
Variation of Porosity,Specific Yield, and Specific Retention with Grain Size
45
40
35
30
25
*
20
15
10
5
0
Porosity
3
u
Source: Everett et al. 1984
6.2.4 Waste Matrix
The physical, chemical, or biological mechanism with which the waste is
bound to the soil matrix dictates the type of remediation strategy. Wastes that
are soluble and loosely held to the soil matrix are good candidates for water
flooding. Those that have a high interfacial tension require EOR techniques
and those that result in toxicity problems when interacting with the wash solu-
tion need to be carefully evaluated. Finally, wastes that result in plugging from
fines movement, inorganic precipitation, formation of stable emulsions, or
biological activity need to be measured to prevent permeability problems.
6.8
-------
Chapter 6
6.2.5 Risk Considerations
Although vadose zone models are used as a guide in many soil flushing
applications, the California Water Resources Control Board has taken the posi-
tion that solute transport models in the vadose zone are not reliable and that
vadose zone monitoring will be required to confirm all vadose zone character-
ization and remediation programs.
The dispersion of solutes during transport through many types of fractured
rocks cannot be described by the same relationships for homogeneous granular
materials. Fractured geologic materials are notoriously anisotropic with respect
to the orientation and frequency of fractures. For example, distribution coeffi-
cients are more commonly expressed on the basis of media surface area rather
than mass. Little is known about predicting dispersion in fractured media. If
Figure 6.3
Relationship of Pressure Potential to Relative Permeability to Water
Soil properties: y versus /fw (wetting curve).
-350 I
0.20 0.40 0.60 0.80 1.00
Relative Permeability to Water, km
6.9
-------
Limitations
the transverse dispersivity is very large, contaminants transported along rela-
tively horizontal flow paths can migrate deep into the flow system. Dispersivity
can be established only by detailed field testing and experiments.
6.2.6 Process Needs
Shaker table and column bench studies (see figure 6.4) are required to deter-
mine the appropriate surfactant type, dosage, and pore volumes (see figure 6.5
on page 6.11). The bench-scale approach does appear to present a problem.
Figure 6.4
Bench-Scale Flushing Apparatus
Gllass tube
Glass bell top
Steel plate
Threaded steel rod
Stainless steel shelby tube
Steel plate
Glass tube
TEFLON* influent bag
TEFLON«
TEFLON* cap
Glass beads
Soil
Glass wool
Glass beads
TEFLON* cap & valve
TEFLON* effluent bag
• TEFLON™
6.10
-------
Chapter 6
Figure 6.5
Bench-Scale Soil Flushing Study
Actual and Simulated Trlchloroethene vs. Pore Volume
Equation 1 (Kd=0.502 ml/g)
- Column 8 soil concentration ratio
during flushing
Cv - Soil concentration at pore volume v
Co - Initial soil concentration
40
Cumulative Pore Volume
The field process suffers from a lack of site characterization and flow under-
standing. Site characterization in the vadose zone is a complex problem
(Everett, Wilson, and Hoylman 1984), and only a few companies specialize in
vadose zone investigations. The problems of channeling, instabilities, and
preferential flow need further technical understanding at some sites.
6.11
-------
-------
Chapter 7
TECHNOLOGY PROGNOSIS
7.7 Soil Washing
7.1.1 Further Treatment of Fines
Most technical development will take place in the additional treatment of the
fine-grained fractions. Success in this area has the potential of decreasing the
amount of residual material that must be disposed of off site, reducing the unit
treatment prices. Work is currently being done to develop the use of bioslurry
reactors for use in further degrading the organic constituents in the fines, and in
developing extraction and recovery techniques to remove inorganics. Improved
extraction and recovery techniques may also enable the production of some
after treatment market value from valuable materials existing as contaminants.
Examples may be the recovery of metallic copper through the cementation
process, the recovery of high concentration ferrous materials that may be intro-
duced back into a steel plant through the sintering plant, and recovery of an
iron-chromium complex. In some cases, both organic and inorganic treatment
of the fines may be conducted, and although some sludge will result from the
treatment, the volume may be only 10% of the volume of sludge cake that may
be produced without further fines treatment.
Further treatment of the fines means the ability to truly recover valuable
materials from the contaminant stream. In addition, the oversize materials may
also have value after they have been cleaned. Examples are wood products that
may be chipped and burned in a cogeneration facility for the production of
electricity, scrap steel products that can be sold to steel "minimills" for produc-
ing pipe and rebar, tires that can be introduced into tire recycling facilities, and
construction debris that can be crushed and used as construction grade aggre-
gates.
7.1
-------
Technology Prognosis
7.1.2 Fixed Plant Operations
Soil washing is currently offered as a mobile treatment unit, and undoubt-
edly will remain available in this configuration. The European experience,
however, has clearly demonstrated that fixed plant operations are more efficient
and provide corresponding cost advantages. In a fixed plant, the mobilization
and demobilization costs, the site set-up costs, and other costs attending mobile
treatment are not incurred. More unit operations can be made available and
thus provide broader treatment capability. The key barrier that will need to be
addressed is the ultimate disposal of residuals that are generated in the fixed
plant, particularly, the clean products. In the Netherlands, for example, the sand
and oversize materials, once they have been treated to the required standard, are
sold as construction-grade materials on the open market. This would require a
change in current regulations in the U.S.
72 Soil Flushing
Soil flushing that relies on fluid movement in the subsurface has a strongly
positive prognosis for sites where the depth to contamination, contaminant
distribution, permeability, and permeability heterogeneities are compatible with
the process. Additional research is required, however, as to such matters as,
soil/water incompatibility, permeability reductions, and flushing chemical reten-
tion in the subsurface.
Recent breakthroughs in developing a "supersurfactant" reduce the concerns
about soil/water incompatibility and permeability reductions. The supersurfac-
tant developed by Sadeghi (Sadeghi et al. 1988,1989a, 1989b; Sadeghi,
Sadeghi, and Yen 1990; Sadeghi, Everett, and Yen 1992) has the ability to form
a surfactant from the contaminated soil at the site. Based upon the old chemical
engineering adage that "like dissolves like," the supersurfactant is capable of
improving soil/water/contaminant compatibility.
Various investigators have reported that vadose zone permeability is reduced
with successive water flooding (Nash and Traver 1989; Nash, Traver, and
Downey 1987). Explanations of permeability reductions relate to fine-grained
material transport and plugging, chemical precipitation, and micelle (surfactant)
size. The REMSOL process, which produces the supersurfactant, utilizes a
7.2
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Chapter?
sonication stage that has been optimized to create a micelle size that is much
smaller than the normal surfactant and consequently results in minimizing the
permeability impacts.
The issue of chemical retention in the vadose zone and in the saturated zone
must be recognized. Chemically enhanced soil flushing is applicable at many
sites as a cost-effective step between water flooding and other technologies,
such as, in situ passive bioremediation, that have the potential over time to
lower cleanup levels. Since chemical additives may not be hazardous, their
presence in the subsurface should not add to the risk. Residual contamination,
however, has the potential to slowly degrade over time. Chemical retention in
the saturated zone is subject to all of the problems identified with pump-and-
treat systems.
The limitations discussed in Section 6.2.3 notwithstanding, pump-and-treat
systems have been successful in hydraulically containing contaminated fluids at
a particular site. For soil flushing activity, therefore, the principal value of
pump-and-treat is to hydraulically contain the fluids as they are flushed from
the system and to treat the contamination at the surface. To this extent, there-
fore, pump-and-treat systems are more applicable to soil flushing technologies.
It is important to realize, however, that velocity plots and capture zones of
pumping systems, as represented in figure 7.1 (on page 7.4), must be under-
stood. Clearly, the flow rates within the boundary of the capture are substan-
tially different than the downgradient stagnant area represented in figure 7.1 (on
page 7.4). The hydrodynamic isolation (dead spots) within well fields need to
be understood.
Typically, a concentration/time plot of contamination residual, as repre-
sented in figure 7.2 (on page 7.5), shows that after pumping cessation, the re-
sidual concentration increases. As a part of a soil flushing operation, however,
the source of contamination in the vadose zone will have been removed, and as
such, this contaminant level rebound should not occur.
Soil flushing must, however, be effective in removing contaminants which
have diffused into low permeability sediments. In addition, it must be able to
desorb contaminants from sediment surfaces. Further, liquid-liquid partitioning
of immiscible contaminants must occur in order to mobilize the pollutants of
concern. The permeability variations which can affect the success of soil flush-
ing are represented in figure 7.3 (on page 7.5).
7.3
-------
Technology Prognosis
Figure 7.1
Cross-Sectional and Three Dimensional Conceptualizations of
Capture Zone vs. Cone of Depression
Cone of depression ^——f Cone of depression
^= Saturated zone = Saturated zone
Cross-sectional conceptualization Cross-sectional conceptualization
Capture zone — cone of depression
Capture zone — cone of depression
Three dimensional conceptualization
Figure A. Stagnant aquifer conditions
Three dimensional conceptualization
Figure B. Mild natural gradient
Cone of depression
Saturated zone
Cross-sectional conceptualization
—— Saturated zone
Cross-sectional conceptualization
Capture zone — cone of depression
Three dimensional conceptualization
Figure C. Moderate natural gradient
Three dimensional conceptualization
Figure D. Steep natural gradient
Based upon. US EPA 1989
7.4
-------
Chapter?
Figure 7.2
Contaminant Level Increases After Remediation Stops
Contaminant Levels May Rebound When Pump-and-Treat Operations Cease,
Because of Contaminant Residuals.
ON
OFF
MAX
APPARENT
RESIDUAL
CONTAMINATION
CESSATION
OF
PUMPING
(CLOSURE?)
-TIME-
TARGET
CONCENTRATION
Based upon: US EPA 1989
Figure 7.3
Permeability Variations Limit Remediations
High-Permeability Sediments Conduct Most of the Row; Low-Permeability Sediments
Act As Leaky Contaminant Reservoirs
ADVECTION
7.5
-------
-------
Appendix A
APPENDIX A
List Of Vendors and Contacts
Soil Washing Vendors
Alternative Remedial Technologies, Inc.
14497 North Dale Mabry Hwy.
Suite 140
Tampa, FL 33618
Phone:813-264-3571
Bergmann USA
1550 Airport Road
Gallatin,TN 37066
Phone: 615-230-2100
Bio-Recovery System, Inc.
2001 Copper Avenue
LasCruces,NM 88005
Phone: 505-523-0405
Biotrol, Inc.
11 Peavey Road
Chaska,MN 55318
Phone:612-448-2515
Canonie Environmental Services Corp.
94 Inverness Terrace East, Suite 100
Englewood,CO 80112
Phone: 303-790-1747
Environmental Technology Applications
2000 Tech Center Drive
Monroeville, PA 15146
Phone:412-829-5202
Flo Trend System, Inc.
707 Lehman
Houston, TX 77018
Phone: 800-762-9893
Geochem, Inc.
12265 West Bayaud Avenue
Suite 140
Lakewood,CO 80228
Phone: 303-988-8902
Northwest Enviroservice, Inc.
P.O. Box 24443
1700 Airport Way South
Seattle, WA 98124
Phone: 206-622-1085
OHM Corporation
2950 Buskirk Avenue
Suite 315
Walnut Creek, CA 94596
Phone:510-256-7187
On-Site Technologies, Inc.
1715 South Bascom Avenue
Campbell, CA 95008
Phone:408-371-4810
Onsite-Offsite, Inc./Battelle PNL
2500 East Foothill Boulevard
Suite 201
Pasadena, CA 91107
Phone: 818-405-0655
A.1
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List of Vendors and Contacts
REMSOL (USA) Corporation
P.O. Box 6630
Santa Barbara, CA 93160-6630
Roberts & Schaefer Company
Suite 400
120 South Riverside Plaza
Chicago, IL 60606
Phone:312-236-7292
Scientific Ecology Group, Inc.
Nuclear Waste Technology
Department
P.O. Box 598
Pittsburgh, PA 15330
Phone: 412-247-6255
Waste-Tech Services, Inc.
800 Jefferson County Parkway
Golden, CO 80401
Phone: 303-279-9712
A.2
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Appendix A
Soil Flushing Contacts
Robert Haines
B.C. Excavating Inc.
2251 Cinnabar Loop
Anchorage, AK 99507
Phone: 907-344-4490
Joe Henry
Arkansas Research & Inst. Co. Inc.
10310W.Markham, Suite 165
Little Rock, AR 72205
Phone: 501-224-2793
Glen Turney
Western Tech.
4625 S. Ash, Suite J12
Tempe, AZ 85282
Phone: 602-820-6733
Anneline Osterberg
American Environmental Mgt. Corp.
10960 Boatman Way
Stanton, CA 90680
Phone:714-826-6320
Stephen Testa
Applied Environmental Services
23223 Plaza Pointe Drive, Suite 100
Laguna Hills, CA 92653
Phone:714-455-4080
Rob Eisele
Envirodyne Inc.
2840 A Howe Rd.
Martinez, CA 94553
Phone:510-370-7800
James Lu
Unitech Engineering Inc.
16331GothardSt.#D
Huntington Beach, CA 92647
Phone:714-842-8888
Sharon Perry
Eneco-Techlnc.
1580 Lincoln St., Suite 1000
Denver, CO 80203
Phone: 303-861-2200
Daniel Kogut
Aaron Environmental Specialists
937 S. Main St.
Plantsville, CT 06479
Phone: 203-628-9858
Robert Penoyer
BRA Environmental Inc.
1067 N. Hercules Ave.
Clearwater, FL 34625
Phone: 813-449-2323
Richard Gion
ETUS Inc.
ISllKastnerPl.
Sanford,FL 32771
Phone:407-321-7910
Robert Pierce
Florida Spill Response Corp.
605 Townsend Road
Cocoa, FL 32926
Phone: 800-282-4584
NEECO
Box 1046
Gonzalez, FL 32560
Neville Kingham
Kibner Associates Inc.
400 DeKalb Tech. Pkwy., Suite 200
Atlanta, GA 30340
Phone: 404-455-3944
Lome G. Everett
Geraghty & Miller, Inc.
5425 Hollister Ave., Suite 100
Santa Barbara, CA 93111
Phone: 805-964-2399
James Kuipers
Environmental Control Tech. Inc.
17062 S. Park Ave.
S. Holland, IL 60473
Phone: 708-333-6065
A.3
-------
List of Vendors and Contacts
Karen Jensen
Environmental Science &
Engineering Inc.
300 Hamilton St. Suite 330
Peoria, EL 61602
Phone: 309-655-3350
Larry Schneider
Massac Env. Tech. Inc.
Route #4 Box 279
Metropolis, IL 62960
Phone:618-524-9615
Jeff Pope
MittelhauserCorp.
27010 Iroquois Dr.
Naperville, IL 60563
Phone: 708-369-0201
Jim Powell
Warzyn Inc.
2100 Corporate Drive
Addison, IL 60101
Phone: 708-691-5000
J. Anthony Rogers
The-HydroTech Corp.
1106 Meridian Plaza, Suite 340
Anderson, IN 46016
Phone: 317-642-1581
E.J. Foltz
Cartec Technical
618 Buttermilk Pike
Covington, KY 41017
Phone: 606-341-6006
Tom Wackerman
Applied Science & Tech Inc.
Box 1328
Ann Arbor, MI 48106
Phone:313-663-3200
Ellin Glynn
Carlo Env. Tech. Inc.
44907 Trinity Dr., Box 744
Mt. Clemens, MI 48046
Phone:313-468-9580
Jim Dragun
The Dragun Corp.
30445 Northwestern Hwy., Suite 260
Farmington Hills, MI 48334
Phone:313-932-0228
Jim Pratt
Superior Environmental Corp.
14641 16th Ave., Box 118
Marne, MI 49435
Phone: 616-677-5255
William Kwasny
GME Consultants Inc.
14000 21st Ave. N.
Minneapolis, MN 55447
Phone:612-559-1859
Cameron Reynolds
Ecotechnology Inc.
Box 7029
Columbia, MO 65202
Phone: 314-875-8434
Ben Sharp
Kingston Environmental Services
1600 S.W. Market St.
Lee's Summit, MO 64081
Phone:816-524-8811
Stewart Ryckman
REACT Environmental Engineering
2208WelschInd.Ct.
St. Louis, MO 63146
Phone: 314-569-0991
Randy Alewine
Terracon Environmental Inc.
7810N.W. 100th St., Box 901541
Kansas City, MO 64190
Phone: 816-891-7717
Thomas Benthall
Coastal Environmental Services Inc.
Box 772
Ahoskie, NC 27910
Phone: 919-332-2061
A.4
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Appendix A
Bob Graziano
Four Seasons Ind. Services, Inc.
3107 S. Elm-Eugene St.
Greensboro, NC 27406
Phone:919-273-2718
Stephen Fauer
Environmental Strategies &
Applications
Route #203, Suite 100
Flemington,NJ 08822
Phone: 908-782-0122
Tracy Straka
Environmental Waste Management
Assoc.
1235 Route 23 South, Box 648
Wayne, NJ 07474
Phone: 201-633-7900
MelWolkstein
Reach Assoc. Inc.
75 S. Orange Ave.
South Orange, NJ 07079
Phone: 201-263-2877
Robert Chernow
Recon Systems Inc.
5 Johnson Dr., Box 130
Raritan,NJ 08869
Phone:908-526-1000
Gary Kirsch
O'Brien & Gere Eng. Inc.
Box 4873,5000 Brittonfield Pkwy.
Syracuse, NY 13221
Phone: 315-437-6100
Terry Brown
OBG Tech. Services Inc.
5000 Brittonfield Pkwy., Box 5240
Syracuse, NY 13220
Phone:315-437-6400
David Tagg
Specialized Process Equipment Inc.
5000 Brittonfield Pkwy., Box 3283
Syracuse, NY 13220
Phone: 315-437-2400
Ria Davidson
Brack Hartman Env. Inc.
4055 Executive Park Dr.
Cincinnati, OH 45241
Phone:513-483-3000
Brad Schneider
Encore Environmental
344 W. Henderson Rd.
Columbus, OH 43214
Phone: 614-263-9287
Bill Sanders
Environment One
7777 Wall Street
Cleveland, OH 44125
Phone: 216-524-0888
Sandra Fox
Foppe Thelen Group Inc.
11415 Century Blvd.
Cincinnati, OH 45246
Phone: 800-468-8144
Gary Rail
MHC Env. Inc.
2237 E. Enterprise Inc.
Twinsburg, OH 44087
Phone: 216-425-2393
Patricia Ziegler
OHM Corp.
16406 US Rt. 224 E.
Findlay, OH 45840
Phone: 800-537-9540
David Emery
Bioremediation Services, Inc.
Box 2010
Lake Oswego, OR 93705
Phone: 503-624-9464
R.D. Bleam
Bioscience Inc.
1530 Valley Center Pkwy., #120
Bethlehem, PA 18017
Phone: 215-974-9693
A.5
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List of Vendors and Contacts
Thomas Trent
Earth Sciences Consultants Inc.
One Triangle Drive
Export, PA 15632
Phone:412-733-3000
D. Buffington
The ERM Group
855 Springdale Drive
Exton,PA 16341
Phone:800-544-3117
P. Kipin
Kipin Ind. Inc.
513 Green Garden Rd.
Aliquippa,PA 15001
Phone:412-495-6200
NedWehler
R.E. Wright Assoc. Inc.
3240 Schoolhouse Rd.
Middleton, PA 17057
Phone: 717-944-5501
Dennis Whittington
CW Environmental Services Inc.
2308 Watauga Rd., Suite #2
Johnson City, TN 37601
Phone: 615-926-3999
Kenneth Lee
Pickering Enviro Ram Inc.
1750 Madison Ave.
Memphis, TN 38104
Phone: 901-726-0810
Bob Brachter
Universal Engineering Svcs.
Box 3233
Midland, TX 79702
Phone: 915-686-0403
GaryLaasko
Applied Geotechnology, Inc.
Box 3885
Bellevue, WA 98031
Phone: 206-453-8383
Scott Gladden
RZA Agra Inc.
11335 N.E. 122nd Way, Suite 100
Kirkland,WA 98034
Phone: 206-820-4669
Shannon & Wilson Inc.
400 N. 34th St., Suite 100
Box 300303
Seattle, WA 98103
Phone: 206-632-8020
Marcy Sawall
RMTInc.
744 Heartland Trail
Madison, WI 53708
Phone:608-831-4444
Rudy Gaudin
Delta Omega Technologies Inc.
P.O. Box 81518
Lafayette, LA 70798-1518
Phone: 318-237-5091
Tom Sale
CH2MHU1
6060 S. Willow Drive
P.O. Box 22508
Englewood, CO 80111-5142
Phone:303-711-0900
Malcom Pitts
Surtek
1511 Washington Ave.
Golden, CO 80401
Phone: 303-278-0877
Richard Steimle
US EPA - Technology Innovation
Office
OS 110 W - 401 M Street SW
Washington, DC 20460
Phone:703-308-8846
Chuck Orwig
Tricil Environmental Response Inc.
P.O. Box 19529
Houston, TX 77224-9529
Phone: 800-283-3433
A.6
-------
Appendix A
Ann Clarke
Eckenfelder, Inc.
227 French Landing Drive
Nashville,TN 37228
Phone: 616-255-2288
Kenton Oma
Eckenfelder, Inc.
227 French Landing Drive
Nashville, TN 37228
Phone: 616-255-2288
David Wilson
Vanderbilt University
Department of Chemistry
Nashville, TN 37235
Phone: 615-322-2861
Abdul Adbul
General Motors Research Laboratory
Environmental Science Division
Warren, MI 48090-9005
Phone: 313-986-1600
Robert Knox
University of Oklahoma, Civil
Engineering
202 West Boyd Street, Room 334
Norman, OK 73019-0631
Phone: 405-325-4256
Richard Luthy
Carnegie Mellon University
Civil Engineering Department
Pittsburgh, PA 15213
Phone:412-268-2940
John Fountain
SUNY at Buffalo
4240 Ridge
Buffalo, NY 14260
Phone:716-831-2464
William Rixy
Shell Development Company
Westhollow Research Center
Houston, TX 77251-1380
Phone:717-493-8311
Dick Krei
Unique Products, Inc.
2228 S. El Camino Real #175
San Mateo, CA 94403
Phone: 800-325-6747
John Cherry
University of Waterloo
Center for Groundwater Research
200 University Ave. West
Waterloo, Canada N2L3G1
Phone:519-888-4516
Robert Wunderlich
Interra, Inc.
6850 Austin Center Blvd., Suite 300
Austin, TX 78731
Phone:512-346-2000
A.7
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-------
Appendix B
APPENDIX B
Soil Washing Case Histories
Case 1
Project Performance Date: January 1992 — October 1992
Project Name: King of Prussia Technical Corporation Site
Location: Winslow Township, Camden County, N.J.
Key Contaminants: Chromium, Copper, and Nickel
Technical Team: Alternative Remedial Technologies, Inc. (ART)
(A Joint Venture of Geraghty & Miller, Inc. and
Heidemij Realisatie of the Netherlands)
Point of Contact: Michael J. Mann, P.E.
Phone: (813)264-3571
Project Summary. This National Priorities List (NPL) site is known as the
King of Prussia (KOP) Technical Corporation site. The ten-acre site is in a
rural area approximately 48 km (30 miles) southeast of Philadelphia. The site
was operated for approximately three years with the intention of converting
industrial sludges into materials that could be marketed as construction-grade
materials. That plan did not materialize, and, over the operational period, about
57 MM L (15 MM gal) of sludges were transported and treated at the site. The
Remedial Investigation identified soil and groundwater contamination, a Feasi-
bility Study was completed, and the Potentially Responsible Parties (PRP)
Group chose to take the lead responsibility in remediating the site. The Record
of Decision (ROD) specified soil washing as the remedial technology to be
used to treat the source materials. Five key contaminants were identified in the
soils, and treatment standards were established.
The PRP Group took a strong, proactive approach to working with the U.S.
EPA Region n and the New Jersey Department of Environmental Protection
(NJDEP) to implement the requirements of the ROD. It was clear that substan-
tial time and money could be saved by taking action and completing the re-
B.1
-------
Soil Washing Case Histories
quirements. Additionally, because an aggressive approach could move forward
on a pace faster than the consent order required, the regulators were interested
in being part of an effort that posted a possible early construction completion.
With that goal, several contractors performed initial soil evaluations, and it
became clear mat several distinct subsources exist at the site: lagoons with pure
sludge, lagoons with sludge and soil-like material, and an area of natural soils
with sludge intermittently disposed. Additionally, it was found that the soil
matrix, in terms of its particle size distribution, was a good candidate for vol-
ume reduction activities, with about 10-15% fines.
Soil Washing Treatability Study. Alternative Remedial Tecnologies was
selected to perform a detailed treatability study in accordance with the Compre-
hensive Environmental Response Compensation Liability Act (CERCLA) guid-
ance document. The treatability study first defined the particle size and con-
taminant relationships for each source area, examined the nature of the particle
and soil relationships using Scanning Electron Microscopy/Electron Probe
Microanalysis. It was found in this first phase, that the contaminants were pri-
marily bound in the fine-grained fraction of the soils, but, that in some cases,
several of the coarse-grained fractions also exceeded the treatment standards.
Next, bench-scale work was conducted to specifically evaluate screening, sepa-
ration, and treatment steps that could be used in the configured full-scale treat-
ment plant.
Process Equipment and Configuration. During this phase, mechanical
screening to 500 um (30 mesh), hydrocycloning, gravity separation, flotation,
dewatering, sludge handling and processing testing were performed and docu-
mented. After the unit operations were selected, the combined treatment train
was operated on a sequential batch basis in the laboratory in what was called a
process simulation run. The results of this study provided the basis for develop-
ment of a system mass balance and design/operational parameters.
Results of Treatability Study. As a result of the treatability study it was con-
cluded that soil washing, as proposed and configured in the report, could meet
the requirements of the ROD.
Soil Washing Demonstration Run. To confirm the findings of the treatability
study and to provide additional assurance to all parties, it was proposed and
accepted to perform a Demonstration Run on actual KOP site materials at the
full-scale Heidemij plant located at Moerdijk, The Netherlands. First, approvals
were obtained from the United States Environmental Protection Agency (U.S.
EPA) and the Dutch equivalent organization (VROM). The project team
(PRP's, U.S. EPA, the soil washing contractor, and the consultant) developed a
detailed plan, excavated representative soils totalling 180 tonne (200 ton), pack-
aged the material in "Super Sacks", loaded the material into transportation con-
tainers, and shipped the material to the Port of Rotterdam. There, the material
was downloaded to the plant and prepared for the demonstration.
B.2
-------
Appendix B
Process Equipment and Configuration. The Heidemij plant is a Treatment,
Storage, and Disposal Facility (TSDF) equivalent with an annual treatment
capacity of approximately 70,000 tonne (80,000 ton). The plant consists of all
the unit operations to be used at the KOP site and was configured in exactly the
same manner as proposed in the KOP treatability study. The treatment included
feed preparation, loading, wet screening, hydrocyclone separation, surfactant
addition, flotation and dewatering of the sand fraction, and sedimentation,
thickening, and dewatering of the fines. Three process residuals — oversize
material, sand, and a dense sludge cake — were produced, staged, examined,
sampled, and analyzed. The oversize sand products are intended for placement
back onsite and were analyzed for the target contaminants. The sludge cake
will be disposed at a hazardous waste landfill and was analyzed to confirm
compliance with applicable land disposal restrictions. The process plant is now
in the design process. The team will move to the KOP site in early 1993 when
full-scale operations will begin.
Results of the Demonstration Run. The demonstration run was extremely
successful in meeting the stated objectives of confirming that the soil washing
plant, configured as recommended in the KOP treatability study, can effectively
treat KOP soils in compliance with the ROD requirements.
Full-Scale Operations. Prior to full-scale operations, a pilot run was per-
formed on 1,000 tons of composited site soils. The pilot-run was successful
and cleanup levels below the ROD-specified standards were reached. Record
of Decision standards are:
• Chromium — 483mg/kg
• Copper — 3,571 mg/kg
• Nickel—1,935 mg/kg
Full-scale operations began on June 28,1993 and ran until mid-October,
1993. During the operation of the soil washing facility, clean soils were re-
turned to the site as backfill. The contaminated fraction was disposed of at an
appropriate disposal facility. The site was then revegetated and returned to its
natural condition.
B.3
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Soil Washing Case Histories
Case 2
Project Performance Date: October 1989
Project Name:
Location:
Key Contaminants:
Technical Team:
Point of Contact:
MacGillis and Gibbs Site
New Brighton, Minn.
PAH's, PCP, Cu, Cr, As
Biotrol, Inc.
11 PeaveyRoad
Chaska,Minn. 55318
Phone: (612) 448-2513 Fax: (612) 448-6050
Mr. Dennis Chilcote, President, Biotrol, Inc.
Project Summary. A SITE Program demonstration of the soil washing tech-
nology developed by Biotrol, Inc., was carried out. The demonstration showed
that the contamination in the bulk of the soil can be greatly reduced. The con-
taminants were concentrated in a much smaller volume of soil fines than could
be successfully treated biologically.
Process Equipment and Configuration. The overall operation consisted of
three units — the soil washing process, a fixed-film bioreactor to treat process
water prior to recycling, and a slurry bioreactor to treat the residuals from the
soil washing process.
Treatment Standards and Results. Since this was a demonstration, there
were no treatment standards. Removal of pentachlorophenol during soil wash-
ing ranged from 87 to 89%. For polynuclear aromatic hydrocarbons (PAHs),
the removal ranged between 83 and 88%. The bioreactor removed 91 to 94%
of the pentachlorophenol in the influent washwater. Removal efficiencies in the
slurry bioreactor increased 90%.
Cost Information. Based on the results of this demonstration, the cost to
treat one ton of soil (18 tonne/hr (20 ton/hr)), including water treatment, slurry
biodegradation, and incineration of woody debris, was estimated at $168.00.
B.4
-------
Appendix B
Case 3
Project Performance Date: September 1991 through June 1992
Project Name: U.S. Army Corps of Engineers, Saginaw, Mich.
Location: Saginaw, Mich.
Volume: 450 tonne (500 ton)
Key Contaminants: PCBs
Technical Team: Bergmann USA
Point of Contact: Richard Traver, Program Director
Bergmann USA
Project Summary. Bergmann USA was invited to present an overview on
river and harbor sediment treatment technology to the joint U.S. EPA and Army
Corps of Engineers'(ACOE) Assessment and Remediation of Contaminated
Sediments (ARCS) Work Group in March, 1991. Bergmann was contracted
by Jim Galloway, ACOE, Detroit, to conduct a Pilot Sediment Washing Dem-
onstration on the Saginaw River Project, In-house, bench-scale treatability
evaluations were performed, followed by the design and fabrication of a 5-10
ton/hr pilot-scale Bergmann USA field demonstration sediment washing plant
to effectively separate contaminated fines from coarse fractions of river dredge
sediments. This plant was placed into operation in October 1991 a mile and a
half off-shore aboard a 37 m x 10 m (120 ft x 33 ft) ACOE dredge support
barge for the processing of approximately 450 tonne (500 ton) of PCB-contami-
nated soil.
Preliminary results indicate a reduction of 91% of the initial polychlorinated
biphenyl (PCB) concentration with only .2 mg/kg of PCBs remaining in the
"clean" coarse >74 urn (>200 mesh) fraction. The <74 um (<200 mesh) fines
were enriched to a level of 14 mg/kg PCBs, and the humic fraction (leaves,
twigs, roots, grasses, etc.) contained 24 mg/kg of PCBs. These materials are
scheduled for biodegradation during the Spring/Summer of 1992.
This system was evaluated by the Superfund Innovative Technology (SITE)
Program in May and June, 1992 by SAIC, Inc., working with Jack Hubbard, of
the EPA Hazardous Waste Engineering Research Laboratory in Cincinnati.
Preliminary analytical test results will be available in July, 1992 followed by
the Applications Analysis Report in August, 1992 and the Technology Evalua-
tion Report in February 1993.
This 9 tonne/hr (10 ton/hr) plant processed approximately 180 tonne (200
ton) of PCB-contaminated dredge sediments prior to winterization. An addi-
tional 270 tonne (300 ton) of material was washed during the May through
June, 1992 evaluation period.
B.5
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Soil Washing Case Histories
Project Performance Date:
Project Name:
Location:
Volume:
Key Contaminants:
Technical Team:
Point of Contact:
Cose 4
January 1992 to September 1992
Toronto Harbour Commission's (THC) Soil Re-
cycling Demonstration Project
Toronto, Ontario, Canada
4,000 tonne (4,400 ton)
Cadmium, Arsenic, Copper, Lead, Mercury, Zinc,
Nickel, Oil and Grease, PAH's
THC, SNC, Inc., Bergmann USA,
Bodemsaneling Nederland, B.V. (BSN)
Dennis Lang, Director of Engineering
Toronto Harbour Commission
Phone: (416) 863-2047 Fax: (416) 863-4830
Project Summary:
• demonstration project costing $8,000,000, entirely privately funded;
• demonstration integrated soil washing, metal extraction by chela-
tion, and organics reduction by aerobic bioremediation in upflow air
reactors;
• two soil washing processes evaluated; Bergmann USA's chemical
attrition scrubbing system at 4.5 to 9 tonne/hr (5 to 10 ton/hr), and
BSN's high-pressure wash system at 50 ton/hr at a wash plant in
Holland; and
• objective was to treat soil so that cleaned soil can be reused on
industrial land and metals removed can be recycled.
Process Equipment and Configuration:
• BSN wash system tested by shipping three 320-tonne (350-ton)
bagged samples to Holland for washing. Residual soil returned in
bags; residual slurry with concentrated contaminants returned in
2,600170-L (45-gal) drums for metal removal and bioremediation;
• Bergmann USA leased a 4.5 to 9 tonne/hr (5 to 10 ton/hr) demon-
stration soils unit which was located on site; and
• Process - soil wash for volume reduction, then metals reduction,
and then organics reduction by bioremediation.
Treatment Standards and Results:
• Objective was to meet Ontario Ministry of The Environment stan-
dards for cleaning soil for industrial use;
B.6
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Appendix B
• Soil wash systems effectively cleaned coarse (>6 mm (>0.2 in.))
and intermediate streams (0.063 to 6 mm (0.002 to 0.2 in.)) to in-
dustrial standards;
• Metal extraction process can remove metals to meet residential and
agricultural standards; and
• Bioremediation process can reduce oil and grease to industrial lev-
els.
Cost Information:
• Total project cost $8,000,000 (Canadian); and
• Estimate a 45 tonne/hr (50 ton/hr) commercial-scale treatment plant
would cost about $25,000,000 and would charge $175/tonne ($1607
ton) to clean soil.
B.7
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Soil Washing Case Histories
CaseS
Project Performance Date: December 1991 — Ongoing
Project Name:
Location:
Volume:
Key Contaminants:
Technical Team:
Point of Contact:
Bruni Soil Washing Project
Bruni, Tex.
12,000 m3 (16,000 yd3) (15,000 tonne (16,000
ton))
Uranium and Radium
Scientific Ecology Group (SEG) and
Westinghouse Science and Technology Center
C. P. Keegan
Scientific Ecology Group
1501 Ardmore Blvd., 3rd Floor
Pittsburgh, PA 15221
Phone: (412)247-6255
Project Summary. Bruni, Texas was the site of a Westinghouse in situ ura-
nium mining operation between 1975 and 1981. Borings containing uranium
and radium ore were left on the surface during the drilling of over 1,000 wells.
Additionally, solution spills during plant operations added uranium and radium
to the soil. Over the years, uncontaminated soil built up over the contaminated
soil in a nonuniform manner.
The characteristics of this site are particularly difficult for the application of
soil washing: fresh water supplies are limited to 150 L/min (40 gal/min), the
area is semiarid and humid, and the clay content of the soil is very high (be-
tween 40 and 60%). In addition, contaminated root hairs from site vegetation
and ion exchange resins from solution spills must be removed from the soil.
The SEG Soil Washing System arrived on the Bruni Site in December, 1991.
Assembly, start-up and calibration were completed in March, 1992, and produc-
tion began. Processing rates were increased until the rated capacity of 18 tonne/
hr (20 ton/hr) was achieved. Over 7,000 tonne (8,000 ton) were successfully
processed as of August 1,1992. Processing at Bruni and demobilization are
scheduled for completion by the end of 1992.
Process Equipment and Configuration. The patented soil washing process is
based upon commonly-available mineral treatment equipment and processes. It
consists of several unit operations tied together in an integrated process to wash
and separate soil components from contaminating materials and to separate the
contaminants from each other. It does this through a combination of particle
separation by size and density and by chemical extraction using environmen-
tally-acceptable extraction solutions. The general process can be modified to fit
the needs of a particular site by changing the extraction solution chemistry and
particle separations. The almost infinite combinations of soil and contaminant
characteristics made the use of a treatability study mandatory, but the flexibility
B.8
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Appendix B
inherent in the soil washing process allows a wide degree of latitude in its appli-
cation.
In the SEG Soil Washing System, the excavated soil is first processed to
remove large rocks and debris, which are cleaned for return to the site. The soil
is then processed in a rotating drum to sort and prewash the soil. The large
fraction is washed with leachate solution to remove the fines, rinsed with water,
and returned to the site. The remaining contaminated soil is then processed
using mineral processing equipment in which the soil contacts with the leachate
solution and the resins and root hairs are separated from the soil for disposal.
The washed soil is then rinsed, monitored, and returned to the site. The
leachate is further treated and sent to the leachate make-up tanks for reuse.
The SEG Soil Washing System is permanently mounted on three trailers.
Auxiliary equipment, such as, the feed hopper and conveyors, is transported on
additional trailers. The system is therefore mobile for rapid transport, mobiliza-
tion, and demobilization.
Treatment Standards and Results. Table B.I shows the average contamina-
tion levels at the Bruni site and the limits established by the Texas Department
of Health:
Table B.I
Treatment Standards for the Bruni Soil Washing Project
Average Soil Required Levels
Contaminant Contamination Level Above Background Background
U 70 ppm 42 ppm (30 pCi/g) 1 ppm
Ra 6 pCi/g 5pCi/g(5 \ W6 ppm) 1 pCi/g
From a volume standpoint, the uranium is to be removed to parts per million
levels and the radium is to be removed to parts per trillion levels. Generally, the
concentration of contamination on the site is one to five times the acceptable
levels.
The terms for the lease of the Bruni site property require that when returned
to the landowner, the land must be capable of sustaining the growth of buffalo
grass, a prominent local vegetation in the Bruni area. The soil must therefore
remain fertile after processing.
B.9
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Soil Washing Case Histories
Bruni Results. Essentially 100% of the soil is being recovered as clean soil.
The uranium and radium are extracted in the resin and zeolite columns. The
uranium can be stripped and used by uranium processors and is therefore not a
waste stream. The zeolite, resins and root hairs are the waste streams requiring
disposal. Incineration of the resins and root hairs in the SEG incinerator at its
Oak Ridge, Tennessee facility will reduce their volume by over 100:1.
The average concentration of uranium in the clean soil to date is 20.7 ppm
and the average concentration of radium in the clean soil, including back-
ground, is 5.9 pCi/g. Laboratory testing of processed soil showed that it is
capable of sustaining buffalo grass growth.
Cost Information. Soil washing prices generally range 25-75% below pack-
aging, hauling and burying. The cost is a function of the contaminants, the soil
type, the cleanup limits, the available utilities, etc.
Additional advantages of soil washing are:
• sometimes possible to separate a mixed waste into a radioactive and
hazardous component;
• final solution to contamination on-site;
• allows free-release of treated soil;
• significantly reduces the amount of waste requiring disposal;
• reduces disposal cost;
• processing performed on site;
• flexible process meets the specific needs of various sites;
• no damage to the environment;
• closed-cycle process guarantees no air or water pollution;
• quick site remediation with 18 tonne/hr (20 ton/hr) capacity mobile
system;
• in some cases, concentrated metal removed from the soil can be
sold as a useable product; and
• reduces liability.
B.10
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Appendix B
Project Performance Date:
Project Name:
Location:
Key Contaminants:
Technical Team:
Point of Contact:
Case 6
1987 — 1988
Poly-Garb Site
Wells, Nev.
Phenol and Creosol
CH2M Hill/EPA Region 9
Mr. Bob Mandel, EPA Region 9
Phone: (415)744-2290
Project Summary. Soils contaminated with phenol and creosol were placed
in a double-lined, half-acre leach field. The leach field extraction system con-
tained a water supply, an irrigation system to distribute water onto the soil, a
leachate collection system above the top liner, a holding tank, disposable granu-
lar activated carbon (GAC) cartridges, and necessary pumps.
Process Equipment and Configuration. Contaminated soils were treated in a
"passive" soil washing system. Clean water was spray irrigated onto the waste,
collected as leachate, treated and reused.
Treatment Standards and Results. Soil leaching reduced phenol concentra-
tions in the soil by'99.9% and lowered creosols by 99.7%. Influent phenol
concentrations averaged 980 mg/kg and after treatment were less than 1 mg/kg.
B.n
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Soil Washing Case Histories
Case?
Project Performance Date: August 1990
Project Name:
Location:
Size:
Key Contaminants:
Technical Team:
Point of Contact:
Union Pacific Railroad
Pocatello, Idaho
11 Recovery Wells
Nonaqueous phase liquids (NAPLs)
Kennedy, Jenks, and Chilton
Ann Williamson, EPA Region 10
Phone: (206)553-1090
Project Summary. Upper-aquifer groundwater was extracted from eleven
wells at 75 L/min (20 gal/min) each. The recovered groundwater was treated
and discharged to the Pocatello Publicly Owned Treatment Works. Clean water
was injected into the infiltration galleries located within the capture zone. The
reinjected water assisted in mobilizing contaminants that could then be col-
lected by the recovery well.
Process Equipment and Configuration. The process equipment included the
recovery wells, the treatment system, and the infiltration galleries. The treated
water was enhanced with in-line oxygen and nutrients to stimulate biodegrada-
tion during the soil flushing process.
Treatment Standards and Results. The system involved the recovery and
treatment of approximately 439 MM L/yr (116 MM gal/yr) for five years.
Clean water was used for the flushing.
Cost Information. The cost estimate for the project, including capital and
operation and maintenance (O&M), was $1,191,000.
B.12
-------
Appendix B
CaseS
Project Performance Date: 1988 -1990
Project Name: Private Wood Treating Site - Pilot Test
Location: Western U.S.
Key Contaminants: Polynuclear aromatic hydrocarbon (PNA), com-
pounds and carrier oils
Technical Team: CH2M Hill and Surtek
Point of Contact: Tom Sole, CH2M Hill, Denver, Colo.
Phone: (303)771-0900
Project Summary. This privately-owned former wood-treating site contains
over 400,000 m3 (500,000 yd3) of PNA-contaminated alluvial deposits with
significant dense non-aqueous phase liquids (DNAPLs) and a floating free-
product layer. Contaminants are contained by underlying impermeable shale, a
perimeter bentonite slurry wall, and a negative hydraulic gradient.
The soil volume and proximity to residences preclude excavation and on-site
treatment. The PNA concentrations limit the effectiveness of pump-and-treat
remedies. These conditions encourage the use of in situ technologies, such as
primary oil recovery and soil flushing.
Process Equipment and Configuration. The field test was conducted in a
3.6-m (12-ft) deep test cell isolated from the surrounding alluvium by a 8.2 x
8.2 m (27 x 27 ft) sheet-pile wall. Alluvial sediments graduated from fine
sands, silts, and clays at the surface to coarse sands and fine gravels at the base.
The lower three feet of alluvium was saturated by a waste wood-treating oil.
The density and viscosity of the oil were approximately 1.04 g/cm3 and 54 cp,
respectively.
Delivery and recovery of the soil-washing solutions were accomplished
using 10.16-cm (4-in.) horizontal drain lines spaced 4.6 m (15 ft) apart in paral-
lel and located at the alluvium-bedrock contact.
Above-ground process facilities required to complete the pilot included:
• tankage and controls for storage and regulated delivery of the soil-
washing solution;
• pumps for recovery of fluids from the alluvium; and
• reactors for treatment of the produced fluids.
A summary of the sequence used in the pilot test is presented in table B.2 (on
page B. 14). A pore volume is defined as the volume of liquid required to satu-
rate the cell and was estimated at 19,000 L (5,000 gal).
The first step was to cycle water between the recovery and delivery drain
lines and to displace all of the mobile free-phase oil. Recovery of oil and water
B.13
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Soil Washing Case Histories
Table B.2
Delivery Sequence and Volumes
Volume
Delivered
Sequence Fluid (gallons) (pore volumes)
Viiiterflooding
Soil Flushing
Reconditioning
Witer
PolystepA-7R
Makon-10*
Vfcter
Makon-lO"
Water
144,000
10,000
10,000
10,000
10,000
150,000
28
2
2
2
2
30
phases from the alluvium was accomplished using a dual drain recovery con-
cept. The primary purpose of the waterflood or primary oil recovery sequence
was to remove all mobile oil so the efficacy of soil flushing could be gauged
under conditions where only immobile, residual oil remained.
The second phase of the pilot test was to deliver 100,000 L (30,000 gal) of
soil washing solutions consisting of a mixture of alkaline agents, polymer, and
surfactants. The composition of the soil washing solution was determined hi
the laboratory studies described earlier and is presented in table B.3 (on page
B.15). Two different soil washings were used in the pilot test. Based on the
laboratory tests, it was believed that optimal results could be obtained by using
the Polystep A-7R initially to produce reusable wood-preserving oil, followed
by the Makon-lO" system to achieve lower cleanup levels.
Included in the delivery phase was 38,000 L (10,000 gal) of water delivered
after the first 76,000 L (20,000 gal) of soil-washing solution had been delivered.
The intermediate water cycle kept fluids moving while the arrival of more soil-
washing solution was awaited.
The final phase of the test involved flooding the cell with water to displace
the mobilized oil and soil-washing solution remaining in the alluvium.
Treatment Results And Conclusions. It was concluded that in situ soil flush-
ing could play an important role in recovery of waste wood-treating oils at the
site.
A total of 7,200 L (1,900 gal) of PNA-contaminated oil was removed from
the test cell. On average, primary oil recovery was able to reduce oil concentra-
tion from 93,000 to 15,500 mg/kg, and in situ soil flushing further removed the
oil to achieve a final concentration of 5,100 mg/kg, or a 94% reduction overall.
The test primarily used petroleum industry methods for the recovery of free-
phase, non-aqueous hydrocarbons. More aggressive soil adsorption and viscos-
B.14
-------
Appendix B
Table B.3
Soil Washing Solutions
Makon-lO" System
Compound Concentration
PolystepA-7R System
Compound Concentration
Alkaline
Polymer
Surfactant
PH
Viscosity
Na2C03
NaHCO3
Xanthan Gum
Biopolymer
Makon-lO""
9.2
54 cp
0.825 by wt
0.65% by wt
l,050mg/L
1.4% by wt
Na2C03
NaHCO3
Xanthan Gum
Biopolymer
PolystepA-7Rb
10.2
54 cp
0.1% by wt
0.72% by wt
l,050mg/L
1% by wt
"Ethoxylated nonylphenol
bSodium dodecyl benzene sulfonate
ity, or in situ bioremediation were recommended to lower cleanup levels fur-
ther.
The removal of pore space oil also increased the soil bulk permeability from
15 to 30 Darcy. Soil flushing solution enhancement chemicals were 61 to 99%
recovered.
Key questions still to be answered include the following:
• Is the permeability of the contaminated porous media sufficient to
effectively deliver and recover fluids to and from the subsurface?
• Can delivery and recovery systems be constructed that will effec-
tively move the soil-washing solutions through contaminated por-
tions of the subsurface?
• Using the identified delivery and recovery system, can the soil-
washing solution and mobilized oils effectively be contained and
recovered? and
• Can conventional oil and water separation techniques be effective
on the oily emulsions that can result from enhanced flushing solu-
tions?
Once these questions are answered, the next step is to select a soil-washing
solution. This step should be done in the laboratory, using materials from the
site. Issues to be resolved in the laboratory include the following:
• Does the solution effectively mobilize residual oil?
B.15
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Soil Washing Case Histories
• To what degree are the components of the soil-washing solution
consumed by the subsurface materials, and how does this consump-
tion affect economic feasibility?
• Are unfavorable reactions leading to inorganic leaching or forma-
tion plugging likely to occur? and
• What is the most practical approach to managing the fluids pro-
duced in a field application?
The final step in evaluating in situ soil washing as a cleanup approach should
be a small-scale field demonstration. Through a field demonstration, prelimi-
nary evaluation of these issues can be confirmed, design data for larger-scale
applications can be developed, and accurate estimates of full-scale cost can be
made.
B.16
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Appendix B
Case 9
Project Performance Date: 1988 to present
Project Name: United Chrome Products
Location: Corvallis, Oreg.
Area: 8-acre shallow aquifer plume
Key Contaminants: 19,000 ppm of Hexavalent Chromium
Technical Team: CH2MHill
Point of Contact: Randy Pratt, CH2M Hill
Project Summary. The United Chrome Products site is a former industrial
hard-chrome plating facility sited on approximately eight acres just north of the
Corvallis Airport Facility. Operations and waste management practices resulted
in hexavalent chromium (Cr(VI)) contamination of surface water, soils, and
groundwater. The local subsurface is characterized by two water-bearing zones
separated by a silty-clay aquitard. The upper zone consists mostly of silt and is
the primary zone of contamination. The contaminant extended about 90 m (300
ft) downgradient from the source areas with Cr(VI) concentrations up to 19,000
mg/L. The deep aquifer consists of a sand and gravel mixture that is capable of
supplying potable water for commercial and residential use. The deep aquifer
plume extends about 100 m (400 ft) downgradient from the source area with
Cr(VI) concentrations up to 223 mg/L. The selected remedy consisted of the
installation of two infiltration basins and one infiltration trench, along with a
series of shallow wells to extract groundwater from the upper zone and an on-
site treatment facility to remove chromium prior to Publicly Owned Treatment
Works (POTW) discharge.
Process Equipment and Configuration. Two open-bottom infiltration basins
and one infiltration trench were constructed to release water to the subsurface
flushing Cr(VI) from soils in the vadose zone to the water table for recovery by
adjacent extraction wells. The flushing process also provides a source of
groundwater recharge for the upper zone extraction wells to replace approxi-
mately half of the water removed by pumping. Water is discharged into each
basin through an outlet controlled manually or by a float valve that maintains
the water level at a relatively constant depth. Precipitation recharge contributes
another 30% of the pumped volume.
The success of the basins is demonstrated by a 100% to 200% increase in
extraction gallons for adjacent wells and concurrent decrease of up to 95% in
Cr(VT) concentrations. The infiltration trench increases extraction well yields
along the longitudinal axis of the plume and operates primarily during the sum-
mer and early fall months to provide supplemental recharge as decreased pre-
cipitation and underflow reduce the amount of water available for extraction.
Another important benefit of the trench is the high groundwater velocities cre-
B.17
-------
Soil Washing Case Histories
ated by the increased hydraulic head. This condition should accelerate removal
of contaminated groundwater from wells in this vicinity.
The water used for basin and trench inflows has been obtained from the City
drinking-water system. In the future, groundwater extracted from deep aquifer
remediation may be used to supplement this source.
Treatment Standards and Results. The extraction and treatment system has
been in operation for three years, during which time approximately 37 MM L
(9.7 MM gal) of contaminated groundwater containing 12,125 kg (26,732 Ib) of
hexavalent chromium Cr(VI) have been removed. To accelerate removal of
Cr(VI) from contaminated soils and to provide supplemental recharge for the
upper zone, 20 MM L (5.2 MM gal) of city-supplied water have been recharged
through two infiltration basins and one infiltration trench.
Evaluation of site operations data indicates the 100,000-gal extraction sys-
tem has reduced the magnitude of Cr(VT) concentrations present in the upper
zone, has prevented off-site migration of the contaminant plume, and reduced
discharges of contaminated groundwater to local surface drainage ditches.
Hexavalent chromium concentrations have been reduced from an overall aver-
age of 1,923 mg/L in August 1988 to 87 mg/L in June 1991. Maximum
groundwater concentrations have been reduced from over 19,000 to 530 mg/L.
Four of 23 extraction wells and 10 of the 11 monitoring wells tested in April
1991 were below the site cleanup goal of 10 mg/L Cr(VI).
Cleanup Trends. Monitoring data indicate that remediation progress is
highly variable with cleanup rates influenced primarily by the well location and
volume of water that can be flushed through a given area. This results from a
variable distribution of contaminant mass in the upper zone. Extraction wells in
the vicinity of the infiltration basin have yielded the largest volume of ground-
water and exhibit the greatest overall decrease in Cr(VI) concentration.
The average concentration of chromium in extracted groundwater for the
combined well flows has decreased dramatically from 1,923 mg/L to 87 mg/L.
The rate of decline has decreased in recent months and is beginning to exhibit
an asymptotic or "tailing" effect. This condition is also present at individual
weh1 locations and may result from any one or combination of contaminant
transport and geochemical processes occurring in the subsurface. The pro-
cesses include:
• Variable length contaminant flow paths - Contaminated water at
the perimeter of a well capture zone must travel a greater distance
(at lower velocity) to reach the extraction point;
• Diffusion of Cr(VI) from fine-grained sediments - Localized varia-
tions in the rate of groundwater flow arise in heterogenous settings
because of the interlayering of high and low permeability sedi-
ments. Pumping induces rapid flushing of the high permeability
zones; however, contaminants are removed very slowly by diffu-
B.18
-------
Appendix B
sion from the low permeability zones. The rate of diffusion is de-
pendent primarily on the concentration gradient present between the
two zones. Low permeability sediments can act as leaky contami-
nant reservoirs;
• Hydrodynamic isolation - Localized areas of velocity stagnation
(zero flow) often develop between pumping wells. These zones can
only be remediated by modifying existing flowline patterns by
changing the location of pumping wells, or by altering pumping
rates among existing wells; and
• Desorption of Cr(VI) from soil particles and dissolution of solid
phase Cr(VI) - Both of these processes frequently result in the slow
release of contaminants, often at concentrations well below their
chemical equilibrium levels. This condition results in extraction of
large volumes of high concentration water, unless the pumping
approach is modified to account for these effects.
As the total mass of recoverable Cr(VI) in the subsurface is reduced, the
influence of these processes becomes more apparent. Because these processes
are not well understood, accurate prediction of future remediation progress is
increasingly difficult.
Cleanup Duration. The time required to attain the remediation goal of 10
mg/L in the upper-zone groundwater is directly related to the time required to
remove a pore volume of contaminated groundwater.
A pore volume is defined as the volume of contaminated groundwater
present within the pore spaces (water-filled voids) of aquifer material bounded
by the contaminant plume boundary. At the United Chrome site, a single pore
volume has been estimated to contain 9.8 MM L (2.6 MM gal) of water (within
the 10 mg/L concentration contour). The time required to remove a pore vol-
ume is simply the pore volume (gal) divided by the total pumping rate (gal/
min). At a sustained rate of 40 L/min (10 gal/min), a pore volume at United
Chrome is extracted every six months. However, due to the highly variable
well yields at the site, some areas are flushed more rapidly than others, result-
ing in reduced cleanup rates at low water yield areas of the site.
Uncertainties about sediment heterogeneity, distribution of contaminant
mass, variable groundwater extraction rates, and seasonal weather patterns that
limit groundwater availability make it difficult to estimate the time frame re-
quired to achieve the remediation goals. Cleanup time estimates have ranged
from 5 to 15 years to attain the goal of 10 mg/L at different times.
Evaluation of monitoring data collected during three years of system opera-
tion has identified several operational procedures and monitoring schedules that
should be modified. These changes may increase Cr(VI) recovery per gallon of
groundwater extracted and will permit a reduced level of effort in terms of data
B.19
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Soil Washing Case Histories
gathering requirements necessary to establish extraction system performance.
These recommendations include:
• Infiltration Basin Operations - The basins have flushed most of the
soluble chromium from vadose zone soils. Removal of solid phase
hexavalent chromium (BaCrO4) and soluble Cr(VI) may require
longer contact times to generate higher Cr(VI) concentrations per
gallon extracted. Operation of the basins should be modified to
increase contact time between infiltration water and solid phase
Cr(VI) and/or sorbed Cr(VI). The basins should also be used to
deliver recharge water to other areas within the extraction well
network;
• Extraction System Operations - Aggressive operation of wells
adjacent to the infiltration basins initially resulted in the removal of
significant mass, but the high pumping rate may have created short
circuiting and resulted hi the production of large volumes of low
concentration water, while also decreasing the amount of recharge
available to other wells. Operation of marginally producing wells
should be reduced or discontinued; and
• Monitoring Schedules - Increased confidence in system operations
and aquifer response to pumping will permit a reduction in the
monitoring frequency and number of monitoring locations. Moni-
toring activities in the upper zone will also be modified to gather
data on the hydraulic interaction between the upper zone and deep
aquifer once deep aquifer groundwater extraction begins.
Cost Information. The cost estimates compare each alternative in terms of
annual and present value costs and cost per pound of Cr(VI) removed. The cost
estimates indicate that treatment costs, presently estimated at $88/kg ($40/lb) of
Cr(VI) removed for the first 11,000 kg (25,000 Ib) will double to $176/kg ($80/
Ib) of Cr(VI) removed as Cr concentrations drop in the later phases of opera-
tion.
B.20
-------
Appendix C
APPENDIX C
Guide for Conducting Treotability Studies
Under CERCLA: Soil Washing
Section 121 (b) of CERCLA mandates that EPA should select remedies that
"utilize permanent solutions and alternative treatment technologies or resource
recovery technologies to the maximum extent practicable" and that EPA should
prefer remedial actions in which treatment that "permanently reduces the vol-
ume, toxicity, or mobility of hazardous substances, pollutants, and contami-
nants is a principal element." Treatability studies provide data to support treat-
ment technology selection and remedy implementation and should be per-
formed as soon as it is evident that insufficient information is available to en-
sure the quality of the decision. Conducting treatability studies early in the
remedial investigation/feasibility study (RI/FS) process should reduce uncer-
tainties associated with selecting the remedy, and provide a sounder basis for
the ROD. Regional planning should factor in the time and resources required
for these studies.
This fact sheet provides a summary of information to facilitate the planning
and execution of soil washing remedy selection treatability studies in support of
the RI/FS and the remedial design/remedial action (RD/RA) processes. This
fact sheet follows the organization of the "Guide for Conducting Treatability
Studies Under CERCLA: Soil Washing", Interim Guidance, EPA/540/000/
OOOA September 1991. Detailed information on designing and implementing
remedy selection treatability studies for soil washing is provided in the guid-
ance document.
C.I
-------
Guide for Conducting Treatability Studies Under CERCLA Soil Washing
INTRODUCTION
There are three levels or tiers of treatability studies: remedy screening, rem-
edy selection, and remedy design. The "Guide for Conducting Treatability
Studies Under CERCLA: Soil Washing Remedy Selection" discusses the rem-
edy screening and remedy selection levels.
Remedy screening studies are designed to provide a quick and relatively
inexpensive indication of whether soil washing is a potentially viable remedial
technology. Soil washing remedy screening studies should not be the only level
of testing performed before final remedy selection. Remedy selection and rem-
edy design studies will also be required to determine if soil washing is a viable
treatment alternative for a site. The remedy selection evaluation should provide
an indication that reductions in contaminant concentrations or in the volume of
contaminated soil will meet site-specific cleanup goals. It will also produce the
design information required for the next level of testing. Remedy design studies
may be needed to optimize process design.
TECHNOLOGY DESCRIPTION AND
PRELIMINARY SCREENING
Technology Description
Soil washing is a physical/chemical separation technology in which exca-
vated soil is pretreated to remove large objects and soil clods and then washed
with fluids to remove contaminants. To be effective, soil washing must either
transfer the contaminants to the wash fluids or concentrate the contaminants in
a fraction of the original soil volume, using size separation techniques. In either
case, soil washing must be used in conjunction with the other treatment tech-
nologies. Either the washing fluid or the fraction of soil containing most of the
contaminant, or both, must be treated.
At the present time, soil washing is used extensively in Europe and has had
limited use in the United States. During 1986-1989, the technology was one of
the selected source control remedies at eight Superfund sites.
C.2
-------
Appendix C
The determination of the need for and the appropriate level of treatability
studies required is dependent on the literature information available on the tech-
nology, expert technical judgment, and site-specific factors. Several reports and
electronic data bases exist that should be consulted to assist in planning and
conducting treatability studies as well as help prescreen soil washing for use at
a specific site. Site-specific technical assistance is provided to Regional Project
Managers (RPMs) and On-Scene Coordinators (OSCs) by the Technical Sup-
port Project (TSP).
Prescreening Characteristics
Prescreening activities for the soil washing treatability testing include inter-
preting any available site-related field measurement data. The purpose of
prescreening is to gain enough information to eliminate from further treatability
testing those treatment technologies which have little chance of achieving the
cleanup goals.
The three most important soil parameters to be evaluated during
prescreening and remedy screening tests are the grain size distribution, clay
content, and cation exchange capacity. Soil washing performance is closely
tied to these three factors. Soil with relatively large percentages of sand and
gravel (coarse material >2 mm in particle size) respond better to soil washing
than soils with small percentages of sand and gravel. Larger percentages of
clay and silt (fine particles smaller than 0.25 mm) reduce soil washing contami-
nant removal efficiency. In general, soil washing is most appropriate for soils
that contain at least 50 percent sand/gravel, i.e., coastal sandy soils and soils
with glacial deposits. Soils rich in clay and silt tend to be poor candidates for
soil washing. Cation exchange capacity measures the tendency of the soil to
exchange weakly held cations in the soil for cations in the wash solution, which
will be more strongly bound to the soil. Soils with relatively low CEC values
(less than 50 to 100 meq/kg) respond better to soil washing than soils with
higher CEC values. Early characterization of these parameters and their vari-
ability throughout the site provides valuable information for the initial screening
of soil washing as an alternative treatment technology.
Chemical and physical properties of the contaminant should also be investi-
gated. Solubility in water (or other washing fluids) is one of the most important
physical characteristics. Reactivity with wash fluids may, in some cases, be
another important characteristic to consider. Other contaminant characteristics
such as volatility and density may be important for the design of remedy
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Guide for Conducting Treatability Studies Under CERCLA: Soil Washing
screening studies and related residuals treatment systems. Speciation is impor-
tant in metal-contaminated sites. Specific metal compounds should be quanti-
fied rather than total metal concentration for each metal present at the site.
There is no steadfast rule that specifies when to proceed with remedy screen-
ing and when to eliminate soil washing as a treatment technology based on a
preliminary screening analysis. A literature search indicating that soil washing
may not work at a given site should not automatically eliminate soil washing
from consideration. On the other hand, previous studies indicating that pure
chemicals will be effectively treated using soil washing must be viewed with
caution. Chemical interactions in complex mixtures frequently found at
Superfund sites or interactions between soil and contaminants can limit the
effectiveness of soil washing. An analysis of the existing literature, coupled
with the site characterization, will provide the information required to make an
"educated decision." However, when in doubt, a remedy screening study is
recommended.
Technology Limitations
Many factors affect the feasibility of soil washing. These factors should be
addressed prior to the selection of soil washing, and prior to the investment of
time and funds in further testing. A detailed discussion of these factors is be-
yond the scope of this document.
THE USE OF TREATABILITY STUDIES IN REMEDY
SELECTION
Treatability studies should be performed in a systematic fashion to ensure
that the data generated can support the remedy evaluation and implementation
process. A well-designed treatability study can significantly reduce the overall
uncertainty associated with the decision but cannot guarantee that the chosen
alternative will be completely successful. Care must be exercised to ensure that
the treatability study is representative of the treatment as it will be employed
(e.g., the sample is representative of the contaminated soil to be treated) to
minimize the uncertainty in the decision. The method presented below pro-
vides a resource-effective means for evaluating one or more technologies.
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Appendix C
There are three levels or tiers of treatability studies: remedy screening, rem-
edy selection, and remedy design. Some or all of the levels may be needed on a
case-by-case basis. The need for, and the level of, treatability testing required
are management decisions in which the time and cost necessary to perform the
testing are balanced against the risks inherent in the decision (e.g., selection of
an inappropriate treatment alternative). Figure 1 shows the relationship of three
levels of treatability study to each other and to the RI/FS process.
Remedy Screening
Remedy screening is the first level of testing. It is used to establish the abil-
ity of a technology to treat a waste. These studies are generally low cost (e.g.,
$10,000 to $50,000) and usually require hours to days to complete. The lowest
level of quality control is required for remedy screening studies. They yield
data enabling a qualitative assessment of a technology's potential to meet per-
formance goals. Remedy screening tests can identify operating standards for
investigation during remedy selection or remedy design testing. They generate
little, if any, design or cost data, and should never be used as the sole basis for
selection of a remedy.
Remedy screening soil washing treatability studies are frequently skipped.
Often, there is enough information about the physical and chemical characteris-
tics of the soil and contaminant to allow an expert to evaluate the potential
success of soil washing at a site. When performed, remedy screening tests are
jar tests. However, remedy selection tests are normally the first level of
treatability study executed.
Remedy Selection
Remedy selection testing is the second level of testing. Remedy selection
tests identify the technology's performance for a site. These studies have a
moderate cost (e.g., $20,000 to $100,000) and require several weeks to com-
plete. Remedy selection tests yield data that verify that the technology can meet
expected cleanup goals, provide information in support of the detailed analysis
of alternatives (i.e., seven of the nine evaluation criteria), and give indications
of optimal operating conditions.
The remedy selection tier of soil washing testing generally consists of labo-
ratory tests which provide sufficient experimental controls such that a semi-
quantative mass balance can be achieved. Toxicity testing of the cleaned soil is
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Guide for Conducting Treatability Studies Under CERCLA: Soil Washing
Figure 1
The Role of Treatability Studies in the RI/FS and RD/RA Process
Scoping
— the —
RI/FS
— Remedial Investigation/—
Feasibility Study (RI/FS)
Identification
of Alternatives
Literature
Screening
and
Treatability
Study Scoping
Site
.Characterization
and Technology
Screening
REMEDY
SCREENING
to Determine
Technology Feasibility
Evaluation _
of Alternatives
REMEDY SELECTION
to Develop Performance
and Cost Data
Record of Remedial Design/
Descisiorr^ Remedial Action -
(ROD) (RD/RA)
Remedy
Selection
implementation
of Remedy
REMEDY DESIGN
to Develop Scale-Up, Design,
and Detailed Cost Data
typically employed in the remedy selection tier of treatability testing. The key
question to be answered during remedy selection testing is how much of the soil
will this process treat by either particle size separation or solubilization to meet
the cleanup goal. The exact removal efficiency needed to meet the specified
goal for the remedy selection test is site-specific. In some cases, pilot-scale
testing may be appropriate to support the remedy evaluation of innovative tech-
nologies. Typically, a remedy design study would follow a successful remedy
selection study.
Remedy Design
Remedy design testing is the third level of testing. It provides quantative
performance, cost, and design information for remediating an operable unit.
This testing also produces remaining data required to optimize performance.
These studies are of moderate to high cost (e.g., $100,000 to $500,000) and
C.6
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Appendix C
require several months to complete. For complex sites (e.g., sites with different
types or concentrations of contaminants in different areas or with different soil
types in different areas), longer testing periods may be required, and costs will
be higher. Remedy design tests yield data that verify performance to a higher
degree than the remedy selection and provide detailed design information.
They are performed during the remedy implementation phase of a site cleanup.
Remedy design tests usually consist of bringing a mobile treatment unit onto
the site, or constructing a small-scale unit for nonmobile technologies. Permit
exclusions may be available for offsite treatability studies under certain condi-
tions. The goal of this tier of testing is to confirm the cleanup levels and treat-
ment times specified in the Work Plan. This is best achieved by operating a
field unit under conditions similar to those expected in the full-scale
remediation project.
Data obtained from the remedy design tests are used to:
• Design the full-scale unit
• Confirm the feasibility of soil washing based on target cleanup
goals
• Refine cleanup time estimates
• Refine cost predictions.
Given the lack of full-scale experience with innovative technologies, remedy
design testing will generally be necessary in support of remedy implementation.
REMiDY SELECTION TREATABILITY STUDY
WORKPLAN
Carefully planned treatability studies are necessary to ensure that the data
generated are useful for evaluating the validity or performance of a technology.
The Work Plan, which is prepared by the contractor when the Work Assign-
ment is in place, sets forth the contractor's proposed technical approach for
completing the tasks outlined in the Work Assignment. It also assigns responsi-
bilities and establishes the project schedule and costs. The Work Plan must be
approved by the RPM before initiating subsequent tasks. A suggested organi-
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Guide for Conducting Treatability Studies Under CERCLA: Soil Washing
zation of the Work Plan is provided in the "Guide for Conducting Treatability
Studies Under CERCLA: Soil Washing."
Test Goals
Setting goals for the treatability study is critical to the ultimate usefulness of
the data generated. Goals must be defined before the treatability study is per-
formed. Each tier of treatability study needs performance goals appropriate to
that tier.
Remedy screening tests are not always performed for soil washing pro-
cesses. If remedy screening tests are performed, an example of the goal for
those tests would be to show that the wash fluid will solubilize or remove a
sufficient percentage (e.g., 50 percent) of the contaminants to warrant further
treatability studies. Another goal might be to show that contaminant concentra-
tions can be reduced in the >2 mm soil fraction by at least 50 percent, as com-
pared to the original soil concentrations, using particle size separation tech-
niques. These goals are only examples. The remedy screening treatability
study goals must be determined on a site-specific basis.
Achieving the goals during this tier should merely indicate that soil washing
has at least a limited chance of success and that further studies will be useful.
Frequently, such information is available based on the type of soil and contami-
nant present at the site. Based on such information, experts in soil washing
technology can often assess the potential applicability of soil washing without
performing remedy screening.
The main objectives of the remedy selection tier of testing are to:
• Measure the percentage of the contaminant that can be removed
from the soil through solubilization or from the >2 mm soil fraction
by particle size separation.
• Produce the design information required for the next level of test-
ing, should the remedy selection evaluation indicate remedy design
studies are warranted.
• The actual goal for removal efficiency must be based on site- and
process-specific characteristics. The specified removal efficiency
must meet site cleanup goals, which are based on a site risk assess-
ment or on the applicable or relevant and appropriate requirements
(ARARs).
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Appendix C
Experimental Design
Ajar test is the type of remedy screening test that can be rapidly performed
in an onsite laboratory to evaluate the potential performance of soil washing as
an alterative technology. Such studies should be designated to maximize the
chances of success at the remedy screening level. The object of this guidance
document is not to specify a particular remedy screening method but rather to
highlight those critical parameters which should be evaluated during the labora-
tory test.
Contaminant characteristics to examine during remedy screening include
solubility, miscibility, and dispersibility. Properties of organic contaminants are
generally easier to evaluate than those of inorganic contaminants. Inorganics,
such as heavy metals, can exist in many compounds (e.g., oxides, hydroxides,
nitrates, phosphates, chlorides, sulfates, and other more complex mineralized
forms), which can greatly alter their solubilities. Metal analysis typically pro-
vide only total metal concentrations. More detailed analyses to determine
chemical speciation may be warranted.
The liquid used in the jar test is typically water, or water with additives
which might enhance the effectiveness of the soil washing process. To save
time and money, chemical analyses should not be performed on the samples
until there is visual evidence that physical separation has taken place in the jar
tests. Jar tests can yield three separation fractions from the original soil sample.
These include a floating layer, a wastewater with dispersed solids, and a solid
fraction. Chemical analysis can be performed on each fraction.
When performing the jar test, observe if any floating materials can be
skimmed off the top. Observe whether an immiscible, oily layer forms, either
at the top or the bottom, indicating release of an insoluble organic material.
Observe and time the solids settling rate and depth. Sand and gravel settle first,
followed by the silt and clay. The rate and the relative volume of the settling
material will provide some indication of the particle size distribution in the
waste matrix and the potential for soil washing as a treatment alternative. Fur-
ther evidence can be gained by analyzing the settled and filtered wash water for
selected indicator contaminants of concern. If simple washing releases a large
percentage of these contaminants into the wash water, then soil washing can be
viewed favorably and more detailed laboratory and bench tests must be con-
ducted.
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Guide for Conducting Treotability Studies Under CERCLA: Soil Washing
Variations on the jar tests can include the addition of surfactants, chelants, or
other dispersant agents to the water; sequential washing; heated water washing
versus cold water; acidic or basic wash water; and tests that include both a wash
and a rinse step. The rinse water and fine soil fraction (<2 mm particle size)
should be separate from the coarse soil fraction (>2 mm particle size) using a
#10 sieve. No attempt should be made during jar tests to separate the soil into
discrete size fractions; this is done at the bench-scale tier of testing. Normally,
only the coarse soil fraction should be analyzed for contamination. In general,
at least a 50 percent reduction in total contaminant concentration in the >2 mm
soil fraction is considered adequate to proceed to the remedy selection tier. The
separation of approximately 50 percent of the total soil volume as clean soil
also indicates remedy selection studies may be warranted.
To reduce analytical costs during the remedy screening tier, a condensed list
of known contaminants must be selected as indicators of performance. The
selection of indicator analytes to track during jar testing should be based on the
following guidelines:
• Select one or two contaminants present in the soil that are most
toxic or most prevalent.
• Select indicator compounds to represent other chemical groups if
they are present in the soil (i.e., volatile and semivolatile organics,
chlorinated and nonchlorinated species, etc.)
• If polychlorinated biphenyls (PCBs) and dioxins are known to be
present, select PCBs as indicators in the jar tests and analyze for
them in the washed soil. It is usually not cost-effective to analyze
for dioxins and other highly insoluble chemicals in the wash water
generated from jar tests. Check for them later in the wash water
from remedy selection tests.
Remedy selection tests require that electricity, water, and additional equip-
ment are available. The tests are run under more controlled conditions than the
jar tests. The response of the soil sample to variable washing conditions is fully
characterized. More precision is used in weighing, mixing, and particle size
separation. There is an associated increase hi QA/QC costs. Treated soil par-
ticles are separated during the sieve operations to determine contaminant parti-
tioning with particle size. Chemical analyses are performed on the sieved soil
particles as well as on the spent wash waters. The impact of process variables
on washing effectiveness is quantified. This series of tests is considerably more
C.10
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Appendix C
costly than jar tests, so only samples showing promise in the remedy screening
phase (jar test) should be carried forward into the remedy selection tier. If suffi-
cient data are available in the prescreening step, the remedy screening step may
be skipped. Soil samples showing promise in the prescreening step are carried
forward to the remedy selection tier.
A series of tests should be designed that will provide information on wash-
ing and rinsing conditions best suited to the soil matrix under study. The RREL
data base should be searched for information from previous studies. To estab-
lish percent of contaminant removal, particle size separation, and distribution of
contaminants in the washed soil, the following should first be studied: 1) wash
time, 2) wash water-to-soil ratio, and 3) rinse water-to-wash water ratio. Fol-
lowing those studies, the effect of wash water additives on performance should
be evaluated.
Several factors must be considered in the design of soil washing treatability
studies. A remedy selection design test should be geared to the type of system
expected to be used in the field. Soil-to-wash water ratios should be planned
using the results from the jar tests, if jar tests were performed. In general, a
ratio of 1 part of soil to 3 parts of wash water will be sufficient to perform rem-
edy selection tests. The soil and wash water should be mixed on a shaker table
for a minimum of 10 minutes and a maximum of 30 minutes. The soil-to-wash
water ratio and mix times presented here are rules of thumb to be used if no
other information is available.
Another factor to consider is the variability of the grain size distribution.
Gilsen Wet Sieve devices are recommended for remedy selection studies. Ro-
Tap or similar sieve systems may also be used. Such devices will enhance the
completeness and reproducibility of grain size separation. However, they are
messy, expensive, and very noisy when in operation. An alternative choice is to
complete a series of four to six replicate runs under exactly the same set of
conditions to obtain information on the variability of the grain size separation
technique. Variability in the separation technique can be evaluated by compar-
ing sieve screen weights across runs and soil contaminant data for the same
fractions from each run. By identifying the range of variability associated with
repeated runs at the same conditions, estimates can be made of the variability
that is likely to be associated with other test runs under slightly different condi-
tions.
Normally, only the wash water and the soil particles captured by the sieve
screen need to be analyzed for contaminants. Experience has shown that little
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Guide for Conducting Treatability Studies Under CERCLA: Soil Washing
additional contaminant removal is likely to be found in the rinse water. Rinsing
is important and must be included in the procedure since it improves the effi-
ciency of the grain size separation/sieving process. Rinsing separates the fine
from the coarse material. This can result in a cleaner coarse fraction and more
contaminant concentrated in the fine fraction. Contaminant concentration in the
rinse water may be determined periodically (e.g., 10 percent of the samples) to
evaluate the performance of the wash solution. However, very little contamina-
tion is typically dissolved in the rinse solution. Therefore, analyses of the rinse
solution may have limited value in verifying wash solution performance.
Initially, only the coarse soil fraction and the wash water should be analyzed
for indicator contaminants. If the removal of the indicator contaminants con-
firms that the technology has the potential to meet cleanup standards at the site,
additional analyses should be performed. All three soil fractions and all wash
and rinse waters must be analyzed for all contaminants to perform a complete
mass balance. The holding time of soil fractions in the lab before extraction
and analysis can be an important consideration for some contaminants.
The decision on whether to perform remedy selection testing on hot spots or
composite soil samples is difficult and must be made on a site-by-site basis.
Hot spot areas should be factored into the test plan if they represent a significant
portion of the waste site. However, it is more practical to test the specific waste
matrix that will be fed to the full-scale system over the bulk of its operating life.
If the character of the soil changes radically (e.g., from clay to sand) over the
depth of contamination, then tests should be designed to separately study sys-
tem performance on each soil type.
Additives such as oil and grease dispersants and chelating agents can aid in
removing contaminants from some soils. However, they can also cause pro-
cessing problems downstream from the washing step. Therefore, use of such
additives should be approached with caution. Use of one or a combination of
those additives is a site-by-site determination. Some soils do not respond well
to additives. Surfactants and chelating agents may form suspensions and foams
with soil particles during washing. This can clog the sieves and lead to ineffi-
cient particle size separation during screening. The result can be the recovery
of soil fractions with higher contamination than those cleaned by water alone.
Such results can make the data impossible to understand. Additives can also
complicate the rinse water process that might follow the soil washing. Recent
studies have shown that counter-current washing-rinsing systems, incorporating
the use of hot water for the initial wash step, offer the best performance in terms
C.12
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Appendix C
of particle size separation, contaminant removal, and wastewater management
(treatment, recycling and discharge).
SAMPLING AND ANALYSIS PLAN
The Sampling and Analysis Plan (SAP) consists of two parts - the Field
Sampling Plan (FSP) and the Quality Assurance Project Plan (QAPjP). A SAP
is required for all field activities conducted during the RI/FS. The purpose of
the SAP is to ensure that samples obtained for characterization and testing are
representative and that the quality of the analytical data generated is known.
The SAP addresses field sampling, waste characterization, and sampling and
analysis of the treated wastes and residuals from the testing apparatus or treat-
ment unit. The SAP is usually prepared after Work Plan approval.
Field Sampling Plan
The FSP component of the SAP describes the sampling objectives; the type,
location, and number of samples to be collected; the sample numbering system;
the necessary equipment and procedures for collecting the samples; the sample
chain-of-custody procedures; and the required packaging, labeling, and ship-
ping procedures.
Field samples are taken to provide baseline contaminant concentrations and
material for the treatability studies. The sampling objectives must be consistent
with the treatability test objectives. Because the primary objective of remedy
screening studies is to provide a first-cut-evaluation of the extent to which spe-
cific chemicals are removed from the soil or concentrated in a fraction of the
soil by soil washing, the primary sampling objectives should include, in gen-
eral:
• Acquisition of samples representative of conditions typical of the
entire site or defined areas within the site. Because this is a first-cut
evaluation, elaborate statistically designed field sampling plans may
not be required. Professional judgment regarding the sampling
locations should be exercised to select sampling sites that are typi-
cal of the area (pit, lagoon, etc.) or appear above the average con-
centration of contaminants in the area being considered for the
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Guide for Conducting Treatability Studies Under CERCLA: Soil Washing
treatability test. This may be difficult because reliable site charac-
terization data may not be available early in the remedial investiga-
tion.
• Acquisition of sufficient sample volumes necessary for testing,
analysis, and quality assurance and quality control.
The sampling plan for remedy selection will be similar. However, because a
mass balance is required for this evaluation, a statistically designed field sam-
pling plan will be required.
Quality Assurance Project Plan
The Quality Assurance Project Plan should be consistent with the overall
objectives of the treatability study. At the remedy screening level the QAPjP
should not be overly detailed.
The purpose of the remedy selection treatability study is to determine
whether soil washing can meet cleanup goals and provide information to sup-
port the detailed analysis of alternatives (i.e., seven of the nine evaluation crite-
ria). An example of a criterion for this determination is removal of approxi-
mately 90 percent of contaminants. The exact removal efficiency specified as
the goal for the remedy selection test is site-specific. The suggested QC ap-
proach will consist of:
• Triplicate samples of both reactor and controls
• The analysis of surrogate spike compounds in each sample
• The extraction and analysis of a method blank with each set of
samples
• The analysis of a matrix spike in approximately 10 percent of the
samples.
The analysis of triplicate samples provides for the overall precision measure-
ments that are necessary to determine whether the difference is significant at the
chosen confidence level. The analysis of the surrogate spike will determine if
the analytical method performance is consistent (relatively accurate). The
method blank will show if laboratory contamination has had an impact on the
analytical results.
C.14
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Appendix C
Selection of appropriate surrogate compounds will depend on the target
compounds identified in the soil and the analytical methods selected for the
analysis.
TREATABIUTYDATA INTERPRETATION
The information and results gathered from the remedy screening are used to
determine if soil washing is a viable treatment option and to determine if addi-
tional remedy selection and remedy design studies are warranted. A reduction
of approximately 50 percent of the soil contaminants during the test indicates
additional treatability studies are warranted. Contaminant concentrations can
also be determined for washing water and fine soil fractions. These additional
analyses add to the cost of the treatability test and may not be needed. Before
and after concentrations can normally be based on duplicate samples at each
period. The mean values are compared to assess the success of the study. If the
remedy screening indicates that soil washing is a potential cleanup option then
remedy selection studies should be performed.
In remedy selection treatability studies, soil contaminant concentrations
before soil washing and contaminant concentrations in the coarse fraction after
soil washing are typically measured in triplicate. A reduction of approximately
90 percent in the mean concentration indicates soil washing is potentially useful
in site remediation. A number of other factors must be evaluated before decid-
ing to proceed to remedy design studies.
The final concentration of contaminants in the recovered (clean) soil frac-
tion, in the fine soil fraction and wastewater treatment sludge, and in the wash
water are important to evaluating the feasibility of soil washing. The selection
of technologies to treat the fine soil and wash water wastestreams depends upon
the types and concentrations of contaminants present. The amount of volume
reduction achieved is also important to the selection of soil washing as a poten-
tial remediation technology.
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Guide for Conducting Treatability Studies Under CERCLA: Soil Washing
TECHNICAL ASSISTANCE
Literature information and consultation with experts are critical factors in
determining the need for and ensuring the usefulness of treatability studies. A
reference list of sources on treatability studies is provided in the "Guide for
Conducting Treatability Studies Under CERCLA" (EPA/540/2-89-058).
It is recommended that a Technical Advisory Committee (TAG) be used.
This committee includes experts on the technology who provide technical sup-
port from the scoping phase of the treatability study through data evaluation.
Members of the TAG may include representatives from EPA (Region and/or
ORD), other Federal Agencies, States, and consulting firms.
OS WER/ORD operate the Technical Support Project (TSP) which provides
assistance in the planning, performance, and/or review of treatability studies.
For further information on treatability study support or the TSP, please contact:
Groundwater Fate and Transport Technical
Support Center
Robert S. Kerr Environmental Research Laboratory
(RSKERL), Ada, OK
Contact: Don Draper
FTS 743-2200 or (405) 332-8800
Engineering Technical Support Center
Risk Reduction Engineering Laboratory (RREL),
Cincinnati, OH
Contact: BenBlaney
FTS 684-7406 or (513) 569-7406
FOR FURTHER INFORMATION
hi addition to the contacts identified above, the appropriate Regional Coordi-
nator for each Region located in the Hazardous Site Control Division/Office of
Emergency and Remedial Response or the CERCLA Enforcement Division/
Office of Waste Programs Enforcement should be contacted for additional
information or assistance.
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Appendix C
ACKNOWLEDGEMENTS
The fact sheet and the corresponding guidance document were prepared for
the U.S. Environmental Protection Agency, Office of Research and Develop-
ment (ORD), Risk Reduction Engineering Laboratory (RREL), Cincinnati,
Ohio, by Science Applications International Corporation (SAIC) under Contract
No. 68-C8-0061. Mr. Mike Borst and Ms. Malvina Wilkens served as the EPA
Technical Project Monitors. Mr. Jim Rawe and Dr. Thomas Fogg served as
SAIC's Work Assignment Managers. The project team included Kathleen
Hurley, Curtis Schmidt, Cynthia Eghbalnia, and Yueh Chuang of SAIC; Pat
Esposito of Bruck, Hartman & Esposito, Inc.; James Nash of Chapman, Inc.
Mr. Clyde Dial served as SAIC's Senior Reviewer.
Many other Agency and independent reviewers have contributed their time
and comments by participating in the expert review meetings and/or peer re-
viewing the guidance document.
C.17
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Appendix D
APPENDIX D
List of References
Applied Geotechnology Inc. 1990. Unpublished internal report used to evalu-
ate the Union Pacific Railroad sludge pit at Pocattillo, Ohio. Belleview, Wash.
Clarke, A. N., P. D. Plumb, T. K. Subramanyan and D. J. Wilson. 1991. Soil
clean-up by surfactant washing. I. Laboratory results and mathematical model-
ing. Separation Science and Technology 26:.
Domenico, P.A. and F.W. Schwartz. 1990. Physical and chemical hydrogeol-
ogy. New York: John Wiley and Sons.
Everett, L. G. 1986. Permit guidance manual on unsaturated zone monitroing
for hazardous waste land treatment units. EPA/530-SW-86-040. US EPA,
Office of Solid Waste and Emergency Response. Las Vegas.
Edwards, D.A., R.G. Luthy, and Z. Liu. 1991. Solubilization of polycyclic
aromatic hydrocarbons in micellar nonionic surfactant solutions. Environmental
Science & Technology 25:127.
Everett, L. G. 1992. Direct and indirect pore-liquid monitoring in the vadose
zone, eurocourses: technologies for environmental cleanup. Ispera, Italy: Soil
and Groundwater Commission on the European Communities Joint Research
Center.
Everett, L. G., L. G. Wilson, and E. W. Hoylman. 1984. Vadose zone monitor-
ing for hazardous waste sites. Park Ridge, N.J.: Noyes Data Corporation.
Freeze, R.A. and J.A. Cherry. 1979. Groundwater. Englewood Cliffs, N.J.:
Prentice Hall.
Jackson, R. E., J. C. Fontaine, and R. W. Wunderlich. 1992. Chemically-en-
hanced solubilization of DNAPL, advancing the state of pump and treat
remediation by injection and withdrawal of biodegradable surfactants.
Hamilton, Ontario: International Association of Hydrogeologists, Canadian
Chapter.
D.I
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List of References
Kimball, S. 1992. Surfactant-enhanced soil flushing of hydrophobic hydrocar-
bons from contaminated soil. In Proc. Seventh Annual Conference On Hydro-
carbon Contaminated Soils. Univ. Of Massachusetts, Amherst, Mass. Sep. 21-
24.
McKee, C. R. and D. Whitman. 1991. Design in situ waste recovery systems
short course. Dublin, Ohio: The Association of Groundwater Scientists and
Engineers.
Nash, J.H. and R.P. Trevor. 1989. Field studies of in-situ soil washing in petro-
leum contaminated soils, hi Petroleum Contaminated Soils — Remediation
Techniques, Environmental Fate and Risk Assessment. Vol. 1. Ed. P.T.
Kostecki, and E.J. Calabrese, 13. Chelsea, Mich.: Lewis Publishers.
Nash, J., R. T. Trevor, and D. C. Downey. 1987. Surfactant-enhanced in situ
soil washing. AFESE Report ESL-TR87-182. US EPA/HWERL.
Oma, K. H., D. J. Wilson, and R. D. Mutch, Jr. 1991. Surfactant flushing/wash-
ing: economics of an innovative remedial process including recovering and
recycle. In Proc. 4th Ann. Haz. Mat. Manag. Conf./Central. Hazmat Central,
Rosemont, 111.
Sadeghi, K.M., M.A. Sadeghi, G.V. Ghilingarian, and T.F. Yen. 1988. Devel-
oping a new method for bitument recovery from bituminous sands using ultra-
sound and sodium silicate, (in Russian) Geologiva Nefti i Gaza (Geology of Oil
and Gas) 8: 53-57.
Sadeghi, K.M., M.A. Sadeghi, G.V. Ghilingarian, and T.F. Yen. 1989a. Extrac-
tion of bitumen from bituminous sands using ultrasound and sodium silicate, (in
Russian) Khimiva i Tekhnologiva Topliv i Masel 8:24-28. translated into En-
glish Chemistry and Technology of Fuels and Oils 1-2:3-10.
Sadeghi, K.M., M.A. Sadeghi, D. Momeni, W.H. Wu, and T.F. Yen. 1989b.
Useful surfactant from polar fractions of petroleum and shale oil. Oil Field
Chemistry: Enhanced Recovery and Production Stimulation, ACS Symposium
Series No. 396. 20:378-92
Sadeghi, K.M., M.A. Sadeghi, and T.F. Yen. 1990. Uses of generated surfac-
tants from a new tar sand process for extracting hydrocarbons from natural and
man-made materials. In Proc. 1989 Eastern Oil Shale Symposium. Lexington,
Ky.
Sadeghi, K.M., L.G. Everett, and T.F. Yen. 1992. Remediation of oil spills: a
new decontamination technology based on tar sand extraction process. In prepa-
ration.
Sale, T. and M. Pitts. 1988. Chemically enhanced in situ soil washing. In Proc.
Conference on Petroleum Hydrocarbons and Organic Chemical in Ground
Water: Prevention, Detection and Restoration, 487. Houston. Dublin, Ohio:
National Water Well Association.
D.2
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Appendix D
US EPA. 1985. In situ flushing and soils washing technologies for superfund
sites. Presented at RCRA/Superfitnd Engineering Technology Transfer Sympo-
sium by RREL, Cincinnati.
US EPA. 1988a. Assessment of international technologies for superfund appli-
cations. EPA 540/2-88/003. Office of Solid Waste and Emergency Response,
Office of Program Management and Technology. Washington, D.C.
US EPA. 1988b. Technology screening guide for treatment ofCERCLA. soils
and sludges. EPA 540/2-88/004.
US EPA. 1990. Engineering bulletin: soil washing treatment. EPA 540/2-90/
017. Office of Emergency and Remedial Response, Washington, D.C., Office
of Research and Development, Cincinnati. September.
US EPA. 1992a. Innovative treatment technologies: semi-annual status report.
3rd ed. EPA/540/2-91/001. Washington, D.C. April.
US EPA. 1992b. Innovative treatment technologies: semi-annual status report.
4th ed. EPA 542-R-92-011. Washington, D.C. April.
US EPA. 1992c. Vendor Information System for Innovative Treatment Tech-
nologies (VISITT) Version 1.0 (data base). EPA/542/R-92/001 No. 1. Office of
Solid Waste and Emergency Response, Technology Innovation Office. Wash-
ington, D.C. June.
Wilson, D.S. and A.N. Clark. 1991. Soil cleanup by in situ surfactant flushing.
Part 4. A two component model. Separation Science and Technology 26(9):
1177-95.
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Appendix E
APPENDIX E
Suggested Reading Ust
Abdul, A. S., and T. L. Gibson. 1990. Laboratory studies of surfactant-en-
hanced washing of polychlorinated from sandy material. ES&T25(4): 665-71.
Assink, J. W. 1985. Extractive methods for soil decontamination: a general
survey and review of operational treatment installations. In Proc. First Interna-
tional TNO Conference on Contaminated Soil. Uitrecht, Netherlands.
Bell, C. F. 1977. Principles and applications of metal chelation. Oxford:
Clarendon Press.
Cederberg, G., et al. A groundwater mass transport and equilibrium chemistry
model for multicomponent systems. Water Resources Research 25(5): 449-528.
Cussler, E. L. 1984. Mass transfer in fluid systems. Cambridge University
Press.
Everson, F. 1989. Overview: soils washing technologies, for comprehensive
and liability act resource conservation and recovery act leaking underground
storage tanks, site remediation. US EPA 1:440. June.
Grasso, D. 1993. Hazardous waste site remediation (source control). Lewis
Publishers. Boca Raton: CRC Press.
Keely, J. 1989. Performance ofpump-and-treat remediation. EPA/540/4-89/
005. US EPA. Cincinnati.
Keely, J. F. 1984. Optimizing pumping strategies for contaminant studies and
remedial actions. Ground Water Monitoring Review. National Water Well As-
sociation. Summer.
Mackay, D., and J. Cherry. 1989. Groundwater contamination: pump-and-treat
remediation. Env. Sci. and Tech. 23:6.
Mercer, J., D. Skipp, and D. Giffin. 1990. Basics of pump-and-treat ground-
water remediation technology. EPA/600/8-90/003. US EPA. Cincinnati.
Myers, D. 1988. Surfactant science and technology. New York: VCH Publish-
ers.
E.I
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Suggested Reading List
Nash, J. 1988. Field application of pilot scale soils washing system. Presented
at Workshop on the Extracting Treatment of Excavated Soil. US EPA, Edison,
N.J.
Nirel, P. M. and F. M. Morel. 1990. Pitfalls of sequential extraction. Water
Resources Research 24:1055-56.
Nunno, T. J., J. A. Hyman, and T. Pheiffer. 1988. Development of site
remediation technologies in european countries. Presented at Workshop on the
Extractive Treatment of Excavated Soil. US EPA, Edison, N. J.
Pflug, A.D. (undated). Abstract of Treatment Technologies. Chaska, Minn.:
Biotrol, Inc.
Shuring, J., and P. Chan. 1990. Application of pneumatic fracturing to remove
contaminants from the vadose zone. In Proc. Water Quality Management of
Landfills. Water Pollution Control Federation, Chicago.
Snoeyink, V. C. and D. Jenkins. 1980. Water Chemistry. New York: John
Wiley and Sons.
Thomas, J. and H. Ward. 1989. In situ biorestoration of organic contaminants in
the subsurface. Env. Sci. and Tech. 23:7.
Treybal, Robert E. 1980. Mass Transfer Operations. 3d ed. New York:
McGraw-Hill Book Company.
Trost, P. B. and R. S. Rickard. 1987. On-site soil washing - a low cost alterna-
tive. Presented aiADPA. Los Angeles.
US EPA. 1988. Biotrol Technical Bulletin, No. 87-1A. Presented at Workshop
on the Extraction Treatment of Excavated Soil. Edison, N.J.
US EPA. 1989a. Innovative technology: soil washing. Office of Solid Waste
and Emergency Response Directive 9200.5-250FS. Washington, D.C.
US EPA. 1989b. Lead battery site treatability studies, Project Summary.
US EPA. 1989c. Performance evaluations of pump and treat remediations.
Office of Research and Development, Robert S. Kerr Laboratory. Ada, Okla.
Oct.
US EPA. 1989e. Superfund LDR Guide #68: Obtaining a soil and debris
treatability variance for removal actions. Office of Solid Waste and Emergency
Response Directive 9347.3-07FS. Washington, D.C.
US EPA 1990. Second forum on innovative treatment technologies, domestic
and international. EPA/540/2-90/006 (Abstracts) or EPA/540/2-90/010 (Tech-
nical Papers). Philadelphia. May 15-17.
Wayt, H. J. and D. J. Wilson. 1989. Soil clean up by in situ surfactant flushing
II: theory of micellar solubilization. Separation Sci. and Tech. 24(12 & 13):
905-37.
E.2
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Appendix E
Wilson, D. J. 1989. Soil clean up by in situ surfactant flushing, 1. mathematical
modeling. Separation Sci. and Tech. 24(1): 863-92.
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