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PDHonline Course C529 (3 PDH)

Phytoremediation: Selecting and UsingPhytoremediation for Site Cleanup

2012

Instructor: Dennis G. Shin, PE

PDH Online | PDH Center5272 Meadow Estates Drive

Fairfax, VA 22030-6658Phone & Fax: 703-988-0088

www.PDHonline.orgwww.PDHcenter.com

An Approved Continuing Education Provider

http://www.PDHonline.org

http://www.PDHcenter.com

EPA

United StatesEnvironmental ProtectionAgency

Office of Solid Waste and Emergency Response (5102G)

EPA 542-R-01-006July 2001www.brownfieldstsc.orgwww.epa.gov/TIO

Brownfields Technology Primer:Selecting and Using Phytoremediationfor Site Cleanup

Brownfields Technology Primer: Selecting and Using Phytoremediation

for Site Cleanup

U.S. Environmental Protection AgencyOffice of Solid Waste and Emergency Response

Technology Innovation OfficeWashington, DC 20460

BROWNFIELDS TECHNOLOGY PRIMER:SELECTING AND USING PHYTOREMEDIATION FOR SITE CLEANUP

Notice

This document has been funded by the United States Environmental Protection Agency (EPA)under Contracts 68-W-99-003 and 68-W-99-020 to Tetra Tech EM Inc. The document wassubjected to the Agency’s administrative and expert review and was approved for publication asan EPA document. Mention of trade names or commercial products does not constituteendorsement or recommendation for use.


Acknowledgments

The Technology Innovation Office would like to acknowledge and thank the individuals whoreviewed and provided comments on draft documents, and provided current information on theapplication of phytoremediation at various sites across the country.


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CONTENTS

Section Page

1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2.0 WHAT IS PHYTOREMEDIATION? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.1 Types of Sites and Contaminants Treated by Phytoremediation . . . . . . . . . . . . . . . . . . . 52.2 Plants Species Used for Phytoremediation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3 Phytoremediation Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.0 APPLICATION OF PHYTOREMEDIATION FOR THE CLEANUP OF SOIL, SEDIMENT, SURFACE WATER, AND GROUNDWATER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.1 Advantages to the Selection of Phytoremediation at Brownfields Sites . . . . . . . . . . . . . . 93.2 Related Uses of Plants at Brownfields Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.3 Discussions with Regulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.4 Community Involvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.0 PRACTICAL CONSIDERATIONS AND LIMITATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.0 SELECTION AND DESIGN OF A PHYTOREMEDIATION SYSTEM . . . . . . . . . . . . . . . . . . . . . 145.1 Technical Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145.2 Strategies for Contaminant Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165.3 Innovative Technology Treatment Trains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165.4 Design Team . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6.0 OPERATION AND MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186.1 Operation and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186.2 Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186.3 Performance Evaluation and Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

7.0 COST OF PHYTOREMEDIATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207.1 Cost Savings Based on Actual Cost Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207.2 Sample Phytoremediation Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

8.0 SUPPORTING RESOURCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Tables

1 Selected Phytoremediation Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Types of Plants, Contaminants, and Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Estimated Cost Savings Through the Use of Phytoremediation Rather Than

Conventional Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 References by Topic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Appendices

1 LIST OF ACRONYMS AND GLOSSARY OF KEY TERMS2 THE PROCESSES OF PHYTOREMEDIATION3 PHYTOREMEDIATION DECISION TREE MODELS


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Brownfields Technology Support Center

EPA recently established theBrownfields Technology Support Centerto ensure that brownfields decisionmakers are aware of the full range oftechnologies available for conductingsite assessments and cleanup, and canmake informed decisions about theirsites. The center can help decisionmakers evaluate strategies tostreamline the site assessment andcleanup process, identify and reviewinformation about complex technologyoptions, evaluate contractor capabilitiesand recommendations, explain complextechnologies to communities, and plantechnology demonstrations. The centeris coordinated through EPA’s TIO andworks through the laboratories of EPA’sOffice of Research and Development. Localities can submit requests forassistance directly through their EPARegional Brownfields Coordinators;online at <http://brownfieldstsc.org>; orby calling 1-877-838-7220 (toll free). For more information about theprogram, the point of contact is DanPowell of EPA TIO at 703-603-7196 or<[email protected]>.

1.0 INTRODUCTION

1.1 Purpose

The Brownfields Technology Support Center(BTSC) (see box) has developed thisdocument to provide an educational tool forsite owners, project managers, and regulatorsto help evaluate the applicability of thephytoremediation process at brownfields sites. Cleanup technologies that reduce costs,decrease time frames, or positively affectother decision considerations (for example,community acceptance) can have a significanteffect on the redevelopment potential ofbrownfields sites. Increased attention tobrownfields sites and the manner in whichthey are redeveloped places greaterimportance on the selection of cleanuptechnologies.

Phytoremediation represents a group of innovative technologies that use plants andnatural processes to remediate or stabilizehazardous wastes in soil, sediments,surface water, or groundwater. Because itis based on natural processes,phytoremediation may be easily adaptableto many redevelopment plans forbrownfields sites. Phytoremediation isbeing evaluated at a variety of sites and onmyriad contaminants to determine theconditions under which phytoremediationsystems are effective in reducingcontamination. The primer presents someof the advantages and technical limitationsof phytoremediation that the evaluationsindicate. The primer illustrates thepotential of phytoremediation to serve as:

� An interim approach for stabilizing siteswhile other cleanup strategies are beingevaluated

� An approach that augments the overalleffectiveness of other cleanuptechnologies

� A stand-alone approach for providingcost-effective, long-term cleanupsolutions

The primer also illustrates the potentiallimitations of phytoremediation and how suchfactors as levels of contaminants andproperties of the soil, as well as concernsabout potential risk of exposure may affect theuse of phytoremediation at brownfields sites. Because phytoremediation is more thansimply planting vegetation, brownfieldsdecision makers must: (1) select the correctplants, (2) work effectively with regulators andthe local community, (3) understandmaintenance and monitoring requirements,and (4) compare the costs ofphytoremediation with the costs of othertechnology options.

Until phytoremediation is a more proven andestablished technology, advocates for its usemay find it necessary to demonstrate itspotential applicability and efficacy on a site-specific basis. To do so may require an up-


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front commitment of time and resources todemonstrate that the performance ofphytoremediation is comparable to theperformance of traditionally acceptedtechnology options. Such an investment ultimately could save site owners significantamounts of money when they clean up theirproperties for redevelopment.

1.2 Background

The U.S. Environmental Protection Agency(EPA) has defined brownfields sites as“abandoned, idled or under-used industrialand commercial facilities where expansion orredevelopment is complicated by real orperceived environmental contamination.” Numerous technology options are available toassist those involved in the cleanup ofbrownfields sites. EPA’s TechnologyInnovation Office (TIO) encourages the use ofinnovative, cost-effective technologies tocharacterize and clean up contaminated sites. An innovative technology is a technology thathas been field-tested and applied to ahazardous waste problem at a site, but thatlacks a long history of full-scale use. Although readily available information aboutits cost and how well it works may beinsufficient to encourage use under a widevariety of operating conditions, an innovativetechnology has the potential to significantlyreduce the cost and time required toredevelop brownfields sites.

Historically, fear of contamination and itsassociated liability has hamperedredevelopment of brownfields sites. Phytoremediation offers a unique advantageover other remediation technologies. Itprovides ecosystem restoration and “greenareas” that may be desired by the localcommunity.

The process of redeveloping brownfields sitesprovides an excellent framework for usinginnovative technologies because: (1) stateand federal regulators tend to be flexible inapproving cleanup plans for brownfields sites,particularly those sites for which voluntarycleanup plans have been submitted; (2) mostof the current brownfields sites are not

encumbered by a history of litigation orenforcement actions for which traditionaltechnologies already may have beenspecified; and (3) redevelopment plans havebeen prepared for many brownfields sites andare used to establish site-specific cleanuptargets and the time frames for cleanup – thatinformation provides an excellent basis fortailoring innovative approaches to theinvestigation and cleanup of individual sites.

1.3 Approach

This primer will assist brownfields decisionmakers in considering phytoremediation as aninnovative treatment technology option forcleanup at brownfields sites. The documentdiscusses the factors important in theselection of phytoremediation, such asregional climate and local growing conditions,location and type of contaminants to betreated, and site-specific redevelopmentobjectives. The primer illustrates how thosefactors can be potential advantages (orlimitations) in the selection ofphytoremediation at a brownfields site;presents examples that illustrate the fieldapplications of phytoremediation atbrownfields sites; and identifies additionalresources to assist brownfields decisionmakers in evaluating phytoremediation as anoption for their sites.

In addition, this document provides thefollowing information in appendices:

� A list of acronyms

� A glossary that explains technicalterms related to phytoremediation

� A description of the processes ofphytoremediation;

� Decision tree diagrams developed by thePhytoremediation Work Group of theInterstate Technology and RegulatoryCooperation Work Group. The decisiontree diagrams provides guidelines fordetermining the applicability ofphytoremediation at a brownfields siteafter site characterization has beencompleted.


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This primer is not an authoritative or originalsource of research on phytoremediation. Instead, it is intended to briefly describe thephytoremediation process and its potentialapplicability in a brownfields setting in a toneappropriate for audiences who have only alimited technical background.

It is important to note that this primer cannotbe used as the sole basis for determining thistechnology’s applicability to a specific site. That decision is based on many factors andmust be made on a case-by-case basis. Technology expertise must be applied andtreatability studies conducted to support afinal remedy decision. For a more technicaland thorough treatment of the topic and ofissues described in this primer, consult EPA’sIntroduction to Phytoremediation (EPA/600/R-99/107, February 2000). Ordering informationis provided in the Supporting Resourcessection of this primer.


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Figure 1: Examples of Mechanisms Involved in Phytoremediation

Accumulation in rootstranslocated to shootsand leaves

Physical Effects -Transpiration of volatilesand hydraulic control ofdissolved plume

Phytodegradation - The breakdown of contaminants taken up bythe plant through metabolic processes within the plant, or thebreakdown of contaminants external to the plant through theeffect of compounds (such as enzymes) produced by the plant

Enhancedrhizosphere

biodegradation

Successful Reduction of Lead ContaminationPhytoextraction was demonstrated at a site inTrenton New Jersey that had been used for themanufacture of lead acid batteries. Phytoextractionusing Indian mustard (Brassica juncea) andethylenediaminetetraacetic acid (EDTA) soilamendment reduced the average surface leadconcentration by 13 percent in one growing season.The target soil concentration of 400 milligrams perkilogram (mg/kg) was achieved in approximately 72percent of a 4,500 square-foot area. (Some of thereduction may be attributed to dilution as a result oftilling and spreading contaminants deeper into thesoil column.) For more information, contact LarryD’Andrea of EPA at (202) 673-4314 orD’Andrea.Larry @epa.gov.

2.0 WHAT IS PHYTOREMEDIATION?

Phytoremediation is the directuse of living green plants for insitu (in-place or on-site) riskreduction for contaminated soil,sludges, sediments, andgroundwater, through removal,degradation, or containment ofthe contaminant (synonyms: green remediation and botano-remediation). Figure 1illustrates the mechanismsinvolved in thephytoremediation process.

Phytoremediation warrantsconsideration for cleaning upbrownfields sites at which thereare relatively lowconcentrations of contaminants(that is, organics, nutrients, ormetals) over a large cleanup area and atshallow depths. Another potential applicationfor phytoremediation is at sites that currentlyare “mothballed” and may be redeveloped inthe future. Phytoremediation can be a cost-effective alternative approach for reducingthe leaching of contaminatnts through soil orgroundwater, reducing the run-off ofcontaminated stormwater, beginning an initiallevel of cleanup, and improving the aestheticcondition of a site. Phytoremediationwarrants consideration for use in conjunctionwith other technologies when theredevelopment and land use plans for thesite include the use of vegetation.

Phytoremediation is distinct from MonitoredNatural Attenuation (MNA), that is, acontrolled and monitored site cleanupapproach that relies on natural attenuationprocesses to achieve remediation objectiveswithin time frames that are reasonablevis-à-vis more active methods. Though bothprocesses involve some similar elementssuch as biodegradation, sorption,volatilization, stabilization, phytoremediationtechnologies represent active processes thatare designed and implemented to control andeliminate contamination. MNA and

phytoremediation also are similar in that bothmight be considered significant componentsof a treatment-train approach to hazardouswaste cleanup at brownfield sites. For moreinformation on EPA's directives regarding the the use of MNA refer to <http://www.epa.gov/superfund/resources/gwdocs/monit.htm>.


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2.1 Types of Sites and ContaminantsTreated by Phytoremediation

There is potential to use phytoremediationbeneficially under a wide variety of siteconditions. Types of sites at whichphytoremediation has been applied orevaluated include: pipelines; industrial andmunicipal landfills; agricultural fields; woodtreating sites; military bases; fuel storagetank farms; gas stations; army ammunitionplants; sewage treatment plants; and miningsites.

Phytoremediation is being tested andevaluated for its effectiveness in containingand treating a wide array of contaminantsfound at brownfields sites. While much moretesting is needed, current results indicate thatplants have the potential to enhanceremediation of the following types ofcontaminants:

� Petroleum hydrocarbons� Benzene, toluene, ethylbenzene, and

xylene (BTEX)� Polycyclic aromatic hydrocarbons (PAH)� Polychlorinated biphenyls (PCB)� Trichloroethene (TCE) and other

chlorinated solvents� Ammunition wastes and explosives� Heavy metals� Pesticide waste� Radionuclides� Nutrient wastes (such as phosphates and

nitrates)

One of the more optimal applications ofphytoremediation is as a containmenttechnology. Since many brownfields sitesare characterized by wide-spreadcontamination at low concentrations that areclose to target cleanup levels,phytoremediation is a good containmentalternative if geology and rainfall amounts arefavorable.

Table 1 lists types of sites at whichphytoremediation has been employed withsome level of success in cleaning up thesites. The table provides only a

representative sample of sites andcontaminants.

2.2 Plants Species Used forPhytoremediation

Plants species are selected for use accordingto their ability to treat the contaminants ofconcern and achieve the remedial objectivesfor redevelopment (for example, time frameand risk management), and for theiradaptability to other site-specific factors suchas adaptation to local climates, depth of theplant’s root structure, and the ability of thespecies to flourish in the type of soil present. Often the preferred vegetation characteristics include: an ability to extract or degrade thecontaminants of concern to nontoxic or lesstoxic products, fast growth rate, adaptabilityto local conditions, ease of planting andmaintenance, and the uptake of largequantitities of water by evapotranspiration(see the glossary of terms in Appendix 1 fordefinitions of technical terms). The selectionand use of plant species must be conductedwith care to prevent the introduction of non-native species into areas where thosespecies are not already present. Plantspecies that are benign under mostcircumstances may become a problem whenintroduced into a new area. For example,water hyacinth is considered a noxiousaquatic weed that should be used only inisolated bodies of water from which there areno risks of unintentional transport (forexample, by flood).

Maintenance requirements should beconsidered when selecting plant species foruse at brownfields sites; those requirementsmay include the frequency with which theplant must be mowed; the need for fertilizer;and the need for replanting, pruning,harvesting, and monitoring programs.


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Table 1Selected Phytoremediation Projects

Contaminant(s)/ Purpose of Project

Media/Mechanism

Plant Species

Location(Scale*)

Point of Contact

Chlorinated solvents/Control groundwatermigration at an urbanbrownfields site andremove TCE andderivatives fromgroundwater

Groundwater/Phytoextraction,phytovolatilization,rhizodegradation

Hybrid poplarand willow

Findlay, OH(Full scale)

Steve Synder, OhioEnvironmental ProtectionAgency (OEPA) (419) 352-8461Ed Gatliff, Applied NaturalSciences, Inc. (ANS)(513) 942-6061

Chlorinated solvents/Biologically (pumpand treat)contaminatedgroundwater

Soil/Rhizodegradation,phytovolatilization

Hybrid poplar,white willow,native species

SolventsRecoverySystems of NewEngland,Southington, CT(Full scale)

Steve Rock, U.S. EPA(513) 569-7149Ari Ferro, Phytokinetics(801) 750-0950

Chlorinated solvents/Control groundwatermigration and removesolvents fromgroundwater

Groundwater/Phytovolatilization,rhizospherebiodegradation,phytodegradation

Easterncottonwood

Carswell AFB, TX(Pilot)

Steve Hitt, U.S. EPA(214) 665-6736Greg Harvey, USAF(937) 255-7716

Heavy metals/Reduce leadconcentration in soil

Phytoextraction Indianmustard

Trenton, NJBrownfields Site(Pilot)

Larry D'Andrea, U.S. EPA(212) 637-4314Dr. Michael Blaylock,Edenspace (703) 961-8700

BTEX compounds/Treat petroleum andorganic contaminants;prevent contaminatedgroundwater frommigrating

Soil andgroundwater/Hydraulic control,phytoextraction,phytovolatilization,rhizodegradation

Hybrid poplar AshlandChemical Co,Milwaukee, WI(Full scale)

Scott Ferguson, WisconsinDepartment of NaturalResources (WDNR)(414) 263-8685Dr. Louis Licht, Ecolotree(319) 358-9753

PAH’s/Controlgroundwater andsurface watermigration, stabilizesoil, and degradecontaminants

Soil andgroundwater/Hydraulic control,rhizodegradation

Grasses,hybrid poplar

Oneida, TN (Fullscale)

Dr. John Novak, VA Tech(540) 231-6132Dr. Louis Licht, Ecolotree(319) 358-9753

Explosives andfertilizers/Contain and treattoxic solvents

Soil andgroundwater/Phytodegradation,phytovolatilization

Hybrid poplar AberdeenProving Ground,MD (Pilot)

Harry Compton, U.S. EPA(732) 321-6751Steve Hirsh, U.S. EPA(215) 814-3352

Wood preservatives/Treat PAHs andDNAPLs

Soil andgroundwater/Rhizodegradation,hydraulic control

Herbaceousspecies andhybrid poplar

Laramie, WY(Full scale)

Marisa Latady, WyomingDepartment of EnvironmentalQuality, (307) 777-7752Jennifer Uhland, CH2M Hill(303) 771-0900

Source: Various research documents, internet web sites, and discussions with points of contact.Notes:* Full scale = Phytoremediation is part of the final remedy for site cleanup

Pilot scale = Phytoremediation is being evaluated as a potential treatment technology for the site.


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Phytoremediation Selected for RCRA Corrective Action

An Ashland Chemical Company tank farm inMilwaukee, Wisconsin shows the potential for theuse of phytoremediation at active industrial sites, aswell as the adaptability of the technology forbrownfields sites. Under the Resource Conservationand Recovery Act (RCRA), the facility was requiredto remediate contamination with petroleum productsand organic solvents that resulted from years of fueland solvent handling at the facility. Hybrid poplartrees have been arrayed to prevent contaminatedgroundwater from discharging into an adjacent riverwhile remediating concentrations of contaminants insoil and groundwater. An extensive monitoringprogram, consisting of several monitoring wellstransects and frequent groundwater and soilsampling, assesses the project’s impact ongroundwater migration, concentrations ofcontaminants, and growth conditions for the trees. Despite that rigorous program, the project wasconsiderably less expensive than excavating andlandfilling contaminated soil and pumping andtreating contaminated groundwater. For moreinformation, contact Scott Ferguson of theWisconsin Department of Natural Resources at(414) 263-8685.

Several types of plants and sample speciesfrequently used for phytoremediation arelisted below:

� Hybrid poplars, willow, and cottonwoodtrees

� Grasses (rye, Bermuda grass, sorghum,and fescue)

� Legumes (clover, alfalfa, and cowpeas)� Aquatic and wetland plants (water

hyacinth, reed, bullrush, and parrotfeather)

� Hyperaccumulators for metals (such asalpine pennycress for zinc or alyssum fornickel)

Herbaceous species, such as mustard,alfalfa, and grasses, can be used in theremediation of contaminants in surface soil. Hybrid poplars, willows, cottonwood, andother woody species that have rapid growthrates, deep roots, and high transpiration rates(resulting in uptake of abundant quantities ofwater), can be in the remediation ofcontaminants in groundwater or can be usedto provide hydraulic control.

Constructed wetlands also are being used toremediate contaminated sites. There are twobroad categories of wetland plants --emergent and submerged species. Emergent plants, those rooted in shallowwater with most of the plant exposed abovethe water’s surface, transpire water and canbe easier to harvest, if necessary. Submerged species, which lie entirelybeneath the water’s surface, do not transpirewater but provide more biomass (increasedvegetative growth and density) for the uptakeand sorption of contaminants. (See theglossary). Plant species that have arelatively high biomass generally improve theoverall effectiveness of phytoremediation. (See the Selection and Design of aPhytoremediation System section of thisprimer for a more detailed discussion of therole biomass plays in phytoremediation).

2.3 Phytoremediation Processes

Phytoremediation is the broad term for theuse of plant systems to remediatecontamination. Phytoremediation can beclassified further on the basis of the physicaland biological processes involved. Thoseprocesses include:

Hydraulic control: The use of plants torapidly uptake large volumes of water tocontain or control the migration of subsurfacewater (synonym: phytohydraulics).

Phytodegradation: The breakdown ofcontaminants taken up by the plant throughmetabolic processes within the plant, or thebreakdown of contaminants external to theplant through the effect of compounds (suchas enzymes) produced by the plant(synonym: phytotransformation).

Phytoextraction: The uptake of acontaminant by plant roots and thetranslocation of that contaminant into theaboveground portion of the plants; thecontaminant generally is removed byharvesting the plants. This technology isapplied most often to soil or watercontaminated with metals.


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Phytostabilization: The immobilization of acontaminant through absorption andaccumulation by roots, adsorption onto roots,or precipitation within the root zone of plants.

Phytovolatilization: The uptake andtranspiration of a contaminant by a plant, withrelease of the contaminant or a modified formof the contaminant to the atmosphere fromthe plant.

Rhizodegradation: The breakdown of acontaminant in soil through microbial activitythat is enhanced by the presence of the rootzone (synonyms: plant-assisted degradation,plant-assisted bioremediation, plant-aided insitu biodegradation, and enhancedrhizosphere biodegradation).

Rhizofiltration: The adsorption orprecipitation onto plant roots or theabsorption into the roots of contaminants thatare in solution in the root zone.

Appendix 2 to this document provides a briefexplanation of the mechanisms ofphytoremediation. For more technicalinformation about the various processes ofphytoremediation, refer to EPA’s Introductionto Phytoremediation (EPA/600/R-99/107,February 2000). Table 2 shows the types ofcontaminants and media that can be treatedby commonly used plants. The table alsoincludes the type(s) of phytoremediationprocess that occur in each situationidentified.

Table 2Types of Plants, Contaminants, and Media

Type ofContaminant Medium

Type of Plant

Alf

alfa

Aly

ssum

Bal

d cy

pres

s

Bla

ck lo

cust

Cot

tonw

ood

Gra

sses

Hyb

rid

popl

ars

Indi

an m

usta

rd

Pen

nycr

ess

Red

Mul

berr

y

Sto

new

ort

Sun

flow

er

Wat

er h

yaci

nth

Wil

low

Organic Soil �PDRD

�RD

�PDRD

�RD

�PD

�PDRD

Sediment �PDRD

�RD

�PDRD

�RD

�PD

�PDRD

Groundwater �PD

�HC

�HCPD

�PD

�HCPD

Inorganic Soil �PV

�PE

�PV

�PS

�PEPSPV

�PEPSPV

�PE

�PE

Sediment �PV

�PE

�PV

�PS

�PEPSPV

�PEPSPV

�PE

�PE

Groundwater �HC

�HC

�RF

�RF

�RF

�HC

x Plant is effective for the type ofcontamination and medium shown.

HC Hydraulic controlPD PhytodegradationPE Phytoextraction

PS PhytostabilizationPV PhytovolatilizationRD RhizodegradationRF Rhizofiltration


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3.0 APPLICATION OF PHYTOREMEDIATION FOR THE CLEANUP OF SOIL, SEDIMENT, SURFACE WATER, AND GROUNDWATER

Phytoremediation has been attempted on afull- or demonstration-scale basis at morethan 200 sites nationwide. Althoughphytoremediation is a naturally-occurringprocess, discovery of its effectiveness andadvances in its application as an innovativetreatment technology at waste sites, includingbrownfields sites, have been recent. Thetechnology first was tested actively at wastesites in the early 1990s, and use of theapproach has been increasing. As thenumber of successful demonstration projectsgrows and new information about theapplication of phytoremediation becomesavailable, the use of phytoremediation as atreatment technology is increasing becausethe technology has been proven an efficientand effective approach at brownfields sites.

3.1 Advantages to the Selection ofPhytoremediation at BrownfieldsSites

When deciding on the applicability ofphytoremediation at a brownfields site,decision makers should compare thepotential effectiveness and efficiency ofphytoremediation technology with othertreatment technologies that might beappropriate for the site. The comparison

should address any specific needs of andconditions at the site. Several characteristics that are common to brownfields sites should be considered duringthe decision-making process. Thosecharacteristics include the need to enhancethe redevelopment potential and economicvalue of the affected properties; the desire toavoid indirect impacts on the community(such as hauling large quantities of excavatedsoil through neighborhoods); sensitive publicrelations issues; and the fact that, sometimes,the problem at a brownfields site is a“perceived” one, rather than actualcontamination. Some advantagesphytoremediation offers in a brownfieldsredevelopment setting are listed below.

� Potentially treats a wide variety ofcontaminants. Relevance: Brownfieldssites often are made up of a collection offormer manufacturing facilities ormanufacturing processes that have leftbehind a legacy of contaminants. Research has shown that plant speciesused in remediation can potentially treat awide variety of contaminants or families ofcontaminants (for example, treating bothorganics and metals).

� Provides in situ treatment. Relevance: Stakeholders’ concern about potentialhealth risk at brownfields sites can play asignificant role in the selection of atreatment remedy. If a site is located in apopulated area, as is often the case, ornear sensitive receptors, such as schoolchildren or residents, phytoremediationoffers a solution through which soil remainsin place during treatment and is usableafter treatment. Phytoremediation does notrequire excavation of soil, and itsapplication may require only minimummaterials handling. Further,


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Using Poplars to “Pump and Treat” GroundwaterA system consisting of a dense stand of hybrid poplar,white willow, and six native tree species was installed atthe Solvents Recovery Systems of New England(SRSNE) Superfund Site in Southington, Connecticut. The overall objective of the project was to biologically“pump and treat” contaminated groundwater, reducingthe amount and toxicity of contaminated groundwaterthat reaches the traditional mechanical extraction wellsand ultraviolet-oxidation system. Initial greenhousestudies found that the concentration of total volatileorganic compounds (VOC) at the site did not limit thegrowth of the trees. Sap flow measurements reportedas field results indicate that the stand of trees isaccomplishing both its goals, pumping contaminatedgroundwater and removing some pollutants in theprocess. For more information, contact Steve Rock ofEPA at (513) 569-7149 or [email protected].

phytoremediation can have a positiveeffect on the aesthetic character of a site.

� Offers a permanent solution. Relevance: In some cases,phytoremediation can destroy most or allthe pollutants, leaving little or no residualcontamination. Permanent mitigation ofpotential risks can broaden the appeal of asite to a potential developer. In addition,future redevelopment may be encouragedif the developer is not required to placesuch institutional controls as deedrestrictions because there are no residualcontaminants of concern.

� Serves as an interim solution. Relevance: In addition to offering apermanent solution, in some casesphytoremediation can act as a stop-gapmeasure to contain the spread ofcontaminants and begin the treatmentprocess. Although phytoremediation maynot be the selected final technology, thebenefits of a well designed and capablymanaged phytoremediation system may bepreferable to the risks that might be posedshould a brownfields site be left completelyuntreated during preparation of the finalredevelopment plan and selection of a finalremedy.

� Installation and operating andmaintenance costs can be low. Relevance: Phytoremediation systems areinstalled and maintained by traditionalagricultural or landscaping equipment,materials, and practices. Thosetechniques typically are less expensive inup-front and long-term costs thantechnology-intensive alternatives that mayrequire the use of sophisticatedequipment.

� Can be integrated into the naturalenvironment and landscaping plans. Relevance: Phytoremediation can bedesigned to be unobtrusive andaesthetically pleasing in a variety of sitelayout conditions. Wetlands, forests, orgrasslands are examples of natural areas

that can be used in phytoremediationdesign to enhance or restore the physicalappearance of a brownfields site. Othertreatment technologies that may employheavy construction equipment, largepumps or wells, or other equipment (forexample, an incinerator) may have lessvisual appeal and may be objectionable tocertain stakeholder groups.

� Can be an effective element of a unifiedtreatment-train remediation approach. Relevance: From a cost savings andtreatment effectiveness point of view, it isoften advisable to combine, spatially and/orover time, different treatment technologiesinto a unified cleanup strategy. Treatmenttrains are implemented in cases where nosingle technology is capable of treating allof the contaminants in a particular mediumor where one technology might be used torender a medium more easily treatable by asubsequent technology. Phytoremediationis a technology that can provide benefitwhen used in concert with more intensiveand therefore more expensivetechnologies. It thus reduces overallproject costs, while achieving cleanupgoals.


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3.2 Related Uses of Plants atBrownfields Sites

Aside from landscaping applications, plantswith potential use for phytoremediation alsohave other potential applications forprotecting the environment at brownfieldssites. Installing vegetated areas, calledriparian buffers, next to surface waterresources can provide protection from non-point source pollution, while at the same timestabilize the banks of the water bodies andprovide a habitat area for wildlife. Vegetationis often a crucial component in the abatementof soil erosion in riparian zones, as well asany area in which soil erosion could occur ifthe soil is not protected. Hybrid poplars andother trees are being tested as an alternativeto grassy clay caps, which often are used atlandfills to direct rainwater away and helpminimize the volume of leachate from thoselandfills. The mechanism is a similar to thatinvolved in using plants to control sitehydrology. Species of trees, such as hybridpoplars, quickly take up large quantities ofwater and can be used to reduce plumes ofgroundwater.

3.3 Discussions with Regulators

Many regulators have been receptive to theuse of phytoremediation at brownfields sitesbecause of the increasing number of positiveresults demonstrated. However, as in theselection of any innovative treatmenttechnology, it is important to consider site-specific conditions and develop a level ofcertainty that phytoremediation is applicablefor the site. Stakeholders that wish to usephytoremediation should be prepared todemonstrate that the performance of thesystem would compare favorably with that ofother traditional and innovative technologyoptions and that phytoremediation is thepreferred option for the site. In addition,regulatory requirements may vary by state orregion; federal, state, and local regulatoryagencies should be consulted to determinethose requirements. Consulting with theregulatory agencies will provide access to

members of those agencies’ staff who mayhave expertise in and experience withphytoremediation at similar sites. Demonstrating the technical results andsuccess stories of implementation ofphytoremediation at similar sites can help tipthe scales toward regulatory acceptance. Up-front efforts to evaluate the advantages ofusing phytoremediation will pay off inincreased overall support of the process ofremedy selection and expedited approval ofthe redevelopment plans by regulatoryagencies.

3.4 Community Involvement

Acceptance of a redevelopment plan thatinvolves the use of any cleanup technologycan be a sensitive community issue. It isimportant to promote acceptance of theredevelopment plan and the cleanupalternatives by involving the community earlyin the decision-making process throughcommunity meetings, newsletters, or otheroutreach activities. An advantage ofphytoremediation is that it is an easilyunderstood approach. Phytoremediation ismore intuitive than many other treatmenttechnologies and therefore may gain greateracceptance in the community. For anindividual site, the community should beaware of how use of the technology mayaffect redevelopment plans and the adjacentneighborhood. For example, there may beaesthetic or visual improvements that resultfrom the planting of trees or the creation of awetland; there may be site-security issues orlong-term maintenance issues which mayaffect site access; or there may be riskfactors that must be conveyed to thecommunity and may require the preparationof a risk-management plan.


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Soil

Soil

Soil

Waste

Waste

Waste

Year 0Trees planted

Year 1Tree roots penetratewaste – Remediation

Tree continues to mature –Soil created –

Water balance established

0

2’

4’

8’

60’

Figure 2. Phytoremediation Developmental Stages

Source: EPA. 2000. Introduction to Phytoremediation (EPA/600/R-99/107). National Risk Management Research Laboratory. February.

4.0 PRACTICAL CONSIDERATIONS AND LIMITATIONS

As is true of any cleanup alternative,phytoremediation offers a number ofadvantages, as described in the precedingsection. However, it also has technicallimitations related to the types and levels ofcontaminants present, soil properties,acceptable exposure risks, and other site-specific considerations. Discussed in thissection are a number of factors that decisionmakers may find necessary to consider whenevaluating phytoremediation as a cleanupoption for their site. A more comprehensivediscussion of potential limitations to theimplementation of phytoremediation can befound in the documents listed in theSupporting Resources section ofthis primer.

The total length of time required toclean up a site throughphytoremediation may be too longto be acceptable for someredevelopment objectives.Phytoremediation is limited by thenatural growth rate of plants andthe length of the growing season.Several growing seasons may berequired before phytoremediationsystems become effective, whiletraditional methods may require afew weeks to a few months.Therefore, low removal rates mayprohibit the use ofphytoremediation in cases in which

the time period available for cleanup is limitedand is a key criterion in selecting atechnology.

The growth rate of a plant species will have adirect effect on the potential for use at aparticular site. For example, fast-growinggrasses will begin treating soil contaminationmore quickly than a tree, which mustestablish deeper roots to treat targetcontaminants. As plants, particularly treesused in phytoremediation, mature their rootstructures deepen and their capacity to treatdeeper levels of contamination improves. Phytoremediation can provide a number ofbenefits during the course of vegetationmaturation. Plantings during initial stagescan provide a cover that minimizes waterinfiltration. As the tree roots mature,phytodegradation, rhizodegradation, and/orphytovolatilization processes can take placeto treat contaminants at increasing depthsbelow the surface. In fully mature stages,phytoremediation cover can develop ahydraulic control, hydrostatic barrier function. Figure 2 illustrates the progressivedevelopment stages for phytoremediation to


13

support capping to reduce infiltration,degradation, and then hydraulic control. While this developmental process can bebeneficial, consideration also must be givento whether phytoremediation is a safe andprotective remedy during the time it takes forthe plants to establish themselves to a pointat which they are treating the contaminantseffectively.

It must be determined whetherphytoremediation can be effective for thesite-specific conditions and contaminants. For example, phytoremediation works betterin shallow soils and groundwater, unlessdeep-rooted plants are suitable for the site. In addition, phytoremediation works best oncertain types of contaminants or mixed wasteand may be less effective when used onother combinations of waste. For example,phytoremediation may not be the mosteffective treatment option if levels ofcontamination are so high that concentrationsof contaminants are toxic to plants (phytotoxic).

In some cases, phytoremediation might notprovide adequate protection, from an eco-receptor perspective. For example,contamination that is below ground can betransferred into the leaves and stems ofplants that are a food source. Further, insome cases, contaminants are not destroyedin the phytoremediation process; instead,they are transferred from the soil onto theplants and then are transpired in to the air.

Phytoremediation could also increase therates of bioaccummulation of contaminantsthan might otherwise occur.

Potential costs associated with monitoringand maintaining the phytoremediationprocess at the site also must be factored intothe selection process. Maintenance costsoften are lower with phytoremediation thanwith conventional treatment technologies. On the other hand, monitoring costs could behigher, especially if the cleanup rates areslower and monitoring of the site continueslonger than monitoring for conventionaltreatment technologies. An activity that willincrease the cost of long-term maintenance isthe harvesting and proper disposal of plantmaterials that contain contaminants.The state of phytoremediation technology isemerging, and more information fromtreatability studies and long-term applicationsare needed to support its consideration as aviable technology. Until that information isavailable, the diversity of opinions about theconditions and contaminants for whichphytoremediation may be a well-suitedcleanup technology will continue. Consulting with technical experts todetermine the applicability ofphytoremediation on a site-by-site basis isadvised. Further, in many cases, it will beimportant to identify a contingency plan forcleaning up the site in the event thatphytoremediation will not meet cleanupobjectives in an effective and timely manner.


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5.0 SELECTION AND DESIGN OF A PHYTOREMEDIATION SYSTEM

The design of a phytoremediation systemvaries according to the contaminants, theconditions at the site, the level of cleanuprequired, and the plants used. As previouslynoted, contaminants and site conditions areperhaps the most important factors in thedesign and success of a phytoremediationsystem. Other factors that influence theselection and design of a phytoremediationsystem are discussed below.

5.1 Technical Factors

Because phytoremediation is an agronomicprocess, it is highly dependent on climateand site-specific characteristics. Soilproperties determine the ability of a plantspecies not only to become established in thesoil, but also to maximize biomass and,therefore, removal of contaminants. Soilparameters typically analyzed to determinewhether phytoremediation is applicableinclude texture; pH; moisture content; organicmatter content; lime content; cation exchangecapacity; and content of nutrients, such ascalcium, magnesium, potassium, phosphate,and sulfate.

As with most treatment technologies,innovative or not, a treatability study shouldbe conducted before a final remediationtechnology can be selected for use at a siteto demonstrate that the technology will workat that specific site. Information to assessthe effectiveness of phytoremediation alsomay be available in existing literature. Forexample, research may reveal phytotoxicitylevels or regional agronomic practices for thesimple application of phytoremediation, givenadequate site characterization andmonitoring.

Where treatability studies are necessary, sitecharacterization and bench-scale tests maybe used to determine system performance inthe field and evaluate whether the design will

meet the desired level of cleanup in thespecified time period. For phytoremediation,it may be necessary to conduct treatabilitystudies under laboratory conditions (forexample, in an artificial hydroponic system) tosimulate site conditions and obtain an initialresult that proves the effectiveness of thedesign. Acceleration of the process can beexpedited by typical approaches, includingartificial light, water, and temperatureconditions. The advantage of suchlaboratory studies is that the process can beaccelerated to provide early results andreduce implementation time.Local climatic conditions, particularly thelength of the growing season, govern thetype and number of crops that can be plantedeach year and therefore the annual rate ofremoval of contaminants. Climaticconditions, such as rainfall and temperatures,also influence irrigation strategies and theselection of plant species. Plant species thatgrow well in the Pacific Northwest may notsurvive in the arid Southwest.

Hydrologic models allow the calculation of theflow of water and how that flow might beaffected by the application ofphytoremediation. Irrigation flows can havean impact on groundwater conditions andultimately on the movement of thecontaminants to be treated. Althoughirrigation of plants may be necessary toensure a robust start for a phytoremediationsystem, even in drought conditions, carefulmodeling may be necessary to predict withany certainty the effects of phytoremediationat a site.

Agronomic techniques include the addition ofnutrients necessary for vigorous growth invegetation. To maximize the efficiency of thephytoremediation treatment system, the soiltype first must be determined. Analysis willhelp determine the need for amendments,such as nitrogen, potassium, phosphorous,


15

Remediating Wood Preservatives and Residual DNAPLsPhytoremediation is being tested as an approach toaddressing both wood preservatives and dense non-aqueous phase liquids (DNAPL) at a RCRA site in Laramie,Wyoming. The active Union Pacific Railroad (UPRR) facilitybecame contaminated with polycyclic aromatichydrocarbons (PAH) during almost 100 years of treatingrailroad ties with creosote. UPRR installed a bentonite-filledtrench to contain contaminated groundwater but had nomeans of addressing residual PAHs in soil and groundwaterbecause of the perceived technical infeasibility of cleaningup to the relatively low maximum contaminant levels (MCL). The Wyoming Department of Environmental Quality(WDEQ) approved a phytoremediation demonstration thatwill serve as a research project for the WDEQ as well as thefacility and therefore includes rigorous requirements formonitoring. More than 10,000 plants are being installed at a50-acre site, including test plots in highly contaminated “hotspots” at which the technique’s ability to address high levelsof contamination will be assessed. Particular attention hasbeen paid to selecting native species that will be tolerant ofLaramie’s harsh climate, and seed and plant stock for theplantings have been harvested from the Laramie area. Thepublic has been included in planning for the project, as well,and the phytoremediation plot has been integrated intoLaramie’s greenspace plan and bicycle trail system. A biketrail to the site was completed in early 2001, and a 1.5-milebike loop through the phytoremediation plot is beingplanned. For more information, contact Marisa Latady ofWDEQ at (377) 777-7752.

Figure 3: Root Depth

AlfalfaGrasses Indian

Mustard

Poplar Trees 15 ft.

4-6 ft.

2 ft.

1 ft.

15 ft.

Source: EPA. 2000. Introduction to Phytoremediation (EPA/600/R-99/107). National Risk Management Research Laboratory. February.

manure, sewage sludge compost, straw,or mulch, which are added as required toimprove the performance of the plant. For example, maintenance of thephytoremediation system may requirethe addition of chemicals to stabilizemetals in the soil or the addition ofchelates to ensure that plants take upthe contaminants. A close workingrelationship with regulators is especiallyimportant in such a situation to quicklydetermine any rules, regulations, orprohibitions related to the addition ofamendments to the subsurface. Anychanges made in the soil through theapplication of soil amendments,however, should be evaluated andmonitored for their effects on the siteconditions.

Biomass is the amount of living ororganic matter produced by plants. Increased biomass results in higherlevels of treatment and containmentbecause more materials available to theplant (including contaminants) are usedto support growth. Phytoremediationdesigns commonly involve higher

planting densities than standardagronomic rates for various speciesto overcome decreasedgermination because ofcontaminated soils and to maximizeoverall production of biomass forthe area. Consulting with anexperienced agronomist is essentialto designing a healthy andproductive phytoremediationsystem.

Because various plant specieshave different root structures,careful consideration must be givento selecting the most appropriatespecies to address contaminants atindividual sites. Figure 3 illustratestypical root depths of four plantscommonly used inphytoremediation and


16

demonstrates the depth to which each of thespecies may be most effective. The figureillustrates the potential limitation ofphytoremediation to shallow soils.

5.2 Strategies for Contaminant Control

Phytoremediation can support a variety ofcleanup strategies. One such strategy is toplant the contaminated area with a specificspecies known to extract the targetedcontaminant, subsequently harvest theresulting biomass, and then reduce theharvested material by composting or burning. The resulting pile then becomes aconcentration of the extracted chemical thatcan be treated as hazardous waste or, if thecontaminant is a metal, recycled. Anotherstrategy, which focuses on containment, is tosurround an underground plume ofcontaminants with a selected species ofplants to prevent further movement of theplume through the establishment of ahydrostatic barrier of tree roots, that is, thegroundwater is taken up by the tree roots andtherefore does not migrate beyond the roots. Hybrid poplars have achieved successes insuch approaches.

A common interim approach for brownfieldssites has been capping or paving over a siteto minimize infiltration of water. Severalexperiments have been conducted to create“phytocaps” as improvements of asphaltcoverings. A phytocap is a combination oftrees and other vegetation capable ofabsorbing and transpiring most of theinfiltration water, thereby reducing the riskthat contaminants will spread. A phytocapmust be planted densely so that the rate atwhich the evaporative processes of the plantstake place matches the rate of infiltration ofwater. The approach thereby eliminates theneed to construct an impermeable surface.

Treatment or capture of contaminatedgroundwater under a site may require acertain minimum surface area andconfiguration of trees, depending on

groundwater flow rates and considerationsrelated to the contaminant. Surface waterbuffers and corridors, groundwaterinterceptor strips, and vegetative covers areexamples of applications of phytoremediationthat can be integrated into redevelopmentlandscaping plans on both large and smallsites.

5.3 Innovative Technology TreatmentTrains

Phytoremediation can be an effectivecomponent of treatment train approachesthat combine innovative technologies withtraditional remediation technologies. Thepurpose of combining technologies can be toreduce the volume of material that requiresfurther treatment, to prevent emission ofvolatile contaminants during excavation andmixing, or to treat several contaminants in asingle medium.

An example might be to usephytoremediation as part of a treatment traininvolving soil vapor extraction and/or airsparging. If the volatized compounds arepassed through a properly designed plantrhizoshere zone before being extracted ordischarged to the atmosphere, there can beenhanced degradation of hazardouscompounds.

Hybrid poplars or other deep-rooted specieswith high groundwater uptake rates couldserve in a treatment wall capacity wheninstalled in a way that intercepts migratingcontaminated groundwater plumes. Thegroundwater that flows through the planttreatment wall would in many cases becomeadequately treated such that MNA could beimplemented as the final stage of the train. In shallow aquifer situations phytoremediationcould replace more costly and intensivetechnologies such as pumping and treating.

Anaerobic, reducing conditions are requiredfor effective degradation of chlorinatedsolvents and other organic compounds. A


17

Design Team Disciplines

� Soil Science or Agronomy

� Hydrology

� Plant Biology

� Environmental Engineering

� Regulatory Analysis

� Cost Engineering and Evaluation

� Risk Assessment and Toxicology

� Landscape Architecture

Design Team Disciplines

� Soil Science or Agronomy

� Hydrology

� Plant Biology

� Environmental Engineering

� Regulatory Analysis

� Cost Engineering and Evaluation

� Risk Assessment and Toxicology

� Landscape Architecture

process whereby chemicals secreted fromtree roots lead to anaerobic degradation ofchlorinated solvents currently is receivingresearch attention. This research hasexamined the process in naturally occurringtrees, therefore in the context of MNA. Foradditional information see the InternationalJournal of Phytoremediation, Vol. 2 (3), 2000.

5.4 Design Team

It is important that the development andevaluation of a particular phytoremediationdesign and long-term performance strategyat a brownfields site be performed by anexperienced multidisciplinary team. Thedesign team can help the decision makersweigh the advantages and limitations ofphytoremediation and select and design asystem that best addresses the factorsdiscussed in this section. The team mightinclude experts in the following disciplines orfields:


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6.0 OPERATION AND MAINTENANCE

A phytoremediationtreatment system mustbe monitored andevaluated periodically tomeasure theeffectiveness ofoperations and progresstoward attainment of theremedial objectives forbrownfieldsredevelopment. Monitoring can helpdetermine the mosteffective course forcontinued operation and maintenance. Thissection describes responsibilities foroperation and maintenance at aphytoremediation site.

6.1 Operation and Maintenance

Maintenance is required to obtain a healthystand (or growth of plants). Weed controland irrigation probably are the two mostimportant practices. Because of theproliferation of specific weeds, predators, anddiseases that can cause significantreductions in yields, it may be necessary torotate crops to maintain increased biomassproduction. Weeds also can be controlled byemploying mechanical (cultivation) orchemical (herbicides) methods. Irrigationwater should compensate for normal lossesto evaporation and transpiration. Themethod of irrigation also must be consideredcarefully. Drip irrigation tends to minimizeevaporation of water, improve efficiency, andreduce costs. The long-term maintenanceneeds of wetland systems typically areminimal and may consist of monitoring thedistribution and level of water, removingvegetation and contaminants, and otherpredominantly land-management activities,such as control of access and maintenanceof berms.

6.2 Disposal

In phytoextractionsystems, plant materialmust be harvested anddisposed of. Plants thataccumulatecontaminants may posea risk of spreadingcontamination into thefood chain if they areconsumed by insects orother animals. Consideration should be

given to addressing the need to avoidconsumption of contaminated plants bywildlife or livestock before plants areharvested. At brownfields sites, the end usesunder a redevelopment plan can be adetermining factor in the potential risk tohuman and environmental receptors thataccumulated contaminants may pose. Thebrownfields site redevelopment plantherefore can affect the need for disposal.

It is important to monitor the system and testwhether the plants contain any hazardoussubstances. If there are no hazardoussubstances present, the material could becomposted or worked into the soil on site. Ifthat is not possible, off-site disposal will berequired. The harvest of contaminatedbiomass and possible disposal of the materialas hazardous waste would be subject toapplicable regulations, such as thoseestablished under the ResourceConservation and Recovery Act (RCRA). One option is disposal of contaminatedmaterial in a regulated landfill. Disposalunder RCRA can add costs to aphytoremediation project. However, theremoval and disposal of plant material usedin phytoremediation generally involves thetransporting and handling of materials thatare of far less volume and that probably areless hazardous than materials generated byoperations that involve soil excavation or


19

other innovative or traditional remediationtechnologies. Therefore, phytoremediationcan be a strategy for decreasing the costs ofhandling, processing, and possibly landfillingthe materials.

6.3 Performance Evaluation andMonitoring

To evaluate the short-term performance andeffectiveness of phytoremediation, theconcentrations of contaminants anddegradation products should be measured. Monitoring should be conducted for soil,groundwater, plant root and mass, andevapotranspiration vapor. Rigorousperformance evaluation will help demonstratethe system’s ability to meet cleanup goalsand objectives. Because phytoremediation isan emerging technology, standardperformance criteria for phytoremediationsystems have not yet been established, andperformance must be determined on a site-by-site basis.

Long-term monitoring typically is necessaryfor phytoremediation systems that requirelong time horizons to demonstrate theircontinued effectiveness. Monitoring may becontinued after short-term cleanup goalshave been met to determine the impact of thephytoremediation system on the ecosystem.

A monitoring plan should be developed toguide both short- and long-term monitoring. The plan should discuss the followingelements: constituents or other parametersto be monitored; the frequency and durationof monitoring; monitoring and samplingmethods; analytical methods; monitoringlocations; and quality assurance and qualitycontrol (QA/QC) requirements.


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7.0 COST OF PHYTOREMEDIATION

Phytoremediation is an emerging technology;standard cost information still is beingdeveloped on the basis of experiences inimplementing phytoremediation projects. This section provides information thatcompares costs associated with the use ofphytoremediation to costs associated with theuse of conventional treatment technologiesbased on actual cost estimates for threesites, as well as other sample costs based onlaboratory and pilot scale work and fieldinformation.

Many of those costs associated withphytoremediation are not unique tophytoremediation, but are common toremediation technologies. The major costcomponents for the implementation ofphytoremediation include the costs of:

� Site characterization

� Treatability studies

� Full-scale design (costs will vary accordingto the contaminants, the sitecharacteristics, and the variety and amountof vegetation needed)

� Construction costs (includes direct capitalcosts for site preparation, plant material,and irrigation and monitoring equipmentand indirect costs, such as those forpermitting during construction, contingencydesign, and startup)

� Operation and maintenance andmonitoring costs (includes the cost oflabor, materials, chemicals, utilities,laboratory analysis, disposal, andmonitoring)

As discussed in other sections of this primer,startup and maintenance costs often are lesswith phytoremediation than with conventionaltreatment technologies because: (1)phytoremediation is a natural process usingsolar energy; (2) phytoremediation is in situand requires no digging or hauling of

contaminated soil; and (3) little or nomechanical equipment is required to operatethe phytoremediation process. On the otherhand, monitoring costs could be higher thanwith conventional treatment technologiesbecause monitoring typically is required for alonger period of time at sites wherephytoremediation is used.

In comparing the potential costs to usephytoremediation with the potential cost to useconventional treatment technologies at a site,care must be taken to compare the costs ofthe entire system for the entire life cycle. Under phytoextraction, the cost of processingand ultimate disposal of biomass generated islikely to account for a major percentage ofoverall costs.

7.1 Cost Savings Based on Actual CostEstimates

Table 3 provides site-specific estimates thathave been reported of the cost savingsrealized by using phytoremediation rather thanconventional treatment technologies

7.2 Sample Phytoremediation Costs

The estimated 30-year costs (1998 dollars) forremediating a 12-acre lead site were$12,000,000 for excavation and disposal,$6,300,000 for soil washing, $600,000 for asoil cap, and $200,000 for phytoextraction(Cunningham 1996 in Introduction toPhytoremediation (EPA/600/R-99/107)). Thecosts of cleanup of various heavy metals atthe Twin Cities Army Ammunition Plant,Minneapolis-St. Paul, MN Project werereported in the Federal RemediationTechnologies Roundtable (see SupportingResources) to be $153 per cubic yard of soilover the life of the project.

The costs of removing radionuclides fromwater with sunflowers has been estimated tobe $2 to $6 per thousand gallons of water(Dushenkov et al. 1997 in Introduction toPhytoremediation (EPA/600/R-99/107)). The


21

costs of cleanup of explosives at the MilanArmy Ammunition Plant, Milan, TN werereported in the Federal RemediationTechnologies Roundtable (see SupportingResources) to be $1.78 per thousand gallonsof water over the life of the project.

Estimated costs for hydraulic control of anunspecified contaminant in a 20-foot-deepaquifer at a 1-acre site were $660,000 forconventional pump-and-treat and $250,000for phytoremediation (Gatliff 1994 inIntroduction to Phytoremediation (EPA/600/R-99/107)).

Cost estimates indicate savings for anevapotranspiration cover compared to atraditional cover design to be 20-50%,depending on availability of suitable soil(RTDF 1998 in Introduction toPhytoremediation (EPA/600/R-99/107)).

Studies indicate that phytoremediation iscompetitive with other treatment alternatives,as costs are approximately 50 to 80 percent ofthe costs associated with physical, chemical,or thermal techniques at applicable sites.

Table 3Estimated Cost Savings Through the Use of Phytoremediation

Rather Than Conventional Treatment

Contaminant and Matrix

Phytoremediation Conventional Treatment ProjectedSavingsApplication Estimated Cost Application Estimated Cost

Lead in soil (1 acre)a

Extraction, harvest,and disposal

$150,000 -$250,000 Excavate andlandfill

$500,000 50-65 percent

Solvents ingroundwater(2.5 acres)b

Degradation andhydraulic control

$200,000 forinstallation andinitial maintenance

Pump andtreat

$700,000 annualoperating cost

50 percent costsaving by thirdyear

Total petroleumhydrocarbonsin soil (1 acre)c

In-situ degradation $50,000 - $100,000 Excavate andlandfill orincinerate

$500,000 80 percent

Source: Introduction to Phytoremediation. EPA/600/R-99/107. February 2000.a Phytotech estimate for Magic Marker siteb Potentially responsible party estimate for SRS sitec PERF estimate


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8.0 SUPPORTING RESOURCES

This section identifies Internet sites anddocuments that will help the user obtainadditional information aboutphytoremediation. In addition, Table 4presents a list of references used to preparethis document and a guide to the subjectmatter included in each reference.

� EPA. Office of Research andDevelopment (ORD) Internet web site(http://www.epa.gov/ord). ORD is theprincipal scientific and research arm ofEPA. ORD conducts research andfosters the use of science and technologyin fulfilling EPA's mission. ORD isorganized as three national laboratoriesand two national centers located in adozen facilities around the country and inWashington, D.C. Several EPAlaboratories have work underway todetermine the fate of contaminants inphytoremediation applications. Much ofthis work is based at the EPA NationalRisk Management Research Laboratory(NRML). (Refer to the description below.) ORD along with the Office of Solid Wasteand Emergency Response (OWSER)supports the Remediation TechnologiesDevelopment Forum (RTDF) that also isdescribed in more detail below. Inaddition within ORD, the EPA NationalExposure Research Laboratory (NERL)http://www.epa.gov/NERL/, is exploringtopics such as the degradation of TNT bywetland plants and plantenzyme-contaminant interactions. TheEPA-supported Hazardous SubstanceResearch Center at Kansas StateUniversity engages in research on plantand contaminant interactions. EPARegion 10 continues to explore andencourage innovative applications andinteractions between phytoremediationand ecosystem restoration.

� EPA. National Risk ManagementResearch Laboratory (NRMRL).Introduction to Phytoremediation(EPA/600/R-99/107). February 2000.(Web site availability http://cluin.org/techfocus). The National RiskManagement Research Laboratory,(NRMRL), part of EPA's Office ofResearch and Development, conductresearch into ways to prevent and reducerisks from pollution that threaten humanhealth and the environment. Thelaboratory has a broad program ofinvestigating methods and their cost-effectiveness for prevention and controlof pollution including those relevant toremediation of contaminated sites,sediments and groundwater. NRMRLcollaborates with both public and privatesector partners to foster technologies thatreduce the cost of compliance and toanticipate emerging problems. ItsSuperfund Innovative TechnologyEvaluation (SITE) Program encouragesthe development and implementation ofinnovative treatment technologies forhazardous waste site remediation. Thephytoremediation document has beendeveloped to provide a tool for siteregulators, owners, neighbors, andmanagers to evaluate the applicability ofphytoremediation to a site. Informationon the SITE program or individualprojects can be found athttp://www.epa.gov/ORD/SITE.

� Federal Remediation TechnologiesRoundtable (FRTR) Case Studies http://www.frtr.gov/costThe Federal Remediation TechnologiesRoundtable (FRTR) case studies containdetailed information about specificremedial technology applications. FRTRcase studies are developed by the U.S.Department of Defense (DoD), the U.S.Army Corps of Engineers (USACE), the


23

U.S. Navy, the U.S. Air Force (USAF), theU.S. Department of Energy (DOE), theU.S. Department of the Interior (DOI),and the U.S. Environmental ProtectionAgency (EPA). As of September 1998,FRTR published and made available onits Internet site 140 cost and performancecase studies. The case studies focus onfull-scale and large field demonstrationprojects and include backgroundinformation about the site, a descriptionof the technology, cost and performancedata for the technology application, and adiscussion of lessons learned. Bothinnovative and conventional treatmenttechnologies for contaminated soil,groundwater, and solid media areincluded. A search function on the website allows a user to search the casestudies using key words for media,contaminant, and primary andsupplemental technologies.

� Interstate Technology and RegulatoryCooperation Work Group (ITRC).Phytoremediation Decision Tree.November 1999 (Web site availabilityhttp://www.itrcweb.org). ITRC is astate-led national coalition dedicated toachieving better environmental protectionthrough the use of innovativetechnologies. ITRC helps regulatoryagencies and technology developers,vendors, and users reduce the technicaland regulatory barriers to the deploymentof new environmental technologies. ITRCproducts and services are building thecollective confidence of the environmentalcommunity about using new technologies. Phytoremediation is one such technology. ITRC has provided a tool that can beused to determine whetherphytoremediation can be effective at agiven site. It allows the user to use basicinformation about a specific site todecide, through the use of a flow chartlayout, whether phytoremediation isfeasible at that site.

� EPA. Phytoremediation ResourceGuide. June 1999 . (EPA 542-B-99-003)(Web site availability http://cluin.org/techfocus). The document identifies across-section of information intended toaid users in remedial decision-making,including abstracts of fielddemonstrations, research documents,and information about orderingpublications.

� EPA. A Citizen’s Guide toPhytoremediation. April 2001. (EPA542-F-01-002) (Web site availabilityhttp://cluin.org/techfocus). Thedocument is a technology fact sheetdeveloped to help communicate to citizenstakeholders issues related to the use ofphytoremediation.

� The Remediation TechnologiesDevelopment Forum (RTDF).Internet web site (http://www.rtdf.org) -EPA established the RTDF in 1992 bydetermining what government andindustry can do together to develop andimprove the environmental technologiesneeded to address their mutual cleanupproblems in the safest, most cost-effective manner possible. The RTDFfosters public- and private-sectorpartnerships to undertake research,development, demonstration, andevaluation efforts focused on findinginnovative solutions to high-priorityproblems. The RTDF has grown toinclude partners from industry, severalfederal and state government agencies,and academia who voluntarily shareknowledge, experience, equipment,facilities, and even proprietary technologyto achieve common cleanup goals. ThePhytoremediation of Organics ActionTeam and the In-Place Inactivation andNatural Ecological RestorationTechnologies (IINERT) Soil- MetalsAction Team are two of eight ActionTeams that foster collaboration between


24

the public and private sectors indeveloping innovative phytoremediationsolutions to hazardous waste problems.The Action Teams includerepresentatives from industry,government, and academia who share aninterest in further developing andvalidating the of use of plants and trees toremediate organic hazardous wastes insoil and water.

� Public Technologies, Inc.Brownfieldstech Internet web site(http://www.brownfieldstech.org) - Thesite is a source of information aboutcharacterization and remediation ofbrownfields sites. The web site issponsored by EPA's TIO. It is hosted andmaintained by Public Technology, Inc.(PTI), the technology development arm ofthe National League of Cities, theNational Association of Counties, and theInternational City/County ManagementAssociation. The site focuses on thedemonstration, dissemination, and

promotion of innovative characterizationand remediation technologies forbrownfields. Its goal is to help localgovernments increase efficiencies andreduce costs associated with brownfieldsredevelopment. See “Hot Technologies”page for links to reports on projectsutilizing phytoremediation.

� EPA. The Hazardous Waste Clean-UpInformation (Clu-In) SystemInternet web site (http://cluin.org/techfocus) - EPA’s Clu-In providesinformation about innovative treatmenttechnologies to the hazardous wasteremediation community. It describesprograms, organizations, publications,and other tools for federal and statepersonnel, consulting engineers,technology developers and vendors,remediation contractors, researchers,community groups, and individualcitizens. The site is managed by EPA’sTIO and is intended as a forum for allwaste remediation stakeholders.


25

Table 4References by Topic

ReferenceWhat is

PhytoremediationExamples of

Phytoremediation

Advantages andConsiderations in

SelectingPhytoremediation

Significance ofSite

Characterization

Rock, Steven. 1997. “Phytoremediation.” The Standard Handbook ofHazardous Waste Treatment and Disposal, Second Edition. Harry Freeman,ed. McGraw Hill.

� �

CERCLA Education Center. 2000. Innovative Treatment Technology Course,Module on Phytoremediation. � �

Phytoremediation Work Team, Interstate Technology and RegulatoryCooperation Work Group. 1999. Decision Tree Document. November. � � �

EPA. 1998. A Citizen’s Guide to Phytoremediation, Technology Fact Sheet (EPA 542-F-98-011). August. �

Brownfieldstech.org Internet web site (particularly for case studies). 2000. � �

Rock, Steven and Philip Sayre. 1998. “Phytoremediation of HazardousWastes: Potential Regulatory Acceptability.” Vol. 8, No. 4. � �

Black, Harvey. 1999. “Phytoremediation: A Growing Field with SomeConcerns.” The Scientist. Volume 13, Number 5. March. �

Interstate Technology and Regulatory Cooperation Work Group. 1999.Phytoremediation Technical and Regulatory Guidance. � � �

CH2MHill. 1999. Guidance for Successful Phytoremediation. Prepared forCWRT. March. � � �

Lasat, Mitch. 2000. “Notes of a Plant Scientist.” �

EPA. 2000. Introduction to Phytoremediation (EPA/600/R-99/107). February. � � � �

EPA. 1999. Phytoremediation Resource Guide (EPA 542-B-99-003). June. �

EPA. 1998. Electrokinetic and Phytoremediation In Situ Treatment of Metal-Contaminated Soil: State-of-the-Practice. � � �

Note: The table provides a list of references that were used to develop this primer.

APPENDIX 1 – List of Acronyms and Glossary of Key Terms 1

APPENDIX 1

LIST OF ACRONYMS AND GLOSSARY OF KEY TERMS

bgs Below ground surface

BTEX Benzene, toluene, ethylbenzene, and xylene

BTSC Brownfields Technology Support Center

cm Centimeter

EPA U.S. Environmental Protection Agency

ITRC Interstate Technology Regulatory Cooperation Work Group

NRMRL National Risk Management Research Laboratories

PAH Polycyclic aromatic hydrocarbons

PCB Polychlorinated biphenyl

PCP Pentachlorophenol

QA/QC Quality assurance and quality control

RCRA Resource Conservation and Recovery Act

TCA Trichloroethane

TCE Trichloroethylene

TIO Technology Innovation Office

TNT Trinitrotoluene

UPRR Union Pacific Railroad

VOC Volatile organic compound

2 APPENDIX 1 – List of Acronyms and Glossary of Key Terms

AbioticNot biotic or living.

AbsorptionThe process of onesubstance actuallypenetrating into the structureof another substance. Theprocess is different fromadsorption, in which onesubstance adheres to thesurface of another substance.

Adsorption The physical process thatoccurs when liquids, gases,or suspended matter adheresto the surfaces of, or in thepores of, an adsorbentmaterial. The process isphysical and occurs without achemical reaction.

AgronomicThe application of soil andplant sciences to soilmanagement and cropproduction; scientificagriculture.

Bench-ScaleTesting phase conducted todemonstrate effectiveness ofan emerging treatmenttechnology; usually a small-scale version is tested underlaboratory conditions.

BioaccumulationThe absorption andconcentration ofcontaminants, such as heavymetals, in plants and animals. Bioconcentration is asynonym for bioaccumulation.

BiomassAll the living matter present ina given area; organicstructures produced by livingorganisms. The generic termfor any living matter that canbe converted into usableenergy through biological orchemical processes. Can beexpressed numerically as amass-density or as caloriesper unit area.

BioticRelated to life or specific lifeconditions; living.

Brownfields An abandoned, idled, orunder-used industrial orcommercial facility whereexpansion or redevelopmentis complicated by real orperceived environmentalcontamination.

CapA barrier that coverscontaminated media and thatprevents rainwater frompercolating into the groundand causing contaminantsunder the cap to leach intogroundwater. Also mayprevent surface exposure tocovered contaminants.

Cation ExchangeA chemical process in whichpositively charged ions of likecharge are exchangedequally between a solid and asolution (such as water).

ChelatesA compound in which ametallic ion is attached bycovalent bonds to two ormore nonmetallic atoms inthe same molecule. Chelating agents are used toremove metals, particularlylead, from insoluble soilfractions and keep them insolution.

Concentration The amount of a specifiedsubstance in a unit amount ofanother substance; therelative abundance of asolute in a solution.

Degradation Decomposition of acompound by stages,exhibiting well-definedintermediate products.

Drip Irrigation Irrigation whereby water isslowly applied to the soilsurface through smallemitters that have a low rateof discharge.

Emergent PlantAn herbacious plant standingerect and rooted in shallowwater, with most of the plantgrowing above the water’ssurface.

APPENDIX 1 – List of Acronyms and Glossary of Key Terms 3

EvapotranspirationThe loss of water from thesoil both by evaporation andby transpiration from theplants growing in the soil. Evaporation involves thechange of state of water fromliquid to gas form as watermolecules escape from thesurface of a body into theatmosphere. Transpiration isthe process by which water isdrawn from the soil byosmotic pressure of the rootsystems of vegetation andmoved through the leaves tothe surrounding atmosphere.

ExtractionRemoval by chemical ormechanical action.

Full-Scale TechnologyAn established technology forwhich cost and performanceinformation is readilyavailable.

Groundwater The supply of fresh waterfound beneath the Earth'ssurface, usually in aquifers,that supplies wells andsprings.

Herbacious PlantA plant with no persistentwoody stem above ground.

Hydrostatic BarrierIn phytoremediation, the useof plants to control movementof water, generally from anarea of higher levels ofcontamination to an area oflower levels of contamination.

HyperaccumulatorsMetallophytes thataccumulate an exceptionallyhigh level of a metal to aspecified concentration or toa specified multiple of theconcentration found innonaccumulators. Alpinepennycress is an example(see metallophytes).

Immobilize To make incapable of furthermovement.

In Situ In place, without excavation. In situ soil technologies treatcontamination without diggingup or removing thecontaminants.

Indian Mustard (Brassicajuncea)A potentially useful plant withrelatively high biomass that isnot a hyperaccumulator. Theplant has been frequentlyused in toxic metal andradionuclide phytoextraction.

InfiltrationTo pass into or through asubstance (such as soil) bypenetrating its pores orinterstices; generally refers towater entering a physicalarea.

Innovative TreatmentTechnologiesA technology that has beenfield-tested and applied to ahazardous waste problem ata site, but lacks a long historyof full-scale use. Informationabout its cost and how well itworks may be insufficient toencourage use under a widevariety of operatingconditions. Innovativetreatment technologies arebetter analyzed on a site-by-site basis.

Inorganic Chemical orCompoundA chemical or compound thatgenerally does not containcarbon atoms (carbonate andbicarbonate compounds arenotable exceptions). Examples of inorganiccompounds include variousacids and metals.

LeachingA process through which aliquid in contact with ormoving through a solidmobilizes constituents fromthe solid through the actionsof dissolution and physicaltransport.

LignificationFormation into wood throughthe formation and deposit oflignin (a polymer functioningas a natural binder andsupport for the cellulose fiberof woody plants) in cell walls;the process of makingsomething woody.

4 APPENDIX 1 – List of Acronyms and Glossary of Key Terms

Mass TransferThe conveyance of anymaterial like liquids, gases, orsolid materials from onelocation to another location;in phytoremediation, the termmight refer to the conveyanceof a contaminant from soil orgroundwater to a plant.

MetallophytesPlants that preferentiallycolonize in metal-rich soils.

Microorganisims An organism too tiny to beseen by the unaided eye. Includes bacteria, algae,fungi, and viruses.

Natural AttenuationAn approach to cleanup thatuses natural processes overtime to contain contaminationand reduce theconcentrations and amountsof pollutants in contaminatedsoil and groundwater. Theprocesses of naturalattenuation include dilution,volatilization, biodegredation,and adsorption.

Nutrients Elements or compoundsessential for the growth anddevelopment of an organism. Nitrogen, phosphorous, andpotassium are examples ofessential plant nutrients.

Organic Chemical orCompoundA chemical or compoundproduced by animals orplants that contains mainlycarbon, hydrogen, andoxygen.

PhreatophyteA deep-rooted plant thatobtains water from the watertable.

Phytocap (or VegetativeCap) A long-term, self-sustainingplanted area growing in andover materials that pose anenvironmental risk. Thephytocap requires minimalmaintenance and is designedto reduce the risk that thecontaminant will leach.

Phytoremediation A technology that uses livingplants to remediate orstabilize contaminants in soil,sediment, surface water, orgroundwater.

Phytotoxic Harmful to plants.

Pilot-Scale TestingTesting stage of a treatmenttechnology, between bench-and full-scale, that isconducted in the field toprovide data on performance,cost, and design objectivesfor the treatment technology.

PlumeA visible or measurableemission or discharge of acontaminant from a givenpoint of origin into anymedium.

Poplar (EasternCottonwood or Populusdeltoides) A tree widely studied for itspotential for hydraulic control,phytodegredation, andphytovolatilization.

Rhizosphere The zone of soil adjacent toplant roots that exhibitssignificantly higher microbialnumbers, species, andactivity than bulk soil.

Root ZoneGenerally considered to bethe area surrounding theunderground part of a plant,the functions of which includeabsorption, aeration, andstorage for the plant.

SorptionThe action of soaking up orattracting substances—ageneral term used toencompass the processes ofabsorption and adsorption.

Submergent SpeciesPlant species that lie entirelyunder water.

TranspirationThe plant-based process thatinvolves the uptake,transport, and eventualvaporization of water throughthe plant’s leaves.

Volatile OrganicCompounds (VOC)Organic chemicals capable ofbecoming vapor at relativelylow temperatures.

Volatilization The transfer of a chemicalfrom the aqueous or liquidphase to the gas phase. Solubility, modular weight, thevapor pressure of the liquidand the nature of the gas-liquid affect the rate ofvolatilization.

APPENDIX 2 – The Process of Phytoremediation 1

APPENDIX 2

THE PROCESSES OF PHYTOREMEDIATION

Phytoremediation can be classified according to the biological processes involved. Thoseprocesses are described below.

Hydraulic Control, also known as phytohydraulics, is designed to control groundwatertransport mechanisms through plant transpiration. The process uses plants that have a hightranspiration rate to take up large quantities of water, thereby achieving hydraulic control of thesite to contain contaminants and prevent their further migration. The transpiration rate dependson the type of plant, leaf area, nutrients, soil moisture, temperature, wind conditions, andrelative humidity.

Phytodegradation, also known as phytotransformation, is the uptake of organic contaminantsfrom soil and groundwater, followed by their degradation in plant tissue. The extent ofdegradation depends on the efficiency of contaminant uptake and the concentration ofcontaminants in soil and groundwater. Uptake efficiency depends on the contaminant’sphysical and chemical properties and the plant itself. After uptake, the plant either stores thecontaminants or volatizes or metabolizes the contaminants completely to carbon dioxide andwater. The process is an efficient removal mechanism at shallow depths for moderatelyhydrophobic organic contaminants like benzene, toluene, ethylbenzene, and xylene (BTEX);chlorinated solvents; and short-chain aliphatic hydrocarbons.

Phytoextraction uses plants to transport metals from the soil and concentrate them into rootsand aboveground shoots that can be harvested. Many types of plants can be used to removemetals. Some grasses accumulate surprisingly high levels of metals in their shoots withoutexhibiting toxic effects. However, their low biomass production results in a relatively lowextraction rate for metals. Genetic engineering or breeding of hyperaccumulating plants forhigh biomass production could make the extraction process highly effective. Using crop plantsto extract metals from the soil seems practical because of their high biomass production andrelatively fast growth rate. Crop plants also are easy to cultivate and exhibit genetic stability. However, using crop plants to accumulate metals is a potential threat to the food chain.

Phytostabilization uses plants to limit the mobility and bioavailability of metals in soil bysorption, precipitation, complexation, or the reduction of metal valences. The process helps tostabilize the soil matrix to minimize erosion and migration of sediment. To eliminate thepossibility that residues in harvested shoots might become hazardous wastes, phytostabilizingplants should exhibit low levels of accumulation of metals in shoots. Phytostabilizationimmobilizes metal contaminants in the soil through a combination of processes, includingreaction with soil amendments, adsorption or accumulation in the rhizosphere, and physicalstabilization of the soil. In addition, the process minimizes the generation of airbornecontaminants caused by wind erosion. Some researchers consider an interim measure to beapplied until extraction becomes fully developed. Other researches are developingphytostabilization as a standard protocol of metal remediation technology, especially at sites atwhich removal of metals does not seem economically feasible.

2 APPENDIX 2 – The Process of Phytoremediation

Phytovolatilization uses plants to takeup volatile organic compounds (VOC) and the metabolicproducts of the plant and transpire them into the atmosphere. Because VOCs are released intothe atmosphere through plant transpiration, air monitoring may be required. This form ofphytoremediation may not be as desirable as in situ degradation, but it may be preferable toprolonged contamination of soil and groundwater contamination.

Rhizodegradation also known as phytostimulation, plant-assisted bioremediation, or enhancedrhizosphere bioremediation, is root-stimulated microbial degradation of organic contaminants. Rhizodegradation involves a root zone that provides a habitat for beneficial microbial growthand fungi associated with plant roots that help in metabolizing organic contaminants. Rootturnover for trees like mulberry, osage orange, and apple release flavonoids and coumarin thatstimulate the degradation of polychlorinated biphenyls (PCB).

Rhizofiltration is the removal or concentration of metal contaminants from an aquaticenvironment such as contaminated surface water and groundwater in the root zone. Onevariation of rhizofiltration removes metals by sorption, which involves biochemical processes. The roots absorb, concentrate, and precipitate metals from polluted effluent, which may includeleachate from soil. Another variation of rhizofiltration is the construction of wetlands or reedbeds for the treatment of contaminated water or leachate. The technology generally has beenfound to be cost-effective for the treatment of large volumes of wastewater that contain lowconcentrations of metals. Plant species used for rhizofiltration often are raised hydroponicallyin greenhouses and transplanted to a floating system in which the roots are in contact withcontaminated water.

APPENDIX 3 – Phytoremediation Decision Tree Models 1

APPENDIX 3

PHYTOREMEDIATION DECISION TREE MODELS

The three decision tree charts on the following pages were developed by the PhytoremediationWork Group of the Interstate Technology and Regulatory Cooperation Work Group (ITRC). The Phytoremediation Work Team effort, as part of the broader ITRC effort, is funded primarilyby the U.S. Department of Energy. Additional funding and support is provided be the U.S.Department of Defense and the U.S. Environmental Protection Agency.

These charts provide guidelines for determining the applicability of phytoremediation at abrownfields site after site characterization for the treatment of soil, groundwater, or sedimentshas been completed.

2 APPENDIX 3 – Phytoremediation Decision Tree Models

Decision Tree for PhytoremediationSoil

Are there hotspots that can beremoved or treated?YES

NOIs the contaminant at phytotoxic concentrations (this may require a greenhouse dose-response test)?

YES

NO

Is the log Kow of the contaminant or metabolicproducts between 1 and 3.5 (will uptake occur)?NO

YES

Phytoremediation has the potentialto be effective at the site

Can controls be put in place to preventthe transfer of the contaminant or metabolicproducts from a plant to humans/animals?

NO

YES

Is the final disposition of the contaminantor metabolic products acceptable?

NO

YES

Will the plant degrade thecontaminant after uptake and are

the metabolic products acceptable?YES

NO

Will the plant accumulate the contaminant or metabolic products after uptake?NO

YES

Phytoremediation is NOT an optionat the site; consider other options

Can the contaminant or metabolic productbe immobilized to acceptable levels?

NO

YES

Can the plant waste be economically disposed?YES NO

Does the plant material constitute a waste if harvested? YESNO

Can engineering controls make it acceptable? NOYES

NOIs the quantity and rate of transpiration acceptable for this site?YES

Will the plants transpire thecontaminant or metabolic products?

YES

NOIs the level of accumulation acceptable

for this site throughout the growth of the plant?YES

NO

Will the rhizosphere microbes and plant-exuded enzymes degrade the target contaminants in the rhizosphere and are the metabolic products acceptable?YES

NO

Is the contaminant physically within the range of the proposed plant (typically less than 1-2 feet bgs )?YES NO

Will the climate support the proposed plants?YES NO

Is time or space a constraint?NO YES

APPENDIX 3 – Phytoremediation Decision Tree Models 3

Decision Tree for PhytoremediationGroundwater


Will the plants be used for hydrauliccontrol ONLY (prevent water from

REACHING the contaminated zone)?YES

NO

Is the contaminant physically within the range of the proposed plant (typically less than 10-20 feet bgs for Salix species - willows, cottonwoods, poplars)?YES

NO

Will the water be mechanically pumped and applied to the phytoremediation system?YES

NO

Will state regulations allowthis type of phytoremediation?YES

NO

Is the contaminant at phytotoxic concentrations (this may require a greenhouse dose-response test)?

YES

NO


YES





NO

YES


NO

YES



NO


YES



NO

YES





YES

NOIs the level of accumulation acceptable

for this site throughout the growth of the plant?YES

NO


NO

4 APPENDIX 3 – Phytoremediation Decision Tree Models

Decision Tree for PhytoremediationSediments

Is the contaminant physically within the range of the proposed plant (typically less than 1-2 feet bgs )?YES NO

Are there hotspots that can beremoved or treated?YES

NOIs the contaminant at phytotoxic concentrations (this may require a greenhouse dose-response test)?

YES

NO


YES


Is the level of accumulation acceptable for this site throughout the growth of the plant?YES

NO



NO

YES


YES

NO


NO

YES



NO


NO





NO

YES



YES

Are the sediments to be dredged?YES

NOCan the sediments be treated in place (wetlands)?YES NO

Will the regulatory statutes allow the dredged sediments to be treated as a soil?YES NO

Is there strong public support to treat the sediment as a soil?YES NO



For additional information, please see these other publicationsissued by the Brownfields Technology Support Center:

• Road Map to Understanding Innovative Technology Options forBrownfields Investigation and Cleanup, Second EditionEPA 542-B-99-009

• Directory of Technology Support Services to Brownfields LocalitiesEPA 542-B-99-005

• Assessing Contractor Capabilities for StreamlinedSite InvestigationsEPA 542-R-00-001

• Brownfields Technology Primer: Requesting and EvaluatingProposals That Encourage Innovative Technologies for Investigation and CleanupEPA 542-R-01-005

These publications are available online at:http://www.brownfieldstsc.org

or can be ordered by contacting:

U.S. Environmental Protection AgencyNational Service Center for Environmental Publications

(NSCEP)P.O. Box 42419

Cincinnati, OH 45242-24191 (800) 490-9198

FAX (513) 489-8695

EPAEPA 542-R-01-006

July 2001

Brownfields Technology Primer: Selecting and Using Phytoremediation for Site Cleanup

Visit the Brownfields TechnologySupport Center Web Site at:

http://www.brownfieldstsc.org

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