Phytoremediation of TCE in
C Groundwater using Populus
Prepared by
Jonathan Chappell
National Network of Environmental
Studies (NNEMS) Fellow
February 1998
Prepared for
U.S. Environmental Protection Agency
Office of Solid Waste and Emergency Response
Technology Innovation Office
401 M Street, SW (5102G)
Washington, DC 20460
(703)603-9910
(703)603-9135 fax
http://clu-in.com/
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NOTICE
This document was prepared by a NNEMS grantee under a fellowship from the U.S.
Environmental Protection Agency. This report was not subject to EPA peer review or technical
review. The U.S. EPA makes no warranties, expressed or implied, including without limitation,
warranty for completeness, accuracy, or usefulness of the information, warranties as to the
merchantability, or fitness for a particular purpose. Moreover, the listing of any technology,
corporation, company, person, or facility in this report does not constitute endorsement, approval
or recommendation by the U.S. EPA.
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FOREWORD
The potential use of plants to remediate contaminated soil and groundwater has recently received a
great deal of interest. EPA's Technology Innovation Office (TIO) provided a grant through the
National Network for Environmental Management Studies (NNEMS) to assess the status of
phytoremediation technologies to clean up shallow groundwater. This report was prepared by a
graduate student from Duke University during the summer of 1997. It has been reproduced to help
provide federal and state project managers responsible for hazardous waste sites with information
on the current status of this technology.
About the National Network for Environmental Management Studies (NNEMS)
NNEMS is a comprehensive fellowship program managed by the Environmental Education
Division of EPA. The purpose of the NNEMS Program is to provide students with practical
research opportunities and experiences.
Each participating headquarters or regional office develops and sponsors projects for student
research. The projects are narrow in scope to allow the student to complete the research by
working full-time during the summer or part-time during the school year. Research fellowships
are available in Environmental Policy, Regulations, and Law; Environmental Management and
Administration; Environmental Science; Public Relations and Communications; and Computer
Programming and Development.
NNEMS fellows receive a stipend determined by the student's level of education and the duration
of the research project. Fellowships are offered to undergraduate and graduate students. Students
must meet certain eligibility criteria.
About this Report
This report is intended to provide a basic orientation and current status of phytoremediation for
shallow groundwater. It contains information gathered from a range of currently available sources,
including project documents, reports, periodicals, Internet searches, and personal communication
with involved parties. No attempts were made to independently confirm the resources used.
Jonathan Chappell, NNEMS fellow, would like to acknowledge the support and encouragement
received for the completion of this report from the EPA's Technology Innovation Office and from
the contributors to this report for the invaluable information and comments they provided for the
completion of this paper.
While the original report included color images, this copy is printed in one color. Readers are
directed to the electronic version of this report to view the color images; it is located at
http://cIu-in.com/phytoTCE.htm
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ACKNOWLEDGMENTS
The Technology Innovation Office (TIO) would like to acknowledge and thank the individuals
who reviewed and provided comments on draft documents. The reviewers included representatives
of business, community and grassroots organizations, EPA Headquarters and regional offices
local government and city planning offices, and professional associations representing local and
state government officials.
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Phytoremediation of TCE using Populus
Jonathan Chappell
Status Report prepared for the U.S. EPA Technology Innovation Office
under a National Network of Environmental Management Studies Fellowship
Compiled June - August 1997
Hybrid poplar (Populus charkowiiensis x incrassata, NE 308) at Edward Sears Property
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Table of Contents
Page
Purpose 1
1. Overview of Phytoremediation j
1.1 Advantages and Disadvantages of Phytoremediation 3
1.2 Performance 4
1.3 Cost 4
2. Phytoremediation of TCE with Trees in the Genus Populus 7
2.1 Description of TCE 7
2.1.1 Physical and Chemical Properties of TCE 7
2.1.2 TCE Availability to Plant Roots 8
2.1.3 Toxicity of TCE to Animals 9
2.1.4 Toxicity of TCE to Plants 9
2.2 Description of Populus sp. 9
2.3 Mechanisms of TCE Phytoremediation by Populus sp. 12
2.3.1 Overview of Mechanisms 12
2.3.2 Enzymatic Degradation and Mineralization in Populus 13
2.3.3 Enhanced TCE Degradation and Mineralization in the 14
Rhizosphere
2.3.4 Insoluble Residues of TCE 15
2.3.5 TCE Volatilization 15
2.4 Field Trials 16
2.5 Uncertainties of Phytoremediation with Populus sp. 16
2.6 Other Types of Populus Phytoremediation Projects 17
2.7 Populus versus Other Treatment Technologies 17
3. Case Studies 19
3.1 Aberdeen Proving Grounds - Edgewood Area J Fields 21
Site (Edgewood, MD)
3.1.1 Site Design, Monitoring, and Goals 21
3.1.2 Cost 23
3.1.3 Performance to Date 23
3.2 Edward Sears Property (New Gretna, NJ) 24
3.2.1 Site Design, Monitoring, and Goals 26
3.2.2 Cost 27
3.2.3 Performance to Date 27
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Page
3.3 Carswell Air Force Base (Ft. Worth, TX) 28
3.3.1 Site Design, Monitoring, and Goals 28
3.3.2 Cost 29
3.3.3 Performance to Date 29
4. The Future of Phytoremediation 31
4.1 Future Research 31
Figure 1 - Image of Leaves from Parent Poplar Species (Populus 33
tricocarpa and Populus deltoides) and Hybrid Offspring
Figure 2 - J Fields Phytoremediation Tree Planting Area Map, 34
Aberdeen Proving Grounds - Edgewood, MD
Figure 3 - Edward Sears Property Tree Planting Layout 35
Figure 4 - Photograph of Hybrid Poplar Field at Edward Sears Property 36
Figure 5 - Photograph of Hybrid Poplar Tree at Edward Sears Property 37
Figure 6 - Air Force Plant 4 Phytoremediation Site Layout, Carswell 38
Air Force Base - Ft. Worth, TX
Appendix A - Companies Specializing in Phytoremediation Technologies 39
Appendix B - Phytoremediation Enzymes 40
Appendix C - Some Representative Examples of Phytoremediation Projects 41
Appendix D - Phytoremediation Web Sites 42
References 43
Table Index 47
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Purpose
The purpose of this report is to briefly summarize the current state of phytoremediation
technology, and then focus on the use of poplar trees {Populus sp.) to degrade trichloroethylene
(TCE) in groundwater. The summary of phytoremediation will serve as an introduction to this
technology. It will address some common concerns such as the cost and performance of
phytoremediation. The analyzation of TCE phytoremediation will begin with separate
discussions of TCE and poplars, followed by a detailed section on the use of poplars to treat TCE
contamination. The final section will present three case studies detailing Department of Defense
and Superfund sites where poplars have been planted in order to treat TCE contamination in
groundwater.
1. Overview of Phytoremediation
Phytoremediation is an emerging technology which uses plants and their associated
rhizospheric microorganisms to remove, degrade, or contain chemical contaminants located in
the soil, sediments, groundwater, surface water, and even the atmosphere. Researchers have
found that plants can be used to treat most classes of contaminants, including petroleum
hydrocarbons, chlorinated solvents, pesticides, metals, radionuclides, explosives, and excess
nutrients. Plant species are selected for phytoremediation based on their potential to
evapotranspirate groundwater, the degradative enzymes they produce, their growth rates and
yield, the depth of their root zone, and their ability to bioaccumulate contaminants.
Table 1 lists the various applications of phytoremediation technologies. This list
indicates that phytoremediation is actually a broad class of remediation techniques which include
many treatment strategies. Obviously, the common thread through all of these techniques is the
use of plants to treat a contaminant problem. However, due to the diverse nature of chemical
contamination and the diversity of plants with the potential to treat them, remedial project
managers must choose between a wide variety of phytoremediation techniques to solve the
problem at hand.
Despite the diversity of phytoremediation technologies, its application is limited by a
number of factors. Phytoremediation can only work at sites that are well suited for plant growth.
This means that the concentration of pollutants cannot be toxic to the plants, and the pollution
cannot be so deep in the soils or groundwater that plant roots cannot reach it. As a result,
phytoremediation may be a good strategy for sites conducive to plant growth with shallow
contamination, it may be a good secondary or tertiary phase in a treatment train for highly
polluted sites, or it may not be a viable option for a site.
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Table 1: Types of Phytoremediation Systems
Treatment Method
Mechanism
Media
Rhizofiltration
Uptake of metals in plant roots
surface water and water pumped
through troughs
Phytotransformation
Plant uptake and degradation of
organics
surface water, groundwater
Plant-Assisted
Bioremediation
Enhanced microbial degradation in
the rhizosphere
soils, groundwater within the
rhizosphere
Phytoextraction
Uptake and concentration of metals
via direct uptake into plant tissue
with subsequent removal of the
plants
soils
Phytostabilization
Root exudates cause metals to
precipitate and become less
bioavailable
soils, groundwater, mine tailings
Phytovolatilization
Plant evapotranspirates selenium,
mercury, and volatile organics
soils, groundwater
Removal of organics from
the air
Leaves take up volatile organics
air
Vegetative Caps
Rainwater is evapotranspirated by
plants to prevent leaching
contaminants from disposal sites
soils
Source: Adapted from Miller (1996) and Workshop on Phytoremediation of Organic Contaminants (1997)
Even though phytoremediation appears to have limited application, researchers in
industry, academia, and government are looking into phytoremediation as a useful treatment
technology. In fact, a number of companies that offer phytoremediation technologies have been
started in the last few years, and many larger consulting firms are beginning to offer
phytoremediation services as well. Appendix A lists many of these companies, but this list is not
complete; there are likely many more companies who either currently offer phytoremediation
services or will offer them in the near future. Again, since phytoremediation covers a broad
spectrum of pollutants and treatments, many of these companies focus most of their attention on
one niche of the phytoremediation field (e.g., metal extraction from soils, poplar tree buffers,
etc.).
Most of the phytoremediation companies in Appendix A have already used, or are using,
phytoremediation in the field. For example, four phytoremediation projects have been accepted
for the Superfund Innovative Technology Evaluation (SITE) program. One project by Phytotech,
Inc. involves the use of plants to extract metals from soils. The second project by Phytokinetics
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involves the use of poplar trees to treat PAH contaminated groundwater. Another project by
Phytokinetics uses grasses to remediate surficial soils contaminated with PCP and PAHs. The
fourth phytoremediation SITE project involves the use of cottonwoods to treat a plume of TCE in
shallow groundwater at the Carswell Air Force base in Ft. Worth, TX. This last project will be
detailed as a case study later in this report. In addition, a number of other pilot and field scale
projects have taken place around the country. Appendix B summarizes some of these projects,
including the types of contaminants present and treatment techniques employed at these sites.
1.1 Advantages and Disadvantages of Phytoremediation
Early research indicates that phytoremediation technology is a promising cleanup
solution for a wide variety of pollutants and sites, but it has its limitations. Table 2 summarizes
some of the advantages and limitations of phytoremediation. An examination of the table
reveals that many of phytoremediation's limitations and advantages are a direct result of the
biological aspect of this type of treatment system. Plant-based remediation systems can function
with minimal maintenance once they are established, but they are not always the best solution to
a contamination problem. One way to summarize many of phytoremediation's limitations is
that the pollutant must be bioavailable to a plant and its root system. If a pollutant is located in a
deep aquifer, then plant roots cannot reach it. If a soil pollutant is tightly bound to the organic
portion of a soil, then it may not be available to plants or to microorganisms in the rhizosphere.
On the other hand, if a pollutant is too water soluble it will pass by the root system without any
uptake.
Table 2: Advantages and Limitations of Phytoremediation
Advantages of Phytoremediation
Limitations of Phytoremediation
in situ
Limited to shallow soils, streams, and
groundwater
Passive
High concentrations of hazardous materials can
be toxic to plants
Solar driven
Mass transfer limitations associated with other
biotreatments
Costs 10% to 20% of mechanical treatments
Slower than mechanical treatments
Transfer is faster than natural attenuation
Only effective for moderately hydrophobic
contaminants
High public acceptance
Toxicity and bioavailability of degradation
products is not known
Fewer air and water emissions
Contaminants may be mobilized into the
groundwater
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Advantages of Phytoremediation
Limitations of Phytoremediation
Generate less secondary wastes
Potential for contaminants to enter food chain
through animal consumption
Soils remain in place and are usable following
treatment
Unfamiliar to many regulators
1.2 Performance
A major hurdle for innovative technologies to overcome is a lack of performance data,
and phytoremediation is no exception. One of the current barriers to performance data is the
length of time involved in a phytoremediation project. Plants can only grow so fast, so obtaining
long term performance results is dependent on the rates of plant growth and activity. There are
currently a number of pilot scale projects in existence, but they have not resulted in conclusive
performance data at this time. These sites are being monitored and will report results over the
next few years. Also, a number of firms have installed phytoremediation systems at polluted
sites owned by private clients, so results from those sites are not publicly available.
Some performance data is included in the "Case Studies" section of this report. However,
these studies are not complete, so the data presented is from early in those treatments. When
looking at performance data, one needs to keep in mind that most data is very site specific,
especially for a biological system like phytoremediation. For example, transpiration rates
reported for a hot, arid region may not match those from a cooler climate. Performance may
also be seasonal since many plants are dormant during the winter months. This is especially
important when planning projects or comparing results of projects from different regions.
1.3 Cost
In addition to performance data, accurate cost data is often difficult to predict for new
technologies. Most lab, pilot, and field scale tests include monitoring procedures far above those
expected at a site with a remediation goal. This inflates the costs of monitoring at these test sites.
As a result, it is difficult to predict the exact cost of a technology that has not been established
through years of use. However, since phytoremediation involves the planting of trees or grasses,
then it is by nature a relatively inexpensive technology when compared to technologies that
involve the use of large scale, energy consuming equipment.
Phytoremediation costs will vary depending on the treatment strategy. For example,
harvesting plants that bioaccumulate metals can drive up the cost of treatment when compared to
treatments that do not require harvesting. Regardless, phytoremediation is often predicted to be
cheaper than comparable technologies.
Tables 3 and 4 were included to outline some of the predicted costs of phytoremediation.
Table 3 presents some estimates of phytoremediation's costs in relation to conventional
technologies. This table represents some vague and variable estimates due to the current dearth
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of cost information. Since the bulk of this report deals with the use of poplar tree systems, Table
4 lists some of the costs listed by two companies who specialize in poplar designs. Keep in mind
that costs of phytoremediation are highly site specific, so that any estimate found in these tables
is merely a rough estimate of potential costs. Many of these estimates are speculative based on
laboratory or pilot scale data.
Table 3: Estimates of Phytoremediation Costs Versus Costs of Established Technologies
Contaminant
Phytoremediation Costs
Estimated Cost using Other
Technologies
Source
Metals
$80 per cubic yard
$250 per cubic yard
Black (1995)
Site contaminated with
petroleum hydrocarbons
(site size not disclosed)
$70,000
$850,000
Jipson (1996)
10 acres lead
contaminated land
$500,000
$12 million
Plummer
(1997)
Radionuclides in surface
water
$2 to $6 per thousand gallons
treated
none listed
Richman
(1997)
1 hectare to a 15 cm
depth (various
contaminants)
$2,500 to $15,000
none listed
Cunningham
etal. (1996)
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Table 4: Ecolotree's and Applied and Natural Science, Inc.'s Cost Estimates of a Poplar Tree
Phytoremediation System*
Ecolotree
Activity
Cost
Installation of trees at 1450 trees/acre
$12,000 to $15,000
Predesign
$15,000
Design
$25,000
Site Visit
$5,000
Soil cover and amendments
$5,000
Transportation to site
$2.14/mile
Operation and Maintenance
$l,500/acre with irrigation
$l,000/acre without irrigation
Pruning (not every year)
$500
Harvest (during harvest years)
$2,500
Applied Nat
ural Science
Activity
Cost
Treemediation program design and implementation
$50,000
Monitoring equipment
Hardware - $10,000
Installation - $ 10,000
Replacement - $5,000
Five-year monitoring
Travel and Meetings - $50,000
Data collection- $50,000
Annual reports - $25,000
Sample collection and analysis - $50,000
* Estimates will vary with type of contaminant, goal of project (i.e., containment vs. removal), and location.
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2. Phytoremediation of TCE with Trees in the Genus Populus
Researchers have been investigating the possibility of using trees in the genus Populus to
hydraulically contain and ultimately remediate plumes of TCE in groundwater. In addition,
managers at several Department of Defense and Superfund hazardous waste sites have planted
Populus sp. in an effort to treat groundwater contaminated with chlorinated solvents. This
section will focus on the available information about the use of Populus sp. to phytoremediate
plumes of TCE. Included are background sections on TCE and poplar trees, followed by
sections on mechanisms of TCE phytoremediation, other phytoremediation applications of
poplars, and a comparison of conventional remediation methods to poplar systems.
2.1 Description of TCE
Trichloroethylene (TCE) is a common contaminant at many of the nation's hazardous
waste sites. It can be found at 50% of Superfund National Priority List (NPL) sites with
completed Records of Decision (RODs), and it is above action levels in the groundwater of 17%
and soils of 16% of RCRA corrective action facilities (USEPA 542-R-96-005). TCE pollution
became prevalent primarily through its use as an industrial degreasing agent. Other uses of TCE
include its use as a solvent for dry cleaning, an anaesthetic for medical and dental use and as an
ingredient in paints, inks, cosmetics, disinfectants, and cleaning fluids. Due to widespread TCE
contamination, finding innovative ways to clean this pollutant has become a priority in the
remediation field.
2.1.1 Physical and Chemical Properties of TCE
Examining the physical and chemical characteristics of a target compound is veiy
important when choosing a remediation strategy. The physical characteristics of TCE, which are
listed in Table 5, make it difficult to remove from the groundwater using traditional
technologies. TCE is a dense non-aqueous-phase liquid (DNAPL), meaning that it is denser than
water and therefore tends to exist in undissolved pools in the bottom an aquifer. This property
makes it very difficult to treat TCE by methods such as pump and treat because it is almost
impossible to tap into small pools of undissolved TCE that reside in the groundwater. Pump and
treat methods can remove TCE that is in the aqueous phase, but since pools of non-aqueous TCE
are in equilibrium with the groundwater, more TCE will dissolve into the aqueous phase as the
groundwater is treated. This results in a continuous cycle of slow dissolution from the non-
aqueous to the aqueous phase that could take many years and large amounts of money and
energy to treat.
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Table 5: Physical and Chemical Properties of TCE
Property
Value
Molecular weight
131.5
Boiling point
87° C
Melting point
-73° C
Specific gravity
1.4642 at 20° C
Solubility in water
1,000 mg/liter
Log octanol/water partitioning coefficient
2.29
Vapor pressure
60 mm Hg at 20° C
Vapor density -
4.53
Source: Clement Associates (1985)
Many scientists and hazardous waste site managers, such as those involved with the three
case studies included in this report, believe that it is more efficient to use trees as a solar driven
pump and treat mechanism in a long term treatment process for TCE contamination. Others,
however, remain skeptical. Cunningham et al. (1996) stated that TCE and perchloroethylene
(PCE) are "a relatively poor choice of targets for phytoremediation" because they tend to form
dense pools near the bottom of an aquifer, out of the reach of tree roots. Current studies will
likely provide some answers to this debate.
2.1.2 TCE Availability to Plant Roots
In order for a plant to directly degrade, mineralize, or volatilize a compound, it must be
able to take that compound up through its roots. The ability of a plant to take up a chemical from
the soil and groundwater and translocate it to its shoots is described by a chemical's root
concentration factor (RCF) and transpiration stream concentration factor (TSCF). The RCF is a
measure of the root concentration of a contaminant versus the concentration in the external
solution, while the TSCF is a measure of the concentration in the xylem sap in relation to the
concentration in the external solution. Both of these factors vary directly with a chemical's
water solubility, commonly expressed as its log Kow. According to Briggs et al. (1982),
contaminants in solution with the highest TSCF are moderately soluble compounds with a
solubility in the range of log Kow 1.5 to 2. However, several reviews expand this optimum range
to include log Kow values as low as 0.5 and as high as 3 (Schnoor et al. 1995, Schimp et al. 1993).
Most chlorinated solvents, including TCE, fall within this expanded range, along with BTEX
chemicals and short chain aliphatics. As a result, phytoremediation appears to be a viable option
for treating dissolved TCE in groundwater.
Soils, on the other hand, pose a potential problem for plants because may they contain
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high levels of organic matter. In soils, the log Kow for maximum TSCF can be shifted down to
favor more polar molecules because of the competing process of sorption to soil organic matter
(Cunningham et al. 1996). As a result, plant roots alone may have a difficult time extracting
TCE from soils containing significant amounts of organic matter. However, microorganisms in
the rhizosphere are capable of degrading TCE. Anderson and Walton (1995) found that TCE
mineralization was significantly enhanced in the rhizoshpere of a number of plant species, such
as Pinus taeda (loblolly pine) and Lespedeza cuneata, when compared with nonvegetated soils.
The exact mechanisms of rhizospheric degradation will be discussed in a later section.
2.1.3 Toxicity of TCE to Animals
TCE has been found to be carcinogenic to laboratory mice in a number of studies
reported by the National Institute of Environmental Health Sciences (T-2, TR-243). However,
these studies did not find TCE carcinogenic to laboratory rats. TCE was found to be a mutagen
when tested using microbial assay systems, and chronic inhalation exposure to TCE causes liver,
kidney, neural, and dermatological reactions in animals (Clement Associates 1985). The EPA
drinking water standard for TCE has been set at 5 parts per billion (ppb), and the EPA has also
reported that drinking 1 part per million (ppm) TCE in water over a lifetime will cause 32
humans in a population of 100,000 to be at risk of cancer (EPA 540/R-94/044).
Vinyl chloride, which may result from the anaerobic breakdown of TCE by
microorganisms, is regarded as a more potent human carcinogen than TCE. The EPA drinking
water standard for vinyl chloride is 2 ppb, and the EPA estimates that drinking 1 ppm vinyl
chloride over a lifetime will cause 9,570 cases of cancer in a population of 100,000 people (EPA
540/R-94/044). Since this microbial breakdown product is more chronically toxic than its parent
compound, regulators are concerned with the exact fates of TCE in a remediation system.
2.1.4 Toxicity of TCE to Plants
While it is important to understand the concentrations of TCE that are toxic to plants, few
studies report the phytotoxic effects of TCE. Gordon et al. (1997) reported that poplars were
able to survive when grown in water containing 50 ppm TCE. Another experiment found TCE to
be acutely toxic to a variety of crop plants at concentrations of about 2 mM in the gas phase (Ryu
et al. 1996). The later study hypothesized that an increase in electrolyte leakage or interference
with the photosynthetic system was the mechanism of acute toxicity in the plants, but the exact
mechanism is not known.
2.2 Description of Populus
The genus Populus includes a number of species of trees such as poplars, cottonwoods,
and aspens. Populus is a member of the Salicaceae family, which also includes willows. There
are around 30 species of Populus distributed around the Northern Hemisphere, with eight species
indigenous to North America and others that have been introduced. In addition, Populus sp. have
the ability to cross within the genus both in the wild and through controlled breeding, so there are
a large number of potential hybrids (Dickmann and Stuart 1983).
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Due to their ability to readily form hybrids, poplars have been crossed by foresters for
years in order to maximize growth rates and yield. Hybrid poplars were originally bred and
grown as a cash crop for such uses as pulp wood and as a renewable energy source (Poplars and
Willows on the WWW), but because of their rapid growth rates and high evapotranspiration
rates, they make ideal candidates for phytoremediation. Table 6 summarizes many of the
advantages of using poplars for phytoremediation.
Table 6: Advantages of Populus sp. in Phytoremediation
~ Greater than 25 species worldwide
~ Fast growing (3 to 5 meters/year)
~ High transpiration rates (100 liters/day optimally for 5 year old tree)
~ Not part of food chain
Trees can be used for paper production or as biomass for energy
~ Long lived (25-30 years)
Grow easily from cuttings
~ Can be harvested and then regrown from the stump
Source: Adapted from Gordon (1997) and Schnoor et al. (1995)
The goal of poplar hybridization is to achieve heterosis, which means that the genetic
traits of hybrids exceed those of the parents (Dickmann and Stuart 1983). Two species of
poplars, Populus deltoides (eastern cottonwood) and Populus trichocarpa (black cottonwood),
are commonly crossed for use in phytoremediation. Populus trichocarpa x deltoides, pictured in
Figure 1, have leaves that are about four times as large as the leaves of parent plants (ORNL
1996). Increasing leaf size increases the potential evapotranspiration rates of these trees due to
increased total leaf surface area. Another common cross that has been used in phytoremediation
studies is P. deltoides x P. nigra (black poplar). This cross is sometimes referred to as P. x
euramericana due to the original distribution of the two species, the black poplar in Europe and
the eastern cottonwood in North America. There are many other hybrids of poplars that have
been developed, some of which have been or will likely be used in phytoremediation systems
One piece of information that concerns most of those interested in poplar
phytoremediation projects is the evapotranspiration rates of the trees. Poplars and cottonwoods
are phreatophytic plants, which means that they can extend their roots to the water table and
pump from the zone of saturation. For this reason, the presence of a number of cottonwood
species in desert regions, such as Populus fremontii and Populus wizlizeni, has been historically
used as an indicator of relatively shallow groundwater (Meinzer 1927). This ability to pump
groundwater has earned poplars the name "solar driven pump and treat systems" in the
phytoremediation field. Knowing how well these trees can act as a solar powered pump will aid
in deciding whether or not they can be used to treat a particular site. A plot of trees with high
evapotranspiration rates can cause a significant draw-down in the water table, which results in a
hydraulic barrier to contaminant transport. Results of a number of studies indicate that a stand of
poplars can cause a depression in the water table ranging from several inches (Workshop on
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Phytoremediation of Organic Contaminants 1996) to several feet (see Aberdeen case study).
Unfortunately, since trees are solar driven and biological, as opposed to mechanical,
pumping rates will vary with tree age and species as well as time of day, time of year, amounts of
solar radiation, and other climatic and geographic factors. As a result, pumping rates will be
highly site specific. Table 7 lists some reported evapotranspiration rates for individual poplar
trees. This list includes a wide range of pumping rates, from 1.6 gpd/tree for a young tree to 53
gpd/tree for a five year old poplar.
Table 7: Estimates of Evapotranspiration Rates by Hybrid Poplars
Rate
Source
100 to 200 L/day/tree (-26 to 53 gallon/day) for 5 year old trees
Newman et al (1997)
100 L/day/tree for a 5 year old tree under optimal conditions
Stomp et al. (1994)
13 gallons per day (estimated) when trees are calculated as low-flow
pumping wells
Sheldon Nelson - Workshop on
Phytoremediation of Organic
Contaminants (1996)
1.6 to 10 gpd/tree (observed) sap flow rates for young hybrid poplars at
the Aberdeen Proving grounds in Maryland
Compton (1997)
10-11 kg/tree/day (observed) in early summer for 1-2 year old
Eastern cottonwoods growing in Texas
Greg Harvey (personal
communication)
40 gallons per day (observed) for 5 year old trees in Utah in the
summer
Ari Ferro - Workshop on
Phytoremediation of Organic
Contaminants (1996)
Trees will transpire at different rates when grown together as a stand than they would
when grown individually. This is because evapotranspiration varies with the total leaf surface
area, whether it be for an individual tree or an entire stand. This means that tree density is an
important consideration for phytoremediation. A dense stand will have less leaf surface area per
tree, but the combined leaf surface area of a dense stand will be greater than the combined
surface area of a thin stand. Some information on evapotranspiration is available for stands of
poplar trees. For example, Gordon et al. (1997) reported that a stand of 5 year old poplars could
cause a 140 cm/year draw-down in the water table when grown at a density of 1,750 trees/ha in
the warm, arid conditions of eastern Washington state. Table 8 provides measured water uptake
per hectare and per acre of poplars grown at a density of 2,170 trees/acre at varying tree ages.
This table, along with Table 7, provides some good approximations of the pumping efficiencies
of Populus sp. However, evapotranspiration rates will vary from site to site.
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Table 8: Growth and Water Uptake Potential in Five Growing Seasons in Amana, IA for Poplars Planted at
2,170 Trees/acre Density*
Growing Season
Water Uptake (liter/hectare)
Water Uptake (gallons/acre)
1
437,545
46,766
2
2,99,035
319,795
3
8,329,440
890,258
4
9,957,364
1,064,264
5
21,845,073
2,334,847
5 year average
8,712,291
931,188
*The water uptake is calculated using 600:1 water to stem growth ratio
Source: Ecolotree, Inc.
23 Mechanisms of TCE Phytoremediation by Populus sp.
The following sections will discuss the phytoremediation mechanisms that have been
reported when poplars are used to treat TCE. However, the use of these plants to degrade TCE is
still a relatively new idea, so not all of the mechanisms are clearly understood at this time.
Therefore, the following sections will outline the current body of knowledge on the subject of
TCE remediation mechanisms by Populus sp. This section begins with a brief overview of
Populus remediation mechanisms, followed by individual sections detailing what is known about
those mechanisms. Also included are some results of controlled field trials of TCE
phytoremediation using poplars.
2.3.1 Overview of Mechanisms
A recent study by Newman et al. (1997a) investigated phytoremediation of TCE using
two varieties of hybrid poplars (P. trichocarpa x P. deltoides and P. trichocarpax P.
maximowiczii). These experiments were conducted using axenic poplar cell cultures and whole
poplar trees grown in a greenhouse. The investigators reported the formation of TCE
metabolites in hybrid poplar tree tissues. They confirmed that the trees were responsible for the
metabolites in their tissue, and not microorganisms, by finding the same metabolites in sterile
poplar cell cultures. They also found that TCE was evapotranspirated by the trees in the
greenhouse studies, and that some TCE was incorporated into an insoluble residue within the
trees. In addition, Walton and Anderson (1990) reported that TCE degradation by microbial
organisms was enhanced in the rhizosphere of various plant and tree species. Results of these
and other related studies of TCE fate in plants are summarized in Table 9.
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Table 9: Mechanisms of TCE Phytoremediation by the Populus sp.
Process
Product
Metabolism"
chloral hydrate, trichloroethanol
di- and trichloroacetic acid
Incorporation"
Insoluble residue
Mineralization'
C02
Transpiration"
TCE vapor
Rhizospheric degradation via microorganisms
C02b, dehalogenation metabolites such as cis-1,2-
dichloroethylenec, vinyl chloride4, and others
a - Newman et al. (1997)
b - Walton and Anderson (1990)
c - Gordon et al. (1997)
d - Workshop on Phytoremediation of Organic Contaminants (1996)
2.3.2 Enzymatic Degradation and Mineralization in Populus
As stated in the previous section, poplar trees have been found to degrade TCE, but the
exact metabolic mechanism or mechanisms of enzymatic degradation is currently under some
speculation. Two lines of research have been reported to date. Both are similar in that they
indicate an enzymatic process involved in oxidizing TCE to various metabolites. Regardless of
the enzyme or enzymes involved, the oxidative process will ultimately mineralize the carbon in
TCE to C02. Also, there is always the possibility of more than one mechanism taking place
within a plant or between plant species.
The research of Newman et al. (1997a) suggests that TCE metabolism in poplars may be
similar to the mammalian breakdown of TCE. This belief is based on the production of similar
TCE metabolites in both plants and mammals. However, the exact mechanism was not
determined by these researchers, only hypothesized based on the presence of the metabolism
products (Table 9). According to a review by Cunningham et al. (1996), many of the enzyme
systems involved in mammalian metabolism of TCE are also found in plants (e.g., cytochrome p-
450 oxygenases and glutathione S-transferases), so this hypothesis seems possible.
Another line of research indicates that TCE metabolism in poplars is the result of a
dehalogenase enzyme (Schnoor at al. 1995). According to Dr. Laura Carreira, who has isolated
the enzyme, dehalogenase is an ethylene degrading enzyme (personal communication). It
oxidizes alkanes, alkenes, and methanes and their halogenated analogues. Dehalogenase will
ultimately mineralize TCE to C02 via an oxidative pathway. Dr. Carreira has developed an
antibody assay for the ethylene degrading enzyme to use as an indicator of its presence in various
plant species. This antibody technique can be used to predict the ability of a plant or tree species
to degrade chlorinated solvents before that organism is chosen for use at a particular
phytoremediation site. In the case of poplars, some species or hybrids can produce more of this
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enzyme than others, and some may not produce the enzyme at all. As a result, using different
hybrids or species at various sites without assaying for the dehalogenase may yield contrasting
results. A tree that manufactures large quantities of the enzyme will have the ability to degrade
TCE, while plants that produce little or no quantities of the enzyme will tend to volatilize it.
A wide variety of plants can potentially produce the dehalogenase enzyme, so Dr.
Carreira's antibody technique may be used to find species of ethylene degrading plants or trees
that are native to a site. Table 10 lists some species that have been reported to produce
dehalogenase enzyme and the half lives of hexachloroethane, a halogenated hydrocarbon, in the
presence of these plants.
Table 10: Some Plant Species Containing Dehalogenase
Plant Species
Half-life (hours) of Hexachloroethane
Algae Nitella (stonewort)
90
Anthrocerotae sp.
120
Algae Spirogyra
95
Myriophyllium spicatum (parrot feather)
120
Populus sp.
50
Source: Adapted from Schnoor et al. 1995.
2.3.3 Enhanced TCE Degradation and Mineralization in the Rhizosphere
The root zone of plants provides an environment conducive to the growth and activity of
microorganisms (Kunc 1989). These enhanced populations of microorganisms have been found
to degrade TCE in the rhizosphere of a number of plant species growing on contaminated sites
(Walton and Anderson 1990). In addition to bacteria, microrhizal fungi are capable of
metabolizing chlorinated organics (Donnelly and Fletcher 1995). Initial research determined the
plant species capable of promoting TCE degradation in soils (Anderson and Walton 1995).
Recent studies have focused on determining the mechanisms of degradation within the
rhizosphere.
A review on this subject by Davis et al. (1996) reports that microbial degradation of TCE
can take place either aerobically or anaerobically. The aerobic process is an oxidative
mechanism catalyzed by a mono-oxygenase enzyme. Methane mono-oxygenases (MMO) and
alkene oxygenases are reported as the primary enzymes involved in the oxidative mechanism.
Each enzyme uses either methane or an alkene as its primary substrate, but can also oxidize TCE
in a fortuitous reaction. Plants may support this mechanism by transferring exudates to
anaerobic sites, stimulating methanogens to produce methane. The methane in turn stimulates
aerobic methanotrophs, who cometabolize TCE via the MMO enzyme. Products of this reaction
include chloral, dichloroacetic acid, trichloroacetic acid, trichloroethanol, and ultimately C02.
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The other microbial mechanism responsible for TCE metabolism is dechlorination
catalyzed anaerobically via a dehalogenase enzyme. The review by Davis et al (1996) also
describes this mechanism in the rhizosphere, which is primarily carried out by methanogens.
Contaminants such as TCE have too low an energy yield to stimulate a population of
methanogenic organisms, but plant exudates can supply enough carbon for use as a reductant by
the microbes. Once a microbial population increases in density, it will begin to cometabolically
dehalogenate TCE. The common products of this reaction are dichloroethylene, vinyl chloride,
and eventually ethene and ethane.
2.3.4 Insoluble Residues of TCE
The research of Newman et al. (1997a) also found that a small percentage (3-4%) of TCE
remained as an insoluble residue in the poplar tree cell. It is believed that this is due to abiotic
binding of TCE to the cell walls of the plant, but the exact mechanism is still under investigation.
2.3.5 TCE Volatilization
Understanding TCE volatilization rates in poplar trees is critical for this technology to
gain widespread acceptance amongst hazardous waste site managers and regulators. There may
be concern if the trees are transpiring high concentrations of TCE into the atmosphere, where the
pollutant becomes an air quality concern. Proponents of phytoremediation argue that VOCs will
volatilize from the groundwater, through the soil, and into the air in the absence of trees. For
example, plants will invade sites that are left unattended for extended periods of time, and
invasive plants may evapotranspirate the contaminant. That being the case, there would be some
evapotranspiration in the absence of a treatment strategy. Phytoremediation schemes would
only accelerate the process of volatilization that occurs naturally. Still, volatilization
concentrations are decreased by a number of factors, such as exclusion of nonpolar compounds at
the roots. According to Davis et al. (1996), "Very few contaminants are sufficiently water
soluble, non-toxic to plants, and volatile enough to reach atmospheric concentrations that would
be of concern by [evapotranspiration]."
Despite the fact that evapotranspiration rates are still unclear, Davis et al. (1996) used
energy input estimates to calculate a maximum transfer rate of TCE to the atmosphere. They
predicted a maximum transfer rate of 10 g/m2/day. This estimation assumes that the water is
totally saturated with TCE at 1.5 g/L and the TSCF of TCE is 0.67, based on the equations of
Briggs et al. (1982). Using a more realistic groundwater concentration of 1-15 mg/L TCE and a
mixing height of 100-300 meters in the atmosphere, the investigators estimated that transfer to
the atmosphere would be 4 to 6 orders of magnitude smaller than the maximum. The result is a
very low air concentration of TCE downwind in a worst case scenario.
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2.4 Field Trials
Investigations were conducted to follow up the work of Newman et al. (1997a) by
conducting field trials of TCE phytoremediation in the state of Washington (Gordon et al. 1997,
Newman et al. 1997b). These field experiments were conducted by Occidental Chemical
Corporation along with researchers from the University of Washington and Washington State
University. The state of Washington approved a two year field experiment where TCE was
added to 3.7 x 6.1 meter cells that were VA meters deep and double lined with polyethylene.
Hybrid poplars (Populus tricocarpa x deltoides, H-l 1-11) were planted in the experimental cells
and soil was only added to the controls. TCE was added to the cells at a concentration of 50
ppm in the water. The investigators found that over 95% of the TCE was removed from the
stream water in the plots with trees. During the first year of the trial, however, 65% of the
added TCE was removed in the control plot without trees. This probably meant that a significant
portion of the TCE was bound in the soils (Newman et al. 1997b). At the end of the second
growing season, 65-70% of the added TCE remained in the water stream in the control cells
(Workshop on Phytoremediation of Organic Contaminants), indicating that the loss to the soil
decreased substantially after the soil became saturated with TCE. Still, during the second year
over 97% of the added TCE was removed from the water stream in the cells containing trees
(Newman 1997c). The investigators also found products of anaerobic microbial dehalogenation,
such as three isomers of dichloroethylene and small amounts of vinyl chloride, in the water
streams (Lee Newman, personal communication).
2.5 Uncertainties of Phytoremediation with Populus sp.
Research indicates that phytoremediation of TCE using hybrid poplars will work. The
question that remains to be answered is, "To what extent does it work?". Unfortunately, there is
no answer to that question at this time. The case studies presented later in this report represent
some of the most current data on pilot studies. However, these sites are still very new and
phytoremediation is a long, slow process. Currently, managers at these sites do not know if
poplars can clean TCE plumes to regulatory standards or how long it will take. Results of these
studies are at least a year or two away, possibly more.
Another uncertainty surrounding poplar phytoremediation systems is the fate of the
contaminant. Only a few mass balance studies of TCE fate in the field have been attempted.
Mass balance predictions are further complicated by the fact that field conditions will vary
greatly between sites and geographic regions. In addition, different species or hybrids of
Populus sp. will have variable abilities to treat TCE in the groundwater. Again, results from the
three case studies in this report as well as basic research currently taking place will address some
of these uncertainties.
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2.6 Other Types of Populus Phytoremediation Projects
Populus sp. have been used to treat contaminant problems other than TCE in
groundwater. One project in Iowa investigated the ability of poplar strips to act as a buffer to
protect water bodies from nutrient runoff (Paterson and Schnoor 1993). A similar study in Iowa
looked at the ability of poplars to buffer triazine pesticide runoff from an agricultural field
(Dhileepan et al. 1993). Both of these studies indicated that poplars could successfully act as a
buffer, although they were less effective at buffering nutrients once the trees dropped their leaves
in the fall. In addition, hybrid poplars are currently being used to act as a hydraulic barrier to
contain a plume of gasoline and diesel fuel in the groundwater at a site in Ogden, UT
(EPA/540/R-97/502). Another way that poplars have been used is as a component of vegetative
caps for landfill facilities (Schnoor et al. 1995). Poplars are also being tested for their ability to
phytostabilize metals such as lead, and they have been planted as a part of a constructed wetland
design to treat explosives such as TNT and RDX in the soil (Schnoor 1997). There is also a
report on the use of poplars to phytoextract zinc from soils (Gatliff 1994).
2.7 Populus Phytoremediation Versus Other Treatment Technologies
For those unfamiliar with groundwater treatment options, Table 11 lists many of the other
technologies that have been used to treat plumes of chlorinated solvents. Table 11 includes the
cost of cleaning a plume of chlorinated solvents using these technologies under an idealized set
of conditions. Unfortunately, phytoremediation was not included in this economic analysis.
However, phytoremediation would be somewhat more expensive than natural attenuation
because it involves tree planting and maintenance as well as monitoring, and it would be
significantly less expensive than pump and treat due to decreased energy needs. Therefore the
costs of a poplar phytoremediation system would likely fall somewhere in the middle of Table
11, and probably near the less expensive end of the spectrum.
Table 11: Estimated Costs of Treating PCE in the Groundwater
(Assumes PCE plume averages 1 ppm, the remedial goal is 5 ppb, there is no pooled PCE in the aquatard, plume is
in the aqueous phase, and the remediation time is 30 years)
Treatment Technology
Total Present
Cost (x $1,000)
Cost / Pound
PCE removed
Cost /1,000
Gallons Treated
Pump and treat with air stripping and carbon
absorption
$9800
$1600
$8.90
Iron reactive barrier
$3900
$640
$5.30
Biobarrier (substrate enhanced anaerobic
bioremediation)
$3100
$520
$4.20
In situ bioremediation (substrate enhanced,
recirculating source zone)
$1300
$220
$1.80
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Treatment Technology
Total Present
Cost (x $1,000)
Cost / Pound
PCE removed
Cost /1,000
Gallons Treated
Natural attenuation (intrinsic bioremediation)
S890
$150
$1.20
Source: Quinton 1997
Since poplar phytoremediation systems are primarily used as hydraulic barriers and solar
powered pumps, the most closely related engineering technology is a pump and treat system.
The major advantage of poplars over pumps is that poplars provide their own energy, where
pumps often consume large amounts of electricity. This could save tremendous amounts of
money over the course of a long remediation project. On the other hand, a major disadvantage of
poplars is the fact that their pumping rates vary over the course of a year. In addition, poplar
systems will only work at sites where the groundwater contamination is within reach of their
roots.
Despite some limitations of poplars when compared to pump and treat, the potential
economic advantages of this treatment system are tremendous. A report by the Environmental
Security Technology Certification Program (ESTCP) estimates that poplar trees can be used to
treat contaminants such as chlorinated solvents and petroleum hydrocarbons at 1,000 DOD
cleanup sites around the world (ESTCP). This could save the government hundreds of millions
of clean-up dollars.
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3. Case Studies
Since poplars have been shown to remediate TCE under controlled experimental settings,
several Department of Defense and Superfund sites are conducting pilot scale phytoremediation
projects. The goals of these projects are to use poplars to remediate plumes of chlorinated
solvents in the groundwater. Table 12 provides some general information about each site,
including contacts. All three were still in early stages of sampling at the time of this writing, so
very little performance data is available. However, results to date indicate that the
phytoremediation systems are working. For example, several of the sites are reporting a
depression in the water table beneath the plots and some contaminant volatilization from the
trees. Future monitoring will help determine the extent of TCE removal that can be achieved
using this technology.
Table 12: Case Studies Overview of Sites
Site
Size of
Planting
on Site
Number of
Trees Planted
Species or Hybrid
Contacts
Aberdeen Proving
Grounds - J Fields
Site
~1 acre
183
Populus
trichocarpa x
deltoides, HP-510
Steve Hirsh
EPA Region 3
(215) 566-3352
Harry Compton
EPA ERT
(908) 321-6751
Edward Sears
Properties
—1/3 acre
118 deep rooted
-90 shallow
rooted
Populus
charkowiiensis x
incrassata, NE 308
George Prince
EPA ERT
(908) 321-6649
Michael Moan
Roy F. Weston/REAC
(908) 321-4200
Carswell Air Force
Base
-1 acre
660
Populus deltoides
Greg Harvey
Acquisition and Environmental
Management
Restoration Division
(513) 255-7716x302
Steven Rock
US EPA National Risk
Management Laboratory
(513) 569-7105
Tables 13 and 14 provide some meteorological data for the geographic regions of each
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site. While climate information will not be directly used in this report, it may be important in the
future when people are comparing the effectiveness of treatment strategies at these three sites.
The information in the following two tables only provides yearly averages, not data recorded at
the sites. When data from these projects are analyzed, actual weather data taken during the
treatments will be compared to determine the extent of climate's effect. Data in Tables 13 and
14 indicates that Edward Sears and Aberdeen, which are both located in the mid-Atlantic region,
have similar temperature and rainfall averages. Carswell, which is located in Texas, has a
warmer climate and less rainfall.
Table 13: Average Temperature in °F for Geographic Regions of the Case Study Sites
Site
Jan
Feb
May
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
Aberdeen
32
35
44
53
64
72
76
75
69
57
48
37
55
Ed Sears
31
33
42
50
60
70
75
74
67
56
47
37
53
Carswell
45
50
56
66
74
82
86
85
78
68
56
48
66
Source: Adapted from data found at http://www.worldclimate.com
Table 14: Average Rainfall in Inches for Geographic Regions of the Case Study Sites
Site
Jan
Feb
May
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
Aberdeen
2.0
3.9
3.7
3.5
2.6
6.2
2.1
0.8
2.7
1.8
5.1
2.9
37.2
Ed Sears
3.7
3.1
4.1
3.9
3.4
3.1
4.1
5.4
3.3
3.2
3.8
3.7
44.9
Carswell
1.8
2.2
2.8
3.5
4.9
3.0
2.3
2.2
3.4
3.5
2.3
1.8
33.7
Source: Adapted from data found at http://www.worldclimate.com
There is some cost information available for each site, but any cost data is skewed
because these are pilot scale projects. The projected costs include monitoring and analytical
procedures that exceed those normally associated with a remediation project. In addition, costs
presented here are those that exceed the baseline investigations at a site. In other words, all sites
have certain costs of sampling to determine the nature and extent of contamination. These initial
costs would be the same regardless of the technology chosen.
A lack of cost and performance data is normal for innovative technologies at the pilot
stage. That being the case, the goal of these case studies is to outline the information that is
currently available. This information will hopefully provide a history of each site and the
reasons for choosing phytoremediation as a treatment. In addition, these studies will provide a
snapshot of the current status of these projects.
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3.1 Aberdeen Proving Grounds - Edgewood Area J Fields Site (Edgewood, MD)
The Aberdeen Proving Grounds in Maryland began serving as a U.S. Army weapons
testing facility in 1918. The installation is divided into two sections, the Edgewood Area and the
Aberdeen Area, separated by the Bush River. Military weapons testing and past disposal
activities over the years have caused extensive pollution throughout the soil and groundwater of
the Proving Grounds. As a result, the entire Edgewood area of Aberdeen appears on the
Superfund National Priority List (NPL). Today the Department of Defense (DOD) and the
Environmental Protection Agency (EPA) are jointly funding pilot scale applications of
innovative treatment technologies around the facility. At the J Fields Site in the Edgewood Area,
the EPA's Environmental Response Team (ERT) coordinated the planting of hybrid poplars
over a shallow plume of chlorinated solvents in an effort to hydraulically contain the
contaminants and treat the groundwater.
3.1.1 Site Design, Monitoring, and Goals
The J Fields Toxic Pits Site had been used for many years as an open pit burning facility
for munitions and chemical agents. During this process, large volumes of various chlorinated
solvents were discharged. As a result, there is a plume of chlorinated solvents located in the
aquifer below the burning pits. Table 15 lists the contaminants of concern at the J Fields site and
their concentrations in the groundwater. Concentrations of total VOCs in the groundwater range
from less than 20,000 fig/L in some areas to over 220,000 ng/L in others.
Table 15: Contaminants of Concern at Aberdeen Proving Grounds' J Fields Phytoremediation Site
Contaminant
Groundwater (pg/L)
Percent (%)
1,1,2,2-tetrachloroethane (1122)
170,000
65.9
Trichloroethene (TCE)
61,000
23.7
Cis-l,2-dichloroethene (c-DCE)
13,000
5.0
Tetrachloroethene (PCE)
9,000
3.5
Trans-1,2-dichloroethene (t-DCE)
3,900
1.5
1,1,2-trichloroethane (TCA)
930
0.4
Source: Tobia and Compton (1997)
Personnel from Roy F. Weston, Inc. were contracted to assess the J Fields site and
conduct treatment activities. Several technologies were considered for cleaning the soil and
groundwater at the site. Soil washing, vapor extraction, and capping were considered for soils,
and pump and treat and air sparging were considered for the groundwater. These technologies
were eliminated from consideration for a number of reasons. Technologies that involved a rigid
installation design were eliminated because of a perched water table and the potential for
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unexploded bombs buried on-site. Pumping and treating the water would be difficult because of
the high concentrations of contaminants and strict discharge regulations. In other words, the
pump and treat system would need to remove high concentrations of contaminants from large
volumes of groundwater, and then discharge the groundwater after it had been treated. Soil
excavation was eliminated from consideration due to its high cost. After eliminating the other
possibilities, project managers decided the J Fields site was a candidate for a pilot scale
phytoremediation system (Tobia and Compton 1997).
Applied Natural Sciences, Inc. was subcontracted to design and install the
phytoremediation system. The phytoremediation strategy employed at the J Fields site began in
September of 1995 with an assessment for phototoxicity of on-site pollutants and to determine
any nutrient deficiencies that would hinder tree growth. In March and April of 1996,183 hybrid
poplars (P. trichocarpa x deltoides [HP-510]) were purchased from a tree farm in Pennsylvania
and planted over the areas of highest pollutant concentration around the leading edge of the
plume, totaling about one acre of trees. A sweetgum tree was growing on-site prior to
installation of the phytoremediation system, so it was left standing. It will be monitored along
with the poplars. See Figure 2 for a map of the site's layout.
In order to promote growth down to the saturated zone, each tree was planted with a
plastic pipe around its upper roots. A long piece of rubber tubing was also added from the surface
to the deeper roots in order to provide oxygen. A drainage system was installed in May 1996 to
remove rainwater and therefore promote the plants' roots to seek groundwater.
Since the Aberdeen project involves a new treatment strategy, extensive monitoring is
taking place to determine the fates of the pollutants, the transpiration rates of the trees, and the
best methods for monitoring phytoremediation sites. The monitoring approaches are
summarized in Table 16. The sampling design of the site involves collecting soils, transpiration
gases, and tree tissues from the roots, shoots, stems, and leaves. Results will help determine the
concentrations of contaminants and their metabolites along each step of the translocation
pathway.
Table 16: Monitoring Approaches at the J Fields Site
Type of Analysis or Observation
Parameters Tested or Methods Used
Plant growth measurements and visual observations
Diameter, height, health, pruning, replacement
Groundwater and vadose zone sampling and analysis
14 wells and 4 lysimeters to sample for VOCs, metals,
and nutrients
Soil sampling and analysis
Biodegradation activity, VOCs, metals
Tissue sampling and analysis
Degradation products, VOCs
Plant sap flow measurements
Correlate sap flow data to meteorological data
Transpirational gas sampling and analysis
Explore various methods
Source: Tobia and Compton (1997)
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Eight monitoring wells were in place at the time of tree planting, and five additional wells
were installed in November 1996. Two pairs of lysimeters were also installed on site. Tree sap
flow rates are also being monitored in order to determine the pumping rates of the trees. An on-
site weather monitor was used during sampling events to correlate tree evapotranspiration rates
with weather fluctuations ranging from hourly to seasonal changes.
Several different protocols were used for transpirational gas studies to investigate the
most accurate and efficient monitoring methods. All gas samples were collected in a 100 L
Tedlar bag sealed over tree branches. Two of the sample collection media involved collection
followed by analysis with a gas chromatograph (GC)/mass spectrometer(MS). One of these
collection mediums was a Tennax/Carbon Molecular Sieve tube at collection rates ranging from
20-40 mL/min, and the other a 6 liter Summa canister. Perhaps the most accurate method
involved a direct connection of Teflon tubing from the sample collection bag to a mass
spectrometer/mass spectrometer quadrapole system. This method allowed real time analysis of
the transpiration gases. However, this method involves expensive monitoring equipment, so it
probably will not be practical at most cleanup sites.
3.1.2 Cost
The trees cost about $80/tree to install. This works out to roughly $ 15,000 for
installation of 183 trees. Costs of monitoring are highly varied due to the numerous monitoring
techniques that have been employed at the site.
3.1.3 Performance to Date
Sap flow rate data indicates that on a daily scale, maximum flow occurs in the morning
hours. In addition, increasing amounts of solar radiation seems to increase sap flow rates, as
would be expected in a tree. Groundwater monitoring data from May of 1997 indicates that the
trees are pumping large amounts of groundwater. Data indicates that there is roughly a 2 foot
depression in the water table beneath the trees in comparison to data from April of 1996 (Harry
Compton, personal communication). Tree tissue samples indicate the presence of trichloroacetic
acid (TCAA), a breakdown product of TCE. This correlates with the results of Newman et al.
(1997a), who also found TCAA in plant tissues in both axenic poplars cell cultures and hybrid
poplar tissues in a greenhouse scale study. Site managers at Aberdeen are also finding that
chlorinated solvents (TCE and 1,1,2,2-tetrachloroethane) are being evapotranspirated by the
trees. To date, no mass balance studies have been performed to quantitatively determine the
different fates of chlorinated solvents in this treatment system. Future monitoring of the site will
hopefully answer some of the questions about solvent fate. In order to accomplish this,
additional types of monitoring will be employed, such as on-site infrared spectrometry and an
on-site gas chromatograph/mass spectrometer.
One other piece of noteworthy information is that the J Fields site experienced about 10%
tree loss during the first year. While some of this loss was due to the transplant process, many
trees were damaged by deer rutting. In an attempt to keep deer away from the trees, the site
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Phytoremediation of TCE using Populus
managers hung bars of Ivory soap tied to string from the tree branches. The theory was that deer
avoid the scent of humans, so they would think that there were humans nearby if they smelled
soap. However, this did not completely deter the deer because there was still some rutting
damage. Site managers plan to initiate some new strategies for the next fall. One possibility is
placing metal fencing around the trees.
3.2 Edward Sears Property (New Gretna, NJ)
From the mid-1960's to the early 1990's, Edward Sears repackaged and sold expired
paints, adhesives, paint thinners, and various military surplus materials out of his backyard in
New Gretna, NJ. As a result, toxic materials were stored in leaky drums and containers on his
property for many years. The soil and groundwater were contaminated with numerous hazardous
wastes, including methylene chloride, tetrachloroethylene, trichloroethylene, trimethylbenzene,
and xylene. After his death, no one could be found responsible for the site or its clean-up, so
On-Scene Coordinators (OSC) from EPA's Region II Removal Action Branch were called in to
remove the leaking drums of hazardous materials, including off-spec, paints and solvents. Soil
sampling indicated that two areas, 35 x 40 feet and 15 x 20 feet, were very heavily contaminated
with solvents. These soils were removed to 8 feet below ground surface (just above the water
table). Further excavation could not be achieved without pumping and treating large volumes of
ground water. The excavated area were backfilled with clean sand and the OSC activated the
EPA's Environmental Response Team (ERT) of Edison, NJ to determine the extent of ground
water and deep soil contamination.
Using innovative, hydraulic push ground water sampling techniques, the ERT
investigation revealed localized, but highly contaminated ground water. Based on this
information, a limited number of monitoring wells were installed to determine vertical
contaminant migration and to conduct aquifer tests necessary to evaluate pump and treat options.
A test pilot for a pump and treat system with air stripping and activated carbon was then
conducted. The aquifer tests revealed a high yield aquifer, which required severe over pumping
to create any substantial cone of influence around the pumping wells. Contaminants trapped in
the silty-clay lens beneath the site would be difficult to extract in this manner because the
transfer rate of contaminants into the groundwater is slow. As a result, large volumes of
groundwater would need to be pumped to the surface for treatment, and this water would contain
low concentrations of contaminant. Also, neighbors of the property would be disturbed by the
noise created by a pump and treat system.
Based on these results, a pump and treat option would be expensive and inefficient for the
Edward Sears site. Site managers then moved to a phytoremediation option. This site was
judged as a potential candidate for a phytoremediation system due to the nature of the soils and
groundwater. There is a highly permeable sand layer about 4-5 feet below ground surface, but
below that exists a much less permeable layer of sand, silt, and clay from 5 to 18 feet bgs. This
silt, sand, and clay layer acts as a semiconfining unit for water and contaminants percolating
down toward an unconfined aquifer from 18 to 80 feet bgs. This unconfined aquifer is composed
primarily of sand and is highly permeable. The top of the aquifei is about 9 feet bgs, which lies
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in the less permeable sand, silt, and clay layer. The top of the aquifer is relatively shallow and
most of the contamination is confined from 5 to 18 feet bgs, so managers decided to plant hybrid
poplars in order to prevent further migration of the contaminants and ultimately remove the
contaminants from the groundwater.
Samples were taken from temporary well points throughout the site. Data from these
sampling efforts indicated TCE concentrations in the groundwater ranged from 0 to 390 ppb.
Most of the TCE was concentrated into a small area on-site. Seven monitoring wells were
installed based on the information obtained from the temporary well points. Data from
Monitoring Well 1 can be found in Tables 17 and 18. Keep in mind that these tables only
provide information from Monitoring Well 1, and there were a total of 7 wells. Monitoring Well
1 was installed in the area of highest TCE contamination. There was little or undetectable TCE
found in the groundwater samples from the other 6 wells. That does not mean that there were no
contaminants found in those wells. Recall that the site was polluted with a wide variety of
organic chemicals and metals due to the storage practices of Mr. Edward Sears. However, since
this report focuses mainly on TCE, only data on TCE from Monitoring Well 1 was included.
Table 17: Concentrations of TCE Sampled from Groundwater in Monitoring Well 1 on Edward Sears
Property
Sampling Date
TCE Concentration
(ug/L)
12/8/95
28
8/8/96
1.2
8/19/96
2.3
Source: Roy F. Weston/REAC (1997)
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Table 18: Concentrations of TCE in Soil Samples During Monitoring Well Installation of Monitoring Well 1
at Edward Sears Property
Feet
bgs
1
4
6
8
10
11
12
14
16
18
20
ug/kg
130
18,000
540
270
120
140
48
17
35
180
8
Feet
bgs
21
27
32
37
42
47
52
57
62
67
72
ug/kg
120
130
6
62
3
65
100
16 .
6
5
6
Feet
bgs
75
77
82
87
ug/kg
52
U
4
7
U - Under Detection Limited
Source - Roy F. Weston/REAC (1997)
3.2.1 Site Design, Monitoring, and Goals
Roy F. Weston, Inc., under the Response Engineering and Analytical Contract (REAC),
was tasked by the ERT to conduct a pilot phytoremediation test at the Sears site. The test is
being conducted to determine whether hybrid poplar trees can be used to reduce soil and
groundwater VOC contamination levels in the planted area and to prevent further offsite
migration of contaminated groundwater. In October and November of 1996, the site was cleared
of debris and a 4-inch clay layer was placed approximately 1 foot bgs to prevent penetration of
rainwater into the upper root zone, thus promoting root growth into the underlying aquifer. This
was followed by the replacement and grading of the native surface soil.
Thomas Consultants of Cincinnati, OH were subcontracted to layout the
phytoremediation design. In December 1996, one hundred and eighteen hybrid poplar saplings
(Populus charkowiiensis x incrassata, NE 308) were planted by ERT, REAC and Thomas
Consultants personnel in a plot approximately one third of an acre in size. The trees were
planted 10 feet apart on the axis running from north to south and 12.5 feet apart on the east-west
axis. Figure 4 contains maps of the site's location and tree planting design.
The trees at Ed Sears were planted using a process called deep rooting. In deep rooting,
the roughly 12 foot trees were buried nine feet under the ground so that only about 2-3 feet
remained on the surface. Deep rooting the trees involved drilling 12 inch diameter holes to a
depth of 13 feet. These holes were then back filled to 5 feet below ground surface with
amendments such as peat moss, sand, limestone, and phosphate fertilizer. This backfill was
installed to provide nutrients to the roots as they penetrated down through the soils. Waxed
cardboard cylinders 12 inches in diameter and four feet long were installed to promote root
growth down into the groundwater. These barriers settled about a foot into the planting holes, so
5 gallon buckets with the bottoms cut out were placed on top of the cylinders to create a 5 foot
bgs root barrier. The trees were placed in the cylinders and the remaining five feet to surface was
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Phytoremediation of TCE using Populus
filled with clays removed during the boring process.
There were about 90 extra poplars left after the deep rooting was completed. These extra
trees were planted along the boundary of the site to the north, west, and east sides of the site.
These trees were only planted to a depth of 3 feet, or shallow rooted. The purpose of the shallow
rooted trees was to prevent rainwater infiltration from off-site and to serve as a source of
replacement trees in the event that there was a loss of some deep rooted trees. These trees were
planted very close together (about 3 feet apart) under the assumption that natural thinning would
take place over subsequent growing seasons. A surface water control system was then installed
by planting grasses over the entire site. These grasses came from commercially available seeds
purchased from a lawn and garden store.
ERT is conducting an ongoing maintenance and monitoring program at Ed Sears.
Monitoring of the site includes periodic sampling of groundwater, soils, soil gas, plant tissue,
evapotranspiration gas. Continued growth measurements will also be made as the trees mature.
In the fall, the surface water control system will be replaced due to a summer drought that killed
much of the grass. Site maintenance also involves the prevention of deer and insect damage.
Bars of soap were hung from the trees to deter deer from rubbing their antlers on the trees. Some
damage was inflicted by an insect larva known as the poplar leaf caterpillar. This caterpillar
lives on poplar trees and makes its cocoon by rolling itself in a poplar leaf. A spray containing
Bacillus thuringesis, a bacteria which produces toxins that are specific to various insects, was
applied to the site. This spray has been effective in killing most of the caterpillars that were
living on the trees.
3.2.2 Cost
Total cost of installation of the 118 deep rooted and 90 shallow rooted trees was about
$25,000. Additionally, installation of the surface water control system and one year of on-site
maintenance totaled about $15,000.
3.2.3 Performance to Date
The trees have been in the ground for less than one growing season, so as of now there is
very little performance data available. Some sampling of evapotranspiration gas was conducted
by placing Tedlar bags over entire trees. Data from these air samples suggests that the trees are
evapotranspirating some VOC's. However, the VOC concentration in the Tedlar bags matches
the background concentrations of VOCs in control samples. This could be due to VOCs
volatilizing from the soils, or it could be due to evapotranspirated VOCs that may have gotten
into the control samples. Future sampling designs will attempt to determine accurate background
VOCs. Additionally, there is some tree growth data for the trees. They have grown about 30
inches above ground since planting. Figures 4 and 5 are photographs of the trees at Edward
Sears taken in July 1997 showing their size after about 7 months of growing on site. Site
managers plan to sacrifice one tree either after or during the next growing season to determine
the extent of root growth.
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3.3 Carswell Air Force Base (Ft. Worth, TX)
In Ft. Worth, TX, the U.S. Air Force planted Eastern cottonwoods (Populus deltoides) to
investigate the ability of these trees to control and degrade a plume of TCE in a shallow aquifer.
The plume is located near Air Force Plant 4 at the Naval Air Station Ft. Worth, which was
formerly known as the Carswell Air Force Base (for the purpose of this case study, it will be
referred to as the Carswell site). The initial funding and much of the ongoing support for this
project was provided by the Environmental Security Technology Certification Program
(ESTCP), a division of the Department of Defense. The Carswell site was chosen as an EPA
Superfund Innovative Technology Evaluation (SITE) project in 1996 (EPA/540/R-97/502).
3.3.1 Site Design, Monitoring, and Goals
Greg Harvey of the U.S. Air Force Acquisition and Environmental Management
Restoration Division and Steve Rock of the US EPA National Risk Management Research
Laboratory carried out the design and implementation of the phytoremediation strategy at
Carswell. In April of 1996, the USAF planted 660 cottonwoods in an effort to contain and
remediate a plume of dissolved TCE located in a shallow alluvial aquifer (6 to 11 feet below
grade). The species P. deltoides was chosen over a hybridized species of poplar because it is
indigenous to the region. Therefore it has proven its ability to withstand the Texas climate, local
pathogens, and other localized variables that may affect tree growth and health (Greg Harvey,
personal communication).
Two sizes of trees were planted: whips and five gallon buckets. The whips were about
the thickness of one's thumb and were about eighteen inches long at planting. The whips were
planted so that about two inches remained above ground and the rest of the tree was below
ground to take root. The five gallon bucket trees were about an inch in diameter and seven feet
tall when planted. The five gallon bucket trees were estimated to have about twice as much leaf
mass as the whips when planted, so they were expected to have higher evapotranspiration rates.
The layout for the project involved planting a separate plot of trees for the whips and the
5 gallon buckets, with both plots perpendicular to the contaminant plume. The plume is moving
to the south and east, so the plots were laid out on a north and east axis. The whips section was
planted to the north and west of the 5 gallon buckets, so that the plume would first travel through
the root zone of the whips and then through the root zone of the 5 gallon buckets. A control area
with monitoring wells was placed to the north and west of the whips, and another in between the
whips and the five gallon buckets, along with monitoring wells throughout the treatment site.
These control areas enable data to be collected on the amount of contaminant that enters each of
the treatment areas (whips and five gallon buckets), so that a comparison of the performance of
each type of tree can be made. Figure 6 contains the basic layout of this site.
One unique aspect of Carswell is that there is already a mature cottonwood growing on
the site. This 70 foot tall tree is located just south and east of the planting area on the other side
of a cart path. Groundwater monitoring wells were installed around this tree, and it will be
sampled in a similar manner to the planted cottonwoods to see how well a mature tree functions
in this phytoremediation system. Data from the first three groundwater samplings that have
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Phytoremediation of TCE using Populus
taken place indicate that the wells near the mature tree have lower concentrations of TCE. This
observation is promising because it may be indicating that the older tree is treating the TCE in
the groundwater at a higher rate than the younger trees. However, these observations are only
speculative at this time.
3.3.2 Costs
Some rough estimates of cost for the Carswell site were provided by Mr. Greg Harvey.
These estimates can be found in Table 19. Since this site involves an innovative treatment
technology, these costs are substantially inflated due to the heavy monitoring taking place at the
site. Also, there are no long term projected costs available or total costs for-the project available
because the time involved in remediating the site is uncertain. In addition to the costs in Table
19, $200,000 will be spent for extensive site monitoring that would not normally be associated
with a phytoremediation system, so this amount was not included in the cost estimates.
Table 19: Rough Estimate Costs of Phytoremediation at Carswell Air Force Base
Activity
Estimated Cost
Wholesale cost of trees (does not include delivery or
installation costs)
$8/tree for five-gallon bucket tree
$0.20/tree for whips
29 wells (including surveying, drilling, and testing)
$200,000
Subsurface fine biomass
$60,000
Source: Greg Harvey (personal communication)
3.3.3 Performance to Date
Evapotranspiration rates at Carswell for May 13 and 15 and June 10, 11, and 12 of 1997
have been determined. Unfortunately, no quantitative evapotranspiration data was available to
include in this report. Qualitatively, both types of trees were capable of evapotranspiring TCE,
and the 5-gallon trees are evapotranspiring more water than the whips. This was to be expected
because of the greater total surface area of the 5-gallon trees' leaves. In addition, the
transpiration rates were generally higher in June than May, which is likely due to a combination
of warmer weather and more fully developed leaves. There also appeared to be a midday decline
in transpiration during June, indicating that the plants were experiencing water stress during the
hottest part of the day in the summer months. In other words, the water demand for the tree
exceeded the supply during that time. There was also a notable difference in transpiration rates
between days in June, with cloudier days resulting in lower transpiration rates. In addition to
evapotranspiration information, some tree growth data has also been collected. In 16 months the
whips have grown about 20 feet, and the 5 gallon bucket trees have grown faster than the whips.
Groundwater samples were collected from the 29 monitoring wells and analyzed on three
occasions to date. Concentrations of TCE, cis-DCE, and trans-DCE, and vinyl chloride were
determined from these samples. They ranged from 2 to 930 ug/L TCE in the groundwater, with
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Jonathan Chappell
Phytoremediation of TCE using Populus
most samples falling in the 500-600 ug/L range. Average concentrations of the contaminants on
the three sampling dates are provided in Table 20, with the exception of vinyl chloride. Vinyl
chloride was only detectable in a handful of samples and generally in low levels, so an average
concentration was not determined.
Table 20: Average Concentrations of TCE, cis-DCE, and trans-DCE at Carswell
Contaminant
Average Concentration (ug/L)
December 1996
May 1997
July 1997
TCE
610
570
550
cis-DCE
130
140
170
trans-DCE
4
2
4
Source: Steve Rock (unpublished data)
Some analytical work has been done on the tree tissues at the site, but this type of
information is still in the early stages of collection. Data from November of 1996 indicated a
TCE signature in the whips that were planted over an area where the groundwater was the
shallowest. This indicates that the young trees were capable of evapotranspirating TCE after just
one growing season. Now that the trees have been on site for more than an entire growing
season, site managers at Carswell plan to increase monitoring at the site to include a whole suite
of water, soil, air, and tree tissue sample analysis. Some of the more unique data they plan to
collect (in relation to the other case study sites) are analyses of microbial populations and assays
of TCE degrading enzymes in the trees.
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Phytoremediation of TCE using Populus
4. The Future of Phytoremediation
The use of phytoremediation will most likely increase in the near future. As an example,
Table 21 provides an analysis of the phytoremediation market for organics in groundwater
through the year 2005. Assuming these predictions are accurate, phytoremediation will likely
grow into a substantial market over the next decade. Of course, the results of the three case
studies and other similar studies currently being designed and implemented may have an effect
on these predictions.
Table 21: Estimated U.S. Phytoremediation Market Share for Organics in Groundwater
Market
Cost in Millions of Dollars
1997
2000
2005
Total Segment
2,600
2,600
2,600
Phytoremediation
2-3
6-12
20-45
Source: Glass (1997)
4.1 Future research
Table 22 outlines some of the research needs that the Remediation Technology
Development Forum (RTDF) for Phytoremediation of Organics believes are needed in the near
future. Because phytoremediation is such a new technology, most of the needs outlined in this
list are still at a fundamental level. For example, very little is known about the mass balance of
fates for many pollutants within plants and the degree that the rhizosphere can increase
degradation.
Table 22: Basic Research Needs for Phytoremediation
• More basic data is needed on the phytoremediation process
-Validation of rhizosphere effects
-Determine the fate of a contaminant in phytoremediation systems
-Determine factors that affect mass balance, such as species, climate, soils, etc.
• Determine acceptable endpoints for phytoremediation
Selecting a contaminant and site that will effectively convince regulators that phytoremediation is a
valid technology ,
Source - Adapted from RTDF Phytoremediation Action Team Meeting, April 30, 1997
Once many of the basic questions have been answered, research will need to focus on
optimization of phytoremediation for different clean-up situations and goals. This can be
accomplished through a number of mechanisms, from complex studies such as genetic
engineering to simply finding better ways to choose native plants. One way to accomplish this
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Jonathan Chappell
Phytoremediation of TCE using Populus
is to choose native plants that produce high concentrations of enzymes that are known to degrade
a site's contaminants of concern. Table 1 of Appendix C outlines some of the enzymes known to
work in phytoremediation systems and some of the plants that contain these enzymes.
Researchers need to screen more plants for these and other enzymes potentially useful to
phytoremediation (Appendix C Table 2) in order to create a catalogue of plants.
Today, trees such as poplars are commonly used in phytoremediation schemes because
they can grow in a wide variety of climates and they are known to have high evapotranspiration
rates. However, there may be plants that are better than poplars at degrading specific pollutants.
For example, cypress trees and rice plants were found to contain much higher concentrations of
dehalogenase than poplars, so in theory they are better equipped to degrade TCE than a poplar
tree (Laura Carreira, personal communication). In addition, there may be certain trees native to
an area that would be much heartier under local conditions and more resistant to local pathogens
and parasites, so it is often beneficial to chose a native plant when designing a phytoremediation
scheme (Greg Harvey, personal communication). Choosing native species and screening them
for their ability to metabolize specific contaminants may be the key to optimizing
phytoremediation in the future.
Currently, there is speculation as to how well phytoremediation works and under what
conditions it will be useful. Many of these questions will be answered, at least in part, by pilot
scale projects such as Aberdeen, Carswell, and Edward Sears, as well as the numerous other
types of phytoremediation projects underway around the country (Appendix B). Early results
from these current sites are promising, so it appears that phytoremediation will be an effective
tool for cleaning hazardous waste in the future.
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Jonathan Chappell
Phytoremediation of TCE using Populus
Figure 1 - Image of Leaves from Parent Poplar Species (Populus tricocarpa and Populus
deltoides) and Hybrid Offspring*
Source: ORNL (1996)
~For clearer, color images, this report is also available electronically at http://clu-in.com/phytoTCE.htm
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Jonathan Chappel!
Phytoremediation of TCE using Populus
Figure 2 - J Fields Phytoremediation Tree Planting Area Map, Aberdeen Proving
Grounds -Edgewood, MD
"r"~T~ ,
11 \ \ \ \ \
I 1 Q ft 7 9
\ \ \ 1
12^ N \ ,
\ i \
V
\
D
\
V
\*
*1
9
i
i
A,
¦ •.v
V-
8
\
v. v *--i e • ' 't 1 ~ '
* /•- * / . • • /" T • ! / *
S7>" :A—''
*
Source: Tobia and Compton (1997)
Legend:
Toxic Pit
L'.j Tree Planting Area
• Hybrid Poplar Tree
Sweet Gum Tree
V- Monitor Well
—5— Contour Interval
Road
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Jonathan Chappeli
phyi°remediation of TCE using Populus
Figure 3 - Edward Sears Property Tree Planting Layout
Source: Roy F.Weston (1997)
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Jonathan Chappell
Phytoremediation of TCE using Populus
Figure 4 - Photograph of Hybrid Poplar Field at Edward Sears Property
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Jonathan Chappell
Phytoremediation of TCE using Populus
Figure 5 - Photograph of Hybrid Poplar Tree at Edward Sears Property
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Jonthan Chappell
Phytoremediation of TCE using Populus
Figure 6 - Air Force Plant 4 Phytoremediation Site Layout, Carswell Air Force Base - Ft.
Worth, TX
Roaring
Springs
Road
Legend
• Monitoring WeH
fjjgj Monitoring well
with Recorder
¦ Nested Wells
A. Piezometer
200
Scale In Feet
Source: EPA/540/R-97/502
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Jonathan Chappell
Phytoremediation of TCE using Populus
Appendix A - Companies Specializing in Phytoremediation Technologies
Company Name
Types of Treatment
Contact
Applied Natural Sciences,
Inc.
Dayton, OH
Treemediation, hybrid poplars and grasses
used to treat contaminants such as chlorinated
solvents and zinc
Edward Gatliff,
President
BEAK
Guelph, ON office
Tree buffers to contain arsenic in groundwater,
PAHs and PCBs using grasses, legumes, and
trees, phyto as a polishing step in treatment
Bob Tossell
Ecolotree
Iowa City, IO
Ecolotree Cap (vegetative cap), Ecolotree
Buffers - poplars and grasses used as a
hydraulic barrier
Louis-Licht,
President
D. Glass Associates, Inc.
Needham, MA
Phyto- and Bioremediation market analyzation
and technology transfer
David Glass
Phytotech
Monmouth Junction, NJ
Metals, radionuclides
Burt Ensley,
President
Phytokinetics
North Logan, UT
plants such as poplars and alfalfa used to
contain petroleum hydrocarbon plumes,
tolulene spills, and excess nitrate and ammonia
in groundwater
Ari Ferro,
President
PhytoWorks
Athens, GA
Phytoremediation of mercury, plant enzyme
antibodies, phytoremediation of organics
George E. Boyajian,
Principle, Science
and Technology
Thomas Consulting
Cincinnati, OH
Poplar projects
Paul Thomas
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Jonathan Chappell
Phytoremediation of TCE using Populus
Appendix B - Some Representative Examples of Phytoremediation Projects
Name and Location
Party Conducting
Treatment
Type of
Contaminant
Type of Treatment
Aberdeen Proving
Grounds
Aberdeen, Maryland
DOD, EPA ERT
TCE in groundwater
Poplars used to contain the
movement of the plume
Carswell Air Force
Base
Ft. Worth, TX*
DOD, EPA
TCE in groundwater
Cottonwoods to contain the
movement of the plume
Chernobyl Nuclear
Power Plant
Chernobyl, Ukraine
and a DOE site in
Ashtabula, OH
Phytotech, Inc
Radionuclides
Rhizofiltration in a continuous
flow system
Chevron
Ogden, UT*
Phytokinetics, Inc.,
EPA (monitoring)
Petroleum
hydrocarbons
Poplars used to contain the
movement of the contaminant
plume
Edward Sears
New Gretna, NJ
EPA ERT
Solvents in
groundwater
Poplars used to contain the
movement of the contaminant
plume
Lakeside Landfill
Beaverton, Oregon
Ecolotree
Landfill cap
Poplar tree cap used to prevent
landfill from leaching
Metal plating facility in
Findlay, OH*
Phytotech, Inc.
Metals in soils (lead,
chromium, nickel,
zinc, and cadmium)
Plants used to extract metals from
soils.
Milan Army
Ammunition Plant
Tennessee
DOD
Explosives in
groundwater (TNT,
RDX, HMX, DNT)
Constructed wetland containing
nitrogen reducing species of
plants
* SITE demonstration project
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Jonathan Chappell
Phytoremediation of TCE using Populus
Appendix C: Phytoremediation Enzymes
Table 1: Some Enzymes Found to be Involved in Phytoremediation
Enzyme
Pollutant Degraded
Some Plants Known to Produce
Enzyme
Dehalogenases1'2
chlorinated solvents, ethylene
containing compounds
Populus sp. (Hybrid poplars),
Myriophyllium spicatum (parrot
feather), Algae Nitella (stonewort),
Algae spirogyra, Anthrocerotea sp.
Lactase'
oxidative step in munitions
degradation
Algae Nitella (stonewort),
Myriohyllium spicatum (parrot
feather)
Nitroreductase1
munitions (TNT, RDX, etc.)
Populus sp. (Hybrid poplars),
Myriohyllium spicatum (parrot
feather), Lemna minor
(duckweed),Algae Nitella
(stonewort), plus more
Nitrilase3
herbicides
Peroxidases3 4
phenols
Armoracia rusticana (Horseradish)
1 - Schnoor et al. (1995)
2 - Laura Carreira, personal communication
3 - Workshop on Phytoremediation of Organics (1996)
4 - Cunningham et al. (1996)
Table 2: Plant Enzymes Believed Probable for Phytoremediation but Not Tested
Enzyme
Contaminants Potentially Degraded
Phosphatase
organophosphates
Aromic Dehalogenase
chlorinated aromatics (DDT, PCB's, etc.)
o - demethylase
pendimethaline, alachlor, metolachor
Source: PhytoWorks, Inc.
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Phytoremediation of TCE using Populus
Appendix D - Phytoremediation Web Sites
Page Name
Address
Bioresource Engineering - Oregon State University
www.bre.orst.edu
Dr. Ilya Raskin's Laboratory
cook~college.rutgers.edu/~halpem/index.html
Envirobiz - Chevron Grows New Remediation
Technology: Alfalfa and Poplars
www.envirobiz.com/newsdaily/960502e 1 .htm
Environmental Security Technology Certification
Program - Cleanup Projects page
scaffold.walcoff.com/estcp2/projects/cleanup/index.html
Ground-Water Remediation Technologies Analysis
Center: Phytoremediation - Technology Overview
www.gwrtac.org/htm l/tech_over.html#PHYTOREM
HSRC's Phytoremediation page
www.engg.ksu.edu/HSRC/phytorem
Hyperaccumulators and Phytoremediation
bob.soils.wisc.edu/~barak/soilscience326/agres.htm
Phytoremediation at Utah State University
www.usu.edu/~cpl/phytorem.html
Phytotech, Inc.
www.phytotech.com
Poplars and Willows on the World Wide Web
poplar 1 .cfr.washingtion.asedu
The RTDF Phytoremediation of Organics Action
Team
www.rtdf.org/phyto.htm
USDA Economic Research Service - Industrial Uses
of Agricultural Materials page
www.econ.ag.gov/epubs/pdf/IUS6/INDEX.HTM
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Phytoremediation of TCE using Populus
References
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zone of plants from a former solvent disposal site. Environmental Toxicology and Chemistry.
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Briggs, G. G., Bromilow, R.H., Evans, A. A. 1982. Relationships between lipophilicity and root
uptake and translocation of non-ionized chemicals by barley. Pesticide Science. 13: 495-504.
Clement Associates, Inc. 1985. Chemical, Physical, and Biological Properties of Compounds
Present at Hazardous Waste Sites. Prepared for US EPA under contract.
Cunningham, S.D., Anderson, T.A., Schwab, A.P., Hsu, F.C. 1996. Phytoremediation of soils
contaminated with organic pollutants. Advances in Agronomy. 56: 55-114.
Davis, L.C., Banks, M.K., Schwab, A.P., Muralidharan, N., Erickson, L.E.,Tracy, J.C. 1996.
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triazine pesticide in soil-plant systems. Journal of Environmental Engineering. 119(5): 842- 854.
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Bioremediation of Contaminated Soil and Groundwater.
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http://estcp.xservices.com/projects/cleanup/remed/remjp3.htm
Gatliff, E.G. 1994. Vegetative remediation process offers advantages over traditional pump-and-
treat technologies. Remediation. 4(3): 343-352.
Gordon, M., Choe, N., Duffy, J., Ekuan, G., Heilman, P., Muiznieks, I., Newman, L., Raszaj, M.,
Shurtleff, B., Strand, S., Wilmoth, J. 1997. Phytoremediation of trichloroethylene with hybrid
poplars. In: Phytoremediation of Soil and Water Contaminants. American Chemical Society,
Washington, DC.
Jipson, E. 1996. Chevron grows new remediation technology: Alfalfa and poplars. Envirobiz
News and Press Release Archive, http://www.envirobiz.com/newsdaily/960502el .htm.
Meinzer, O.E. 1927. Plants as indicators of ground water. U.S. Geological Survey. Water
supply paper 577.
Miller, R.R. Phytoremediation: Technology Overview Report. Ground Water Remediation
Technologies Analysis Center. 1996.
http://www.gwrtac.0rg/html/tech_over.html#PHYTOREM
Newman, L., Strand, S., Duffy, J., Ekuan, G., Raszaj, M., Shurtleff, B., Wilmoth, J., Heilman,
P., Gordon, M. 1997a. Uptake and biotransformation of trichloroethylene by hybrid poplars.
Environmental Science and Technology. 31:1062-1067.
Newman, L.A., Strand, S.E., Domroes, D., Duffy, J., Ekuan, G., Karscig, G., Muiznieks, I.A.,
Ruszaj, M., Heilman, P., Gordon, M.P. 1997b. Abstract: Removal of trichloroethylene from a
simulated aquifer using poplar. Fourth Annual In Situ an On-Site Bioremediation Symposium.
New Orleans, April 28-May 1, 1997.
Newman, L.A. Bod, C., Cortellucci, R., Domroes, D., Duffy, J., Ekuan, G., Fogel, D., Heilman,
P., Muiznieks, I.A., Newman, T., Ruszaj, M., Strand, S., Gordon, M.P. 1997c. Abstract: Results
from a Pilot Scale Demonstration: Phytoremediation of trichloroethylene and carbon
tetrachloride. 12th Annual Conference on Contaminated Soils. October
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Phytoremediation of TCE using Populus
Poplars and Willows on the World Wide Web. University of Washington.
http://poplarl .cfr.washington.edu/.
Oak Ridge National Laboratory (ORNL). 1996. Energy Efficiency and Renewable Energy
Program: Poplar Breeding Success, http://www.ornl.gov/~vhk/success/poplar.html.
Quinton, G.E. A method to compare groundwater cleanup technologies. Remediation. Fall 1997
(in press).
Remediation Technologies Development Forum (RDTF) - Phytoremediation of Organics Action
Team. 1997 Summary of the RDTF Phytoremediation of Organics Action Team Meeting. New
Orleans, LA. April 30,1997. http://www.rtdf.org/phytosum.htm
Richman, M. 1996. Terrestrial plants tested for cleanup of radionuclides, explosives' residue.
Water Environment and Technology. 8(5): 17-18.
Roy F. Weston, Inc. August 1997. Phytoremediation Test Setup, Edward Sears Site, New
Gretna, NJ. Work Assignment 2-120 - Technical Memorandum.
Roy F. Weston, Inc./REAC. March 1997. Hydrogeological Investigation: Edward Sears Site,
New Gretna, New Jersey. Work Assignment 1-120 - Final Report.
Ryu, S.B., Davis, L.C., Dana, J., Erickson, L.E. 1996. Evaluation of toxicity of
trichloroethylene for plants. HSRC/WERC Joint Conference on the
Environment, May 1996. http://www.engg.ksu.edu/HSRC/96Proceed/ryu.html.
Schnoor, J. L., Licht, L.L., McCutcheon, S.C., Wolfe, N.L. Carreira, L.H. 1995.
Phytoremediation of Organic and Nutrient Contaminants. Environmental Science and
Technology. 29(7): 318-323.
Schnoor, J.L. 1997. Design of phytoremediation at contaminated sites. Groundwater
Remediation and Technologies Analyses Center, Presentations: Advances in Innovative
Groundwater Remediation Technologies. Philadelphia, PA. July 31, 1997
Stomp. A.M., Han, K.H., Wibert, S., Gordon, M.P., and Cunningham, S.D. 1994. Genetic
Strategies for Enhancing Phytoremediation. Annals of the New York Academy of Science. 721:
481-491.
Tobia, R. and Compton H. 1997. Pilot scale use of trees to address VOC contamination in
groundwater and explosives contaminated soil at Aberdeen Proving Ground, MD. IBC's Second
Annual Conference on Phytoremediation. Seattle, WA. June 18-19, 1997.
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Phytoremediation of TCE using Poputus
TR-2. 1976. Carcinogenesis Bioassay of Trichloroethylene (CAS No. 79-01-6).
http://ntp-server.niehs.nih.gov/htdocs/LT-studies/tr002.html
TR-243. 1990. Carcinogenesis Studies of Trichloroethylene (Without Epichlorohydrin) (CAS
No. 79-01-6) in F344/N Rats and B6C3F1 Mice (Gavage Studies).
http://ntp-server.niehs.nih.gov/htdocs/LT-studies/tr243.html
Walton, B.T., and T.A. Anderson. 1990. Microbial degradation of trichlorethylene in the
rhizosphere: potential application to biological remediation of waste sites. Applied
Environmental Microbiology. 56:1012-1016.
Workshop on Phytoremediation of Organic Contaminants. Forth Worth, TX. December 18-19,
1996. http://clu-in.eom/pubalpha.htm#P
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Phytoremediation of TCE using Populus
Table Index Page
Table 1: Types of Phytoremediation Systems 2
Table 2: Advantages and Limitations of Phytoremediation 3
Table 3: Estimates of Phytoremediation Costs Verses Costs of Established 5
Technologies
Table 4: Ecolotree's and Applied and Natural Science, Inc.'s Cost Estimates 6
of a Poplar Tree Phytoremediation System
Table 5: Physical and Chemical Properties of TCE 8
Table 6: Advantages of Populus sp. in Phytoremediation 1 o
Table 7: Estimates of Evapotranspiration Rates by Hybrid Poplars 11
Table 8: Growth and Water Uptake Potential in Five Growing Seasons in 12
Amana, IA for Poplar Planted at 2,170 Trees/acre Density
Table 9: Mechanisms of TCE Phytoremediation by the Populus sp. 13
Table 10: Some Plant Species Containing Dehalogenase 14
Table 11: Estimated Costs of Treating PCE in the Groundwater 17
Table 12: Case Studies Overview of Sites 19
Table 13: Average Temperature in °F for Geographic Regions of the Case Study Sites 20
Table 14: Average Rainfall in Inches for Geographic Regions of the Case Study Sites 20
Table 15: Contaminants of Concern at Aberdeen Proving Grounds' J Fields 21
Phytoremediation Site
Table 16: Monitoring Approaches at the J Field Site 22
Table 17: Concentrations of TCE Sampled from Groundwater in 25
Monitoring Well 1 on Edward Sears Property.
Table 18: Concentrations of TCE in Soil Samples During Monitoring Well 26
Installation of Monitoring Well 1 at Edward Sears Property
Table 19: Rough Estimates Costs of Phytoremediation at Carswell Air Force Base 29
Table 20: Average Concentrations of TCE, cis-DCE, and trans-DCE at Carswell 30
Table 21: Estimated U.S. Phytoremediation Market Share for Organics in Groundwater 31
Table 22: Basic Research Needs for Phytoremediation 3 \
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