Recent Developments for In Situ Treatment of Metal

Contaminated Soils

Prepared for:

U.S. Environmental Protection Agency

Office of Solid Waste and Emergency Response

Technology Innovation Office

Washington D.C. 20460

Work Assignment Number:

Date Prepared:

Contract Number:

EPA Work Assignment Manager:

Telephone:

Prepared by:

PRC Work Assignment Manager:

Telephone:

011059

March 5, 1997

68-W5-0055

Carl Ma & John Kingscott

(703) 603-9903; (703) 603-7189

PRC Environmental Management, Inc.

Mark Evans

(703) 287-8811 
Disclaimer

The information in this document has been funded wholly or in part by the United States Environmental

Protection Agency under contract number 68-W5-0055 to PRC Environmental Management, Inc. It has

been subjected to the Agency’s peer and administrative review and has been approved for publication as an

EPA document. Mention of trade names or commercial products does not constitute endorsement or

recommendation for use.
i

CONTENTS

Section Page

ABSTRACT ........................................................................ 1

EXECUTIVE SUMMARY ............................................................ 2

INTRODUCTION ................................................................... 4

1.0 PURPOSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.0 REPORT ORGANIZATION .............................................. 6

OVERVIEW OF IN SITU TECHNOLOGIES FOR REMEDIATION OF

SOILS CONTAMINATED WITH METALS .............................................. 7

STATUS OF ELECTROKINETIC REMEDIATION TECHNOLOGY .......................... 9

1.0 DESCRIPTION ........................................................ 9

2.0 OVERVIEW OF STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.1 Electrokinetics, Inc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.2 Geokinetics International, Inc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.3 Isotron Corporation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.4 Battelle Memorial Institute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.5 Consortium Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.0 PERFORMANCE AND COST SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.1 Louisiana State University - Electrokinetics, Inc. . . . . . . . . . . . . . . . . . . . . . . . 18

3.2 Geokinetics International, Inc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.3 Battelle Memorial Institute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.4 Consortium Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.0 ANALYSIS OF APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

5.0 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

STATUS OF IN SITU PHYTOREMEDIATION TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

1.0 DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

1.1 Phytoextraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

1.2 Phytostabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

1.3 Rhizofiltration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

1.4 Future Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2.0 OVERVIEW OF STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.0 PERFORMANCE AND COST SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
CONTENTS (continued)

Section Page

ii

3.1 Results of Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.2 Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.3 Future directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.0 ANALYSIS OF APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.1 Site Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.2 Waste Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

5.0 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

STATUS OF SOIL FLUSHING TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

1.0 DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2.0 OVERVIEW OF STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

2.1 Cation Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

2.2 Lead Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

2.3 Chrome Flushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

2.4 Twin Cities Army Ammunition Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.0 PERFORMANCE AND COST SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.0 ANALYSIS OF APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5.0 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

STATUS OF IN SITU SOLIDIFICATION/STABILIZATION TECHNOLOGY . . . . . . . . . . . . . . . . . . 41

1.0 DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

1.1 Reagent-based S/S Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

1.2 Thermal-based S/S Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

2.0 OVERVIEW OF STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

3.0 PERFORMANCE AND COST SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

3.1 Reagent-based S/S Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

3.2 Thermal-based Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

4.0 ANALYSIS OF APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

5.0 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
iii

FIGURES

Figure Page

1 Contaminants Most Commonly Present in All Matrices at Superfund Sites ................. 5

2 A Schematic Diagram of One Electrode Configuration and Geometry Used

in Field Implementation of Electrokinetic Remediation [13, 23] . . . . . . . . . . . . . . . . . . . . . . . . 11

3 Schematic View of Contaminated Plume Stopped by An Electrokinetic Fence [10] . . . . . . . . . 13

4 Setup of Electroheating with Vapor/Water Extraction: Results in Unsaturated Zone

and in Saturated Zone [10] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

5 Electroacoustical Soil Decontamination Process [13] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6 Schematic Diagram of the Lasagna Process [11] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 TM

7 Integrated In-Situ Remediation: Consortium [11] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

8 Typical Soil Flushing System (Surface Sprinklers) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

9 Geosafe In Situ Vitrification Process [3] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

TABLES

Table Page

1 OVERVIEW OF IN SITU TECHNOLOGIES FOR REMEDIATION

OF SOILS CONTAMINATED WITH METALS .................................... 8

2 OVERVIEW OF ELECTROKINETIC REMEDIATION TECHNOLOGY . . . . . . . . . . . . . . . 10

3 PERFORMANCE SUMMARY OF ELECTROCHEMICAL SOIL REMEDIATION

TECHNOLOGY APPLIED AT FIVE FIELD SITES IN EUROPE (1987-1994) . . . . . . . . . . . 20

4 OVERVIEW OF PHYTOREMEDIATION TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5 TYPES OF PHYTOREMEDIATION TECHNOLOGY:

ADVANTAGES AND DISADVANTAGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

6 EXAMPLES OF METAL HYPERACCUMULATORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

7 OVERVIEW OF SOIL FLUSHING TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

8 UNITED CHROME PRODUCTS SUPERFUND SITE

EXTRACTION AND TREATMENT SYSTEM SUMMARY

AUGUST 1988 THROUGH DECEMBER 1995 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

9 OVERVIEW OF SOLIDIFICATION/STABILIZATION TECHNOLOGY . . . . . . . . . . . . . . . . 41

APPENDIX

A METHODOLOGY

B ENGINEERING BULLETIN: TECHNOLOGY ALTERNATIVES FOR THE REMEDIATION OF

SOILS CONTAMINATED WITH ARSENIC, CADIUM, CHROMIUM, MERCURY, AND LEAD
1

ABSTRACT

Metals contamination is a common problem at

hazardous waste sites. This report assists the

remedy selection process by providing

information on four in situ technologies for

treating soil contaminated with metals. The four

approaches are electrokinetic remediation,

phytoremediation, soil flushing, and

solidification/stabilization. The report discusses

different techniques currently in practice or

under development; identifies vendors and

summarizes performance data; and discusses

technology attributes that should be considered

during early screening of potential remedies.
2

EXECUTIVE SUMMARY

Metals are prevalent at most Superfund sites. At

sites with signed Records of Decision (ROD), Experience with this technology is limited to

metals are the sole contaminants (approximately bench and pilot scales, with the notable

16 percent) or are found in combination with exception of a metal removal process that has

other contaminants are found such as volatile or been commercially operated by a single vendor

semi-volatile organic compounds (approximately in Europe and recently licensed in the United

49 percent). In general, in situ remedies are States. Limited performance data from this

often capable of providing cost savings, when vendor illustrate the potential for achieving

compared with traditional treatment methods, removals greater than 90 percent for some

and are being selected more frequently at contaminants.

Superfund sites. However, relatively few

alternatives exist for the in situ treatment of The range of potential metals is broad. The

metals. This report presents an overview of four commercial applications in Europe treated

of the most promising technologies for in situ copper, lead, zinc, arsenic, cadmium, chromium,

soil treatment: and nickel. There is also potential applicability

i Electrokinetics compounds. The electrode spacing and duration

ii. Phytoremediation of remediation is site-specific. The process

iii. Soil Flushing requires adequate soil moisture in the vadose

iv. Solidification/stabilization zone, so the addition of a conducting pore fluid

The report is intended to assist in screening new for soil drying near the anode). Specially

technologies early in the remedy evaluation and designed pore fluids also are added to enhance

selection process. the migration of target contaminants. The pore

Electrokinetics

Electrokinetic remediation relies on the

application of low intensity direct current

between electrodes placed in the soil. This technology is in the early stage of

Contaminants are mobilized in the form of commercialization for treatment of soils

charged species, particles, or ions. Several contaminated with metals, and in the future may

organizations are developing technologies for the provide a low cost option under specific

enhanced removal of metals by transporting circumstances. At the current stage of

contaminants to the electrodes where they are development, this process is best suited for sites

removed and subsequently treated above ground. with widely dispersed contamination at low

A variation of the technique involves treatment concentrations where only treatment of soils at

without removal by transporting contaminants the surface (in other words, within depth of the

through specially designed treatment zones that root zone) is required.

are created between electrodes. This process is

undergoing early field testing and is initially Two basic approaches for metals remediation

being targeted to treat chlorinated volatile include phytoextraction and phytostabilization. 

compounds in low-permeability clay. Phytoextraction relies on the uptake of

Electrokinetics also can be used to slow or contaminants from the soil and their 

prevent migration of contaminants by translocation into aboveground plant tissue,

configuring cathodes and anodes in a manner which is harvested and treated. Although

that causes contaminants to flow toward the hyperaccumulating trees, shrubs, herbs, grasses,

center of a contaminated area of soil. The and crops have potential, crops seem to be most

practice has been named “electrokinetic

fencing.”

for radionuclides and some types of organic

may be required (particularly due to a tendency

fluids are added at either the anode or cathode,

depending on the desired effects.

Phytoremediation

promising because of their greater biomass
3

production. Nickel and zinc appear to be the Leached contaminants are typically recovered

most easily absorbed, although preliminary tests from the underlying ground water by pump-andwith copper and cadmium are encouraging. treat methods. Site-specific conditions must be

Significant uptake of lead, a commonly occurring carefully considered to address the possible

contaminant, has not been demonstrated in any spread of contamination.

of the plants tested thus far. However, one

researcher is experimenting with soil

amendments that would facilitate uptake of lead

by the plants. This process (also referred to as immobilization)

Phytostabilization achieves risk reduction by of the waste in order to immobilize

stabilizing contaminants located near the surface. contaminants. Metals are commonly remediated

This result is achieved by the secretion of by ex situ solidification with pozzolans and

compounds by plants to affect soil pH and to sometimes other additives. This technology has

form metal complexes with reduced solubility. been adapted to in situ applications through the

In addition, the plants help control surface use of various proprietary augers which provide

erosion and reduce leaching through increased reagent delivery and mixing. In situ treatment

evapotranspiration. Laboratory studies indicate will likely have a cost advantage over ex situ

the potential effectiveness of this approach for applications for larger volumes and for depths

lead. greater than 10 feet. However, this technology

Soil Flushing

This technology involves extraction of

contaminants from soil using water or other A second solidification technique involves

suitable aqueous solutions. Although additives vitrification where an electrical current is passed

such as acids and chelating agents have had some between electrodes to melt soil and incorporate

commercial use for full-scale ex situ soil washing metals into a vitrified product. This technology

projects, they have not been demonstrated as is commercially available and has been

feasible for in situ applications. successfully used at two Superfund sites, one of

Soil flushing has been selected at seven which was contaminated with metals.

Superfund sites with metals present; however, at

six of those sites, organic contaminants are the Both processes are broadly applicable to a range

primary targets. For metals, soil flushing would of metals. Vitrification uses a hood to capture

be most effective in removing water-soluable mercury and other volatile metals, such as lead

species, such as hexavalent chrome. Two soil and arsenic, which may be partially vaporized

flushing remedies are currently ongoing at during operations. Vitrification is best suited for

Superfund sites, with some preliminary data wastes that are difficult to treat, such as mixtures

available from a hexavalent chrome application. of organics and metals.

Solidification/stabilization

changes the physical and chemical characteristics

has been only occasionally selected for

Superfund use, largely because of concerns with

long-term reliability.
4

INTRODUCTION

Metals account for much of the contamination frequently selected treatment process in the

found at hazardous waste sites. They are present Superfund program is solidification/

in the soil and ground water at approximately 65 stabilization, which was selected 203 times

percent of the Superfund sites for which the U.S. through fiscal year 1994. This accounts for

Environmental Protection Agency (EPA) has nearly 30 percent of all soil treatment

signed records of decisions (ROD). The metals technologies. By contrast, other technologies

most frequently identified are lead, arsenic, available to address metals in soil were selected

chromium, cadmium, nickel, and zinc. Other only 18 times. No treatment technologies have

metals often identified as contaminants include been selected for sites with low-level radioactive

copper and mercury. Figure 1 shows the most metals, where excavation and either on-site or

common contaminants in all matrices at off-site disposal are typically chosen.

Superfund sites. In addition to the Superfund

program, metals make up a significant portion of The difference between the availability of new

the contamination requiring remediation under technologies for the treatment of metals versus

the Resource Conservation and Recovery Act new technologies for the treatment of organic

(RCRA) and contamination present at federal compounds is illustrated by data from EPA's

facilities, notably those that are the responsibility Vendor Information System for Innovative

of the Department of Defense (DoD) and the Treatment Technologies (VISITT). The system,

Department of Energy (DOE). which is distributed on request to more than

Since the reauthorization of Superfund in 1986, vendors of new technologies about the

there has been a significant increase in the capabilities of their processes. EPA recently

treatment of soil at Superfund sites. In the early released the fifth version of the database, which

days of the program, EPA selected conventional contains information on 346 innovative

technologies (for example, incineration, technologies offered by more than 210 vendors. 

solidification and stabilization, and groundwater Information provided by vendors indicates that

pump-and-treat systems). Subsequently, new 226 technologies treat volatile organics, 208

and improved processes were developed, technologies treat semi-volatile organics, and 66

especially for soils, that are capable of providing technologies treat metals (some technologies can

more cost-effective cleanups. In fiscal year treat several waste groups). While a substantial

1993, EPA for the first time selected innovative portion (about 40 percent) of the organic

technologies as remedies more frequently than treatment technologies are in situ processes, only

conventional processes. The innovative 9 of the 66 technologies that treat metals are

technologies most often selected are in situ soil designed to treat soil or groundwater in situ.

vapor extraction, various bioremediation

processes, and thermal desorption for soils and in

situ air sparging and bioremediation for ground

water. All of these technologies target the This document surveys treatment technologies

treatment of organic compounds. with the potential for providing in situ treatment

Experience under the Superfund program clearly updates project managers and cleanup

demonstrates the successful development of new professionals about the status of four

technologies to treat organic compounds. In technologies which are currently available or

addition, statistics show that more than half of under active development. The information

the new technologies selected for soil treatment should be useful in screening technologies early

are in situ processes. In situ techniques have the in the remedy evaluation and selection process. 

potential to provide significant cost savings and

are generally considered to represent a promising

direction for the development of new

technologies.

Few commercial alternatives exist, however, to

treat metals in soil, especially in situ. The most

12,000 users, contains information submitted by

1.0 PURPOSE

of soil contaminated with metals. The report
Most Common Contaminants in All Matrices at Superfund Sites

460

450

323

306

269

251

235 232 226 224

209 207 201

174

163 154

0

50

100

150

200

250

300

350

400

450

500

Lead

Trichloroethylene

Toluene

Chromium

Benzene

Tetrachloroethene

Arsenic

Trichloroethane

Zinc

Cadmium

Chloroform

Polychlorinated biphenyls

Copper

Xylene

Ethylbenzene

Mercury

Contaminants

Number of sites

5

Figure 1. Contaminants Most Commonly Present in All Matrices at Superfund Sites
6

This document is not meant to provide a rigorous addition of reagents and the other based on the

scientific examination. This document focuses use of energy.

only on contamination in soils; EPA recently

published a series of booklets summarizing The four chapters that address specific in situ

bench- and field-scale efforts for in situ treatment technologies are organized in four sections. The

of organics and metals in groundwater. [In Situ first table of each technology chapter presents an

Remediation Technology Status Reports. overview of the technology. The general

EPA542-K-94-003/005/006/ 007/009. April characteristics of the technology are summarized

1995] in the table, and are discussed in greater detail in

2.0 REPORT ORGANIZATION

This document focuses on the treatment of technology. The approaches described in the

metals, such as cadmium, copper, chromium, summary are discussed further in Section 2,

lead, mercury, arsenic, nickel, and zinc. The Overview of Status. The available performance

four in situ technologies presented are data for each of the technologies are provided in

electrokinetic remediation, phytoremediation, Section 3, Performance and Cost Summary.

soil flushing, and solidification/stabilization

(S/S) techniques. The second chapter of this Appendix A contains a description of the

document presents a brief summary of the methodology followed in the preparation of this

attributes of these technologies. Electrokinetic report and includes a list of technical experts that

remediation, discussed in the third chapter were contacted. It also contains treatment

separates contaminants from soil through options not discussed here, such as the use of

selective migration upon application of an treatment trains. Appendix B contains an

electric current. Phytoremediation, discussed in excerpt of a draft copy of an engineering bulletin

the fourth chapter is an emerging technology that titled Technology Alternatives for the

uses plants to isolate or stabilize contaminants. Remediation of Soils Contaminated with Arsenic,

Soil flushing techniques, described in the fifth Cadmium, Chromium, Mercury, and Lead. This

chapter promote mobility and migration of bulletin provides a background description of

metals by solubilizing contaminants so that they physical properties of metals and discussions of

can be recovered. The sixth chapter describes S/S, soil washing, and soil flushing.

two types of S/S techniques, one based on

Section 4 of the chapter, Analysis of

Applications. Section 1, Description, provides a

detailed description of the principle of the
7

OVERVIEW OF IN SITU TECHNOLOGIES

FOR REMEDIATION OF SOILS

CONTAMINATED WITH METALS

This chapter presents an overview comparison of

the four in situ technologies. The key factors

that were considered in this analysis are: status,

range of metals treated, major limiting factor,

and site-specific considerations. Status refers to

the stage of development of the technology. 

Range of metals treated specifies whether the

technology can address a broad range of metals

or focuses on a limited range of metals. Major

limiting factor refers to process considerations

which may limit broad use of the technology. 

Site-specific considerations refers to those site

characteristics that can influence the

effectiveness of the technology. Table 1

provides an overview of the key factors for each

of the four technologies.

As Table 1 indicates, electrokinetics, soil

flushing, and solidification/stabilization are in

more advanced stages of development than

phytoremediation. Soil flushing currently is

applicable to a limited range of metals. Soil

flushing requires consideration of the potential

risk of aquifer contamination by residual flushing

solution at the site. The permeability of the soil

and the characteristics of the groundwater flow

are the main site-specific considerations affecting

the applicability of soil flushing. Electrokinetics

is most applicable to sites at which the soil is

homogeneous and the moisture level is relatively

high. Phytoremediation requires longer

treatment times than other treatment technologies

and may potentially be applied at sites at which

the contamination is shallow and the

concentration of the contaminants relatively low. 

Solidification/stabilization is limited by the lack

of data concerning the long-term integrity of the

treated material. The technology is most

effective at sites at which little or no debris is

present.
8

TABLE 1

OVERVIEW OF IN SITU TECHNOLOGIES FOR REMEDIATION OF SOILS

CONTAMINATED WITH METALS

TECHNOLOGY

EVALUATION S

FACTOR ELECTROKINETICS PHYTOREMEDIATION SOIL FLUSHING S

Status Full-scale applications in Pilot-scale Commercial Com

EuropeRecently licensed in U.S. Trenton, NJ; Butte, MT; INEL sites

Currently being field-tested in Selected at 4 Superfundat Fernald, OH; andChernobyl, Ukraine

Range of Metals Broad Broad Limited BroTreatedMajor Limiting State-of-the-art State-of-the-art Potential contamination of ConFactor(s) the aquifer from residual inte

Longer time required for flushing solutiontreatmentCrop yields and growthpatterns

Site-Specific Homogeneity of soil Depth of contamination Permeability of soil DebConsiderations

Moisture level in soil Concentration of Groundwater flow and Dep

contamination depth
9

STATUS OF ELECTROKINETIC

REMEDIATION TECHNOLOGY

Electrokinetic remediation involves the The principle of electrokinetic remediation relies

application of low density direct current between upon application of a low-intensity direct current

electrodes placed in the soil to mobilize through the soil between two or more electrodes. 

contaminants in the form of charged species. Most soils contain water in the pores between the

Attempts to leach metals from soils by soil particles and have an inherent electrical

electro-osmosis date back to the 1930s. In the conductivity that results from salts present in the

past, research focused on removing unwanted soil [5]. The current mobilizes charged species,

salts from agricultural soils. Electrokinetics has particles, and ions in the soil by the following

been used for dewatering of soils and sludges processes [6]:

since the first recorded use in the field in 1939

[1]. Electrokinetic extraction has been used in • Electromigration (transport of charged

the former Soviet Union since the early l970s to

concentrate metals and to explore for minerals in

deep soils. By 1979, research had shown that the

content of soluble ions increased substantially in

electro-osmotic consolidation of polluted

dredgings, while metals were not found in the

effluent [2]. By the mid-1980s, numerous

researchers had realized independently that

electrokinetic separation of metals from soils was

a potential solution to contamination [3].

Table 2 presents an overview of two variations of

electrokinetic remediation technology. 

Geokinetics International, Inc.; Battelle

Memorial Institute; Electrokinetics, Inc.; and

Isotron Corporation all are developing variations

of technologies categorized under Approach #1,

Enhanced Removal. The consortium of

Monsanto, E.I. du Pont de Nemours and

Company, General Electric, DOE, and the EPA

Office of Research and Development is

developing the Lasagna Process, which is

categorized under Approach #2, Treatment

Without Removal.

1.0 DESCRIPTION

Electrokinetic remediation, also referred to as

electrokinetic soil processing, electromigration,

electrochemical decontamination, or

electroreclamation, can be used to extract

radionuclides, metals, and some types of organic

wastes from saturated or unsaturated soils,

slurries, and sediments [4]. This in situ soil

processing technology is primarily a separation

and removal technique for extracting

contaminants from soils. An in situ

bioremediation technology by electrokinetic

injection is under development, with support

from EPA and DOE [16].

chemical species under an electric 

gradient)

• Electro-osmosis (transport of pore fluid

under an electric gradient)

• Electrophoresis (movement of charged

particles under an electric gradient)

• Electrolysis (chemical reactions

associated with the electric field)

Figure 2 presents a schematic diagram of a

typical conceptual electrokinetic remediation

application.

Electrokinetics can be efficient in extracting

contaminants from fine-grained,

high-permeability soils. A number of factors

determine the direction and extent of the

migration of the contaminant. Such factors

include the type and concentration of the

contaminant, the type and structure of the soil,

and the interfacial chemistry of the system [7]. 

Water or some other suitable salt solution may be

added to the system to enhance the mobility of

the contaminant and increase the effectiveness of

the technology. (For example, buffer solutions

may change or stabilize pore fluid pH). 

Contaminants arriving at the electrodes may be

removed by any of several methods, including

electroplating at the electrode, precipitation or

coprecipitation at the electrode, pumping of

water near the electrode, or complexing with ion

exchange resins [7].

Electrochemistry associated with this process

involves an acid front that is generated at the

anode if water is the primary pore fluid present. 
10

TABLE 2

OVERVIEW OF ELECTROKINETIC REMEDIATION TECHNOLOGY

General Characteristics

• Depth of soil that is amenable to treatment depends on electrode placement.

• Best used in homogeneous soils with high moisture content and high permeability.

Approach #1 - Enhanced Removal Approach #2 - Treatment Without Removal

Description: Electrokinetic transport of Description: Electro-osmotic transport of

contaminants toward the polarized electrodes to contaminants through treatment zones placed

concentrate the contaminants for subsequent between the electrodes. The polarity of the

removal and ex-situ treatment. electrodes is reversed periodically, which reverses

the direction of the contaminants back and forth

through treatment zones. The frequency with

which electrode polarity is reversed is determined

by the rate of transport of contaminants through

the soil.

Status: Demonstration projects using full-scale Status: Demonstrations are ongoing.

equipment are reported in Europe. Bench- and

pilot-scale laboratory studies are reported in the

U.S. and at least two full-scale field studies are

ongoing in the U.S.

Applicability: Applicability: Technology developed for organic

Pilot scale: lead, arsenic, nickel, mercury, copper, species. Research underway for metals.

zinc.

Lab scale: lead, cadmium, chromium, mercury,

zinc, iron, magnesium, uranium, thorium, radium.

No performance data available for completed fullscale applications.

Comments: The efficiency and cost-effectiveness Comments: This technology is being developed

of the technique have not been fully evaluated at for deep clay formations.

full scale in the U.S. by any federal agency. Field

studies are under evaluation or recently have been

initiated by EPA, DOE, DoD, and Electric Power

Research Institute (EPRI). The technique

primarily would require addition of water to

maintain the electric current and facilitate

migration; however, there is ongoing work in

application of the technology in partially saturated

soils. 
11

Figure 2. Schematic Diagram of One Electrode Configuration and Geometry Used in Field

Implementation of Electrokinetic Remediation [13, 23]

The variation of pH at the electrodes results from can be placed horizontally or vertically,

the electrolysis of the water. The solution depending on the location and shape of the

becomes acidic at the anode because hydrogen plume of contamination.

ions are produced and oxygen gas is released,

and the solution becomes basic at the cathode, Before electrokinetic remediation is undertaken

where hydroxyl ions are generated and hydrogen at a site, a number of different field and

gas is released [8]. At the anode, the pH could laboratory screening tests must be conducted to

drop to below 2, and it could increase at the determine whether the particular site is amenable

cathode to above 12, depending on the total to the treatment technique.

current applied. The acid front eventually

migrates from the anode to the cathode. • Field conductivity surveys: The natural

Movement of the acid front by migration and geologic spatial variability should be

advection results in the desorption of delineated because buried metallic or

contaminants from the soil [4]. The process insulating material can induce variability

leads to temporary acidification of the treated in the electrical conductivity of the soil

soil, and there are no established procedures for and, therefore, the voltage gradient. In

determining the length of time needed to addition, it is important to assess

reestablish equilibrium. Studies have indicated whether there are deposits that exhibit

that metallic electrodes may dissolve as a result very high electrical conductivity, at

of electrolysis and introduce corrosion products which the technique may be inefficient.

into the soil mass. However, if inert electrodes,

such as carbon, graphite, or platinum, are used,

no residue will be introduced in the treated soil

mass as a result of the process. The electrodes
12

• Chemical analysis of water: The pore (supplied externally through the boreholes that

water should be analyzed for dissolved contain the electrodes) serves as the conductive

major anions and cations, as well as for medium. The additives in the processing fluid,

the predicted concentration of the the products of electrolysis reactions at the

contaminant(s). In addition, electrical electrodes, and the dissolved chemical entities in

conductivity and pH of the pore water the contaminated soil are transported across the

should be measured. contaminated soil by conduction under electric

• Chemical analysis of soil: The buffering sorption, precipitation/dissolution, and

capacity and geochemistry of the soil volatilization/complexation, provides the

should be determined at each site. fundamental mechanism that can affect the

• pH effects: The pH values of the pore Electrokinetics, Inc. accomplishes extraction and

water and the soil should be determined removal by electrodeposition, 

because they have a great effect on the evaporation/condensation, precipitation, or ion

valence, solubility, and sorption of exchange, either at the electrodes or in a

contaminant ions. treatment unit that is built into the system that

• Bench-scale test: The dominant contaminated soil [20]. Pilot-scale testing was

mechanism of transport, removal rates, carried out with support from the EPA under the

and amounts of contamination left Superfund Innovative Technology Evaluation

behind can be examined for different (SITE) program, and a design and analysis

removal scenarios by conducting package for the process was developed with the

bench-scale tests. Because many of support of the Gulf Coast Hazardous Substance

these physical and chemical reactions are Research Center of the EPA Office of Research

interrelated, it may be necessary to and Development [19].

conduct bench-scale tests to predict the

performance of electrokinetics

remediation at the field scale [3,4].

2.0 OVERVIEW OF STATUS

Various methods, developed by combining the patent are the use of electrode wells for both

electrokinetics with other techniques, are being anodes and cathodes and the management of the

applied for remediation. This section describes pH and electrolyte levels in the electrolyte

different types of electrokinetic remediation streams of the anode and the cathode. The patent

methods currently under development for use at also includes claims for the use of additives to

contaminated sites. The methods discussed were dissolve different types of contaminants [9]. 

developed by Electrokinetics, Inc.; Geokinetics Fluor Daniel is licensed to operate GII’s metal

International, Inc.; Isotron Corporation; Battelle removal process in the United States.

Memorial Institute; a consortium effort; and P&P

Geotechnik GmbH. GII has developed an alternative that combines

2.1 Electrokinetics, Inc.

Electrokinetics, Inc. operates under a licensing fence, it is possible to:

agreement with Louisiana State University. The

technology is patented by and assigned to • Capture electrically charged (polar)

Louisiana State University [17] and a contaminants while treated water passes

complementing process patent is assigned to through the fence

Electrokinetics, Inc. [18]. As depicted in Figure

2, groundwater and/or a processing fluid

fields. This transport, when coupled with

electrokinetic remediation process.

pumps the processing fluid to and from the

2.2 Geokinetics International, Inc.

On July 18, 1995, Geokinetics International, Inc.

(GII) was awarded a patent for an

electroreclamation process. The key claims in

containment, remediation, and prevention in

electrokinetic fencing. Laboratory experiments

have demonstrated that, with an electrokinetic
13

Figure 3. Schematic View of Contaminated Plume Stopped by An Electrokinetic Fence [10]

• Influence the pH and redox potential of (DNAPL), such as chlorinated solvents, that

the groundwater have sunk deep into the aquifer. Field trials by

• Introduce microorganisms and nutrients and groundwater between the electrodes are

through the electrode system or injection heated uniformly. In combination with vacuum

well or groundwater extraction, the vendor claims the

• Increase soil temperatures in the area be accomplished very effectively [10].

inside the fence to accelerate

biodegradation processes GII has developed and patented electrically

• Retard and prevent migration has an extremely high resistance to corrosion. It

Electrokinetic fences can be installed both self-cleaning. GII also has developed a batch

horizontally and vertically and at any depth [10], electrokinetic remediation (BEK ) process. The

as Figure 3 shows. process which incorporates electrokinetic

Another alternative developed by GII, complete remediation of the substrate. BEK is a

electroheating, uses heat generated by mobile unit that remediates ex situ soils on site. 

electrokinetics in combination with extraction GII also has developed a solution treatment

methods to remove volatile and semivolatile technology (EIX ) that allows removal of

compounds. Figure 4 presents a schematic and contamination from the anode and the cathode

performance data for this electroheating process. solutions up to a thousand times faster than can

Electroheating and extraction can be used to be achieved through conventional means [14].

remove dense non-aqueous phase liquids

GII using electrical current have shown that soil

removal of the contaminants identified above can

conductive ceramic material (EBONEX ) that R

has a lifetime in soil of at least 45 years and is

R

technology, normally requires 24 to 48 hours for R

R
14

Figure 4. Setup of Electroheating with Vapor/Water Extraction: Results in Unsaturated Zone

and in Saturated Zone [10]

2.3 Isotron Corporation

Isotron Corporation is participating in a is being used to trap metal ions. The process is

pilot-scale demonstration of electrokinetic being tested for the removal of lead and

extraction supported by DOE's Office of chromium, although the low concentrations of

Technology Development. The demonstration is mercury (5 milligrams per kilogram [mg/kg]) at

taking place at the Oak Ridge K-25 facility in the site have not been reduced appreciably [12].

Tennessee. Laboratory tests completed in 1994

showed that the Isotron process could effect the

movement and capture of uranium present in soil

from the Oak Ridge site [12]. Another method that uses electrokinetic

Isotron Corporation also is involved with decontamination. This technology combines

Westinghouse Savannah River Company in an electrokinetics with sonic vibration. Through

ongoing demonstration of electrokinetic application of mechanical vibratory energy in the

remediation. The demonstration, supported by form of sonic or ultrasonic energy, the properties

DOE's Office of Technology Development, is of a liquid contaminant in soil can be altered in a

taking place at the old TNX basin at the way that increases the level of removal of the

Savannah River site in South Carolina. Isotron is contaminant. Battelle Memorial Institute of

using the Electrosorb process with a patented Columbus, Ohio developed the in situ treatment R

cylinder to control buffering conditions in situ. 

An ion exchange polymer matrix called IsolockR

2.4 Battelle Memorial Institute

technology is electroacoustical soil
15

Figure 5. Electroacoustical Soil Decontamination Process [13]

process that uses both electrical and acoustical • Creates highly permeable zones in close

forces to remove floating contaminants, and proximity sectioned through the

possibly metals, from subsurface zones of contaminated soil region and turns them

contamination. The process was selected for into sorption-degradation zones by

EPA's SITE program; the technology introducing appropriate materials

demonstration was completed in May 1989 [13]. (sorbents, catalytic agents, microbes,

Figure 5 illustrates the process. oxidants, buffers, and others).

2.5 Consortium Process

Monsanto Company has coined the name treatment zones of degradation.

Lasagna to identify its products and services TM

that are based on the integrated in-situ • Reverses liquid flow, if desired, by

remediation process developed by a consortium. switching the electrical polarity, a mode

The proposed technology combines that increases the efficiency with which

electro-osmosis with treatment zones that are contaminants are removed from the soil;

installed directly in the contaminated soils to allows repeated passes through the

form an integrated in-situ remedial process, as treatment zones for complete sorption or

Figure 6 shows. The consortium consists of destruction.

Monsanto, E.I. du Pont de Nemours and

Company (DuPont), and General Electric (GE), Initial field tests of the consortium process were

with participation by the EPA Office of Research conducted at DOE's gaseous diffusion plant in

and Development and DOE, as Figure 7 shows. Paducah, Kentucky. The experiment tested the

The consortium's activities are being facilitated sorption in treatment zones. In November 1994,

by Clean Sites, Inc., under a cooperative CDM Federal Programs Corporation installed

agreement with EPA's Technology Innovation field demonstration equipment [12]. Technology

Office (TIO) [12]. development for the degradation processes and

The in-situ decontamination process occurs as scheme were carried out in 1994 and 1995 at

follows: bench and pilot scales, with field experiments of

• Uses electro-osmosis as a liquid pump to

flush contaminants from the soil into the

combination of electro-osmosis and in situ

their integration into the overall treatment

the full process planned for 1996 [11].
16

Figure 6. Schematic Diagram of the Lasagna Process [11] TM
17

Figure 7. Integrated In-Situ Remediation: Consortium [11]
18

3.0 PERFORMANCE AND COST

SUMMARY

Work sponsored by EPA, the U.S. Army A pilot-scale laboratory study investigating the

Waterways Experiment Station (WES), DOE, the removal of 2,000 mg/kg of lead loaded onto

National Science Foundation, and private kaolinite was completed in May 1993. Removal

industry (for example, Dow Chemical, Du Pont, efficiencies of 90 to 95 percent were obtained. 

Monsanto, and GE), when coupled with the The electrodes were placed one inch apart in a

efforts of researchers from academic and public two-ton kaolinite specimen for four months, at a

institutions (for example, Sandia National total energy cost of about $15 per ton [13]. 

Laboratories, Argonne National Laboratory,

Louisiana State University, the Massachusetts Currently (in 1996), with the support of DoD’s

Institute of Technology, Texas A&M University, Small Business Innovative Research Program

West Virginia University, and the University of and in collaboration with WES, Electrokinetics,

Massachusetts Lowell [12]), have demonstrated Inc. is carrying out a comprehensive

the feasibility of moving electrokinetics demonstration study of lead extraction from a

remediation to pilot-scale testing and creek bed at a U.S. Army firing range in

demonstration stages [4]. Louisiana. EPA is taking part in independent

This section describes testing and cost summary study under the SITE program. The soils are

results reported by Louisiana State University, contaminated with levels as high as 4,500 mg/kg

Electrokinetics, Inc., GII, Battelle Memorial of lead; pilot-scale studies have demonstrated

Institute, and the consortium. that concentrations of lead decreased to less than

3.1 Louisiana State University -

Electrokinetics, Inc.

The Louisiana State University (LSU) - within the same period. At the site of the

Electrokinetics, Inc. Group has conducted demonstration study, Electrokinetics, Inc. is

bench-scale testing on radionuclides and on using the CADEX electrode system that

organic compounds. Test results have been promotes transport of species into the cathode

reported for lead, cadmium, chromium, mercury, compartment, where they are precipitated and/or

zinc, iron, and magnesium. Radionuclides tested electrodeposited directly. Electrokinetics, Inc.

include uranium, thorium, and radium. uses a special electrode material that is costExperimental data on the transport and removal effective and does not corrode. Under the

of such polar organic compounds as phenol and supervision and support of the Electric Power

acetic acid have been reported, and information Research Institute and power companies in the

about transport of nonpolar organic compounds southern U.S., a treatability and a pilot-scale

such as benzene, toluene, ethylene, and xylene field testing study of soils in sites contaminated

(BTEX) below their solubility values also has with arsenic has been initiated, in a collaborative

been disseminated. effort between Southern Company Services

In collaboration with EPA, the

LSU-Electrokinetics, Inc. Group has completed

pilot-scale studies of electrokinetic soil

processing in the laboratory. WES, in

partnership with Electrokinetics, Inc., is carrying

out a site-specific pilot-scale study of the

Electro-Klean electrical separation process. TM

Pilot field studies also have been reported in the

Netherlands on soils contaminated with lead,

arsenic, nickel, mercury, copper and zinc.

assessments of the results of that demonstration

300 mg/kg in 30 weeks of processing. The

Toxicity Characteristic Leaching Procedure

(TCLP) values dropped from more than 300

milligrams per liter (mg/L) to less than 40 mg/L

TM

Engineers and Electrokinetics, Inc [20].

With support from a Small Business Innovative

Research (SBIR) Phase I grant from DOE,

Electrokinetics, Inc., in collaboration with the

Argonne National Laboratory, has initiated a

project to assess the potential for electrokinetic

transport processes to supplement, enhance, and

engineer in situ bioremediation systems in

contaminated soils that are characterized by
19

numerous zones of significantly different

hydraulic and electrical conductivities [14]. 

Pilot-scale development of the project is

underway at Electrokinetics, Inc., with support

from the EPA’s National Risk Management

Research Laboratory in Cincinnati, Ohio, under

the SITE program [20].

The processing cost of a system designed and

installed by Electrokinetics, Inc. consists of

energy cost, conditioning cost, and fixed costs

associated with installation of the system. Power

consumption is related directly to the

conductivity of the soil across the electrodes. 

Electrical conductivity of soils can span orders of

magnitude, from 30 micro reciprocal ohms per

centimeter (mhos/cm) to more than 3,000

mhos/cm, with higher values being in saturated,

high-plasticity clays. A mean conductivity value

is often approximately 500 mhos/cm. The

voltage gradient often is held to approximately 1

volt per centimeter (V/cm) in an attempt to

prevent adverse effects of temperature increases

and for other practical reasons [4]. It may be

cost-prohibitive to attempt to remediate highplasticity soils that have high electrical

conductivities. However, for most deposits

having conductivities of 500 mhos/cm, the

daily energy consumption will be approximately

12 kilowatt hours (kWh)/cubic meter (m ) per 3

day or about $0.40/m per day, (@ $0.03 /kWh) 3

and $12/m per month. The processing time will 3

depend upon several factors, including the

spacing of the electrodes, and the type of

conditioning scheme that will be used. If an

electrode spacing of 4 m is selected, it may be

necessary to process the site over several months.

Ongoing pilot-scale studies using “real-world”

soils indicate that the energy expenditures in

extraction of metals from soils may be 500

kWh/m or more at electrode spacings of 1.0 m 3

to 1.5 m [19]. The vendor estimates that the

direct cost of about $15/m (@ $0.03 /kWh) 3

suggested for this energy expenditure, together

with the cost of enhancement, could result in

direct costs of $50/m or more. If no other 3

efficient in situ technology is available to

remediate fine-grained and heterogenous

subsurface deposits contaminated with metals,

this technique would remain potentially

competitive.

3.2 Geokinetics International, Inc.

GII has successfully demonstrated in situ

electrochemical remediation of

metal-contaminated soils at several sites in

Europe. Geokinetics, a sister company of GII,

also has been involved in the electrokinetics

arena in Europe. Table 3 summarizes the

physical characteristics of five of the sites,

including the size, the contaminant(s) present,

and the overall performance of the technology at

each site [22].

GII estimates its typical costs for ‘turn key’

remediation projects are in the range of $120-

$200/cubic yard (yd ) [22]. 3

Demonstration of the electrokinetic remediation

process in chromate-contaminated soil at the

Sandia Chemical Waste Landfill is scheduled as

part of the mixed waste landfill integrated

demonstration. The demonstration is being

conducted under the SITE program for the

Sandia National Laboratories in New Mexico,

Naval Air Station Alameda in California, and

Electrokinetics, Inc. in Louisiana.

3.3 Battelle Memorial Institute

The technology demonstration through the SITE

program was completed in May 1989 [13]. The

results indicate that the electroacoustical

technology is technically feasible for the removal

of inorganic species from clay soils (and only

marginally effective for hydrocarbon removal)

[24].

3.4 Consortium Process

The Phase I-Vertical field test of the LasagnaTM

process operated for 120 days and was completed

in May 1995. Scale-up from laboratory units

was successfully achieved with respect to

electrical parameters and electro-osmotic flow. 

Soil samples taken throughout the test site before

and after the test indicate a 98% removal of

trichloroethylene (TCE) from a tight clay soil

(i.e., hydraulic conductivity less 
20

TABLE 3

PERFORMANCE SUMMARY OF ELECTROCHEMICAL SOIL REMEDIATION

TECHNOLOGY APPLIED AT FIVE FIELD SITES IN EUROPE (1987-1994)

Site Description Volume (ft ) Contaminant(s) (mg/kg) (mg/kg) 3

Initial Final

Concentration Concentration

Former paint factory 8,100 peat/clay Cu 1,220 <200

soil Pb >3,780 <280

Operational 1,350 clay soil Zn >1,400 600

galvanizing plant 

Former timber plant 6,750 heavy clay As >250 <30

soil

Temporary landfill 194,400 Cd >180 <40

argillaceous

sand

Military air base 68,000 clay Cd 660 47

Cr 7,300 755

Cu 770 98

Ni 860 80

Pb 730 108

Zn 2,600 289

than 1x 10 cm/sec). TCE soil levels were or the conditioning fluid) across the electrodes -7

reduced from the 100 to 500 mg/kg range to an assists in desorption of species and dissolution of

average concentration of 1 mg/kg [25]. Various carbonates and hydroxides. Electro-osmotic

treatment processes are being investigated in the advection and ionic migration lead to the

laboratory to address other types of transport and subsequent removal of the

contaminants, including heavy metals [25]. contaminants. The contaminated fluid is then

4.0 ANALYSIS OF APPLICATIONS

Electrokinetic remediation may be applied to type and level of contamination and the selected

both saturated and partially saturated soils. One current voltage regime. When higher voltage

problem to overcome when applying gradients are generated, the efficiency of the

electrokinetic remediation to the vadose zone is process might decrease because of increases in

the drying of soil near the anode. When an temperature. A spacing that will generate a

electric current is applied to soil, water will flow potential gradient in the order of one V/cm is

by electro-osmosis in the soil pores, usually preferred. The spacing of electrodes generally

toward the cathode. The movement of the water will be as much as three meters. The duration of

will deplete soil moisture adjacent to the anode, the remediation will be site-specific. The

and moisture will collect near the cathode. remediation process should be continued until

However, processing fluids may be circulated at the desired removal is achieved. However, it

the electrodes. The fluids can serve both as a should be recognized that, in cases in which the

conducting medium and as a means to extract or duration of treatment is reduced by increasing the

exchange the species and introduce other species. electrical potential gradient, the efficiency of the

Another use of processing fluids is to control, process will decrease.

depolarize, or modify either or both electrode

reactions. The advance of the process fluid (acid

recovered at the cathode.

Spacing of the electrode will depend upon the
21

The advantage of the technology is its potential as submerged foundations, rubble, large

for cost-effective use for both in situ and ex situ quantities of iron or iron oxides, large rocks, or

applications. The fact that the technique requires gravel; or submerged cover material, such as

the presence of a conducting pore fluid in a soil seashells, are expected to reduce removal

mass may have site-specific implication. Also, efficiencies [4].

heterogeneities or anomalies found at sites, such

5.0 REFERENCES

The following vendors were contacted during the preparation of this report:

Name Agency/Company Telephone Number

Yalcin Acar Electrokinetics, Inc. (504) 388-3992

Louisiana State University

South Stadium Drive

Baton Rouge, Louisiana, 70803-6100 

Steve Clark Geokinetics International, Inc. (510) 254-2335

Robert Clark Geokinetics International, Inc (510) 254-2335

.

Dr. B. Mason Hughes Monsanto (314) 694-1466

(Project Manager)

Lasagna Process TM

Dr. Sa Ho Monsanto (314) 694-5179

(Contractor Environmental Science Center

Principal St. Louis, Missouri 63167

Investigator)

Lasagna Process TM

LITERATURE CITED

1. Pamukcu, S. and J.K. Wittle. 1992. "Electrokinetic Removal of Selected Metals from Soil." 

Environment Progress. Volume II, Number 3. Pages 241-250.

2. Acar, Y.B. 1992. "Electrokinetic Cleanups." Civil Engineering. October. Pages 58-60.

3. Mattson, E.D. and E.R. Lindgren. 1994. "Electrokinetics: An Innovative Technology for In Situ

Remediation of Metals. " Proceedings, National Groundwater Association, Outdoor

Acnon Conference. Minneapolis, Minnesota. May.

4. Acar, Y.B., R.J., Gale and others. 1995. "Electrokinetic Remediation: Basics and Technology

Status." Reprinted from Journal of Hazardous Materials, Volume 40. Pages 117-137.

5. Will, Fritz. 1995. "Removing Toxic Substances from the Soil Using Electrochemistry." 

Chemistry and Industry. May 15. Pages 376-379.

6. Rodsand, T. and Y.B. Acar. 1995. "Electrokinetic Extraction of Lead From Spiked Norwegian

Marine Clay." Geoenvironment 2000. Volume 2. Pages 1518-1534.

7. Lindgren, E.R., M.W. Kozak, and E.D. Mattson. 1992. "Electrokinetic Remediation of

Contaminated Soils: An Update." Waste Management 92. Tuscon, Arizona. Page 1309.
22

8. Jacobs, R.A., M.Z. Sengun, and others. 1994. "Model of Experiences on Soil Remediation by

Electric Fields." Journal of Environmental Science and Health. 29A (9).

9. U.S. Patent Office. 1995. Patent #5,433,829, "Process for the Electroreclamation of Soil

Material." Wieberen Pool, July 18.

10. Geokinetics International, Inc., (GII). Undated. "Electro-Remediation: A Clean-Up Technology

for The Present and The Future." GII. Orinda, California.

11. U.S. Department of Energy. 1995. "Development of an Integrated In-Situ Remediation

Technology." Technology Development Data Sheet. DE-AR21-94MC31185.

12. EPA Office of Solid Waste and Emergency Response. 1995. "In Situ Remediation Technology

Status Report: Electrokinetics." EPA 542-K-94-007.

13. “Innovative In Situ Cleanup Processes.” 1992. The Hazardous Waste Consultant.

September/October.

14. Environmental Technology Network. 1995. Volume 39, Number 1.

15. Lockheed Missiles and Space Company, Inc., Research and Development Division,

Electroremediation Group, LTD. Undated. "Batch Electrokinetic Remediation of

Contaminated Soils, Muds and Sludges." Prepared for the U.S. Environmental Protection

Agency (EPA), Office of Research and Development, Risk Reduction Engineering

Laboratory.

16. Acar, Y.B., E. Ozsu, A. Alshwabkeh, and others. 1996. “In situ Bioremediation by Electrokinetic

Injection.” Chemtech. April.

17. Acar, Y.B., R. J. Gale. 1992. “Electrochemical Decontamination of Soils and Slurries,”

Commissioner of Patents and Trademarks, Washington, D.C., U.S. Patent No.: 5,137,

608. August 15.

18. Marks, R., Y. B. Acar, R. J. Gale. 1995. “In situ Bioelectrokinetic Remediation of Contaminated

Soils Containing Hazardous Mixed Wastes,” Commissioner of Patents and Trademarks,

Washington, D.C., U.S. Patent No. 5,458,747. October 17.

19. Acar, Y.B. and A. N.Alshawabkeh. 1996. Electrokinetic Remediation: I. Pilot-Scale Tests with

Lead Spiked Kaolinite, II. Theoretical Model, Journal of Geotechnical Engineering,

Volume 122, Number 3. March. Pages 173-196.

20. Acar, Y.B. Letter addressed to Dr. Walter W. Kovalick, Jr. April 6, 1996.

21. Denisor, Gennady and others. 1996. “On the Kinetics of Charged Contaminant Removal from

Soils Using Electric Fields.” Journal of Colloid and Interface Science. Volume 178. 

Pages 309-323.

22. Geokinetics International, Inc. Marketing brochure provided by John B. Parkinson Jr., SRI

International to Dr. Walter Kovalick, Jr. EPA Technology Innovation Office.

23. EPA Office of Solid Waste and Emergency Response. 1995. “Emerging Technology Bulletin:

Electrokinetic Soil Processing. Electrokinetics, Inc.” EPA 540-F-95-504.

24. EPA Office of Research and Development. 1994. “Superfund Innovative Technology Evaluation

Program Technology Profiles. Seventh Edition.” EPA 540-R-94-526.

25. EPA Office of Research and Development. 1996. “LasagnaTM Public-Private Partnership.” EPA

542-F-96-010A.
23

STATUS OF IN SITU

PHYTOREMEDIATION TECHNOLOGY

Phytoremediation is the use of plants to remove, developed through the application of

contain, or render harmless environmental well-established agro-economic technologies are

contaminants. This definition applies to all easily transferable. The development of plants

biological, chemical, and physical processes that for restoring sites contaminated with metals will

are influenced by plants and that aid in the require the multidisciplinary research efforts of

cleanup of contaminated substances [1]. Plants agronomists, toxicologists, biochemists,

can be used in site remediation, both to microbiologists, pest management specialists,

mineralize and immobilize toxic organic engineers, and other specialists [1, 2]. Table 4

compounds at the root zone and to accumulate presents an overview of phytoremediation

and concentrate metals and other inorganic technology.

compounds from soil into aboveground shoots

[2]. Although phytoremediation is a relatively

new concept in the waste management

community, techniques, skills, and theories

TABLE 4

OVERVIEW OF PHYTOREMEDIATION TECHNOLOGY

General Characteristics

• Best used at sites with low to moderate disperse metals content and with soil media that will support

plant growth.

• Applications limited to depth of the root zone.

• Longer times required for remediation compared with other technologies.

• Different species have been identified to treat different metals.

Approach #1 - Phytoextraction (harvest) Approach #2 - Phytostabilization

(root-fixing)

Description: Uptake of contaminants from soil into Description: Production of chemical compounds

aboveground plant tissue, which is periodically by the plant to immobilize contaminants at the

harvested and treated. interface of roots and soil. Additional stabilization

can occur by raising the pH level in the soil.

Status: Field testing for effectiveness on Status: Research is ongoing.

radioactive metals is ongoing in the vicinity of the

damaged nuclear reactor in Chernobyl, Ukraine. 

Field testing also is being conducted in Trenton, NJ

and Butte, MT and by the Idaho National

Engineering Laboratory (INEL) in Fernald, OH.

Applicability: Potentially applicable for many Applicability: Potentially applicable for many

metals. Nickel and zinc appear to be most easily metals, especially lead, chromium, and mercury.

absorbed. Preliminary results for absorption of

copper and cadmium are encouraging.

Comments: Cost affected by volume of biomass Comments: Long-term maintenance is required.

produced that may require treatment before

disposal. Cost affected by concentration and depth

of contamination and number of harvests required.

1.0 DESCRIPTION Metals considered essential for at least some
24

forms of life include vanadium (V), chromium • Rhizofiltration

(Cr), manganese (Mn), iron (Fe), cobalt (Co),

nickel (Ni), copper (Cu), zinc (Zn), and

molybdenum (Mo) [2]. Because many metals are

toxic in concentrations above minute levels, an Phytoextraction technologies use

organism must regulate the cellular hyperaccumulating plants to transport metals

concentrations of such metals. Consequently, from the soil and concentrate them into the roots

organisms have evolved transport systems to and aboveground shoots that can be harvested [1,

regulate the uptake and distribution of metals. 2, 6]. A plant containing more than 0.1 percent

Plants have remarkable metabolic and absorption of Ni, Co, Cu, Cr, or one percent of Zn and Mn

capabilities, as well as transport systems that can in its leaves on a dry weight basis is called a

take up ions selectively from the soil. Plants hyperaccumulator, regardless of the

have evolved a great diversity of genetic concentration of metals in the soil [2, l0].

adaptations to handle potentially toxic levels of

metals and other pollutants that occur in the Almost all metal-hyperaccumulating species

environment. In plants, uptake of metals occurs known today were discovered on metal-rich soils,

primarily through the root system, in which the either natural or artificial, often growing in

majority of mechanisms to prevent metal toxicity communities with metal excluders [2, 11]. 

are found [4]. The root system provides an Actually, almost all metal-hyperaccumulating

enormous surface area that absorbs and plants are endemic to such soils, suggesting that

accumulates the water and nutrients essential for hyperaccumulation is an important

growth. In many ways, living plants can be ecophysiological adaptation to metal stress and

compared to solar-powered pumps that can one of the manifestations of resistance to metals.

extract and concentrate certain elements from the The majority of hyperaccumulating species

environment [5]. discovered so far are restricted to a few specific

Plant roots cause changes at the soil-root hyperaccumulators are found in New Caledonia,

interface as they release inorganic and organic the Philippines, Brazil, and Cuba. Ni and Zn

compounds (root exudates) in the area of the soil hyperaccumulators are found in southern and

immediately surrounding the roots (the central Europe and Asia Minor.

rhizosphere) [6]. Root exudates affect the

number and activity of microorganisms, the Dried or composted plant residues or plant ashes

aggregation and stability of soil particles around that are highly enriched with metals can be

the root, and the availability of elements. Root isolated as hazardous waste or recycled as metal

exudates can increase (mobilize) or decrease ore. The goal of phytoextraction is to recycle as

(immobilize) directly or indirectly the availability "bio-ores" metals reclaimed from plant ash in

of elements in the rhizosphere. Mobilization and the feed stream of smelting processes. Even if

immobilization of elements in the rhizosphere the plant ashes do not have enough concentration

can be caused by: 1) changes in soil pH; 2) of metal to be useful in smelting processes,

release of complexing substances, such as phytoextraction remains beneficial because it

metal-chelating molecules; 3) changes in reduces by as much as 95 percent the amount of

oxidation-reduction potential; and 4) increase in hazardous waste to be landfilled [14]. Several

microbial activity [7]. research efforts in the use of trees, grasses, and

Phytoremediation technologies can be developed phytoremediation as a cleanup technology. The

for different applications in environmental following paragraphs briefly discuss these three

cleanup and are classified into three types: phytoextraction techniques.

• Phytoextraction The use of trees can result in extraction of

• Phytostabilization high biomass production. However, the use of

1.1 Phytoextraction

geographical locations [2, l0]. For example, Ni

crop plants are being pursued to develop

significant amounts of metal because of their
25

trees in phytoremediation requires long-term phytostabilization in poplar trees, which were

treatment and may create additional selected for the study because they can be deepenvironmental concerns about falling leaves. planted and may be able to form roots below the

When leaves containing metals fall or blow zone of maximum contamination.

away, recirculation of metals to the contaminated

site and migration off site by wind transport or Since most sites contaminated with metals lack

through leaching can occur [15]. established vegetation, metal-tolerant plants are

Some grasses accumulate surprisingly high levels and leaching [16]. However, that approach is a

of metals in their shoots without exhibiting toxic containment rather than a remediation

effects. However, their low biomass production technology. Some researchers consider

results in relatively low yield of metals. Genetic phytostabilization an interim measure to be

breeding of hyperaccumulating plants that applied until phytoextraction becomes fully

produce relatively large amounts of biomass developed. However, other researchers are

could make the extraction process highly developing phytostabilization as a standard

effective; however, such work has not yet begun. protocol of metal remediation technology,

It is known that many crop plants can accumulate does not seem to be economically feasible. After

metals in their roots and aboveground shoots, field applications conducted by a group in

potentially threatening the food chain. For Liverpool, England, varieties of three grasses

example, in May 1980 regulations proposed were made commercially available for

under RCRA for hazardous waste (now codified phytostabilization [5]:

at 40 CFR Part 264) include limits on the

amounts of cadmium and other metals that can • Agrostis tenuis, cv Parys for copper

be applied to crops. Recently, however, the wastes

potential use of crop plants for environmental

remediation has been under investigation. Using • Agrosas tenuis, cv Coginan for acid lead

crop plants to extract metals from the soil seems and zinc wastes

practical because of their high biomass

production and relatively fast rate of growth. • Festuca rubra, cv Merlin for calcareous

Other benefits of using crop plants are that they lead and zinc wastes

are easy to cultivate and they exhibit genetic

stability [14].

1.2 Phytostabilization

Phytostabilization uses plants to limit the wastewater [5], which may include leachate from

mobility and bioavailability of metals in soils. soil. Rhizofiltration uses terrestrial plants instead

Ideally, phytostabilizing plants should be able to of aquatic plants because the terrestrial plants

tolerate high levels of metals and to immobilize develop much longer, fibrous root systems

them in the soil by sorption, precipitation, covered with root hairs that have extremely large

complexation, or the reduction of metal valences. surface areas. This variation of

Phytostabilizing plants also should exhibit low phytoremediation uses plants that remove metals

levels of accumulation of metals in shoots to by sorption, which does not involve biological

eliminate the possibility that residues in processes. Use of plants to translocate metals to

harvested shoots might become hazardous wastes the shoots is a slower process than

[5]. In addition to stabilizing the metals present phytoextraction [16].

in the soil, phytostabilizing plants also can

stabilize the soil matrix to minimize erosion and Another type of rhizofiltration, which is more

migration of sediment. Dr. Gary Pierzynski of fully developed, involves construction of

Kansas State University is studying

used to revegetate such sites to prevent erosion

especially for sites at which removal of metals

1.3 Rhizofiltration

One type of rhizofiltration uses plant roots to

absorb, concentrate, and precipitate metals from
26

wetlands or reed beds for the treatment of technology is cost-effective for the treatment of

contaminated wastewater or leachate. The large volumes of wastewater that have low

concentrations of metals [16]. Since

rhizofiltration focuses on treatment of

contaminated water, it is not discussed further in

this report.

Table 5 presents the advantages and

disadvantages of each of the types of

phytoremediation currently being researched that

are categorized as either phytoextraction on

phytostabilization [5].

TABLE 5

TYPES OF PHYTOREMEDIATION TECHNOLOGY:

ADVANTAGES AND DISADVANTAGES

TYPE OF

PHYTOREMEDIATION ADVANTAGES DISADVANTAGES

Phytoextraction by trees High biomass production Potential for off-site migration

and leaf transportation of metals

to surface

Metals are concentrated in plant

biomass and must be disposed of

eventually.

Phytoextraction by grasses High accumulation Low biomass production and

slow growth rate

Metals are concentrated in plant

biomass and must be disposed of

eventually.

Phytoextraction by crops High biomass and increased Potential threat to the food chain 

growth rate through ingestion by herbivores 

Metals are concentrated in plant

biomass and must be disposed of

eventually.

Phytostabilization No disposal of contaminated Remaining liability issues,

biomass required including maintenance for

indefinite period of time 

(containment rather than

removal)

Rhizofiltration Readily absorbs metals Applicable for treatment of water

only

Metals are concentrated in plant

biomass and must be disposed of

eventually.
27

1.4 Future Development 3.0 PERFORMANCE AND COST

Faster uptake of metals and higher yields of

metals in harvested plants may become possible Currently, because it has not been used in any

through the application of genetic engineering full scale applications, the potential of

and/or selective breeding techniques. Recent phytoremediation for cleanup of contaminated

laboratory-scale testing has revealed that a sites cannot be completely ascertained. 

genetically altered species of mustard weed can However, a variety of new research approaches

uptake mercuric ions from the soil and convert and tools are expanding understanding of the

them to metallic mercury, which is transpired molecular and cellular processes that can be

through the leaves [23, 24, 25]. Improvements in employed through phytoremediation [3].

phytoremediation may be attained through

research and a better understanding of the

principles governing the processes by which

plants affect the geochemistry of their soils. In Potential for phytoremediation (phytoextraction)

addition, future testing of plants and microflora can be assessed by comparing the concentration

may lead to the identification of plants that have of contaminants and volume of soil to be treated

metal accumulation qualities that are far superior with the particular plant's seasonal productivity

to those currently known [17]. of biomass and ability to accumulate

2.0 OVERVIEW OF STATUS

Plants have been used to treat wastewater for be effective remediation systems, one ton of

more than 300 years, and plant-based plant biomass, costing from several hundred to a

remediation methods for slurries of dredged few thousand dollars to produce, must be able to

material and soils contaminated with metals have treat large volumes of contaminated soil. For

been proposed since the mid-1970s [1, 13]. metals that are removed from the soil and

Reports of successful remediation of soils accumulated in aboveground biomass, the total

contaminated with metals are rare, but the amount of biomass per hectare required for soil

suggestion of such application is more than a cleanup is determined by dividing the total

decade old, and progress is being made at a weight of metal per hectare to be remediated by

number of pilot test sites [11]. Successful the accumulation factor, which is the ratio of the

phytoremediation must meet cleanup standards in accumulated weight of the metal to the weight of

order to be approved by regulatory agencies. the biomass containing the metal. The total

No full-scale applications of phytoremediation productivity of the plant (tons[t]/hectare[ha]/

have been reported. One vendor, Phytotech, Inc., year[yr]) to determine the number of years

is developing phytostabilization for soil required to achieve cleanup standards--a major

remediation applications. Phytotech also has

patented strategies for phytoextraction and is

conducting several field tests in Trenton, New

Jersey and in Chernobyl, Ukraine [14]. Also, as

was previously mentioned, a group in Liverpool,

England has made three grasses commercially

available for the stabilization of lead, copper, and

zinc wastes [5]. 

SUMMARY

3.1 Results of Testing

contaminants. Table 6 lists selected examples of

plants identified as metal hyperaccumulators and

their native countries. [10, 12]. If plants are to

biomass per acre then can be divided by the

determinant of the overall cost and feasibility of

phytoremediation [3].

As discussed earlier, the amount of biomass is

one of the factors that determines the practicality

of phytoremediation. Under the best climatic

conditions, with irrigation, fertilization, and other

factors, total biomass productivity can approach

100 t/ha/yr. One unresolved issue is the trade-off

between accumulation of toxic elements and

productivity [20]. In practice, a maximum

harvest biomass yield of 10 to 20
28

TABLE 6

EXAMPLES OF METAL HYPERACCUMULATORS

METAL PLANT SPECIES (%) LOCATION

PERCENTAGE OF

METAL IN DRY

WEIGHT OF

LEAVES NATIVE

Zn Thlaspi calaminare <3 Germany

Viola species 1 Europe

Cu Aeolanthus biformifolius 1 Zaire

Ni

Phyllanthus serpentinus 3.8 New Caledonia

Alyssum bertoloni and 50 other >3 Southern Europe and

species of alyssum Turkey

Sebertia acuminata 25 (in latex) New Caledonia

Stackhousia tryonii 4.1 Australia

Pb Brassuca juncea <3.5 India

Co Haumaniastrum robertii 1 Zaire

t/ha/yr is likely, particularly for plants that treatment [5]. One objective of field tests is to

accumulate metals. use commercially available agricultural

These values for productivity of biomass and the reduce costs. Therefore, in addition to their

metal content of the soil would limit annual remediation qualities, the agronomic

capacity for removal of metals to approximately characteristics of the plants must be evaluated.

10 to 400 kg/ha/yr, depending on the pollutant,

species of plant, climate, and other factors. For a The processing and ultimate disposal of the

target soil depth of 30 cm (4,000 t/ha), this biomass generated is likely to be a major

capacity amounts to an annual reduction of 2.5 to percentage of overall costs, particularly when

100 mg/kg of soil contaminants. This rate of highly toxic metals and radionuclides are present

removal of contamination often is acceptable, at a site. Analysis of the costs of

allowing total remediation of a site over a period phytoremediation must include the entire cycle of

of a few years to several decades [3]. the process, from the growing and harvesting of

3.2 Cost

The practical objective of phytoremediation is to cleanup costs at a site. Phytoremediation also

achieve major reductions in the cost of cleanup may be used as a follow-up technique after areas

of hazardous sites. Salt and others [5] note the having high concentrations of pollutants have

cost-effectiveness of phytoremediation with an been mitigated or in conjunction with other

example: Using phytoremediation to clean up remediation technologies, making cost analysis

one acre of sandy loam soil to a depth of 50 cm more difficult.

typically will cost $60,000 to $100,000,

compared with a cost of at least $400,000 for

excavation and disposal storage without

equipment and supplies for phytoremediation to

the plants to the final processing and disposal of

the biomass. It is difficult to predict costs of

phytoremediation, compared with overall
29

3.3 Future directions

Because metal hyperaccumulators generally and as sources of genes for classical

produce small quantities of biomass, they are plant breeding and molecular genetic

unsuited agronomically for phytoremediation. engineering.

Nevertheless, such plants are a valuable store of

genetic and physiologic material and data [1]. • Field evaluation and validation: 

To provide effective cleanup of contaminated Research is being conducted to employ

soils, it is essential to find, breed, or engineer early and frequent field testing to

plants that absorb, translocate, and tolerate levels accelerate implementation of

of metals in the 0.1- to 1.0-percent range. It also phytoremediation technologies and to

is necessary to develop a methodology for provide data to research programs. 

selecting plants that are native to the area. Standardization of field-test protocols

Currently, phytoremediation is generally not to real problems also are needed.

commercially available (although three grasses

are commercially available for the stabilization of Research in this area is expected to grow over the

lead, copper, and zinc wastes [5]). Relatively next decade as many of the current engineering

few research projects and field tests of the technologies for cleaning surface soil of metals

technology have been conducted. An integrated are costly and physically disruptive. 

approach that involves basic and applied Phytoremediation, when fully developed, could

research, along with consideration of safety, result in significant cost savings and in the

legal, and policy issues, will be necessary to restoration of numerous sites by a relatively

establish phytoremediation as a practicable noninvasive, solar-driven, in situ method that, in

cleanup technology [1]. some forms, can be aesthetically pleasing [1].

According to a 1994 DOE report titled

"Summary Report of a Workshop on

Phytoremediation Research Needs," three broad Phytoremediation is in the early stage of

areas of research and development can be development and is being field tested at various

identified for the in situ treatment of soil sites in the U.S. and overseas for its effectiveness

contaminated with metals [3]: in capturing or stabilizing metals, including

• Mechanisms of uptake, transport, and performance data are currently available.

accumulation: Research is needed to Phytoremediation has the potential to develop

develop better understanding of the use into a practicable remediation option at sites at

of physiological, biochemical, and which contaminants are near the surface, are

genetic processes in plants. Research on relatively nonleachable, and pose little imminent

the uptake and transport mechanisms is threat to human health or the environment [1]. 

providing improved knowledge about The efficiency of phytoremediation depends on

the adaptability of those systems and the characteristics of the soil and the

how they might be used in contaminants; these factors are discussed in the

phytoremediation. sections that follow.

• Genetic evaluation of

hyperaccumulators: Research is being

conducted to collect plants growing in The effectiveness of phytoremediation generally

soils that contain high levels of metals is restricted to surface soils within the rooting

and screen them for specific traits useful zone. The most important limitation to

in phytoremediation. Plants that tolerate phytoremediation is rooting depth, which can be

and colonize environments polluted with 20, 50, or even 100 cm, depending on the plant

metals are a valuable resource, both as

candidates for use in phytoremediation

and subsequent application of test results

4.0 ANALYSIS OF APPLICATIONS

radioactive wastes. Limited cost and

4.1 Site Conditions
30

and soil type. Therefore, one of the favorable most heavily contaminated soils do not allow

site conditions for phytoremediation is plant growth without the addition of soil

contamination with metals that is located at the amendments. Unfortunately, one of the most

surface [3]. difficult metal cations for plants to translocate is

The type of soil, as well as the rooting structure of remediation. Although significant uptake of

of the plant relative to the location of lead has not yet been demonstrated, one

contaminants can have strong influence on researcher is experimenting with soil

uptake of any metal substance by the plant. amendments that make lead more available for

Amendment of soils to change soil pH, nutrient uptake [5].

compositions, or microbial activities must be

selected in treatability studies to govern the Capabilities to accumulate lead and other metals

efficiency of phytoremediation. Certain are dependent on the chemistry of the soil in

generalizations can be made about such cases; which the plants are growing. Most metals, and

however, much work is needed in this area [1]. lead in particular, occur in numerous forms in the

Since the amount of biomass that can be soil, not all of which are equally available for

produced is one of the limiting factors affecting uptake by plants [1]. Maximum removal of lead

phytoremediation, optimal climatic conditions, requires a balance between the nutritional

with irrigation and fertilization of the site, should requirements of plants for biomass production

be considered for increased productivity of the and the bioavailability of lead for uptake by

best plants for the site [3]. plants. Maximizing availability of lead requires

4.2 Waste Characteristics

Sites that have low to moderate contamination and vigor of plants [1].

with metals might be suitable for growing

hyperaccumulating plants, although the

lead, which is present at numerous sites in need

low pH and low levels of available phosphate

and sulfate. However, limiting the fertility of the

soil in such a manner directly affects the health

5.0 REFERENCES

The following vendors were contacted during the preparation of this report:

CONTACTS

Name Company/Research Center Telephone Number

Burt Ensley Phytotech, Inc. (908) 438-0900

One Deer Park Drive

Suite 1 

Monmouth Junction, NJ 08852 

Dr. S. Cunningham Central Research (302) 451-9940

and Development 

DuPont Glasgow, Suite 301

Newark, DE 19714
31

LITERATURE CITED

1. Cunningham, S.D. and W.R. Berti. 1993. "Remediation of Contaminated Soils with Green

Plants: An Overview." In Vitro Cell. Dev. Biol. Tissue Culture Association. Volume 29. 

Pages 207-212.

2. Raskin, I. and others. 1994. "Bioconcentration of Metals by Plants." Environmental

Biotechnology. 5:285-290.

3. U.S. Department of Energy. 1994. Summary Report of a Workshop on Phytoremediation

Research Needs. Santa Rosa, California. July 24-26.

4. Goldsbrough, P. and others. 1995. "Phytochelatins and Metallothioneins: Complementary

Mechanisms for Metal Tolerance?" Abstract Book: Fourteenth Annual Symposium 1995

in Current Topics in Plant Biochemistry, Physiology and Molecular Biology. Pages

15-16.

5. Salt, D.E. and others. 1995. "Phytoremediation: A Novel Strategy for the Removal of Toxic

Metals from the Environment Using Plants." Biotechnology. Volume 13. May. Pages

468-474.

6. Kumar, P.B.A. and others. 1995. "Phytoextraction: The Use of Plants to Remove Metals from

Soils." Environmental Science & Technology. Volume 29. Pages 1232-1238.

7. Morel, I.L. 1995. "Root Exudates and Metal Mobilization." Abstract Book: Fourteenth Annual

Symposium 1995 in Current Topics in Plant Biochemistry, Physiology and Molecular

Biology. Pages 31 -32.

8. Farago, M. 1981. "Metal-Tolerant Plants." Chemtech. Pages 684-687.

9. Smith, I.A.C., U. Kramer, and A.l.M. Baker. 1995. "Role of Metal Transport and Chelation in

NickelHyperaccumulation in the Genus Alyssum." Abstract Book: Fourteenth Annual

Symposium 1995 in Current Topics in Plant Biochemistry, Physiology and Molecular

Biology. Pages 11-12.

10. Baker, A.l.M. and R.R. Brooks. 1989. "Terrestrial Higher Plants Which Hyperaccumulate

Metallic Elements - A Review of Their Distribution, Ecology, and Phytochemistry." 

Biorecovery. Volume 1. Pages 81-126.

11. Baker, A.J.M. 1995. "Metal Hyperaccumulation by Plants: Our Present Knowledge of

Ecophysiological Phenomenon." Abstract Book: Fourteenth Annual Symposium 1995 in

Current Topics in Plant Biochemistry, Physiology and Molecular Biology. Page 7.

12. Baker, A.J.M., R.R. Brooks, and R.D. Reeves. 1989. "Growing for Gold...and Copper...and

Zinc." New Scientist. Volume 1603. Pages 44-48.

13. Cunningham, S.D. and C.R. Lee. "Phytoremediation: Plant-based Remediation of Contaminated

Soil and Sediments." Prepared for 1994 Publication the Soil Science Society of America

from Proceedings of a Symposium in Chicago, Illinois. November 1993.
32

14. King Communications Group, Inc. 1995. "Promise of Heavy Metal Harvest Lures Venture

Funds." The Bioremediation Report. Volume 4, Number 1. Washington, D.C. January.

15. PRC Environmental Management, Inc. (PRC). l995. Interview about phytoremediation between

Dana H. Mun, Chemical Engineer, PRC, and Dr. A.J.M. Baker, Scientist. June 8.

16. Ensley, B.D. 1995. "Will Plants Have a Role in Bioremediation?" Abstract Book: Fourteenth

Annual Symposium 1995 in Current Topics in Plant Biochemistry, Physiology and

Molecular Biology. Pages 1-2.

17. PRC. l995. Record of telephone conversation about phytoremediation between Dana H. Mun,

Chemical Engineer, PRC, and S.D. Cunningham, Scientist, Central Research and

Development, E.I. du Pont de Nemours and Company. June 26.

18. Chaney, R.L. and J.S. Angel. 1994. "Green Remediation: Potential Use of Hyperaccumulator

Plant Species to Phyto-remediate Soils Polluted with Zinc and/or Cadmium" (The Revival

Field Project).

19. Berti, W.R. and S.D. Cunningham. 1993. "Remediating Soil Pb With Green Plants." Presented

at the International Conference of the Society for Environmental Geochemistry and

Health. New Orleans, Louisiana. July 25-27.

20. Parry, I. 1995. "Plants Absorb Metals." Pollution Engineering. February. Pages 40-41.

21. Cunningham, Scott D. and David W. Ow. 1996. “Promises and Prospects of Phytoremediation.” 

Plant Physiology. Volume 110. Pages 715-719.

22. Vasudev, Dev and others. 1996. "Removal of Radionuclide Contamination from Water by Metal

Accumulating Terrestrial Plants." Prepared for presentation at the Spring National

Meeting at New Orleans, Louisiana. February 25-29. Unpublished.

23. Rugh, Clayton and others. 1996. "Mecuric Ion Reduction and Resistance in Transgenic

Arabidopsis Thaliana Plants Expressing a Modified Bacterial MerAGene." Proceedings

of the National Academy of Sciences. Volume 93. April 1996. Pages 3182-3187.

24. "Phytoremediation Gets to the Root of Soil Contamination." 1996. The Hazardous Waste

Consultant. May/June.

25. Langreth, Robert. 1996. "Altered Weeds Eat Mercury Particles in Lab Experiments on Toxic

Waste." The Wall Street Journal. April 16.
33

STATUS OF SOIL FLUSHING

TECHNOLOGY

One approach to treating contaminated sites is chemically [3]. Numerous soil factors affect

physical separation and removal of the sorption of metals and their migration in the

contaminants from the soil. Physical separation subsurface. Such factors include pH, soil type,

can be achieved in situ by introducing a fluid to cation exchange capacity (CEC), particle size,

the soil that will flush out the contaminants, permeability, specific types and concentrations of

leaving the soil matrix intact. In situ soil metals, and types and concentrations of organic

flushing is the extraction of contaminants from and inorganic compounds in solutions. 

the soil with water or other suitable aqueous Generally, as the soil pH decreases, solubility

solutions. In situ soil flushing has been used and mobility of cationic metals increase. In most

most often at sites contaminated with organics. cases, mobility and sorption of a metal are likely

This chapter focuses on the application of in situ to be controlled by clay content in the subsoils

soil flushing to sites contaminated with metals. and by the organic fraction in topsoils. Clays can

Table 7 presents an overview of soil flushing reported that surface soils high in organic matter

technology. retained significantly more metal than subsurface

1.0 DESCRIPTION

Soil flushing techniques promote mobility and CEC, which measures the extent to which

migration of metals by solubilizing the cations in the soil can be exchanged, often is

contaminants so that they can be extracted. Soil used as an indication of a soil's capacity to

flushing is an in situ process that is accomplished immobilize metals [6].

by applying the flushing fluid to the surface of

the site or injecting it into the contaminated zone. Once the infiltrated or percolated solution has

The resulting leachate then typically is recovered flushed the contaminants to a certain location,

from the underlying groundwater by the contaminated fluids must be extracted. 

pump-and-treat methods. Figure 8 presents Extraction techniques include vacuum extraction

schematics of different soil flushing systems [1, methods in the vadose zone and pump-and-treat

2]. systems in the saturated zone.

Soil flushing can solubilize contaminants using Recovered groundwater and flushing fluids

either water as the flushing fluid or chemical containing the desorbed contaminants may

additives to enhance the solubility of the require treatment to meet appropriate discharge

contaminant. Water alone can be used to remove standards before such fluids are recycled or

certain water-soluble contaminants (for example, released to publicly owned wastewater treatment

hexavalent chromium). The use of soil flushing works or receiving streams. If state regulations

chemicals may involve adjusting the soil pH, so allow, recovered fluids should be reused in the

chelating metal contaminants, or displacing toxic flushing process to reduce disposal costs.

cations with nontoxic cations. The in situ

flushing process requires that the flushing fluids The treatment system will be configured to

be percolated through the soil matrix. The fluids remove specific contaminants of concern. For

can be introduced by surface flooding, surface treatment of inorganics, the system may include

sprinklers, leach fields, vertical or horizontal standard precipitation systems, electrochemical

injection wells, basin infiltration systems, or exchange, ion exchange, or ultrafiltration

trench infiltration systems. systems. The contaminants of concern may

Several chemical and physical phenomena

control the mobility of metals in soils. The

finer-sized soil fractions (clays, silts, iron and

manganese oxides, and organic matter in soil)

can bind metals electrostatically as well as

adsorb metals present in the soils. It has been

soils that contained less organic matter [4]. 

Organic matter in soil is of significant

importance because of its effect on CEC [5]. 
34

TABLE 7

OVERVIEW OF SOIL FLUSHING TECHNOLOGY

General Characteristics

• Best used in soils with high permeability.

• Different delivery systems available to introduce flushing solutions.

• Cost is primarily influenced by potential need for interim containment, the depth of contamination,

and the time required for operation.

• Associated risk of contamination of underlying aquifer with unrecovered flushing solution that

contains solubilized contaminants; best used at sites with aquifers that have low specific yields.

Approach #1 - Water flushing Approach #2 - Reagent flushing

Description: Use of water to solubilize the Description: Use of a chemical reagent to

contaminants prior to extraction. solubilize the contaminants for extraction.

Status: Commercial. Status: Limited research.

Applicability: Chromium (VI); potentially Applicability: Bench-scale: lead, uranium.

applicable for other water-soluble metals.

Comments: Applicable only for water-soluble Comments: 

metals; focus of water flushing often is on - Some small-scale testing has been conducted

organics. In situ flushing has been selected at 4 with chelators as the primary reagent for

Superfund sites at which soils are contaminated removal of metals from soils; the results of

with metals (most of the sites also are those tests have not led to further testing on a

contaminated with organics). larger scale.

- pH adjusters and chemical binders also are

being studied for potential applicability to

metals.

- Surfactants are primarily targeted for removal

of organic contaminants.
35

Figure 8. Typical Soil Flushing System (Surface Sprinklers)

include organics and inorganics in the same with metals. Most information is related to

waste stream. In posttreatment, once the treatment of organic contaminants rather than

recovery system (that is, pump-and-treat system) metals. Soil flushing has been selected at seven

has been shut down, it may be necessary to Superfund sites which contain metals. At two

control infiltration through the use of caps or sites, Lipari Landfill in New Jersey and the

covers to prevent further migration of residual United Chrome Products site in Oregon, in situ

contaminants. soil flushing is operational [7]. At one other site,

2.0 OVERVIEW OF STATUS

For treatment of metals, soil flushing has been [7].

employed for a limited number of projects, using

the treated effluent from a pump-and-treat One literature reference summarizes a

operation for reinjection and improved bench-scale soil flushing technology called metal

mobilization of contaminants. The use of extraction that was developed by Scientific

chelating additives for treating metals in soil has Ecology Group, Inc. of Pittsburgh, Pennsylvania

not yet been found to be effective. for removing heavy and radioactive metals from

Limited information is available on the use of displacement [10]. Another literature reference

soil flushing to remediate soils contaminated describes the bench-scale use of organic and

in situ soil flushing is listed as the technology in

design, and at four other sites, in situ flushing is

listed as the technology in the predesign stage

soil and groundwater through cation
36

inorganic flushing agents to remove lead from in Organic and inorganic flushing agents to remove

situ soils. Solutions of hydrochloric acid (HCl), lead have been tested on a small scale. In a

ethylenediamine tetraacetic acid (EDTA), and bench-scale experiment, contaminated soil

calcium chloride (CaCl ) were used as flushing columns (coarse, sandy loam with a favorable 2

agents [3]. A third literature reference describes hydraulic conductivity and relatively low organic

an ongoing, full-scale in situ soil flushing content) were flushed separately with solutions

technology that uses water as the flushing agent of 0.1 moles per liter (M) HCl, 0.01 M EDTA,

to treat chromium [8]. The information in these and 1.0 M CaCl . Each soil column was packed

representative references is summarized in the under saturated conditions by maintaining the

following paragraphs. water level above each successive soil layer

2.1 Cation Displacement

The metal extraction method is based on EDTA were used as flushing solutions, the pH

demonstrated in situ uranium mining technology. levels of the effluent appeared to be related

Continuous injection and recapture of an directly to the rate of removal of lead. The

extraction solution flushes heavy or radioactive mechanisms of lead removal appeared to be

metals from the subsurface. The metal extraction desorption caused by a decrease in pH,

process consists of the following steps [11]: dissolution of Pb(OH) or other lead precipitates,

• Introduction of extraction solution: The EDTA, and CaCl , respectively [3].

remedial process begins with the

injection of a solution containing This approach is not practical for use in full scale

sufficient cation concentrations to applications due to the high costs of reagents.

displace the contaminants from the soil.

• Removal of contaminants: The solution

migrates through the treatment zone, A full-scale in situ soil flushing technology is

selectively displacing the target being implemented at the United Chrome

contaminants. Cations that occur Products site, a Superfund site in Corvallis,

naturally, or that are present in the Oregon. The site is a former industrial

extraction solution, remain in the soil. hard-chrome electroplating shop. Leaks from

• Recovery of solution: The contaminated into a disposal pit during the shop's operation

solution is pumped to surface equipment from 1956 to 1985 contaminated soil and

through a network of recovery wells. A groundwater underlying the facility. 

subsequent treatment process Contamination of soil at levels higher than

precipitates the contaminants. 60,000 mg/kg chromium and contamination of

• Stabilization of residual contaminants: chromium were detected in areas adjacent to the

If necessary, a stabilizing solution is plating tanks. In 1985, EPA began remediation

injected after soil flushing has been activities that have continued to the present time

completed. The solution reacts with the (1996). Those activities include construction of

remaining contaminants, produces an two infiltration basins to flush contaminated

immobile species, and prevents further soils, a 23-well groundwater extraction network

migration of residual metals. in low-permeability soils, and an injection and

2.2 Lead Removal

2

during the packing procedures. Significant

amounts of lead were removed from the soil

when HCl and EDTA were used. When HCl and

2

metal chelation, and cation exchange for HCl,

2

2.3 Chrome Flushing

plating tanks and the discharge of rinse water

groundwater at levels exceeding 19,000 mg/L

groundwater extraction network in a deep gravel

aquifer, as well as on-site treatment of

wastewaters containing high concentrations of

chromium [8].
37

At this site, Cr(III) is found in high Another type of groundwater recharge used at the

concentrations in the soils of the upper zone, but, site is water injection. To reverse the downward

because of its very low solubility, it is only a vertical gradient present between the upper zone

minor groundwater contaminant. In contrast, and the deep aquifer, clean water has been

Cr(VI), a potential carcinogen, is found in high injected into the deep aquifer through two wells

concentrations in the upper zone, aquitard soils, [9].

and groundwater, because of its high solubility in

water. EPA has established a maximum

concentration level (MCL) of 0.05 mg/L (total

chromium) as a drinking-water standard. Thus In 1993, the Twin Cities Army Ammunition

far, chromium levels in groundwater have been Plant (TCAAP) soil remediation demonstration

reduced from more than 5,000 mg/L to less than project for removal and recovery of metals (lead

50 mg/L in areas of high concentration [8]. was the main contaminant) began in New

This in situ, full-scale cleanup is unique because: the COGNIS TERRAMET process and was the

1) soil flushing has been applied in first project in which cleaned soil from a soil

low-permeability silt soil, 2) both the shallow washing process was returned on-site. Although

and deep aquifer have been treated, and 3) the COGNIS process currently is operated as a

flushing of the clay aquitard has been soil washing system rather than an in situ soil

accomplished indirectly by using the deep flushing technology, research is being considered

aquifer injection wells in conjunction with the to assess the viability of adapting the COGNIS

upper zone extraction wells to create upward process for in situ remediation applications [10]. 

vertical gradients. No process water is discharged during operation

Three methods of infiltration have been within the plant. Targets for removal of lead

employed: infiltration basins, an infiltration were not achieved; therefore, the treatment was

trench, and injection wells. The two basins are only partially successful.

abovegrade structures that have open bottoms

that permit infiltration of water to the underlying

soils. They were placed at the sites of the highest

observed levels of soil contamination (the former

plating tank and disposal pit areas) [8]. The According to Scientific Ecology Group, Inc., the

basins have been successful in delivering water metal extraction technology demonstrates

to the upper zone, averaging approximately removal efficiencies as high as 90 percent. 

7,600 gallons per day in Basin No. 1 and 3,000 Concentrations of uranium in groundwater of 5

gallons per day in Basin No. 2 during the dry to 20 mg/L were reduced to 1 to 2 mg/L. 

summer months. During the winter months, Groundwater contaminated with 250 to 500

infiltration rates decrease to 50 percent or less of mg/L of ammonium contained only 10 to 50

the summer rates [8]. mg/L after treatment [11].

The infiltration trench was constructed In the soil column experiment, initial

approximately 22 months after the project began. concentrations of lead during the bench-scale

The trench is positioned and operated primarily study were 500 to 600 mg/kg. Lead removal

to increase discharge rates of the extraction wells efficiencies for HCl, EDTA, and CaCl were 96,

along the longitudinal axis of the plume during 93, and 78 percent, respectively. In the soil used

the dry summer months. The trench is in the study, background concentrations of lead

approximately 100 feet long and 8 feet deep, and were approximately 20 mg/kg. Final

a float valve maintains the water level at 4 feet concentrations of lead, after flushing with the

below grade. Infiltration rates have averaged three test solutions, were 23.3 mg/kg (HCl), 37.8

2,500 gallons per day [8]. mg/kg (EDTA), and 135.6 mg/kg (CaCl ) [3]. It

2.4 Twin Cities Army Ammunition Plant

Brighton, Minnesota. The TCAAP project used R

of the COGNIS process; all leachant is recycled

3.0 PERFORMANCE AND COST

SUMMARY

2

2

should be noted that, if the soils contain
38

relatively high levels of calcium, substantial According to the developers of the metal

amounts of the HCl flushing solution would be exchange process, the cost of such a project is

consumed in neutralization reactions. estimated to be approximately 50 percent of that

At the United Chrome Products site, the use of

water as a flushing solution to remove chromium Because in situ soil flushing has had only limited

(VI) from in situ soils appears to be a successful field application, it is difficult to obtain

treatment option. The full-scale cleanup has comprehensive, detailed estimates of the cost of

achieved hydraulic containment of the plume, this treatment technology. The factors that most

while extracting significant amounts of significantly affect costs are the initial and target

chromium from the subsurface. Table 8 presents concentrations of contaminants, permeability of

a summary of recent available performance data the soil, and depth of the aquifer [11].

[13].

The performance of the two infiltration basins solubilization (CES) are similar to those for

constructed at the United Chrome Products site traditional pump-and-treat systems, except for

has been confirmed by the increase in pumping the initial expense of equipment needed to

rates and concurrent decreases in concentrations handle the flushing solution. Operating costs

of Cr(VI) observed in the extraction wells around also are similar, except for the cost of handling

the basins. In many of the wells, pumping rates and replacement of flushing solutions and

have increased from less than 0.5 gallon per additives. Overall, for the life of the treatment

minute (gpm) to 2 or more gpm [8]. process, CES should be significantly less

Concentrations of Cr(VI) decreased from more expensive than pump-and-treat systems because

than 2,000 mg/L to approximately 18 mg/L [13]. of the much shorter time frames for treatment

of a typical pump-and-treat method.

Capital costs for chemically enhanced

and smaller volumes of water to be extracted and

treated [2].

TABLE 8

UNITED CHROME PRODUCTS SUPERFUND SITE

EXTRACTION AND TREATMENT SYSTEM SUMMARY

AUGUST 1988 THROUGH DECEMBER 1995

Parameter Total Daily Average

Groundwater Extracted 58,000,000 gal 11,400 gal

Influent Cr (VI) Concentration 146 mg/L to 1,923 mg/L

Range

Mass of Cr (VI) Removed 31,200 lb 41 lb

Infiltration Recharge 4,700,000 gal 8,000 gal

Average Effluent Cr (VI) 1.7 mg/L (monthly)

Concentration
39

A hypothetical analysis in a recent engineering

monograph on soil washing and soil flushing

compares cost and time estimates for CES with

those for pump-and-treat systems. Based on

interpretation of data from a test site, the

effective aqueous solubility of a contaminant

was compared to the amount of flushing solution

needed to solubilize the contaminant. The pore

volumes required by the two systems to attain

similar levels of cleanup differed dramatically;

the CES system would require 21 pore volumes

and the pump-and-treat system would require

more than 2,000 pore volumes. Likewise, the

time frames for treatment using the two systems

also differed. Using the specified injection rates

of the two systems to calculate time required for

treatment, the CES system would require 4 years

and the pump-and-treat system would require

400 years. [2]. 

4.0 ANALYSIS OF APPLICATIONS

The performance of an in situ soil flushing

system depends largely upon the amount of

contact achieved between the flushing solution

and the contaminants. The appropriateness of

the flushing solution, the soil adsorption

coefficients of the contaminants, and the

permeability of the soil are also key factors. 

Best results will be achieved in highly permeable

soils.

The following types of data are required to

support selection of the flushing solution and to

predict the effectiveness of soil flushing:

• Soil hydrogeology (physical and

chemical properties of the soil),

subsurface vertical and horizontal flow

and velocity, characteristics of the

aquifer, and vadose zone saturation

• Areal and vertical concentration

gradients for contaminants. 

Effective application of the process requires a

sound understanding of soil chemistry (the

manner in which target contaminants are bound

to soil), relative permeability, and hydrogeology. 

In general, soil flushing is most effective in

homogeneous, permeable soils (sands and silty

sands with permeabilities greater than 1x 10-3

centimeters per second [cm/sec]). The

relationships among capillary processes, water

content, and hydraulic conductivity must be

understood before any flushing solution can be

used effectively. In addition, because soil

flushing increases the mobility of contaminants,

the hydrology of the site must be well

understood.

5.0 REFERENCES

The following vendors were contacted during the preparation of this report:

CONTACTS

Name Agency/Company Telephone Number

Donald R. Justice Horizontal Technologies, Inc. 813/995-8777

(Soil Flushing- In Situ)

Ken Wyatt Surtek, Inc. 303/278-0877

(Soil Flushing - In Situ

Surfactant Enhanced Recovery)
40

LITERATURE CITED

1. DoD Environmental Technology Transfer Committee. 1994. "Remediation Technologies

Screening Matrix and Reference Guide." EPA/542/B-94/013, NTIS PB95-104782.

2. American Academy of Environmental Engineers. 1993. "Innovative Site Remediation

Technology: Soil Washing/Soil Flushing."

3. Moore, Roderic E. and Mark R. Matsumoto. 1993. "Investigation of the Use of In-Situ Soil

Flushing to Remediate a Lead Contaminated Site." Hazardous and Industrial Waste:

Proceedings, Mid-Atlantic Industrial Waste Conference. Technical Publishing Company,

Inc. Lancaster, Pennsylvania.

4. Semu, E., B.R. Singh, and A.R. Selmer-Olsen. 1987. "Adsorption of Mercury Compounds by

Tropical Soils." Water, Air, and Soil Pollution. Volume 32, Number 1-10.

5. Elliot, H.A., M.R. Liberati, and C.P. Chuang. 1986. "Competitive Adsorption of Metals by

Soils." Journal of Environmental Quality. Volume 15, Number 3.

6. Dragun, J. 1988. "The Soil Chemistry of Hazardous Materials." Presented at a Meeting of the

Hazardous Materials Control Research Institute. Silver Spring, Maryland.

7. EPA. 1995. "Innovative Treatment Technologies: Annual Status Report." Seventh Edition. 

September. EPA-542-R-95-008.

8. McPhillips, Loren C. and others. 1991. "Case History: Effective Groundwater Remediation at

the United Chrome Superfund Site." Prepared for presentation at the 84th Annual

Meeting and Exhibition of the Air and Waste Management Association. Vancouver,

British Columbia. June 16-21.

9. McKinley, W. Scott and others. 1992. "Cleaning up CHROMIUM." Civil Engineering. Pages

69-71.

10. Fristad, William E. 1995. "Full-scale Soil Washing/Terramet® Soil Leaching." Presented at

Environment Week's Second Annual Soil Remediation Conference: Metals Innovative

Technology Contracting. Washington, D.C. April 24-25.

11. "Innovative In-Situ Cleanup Processes." 1992. The Hazardous Waste Consultant. 

September/October.

12. Cline, S.R. 1993. "Soil Washing Fluid Efficiencies for the Treatment of Lead and Organically

Contaminated Soil." To be Published in the Proceedings of the 48th Annual Purdue

University Industrial Waste Conference. West Lafayette, Indiana.

13. EPA. 1996. “Superfund Fact Sheet: United Chrome Products Inc. Corvallis, Oregon.” June 10.
41

STATUS OF IN SITU

SOLIDIFICATION/STABILIZATION

TECHNOLOGY

Solidification treatment processes change the

physical characteristics of the waste to improve Although many vendors provide S/S

its handling and to reduce the mobility of the technologies for ex situ applications, relatively

contaminants by creating a physical barrier to few companies offer in situ S/S treatment

leaching. Solidification can be achieved through processes. This chapter focuses on the in situ

the use of conventional pozzolans, such as applications of S/S remediation techniques.

Portland cement. Stabilization (or

immobilization) treatment processes convert Table 9 presents an overview of

contaminants to less mobile forms through solidification/stabilization technology.

chemical or thermal interactions.

(Vitrification of soil is an example of a

solidification/stabilization (S/S) process that

employs thermal energy.) S/S treatment

processes can be performed in situ or ex situ.

TABLE 9

OVERVIEW OF SOLIDIFICATION/STABILIZATION TECHNOLOGY

General Characteristics

• Commercially available

• Cost is affected by the depth of the contamination, the degree of homogeneity of soil, the presence

of debris, and excess moisture.

Approach #1 - Reagent-based In Situ Approach #2 - Vitrification

Stabilization

Description: Addition of pozzolanic reagents Description: Use of energy to melt soils and

with or without additives to physically and physically and chemically encapsulate

chemically convert contaminants to less mobile contaminants into less mobile and more stable

forms. forms.

Status: Commercial. Status: Commercial; one firm is licensed.

Applicability: Broad general applicability to most Applicability: Broad general applicability to

metals; applicability to arsenic and mercury most metals.

should be tested on a case-by-case basis. Full-scale: arsenic, lead, chromium.

Hexavalent chromium requires additives that Potential: cadmium, copper, zinc, asbestos,

ensure its conversion to the trivalent state during radioactive metals.

mixing.

Comments: Performance is highly dependent on Comments: It may be necessary to treat, remove,

mixing efficiency. Soils having high clay content or filter mercury or other volatile metals from

or significant debris may be difficult to mix. process off-gases. High moisture content will

Various auger sizes and mixing configurations increase costs substantially. Debris or high

can be used, and various reagents are available. concentrations of organic contaminants may

In situ applications are less common than ex situ decrease performance.

applications because it is difficult to verify

whether mixing is sufficient.
42

1.0 DESCRIPTION

S/S technologies are used to change the physical slurry and decreases the permeability of the

characteristics and leaching potential of waste. treated waste. Silicates form chemical

The term S/S refers to treatment processes that complexes with metals, often providing greater

utilize treatment reagents or thermal energy to insolubility than do hydroxide, carbonate, or

accomplish one or more of the following sulfate precipitates. (Other additives or

objectives [1]: proprietary reagents, such as activated carbon or

• Reduce the mobility or solubility of the semivolatile organic compounds in wastes).

contaminants to levels required by

regulatory or other risk-based standards Wastes containing lead can be stabilized with the

• Limit the contact between site fluids lead phosphate precipitate is insoluble in water. 

(such as groundwater) and the Although solidification of the waste treated with

contaminants by reducing the trisodium phosphate is not necessary to provide a

permeability of the waste, generally to barrier to leaching, it may be done for other

less than 1x10 cm/sec purposes such as providing sufficient bearing -6

• Increase the strength or bearing capacity phosphate is toxic by inhalation. Solidification

of the waste, as indicated by unconfined or other means of encapsulation may be used to

compressive strength (UCS) or measured prevent air-borne particulates from escaping the

by the California bearing ratio treated waste. Alternatively, solidification may

There are two basic types of S/S treatment solutions which could solubilize the lead

processes: reagent-based systems and phosphate.

thermal-based systems. Reagent-based systems

use chemicals to solidify and stabilize the Each of the vendors contacted has a patented

contaminants in the soil matrix. Thermal-based auger consisting of blades or paddles studded

systems use heat to melt the soil to solidify and with injection ports through which the reagent

stabilize the contaminants after cooling. mixture flows. Some vendors emphasize the

1.1 Reagent-based S/S Processes

In situ reagent-based S/S technologies consist of or more mixtures simultaneously. The vendors

a reagent formulation and a delivery system. also differ with respect to the size of injection

With the exception of near-surface applications ports and their operating pressure.

(that is, to depths of 15 feet deep), a reagentbased S/S delivery system usually consists of a Choice of auger diameter varies among the

slurry batch plant, delivery hoses, and one or vendors of reagent-based S/S technologies, but

more augers. Most reagent formulations for in generally depends on depth of drilling,

situ S/S applications consist of ordinary consistency and hardness of the soil, and soil

pozzolanic reagents, although proprietary porosity. For example, augers from 4 to 12 feet

reagents are often used in conjunction with or in diameter generally can be used to a depth of

instead of pozzolanic reagents [7]. Pozzolanic 40 feet. The diameter selected will depend on

mixtures are based on siliceous volcanic ashes the porosity of the soil. Augers of larger

similar to substances used to produce hydraulic diameter may be used in sludges and sands,

cement. Depending on the characteristics of the while silts and clays require augers of a smaller

waste to be treated and the desired properties of diameter. One vendor uses small-diameter

the treated wastes, additives such as bentonite or augers for all depths because large-diameter

silicates may be added to the cement and/or fly augers affect mixing efficiencies. Beyond a

ash mixture. For example, addition of bentonite

increases the ease of pumping of the wet reagent

organophilic clays, can be used to stabilize

addition of trisodium phosphate; the resulting

strength to support a cap. Additionally, lead

be used to provide a barrier to acids or alkaline

kneading and shearing action of their augers,

while other vendors emphasize grout (reagent

mixture) control and the capability to deliver two
43

depth of 35 to 40 feet, a smaller-diameter auger (from 2.5 to 4 feet in diameter) is suggested. 

Using a smaller auger permits treatment to

depths as great as 100 feet or more. Only two of

the five vendors contacted treat soil at depths of

more than 40 feet; however, most soil

contamination is encountered at depths of 10 to

20 feet and only rarely deeper than 40 feet [6]

(although treatment to depths of more than 40

feet is becoming more common).

1.2 Thermal-based S/S Processes

The only thermal-based S/S treatment process

commercially available is in situ vitrification. In

situ vitrification uses electrical power to heat and

melt soils contaminated with organic, inorganic,

and metal-bearing wastes. The molten material

cools to form a hard, monolithic, chemically

inert, stable product of glass and crystalline

material that incorporates and immobilizes the

inorganic compounds and metals. The resultant

vitrified product is a glassy material, with very

low leaching characteristics. Organic wastes

initially are vaporized or pyrolyzed by the

process. Those contaminants migrate to the

surface, where they are treated in an off-gas

treatment system [2].

2.0 OVERVIEW OF STATUS

The vendors that were identified as potential

providers of in situ S/S processes were contacted

to determine whether they have available data

that can be used in the status report for this

technology. Vendors of ex situ stabilization

equipment also were contacted to determine

whether any has made progress in developing an

in situ version of the technology.

A single vendor, Geocon, accounts for most of

the in situ applications reported; however, little

data on applications are available. Each vendor's

system is well established, tracing its roots to

established construction technologies. (Deep soil

mixing and the installation of cement footers and

grout curtains or slurry walls are construction

techniques that have been employed for many

years.) An emerging development for American

vendors is the injection of dry reagents when

high levels of moisture in the soil preclude the

use of liquid reagents. Although this variation of
44

the technology has been employed in Europe for containing glass frit is placed in the soil between

more than 20 years, only one U.S. vendor the electrodes. When power is supplied to the

(Hayward Baker) has used it. Although electrodes, the mixture of graphite and glass frit

conveying dry reagents pneumatically requires conducts the current through the soil, heating the

some expertise, both Millgard and Geocon surrounding area and melting the soil between

currently are experimenting with the technique. and directly adjacent to the electrodes.

It is notable that in situ application of dry

reagents tends to decrease the effective depth of Molten soils are electrically conductive and can

treatment for a given auger diameter and soil continue to transmit the electrical current,

porosity. (Conversely, wet slurries help extend melting soil downward and outward. The

the depth of treatment.) electrodes are lowered further into the soil as the

Only one vendor offers in situ thermal-based S/S process to the desired depth of treatment. One

treatment processes. Geosafe Corporation of setting of four electrodes is referred to as a melt. 

Richland, Washington offers the in situ For the Geosafe system, the melting process

vitrification (ISV) technology commercially. occurs at an average rate of approximately three

Figure 9 is a schematic of the Geosafe ISV to four tons per hour.

process. ISV uses electrical current to heat and

vitrify the contaminated material in place. A

pattern of electrically-conductive graphite

soil becomes molten, continuing the melting
45

Figure 9. Geosafe In Situ Vitrification Process [3]
46

3.0 PERFORMANCE AND COST

SUMMARY

Information on the testing and costs of augers or bid jobs in cases where the depth of

reagent-based and thermal-based S/S processes treatment is 10 feet or less. (Geocon, for

are discussed separately in the following example, uses a backhoe-mounted attachment for

subsections. depths to 10 feet). In addition, auguring requires

3.1 Reagent-based S/S Processes

In most cases involving in situ S/S, the site cost of bringing in backfill can make the cost of

cleanup manager independently contracts with a ex situ treatment competitive with that of in situ

testing laboratory to develop and optimize a S/S.

suitable reagent formulation that will meet the

desired performance objectives for the site of According to the vendors consulted, the cost of

concern. Vendors then submit bids for in situ S/S can range from as low as $20 to $40

delivering the specified formulation in situ. per cubic yard to as much as $100 to $200 per

Occasionally, the vendor of the in situ cubic yard, depending on the volume to be

technology will develop the formulation at the treated, the structure of the soil (porosity), the

bench scale to achieve the desired treatment depth, the type of contaminant, and the

immobilization of contaminants and post-treatment objectives (leachability,

posttreatment permeability and unconfined permeability, or bearing ratio) desired. The low

compressive strength. Therefore, testing at the end of the cost range would apply to solidifying

bench scale consists of optimizing the reagent dredge spoils, while the high end would apply to

formulation. Testing at the pilot or full scale treatment of high concentrations of contaminants

consists of quality control of grout and at great depths. For application at a hazardous

confirmation sampling to determine whether the waste site consisting of sands to silts at a depth

treated material is meeting required performance of 25 feet, $75 to $90 per cubic yard would be

specifications. typical (20 percent of that figure would be the

Although published data generally are limited to

those developed in demonstration projects

sponsored by EPA, in situ S/S is likely to be

effective in reducing leachable concentrations of The Geosafe ISV process was demonstrated

metals to within regulatory or risk-based limits. under the SITE program at the Parsons

The goal of vendors (and site managers) is to Chemical/ETM Enterprises Superfund site in

meet the performance specifications at the lowest Grand Ledge, Michigan from May 1993 to May

cost. Failure to meet the design specifications in 1994. The ISV system that was used at the

the field most often stems from poor grout Parsons site included an air emissions control

control (that is, inconsistently formulated slurries and treatment system to treat the eight-melt

or clogged injection ports that cause incomplete operation. This project was the first application

mixing or a spray pattern that is not uniform). of in situ vitrification at a Superfund site to treat

Interviews with five vendors indicated that costs pesticides, metals, and dioxins.

for in situ S/S are likely to be below ex situ

treatment under certain circumstances. For The Geosafe ISV system used at the Parsons site

contaminated depths of less than eight feet, included eight melt cells and an air emissions

excavation and ex situ treatment are likely to be control system. Because contamination was

cheaper. In situ S/S treatment is likely to be shallow, contaminated soil was excavated and

cheaper for larger volumes because of the high staged at the site. The melt cells were installed

cost of mobilization and demobilization for in in a treatment trench. Eight melts were

situ S/S technologies (four to five times that of

ex situ technologies.) For this reason, vendors of

in situ S/S technologies are not likely to use

a level, stable base. At sites that are not level,

backfill must be brought in to level the site to

support the auguring equipment. Eventually, the

cost of reagent).

3.2 Thermal-based Processes

soils and sediments contaminated with
47

completed, ranging in duration from 10 to 20

days. Mercury concentrations in the treated

waste were reduced by more than 98 percent The most commonly stabilized metal

when compared with untreated soil. In addition, contaminants for reagent-based systems are

TCLP concentrations of arsenic, chromium, lead, chromium, arsenic, and lead, followed by

and mercury in the treated waste were below cadmium, copper, zinc, and mercury. Site

regulatory levels of concern. managers may specify that hexavalent chromium

ISV also subsequently was applied successfully chromium and the second to stabilize it);

the Wasatch Chemical Superfund site, where however, vendors may add reducing agents to

ISV was used to treat dioxin, pentachlorophenol, their formulations to treat hexavalent chromium

pesticides, and herbicides. in one stage.

The major factors affecting cost of ISV are the Limited experience with ISV suggests that it

amount of water present, the treatment zone, should not be recommended at sites at which

depth, combustible waste load, scale of operation organic content in the soil exceeds 10 percent by

and price of electricity. The vendor estimates weight. In addition, it is not recommended at

costs between $375 and $425 per ton, which sites at which metals in the soil exceed 25

makes this process especially suited for hard to percent by weight or where inorganic

treat wastes, such as mixtures of metals and contaminants exceed 20 percent of the soil by

organics. volume. The cost of ISV is influenced

4.0 ANALYSIS OF APPLICATIONS

be treated in two stages (the first to reduce the

principally by the need for electric power, which

increases substantially with increasing moisture

in the soil [8]. 

5.0 REFERENCES

The following vendors were contacted during the preparation of this report:

CONTACTS

Name Agency/Company Telephone Number

Steve Day Geocon (412) 856-7700

David Coleman Millgard Environmental (313) 261-9760

David Yang S.M.W. Seiko (510) 783-4105

George Burke Hayward Baker (410) 551-1995

Neville Kingham Kiber Environmental Services, Inc. (770) 455-3944

Kent Saugier Brown & Root (713) 575-4677

James Hansen Geosafe Corporation (509) 375-0710
48

LITERATURE REFERENCES

1. EPA. 1994. "Selection of Control Technologies for Remediation of Soil Contaminated with

Arsenic, Cadmium, Chromium, Lead, or Mercury." Revised Draft Engineering Bulletin. 

January 31.

2. EPA. 1994. "In Situ Vitrification Treatment." Engineering Bulletin. October.

3. Geosafe Corporation. 1994. "In Situ Vitrification Technology." SITE Technology Capsule. 

November.

4. Member Agencies of the Federal Remediation Technologies Roundtable. 1995. "Remediation

Case Studies: Thermal Desorption, Soil Washing, and In Situ Vitrification." March.

5. Yang, David S., Sigeru Takeshima, Thomas A. Delfino, and Michael T. Rafferty. 1995. "Use of

Soil Mixing at a Metals Site." Proceedings of Air & Waste Management Association, 8th

Annual Meeting. June.

6. Bates, Edward. U.S. Environmental Protection Agency. 1995. Letter to Carl Ma. May 20. 

7. PRC Environmental Management, Inc. 1996. Telephone call with Neville Kingham. August 8.

8. U.S. Environmental Protection Agency. 1995. Geosafe Corporation In Situ Vitrification

Innovative Technology Evaluation Report. Office of Research and Development,

Washington, DC. EPA/540/R-94/520. March. 
APPENDIX A

METHODOLOGY
A-1

METHODOLOGY

Technologies discussed in this report were chosen because they were at or near a point of being

commercially available. The survey work to prepare this report consisted of the following activities:

Literature searches of several on-line databases, including EPA’s Clean Up Information Bulletin

Board (CLU-IN) and Alternative Treatment Technology Information Center (ATTIC) databases

Searches of the EPA record of decision (ROD) database

Searches of back issues of various technical journals and shelf material in EPA’s libraries not

available on-line

Communication with experts at federal agencies, such as DoD, the DOE, and the Bureau of Mines,

who are involved in research and development of environmental restoration technologies

Contacts with technology vendors identified in EPA’s Vendor Information System for Innovative

Treatment Technologies (VISITT)

Interviews with authors of articles relevant to each technology

Several technology vendors and authors identified from the searches were contacted via telephone calls. 

They were asked to comment on the status of the technology, the amount of performance data available

from field applications of the technology, and cost estimates for performing remedial actions with the

technology. Vendors were chosen to contact to provide representative information on different

technologies. Reference information on the vendors contacted is included in each technology chapter. No

attempt was made to identify all vendors and their inclusion or exclusion is purely coincidental. 

Researchers and technical experts that were also contacted are listed on the following pages.
A-2

Researchers and Technical Experts

Name Agency/Company

Electrokinetics

Randy Parker U.S. Environmental Protection Agency (EPA)

National Risk Management

Research Laboratory (NRMRL)

Cincinnati, Ohio

Jack Hubbard EPA NRMRL

Project Manager

(Electrokinetics Technology Site Demonstrations)

Kelly D. Pearce U.S. Department of Energy (DOE)

Project Manager

Gaseous Diffusion Plant

Paducah, KY

Mark Bricka U.S. Army Corps of Engineers Waterways Experiment Station

Vicksburg, MS

Eric R. Lindgren Sandia National Laboratories

P.O. Box 5800

Mailstop 0719

Albuquerque, NM 87185

Ronald F. Probstein Massachusetts Institute of Technology

Department of Mechanical Engineering

Cambridge, MA 02139

Dr. Dennis Kelsh SAIC

Gaithersburg, Maryland
Researchers and Technical Experts

Name Agency/Company

A-3

Phytoremediation

Dr. Alan Baker Department of Animal and Plant Sciences

The University of Sheffield

Sheffield S10 2TN, United Kingdom

E-mail: A.Baker@sheffield.ac.uk

and 100577.1360@compuserve.com

Dr. Gary Pierzynski Department of Agronomy

Kansas State University

Manhattan, KS 66506-5501

Dr. Ilya Raskin AgBiotech Center and Department of Environmental Sciences

Rutgers University

Cook College, P.O. Box 231

New Brunswick, NJ 08903-0231

Steve McCutcheon EPA

Steve Rock EPA - NRMRL

Soil Flushing

John Mathur DOE

Program Manager

Office of Technology Development

MS EM-141

Washington, DC 20585

Jesse Yow DOE

Jeff Walke DOE

Eduardo Gonzales EPA

Alan Goodman EPA
Researchers and Technical Experts

Name Agency/Company

A-4

Neville Kingham Kiber Environmental Services, Inc.

Dr. Brian E. Reed West Virginia University

Dr. M.R. Matsamato University of California at Riverside

Roderic E. Moore West Virginia University

Lorne G. Everett Geraghty & Miller, Inc.

3700 State Street

Suite 350

Santa Barbara, CA 93105

Solidification/Stabilization

Ed Bates EPA - NRMRL

Trish Erickson EPA - NRMRL

Bob Thurnau EPA - NRMRL

Mike Royer EPA - NRMRL

Jeff Marquesse U.S. Department of Defense

Office of Assistant Deputy Under Secretary of Defense

(Environmental Technology)

Len Zintak EPA - Region 5

(Parsons project)

Terri Richardson EPA - SITE Program

(Parsons project)
APPENDIX B

ENGINEERING BULLETIN: TECHNOLOGY ALTERNATIVES FOR THE

REMEDIATION OF SOILS CONTAMINATED WITH ARSENIC,

CADIUM, CHROMIUM, MERCURY, AND LEAD
B-1

Purpose

Section 121(b) of the Comprehensive polymer microencapsulation), and vitrification];

Environmental Response, Compensation, and and separation and concentration (soil washing,

Liability Act (CERCLA) mandates the U.S. pyrometallurgy, and soil flushing). Use of

Environmental Protection Agency (EPA) to treatment trains is also addressed.

select remedies that “utilize permanent solutions

and alternative treatment technologies or Electrokinetics is addressed in the technical

resource recovery technologies to the maximum resource document, but not here, since it had not

extent practical” and to prefer remedial actions in been demonstrated at full-scale in the United

which treatment “permanently and significantly States for metals remediation. Also, an update

reduces the volume, toxicity, or mobility of on the status of in situ electrokinetics for

hazardous substances, pollutants, and remediation of metal-contaminated soil is in

contaminants as a principal element.” The EPA progress and should be available in the near

Engineering Bulletins are a series of documents future. Another change from the original

that summarize the available information on technical resource document is that physical

selected treatment and site remediation separation is addressed in the bulletin under soil

technologies and related issues. They provide washing, whereas it was previously covered as a

summaries and references of the latest separate topic.

information to help remedial project managers,

on-scene coordinators, contractors, and other site It is assumed that users of this bulletin will, as

cleanup managers understand the type of data necessary, familiarize themselves with: (1) the

and site characteristics needed to evaluate a applicable or relevant and appropriate

technology for potential applicability to their regulations pertinent to the site of interest; (2)

hazardous waste sites. Documents that describe applicable health and safety regulations and

individual site remediation technologies focus on practices relevant to the metals and compounds

remedial investigation scoping needs. Addenda discussed; and (3) relevant sampling, analysis,

are issued periodically to update the original and data interpretation methods. The majority of

bulletins. the information on which this bulletin is based

Introduction

This bulletin provides remedial project managers limited, as it was in the original technical

(RPM), On-Scene Coordinators (OSC), and resource document. Most of these site types

other state or private remediation managers and have been addressed in other EPA Superfund

their technical support personnel with documents. The greatest emphasis is on

information to facilitate the selection of remediation of inorganic forms of the metals of

appropriate remedial alternatives for soil interest. Organometallic compounds, organiccontaminated with arsenic (As), cadmium (Cd), metal mixtures, and multimetal mixtures are

chromium (Cr), mercury (Hg), and lead (Pb). briefly addressed.

This bulletin primarily condenses information

that is included in a more comprehensive At the time of this printing, treatment standards

Technical Resource Document (TRD) entitled for RCRA wastes that contain metals (in 40 CFR

“Contaminants and Remedial Options at Selected 268) and for contaminated media (in 40 CFR

Metal-Contaminated Sites.” 269) are being investigated for potential

Common compounds, transport, and fate are selection of the technology for remediating sites

discussed for each of the five elements. A containing these metal-bearing wastes.

general description of metal-contaminated

Superfund soils is provided. The technologies

covered are: immobilization [containment (caps,

vertical barriers, horizontal barriers),

solidification/stabilization (cement-based,

was collected during 1992 to 1994. Information

on lead battery (Pb, As), wood preserving (As,

Cr), pesticide (Pb, As, Hg), and mining sites is

revisions. These revisions may impact the

Overview of As, Cd, Cr, Hg, and Pb and

Their Compounds
B-2

This section provides a brief, qualitative is met by secondary production (i.e., recycling

overview of the physical characteristics and and recovery).

mineral origins of the five metals, and factors

affecting their mobility. More comprehensive

and quantitative reviews of the behavior of these

five metals in soil can be found in other readily

available EPA Superfund documents.

Overview of Physical Characteristics and rolled, and extruded. The most important lead

Mineral Origins ore is galena (PbS). Recovery of lead from the

Arsenic is a semi-metallic element or metalloid roasting, and smelting. Less common forms of

that has several allotropic forms. The most the mineral are cerussite (PbCO ), anglesite

stable allotrope is a silver-gray, brittle, crystalline (ObSO ), and crocoite (PbCrO ).

solid that tarnishes in air. Arsenic compounds,

mainly As O , can be recovered as a by-product 2 3

of processing complex ores mined mainly for

copper, lead, zinc, gold, and silver. Arsenic

occurs in a wide variety of mineral forms, Since metals cannot be destroyed, remediation of

including arsenopyrite (FeAsS ), which is the metal-contaminated soil consists primarily of 4

main commercial ore of As worldwide. manipulating (i.e., exploiting, increasing,

Cadmium is a bluish-white, soft, ductile metal. 

Pure Cd compounds rarely are found in nature,

although occurrences of greenockite (CdS) and

otavite (CdCO ) are known. The main sources of 3

Cd are sulfide ores of lead, zinc, and copper. Cd

is recovered as a by-product when these ores are

processed.

Chromium is a lustrous, silver-gray metal. It is

one of the less common elements in the earth’s

crust, and occurs only in compounds. The chief

commercial source of chromium is the mineral

chromite (FeCr O ). Chromium is mined as a 2 4

primary product and is not recovered as a byproduct of any other mining operation. There are

no chromite ore reserves, nor is there primary

production of chromite in the United States.

Mercury is a silvery, liquid metal. The primary

source of Hg is cinnabar (HgS), a sulfide ore. In

a few cases, Hg occurs as the principal ore

product; it is more commonly obtained as the byproduct of process complex ores that contain

mixed sulfides, oxides, and chloride minerals

(these are usually associated with base and

precious metals, particularly gold). Native or

metallic Hg is found in very small quantities in

some ore sites. The current demand for mercury

Lead is a bluish-white, silvery, or gray metal that

is highly lustrous when freshly cut, but tarnishes

when exposed to air. It is very soft and

malleable, has a high density (11.35 g/cm ) and 3

low melting point (327.4C), and can be cast,

ore typically involves grinding, flotation,

3

4 4

Overview of Behavior of Arsenic, Cadmium,

Chromium, Lead, and Mercury

decreasing, or maintaining) the mobility of metal

contaminant(s) to produce a treated soil that has

an acceptable total or leachable metal content. 

Metal mobility depends upon numerous factors. 

As noted in reference [9]:

“Metal mobility in soil-waste systems is

determined by the type and quantity of

soil surfaces present, the concentration

of metal of interest, the concentration

and type of competing ions and

complexing ligands, both organic and

inorganic, pH, and redox status. 

Generalization can only serve as rough

guides of the expected behavior of

metals in such systems. Use of literature

or laboratory data that do not mimic the

specific site soil and waste system will

not be adequate to describe or predict the

behavior of the metal. Data must be site

specific. Long term effects must also be

considered. As organic constituents of

the waste matrix degrade, or as pH or

redox conditions change, either through

natural processes of weathering or

human manipulation, the potential

mobility of the metal will change as soil

conditions change.”
B-3

Based on the above description of the number In most arsenic-contaminated sites, arsenic

and type of factors affecting metal mobility, it is appears as As O or as anionic arsenic species

clear that a comprehensive and quantitative leached from As O , oxidized to As (V), and

description of mobility of the five metals under then sorbed onto iron-bearing minerals in the

all conditions is well beyond the scope of this soil. Arsenic may be present also in

bulletin. Thus, the behavior of the five metals organometallic forms, such as methylarsenic acid

are described below, but for a limited number of (H AsO CH ) and dimethylarsinic acid

conditions. ((CH ) AsO H), which are active ingredients in

Cadmium, chromium (III), and lead are present compounds arsine (AsH ) and its methyl

in cationic forms under natural environmental derivatives [i.e., dimethylarsine (HAs(CH ) ) and

conditions. These cationic metals are not mobile trimethylarsine (As(CH ) )]. These arsenic forms

in the environment and tend to remain relatively illustrate the various oxidation states that arsenic

close to the point of initial deposition. The commonly exhibits (-III, O, III, and V) and the

capacity of soil to adsorb cationic metals resulting complexity of its chemistry in the

increases with increasing pH, cation exchange environment.

capacity, and organic carbon content. Under the

neutral to basic conditions typical of most soils, As (V) is less mobile (and less toxic) than As

cationic metals are strongly adsorbed on the clay (III). As (V) exhibits anionic behavior in the

fraction of soils and can be adsorbed by hydrous presence of water, and hence its aqueous

oxides of iron, aluminum, or manganese present solubility increases with increasing pH, and it

in soil minerals. Cationic metals will precipitate does not complex or precipitate with other

as hydroxides, carbonates, or phosphates. In anions. As(V) can form low solubility metal

acidic, sandy soils, the cationic metals are more arsenates. Calcium arsenate (Ca (AsO ) ) is the

mobile. Under conditions that are atypical of most stable metal arsenate in well-oxidized and

natural soils (e.g., pH <5 or >9; elevated alkaline environments, but it is unstable in acidic

concentrations of oxidizers or reducers; high environments. Even under initially oxidizing

concentrations of soluble organic or inorganic and alkaline conditions, absorption of CO from

complexing or colloidal substances), but may be the air will result in formation of CaCO and

encountered as a result of waste disposal or release of arsenate. In sodic soils, sufficient

remedial processes, the mobility of these metals sodium is available, such that the mobile

may be substantially increased. Also, compound Na AsO can form. The slightly less

competitive adsorption between various metals stable manganese arsenate (Mn (AsO ) ) forms in

has been observed in experiments involving both acidic and alkaline environments, while iron

various solids with oxide surfaces (y-FeOOH, a- arsenate is stable under acidic soil conditions. In

SiO , and y-Al O ). In several experiments, Cd aerobic environments, H AsO predominates at 2 2 3

adsorption was decreased by the addition of Pb pH <2 and is replaced by H AsO , HAsO and

or Cu for all three of these solids. The addition AsO as pH increases to about 2, 7, and 11.5,

of zinc resulted in the greatest decrease of Cd respectively. Under mildly reducing conditions,

adsorption. Competition for surface sites H AsO is a predominant species at low pH, but

occurred when only a few percent of all surface is replaced by H AsO , HAsO , and AsO as

sites were occupied. pH increases. Under still more reducing

Arsenic, chromium (VI), and mercury behaviors can form. As S is a low-solubility, stable solid. 

differ considerably from cadmium, chromium AsS and AsS are thermodynamically unstable

(III), and lead. Arsenic and Cr(VI) typically with respect to As S . Under extreme reducing

exist in anionic forms under environmental conditions, elemental arsenic and volatile arsine

conditions. Mercury, although it is a cationic (AsH ) can occur. Just as competition between

metal, has unusual properties (e.g., liquid at cationic metals affects mobility in soil,

room temperature, easily transforms among competition between anionic species (chromate,

several possible valence states).

2 3

2 3

2 33

32 2

many pesticides, as well as the volatile

3

3 2

3 3

3 42

2

3

3 4

2 42

3 4

2 4 4

2-

4

3-

3 3

2 3 3 3

- 2- 3-

conditions and in the presence of sulfide, As S2 3

2 3

2 2

2 3

3
B-4

arsenate, phosphate, sulfate, etc.) affects anionic At metal-contaminated sites, mercury can be

fixation processes and may increase mobility. present in mercuric form (Hg ) mercurous form

The most common valence states of chromium in (e.g., methyl and ethyl mercury). Hg and Hg

the earth’s surface and near-surface environment are more stable under oxidizing conditions. 

are +3 (trivalent or Cr(III)) and +6(hexavalent or Under mildly reducing conditions, both

Cr(VI)). The trivalent chromium (discussed organically bound mercury and inorganic

above) is the most thermodynamically stable mercury compounds can convert to elemental

form under common environmental conditions. mercury, which then can be readily converted to

Except in leather tanning, industrial applications methyl or ethyl mercury by biotic and abiotic

of chromium generally use the Cr(VI) form. Due processes. Methyl and ethyl mercury are mobile

to kinetic limitations, Cr (VI) does not always and toxic forms.

readily reduce to Cr (III) and can remain present

over an extended period of time. Mercury is moderately mobile, regardless of the

Cr (VI) is present as the chromate (CrO ) or are adsorbed by clay minerals, oxides, and 4

2-

dichromate (Cr O ) anion, depending on pH organic matter. Adsorption of cationic forms of 2 7

2-

and concentration. Cr (VI) anions are less likely mercury increases with increasing pH. 

to be adsorbed to solid surfaces than Cr (III). Mercurous and mercuric mercury also are

Most solids in soils carry negative charges that immobilized by forming various precipitates. 

inhibit Cr (VI) adsorption. Although clays have Mercurous mercury precipitates with chloride,

high capacity to adsorb cationic metals, they phosphate, carbonate, and hydroxide. At

interact little with Cr (VI) because of the similar concentrations of Hg commonly found in soil,

charges carried by the anion and clay in the only the phosphate precipitate is stable. In

common pH range of soil and groundwater. The alkaline soils, mercuric mercury precipitates with

only common soil solid that adsorbs Cr(VI) is carbonate and hydroxide to form a stable (but not

iron oxyhydroxide. Generally, a major portion of exceptionally insoluble) solid phase. At lower

Cr(VI) and other anions adsorbed in soils can be pH and high chloride concentration, soluble

attributed to the presence of iron oxyhydroxide. HgCl is formed. Mercuric mercury also forms

The quantity of Cr(VI) adsorbed onto the iron complexes with soluble organic matter,

solids increases with decreasing pH. chlorides, and hydroxides that may contribute to

2+

(Hg ), elemental form (Hg ), or alkylated form 2

2+ o

2

2+ 2+

soil. Both the mercurous and mercuric cations

2

its mobility. In strong reducing conditions, HgS,

a very low solubility compound is formed.
B-5

TYPING CONTROL SHEET

Work Assignment No. : 256\01107707.TD

Directory Name : O:\256\01107707.TD

Document Name : metals2.rpt

TYPIST DATE

KO 04/09/97

WORDPERFECT 7.0 DOCUMENT