Intro to Chapter 7
Vadose Zone, Science and Technology Solutions
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CHAPTER 7
REMEDIATION OF ORGANIC CHEMICALS IN THE VADOSE ZONE
by
Lawrence C. Murdoch
7.1 INTRODUCTION
The remediation of organic chemicals in the vadose zone has been blessed by remarkable
success, but it has also been cursed by challenges to even our most advanced capabilities.
This spectrum of outcomes to the remedial process is a result of the diversity of
conditions encountered at contaminated sites. Organic chemicals are rarely stored or
intentionally placed beneath the water table, so the source of most organic contaminants
is at the ground surface or in the shallow vadose zone. As a result, nearly all sites
containing organic contaminants have at least some problems in the vadose zone, and
commonly the greatest concentrations of contaminants occur in the vadose zone near the
source.
The large number of sites requiring vadose zone remediation presents a broad range of
conditions and circumstances, including factors related to geologic conditions, properties
of the contaminants, and the ability to access the subsurface. All are critical to the
performance of the remedial technique, and currently no single technique addresses all
the factors found at contaminated sites. Instead, an array of techniques has been
developed, some to target widespread problems and others to address the more difficult
niches.
The development of soil vapor extraction (SVE) in the mid to late 1980s provided a
method that significantly reduces the mass of volatile compounds at sites underlain by
relatively dry, sandy sediments, in areas readily accessed by conventional drilling. A
significant number of sites meet those criteria, and SVE has been used to close many of
them. SVE is widely available and, along with several companion techniques, it forms the
backbone of our organic chemical remediation capabilities.
A variety of conditions impede SVE performance. Organic contaminants may partition
into the vapor phase only sparingly, or the underlying material may be tight or marked by
significant heterogeneities, or the contaminated region may be beyond the influence of
conventional wells. These factors reduce the effectiveness of SVE, delaying the
completion of remediation and increasing costs.
Performance improvement and cost reduction motivated the development of at least a
dozen other technologies for remediating organic chemicals in the vadose zone. Each of
Intro to Chapter 7
Vadose Zone, Science and Technology Solutions
Battelle Press
the innovative technologies either stretches the limitations caused by geology,
contaminant properties, or access, or reduces the equipment and operating costs of
conventional SVE. Some are designed to improve SVE performance itself, for example,
by heating the ground to accelerate the contaminant evaporation and increase the
recovery rate. Others draw on different physical or chemical processes for remediation.
Contaminant recovery is by no means the only remediation method for the vadose zone.
Bioremediation of hydrocarbons has been widespread and successful in many vadose
settings. Other possibilities include chemically altering contaminants to benign
compounds, or injecting chemicals to markedly reduce the mobility of contaminants and
limit their ability to migrate to potential receptors. At some sites, naturally occurring
processes may reduce the concentrations of contaminants so that subsurface monitoring is
sufficient to ensure remediation.
The purpose of this chapter is to identify the current state of our capability to remediate
organic chemicals in the vadose zone. This is accomplished by first describing the
remedial technologies that are currently available. The second part of the chapter is a
comparison of the performance of these technologies under a variety of conditions at
contaminated sites. Most of the remediation methods considered here fall unambiguously
into one of four major classes of remedial methods: recovery, destruction,
immobilization, and natural processes, and the chapter is organized around these classes.
However, a few of the technologies are capable of more than one type of action; for
example, heating the subsurface will improve recovery but it can also destroy some
contaminants by oxidization or pyrolysis.
All of the technologies described in the following pages have advanced through the
development process and are now offered as a service by private companies. Some are
widely available, while other methods are more specialized and available from one, or
perhaps only a few, companies. A variety of other methods currently show promise in the
laboratory, and it is expected that they will soon be added to the list of commercially
available techniques. However, only methods that are commercially available at this time
are described in this chapter.
7.1.1 Contributors To The Chapter
Methods for remediating organic chemicals in the vadose zone have evolved rapidly over
the past few years, and important advances in technologies have often outpaced
descriptions in technical journals. In order to document the current status of each
technology, we have obtained contributions from leading experts who are aware of the
most recent activities and developments. Contributors to this chapter and the
technologies they describe are cited below.
Recovery Technologies
SVE; John S. Gierke
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Department of Geological Engineering and Sciences
Michigan Technological University
1400 Townsend Drive
Houghton, MI
Passive SVE; Joseph Rossabi
Westinghose Savannah River Company
Bldg 773-42A, Rm 249
Aiken, SC 29808
SVE with heating
Thermal Conduction; John Reed, Denis Conley,
TerraTherm
10077 Grogans’s Mill Road
The Woodlands, TX 77380
Radio-Frequency Heating; James Phelan
PO Box 5800
MS 0719
Sandia National Lab
Albequerque, NM 87185
jmphela@sandia.gov
Steam flooding; Ronald W. Falta,
Department of Geological Sciences
Clemson University
Clemson, SC 29634
Email: faltar@clemson.edu
Electrical resistance heating; William Heath,
Pacific Northwest National Lab
Hanford, WA
Destruction Technologies
Bioremediation; Terry Hazen,
Earth Sciences Division
Lawrence Berkeley National Laboratory
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MS 90-1116
1 Cyclotron Road
Berkeley, CA 94720
Email: tchazen@lbl.gov Phone: 510-486-6223
Injected oxidants;
Robert L. Siegrist, Michael A. Urynowicz
Colorado School of Mines
Environmental Science & Engineering Division
112 Coolbaugh Hall
Golden, CO 80401-1887 USA
Email. rsiegris@mines.edu
Olivia R. West
Oak Ridge National Laboratory
Environmental Sciences Division
1505 Bethel Valley Road
Oak Ridge, TN 37831-6036
Email. qm5@ornl.gov
Lance permeation; Robert L. Siegrist,
Colorado School of Mines
Environmental Science & Engineering Division
112 Coolbaugh Hall
Golden, CO 80401-1887 USA
Email. rsiegris@mines.edu
Gas-phase oxidants; Wilson Clayton,
IT Corporation
5600 S. Quebec St., Suite 200B
Englewood, CO 80111
wclayton@theITGroup.com
Reactive barriers; Lawrence C. Murdoch,
Department of Geological Sciences
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Clemson University
Clemson, SC 29634
and FRx Inc,
Email: lmurdoch@clemson.edu
William W. Slack
FRx, Inc.
P.O. Box 8292
Cincinnati, OH 45249-8292
e-mail: wslack@frx-inc.com
Deep Soil Mixing; Robert L. Siegrist
Colorado School of Mines
Environmental Science & Engineering Division
112 Coolbaugh Hall
Golden, CO 80401-1887 USA
Email. rsiegris@mines.edu
Olivia R. West
Oak Ridge National Laboratory
Environmental Sciences Division
1505 Bethel Valley Road
Oak Ridge, TN 37831-6036
Email. qm5@ornl.gov
Immobilization Technologies
Solidification and Stabilization; Paul Bishop,
University of Cincinnati
Cincinnati, OH 45221
Paul.Bishop@uc.edu
Vikram Hebatpuria
Malcolm Pirnie, Inc.,
Mahwah, NJ 07495-0018
Natural Processes
Phytoremediation; Larry E. Erickson, L. C. Davis, and P. A. Kulakow
Kansas State University
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Manhattan, KS 66506
lerick@ksu.edu