contaminated

ground water

clean

ground water

permeable

reactive

barrier

direction of ground water flow

ground surface

permeable

reactive

barrier

United States Solid Waste and EPA 542-R-99-002

Environmental Protection Emergency Response April 1999

Agency (5102G) www.epa.gov/tio

www.clu-in.org

Field Applications of In Situ

Remediation Technologies:

Permeable Reactive Barriers

i

EPA-542-R-99-002

April 1999

Field Applications of In Situ Remediation Technologies:

Permeable Reactive Barriers

U.S. Environmental Protection Agency

Office of Solid Waste and Emergency Response

Technology Innovation Office

Washington, DC 20460

Walter W. Kovalick, Jr., Ph.D., Director
ii

Notice

This report was prepared by Environmental Management Support, Inc., 8601 Georgia Avenue, Suite

500, Silver Spring, MD 20910 under contract 68-W6-0014, work assignment 104, with the U.S.

Environmental Protection Agency. Mention of trade names or commercial products does not constitute

endorsement or recommendation for use. For more information about this project contact: Dawn

Carroll, U.S. EPA, Technology Innovation Office (5102G), 401 M Street, S.W., Washington DC

20460, phone: 703-603-1234, e-mail: carroll.dawn@epa.gov.
iii

Foreword

Approximately 85% of the hazardous waste sites in the United States have contaminated ground

water. The conventional approach for remediating contaminated ground water has been to extract the

contaminated water, treat it above ground, and reinject or discharge the clean water in a process

known as “pump-and-treat.” The recovered contaminants must be disposed of separately. Pump-andtreat technologies require considerable investment over an extended period of time, and it has been

shown that these technologies often do not actually remove the source of the contamination. Current

policies and laws stress “permanent” remedies over simple containment methods. Consequently, there

is considerable interest in and effort being expended on alternative, innovative treatment technologies

for contaminated ground water.

This report is one in a series that documents recent pilot demonstrations and full-scale applications of

technologies that either treat soil and ground water in place or increase the solubility and mobility of

contaminants to improve their removal by other remediation technologies. It is hoped that this

information will allow more regular consideration of new, less costly, and more effective technologies

to address the problems associated with hazardous waste sites and petroleum contamination. This and

the other reports listed below are available from EPA’s Technology Innovation Office World Wide

Web site at http://clu-in.org/pubitech.htm.

Surfactant Enhancements

Hydrofracturing/Pneumatic Fracturing

Cosolvents

Electrokinetics

Thermal Enhancements

In Situ Chemical Oxidation

Ground-Water Circulation Wells
iv
v

Contents

Introduction ................................................................ 1

Profiles ................................................................... 3

Chlorinated Solvents ....................................................... 3

Full-Scale

Aircraft Maintenance Facility, OR ........................................ 5

Caldwell Trucking, NJ ................................................. 6

Federal Highway Administration (FHA) Facility, Lakewood, CO ............... 8

Former Drycleaning Site, Rheine, Westphalia, Germany ...................... 10

Former Manufacturing Site, Fairfield, NJ .................................. 12

Industrial Site, Belfast, Northern Ireland ................................... 14

Industrial Site, Coffeyville, KS .......................................... 16

Industrial Site, NY ................................................... 17

Industrial Site, SC .................................................... 19

Intersil Semiconductor Site, Sunnyvale, CA ................................ 22

Kansas City Plant, Kansas City, MO ..................................... 24

Lowry Air Force Base, CO ............................................ 27

U.S. Coast Guard Support Center, Elizabeth City, NC ....................... 29

Pilot-Scale 

Area 5, Dover Air Force Base (AFB), DE ................................. 31

Borden Aquifer, Ontario, Canada ........................................ 33

Cape Canaveral Air Station, FL ......................................... 35

Industrial Site, NY ................................................... 37

LEAP Permeable Barrier Demonstration Facility, Portland, OR ................ 39

Massachusetts Military Reservation CS-10 Plume, Falmouth, MA .............. 41

Moffett Federal Airfield, Mountain View, CA .............................. 43

Savannah River Site TNX Area, Aiken, SC ............................... 45

SGL Printed Circuits, Wayne, NJ ........................................ 48

Somersworth Sanitary Landfill, NH ...................................... 50

U.S. Naval Air Station, Alameda, CA .................................... 53

Watervliet Arsenal, Watervliet, NY ...................................... 55

X-625 Groundwater Treatment Facility, Portsmouth Gaseous Diffusion Plant,

 Piketon, OH ..................................................... 57

Metals and Inorganics ..................................................... 59

Full-Scale

Nickel Rim Mine Site, Sudbury, Ontario, Canada ........................... 61

Tonolli Superfund Site, Nesquehoning, PA ................................ 63

U.S. Coast Guard Support Center, Elizabeth City, NC ....................... 65

Pilot-Scale

100D Area, Hanford Site, WA .......................................... 67

LEAP Permeable Barrier Demonstration Facility, Portland, OR ................ 69
vi

Fuel Hydrocarbons ........................................................ 71

 Pilot-Scale

East Garrington, (Near Olds), Alberta, Canada ............................. 73

U.S. Naval Air Station, Alameda, CA .................................... 75

Nutrients ................................................................ 77

Full-Scale

Y-12 Site, Oak Ridge National Laboratory, TN ............................. 79

Pilot-Scale

Public School, Langton, Ontario, Canada ................................. 82

Savannah River Site TNX Area, Aiken, SC ............................... 84

Radionuclides ............................................................ 87

Full-Scale

Fry Canyon Site, UT ................................................. 89

Y-12 Site, Oak Ridge National Laboratory, TN ............................. 92

Other Organic Contaminants ............................................... 95

Full-Scale

Marzone Inc./Chevron Chemical Company, Tifton, GA ...................... 97

Bibliography of Field Applications of Permeable Reactive Barriers ............. 99
1

Introduction

Purpose and Process

This document is a status report on the use of permeable reactive barriers (PRBs) for ground-water

remediation in the United States, Canada, and selected locations abroad. Included in this report are

profiles of ongoing and completed pilot- and full-scale PRB demonstrations as well as full-scale

installations. The profiles are organized by the type of contaminant treated. At some sites, PRBs

are being used to address more than one type of contaminant. Profiles for these site are included in

all applicable sections of this document. 

Sites included were identified by the members of the Permeable Reactive Barriers Action Team

under the Remediation Technologies Development Forum (RTDF). The Action Team was

established in March 1995. Its members include representatives from government, academia, and

the private sector working as partners to achieve public and regulatory acceptance of PRBs for

remediating chlorinated solvents, metals, radionuclides, and other ground-water pollutants.

The profiles included in this document have been developed based on information provided by the

point of contact listed in each profile. The intent is to provide potential users of PRB technology

with information for making more informed decisions and, when possible, to provide pointers to

additional information. 

To the extent it is available, a consistent set of information is presented in each profile. This

includes site name, location, characteristics of the site, major contaminants, PRB installation date,

type of construction, design and installation costs, reactive materials used, results achieved, lessons

learned, and point of contact for further information. This document also includes a bibliography

of PRB-related articles and documents organized alphabetically by author’s name. Some, but not

all, of the entries in the bibliography pertain to the sites profiled in the body of the document.

An Internet version of this report is maintained in the Permeable Reactive Barriers Action Team

section of the RTDF World Wide Web site at www.rtdf.org. Those who have information about

additional PRB sites are encouraged to submit it for inclusion in the Web-based version.

Additional profiles will be developed as sites are identified, and existing profiles will be updated

periodically as new information is received. A copy of a “Permeable Reactive Barriers Profile

Information Request” can be downloaded from the Web site for use in providing appropriate

information.
2

Technology Needs

Numerous hazardous waste sites have significant concentrations of metals, halogenated organic

compounds, and radionuclides that contaminate ground water. Traditional technologies, such as

pump-and-treat, require an external energy source and their cost is high. Subsurface residuals

frequently remain at undesirable levels. Thus, subsurface permeable reactive barriers (PRBs) are

gaining a reputation as a cost-effective alternative. Properly designed and installed PRBs can

reduce the levels of many contaminants to regulatory cleanup goals. The barriers are expected to

have low maintenance costs, though the stability of aging barriers is still being studied.

Technology Description

A PRB is a passive in situ treatment zone of reactive material that degrades or immobilizes

contaminants as ground water flows through it. PRBs are installed as permanent, semi-permanent,

or replaceable units across the flow path of a contaminant plume. Natural gradients transport

contaminants through strategically placed treatment media. The media degrade, sorb, precipitate, or

remove chlorinated solvents, metals, radionuclides, and other pollutants. These barriers may

contain reactants for degrading volatile organics, chelators for immobilizing metals, nutrients and

oxygen to enhance bioremediation, or other agents. 

Choice of reactive media for PRBs is based on the specific organic or inorganic contaminant to be

remediated. Most PRBs installed to date use zero-valent iron (Fe0) as the reactive media for

converting contaminants to non-toxic or immobile species. For example, Fe0 can reductively

dehalogenate hydrocarbons, such as converting trichloroethylene (TCE) to ethylene, and

reductively precipitate anions and oxyanions, such as converting soluble Cr+6 oxides to insoluble

Cr3 hydroxides. The reactions that take place in the barriers are dependent on parameters such as

pH, oxidation/reduction potential, concentrations, and kinetics. The hydrogeologic setting at the

site is also critical—geologic materials must be relatively conductive and a relatively shallow

aquitard must be present to contain the system. 

Most PRBs are installed in one of two basic configurations: funnel-and-gate or continuous trench,

although other techniques using hydrofracturing and driving mandrels are also used. The funneland-gate system employs impermeable walls to direct the contaminant plume through a gate, or

treatment zone, containing the reactive media. A continuous trench is installed across the entire

path of the plume and is filled with reactive media.
3

Chlorinated Solvents
4
5

Aircraft Maintenance Facility, OR

Installation Date:

March 1998

Contaminants:

TCE

Reactive Media:

Fe0

Installation Cost:

$600,000

Construction:

Funnel and Gate

Point of Contact:

James Romer

EMCON Associates

1150 Knutson Road

Suite 5

Medford, OR 97504

Tel: 541-770-6977

Fax: 541-770-7019

E-mail:

jromer@emconinc.com

A full-scale demonstration of a permeable reactive barrier (PRB) to

remediate ground water contaminated with trichloroethylene (TCE)

was installed in March 1998 at an aircraft maintenance facility in

southern Oregon. 

Site Background

Historical use of chlorinated solvents for degreasing purposes

resulted in the ground-water contamination by TCE and other

degradation compounds. Total volatile organic compound (VOC)

concentration in the upper aquifer encountered at the site was

approximately 500 μg/L.

The site is underlain by heterogeneous alluvial deposits ranging

from sandy silts to silty gravels. At a depth of 24-34 ft below ground

surface (bgs) is a fine-grained aquitard. The depth to the water table

varies seasonally between 4 and 8 ft bgs. Average hydraulic

conductivity for the alluvial deposits is 3 ft/day.

Technology Application

The funnel-and-gate system consists of two gates, each 50 ft wide,

and a 650-ft-long funnel. The funnel walls are composed of a

2-ft-thick soil-bentonite slurry installed to the top of the aquitard

with a hydraulic conductivity of 3 x 10-4 ft/day. The first gate is

composed of two layers, each 50 ft wide and 9 in thick, consisting

of 100% zero-valent iron filings (Fe0). Both layers were installed

using a continuous trencher, then connected to the funnel by driven

sheet piles. The second gate, upgradient from the first, is 3 ft wide,

60 ft long, and composed of mixed sand and iron filings. It was

installed with a trackhoe and drag box.

Results

Four monitoring wells, two upgradient and two downgradient, have

been installed for each gate. Sampling began in April 1998. Current

plans call for sampling every two months for four periods and then

quarterly for the foreseeable future.
6

Caldwell Trucking, NJ

Installation Date:

April 1998

Contaminants: 

TCE

Reactive Media: 

Fe0

Installation Cost: 

$1,120,000

Construction: 

Hydraulic Fracturing

Point of Contact:

John Vidumsky 

DuPont Specialty 

Chemicals 

Barley Mill Plaza

27/2226 

Lancaster Pike and 

Route 141 

Wilmington, DE 

19805 

Tel: 302-892-1378 

Fax: 302-892-7641 

E-mail:

john.e.vidumsky@

usa.dupont.com

A full-scale permeable reactive barrier (PRB) system was installed

at Operating Unit (OU) 2 of the Caldwell Trucking Superfund Site

in northern New Jersey in April 1998. The PRB system is being

considered as an alternative to the pump-and-treat system specified

in the site’s Record of Decision (ROD). U.S. EPA agreed to

negotiate an amendment to the ROD if, after one year of operation,

performance data on the PRB system showed success in terms of

achieving remediation objectives. 

The system is expected to achieve the same mass removal (500

kg/yr) as the originally proposed pump-and-treat system. The barrier

is designed to reduce initial trichloroethylene (TCE) concentrations

of 6,000-8,000 μg/L in the ground water to below 50 μg/L. 

Site Background

The Caldwell Trucking site encompasses 11 acres near the Passaic

River that were used for disposal of septic wastes in unlined ponds

from the 1950s to 1984 and industrial waste containing lead and

TCE. The site contains areas of glacial deposition overlying basalt

flows with an average conductivity of approximately 0.1 in/sec. The

majority of ground-water flow occurs in a 25 ft-deep sand and

gravel aquifer confined below an impermeable clay layer at an

average elevation of 160 ft above mean sea level. The water table is

located approximately 5-15 ft below ground surface. A fractured

basalt zone is located below the sand/gravel aquifer at 100-125 ft

above mean sea level. The TCE plume extends 4,000 ft off-site.

Studies indicated that the rate of natural attenuation occurring at this

site is 3,000 kg/yr. 

Technology Application

The PRB system was installed in unconsolidated sands and a

fractured basalt zone using a combination of hydraulic fracturing

and permeation infilling. The barrier system is 50 ft deep, beginning

about 15 ft below ground. The system consists of two 3-in walls,

150 ft and 90 ft in length and uses 250 tons of zero-valent iron (Fe0)

as the reactive material. Construction of the PRB system involved

hydraulic fracturing of the upper sand/gravel zone, using 15

hydrofrac/infilling wells at 15-ft intervals, and permeation infilling

of the lower sedimentary zone (pumping a gel containing the Fe0

down a well into the fractured bedrock through an open borehole).

Cost
7

The total installation cost of the PRB system (both walls) at this site

is estimated at $1,120,000—$670,000 for the 90-ft (hydrofracing)

wall and $450,000 for the 150-ft (permeation infilling) wall. This

includes the cost of design, construction, materials, and the reactive

material. 

Results

Monitoring wells and surface waters have been sampled at least

monthly for volatiles and metals, and other parameters have been

measured. To date, the barrier has achieved 95% degradation of

TCE in the ground water, from an upgradient concentration of

7,000 μg/L to a downgradient concentration of less than 400 μg/L.

TCE ground-water concentrations, affected by variable groundwater flow velocities and desorption of TCE from the site soils, are

expected to reach pseudo steady-state conditions in early 1999.

Lessons Learned 

The low temperature and high pH at which the guar gum gel used

for installation was formulated slowed its enzymatic degradation

after it was in place. As a solution, a pH buffer and additional

enzyme were injected. Guar breakdown then occurred and TCE

reductions were observed. Otherwise, the gel has not interfered with

the barrier’s permeability nor impacted the iron's reactivity.
8

Federal Highway Administration (FHA) Facility, Lakewood, CO

Installation Date:

October 1996

Contaminants:

TCA; 1,1-DCE; TCE;

cDCE 

Reactive Media:

Fe0

Installation Cost:

$1,000,000 

Construction:

Funnel and Multiple Gate

Point of Contact:

Peter McMahon 

U.S. Geological Survey

Denver Federal Center

(MS-415)

Denver, CO 80225 

Tel: 303-236-4882, x286 

FAX: 303-236-4912 

E-mail:

pmcmahon@usgs.gov

A permeable reactive barrier (PRB) system was installed in October

1996 at a site in Lakewood, Colorado. 

Site Background

Contaminants at the site included 1,1,1-trichloroethane (TCA),

1,1-dichloroethylene (1,1-DCE), trichloroethylene (TCE), and cisdichloroethylene (cDCE). The contaminated area is an unconfined

aquifer that is 15-25 ft thick and consists of unconsolidated gravelly

sand overlying weathered (fractured) claystone. These units are in

hydraulic connection and act as one aquifer. The geometry of the

aquifer is irregular, with a local presence of clay lenses in the

unconsolidated sand and sandstone lenses in the claystone. The

aquifer is confined from below by unweathered (unfractured)

claystone. 

Technology Application

The PRB system is comprised of a 1,040-ft funnel section and four

reactive gate sections, each 40 ft wide. This was the first funnel and

multiple gate PRB system using granular zero-valent iron (Fe0). A

high degree of lateral geologic heterogeneity and variation in

volatile organic compound (VOC) concentrations led to varying

iron thicknesses in each gate. The gates were constructed using a

sheet pile “box.” Native material was excavated from the box and

the reactive material installed, separated from the aquifer materials

by a layer of pea gravel. 

Cost

Installation cost of the PRB system was about $1,000,000. This

includes the cost of design, construction, materials, and the

zero-valent iron. 

Results

Ground-water velocities through the gates were expected to range

from 1 ft/day to 10 ft/day, depending upon the hydrogeologic

conditions in the vicinity of the respective gates. Measurements in

the cells using a heat-pulse flowmeter have ranged from < 0.1 ft/day

to about 1.5 ft/day. Design concentrations include up to 700 μg/L of

TCE and 700 μg/L of 1,1-DCE. Half-lives of about 1 hour or less

were measured for these compounds in bench-scale design studies.

The only VOC exiting the cells above the 5 μg/L reporting level is

1,1-dichloroethane, which has been measured up to 8 μg/L on the

downgradient side of the cells. There is some evidence of the

precipitation of calcite and siderite in the cells based on decreases in
9

calcium and inorganic carbon in the treated ground water. This is

estimated to result in a potential porosity loss of 0.5% of the porosity

per year of operation. 

Hydraulic head has increased upgradient of the barrier, with up to

10 ft of head difference measured across the barrier. This increases

the possibility for contaminated water to move around the barrier.

Indeed, VOC concentrations are increasing in ground water moving

around the south end of the barrier and there is some evidence of

VOCs moving under the barrier in one location.
10

Former Drycleaning Site, Rheine, Westphalia, Germany

Installation Date:

June 1998

Contaminants: 

PCE, 1,2-DCE 

Reactive Media: 

Fe0, iron sponge 

Design Cost: 

$30,000 

Installation Cost: 

$93,000 

Construction: 

Continuous Wall 

Point of Contact:

Dr. Martin Wegner 

Dr. Wilfried Moeller 

Mull & Partner

Ingenieurgessellschaft

mbH 

Osteriede 5, 30827

Garbsen, Germany 

Tel: 49-5131-4694-55 or

49-5131-4694-55

Fax: 49-5131-4694-90 

E-mail: Wegner_Mull

@compuserve.com

A full-scale permeable reactive barrier (PRB) was installed at a

former drycleaning site in an urban area in Rheine, Westphalia in

Germany.

Site Background

Tetrachloroethylene (PCE) and 1,2-dichloroethylene (1,2-DCE) are

the primary contaminants of concern at the site. Initial maximum

concentrations in the plume were 20 mg/L for PCE and 0.5 mg/L

for 1,2-DCE. The 1,640-ft-long, 820-ft-wide plume is present in a

loamy sand aquifer that extends 16-33 ft below grade. The water

table is about 10 ft below the ground surface. The hydraulic

conductivity varies between about 0.3 and 2.8 ft/day. The distance

from the center of contamination to the treatment wall is about 1,300

ft. 

Technology Application

The PRB is a continuous reactive wall that varies between 2 and 3 ft

wide and is 74 ft long. The PRB was constructed by drilling a line

of overlapping 3-ft diameter boreholes which were filled with

reactive material to ground-water level, and with clean soil to

ground surface level. The PRB uses two reactive media: 69 tons of

granular iron (Fe0) mixed with gravel at a 1:2 volume ratio (34.5

tons each of Fe0 and gravel) in 33 ft of the wall and 85 tons of iron

sponge in 41 ft of the wall. A concrete-filled borehole separates the

two segments. (Iron sponge consists of wood shavings or wood

chips impregnated with hydrated iron oxide. It is used for removal

of H2S in oil and gas processing operations.)

Cost

The mandrel construction method was chosen because it was

determined to be easier and less expensive than continuous sheet

piling construction. Design costs were $30,000. Installation costs

including construction and reactive material totaled $93,000. An

additional $13,000 was spent on monitoring and $24,000 on the

installation of gas measurement devices.

Results

This is the first continuous treatment wall in Germany and was built

as a research project with no specific target cleanup concentrations.

However, the PRB has resulted in significant reduction in the

concentration of contaminants—especially PCE. The effluent

concentration of PCE from both sections of the wall is less than 100

μg/L. There has been only a low level of metabolite production. No
11

vinyl chloride was observed in the affluent or effluent of the PRB.

There was measurable production of hydrogen only at the very

beginning of the remediation process— simultaneous with a

complete reduction of nitrogen to ammonia. Ground-water samples

are being collected monthly.

Lessons Learned

Due to increasing microbial activity at the site of the PRB, hydrogen

emission is decreasing. Nitrate now is reduced to nitrogen or N2O.

The sulfate effluent concentration is decreasing due to the sulfate

reduction to sulphured hydrogen. 
12

Former Manufacturing Site, Fairfield, NJ 

Installation Date:

September 1998 

Contaminants:

1,1,1-TCA, PCE, TCE,

DNAPL 

Reactive Media:

Fe0

Design Cost:

$150,000 

Installation Cost:

$725,000

Construction:

Continuous Trench 

Point of Contact: 

Stephen Tappert 

VECTRE Corporation 

15 Route 15 South 

Lafayette, NJ

07848-0930 

Tel: 973-383-2500 

Fax: 973-579-0025 

E-mail: set@vectre.com

A full-scale permeable reactive barrier (PRB) was installed at a site

in Fairfield, NJ, to treat chlorinated solvent contamination.

Site Background

The site, a former electromechanical product manufacturing,

assembly, and testing facility is currently in operation as a school. It

consists of a single one-story slab foundation brick building and

paved parking lot covering 60% of a 2.8-acre plot of land. The site

is underlain by 15-20 ft of silty sand with some gravel, overlying a

lacustrine clay 10-15 ft thick. The clay unit varies in depth from

15-23 ft below grade. Ground water at the site occurs under watertable conditions within the glacial sediments above bedrock, and

under confined conditions in the deeper sand aquifer. Shallow

ground-water flow is moving toward a nearby creek at an average

hydraulic gradient of 0.005 ft/ft. Depth-to-water in the shallow zone

has been as high as 4 ft below grade. An upward vertical

ground-water gradient exists between the shallow aquifer and the

silty sand unit underlying the clay, with a head difference of almost

6 ft in some areas.

Environmental investigations at the site identified a plume of

chlorinated solvents, with an apparent source in the vicinity of a

former dry well and septic system. Contamination was limited to the

shallow sandy aquifer. The total VOC concentration at the plume

front was approximately 4,500 μg/L. Key contaminants included

1,200 μg/L trichloroethane (1,1,1-TCA), 19 μg/L

tetrachloroethylene (PCE), and 110 μg/L trichloroethylene (TCE).

A pool of dense nonaqueous-phase liquid (DNAPL) was also

identified with significant concentrations of solvents in saturated

soils below 15 ft. Underground utilities in place at the site included

two storm drains and a sewer line at 13 ft below grade. 

Technology Application

Prior to installation of the PRB, the DNAPL pool was excavated.

As a remedial measure, the excavation was partially backfilled with

a 1:1 mix of zero-valent iron (Fe0) and sand. For the PRB,

conventional sheet piling construction was selected as the most

reliable approach with the most predictable timeframe for

completion. The PRB was constructed as a continuous barrier

located ahead of the highest plume concentrations to prevent offsite

migration. The bottom portion of the barrier used a 4:1 iron/sand

mixture and the upper portion of the barrier used a 3:2 iron/sand

mixture. A total of 720 tons of iron were used. The final barrier was
13

127 ft wide, 25 ft deep, and 5 ft thick. After the barrier was

installed, the site was graded and seeded, and the parking lot was

repaved. Construction was generally straightforward with the only

major problem being the below-grade sewer line that permitted a

large volume of water to enter the excavation. Construction

ultimately required subaqueous excavation to complete that section

of the wall. 

Cost

Design costs for the barrier, including a licensing fee, were

$150,000. Installation costs (which include construction, materials,

and reactive media) totaled $725,000. 

Results

Cleanup goals for chlorinated solvents at the site were New Jersey

Ground Water Quality Criteria: 1 μg/L for PCE, 1 μg/L for TCE,

and 30 μg/L for 1,1,1-TCA. Monitoring wells were installed

upgradient, downgradient, and within the PRB and samples were

collected one month after installation. At that time, VOC

concentrations at the center of the plume decreased to 33 μg/L

within the PRB. Subsequent quarterly sampling results showed an

increase in pH from approximately 6.5 to 9.5, a change in Eh from

-50 mv to -400 mv, and concentrations of VOCs at or near detection

limits in the middle of the wall. Future sampling plans include

quarterly monitoring of selected wells for two years, then continued

monitoring with reduced frequency after that. 

Lessons Learned 

Detailed knowledge of the site and detailed planning were critical to

making this technology work. Also, it was important to get the state

agency on the team early to expedite the project.
14

Industrial Site, Belfast, Northern Ireland

Installation Date:

December 1995

Contaminants:

TCE, 1,2-cDCE

Reactive Media:

Fe0

Installation Cost:

$375,000

Construction:

Slurry Wall Funnel 

In Situ Reaction Vessel

Point of Contact:

Stephanie O’Hannesin 

EnviroMetal

Technologies, Inc. 

42 Arrow Road 

Guelph, Ontario

N1K 1S6 Canada

Tel: 519-824-0432 

Fax: 519-763-2378 

E-mail:

sohannesin@beak.com

A full-scale field test of a permeable reactive barrier (PRB) system

was conducted at an industrial facility in Belfast, Ireland. 

Site Background

A circular in situ reaction vessel filled with iron was installed to a

depth of about 40 ft in December 1995, to treat up to 390 mg/L of

trichloroethylene (TCE) and related breakdown products. Previous

owners of the site had used chlorinated solvents while

manufacturing electronic components. Years of spillages resulted in

an intense but localized plume close to the current site boundary.

The TCE plume at this site is located in an area characterized by a

thick deposit of till (up to 78 ft) underlain by Mercia mudstones. The

till has silt, sand, and gravel lenses that allow contaminants to

migrate from the source; however, migration is constrained by the

specific orientation of the permeable lenses that contain discrete clay

or clayey silt lenses. The depth of the barrier was chosen to intercept

the horizon of low permeability that is present at a depth of around

33 ft. The site is characterized as having a water table approximately

20 ft below ground surface, and an underlying aquifer about 40 ft in

depth.

Technology Application

Two 100-ft bentonite cement slurry walls directed water to the inlet

of the steel reaction vessel, which was 4 ft in diameter and contained

a 16-ft vertical thickness of zero-valent iron (Fe0). Ground water

flowed by gravity through the iron zone and discharged through a

piped outlet on the downgradient side of the slurry wall. The vessel

was equipped with a manhole to access the top of the iron zone, in

the event that periodic scarification of the iron surface proved access

was necessary. The system was designed to provide residence time

of about 5 days. 

Cost

The total cost of the system, including slurry walls, granular iron,

reaction vessel, and engineering was about $375,000.

Results

The system was designed to meet ground-water-quality criteria of

500 μg/L for TCE, which apply to ground water beneath industrial

land slated for redevelopment. Flow rates through the reactor have

varied substantially since its installation, but data have shown an

overall 99.7% reduction in TCE and cis-1,2-dichloroethylene
15

(cDCE) levels through the reaction vessel. Both increased and

decreased levels of cDCE resulting from reductive dehalogenation

have been identified. TCE levels in the system have been decreasing

in the effluent sample ports. Only low levels (in the range of 100

μg/L) of cDCE have been detected. Vinyl chloride, a common

breakdown product of this process, has not appeared in appreciable

quantities.
16

Industrial Site, Coffeyville, KS

Installation Date:

January 1996

Contaminants:

TCE, 1,1,1-TCA

Reactive Media:

Fe0

Installation Cost:

$400,000

Construction:

Funnel and Gate

Point of Contact:

Greg Somermeyer

SECOR International,

Inc.

4700 McMurry Drive

Suite 101

Fort Collins, CO 80525

Tel: 970-226-4040

Fax: 970-226-4099

This permeable reactive barrier (PRB) system was installed at the

property boundary of an industrial site in Coffeyville, KS, in

January 1996.

Site Background

The site covers about 200 acres and is hydrologically and

geochemically complex. Contaminants include trichloroethylene

(TCE) and 1,1,1-trichloroethane (TCA). Prior releases at this site

had generated a dissolved plume approximately 875 yds long

contaminated with 400 μg/L of TCE and 100 μg/L of 1,1,1-TCA.

Contaminant transport occurred to the greatest lateral extent in a

basal sand and gravel unit just above shale bedrock, which lies

about 30 ft beneath the site. There is nearby public use of shallow

ground water necessitating measures to prevent additional off site

migration.

Technology Application

The PRB system uses a funnel-and-gate configuration to direct

ground water through a single, permeable treatment gate that is 20 ft

long and 3 ft thick. The funnel section of the system consists of two

490-ft soil-bentonite slurry walls on either side of the treatment gate.

Zero-valent iron (Fe0) is used as the reactive material. The treatment

wall contains 70 tons of the iron. A low ground-water flow velocity

of 0.2 ft/day permitted the use of this relatively high funnel-to-gate

ratio. The system is installed to a depth of 30 ft in a basal alluvial

aquifer.

Cost

The installation cost for the system, including slurry walls, treatment

gate, and granular iron, was approximately $400,000. 

Results

No determinations of ground-water velocity through the system

have been made to date. Concentrations in the iron zone are below

Maximum Contaminant Levels (MCLs).
17

Industrial Site, NY

Installation Date: 

December 1997 

Contaminants: 

TCE, cDCE, VC 

Reactive Media: 

Fe0

Installation Cost: 

$797,000 

Construction: 

Continuous Trench 

Point of Contact:

Diane Clark 

Stearns & Wheler, LLC 

One Remington Park Dr.

Cazenovia, NY 13035 

Tel: 315-655-8161 

Fax: 315-655-4180 

E-mail: diane.clark@

stearnswheler.com

A full-scale permeable reactive barrier (PRB) was installed at a

former plating facility in Central New York in December 1997. 

Site Background

Trichloroethylene (TCE), cis-1,2-dichloroethylene (cDCE), and

vinyl chloride (VC) are the primary contaminants of concern at this

facility. Initial concentrations ranged from 200-1,280 μg/L for TCE,

300-1,800 μg/L for cDCE, and 26-53 μg/L for VC. Total volatile

organic compounds (VOC) concentrations ranged from 300 μg/L900 μg/L. The goal of this project is to clean the site to New York

ground-water standards, 5 μg/L for TCE, 5 μg/L for cDCE, and 2

μg/L for VC.

The 370-ft plume is present in a sand and gravel aquifer that extends

from 4-21 ft below grade, and the water table is located 4-5 ft below

ground surface. Based on the results of slug tests, the hydraulic

conductivity of the material in the aquifer ranges from about 16 to

230 ft/day. 

Technology Application

The PRB uses 742 tons of bulk granular zero-valent iron (Fe0) for

reductive dehalogenation of chlorinated aliphatic compounds. It was

constructed as a continuous wall, measuring 1 ft thick and 18 ft

deep, across the entire width of the plume. An additional 1-ft-thick

continuous wall was placed 10 ft upgradient of the longer wall and

in the portion of the plume with the highest concentrations of total

VOCs to provide additional residence time in the reactive iron. 

The system was installed with continuous trenching equipment that

uses a large cutting chain excavator combined with a trench box and

loading hopper. To construct the barrier, the cutting chain removed

the native soil along the trench line. As the machine advanced along

the trench line, the granular iron was lowered through the hopper

and trench box into the excavated trench. During this process, the

trenching equipment proved to move faster than the rate at which

the iron settled into the excavated trench. As a result, the top 2 ft of

the trench had to be backfilled with a backhoe to reach the 18-ft

depth. 

A 3-ft bench was excavated prior to the use of the trenching

equipment, allowing the wall to be installed to the maximum depth

of the clay layer, which was 21 ft below normal site grade. The

spoils removed from the trench were then spread on the surface of
18

the bench on the upgradient side of the iron. Finally, the spoils were

covered by backfill of the clean soil excavated for the bench,

amounting to a minimum of 2 ft of clean soil as cover. 

Cost

A predesign study determined that a continuous permeable reactive

barrier was more cost-effective than a funnel-and-gate system at this

site. Installation costs for the full-scale system were $797,000. This

includes construction, materials, and the cost of the reactive material.

In addition, it includes the cost of site improvements allowing access

by the trenching equipment. Design cost for this system is not

available. Because several issues that would not be required for

other installations were included in this system's design cost, site

managers indicate that it probably would not be applicable, as far as

scale-up, to other sites.

Results

Recent sampling results have indicated upgradient concentrations of

2,200 μg/L TCE, 4,900 μg/L 1,2-DCE, and 260 μg/L VC.

Downgradient results showed only 5 μg/L 1,2-DCE and 23 μg/L

VC. Ground-water samples will be collected on a quarterly basis for

a total of 5 years. 

Lessons Learned 

At this particular site, construction of a continuous trench system

was more cost-effective than a funnel-and-gate system. This option

also required the shortest construction period, minimizing disruption

to the landowner. In addition, site managers were able to manage

trench spoils onsite, instead of having to dispose of them offsite.

Spoils were spread in the benched area and capped with a minimum

2 ft of top soil, which had been stripped off prior to construction and

stockpiled.
19

Industrial Site, SC

Installation Date:

November 1997

Contaminants:

TCE, cDCE, VC

Reactive Media:

Fe0

Design Cost:

$50,000

Installation Cost:

$350,000

Construction:

Continuous Trench

Point of Contact:

Steven Schroeder

RMT, Inc.

100 Verdae Boulevard

P.O. Box 16778

Greenville, SC

29606-6778

Tel: 864-281-0030

Fax: 864-287-0288

E-mail:

Steve.Schroeder@

rmtinc.com

Phase 1 of a full-scale permeable reactive barrier (PRB) was

installed at a former industrial site in Manning, SC, in November

1997.

Site Background

Trichloroethylene (TCE), cis-1,2-dichloroethylene (cDCE), and

vinyl chloride (VC) have been detected in two aquifers that underlie

the site at concentrations of 25 mg/L, 3.5 mg/L, and 0.9 mg/L,

respectively. TCE concentrations in the lower of the two

contaminated aquifers are generally one order of magnitude less

than those in the upper aquifer.

The upper aquifer is 5-15 ft below ground surface (bgs). It is

composed primarily of sandy to silty fill material with a hydraulic

conductivity of 2 ft/day. A clay unit forms the lower boundary of

this aquifer. The intermediate aquifer (18-27 ft bgs) is composed of

fine silt laminae and very fine sand layers within the clay unit and

has a hydraulic conductivity of 2.6 ft/day. The lower portion of this

clay unit forms a boundary between the intermediate and lower

aquifers. Monitoring wells did not detect any volatile organic

compounds (VOCs) in the lower aquifer. 

Technology Application

The PRB was installed to the base of the intermediate aquifer. It is a

1-ft-wide continuous trench composed of 50% sand and 50% zerovalent iron (Fe0

) by volume in the form of iron filings. The 400 tons

of Fe0 was homogeneously distributed throughout the sand using

cement-mixing equipment. A one-pass trenching technique was

used from a surface bench 4-6 ft bgs. This surface bench allowed

the trenching equipment to reach the final depth of 29 ft bgs. Phase

1 of the installation called for a 325-ft section to address the highest

concentrations of VOCs and mitigate suspected off-site migration.

Phase I construction—including mobilization, benching, installation,

and demobilization—was completed in 4 weeks.

Cost

Design for this PRB system was $50,000. The total installation cost

for both phases will be approximately $350,000. This includes

construction, materials, and the cost of the reactive media.

Results
20

Cleanup goals for the site are 0.005 mg/L for TCE, 0.070 mg/L for

cDCE, and 0.002 mg/L for VC. After the initial 9 months of system

operation, positive indicators for dechlorination were measured at

downgradient monitoring wells for both VOC concentrations and

indicator compounds (pH, eH, chloride). However, due to the slow

rate of ground-water flow and the fact that VOCs were present

downgradient of the wall at installation, performance evaluations

continue. Construction of Phase 2 will extend the wall to a total

length of 1,000 ft to treat the entire contaminant plume. 

Minor problems were encountered at the start of Phase 1 installation,

with some material cave-in occurring at the top 3-4 ft of the trench

sidewalls. This problem was alleviated by reconfiguring the location

of the feed hopper on top of the boot and by adding steel plates to

the top portion of the boot, to improve material flow. Installation

through the two aquifers has affected ground-water flow in the

vicinity of the treatment wall. By providing a greater connection

between the two aquifers, ground-water velocities have been

reduced and ground-water flowpaths modified slightly. The

reduction in ground-water velocities and modified flowpaths should

not affect the capability of the treatment wall to intercept and

adequately treat VOCs at the site. Increased residence time for

treatment will improve the long term treatment efficacy. 

Modifications to the ground-water monitoring schedule were also

necessary to take into account differences in ground-water flow

rates. Sampling upgradient and downgradient of the wall is

conducted on a quarterly basis. Semi-annual sampling is anticipated

in the future. 

Lessons Learned

Compared with other methods, continuous trenching provided costeffective installation and a high degree of confidence that materials

would be placed according to the design, to create a continuous

treatment wall with equal distribution of the Fe0. 

Because of the reduced ground-water flow velocity at the site, more

time than originally estimated will be required to complete an initial

flushing of VOCs in downgradient ground water. This site may

require 18-24 months to complete dechlorination sufficient to

achieve cleanup levels.

Expectations and data collection efforts relative to performance will

be planned to accommodate a relatively long initial period of

operation and monitoring.
21
22

Intersil Semiconductor Site, Sunnyvale, CA

Installation Date: 

February 1995 

Contaminants: 

TCE, cDCE, VC,

Freon 113® 

Reactive Media: 

Fe0

Installation Cost: 

$1,000,000 

Construction: 

Funnel and Gate 

Point of Contact:

Carol Yamane 

Geomatrix Consultants,

Inc. 

100 Pine Street 

San Francisco, CA

94111 

Tel: 415-434-9400 

Fax: 415-434-1365 

E-mail: cyamane@

geomatrix.com

In January 1995, after being approved by the California Regional

Water Quality Control Board, a permeable reactive barrier (PRB)

was installed at the Intersil Semiconductor Site in Sunnyvale, CA. 

Site Background

Intersil had manufactured semiconductors at the site from the early

1970s until 1983. In 1972, the company had installed a concrete,

epoxy-lined, in-ground system at the facility to neutralize acid in

wastewater before discharge to a sanitary sewer. Soil and

ground-water contamination from halogenated volatile organic

compounds (VOCs) was identified near the neutralization holding

tank site after it was removed early in 1987. Initial concentrations of

contaminants were 50-200 μg/L of trichloroethylene (TCE),

450-1,000 μg/L of cis-1,2,-dichloroethylene (cDCE), 100-500 μg/L

of vinyl chloride (VC), and 20-60 μg/L of Freon 113®.

Ground-water extraction and treatment, using an air stripper, began

late in 1987. The in situ PRB system replaced the existing

pump-and-treat system which was being maintained at a significant

cost. The original system has been removed and the property has

been restored to full economic use. The monitoring wells provide

access to the in situ system for periodic monitoring compliance. 

The contaminated area is in a semiconfined aquifer that is 2-4 ft

thick. It is composed of interfingering zones of silty, fine-grained

sand, fine- to medium-grained sand, and gravelly sand. The

geometry of the aquifer is irregular, with a local presence of clay

lenses. The aquifer is mostly confined by an upper silty-clay and

clay layer, which ranges from 9-12 ft thick, and by a lower aquitard

of clay and silty clay, which is about 65 ft thick. 

Technology Application

The physical constraints of the site helped determine the geometry

of the PRB and the construction technique used. To address

historically changing ground-water flow directions, low

permeability walls were installed upgradient and perpendicular to

the PRB to contain affected ground water onsite prior to flow

through the barrier. The treatment zone is sandwiched between

permeable gravel layers to evenly distribute flow through the zone.

The barrier itself is 4 ft wide, 36 ft long, and 20 ft deep. It is

charged with 220 tons of granular iron (Fe0) to a depth of about 11

ft. A low, permeable “wing” that extends perpendicular from the

treatment wall to about 20 ft downgradient was installed to reduce
23

the impact on ground-water velocity through the wall due to

variations in regional flow direction. 

Cost

Installation cost for the in situ PRB system, including the slurry

walls used to direct ground water toward the permeable reactive

barrier, was $1,000,000. This includes the cost of construction,

materials, and the iron. Design cost for this system is not available.

Results

The cleanup goal established for the site is to reduce contaminant

concentrations to levels below the Maximum Contaminant Level

(MCL) set by the State of California and Primary Drinking Water

Standards—5 μg/L for TCE, 6 μg/L for cDCE, 0.5 μg/L for VC,

and 1,200 μg/L for Freon 113®. Since installation, VOC

concentrations have been reported below cleanup goals from

monitoring wells located within the iron wall. While seasonal

hydraulic mounding has been observed above the PRB, it is not

expected to affect long-term performance of the barrier. Affected

ground water is contained onsite when mounding is present. When

the mounding dissipates, ground water again flows through the

barrier and is treated. 

Lessons Learned 

In addition to helping distribute flow through the PRB, the pea

gravel zone placed upgradient of the PRB has resulted in

precipitation of naturally occurring minerals and partial treatment of

target chemicals upgradient of the iron treatment zone. Some mixing

of the iron into the pea gravel zone is likely to have occurred during

construction and resulted in chemical conditions favorable for some

mineral precipitation (for example, higher pH, lower redox potential

than ambient ground water). This is evidenced by inorganic

chemistry data from wells within the pea gravel. While site

managers did not anticipate this benefit, the result is expected to

extend the life of the treatment zone relative to the potential negative

effects of mineral precipitation.
24

Kansas City Plant, Kansas City, MO

Installation Date: 

April 1998 

Contaminants: 

1,2-DCE, VC 

Reactive Media: 

Fe0

Design Cost: 

$200,000 

Installation Cost: 

$1,300,000 

Construction: 

Continuous Trench 

Point of Contact: 

Paul Dieckmann 

AlliedSignal FM&T 

2000 East 95th St. 

(P.O. Box 419159) 

Kansas City, MO

64141-6159 

Tel: 816-997-2335 

Fax: 816-997-7361 

E-mail:

pdieckmann@KCP.com

A permeable reactive barrier (PRB) was installed in April 1998 at

the U.S. Department of Energy's Kansas City Plant in Kansas City,

MO.

Site Background

Contaminants of concern include 1,2-dichloroethylene (1,2-DCE)

and vinyl chloride (VC). Maximum initial concentrations

encountered at the site were 1,377 μg/L of 1,2-DCE and 291 μg/L

of VC.

The Kansas City Plant site is underlain by alluvial sediments that

range from 20-33 ft in thickness. Lower alluvial sediments are

characterized by low plasticity clays that overlie basal gravels. The

alluvial sediments are underlain by bedrock shales. The basal gravel

is the most permeable unit and acts as a semi-confined aquifer. The

hydraulic conductivity of the basal gravel is 34 ft/day, while the

hydraulic conductivity of the overlying clay unit is 0.75 ft/day. 

Technology Application

The PRB was constructed as a continuous trench measuring 130 ft

long. Sheet piles were driven into bedrock to support the side walls.

The resulting excavation was 6 ft wide. The first 6 ft of the trench

above bedrock was filled with 100% zero-valent iron (Fe0). The

remainder of the trench was filled with 2 ft of Fe0 and 4 ft of sand.

These differing thicknesses were used to compensate for the

increased flow-through thickness required for the basal gravel unit.

Approximately 8,320 cubic feet of reactive iron was used in the

permeable barrier. 

Cost

Design costs were approximately $200,000. Design costs included

pre-design site characterization done to obtain additional chemical,

hydrological, and geotechnical data. Installation costs were

$1,300,000. This includes construction, materials, the reactive

material, and hazardous waste transportation and disposal. 

Results

Cleanup goals for the site are Maximum Contaminant Levels

(MCLs) as defined in 40 CFR 141.2 and listed in 40 CFR 141.61(a)

and 40 CFR 264.94. (70 μg/L for 1,2-DCE and 2 μg/L for VC.)

The VOC plume is predominant in the basal gravel unit. A number

of monitoring wells have been installed. Upper completion wells are

screened in the saturated clay. The clay soil extends from the ground
25

surface to a depth of approximately 25 ft. Lower completion wells

are screened in the basal gravel formation which varies in thickness

from about 3-5 ft and overlays the bedrock (shale). Lower

completion wells were installed at the upgradient face, center, and

downgradient face of the wall at three locations. Sidegradient wells

were installed as well to confirm that the contamination is not going

around the wall. Results of a January 16, 1999, sampling event

indicate that all compliance wells are below MCLs. 

Plans call for investigative fieldwork to be conducted at the PRB in

February 1999. This will include subjecting a number of the wells to

colloidal borescope measurements, heat-pulse flow meter

measurements, and enhanced (nitrogen pressure) single well testing

in order to address the following questions:

Can flow rates and directions within an iron wall be adequately

determined? 

Are there significant flow contrasts within the treatment area?

Can the enhanced single-well testing procedure adequately 

determine permeability contrasts within the treatment zone?

How do the borescope, heat-pulse meter, and enhanced 

single-well testing procedures compare with respect to 

ease-of-use and precision of measurement? 

Lessons Learned 

The two main advantages for choosing the continuous permeable

wall design were predictability and economics. 

A continuous permeable wall impacts the existing ground-water

flow system less than some other designs. Modeling (predicting)

“changes” in flow directions and velocities were not required for

this design as would have been for a funnel-and-gate system. The

upgradient horizontal extent of the plume and ground-water levels

are expected to experience little change.

The cost and time required for constructing a continuous permeable

reactive wall was estimated to be less than for constructing a series

of impermeable wall and gate sections. The continuous wall was

expected to be constructed with a one-pass deep trenching machine.

However, the contractor had difficulties with the trenching machine,

which may have been due to the heavy, wet clay. The problems

encountered resulted in utilization of conventional sheet pile

construction of the permeable wall. This should actually benefit the

long-term performance. For example, there was better opportunity

during the installation process to verify intimate contact of iron

placement with the bedrock surface; additional wall thickness was
26

created by the use of “Z” piles; and uniform, continuous placement

of iron was visually verified.
27

Lowry Air Force Base, CO

Installation Date:

December 1995

Contaminants:

TCE

Reactive Media:

Fe0

Installation Cost:

$530,000

Construction:

Funnel and Gate

Point of Contact:

William A. Gallant

Versar, Inc.

11990 Grant Street

Suite 500

Northglenn, CO 80233

Tel: 303-452-5700

Fax: 303-452-2336

E-mail:

gallabil@versar.com

A demonstration project of a permeable reactive barrier (PRB) to

remediate ground water contaminated with chlorinated

hydrocarbons was initiated at Lowry Air Force Base, CO. 

Site Background

Contamination at Lowry is a result of various base activities

generating contaminants that were transferred to local ground water

via storm drains, septic tanks, or direct infiltration. The total

chlorinated hydrocarbon concentration was approximately 1,400

μg/L, primarily consisting of trichloroethylene (TCE).

The Lowry site is underlain by unconsolidated alluvial deposits and

artificial fill that is approximately 18 ft thick. These surficial deposits

overlie bedrock consisting of silty claystones and sandy siltstones.

The local water table aquifer is approximately 9 ft below ground

surface (bgs) and saturates alluvial material as well as the upper 10 ft

of underlying bedrock in places. Local ground-water flow patterns

are partly controlled by paleochannels eroded into the underlying

bedrock. Hydraulic conductivity for the site averages 35 ft/day, and

the average ground-water velocity is 1 ft/day.

Technology Application

The funnel-and-gate system constructed consists of a 10-ft-wide and

5-ft-thick reactive wall composed of 100% granular, zero-valent iron

(Fe0) and two 14-ft sheet piling walls that were installed to a depth

of 17 ft. 

Cost

The total installation cost for the system was approximately

$530,000. This includes design, construction, materials, and the

reactive material.

Results

Thirty-four wells located within and proximate to the wall were

used to monitor the system’s performance. Seven sets of samples

were taken from December 1995 through June 1996. Data analysis

indicates that a first-order, abiotic reaction involving reductive

dehalogenation is taking place within the reactive iron wall.

Chlorinated hydrocarbons are being completely degraded within the

first foot of the wall. After 18 hours residence time (2 ft into the

wall), all analytes degrade to their respective analytical quantitation

limits. In addition, intermediate breakdown products produced

during the process are also degraded. The wall was resampled in
28

May 1997 with similar results. Since the PRB was designed and

built as a short-term solution, there are no plans to continue the

monitoring. A slurry wall containment area was constructed in

October 1997 30-50 ft upgradient of the PRB as part of a new

source-area remedial system.
29

U.S. Coast Guard Support Center, Elizabeth City, NC

Installation Date:

June 1996

Contaminants: 

Cr+6, TCE

Reactive Media: 

Fe0

Installation Cost: 

$500,000

Construction:

Continuous Trench

 

Point of Contact:

Robert W. Puls 

U.S. EPA/National Risk 

Management Research 

Laboratory 

P.O. Box 1198 

Ada, OK 74820 

Tel: 580-436-8543 

Fax: 580-436-8706 

E-mail:

puls.robert@epa.gov

A full-scale demonstration of a permeable reactive barrier (PRB) to

remediate ground water contaminated with chromium and

chlorinated organic compounds was initiated at the U.S. Coast

Guard Support Center site in Elizabeth City, NC, in 1995. 

Site Background

The primary contaminants of concern are hexavalent chromium

(Cr+6) and trichloroethylene (TCE). Initial maximum concentrations

were more than 4,320 μg/L for TCE and more than 3,430 μg/L for

Cr+6. The contaminant plume was estimated to cover a 34,000-ft2

area. The plume is adjacent to a former electroplating shop that

operated for more than 30 years prior to 1984 when operations

ceased. Ground water begins approximately 6 ft below ground

surface, and a highly conductive zone is located 16-20 ft below the

surface. This layer coincides with the highest aqueous

concentrations of chromium and chlorinated organic compounds

found on the site. A low-conductivity layer—clayey, fine sand to

silty clay—is located at a depth of about 22 ft. This layer acts as an

aquitard to the contaminants located immediately above. 

Technology Application

A continuous wall composed of 100% zero-valent iron (Fe0) was

installed in June 1996 using a trencher that was capable of installing

the granular iron to a depth of 24 ft. The continuous trenching

equipment used for the installation has a large cutting chain

excavator system to remove native soil combined with a trench box

and loading hopper to emplace the iron.

The trenched wall is approximately 2 ft thick and about 150 ft long.

The wall begins about 3 ft below ground surface and consists of

about 450 tons of granular iron. 

Cost

The total installation cost was $500,000. This includes the cost of

design, construction, materials, and the iron, which cost about

$175,000. 

Results

The wall was designed to meet cleanup goal concentrations of 0.05

mg/L of Cr+6 and 5 μg/L of TCE. Performance monitoring has been

conducted on a quarterly basis since November 1996. In addition to

2-in PVC compliance wells, the wall is monitored using a series of

multilevel sampling (MLS) ports to monitor the geochemical

mechanisms occurring in the barrier and in the downgradient

aquifer. Sampling results for chromium indicate that all chromium

has been removed from the ground water within the first 6 inches of

the wall as expected. No chromium has been detected downgradient
30

of the wall either in the MLS ports or in the compliance wells

located immediately behind the wall. Results thus far indicate that

the barrier is successfully reducing TCE, c-DCE, and vinyl chloride

concentrations to less than MCL levels for the vast majority of the

monitored portions of the wall. Of 29 downgradient MLS ports,

MCLs for TCE and vinyl chloride are exceeded in 1 and 3 ports,

respectively. TCE concentrations are generally below 5 μg/L within

the wall, but exceed 50 μg/L at the lowest depth. There are some

indications that the TCE plume may have dipped lower in this part

of the aquifer following wall installation. The slight elevation

beyond target levels for vinyl chloride seen in the MLS ports are not

reflected in adjoining compliance wells. Downgradient vinyl

chloride concentrations in the MLS ports have declined with time.

Nowhere do c-DCE concentrations exceed regulatory limits. 

Numerous vertical and angle cores also have been collected at the

site to examine changes to the iron surface and to evaluate the

formation of secondary precipitates which may affect wall

performance over time. These cores continue to be studied. 

Lessons Learned 

Researchers are investigating the possibility that the TCE plume has

dipped lower in the aquifer after the wall was installed and is now

moving under the wall. A significant amount of recharge occurred

into the reaction zone following installation due to removal of the

concrete parking lot covering the site. This recharge may have

driven the plume deeper than had previously been observed

allowing some of the plume to move under the wall. Interestingly,

there is still significant treatment below the wall where no iron

resides. 

Based on limited preliminary electrical conductivity profiles, the

wall is approximately 19-21 in thick, compared to the design

thickness of 23 in. Some minor vertical discontinuities were

observed in the conductivity data and have been confirmed with

coring. These small gaps are probably due to bridging within the

trencher hopper during iron emplacement.
31

Area 5, Dover Air Force Base (AFB), DE

Installation Date:

January 1998

Contaminants:

PCE, TCE, DCE

Reactive Media:

Fe0

Installation Cost:

$800,000

Construction:

Funnel and Gate

Point of Contact:

1Lt. Dennis O'Sullivan

Air Force Research

Laboratory Airbase &

Environmental

Technology Division

(AFRL/MLQ)

139 Barnes Drive

Suite 2

Tyndall Air Force Base,

Florida 32403-5323 

Tel: 850-283-6239

Fax: 850-283-6064

E-mail:

dennis_o’sullivan@

ccmail.aleq.tyndall.

af.mil

A pilot-scale field demonstration of a permeable reactive barrier

(PRB) is being conducted at the Area 5 site at Dover AFB, DE. The

demonstration is funded by the Strategic Environmental Research

and Development Program (SERDP). 

Site Background

The Dover site is contaminated with perchloroethylene (PCE),

trichloroethylene (TCE), and dichloroethylene (DCE). The

maximum concentrations encountered during site characterization

were 5,617 μg/L of PCE, 549 μg/L of TCE, and 529 μg/L of DCE.

Area 5 lies within the Atlantic Coastal Plain Physiographic

Province, consisting of Cretaceous to Recent sedimentary deposits

of gravel, sand, silt, clay, limestone, marl, and chalk dipping to the

southeast. Ground water is located 5-15 ft below ground surface.

The clay aquitard is located 40-45 ft below the surface. The

hydraulic conductivity values used for design of the permeable

barrier were based on an aquifer conductivity range of 10-50 ft/day.

Technology Application

Major objectives of the demonstration include comparing two

reactive media schemes and examining innovative emplacement

techniques designed to reduce the cost of construction for PRB

systems. The funnel-and-gate system, installed in January 1998,

consists of two gates that are 8 ft wide and 45 ft deep. One gate is

filled with pure, zero-valent iron (Fe0) filings with a 10% iron/sand

pretreatment zone to stabilize flow and remove dissolved oxygen.

The second gate also is filled with iron, but it is preceded by a 10%

pyrite/sand mixture. The mixture serves to moderate the pH of the

reactive bed, thereby decreasing the precipitates formed.

The gates were constructed with 8-ft-diameter caissons that were

removed after reactive media emplacement. The funnel sections

were built using Waterloo interlocking sheet piling driven to the

45-ft depth and keyed into the underlying clay aquitard. 

Cost

The total installation cost for the system was $800,000. This

includes the cost of design, construction, materials, and the reactive

material.

Results
32

Results of the demonstration are unknown at this time. Two

comprehensive monitoring events are planned for July and

December 1998. The demonstration is being used to validate the

document “Design Guidance for Application of Permeable Barriers

to Remediate Dissolved Chlorinated Solvents,” developed with

input from state and federal regulators and published in February

1997. At the completion of the project (approximately December

1998), the guidance document will be updated to reflect lessons

learned.
33

Borden Aquifer, Ontario, Canada

Installation Date:

1991

Contaminants:

TCE, PCE

Reactive Media:

Fe0

Installation Cost:

$30,000 (not including

Fe0 and labor)

Construction:

Continuous Trench

Point of Contact:

Stephanie F. O’Hannesin

Waterloo Centre for

Groundwater Research

University of Waterloo

Waterloo, Ontario

N2L 3G1 Canada

Tel: 519-885-1211 x3159 

Fax: 519-763-2378 

E-mail: sohannesin@

beak.com

A pilot-scale demonstration of a permeable reactive barrier (PRB) to

remediate ground water contaminated with trichloroethylene (TCE)

and perchloroethylene (PCE) was conducted at the Canadian Forces

Base in Borden, Ontario, Canada. The PRB was installed in 1991. 

Site Background

Contamination was the result of a previous site study to determine

the dissolution characteristics of a mixed non-aqueous fluid. The

contaminant plume was about 6.5 ft wide and 3.3 ft thick. Initial

concentrations were 250,000 μg/L TCE and 43,000 μg/L PCE. The

plume source was located about 13 ft below ground surface (bgs)

and 3.3 ft below the water table.

The contaminated surficial aquifer is composed of medium-fine

sand. Its lower boundary is a thick clay deposit located 30 ft below

the surface. The upper boundary of the aquifer varies between 6.5 ft

and 10 ft bgs. Hydraulic conductivity for the surficial sand aquifer is

20.5 ft/day.

Technology Application

Reactive material was installed using sealable joint sheet piling 18 ft

downgradient from the source. Individual piles were interlocked to

create a rectangular cell normal to ground-water flow direction that

was 18 ft long, 5 ft wide, and 32 ft high. The pilings were then

driven as a unit to a depth of 32 ft using a hydraulic vibratory driver

suspended by a crane. The joints were sealed with a bentonite-based

sealant, and the water table was lowered below the depth of

excavation. The cell was then excavated and the native material was

replaced with a mix of 22% (by weight) zero-valent granular iron

(Fe0) and 78% coarse sand from 12.4-20 ft bgs. This mixture had a

hydraulic conductivity of 124 ft/day. After emplacement of the

mixture, the sheet pilings were removed. 

Cost

The cost for installation, exclusive of the cost of reactive iron and

labor, was $30,000. The reactive material and the labor were

donated.
34

Results

A total of 348 monitoring wells were installed upgradient and

downgradient from the wall, as well as within the reactive material.

Concentration distributions were monitored over a period of five

years. The PRB reduced TCE concentrations by 90% and PCE

concentrations by 86%. No vinyl chloride was detected in the

samples. The low amounts of calcium carbonate precipitate detected

in the wall after five years suggests that the wall’s performance

should persist for at least another five years. Since the residual

source was remediated using permanganate flushing, there are no

plans for additional sampling.
35

Cape Canaveral Air Station, FL

Installation Date:

October-November 1997

Contaminants:

TCE, DCE, VC

Reactive Media:

Fe0

Design Cost:

$292,000 (for two

barriers)

Installation Cost:

$279,000 (Mandrel) 

$238,000 (Jet-Assisted

Grout)

Construction:

Continuous Walls with 

Overlapping Panels

Point of Contact:

Maj. Edward Marchand

U.S. Air Force Center for

Environmental

Excellence

3207 North Road

Brooks AFB, TX 78235

Tel.: 210-536-4364

Fax: 210-536-4330 

E-mail:

edward.marchand@

hqafcee.brooks.af.mil

Side-by-side, pilot-scale demonstrations of two emplacement

techniques for permeable reactive barriers (PRBs) are being

conducted at the industrial area of Cape Canaveral Air Station, FL. 

Site Background

The site is contaminated with 90 mg/L of trichloroethylene (TCE), 7

mg/L of vinyl chloride (VC), and 170 mg/L of dichloroethylene

(DCE). The water table at the site is about 5 ft below ground

surface. Ground-water flow is in the range of 0.1-0.5 ft/day and

changes with depth.

Technology Application

A major objective of the demonstration was to compare the two

emplacement methods. Both wall systems included a 50-ft main

wall followed by 10-ft wall placed 4 ft downgradient from it and a

third 10-ft wall placed 4 ft downgradient of the second. This

provided a total target length of 70 linear ft for each technique. In

the first installation, a hollow mandrel, or vibrated beam, created a

void that is 4 in thick, about 45 ft deep, and 32 in long for each

panel of the wall. A vibratory hammer drove the beam to the

required depth. The void was filled with the reactive material

through a chute at the top of the mandrel. About 98 tons of 100%

zero-valent iron (Fe0) was used to construct the wall, and adjacent

panels were overlapped to provide continuity in the wall. In the

second installation, high-pressure water jets, guided by a 36-in

I-beam, were used in addition to the water to create the void for

each wall panel. A vibratory hammer was used to drive the beam to

depth. The void was filled with a slurry made by mixing Fe0 with

guar gum and a binder. About 107 tons of Fe0 was used for this

emplacement. As in the first installation, adjacent wall panels were

overlapped to provide continuity.

Cost

Total installation cost for the two barriers at this site was $809,000.

This includes design, construction, materials, and the reactive media.

The design cost for both walls totaled $292,000. Mobilization and

demobilization, construction, materials, and the reactive material for

the mandrel system was $279,000. Mobilization and demobilization,

construction, materials, and the reactive material for the jet-assisted

grout system was $238,000.

Results
36

Results of the demonstration are unknown at this time. Dedicated in

situ flow sensors and ground-water monitoring wells were installed

after construction of the walls to track performance. 

Quarterly monitoring is scheduled to continue until November 1998,

and a report of demonstration results is expected to be issued in

1999.
37

Industrial Site, NY

Installation Date:

May 1995

Contaminants:

TCE, cDCE, VC

Reactive Media:

Fe0

Installation Cost:

$250,000

Construction:

Funnel and Gate

Point of Contact:

Diane Clark 

Stearns & Wheler 

One Remington Park

Drive 

Cazenovia, NY 13035 

Tel: 315-655-8161 

Fax: 315-655-4180 

E-mail:

diane.clark@

stearnswheler.com

A pilot-scale, in situ funnel-and-gate system using metal-enhanced

reductive dehalogenation was installed at an industrial facility in

New York in May 1995 and operated for 2.5 years. 

Site Background

A 370-ft-wide plume of trichloroethylene (TCE) with

concentrations of 300 μg/L existed at this former plating facility. As

a result of reductive dehalogenation of TCE, 100-500 μg/L of cis1,2-dichloroethylene (cDCE) and 80 μg/L of vinyl chloride (VC)

also were present. These contaminants were present in a 15-ft

shallow sand and gravel aquifer that overlays a dense clay confining

layer about 20 ft below ground surface (bgs). The water table was

located approximately 4-5 ft bgs. Hydraulic conductivity of

materials in this area was approximately 1.6 in/sec.

Technology Application

The reactive section (gate) of the system contained zero-valent iron

(Fe0). It was 12 ft long, 3.5 ft thick, and extended from 3-18 ft

below grade. The gate was flanked by 15-ft sections of sealable

joint sheet piling extending laterally on either side to form the

funnel. Monitoring wells were installed upgradient, within, and

downgradient from the reactive zone.

Cost

Installation costs for the system were approximately $250,000. This

includes the cost of design, construction, materials, and 45 tons of

reactive material, which cost $30,000 (or about $0.12/gal treated).

Results

Data on volatile organic compounds (VOCs) indicated that

chlorinated VOC concentrations were reduced to Maximum

Contaminant Levels (MCLs), or approximately 5 μg/L for TCE and

cDCE and 2 μg/L for VC, within 1.5 ft of travel through the

reactive zone. Consistent performance was maintained over the

2.5-year monitoring period. Based on water-level data, the

ground-water flow velocity through the zone was about 1 ft/day,

and a 24-ft wide portion of the plume was captured and treated.

Microbial analyses on ground-water samples indicated no significant

increase in microbial populations in the Fe0 relative to the population

present in the aquifer.

Approximately 2,098,800 gal of ground water were treated during

operation of the pilot-scale system. 
38

The PRB system was destroyed following completion of the

pilot-scale demonstration to make way for a full-scale installation in

1997.
39

LEAP Permeable Barrier Demonstration Facility, Portland, OR

Installation Date:

October 1997

Contaminants: 

Cr+6, PCE

Reactive Media: 

SMZ

Design Cost:

$75,000

Installation Cost: 

$25,000 

Construction: 

Hanging Barrier in

Perforated Metal Frame 

Point of Contact:

Robert Bowman

Dept. of Earth &

Environmental Science

New Mexico Tech

801 LeRoy Place

Socorro, NM 87801 

Tel.: 505-835-5992

Fax: 505-835-6436

E-mail:

bowman@nmt.edu

A pilot-scale demonstration was conducted at the Large

Experimental Aquifer Program (LEAP) site at the Oregon Graduate

Institute of Science and Technology near Portland, OR. 

Site Background

The main purpose of the demonstration was to quantify the ability of

a surfactant-modified zeolite (SMZ) permeable reactive barrier

(PRB) to intercept and retard the migration of a mixed plume

containing 22 mg/L of chromate (Cr+6) and 2 mg/L of

perchloroethylene (PCE). The goal was to test laboratory-based

predictions of behavior of the SMZ, using Cr+6 and PCE as “type”

contaminants (anionic metal and chlorinated hydrocarbon). The

pilot-test was conducted in a contained, simulated aquifer. The

aquifer was filled with sand and had a hydraulic conductivity of

56.7 ft/day. 

Technology Application

The barrier of SMZ was hung in the center of the simulated aquifer

about 3 ft above the base in order to simulate emplacement in front

of an advancing plume in a shallow, unconfined aquifer. The barrier

had three modules, each about 6.5 ft long. Overall, the barrier was

about 20 ft long, 3 ft thick, and 6.5 ft deep, and used 12 tons of the

reactive medium. Since this was a pilot-scale test under controlled

conditions, the reactive medium was contained in a frame to

facilitate removal and replacement with other test media in the

future. 

Cost

Total design cost for the barrier system was about $75,000. Total

installation cost was about $25,000. This includes the cost of 

construction, materials, and the reactive material. 

Results

The contaminant plume was injected into the simulated aquifer for 2

months, and performance was monitored. Samples were collected

approximately weekly from a network of 63 sample nests (315

sample points) in the aquifer and 18 sample nests (90 sample points)

within the barrier. Analysis of preliminary data indicates that the

barrier performed according to design specifications, with

retardation factors for Cr+6 and PCE both on the order of 50. Final

interpretation of data from the sampling and chemical analyses is in

progress. Pending the results of this of the pilot-scale effort, a

full-scale implementation is anticipated.
40

Lessons Learned 

Barrier performance is very sensitive to the interface between

aquifer material and reactive barrier materials. Sufficient

permeability contrast must be established and maintained to avoid

plume deflection. The causes for poor permeability contrast,

whether due to inherent media property differences or barrier

installation, can be difficult to isolate. Long-term compaction of the

material with resultant loss in hydraulic conductivity needs further

evaluation. Low-conductivity zones in an earlier phase of the project

were difficult to detect and locate.
41

Massachusetts Military Reservation CS-10 Plume, Falmouth, MA

Installation Date:

June 1998

Contaminants:

PCE, TCE

Reactive Media:

Fe0

Installation Cost:

$160,000

Construction:

Hydraulic Fracturing

Point of Contact:

Robert W. Gillham

University of Waterloo

2400 University Avenue

West

Waterloo, Ontario

Canada N2V 1T4

Tel: 519-888-4658

Fax: 519-746-1829

E-mail: rwgillha@

sciborg.uwaterloo.ca

Installation of a permeable reactive barrier (PRB) system to

remediate ground water contaminated with chlorinated solvents was

completed by University of Waterloo researchers at the

Massachusetts Military Reservation (MMR) near Falmouth, MA, in

1998.

Site Background

The uniqueness of the project was the great depth of the site—the

Chemical Spill 10 (CS-10) plume extends to about 120 ft below

ground surface (bgs) near its source area. The demonstration

program was pilot-scale in width, but full-scale in depth. The

primary contaminants of concern at this site are perchloroethylene

(PCE) and trichloroethylene (TCE), for which initial maximum

concentrations of 300 μg/L and 15 μg/L, respectively, were

identified. A 600 ft-wide contamination plume resulting from the

maintenance of BOMARC missiles and related equipment during

the 1960s exists in the area of MMR’s Buildings 4642 and 4601,

now known as the UTES site. The CS-10 demonstration site is

located in an area of glacial outwash sand and gravel, where the

water table is located approximately 80 ft bgs. Ground-water flow

velocity in the area is approximately 1 ft/day, and the horizontal

hydraulic conductivity is approximately 200 ft/day. Maximum

contaminant concentrations were identified at about 100 ft bgs. 

Technology Application

Two iron walls approximately 20 ft apart were installed

perpendicular to the contaminant plume using vertical

hydrofracturing with a guar-based slurry. In the preliminary design

for this project, installation methods were selected for their ability to

emplace granular iron to the required depth. This installation

technique required the drilling of 1-ft-diameter boreholes at 15-ft

intervals along the wall. The “frac wells” were installed from

ground surface to below the base of the contamination zone, and a

specially-designed frac tool was used to cut a vertical notch for

initiation of the fracture. A fracture was then induced and filled with

granular iron suspended in a hydrated and cross-linked guar slurry.

The propagating fracture from one frac well coalesced with the

emplaced material from the adjacent well, thus forming a continuous

vertical wall. The upgradient wall contains 44 tons of fine- to

medium-granular iron (Fe0) (Master Builders GX-027), averages 3.3

inches in thickness and 48 ft in width, and extends from

approximately 78 ft to more than 120 ft in depth. 
42

A second wall, of similar dimensions, but consisting of a mixture of

5 tons of sand and 5 tons of granular iron, was emplaced to

demonstrate the possible use of sand as a filler and permeabilityincreasing amendment for more highly reactive enhanced-iron

materials. The upgradient, 100%-iron wall was verified by active

resistivity and borehole radar tomography, hydraulic pulse

interference testing, and borehole deviation measurements. More

than 30 monitoring wells have been installed to monitor

performance of the demonstration project. 

Installation cost for this demonstration is estimated to be $160,000.

This includes design, construction, materials, and the reactive media. 

Results

Although cleanup goals were not specified for this demonstration,

cleanup to levels below maximum contaminant levels (MCLs)

served as the target. Sampling of the ground water upgradient and

downgradient of the PRB system is conducted every 2-3 months.

Results of the demonstration will be available upon its completion in

mid-2000. 

Lessons Learned

It was recognized early in the demonstration process that, depending

upon the initial contaminant concentrations and flow velocity, this

type of PRB system may require multiple walls to achieve a

sufficient thickness. For the MMR CS-10 source area plume, three

3-in thick commercial Fe0 walls were expected to be needed for full

treatment with an adequate factor of safety. 

The 100% iron wall was installed successfully. During the

installation of the second wall, however, fracturing control was lost

when the propagating fracture came close to two screened

monitoring wells deviating as much as 7 ft horizontally over their

150-ft length. Use of the system to remediate deep plumes such as

this requires that the proximity (3-dimensional coordinates) of

screened monitoring wells to the wall installation be carefully

planned and checked with borehole deviation testing. As a result of

an unanticipated delayed break of the cross-linked guar during

construction of the system, more time was required for

reestablishment of ground water flow through the wall.

Accordingly, it was determined that an improved guar-iron mix

design was needed to establish flow through reactive zones soon

after installation of the walls. 
43

Moffett Federal Airfield, Mountain View, CA

Installation Date: 

April 1996 

Contaminants: 

TCE, 1,2-DCE, PCE 

Reactive Media: 

Fe0

Design Cost: 

$100,000 

Installation Cost: 

$365,000 

Construction: 

Funnel and Gate 

Point of Contact:

Mr. Chuck Reeter 

Naval Facilities

Engineering

Service Center 

1100 23rd Avenue,

Code 411 

Port Hueneme, CA

93043-4370 

Tel: 805-982-0469 

Fax: 805-982-4304 

E-mail: creeter@

nfesc.navy.mil

A pilot-scale permeable reactive barrier (PRB) was constructed in April

1996 at the former NAS Moffett Field in Mountain View, CA, by the

U.S. Navy Engineering Field Activity-West. 

Site Background

Previous investigations identified extensive ground-water

contamination on the site from dissolved chlorinated

hydrocarbons—trichloroethylene (TCE), dichloroethylene (1,2-DCE),

and perchloroethylene (PCE)—much of which originated offsite. Initial

concentrations were 2,990 μg/L (TCE), 280 μg/L (1,2-DCE), and 26

μg/L (PCE) upgradient of the iron gate. The overall Moffett Field

solvent plume is more than 10,000 ft long and about 5,000 ft wide. 

Subsurface sediments at the Moffett Field PRB site are a mixture of

alluvial-fluvial clay, silt, sand, and gravel. Sands and gravels are

present as lens-shaped, interbraided channel deposits that are presumed

to have incised into the clay and silt layers. Contamination is present in

two aquifer zones that extend from 5-60 ft below ground surface (bgs).

These aquifer zones are separated by a discontinuous, semiconfining

clay layer (aquitard) at approximately 25 ft bgs, ranging from 1-15 ft in

thickness. Average linear flow velocities from onsite pumping tests

were calculated to be about 1-4 ft/day. Hydraulic conductivity values

for the separating aquitard layer range from 10-5-10-3 ft/min. Soil

porosity values in the silts and sands ranged from 30-45%. 

Technology Application

A funnel-and-gate system was installed in the upper aquifer zone to just

above the aquitard using a trenching method. The system includes a

reactive iron gate that is 10 ft wide by 6 ft long and contains about 75

tons of granular zero-valent iron (Fe0). The iron cell is bounded by 2-ft

sections of pea gravel at upgradient and downgradient locations. Two

20-ft-long steel sheet pile funnels or wing walls are positioned on either

side of the reactive iron gate. 

Costs

The costs of planning and design of the system was $100,000.

Installation cost, including construction, materials, and the reactive

material, was approximately $365,000. Bench-scale testing required

another $75,000. 

Results

The U.S. Department of Defense Environmental Security Technology

Certification Program (ESTCP) has sponsored the demonstration
44

project at Moffett Field for the past three years. The Naval Facilities

Engineering Service Center has collected performance monitoring and

cost data to validate the PRB technology for potential use at DoD sites

worldwide. Water quality sampling from 1996 (June and September)

and 1997 (January, April, July, and October) from about 70 monitoring

wells in or near the reactive barrier consistently have indicated

significant degradation of chlorinated compounds. All principal

contaminant concentrations had been reduced to below Maximum

Contaminant Levels (MCLs) or non-detectable levels within the first

2-3 ft of the gate (iron cell). Bromide tracer testing at the PRB site

revealed that flow velocities through the cell are about 0.5-2 ft/day. The

final PRB technology evaluation report for the Moffett Field pilot

demonstration project was published in November 1998. A summary

version was published in December 1998. 

Lessons Learned 

Coring results have suggested that conditions exist for potential

long-term formation of chemical precipitates in the iron cell. This may

lead to an eventual reduction in the longevity and efficiency

(permeability and reactivity) of the reactive barrier. The DoD ESTCP,

U.S. Environmental Protection Agency (EPA), and U.S. Department

of Energy (DOE), in partnership with the RTDF Permeable Reactive

Barriers Action Team, are sponsoring additional performance and

longevity evaluations to support widespread regulatory acceptance and

encourage use of PRB technology. As part of these efforts to further

investigate the potential concerns for biological fouling and chemical

precipitation, annual water-quality sampling and iron-cell coring are

planned at several PRB sites across the country, including Moffett

Field, over the next three years.
45

Savannah River Site TNX Area, Aiken, SC

Installation Date: 

July 1997

Contaminants: 

TCE, cDCE, CT, NO3

Reactive Media: 

Fe0

Installation Cost: 

$120,000

Construction: 

GeoSiphon Cell

Point of Contact 

Mark Phifer 

Westinghouse SRC/SRS 

Building 773-42A 

Aiken, SC 29808 

Tel: 803-725-5222 

Fax: 803-725-7673 

E-mail: 

mark.phifer@srs.gov

The GeoSiphon Cell (patent pending) was installed in the TNX

flood plain at the Savannah River Site (SRS) by auger and caisson

methods in July 1997. The cell was installed to demonstrate

treatment of ground water contaminated with chlorinated volatile

organic compounds (CVOCs).

Site Background

Ground-water contamination has been detected in the TNX water

table aquifer, but not in the semi-confined or deep aquifers

underlying the site. Predominant contaminants, and average

concentrations of each, detected in the TNX flood plain are

trichloroethylene (TCE) at 200-250 μg/L, cis-1,2-dichloroethylene

(cDCE) at 20-50 μg/L, carbon tetrachloride (CT) at 15-45 μg/L, and

nitrate (NO3) at 10-70 mg/L. 

The TNX Area is a semi-works facility for the Savannah River

Technology Center, which is located 0.25 mile from the Savannah

River near Aiken, SC. The facility was used for pilot-scale testing

and evaluation of various chemical processes associated with SRS.

The water table elevation averages 100 ft above mean sea level

under the TNX site, while the Savannah River elevation averages

85 ft. In the flood plain where contamination was detected, the

water table aquifer is approximately 35-40 ft thick. It consists of

interbedded sand, silty sand, and relatively thin clay layers. Based

on testing and modeling analysis, the aquifer may be characterized

as having a horizontal hydraulic conductivity of 65 ft/day, vertical

hydraulic conductivity of 30 ft/day, effective porosity of 0.15, pore

velocity of 3 ft/day, and a horizontal gradient of 0.007. 

Technology Application

The TNX GeoSiphon Cell is a large-diameter (8-ft) well containing 

granular zero-valent iron (Fe0) as a treatment media (in place of

gravel pack). The cell passively induces flow by use of a siphon

from the cell to the Savannah River. The flow is induced by the

natural hydraulic head difference between the cell and the river. The

passively-induced flow draws contaminated ground water through

the treatment cell, where the Fe0 reduces the CVOCs to ethane,

ethene, methane, and chloride ions. Treated water is discharged to

the Savannah River. 

During Phase I testing of this technology, which was completed in

December 1997, flow through the TNX GeoSiphon Cell was

induced by pumping and the treated water was discharged to the
46

existing TNX National Pollutant Discharge Elimination System

outfall. Testing indicated that TCE degradation is the limiting

compound to treatment below the Primary Drinking Water Standard

Maximum Contaminant Levels within the TNX GeoSiphon Cell.

Data indicated that approximately 8 gal/hr of ground water

contaminated with 200-250 μg/L of TCE could be treated, while

maintaining the average discharge TCE concentration below 5 μg/L.

Field first-order rate constants produced from the steady state TCE

data increased with flow rate from 0.347 to 0.917/hr. 

During Phase II, flow through the TNX GeoSiphon Cell was

induced by siphon and the treated water was discharged to an

existing outfall ditch that flows into the Savannah River. To allow

continuous operation, the siphon line configuration was optimized to

include an upward rise from the cell to the outfall ditch, an air

chamber at the crest adjacent to the outfall ditch, and a steep drop

into the outfall ditch with line termination in a sump. The head

differential available to drive the system (approximately 1.4 ft)

produced a continuous flow rate of 2.5-2.7 gal/min. Approximately

1.2 ft of head was utilized to drive flow through the 

cell itself, and approximately 0.2 ft of head was utilized to drive

flow through the siphon line. Based on these results, a new siphon

line will be installed between the cell and a target location, thus

producing a 5-ft head differential capable of inducing an estimated

9.5 gal/min through the GeoSiphon Cell. 

Phase III of this demonstration project will involve installation and

operation of a full-scale GeoSiphon Cell system for treatment of the

entire TNX contaminated ground-water plume. 

Cost

Phase I system costs are estimated at $119,155, including $26,400

for iron; $27,411 for other construction materials; and $65,344 for

mobilization, labor, rentals, and related installation expenses.

Approximately 49.7 tons of 0.25-2.0 mm (particle size) granular cast

iron was used in the installation of the first TNX GeoSiphon Cell

(TGSC-1). 

Lessons Learned 

The GeoSiphon Cell was selected for use at the TNX Area because

it offers passive (no power requirements), in situ treatment at lower

operating and maintenance costs than pump-and-treat technology. In

contrast to funnel-and-gate or continuous permeable wall

technologies, the GeoSiphon Cell could be constructed using an

existing foundation and well drilling techniques. In addition, there is

potential for accelerating cleanup through the use of induced flow
47

rates greater than natural flow. With a maximum siphon lift of 25 ft,

application of the GeoSiphon Cell technology was found to be

limited to areas of shallow ground water such as that existing at the

TNX Area.
48

SGL Printed Circuits, Wayne, NJ

Installation Date:

November 1994

Contaminants:

TCE, PCE, cDCE

Reactive Media:

Fe

Installation Cost:

$48,000

Construction:

Reaction Vessel

Point of Contact:

John Vogan 

EnviroMetal

Technologies, Inc. 

42 Arrow Road 

Guelph, Ontario

N1K 1S6 Canada 

Tel: 519-824-0432 

Fax: 519-763-2378 

E-mail:

jvogan@beak.com

Demonstration of a metal-enhanced dechlorination process for

destroying chlorinated volatile organic compounds (CVOCs) in

aqueous media took place from November 1994 to February 1995.

The process was demonstrated under EPA’s SITE Program at the

SGL Printed Circuits site in Wayne, Passaic County, New Jersey,

using a pilot-scale, above-ground treatment reactor containing a

reactive iron medium.

Site Background

Influent ground water was contaminated with trichloroethylene

(TCE) at concentrations ranging from 54-590 μg/L,

perchloroethylene (PCE) at concentrations ranging from

4,100-13,000 μg/L, and cis-1,2-dichloroethylene (cDCE) at

concentrations ranging from 35-1,600 μg/L.

Technology Application

In this technology, ground water pumped from extraction wells and

the sump passes through a check valve, a 5-micron water filter, a

flow meter, and an air eliminator before entering the treatment

reactor. The water filter removes suspended solids from influent

water, eliminating the need for a layer of well sand or pea gravel

above the reactive iron medium.

After entering the treatment reactor, water flows by gravity through

the reactive medium. At the SGL site, an 8-ft-diameter fiberglass

reactor containing a 5.5-ft-thick layer of the reactive medium was

employed. Approximately 20 tons of granular iron were used in the

reactor. The porosity of the iron medium, after placement and

settling in the reactor, was estimated to be about 0.4. The iron rested

on a 6-in layer of coarse silica sand, referred to as “well sand,”

which acted as a strainer and prevented the granular iron from

washing out into the effluent line. The reactor drained through a

collector line located in the well sand at the bottom of the reactor,

and the collector line directed the treated water to the effluent line.

Treated effluent was returned to the shallow, unconsolidated aquifer

through several monitoring wells modified to serve as reinjection

wells. The process provided a reactor contact time of about 1 day.

Cost

Costs for this metal-enhanced dechlorination process were estimated

to be about $91 per 1,000 gal treated. Capital costs for installing an

above-ground treatment reactor such as this were about $48,000,

including equipment and construction but excluding hydrogeologic
49

characterization, bench-scale studies, permitting, and installation of

ground water extraction/reinjection systems. Minimum annual

operation and maintenance costs were approximately $10,000. 

Results

Results indicated that the process achieved the demonstration

effluent target level of 1 μg/L for TCE and PCE, and that PCE

removal efficiencies consistently were greater than 99.9%.

Sedimentation on the reactive iron surface, variations in reactor

temperature, and other factors potentially affected the technology’s

performance. Approximately 61,000 gal of ground water containing

PCE, TCE, and cDCE were treated during the demonstration.
50

Somersworth Sanitary Landfill, NH

Installation Date:

1994

Contaminants: 

TCE, VC 

Reactive Media: 

Fe0

Installation Cost: 

To be determined 

Construction: 

Funnel and Gate

Point of Contact:

Roger Duwart

U.S. Environmental

Protection Agency

Region 1 

John F. Kennedy

Federal Building

Mail Code HBO 

One Congress Street 

Boston, MA 02203 

Tel: 617-573-9628 

Fax: 617-573-9662 

E-mail:

duwart.roger@

epa.gov

Site Background

The Somersworth Sanitary Landfill Superfund Site is a 26-acre landfill

that was constructed in the early 1930s on the site of a former sand and

gravel quarry. The landfill was used to dispose of household trash,

business refuse, and industrial wastes. Waste was burned at the landfill

until 1958. From 1958 to 1981, the waste material was placed in

excavated areas, compacted, and covered with soil. In 1981, use of the

landfill stopped when the City of Somersworth began disposing of its

municipal waste at a regional incinerator. 

In 1981, the City of Somersworth implemented a closure plan for the

landfill that involved the covering of a portion of the landfill with clean

fill. Volatile organic compounds (VOCs), principally trichloroethylene

(TCE) and vinyl chloride (VC), are present in the ground water. TCE

and VC levels have been detected as high as 370 μg/L and 1,900 μg/L,

respectively. 

The site is characterized by sands and gravels having a hydraulic

conductivity ranging from 28-14 ft/day. The hydraulic gradient varies

from 0.01-0.004 ft/ft near the edge of the waste. The top of the water

table ranges from less than 2 ft to about 20 ft below ground surface. As

much as 10% of the waste is in the ground water. The aquifer is about

40 ft thick. 

Technology Application

The clean-up plan selected by EPA uses zero-valent iron (Fe0) to treat

the ground water through reductive dechlorination. Since the

technology has not been implemented at this scale or in a landfill

setting, a pilot-scale wall was installed in 1994 and is currently under

evaluation. The pilot-scale PRB system consists of an 8-ft-diameter

“gate” of iron between layers of gravel. Slurry walls measuring 4.5 ft

funnel ground water through the gate. 

Results for the pilot-scale wall currently under evaluation include: 

VOCs have been reduced 50% between upgradient aquifer and

wall, providing a strong case for biodegradation that occurs via

sequential anaerobic and aerobic processes. 

VOCs have been reduced to non-detectable levels at the first

monitoring point in the wall. 

Ground water velocity has been slower than the design rate due to

reduced hydraulic conductivity (possibly due to soil densification).
51

Reduction in bicarbonate, Ca, Mg, Fe, Mn, and sulfate has been

shown within the first 14 inches of iron zone. 

Within the iron zone, ground water became strongly reducing

(reduced DO, ORP) and alkaline (pH 10). 

The objective of the pilot-scale study has been to provide data to enable

design of a full-scale system to be completed by February 1999. Of

particular interest is whether unacceptable precipitation and/or

biofouling is occurring within or on the iron media. 

The cleanup goals of the full-scale project will be: 

Contaminants Interim Cleanup Level (μg/L) 

Benzene* 5

1,1-Dichloroethylene 7

Methylene chloride* 5

Tetrachloroethylene 5

Trichloroethylene 5

Vinyl chloride 2

cis-1,2-Dichloroethylene 70

trans-1,2-Dichloroethylene 100

(* These contaminants are not affected by the permeable reactive

barrier.) 

Lessons Learned 

During the installation of the pilot-scale wall, contractors attempted to

drive an 8-ft diameter, 48-ft-long steel caisson into the aquifer with a

vibratory hammer. Due to unexpected cobbles which presumably

caused the bottom of the caisson to flare, the caisson became stuck. In

order to remove it (to allow for the placement of pea gravel and iron

filings) the lower 13 ft of the caisson were cut off and plugged. This

allowed the remainder of the caisson to be removed as the gravel and

iron were placed.

The pilot-scale PRB was installed very close to a wetland on the

downgradient side of the landfill. As a result of a nearly snowless

winter, little precipitation infiltrated the landfill; it went into the wetland

instead. This caused a reverse flow (the wetland ground-water level

being somewhat higher than the landfill ground-water level near the

pilot) through the PRB, which made assessment of its effectiveness

difficult. The flow reversal, however, should not negatively affect

long-term performance. 

When a “normal” flow regime was established, less flow than expected

went through the PRB. A “skin effect,” due probably to the installation

technique, was theorized as the cause. Alternate installation techniques

are being investigated to avoid the skin effect and installation problems.
52

A continuous trench of reactive material should allow for flow through

the PRB which more closely emulates flow through the aquifer. 
53

U.S. Naval Air Station, Alameda, CA

Installation Date:

December 1996 

Contaminants:

cDCE, VC, TCE, BTEX

Reactive Media:

Fe0, O

Installation Cost:

$400,000 

Construction:

Funnel and Sequenced

Treatment Gate

Point of Contact:

Michaye McMaster

Beak International Inc.

42 Arrow Rd.

Guelph, Ontario

N1K 1S6 Canada

Tel: 519-763-2325

Fax: 519-763-2378

E-mail:

mmcmaster@beak.com

The second part of a pilot-scale demonstration of an in situ

sequenced permeable reactive barrier (SPRB) for the remediation of

chlorinated solvents and petroleum hydrocarbons was conducted at

Alameda Point (formerly U.S. Naval Air Station Alameda) in

Alameda, California.

Site Background

The initial phase of this demonstration, which had been conducted

at Canadian Forces Base Borden, Ontario, Canada, evaluated three

technologies for their ability to treat perchloroethylene (PCE),

carbon tetrachloride (CCl4) and toluene. The technologies were: (1)

abiotic reductive dechlorination using zero-valent iron (Fe0),

followed by oxygen releasing compound (ORCTM) to promote

aerobic biodegradation; (2) natural attenuation; and (3) a permeable

nutrient injection wall, using benzoate to promote anaerobic

biodegradation, followed by an aerobic (oxygen) biosparge gate for

aerobic biodegradation.

The Alameda demonstration used Fe0 followed by oxygen

biosparging in a funnel-and-gate system to remediate

trichloroethylene (TCE); cis-1,2-dichloroethylene (cDCE); vinyl

chloride (VC); and toluene, benzene, ethyl benzene, and xylene

(BTEX). Total initial (upgradient) concentrations of chlorinated

VOCs exceeded 100 mg/L, and toluene was found at levels of up to

10 mg/L.

Historical air photos of the site indicate open disposal pits

upgradient of the SPRB. The shallow aquifer is composed of 22-24

ft of sandy artificial fill material that was hydraulically placed on bay

silts and clays. The hydraulic conductivity of the overlying sandy fill

material is 0.057 ft/day (~21 ft/year). The underlying bay silts and

clays are 15-20 ft thick and act as a confining unit. Depth to ground

water ranges from 4 to 7 ft below ground surface.

Technology Application

During construction of the funnel-and-gate system, the artificial fill

sand was excavated to the top of the confining bay mud unit. To

prevent settling, a concrete pad (nominally 2 ft thick) was placed at

the bottom of the excavation; the gate was then constructed on this

base. The gate is 10 ft wide and 15 ft long. As ground water passes

through the gate it contacts the following media: about 18 in of

coarse sand mixed with 5% Fe0, 5 ft of Fe0, a 3-ft pea gravel

transition zone, a 3-ft biosparge zone, and a 2-ft pea gravel zone.
54

The 10-ft funnels were placed on either side of the gate,

perpendicular to the direction of water flow.

Between February 1997 and May 1998, two pumping wells were

used to operate the system under controlled conditions. For a period

of about 70 days, the system operated at a flux rate of approximately

45 ft3/day to determine the maximum velocity it could process. At

this velocity, breakthrough was observed in several down-gradient

monitoring points. Then, the system operated for about one year at a

flux rate of approximately 12 ft3/day, more representative of

conditions that would exist as a result of the funnel sections. Finally,

the system was allowed to operate under natural gradient conditions. 

Results

The remedial objectives of the project generally were met, except

with respect to cDCE and VC, with typical effluent concentrations

of about 136 μg/L and 217 μg/L respectively. Retardation of the

toluene or other hydrocarbons as a result of sorption to the granular

iron precluded an assessment of petroleum hydrocarbon

degradation. Breakthrough of cDCE and VC indicated that

biodegradation (likely via aerobic oxidation) of these compounds

was occurring in the biosparge zone. An estimated 66% of the VC

and 30% of the cDCE was volatilized. Assessment of multilevel

data showed excellent degradation (>91%) of the chlorinated

organics using the granular iron at high influent concentrations

(>100 mg/L total VOCs). At lower influent concentrations, almost

complete degradation (>99%) was observed. The biosparge zone

supported aerobic biodegradation of VC and cDCE, and by January

1998 remedial objectives were being met at the last set of sampling

wells in the gate. 

Results obtained to date suggest sparging rates in the biosparge zone

should be minimized to reduce volatilization of contaminants from

the water column. In addition, monitoring should continue so that

long-term performance of the SPRB can be assessed. 

The U.S. Navy has begun to operate the site; current plans call for a

hydraulic study to examine ground-water flow in the funnel-andgate area and for monitoring to continue on a quarterly basis.
55

Watervliet Arsenal, Watervliet, NY

Installation Date:

October 1998

Contaminants:

PCE, TCE, cDCE, 

trans-DCE, VC

Reactive Media:

Concrete, sand, and iron

Design Cost:

$113,000

Installation Cost:

$257,000

Construction:

Excavate and Fill

Point of Contact:

Russell Marsh

U.S. Army Corps of

Engineers, Baltimore

District

P.O. Box 1715

Baltimore, MD 21203

Tel: 410-962-2227

Fax: 404-962-2318

E-mail: russell.e.marsh@

usace.army.mil

A permeable reactive barrier (PRB) pilot system was installed at the

Watervliet Arsenal near Albany, NY, in October 1998 to remediate

ground water contaminated with chlorinated volatile organic

compounds (CVOCs).

Site Background

The contaminated area, known as the Siberia Area, has been used

for the interim storage of raw and hazardous materials involved in

cannon manufacturing. Contaminants and the initial concentrations

found in the area were: perchloroethylene (PCE), 1,100 μg/L;

trichloroethylene (TCE), 1,500 μg/L; cis-dichloroethylene (cDCE),

4,200 μg/L, trans-dichloroethylene (trans-DCE), 11 μg/L; and vinyl

chloride (VC), 1,700 μg/L. Two unconsolidated deposits are

encountered in the area. The upper deposit is a fill material

approximately 2-4 ft thick, and the second is a clayey-silt typically

12-15 ft below grade and extending to the weathered bedrock.

Hydraulic conductivities in the fill material range from 0.4-2.0

ft/day, and from 0.2-1.4 ft/day in the clayey silt. A relatively

conservative ground-water velocity of 0.15 ft/day was used in the

design of the reactive wall. The water table is generally 3-5 ft below

grade.

Technology Application

The PRB system at Watervliet Arsenal consists of two separate

walls. The upgradient wall, which is 205 ft long, is positioned to

capture the majority of the plume source area. The downgradient

wall, which is 83 ft long, was installed to capture a portion of the

plume that is downgradient of the longer wall and to serve as a

polishing wall for the upgradient wall. An excavator with temporary

sheeting and concrete mixing equipment were used to construct the

walls, which contain 163 tons of sand and 165.5 tons of iron.

Excavation was required to remove large debris such as concrete,

rebar, and wood at the site. Use of a nearby concrete plant and truck

provided the ability to obtain a relatively consistent mixture of sand

and iron. 

Design costs for the Watervliet Arsenal PRB system were

$113,000, and installation costs (including construction, materials,

and reactive material) are estimated at $257,000. An additional

$17,000 was incurred for licensing fees.

Results
56

Cleanup goals for the contaminants of concern are: PCE, 5 μg/L;

TCE, 5 μg/L; cis-DCE, 5 μg/L; trans-DCE, 5 μg/L; and vinyl

chloride, 2 μg/L. Monthly ground water sampling will be performed

for six months to monitor remediation progress; semi-annual

sampling will follow. Based on the analytical results of ground

water tests, it is anticipated that concentrations will reach the target

cleanup goals. 

Lessons Learned

Use of this type of PRB system required a thorough understanding

of geohydrologic conditions at the site. It was found that the color of

the sand used in the wall can affect quality-control efforts. Sand

used at the Watervliet Arsenal met the technical requirements such

as gradation and density, but its dark color was similar to that of

iron. As a result, visual differentiation of the material was more

difficult than if a light color of sand had been used.
57

X-625 Groundwater Treatment Facility,

Portsmouth Gaseous Diffusion Plant, Piketon, OH

Installation Date:

March 1996

Contaminants:

TCE

Reactive Media:

Fe0

Installation Cost:

$4,000,000

Construction:

Horizontal Well 

Point of Contact:

Thomas C. Houk

Portsmouth Gaseous

Diffusion Plant

3930 US Route 23S

Piketon, OH 45661

Tel: 614-897-6502

Fax: 614-897-3800

E-mail: uk9@ornl.gov

A pilot-scale field test of reactive media (zero valent iron) for

degrading trichloroethylene (TCE) in ground water is currently in

place at the X-625 Groundwater Treatment Facility at the U.S.

Department of Energy’s (DOE) Portsmouth Gaseous Diffusion

Plant in Piketon, Ohio. 

Site Background

Influent concentrations of TCE for the treatment facility range from

70 to 150 μg/L. Contamination resulted from past waste disposal

practices at the plant.

The uppermost layer underlying the site is composed of

approximately 30 ft of silt. The contaminated aquifer resides below

this layer within a 2 to 10-ft layer of silty gravel and has a hydraulic

conductivity of approximately 20 ft/day. Bedrock is 32-40 ft below

ground surface (bgs).

Technology Application

The X-625 facility consists of a 500-ft horizontal well that collects

TCE-contaminated ground water from within the silty-gravel aquifer

underlying the treatment area at a depth of 30 ft. This ground water

is fed into a building constructed at an elevation that is 3-5 ft below

bedrock. The ground water then is distributed through a series of

canisters filled with zero-valent iron (Fe0). The flow rate into the

facility has been less than 1 gallon per minute (gpm). The facility is

currently being converted to accommodate a higher ground-water

flow rate (5 gpm). After conversion, treatment will be through Fe0 in

the form of foamed pellets. Electrochemical enhancement by

passing a current through the iron media also is being considered.

Results

Testing of Fe0 filings was conducted from March 1996 through

March 1998. Results indicated a reduction of TCE concentrations to

less than 5 μg/L after passage through the treatment system.

Reductions in the hydraulic conductivity of the iron media due to

mineral precipitation (e.g., iron oxides and iron sulfides) were

observed. The life of the reactive media will be dependent on high

Fe0 corrosion rates influenced by the high sulfate levels in the

ground water. 
58

Future sampling plans will be developed during conversion to the

higher flow rate, which is expected to be completed by October

1998.
59

Metals and Inorganics
60
61

Nickel Rim Mine Site, Sudbury, Ontario, Canada

Installation Date:

August 1995

Contaminants:

Ni, Fe, Sulfate 

Reactive Media:

Organic Carbon

Installation Cost:

$30,000 

Construction:

Cut and Fill

Point of Contact:

David W. Blowes 

Waterloo Centre for

Groundwater Research 

University of Waterloo 

Waterloo, Ontario,

Canada 

Tel: 519-888-4878 

Fax: 519-746-5644

A full-scale continuous permeable reactive barrier (PRB) was

installed in August 1995 downgradient from an inactive mine

tailings impoundment at the Nickel Rim Mine site in Sudbury,

Ontario, Canada. 

Site Background

Nickel Rim was an active mine from 1953 to 1958. Primary metals

extracted were copper (Cu) and nickel (Ni). Tailings have been

undergoing oxidation for approximately 40 years. The ground-water

plume emanating from the tailings is discharging to a nearby lake.

The primary contaminants on site are Ni, iron (Fe), and sulfate.

Initial concentrations were 2400-3800 mg/L sulfate, 740-1000 mg/L

Fe, and up to 10 mg/L Ni.

The contaminated aquifer is 10-26 ft thick and composed of

glacio-fluvial sand. The aquifer is confined to a narrow valley,

bounded on both sides and below by bedrock. Ground-water

velocity within the aquifer is estimated to be 49 ft/yr.

Technology Application

The PRB was installed across the valley using a cut-and-fill

technique. The barrier spans the valley and is 50 ft long, 14 ft deep,

and 12 ft wide. It is composed of a reactive mixture containing

municipal compost, leaf compost, and wood chips. Pea gravel was

added to the mixture to increase hydraulic conductivity. Coarse sand

buffer zones were installed on both the upgradient and

downgradient sides of the reactive material. A 12-in clay cap was

placed on top of the PRB to minimize entry of surface water and

oxygen into the PRB. Remediation at the Nickel Rim Mine Site was

accomplished by sulfate reduction and metal sulfide precipitation

resulting from the presence of the organic material.

Cost

The installation cost was approximately $30,000. This includes

design, construction, materials, and the reactive mixture.

Results

Monitoring wells were installed along a transect parallel to

ground-water flow. Samples were collected one month after

installation and again nine months after installation. Passing through

the PRB resulted in a decrease in sulfate concentrations to

110-1,900 mg/L. Iron concentrations decreased to <1-91 mg/L.

Dissolved Ni decreased to <0.1 mg/L within and downgradient of
62

the PRB. In addition, pH increased from 5.8 to 7.0 across the

barrier. As a whole, the PRB converted the aquifer from

acid-producing to acid-consuming. Monitoring is planned to

continue for a minimum of three years with sampling occurring

biannually.
63

Tonolli Superfund Site, Nesquehoning, PA

Installation Date:

August 1998

Contaminants:

Pb, Cd, As, Zn, Cu

Reactive Media:

Limestone

Installation Cost:

To be determined

Construction:

Continuous Trench

Point of Contact:

Steven J. Donohue

U.S. Environmental

Protection Agency,

Region 3

Hazardous Site Control

Division, 3HS22

1650 Arch Street

Philadelphia, PA 

19103-2029

Tel: 215-814-3215

Fax: 215-814-3002

E-mail:

donohue.steven@

epamail.epa.gov

Construction of a full-scale permeable reactive barrier (PRB) was

completed in August 1998 at the Tonolli Superfund Site near

Nesquehoning, PA.

Site Background

The PRB is being used to remediate ground water contaminated

with heavy metals, including lead (Pb), cadmium (Cd), arsenic (As),

zinc (Zn), and copper (Cu). Maximum concentrations of these

contaminants encountered were 328 μg/L of Pb, 77 μg/L of Cd, 313

μg/L of As, 1,130 μg/L of Zn, and 140 μg/L of Cu. 

The Tonolli Corporation operated a battery recycling and secondary

lead smelting plant at the site from 1974 until 1986, and currently is

responsible for cleanup activities. The presence of elevated

dissolved metals in the ground water is attributed to both waste

sources and anthropogenic sources from the dumping of battery acid

during past site operations, and the acid mine drainage effect of the

mine spoils. 

Remedial investigations indicated that contamination is confined to

the underlying overburden aquifer located in coal mine spoil at 0-19

ft below ground surface, and alluvium at 74-113 ft. Ground water in

the area flows horizontally southeast toward Nesquehoning Creek.

Vertical ground-water flow is downward in the northern portion of

the site, and upward in the southern portion of the site, where it

discharges to the creek. The goal of ground-water remediation is to

achieve background levels for contaminants in the overburden

aquifer. 

Technology Application

To construct the PRB, a ground-water trench, approximately 3 ft

wide, 20 ft deep, and 1,100 ft long, was dug using a trackhoe.

Trench boxes were installed parallel to the creek along the southern

site property boundary. 

Cost

Design and installation cost for this PRB system are not currently

available.

Results

PRB performance results will be available upon completion of

remedial activities in 1999. 
64

Lessons Learned

One-pass trenching equipment was evaluated and determined to be

impractical. Problems arose during construction as a result of the

presence of rubble and concrete foundations, sloughing of mine

spoil, and the close proximity of a railroad spur and an onsite landfill

embankment. In addition, the wall was designed to be 1 ft in width

but required expansion to 3 ft.
65

U.S. Coast Guard Support Center, Elizabeth City, NC

Installation Date:

June 1996

Contaminants: 

Cr+6, TCE

Reactive Media: 

Fe0

Installation Cost: 

$500,000

Construction:

Continuous Trench

 

Point of Contact:

Robert W. Puls 

U.S. EPA/National Risk 

Management Research 

Laboratory 

P.O. Box 1198 

Ada, OK 74820 

Tel: 580-436-8543 

Fax: 580-436-8706 

E-mail:

puls.robert@epa.gov

A full-scale demonstration of a permeable reactive barrier (PRB) to

remediate ground water contaminated with chromium and

chlorinated organic compounds was initiated at the U.S. Coast

Guard Support Center site in Elizabeth City, NC, in 1995. 

Site Background

The primary contaminants of concern are hexavalent chromium

(Cr+6) and trichloroethylene (TCE). Initial maximum concentrations

were more than 4,320 μg/L for TCE and more than 3,430 μg/L for

Cr+6. The contaminant plume was estimated to cover a 34,000-ft2

area. The plume is adjacent to a former electroplating shop that

operated for more than 30 years prior to 1984 when operations

ceased. Ground water begins approximately 6 ft below ground

surface, and a highly conductive zone is located 16-20 ft below the

surface. This layer coincides with the highest aqueous

concentrations of chromium and chlorinated organic compounds

found on the site. A low-conductivity layer—clayey, fine sand to

silty clay—is located at a depth of about 22 ft. This layer acts as an

aquitard to the contaminants located immediately above. 

Technology Application

A continuous wall composed of 100% zero-valent iron (Fe0) was

installed in June 1996 using a trencher that was capable of installing

the granular iron to a depth of 24 ft. The continuous trenching

equipment used for the installation has a large cutting chain

excavator system to remove native soil combined with a trench box

and loading hopper to emplace the iron.

The trenched wall is approximately 2 ft thick and about 150 ft long.

The wall begins about 3 ft below ground surface and consists of

about 450 tons of granular iron. 

Cost

The total installation cost was $500,000. This includes the cost of

design, construction, materials, and the iron, which cost about

$175,000. 

Results

The wall was designed to meet cleanup goal concentrations of 0.05

mg/L of Cr+6 and 5 μg/L of TCE. Performance monitoring has been

conducted on a quarterly basis since November 1996. In addition to

2-in PVC compliance wells, the wall is monitored using a series of

multilevel sampling (MLS) ports to monitor the geochemical

mechanisms occurring in the barrier and in the downgradient

aquifer. Sampling results for chromium indicate that all chromium

has been removed from the ground water within the first 6 inches of

the wall as expected. No chromium has been detected downgradient
66

of the wall either in the MLS ports or in the compliance wells

located immediately behind the wall. Results thus far indicate that

the barrier is successfully reducing TCE, c-DCE, and vinyl chloride

concentrations to less than MCL levels for the vast majority of the

monitored portions of the wall. Of 29 downgradient MLS ports,

MCLs for TCE and vinyl chloride are exceeded in 1 and 3 ports,

respectively. TCE concentrations are generally below 5 μg/L within

the wall, but exceed 50 μg/L at the lowest depth. There are some

indications that the TCE plume may have dipped lower in this part

of the aquifer following wall installation. The slight elevation

beyond target levels for vinyl chloride seen in the MLS ports are not

reflected in adjoining compliance wells. Downgradient vinyl

chloride concentrations in the MLS ports have declined with time.

Nowhere do c-DCE concentrations exceed regulatory limits. 

Numerous vertical and angle cores also have been collected at the

site to examine changes to the iron surface and to evaluate the

formation of secondary precipitates which may affect wall

performance over time. These cores continue to be studied. 

Lessons Learned 

Researchers are investigating the possibility that the TCE plume has

dipped lower in the aquifer after the wall was installed and is now

moving under the wall. A significant amount of recharge occurred

into the reaction zone following installation due to removal of the

concrete parking lot covering the site. This recharge may have

driven the plume deeper than had previously been observed

allowing some of the plume to move under the wall. Interestingly,

there is still significant treatment below the wall where no iron

resides. 

Based on limited preliminary electrical conductivity profiles, the

wall is approximately 19-21 in thick, compared to the design

thickness of 23 in. Some minor vertical discontinuities were

observed in the conductivity data and have been confirmed with

coring. These small gaps are probably due to bridging within the

trencher hopper during iron emplacement.
67

100 D Area, Hanford Site, WA

Installation Date: 

September 1997

Contaminants: 

Cr+6 

Reactive Media: 

Sodium dithionite

Installation Cost: 

$480,000 

Construction: 

Injection 

Point of Contact:

Jonathan S. Fruchter 

Batelle Pacific Northwest 

National Laboratory 

P.O. Box 999 (K6-96)

Richland, WA 99352 

Tel: 509-376-3937 

Fax: 509-372-1704

E-mail:

john.fruchter@pnl.gov

A large-scale treatability test of an In Situ Redox Manipulation

(ISRM) method is being conducted at the 100D Area of the U.S.

Department of Energy (DOE) Hanford Site in Washington. 

Site Background

Chromate (Cr+6 ) concentrations of up to 2 mg/L have been detected

within the 100D Area. Contamination resulted from the use of

chromium-bearing anti-corrosion agents in onsite reactors. 

The 100D Area is underlain by both glacial and fluvial sediments,

predominantly sands and gravels. Hydraulic conductivity is

approximately 100 ft/day. The upper surface of the contaminated

aquifer is approximately 85 ft below ground surface and is

approximately 15 ft thick, constrained at its lower boundary by an

aquitard. 

Technology Application

ISRM involves injection of a chemical reducing agent in the

contaminant plume downgradient from the source area. This agent

alters the chemical redox potential of aquifer fluids and sediments.

Redox-sensitive metals migrating through the treatment zone are

immobilized. The treatability test at Hanford’s 100D Area began in

September 1997 and consists of injecting sodium dithionite into a

series of five existing wells to a depth of 100 ft below ground

surface. Treated zones for each well overlap, creating a 150-ft-long

barrier that is approximately 50 ft wide. 

Cost

The installation cost is estimated to be $480,000. This includes the

cost of design, construction, materials, and the reactive material. 

Results

Sodium dithionite was injected into the first of the five wells in

1997. As a result, aqueous chromate concentrations have been

reduced below 8 μg/L. After the completion of a gas tracer test

studying rates of reoxygenation in the treated plume, plans called for

sodium dithionite to be injected into the remaining four wells in

mid-1998, followed by a bromide tracer test to determine the effect

of the treatability test on ground-water flow within the aquifer.

Performance monitoring is expected to continue through the end of

1999. 
68

LEAP Permeable Barrier Demonstration Facility, Portland, OR

Installation Date:

October 1997

Contaminants: 

Cr+6, PCE

Reactive Media: 

SMZ

Design Cost:

$75,000

Installation Cost: 

$25,000 

Construction: 

Hanging Barrier in

Perforated Metal Frame 

Point of Contact:

Robert Bowman

Dept. of Earth &

Environmental Science

New Mexico Tech

801 LeRoy Place

Socorro, NM 87801 

Tel.: 505-835-5992

Fax: 505-835-6436

E-mail:

bowman@nmt.edu

A pilot-scale demonstration was conducted at the Large

Experimental Aquifer Program (LEAP) site at the Oregon Graduate

Institute of Science and Technology near Portland, OR. 

Site Background

The main purpose of the demonstration was to quantify the ability of

a surfactant-modified zeolite (SMZ) permeable reactive barrier

(PRB) to intercept and retard the migration of a mixed plume

containing 22 mg/L of chromate (Cr+6) and 2 mg/L of

perchloroethylene (PCE). The goal was to test laboratory-based

predictions of behavior of the SMZ, using Cr+6 and PCE as “type”

contaminants (anionic metal and chlorinated hydrocarbon). The

pilot-test was conducted in a contained, simulated aquifer. The

aquifer was filled with sand and had a hydraulic conductivity of

56.7 ft/day. 

Technology Application

The barrier of SMZ was hung in the center of the simulated aquifer

about 3 ft above the base in order to simulate emplacement in front

of an advancing plume in a shallow, unconfined aquifer. The barrier

had three modules, each about 6.5 ft long. Overall, the barrier was

about 20 ft long, 3 ft thick, and 6.5 ft deep, and used 12 tons of the

reactive medium. Since this was a pilot-scale test under controlled

conditions, the reactive medium was contained in a frame to

facilitate removal and replacement with other test media in the

future. 

Cost

Total design cost for the barrier system was about $75,000. Total

installation cost was about $25,000. This includes the cost of 

construction, materials, and the reactive material. 

Results

The contaminant plume was injected into the simulated aquifer for 2

months, and performance was monitored. Samples were collected

approximately weekly from a network of 63 sample nests (315

sample points) in the aquifer and 18 sample nests (90 sample points)

within the barrier. Analysis of preliminary data indicates that the

barrier performed according to design specifications, with

retardation factors for Cr+6 and PCE both on the order of 50. Final

interpretation of data from the sampling and chemical analyses is in

progress. Pending the results of this of the pilot-scale effort, a

full-scale implementation is anticipated.
69

Lessons Learned 

Barrier performance is very sensitive to the interface between

aquifer material and reactive barrier materials. Sufficient

permeability contrast must be established and maintained to avoid

plume deflection. The causes for poor permeability contrast,

whether due to inherent media property differences or barrier

installation, can be difficult to isolate. Long-term compaction of the

material with resultant loss in hydraulic conductivity needs further

evaluation. Low-conductivity zones in an earlier phase of the project

were difficult to detect and locate.
70
71

Fuel Hydrocarbons
72
73

East Garrington, (Near Olds), Alberta, Canada

Installation Date:

September 1995

Contaminants:

BTEX

Reactive Media:

O2

Design/Installation

Cost:

$67,200

Construction:

Trench and Gate

Point of Contact:

Marc Bowles

Komex International Ltd.

16th Avenue, NW

Suite 100

Calgary, Alberta

Canada T3B 0M6

Tel: 403-247-0200

Fax: 403-247-4811

Email: mbowles@

calgary.komex.com

A pilot-scale permeable reactive barrier (PRB) was installed at the

East Garrington gas plant in Alberta, Canada in September 1995. 

Site Background

Initial concentrations of up to 12 mg/L of BTEX (benzene, toluene,

ethylbenzene, and xylene) were detected. The gas processing plant

was contaminated by condensate, lube oil, flare pit wastes, and other

materials. The goal of the pilot-scale demonstration was to contain

the BTEX onsite and ensure that only treated ground water migrated

offsite.

The site is underlain by 10-16 ft of low-conductivity glacial till

composed of silty clay and cobble-rich deposits that grade into a

clay-rich sandy to silty basal unit. This is underlain by a silty shale

with occasional interbedded sandstone units. The contaminated

aquifer extends from the near the surface to 10 ft below ground

surface (bgs). 

Technology Application

Two 145-ft-long cut-off tenches were excavated at right angles to

each other through the fine-grained glacial sediments down to the

relatively impermeable bedrock. The bottom, and the downgradient

sides of the trenches were then sealed with an impermeable,

synthetic liner before being filled with highly permeable aggregate.

The PRB systems consists of three 6-foot wide modular treatment

gates in series. They were constructed of vertical culverts that inject

air into the contaminated ground water, which promotes

hydrocarbon degradation. The residence time inside the treatment

gate is approximately 24 hours. The treated ground water then

passes through an infiltration gallery composed of thin vertical

trenches filled with highly permeable gravel. 

A passive permeable reactive barrier was chosen as a remedy for the

site because of its low maintenance costs, despite the longer

timeframe required for remediation. More specifically, a trench-andgate system was selected over a funnel-and-gate system because of

its advantages in low permeability sediments such as glacial tills.

Compared with traditional stand-alone barriers, the combination of a

cut-off wall and adjacent drainage trench (1) improves drainage of

the contaminated zone; (2) increases the size of the capture zone

both horizontally and vertically; and (3) prevents damming effects

such as mounding which force contaminants around or under funnel

walls.
74

Cost

Design and installation costs for the system were approximately

$67,200. This includes design, construction, and materials.

Results

Results of the pilot-scale project show that the contaminant plume

has been captured and treated by the trench-and-gate system. Recent

sampling yielded BTEX concentrations below 10 μg/L at the

treatment gate, and no contaminants have been detected offsite.

Monitoring equipment includes soil moisture sensors, tensiometers,

and pressure transducers installed upgradient, downgradient, and

along the trench. Experiments conducted in the system using

artificially contaminated water suggest that total BTEX

concentrations up to 2.5 mg/L can be effectively treated. Sampling

will continue on a biannual basis. 

Lessons Learned

During installation, an unusually high water table led to trenching

problems. The high water table increased installation costs, but had

no effect on maintenance costs. 

Air sparging was found to be an effective method for enhancing

biodegradation through the addition of oxygen to the treatment cell.

Experiments using Oxygen Releasing Compound were not

effective. However, the addition of phosphorus increased

degradation rates.
75

U.S. Naval Air Station, Alameda, CA

Installation Date:

December 1996 

Contaminants:

cDCE, VC, TCE, BTEX

Reactive Media:

Fe0, O

Installation Cost:

$400,000 

Construction:

Funnel and Sequenced

Treatment Gate

Point of Contact:

Michaye McMaster

Beak International Inc.

42 Arrow Rd.

Guelph, Ontario

N1K 1S6 Canada

Tel: 519-763-2325

Fax: 519-763-2378

E-mail:

mmcmaster@beak.com

The second part of a pilot-scale demonstration of an in situ

sequenced permeable reactive barrier (SPRB) for the remediation of

chlorinated solvents and petroleum hydrocarbons was conducted at

Alameda Point (formerly U.S. Naval Air Station Alameda) in

Alameda, California.

Site Background

The initial phase of this demonstration, which had been conducted

at Canadian Forces Base Borden, Ontario, Canada, evaluated three

technologies for their ability to treat perchloroethylene (PCE),

carbon tetrachloride (CCl4) and toluene. The technologies were: (1)

abiotic reductive dechlorination using zero-valent iron (Fe0),

followed by oxygen releasing compound (ORCTM) to promote

aerobic biodegradation; (2) natural attenuation; and (3) a permeable

nutrient injection wall, using benzoate to promote anaerobic

biodegradation, followed by an aerobic (oxygen) biosparge gate for

aerobic biodegradation.

The Alameda demonstration used Fe0 followed by oxygen

biosparging in a funnel-and-gate system to remediate

trichloroethylene (TCE); cis-1,2-dichloroethylene (cDCE); vinyl

chloride (VC); and toluene, benzene, ethyl benzene, and xylene

(BTEX). Total initial (upgradient) concentrations of chlorinated

VOCs exceeded 100 mg/L, and toluene was found at levels of up to

10 mg/L.

Historical air photos of the site indicate open disposal pits

upgradient of the SPRB. The shallow aquifer is composed of 22-24

ft of sandy artificial fill material that was hydraulically placed on bay

silts and clays. The hydraulic conductivity of the overlying sandy fill

material is 0.057 ft/day (~21 ft/year). The underlying bay silts and

clays are 15-20 ft thick and act as a confining unit. Depth to ground

water ranges from 4 to 7 ft below ground surface.

Technology Application

During construction of the funnel-and-gate system, the artificial fill

sand was excavated to the top of the confining bay mud unit. To

prevent settling, a concrete pad (nominally 2 ft thick) was placed at

the bottom of the excavation; the gate was then constructed on this

base. The gate is 10 ft wide and 15 ft long. As ground water passes

through the gate it contacts the following media: about 18 in of

coarse sand mixed with 5% Fe0, 5 ft of Fe0, a 3-ft pea gravel

transition zone, a 3-ft biosparge zone, and a 2-ft pea gravel zone.
76

The 10-ft funnels were placed on either side of the gate,

perpendicular to the direction of water flow.

Between February 1997 and May 1998, two pumping wells were

used to operate the system under controlled conditions. For a period

of about 70 days, the system operated at a flux rate of approximately

45 ft3/day to determine the maximum velocity it could process. At

this velocity, breakthrough was observed in several down-gradient

monitoring points. Then, the system operated for about one year at a

flux rate of approximately 12 ft3/day, more representative of

conditions that would exist as a result of the funnel sections. Finally,

the system was allowed to operate under natural gradient conditions. 

Results

The remedial objectives of the project generally were met, except

with respect to cDCE and VC, with typical effluent concentrations

of about 136 μg/L and 217 μg/L respectively. Retardation of the

toluene or other hydrocarbons as a result of sorption to the granular

iron precluded an assessment of petroleum hydrocarbon

degradation. Breakthrough of cDCE and VC indicated that

biodegradation (likely via aerobic oxidation) of these compounds

was occurring in the biosparge zone. An estimated 66% of the VC

and 30% of the cDCE was volatilized. Assessment of multilevel

data showed excellent degradation (>91%) of the chlorinated

organics using the granular iron at high influent concentrations

(>100 mg/L total VOCs). At lower influent concentrations, almost

complete degradation (>99%) was observed. The biosparge zone

supported aerobic biodegradation of VC and cDCE, and by January

1998 remedial objectives were being met at the last set of sampling

wells in the gate. 

Results obtained to date suggest sparging rates in the biosparge zone

should be minimized to reduce volatilization of contaminants from

the water column. In addition, monitoring should continue so that

long-term performance of the SPRB can be assessed. 

The U.S. Navy has begun to operate the site; current plans call for a

hydraulic study to examine ground-water flow in the funnel-andgate area and for monitoring to continue on a quarterly basis.
77

Nutrients
78
79

Y-12 Site, Oak Ridge National Laboratory, TN 

Installation Date:

December 1997

November 1997

Contaminants: 

U, Tc, HNO3

Reactive Media: 

Fe0

Installation Cost: 

$1,000,000

Construction: 

Funnel and Gate 

Continuous Trench

Point of Contact:

Baohua Gu

Oak Ridge National 

Laboratory

Environmental 

Sciences Division 

Oak Ridge, TN 

37831-6036 

Tel: 423-574-7286 

Fax: 423-576-8543 

E-mail: b26@ornl.gov

Permeable reactive barrier (PRB) systems have been constructed in

two different ground-water pathways through the Y-12 site at the

U.S. Department of Energy’s (DOE) Oak Ridge National

Laboratory, TN. 

Site Background

Liquid wastes, including nitric acid (HNO3) with uranium (U), and

technetium (Tc), were placed in disposal ponds on the site from

1952 to 1981. The site was capped in 1983. Leached wastes have

contaminated both ground and surface water. 

The site is underlain by unconsolidated clay and regolith overlying

fractured shales. The permeability of the clay is very low

(approximately 4 x 10-7 in/sec), but the weathered bedrock above

the shales generally has a higher permeability (locally as high as 4 x

10-4 in/sec). The depth to ground water is 10-15 ft, and the shallow

unconsolidated unit aquifer is 10-20 ft thick. The PRBs are focused

on capturing ground water in this shallow unconsolidated zone. 

Technology Application

Pathway 1 PRB

A funnel-and-gate system was installed in the area designated

Pathway 1 in December 1997. The system is approximately 220 ft

long and consists of two wing walls designed to funnel ground

water to a concrete vault containing treatment canisters for

evaluating different treatment media. The treatment vault consists of

five vertically stacked reactors. An advantage of vertical reactors is

the ease of cleaning and replacing used or clogged iron. The wing

walls were installed to a depth of approximately 25 ft. The natural

ground-water gradient and permeability contrast between the gravel

backfill in the trench and surrounding native silt and clay is designed

to generate flow through the treatment zone. Barriers were installed

using a guar gum slurry for support to reduce slumping in the

trench. An enzyme breaker was used to digest the guar which was

recycled down the trench as construction progressed. 

Pathway 2 PRB

A continuous trench system was installed in the area designated

Pathway 2 in November 1997. It is 225 ft long, 2 ft wide, 22-30 ft

deep, and filled with gravel except for a 26-ft section in the middle

that is filled with 80 tons of zero-valent iron (Fe0). Guar gum was

added during excavation to keep the trench walls from collapsing.
80

The trench was installed parallel to the direction of ground-water

flow. 

Although total iron and ferrous iron concentrations were initially

high after installation, concentrations have decreased as the pH

within the iron has increased over time (to as high as 9 or 10). This

initial spike is likely a result of enhanced microbial activity from the

guar used in the barrier installation. Due to the effect of the guar on

ground-water chemistry, nitrate concentrations increased in the

upgradient wells over time. Sulfate levels in the ground water have

decreased as sulfate is reduced to sulfide. Additionally, a decreased

concentration of calcium in ground water was observed and may be

attributed to the precipitation of calcium carbonate within the iron

barrier. Continued monitoring and performance evaluation is in

progress to better understand the flow paths through the PRB, the

potential for clogging due to mineral precipitation, and the long-term

effectiveness for uranium removal. 

The total installation cost for the two walls was approximately

$1,000,000. This includes the cost of design, construction, materials,

and the reactive material.

Results

The goals of the project were to investigate the feasibility and

effectiveness of passive in situ treatment systems to remove the

contaminants in the ground water that are migrating to Bear Creek

from the disposal ponds. Early results indicate that Fe0 is an efficient

and cost-effective method of simultaneously removing certain

radionuclides, such as U and Tc, as well as HNO3. Sampling to

monitor performance is occurring on a monthly basis. 

Lessons Learned 

Pathway 1 PRB

The use of guar increased biological activity in the system. 

Pathway 2 PRB

Preliminary evaluation of hydraulic and chemical data suggests that,

under wet-season hydraulic conditions, contaminated ground water

may migrate across the trench instead of down the trench as

designed. Vertical gradients at the site appear to have a significant

impact on ground-water flow and capture. The data suggest that to

effectively operate passively in all hydraulic conditions, the trench

needs to be longer and discharge at a lower hydraulic head

downgradient. The following modifications are planned for the

Pathway 2 PRB in fiscal year 1999 to enhance treatment efficiency: 
81

The trench will be extended an additional 100 ft to increase the

ground-water capture zone.

Guar will not be used to excavate the trench extension because of

potential geochemical impacts on the iron media, native soil, and

ground water observed during initial trench construction.

Ground water from the trench extension will be siphoned

approximately 800 ft to a second Fe0 treatment zone deployed in

subsurface concrete boxes.

The treated water will flow into an infiltration trench

downgradient of the second treatment zone.
82

Public School, Langton, Ontario, Canada

Installation Date:

August 1993

Contaminants:

PO4

3-, NO3-

Reactive Media:

Fe/Ca oxides, 

high-Ca limestone,

organic carbon 

Installation Cost:

$5,000

Construction:

Funnel and Gate

Points of Contact:

Will Robertson (NO3

-

)

David W. Blowes (PO4

3-)

University of Waterloo,

Department of Earth

Sciences

200 University Avenue

West Waterloo, Ontario

N2L 3G1 Canada

Will Robertson

Tel: 519-888-4567 x6800

Fax: 519-746-7484

E-mail: wroberts@

sciborg.uwaterloo.ca

David Blowes

Tel: 519-888-4567 x4878

Fax: 519-746-7484

E-mail: blowes@

sciborg.uwaterloo.ca

A pilot-scale demonstration of a funnel-and-gate system designed to

remediate phosphate (PO4

3-) and nitrate (NO3-

) was installed on the

grounds of a public school in Langton, Ontario, Canada in August

1993. 

Site Background

The system was emplaced to remove PO4

3- and NO3-

 from a

large-capacity conventional septic system located on the school

property that had operated over a 45-year period. The site is

underlain by a thick body of medium sand with a hydraulic

conductivity of 72 ft/day. The water table is located at a depth of 10

ft and the ground-water velocity is 330 ft/yr. The contaminated

aquifer is unconfined.

Technology Application

Ground water was funneled between two walls constructed from

sealable joint sheet pilings that extend 16 ft from the central gate

area. The funnel walls extended 5 ft below the water table. The

central gate was 6 ft wide, 6 ft long, and extended 6 ft below the

water table. The gate contained two distinct treatment zones. The

PO4

3- treatment zone, which was 2 ft thick, contained a reactive

mixture of 6% iron and calcium oxides (Fe/Ca oxides), 9% high-Ca

limestone, and 85% local aquifer sand. The phosphate was removed

by adsorption onto Fe oxides and precipitation of Ca-PO4 phases.

The 2-ft-thick NO3

-

 treatment zone contained wood chips that

removed nitrate by bacterial denitrification.

Cost

The installation cost was $5,000.

Results

Monitoring over one year for NO3 and two years for PO4 indicated

significant drops in concentrations of both. PO4

3- concentrations

decreased from 1.0-1.3 mg/L on the influent side of the barrier to

0.3 mg/L on the effluent side. NO3

-

 concentrations decreased from

23-82 mg/L upgradient of the gate to <2 mg/L within the gate.

There are no plans to continue monitoring.

Lessons Learned
83

One lesson learned from this demonstration is that if walls are not

keyed into a underlying impermeable material, underflow must be

carefully considered.
84

Savannah River Site TNX Area, Aiken, SC

Installation Date: 

July 1997

Contaminants: 

TCE, cDCE, CT, NO3

Reactive Media: 

Fe0

Installation Cost: 

$120,000

Construction: 

GeoSiphon Cell

Point of Contact 

Mark Phifer 

Westinghouse SRC/SRS 

Building 773-42A 

Aiken, SC 29808 

Tel: 803-725-5222 

Fax: 803-725-7673 

E-mail: 

mark.phifer@srs.gov

The GeoSiphon Cell (patent pending) was installed in the TNX

flood plain at the Savannah River Site (SRS) by auger and caisson

methods in July 1997. The cell was installed to demonstrate

treatment of ground water contaminated with chlorinated volatile

organic compounds (CVOCs).

Site Background

Ground-water contamination has been detected in the TNX water

table aquifer, but not in the semi-confined or deep aquifers

underlying the site. Predominant contaminants, and average

concentrations of each, detected in the TNX flood plain are

trichloroethylene (TCE) at 200-250 μg/L, cis-1,2-dichloroethylene

(cDCE) at 20-50 μg/L, carbon tetrachloride (CT) at 15-45 μg/L, and

nitrate (NO3) at 10-70 mg/L. 

The TNX Area is a semi-works facility for the Savannah River

Technology Center, which is located 0.25 mile from the Savannah

River near Aiken, SC. The facility was used for pilot-scale testing

and evaluation of various chemical processes associated with SRS.

The water table elevation averages 100 ft above mean sea level

under the TNX site, while the Savannah River elevation averages

85 ft. In the flood plain where contamination was detected, the

water table aquifer is approximately 35-40 ft thick. It consists of

interbedded sand, silty sand, and relatively thin clay layers. Based

on testing and modeling analysis, the aquifer may be characterized

as having a horizontal hydraulic conductivity of 65 ft/day, vertical

hydraulic conductivity of 30 ft/day, effective porosity of 0.15, pore

velocity of 3 ft/day, and a horizontal gradient of 0.007. 

Technology Application

The TNX GeoSiphon Cell is a large-diameter (8-ft) well containing 

granular zero-valent iron (Fe0) as a treatment media (in place of

gravel pack). The cell passively induces flow by use of a siphon

from the cell to the Savannah River. The flow is induced by the

natural hydraulic head difference between the cell and the river. The

passively-induced flow draws contaminated ground water through

the treatment cell, where the Fe0 reduces the CVOCs to ethane,

ethene, methane, and chloride ions. Treated water is discharged to

the Savannah River. 

During Phase I testing of this technology, which was completed in

December 1997, flow through the TNX GeoSiphon Cell was

induced by pumping and the treated water was discharged to the
85

existing TNX National Pollutant Discharge Elimination System

outfall. Testing indicated that TCE degradation is the limiting

compound to treatment below the Primary Drinking Water Standard

Maximum Contaminant Levels within the TNX GeoSiphon Cell.

Data indicated that approximately 8 gal/hr of ground water

contaminated with 200-250 μg/L of TCE could be treated, while

maintaining the average discharge TCE concentration below 5 μg/L.

Field first-order rate constants produced from the steady state TCE

data increased with flow rate from 0.347 to 0.917/hr. 

During Phase II, flow through the TNX GeoSiphon Cell was

induced by siphon and the treated water was discharged to an

existing outfall ditch that flows into the Savannah River. To allow

continuous operation, the siphon line configuration was optimized to

include an upward rise from the cell to the outfall ditch, an air

chamber at the crest adjacent to the outfall ditch, and a steep drop

into the outfall ditch with line termination in a sump. The head

differential available to drive the system (approximately 1.4 ft)

produced a continuous flow rate of 2.5-2.7 gal/min. Approximately

1.2 ft of head was utilized to drive flow through the 

cell itself, and approximately 0.2 ft of head was utilized to drive

flow through the siphon line. Based on these results, a new siphon

line will be installed between the cell and a target location, thus

producing a 5-ft head differential capable of inducing an estimated

9.5 gal/min through the GeoSiphon Cell. 

Phase III of this demonstration project will involve installation and

operation of a full-scale GeoSiphon Cell system for treatment of the

entire TNX contaminated ground-water plume. 

Cost

Phase I system costs are estimated at $119,155, including $26,400

for iron; $27,411 for other construction materials; and $65,344 for

mobilization, labor, rentals, and related installation expenses.

Approximately 49.7 tons of 0.25-2.0 mm (particle size) granular cast

iron was used in the installation of the first TNX GeoSiphon Cell

(TGSC-1). 

Lessons Learned 

The GeoSiphon Cell was selected for use at the TNX Area because

it offers passive (no power requirements), in situ treatment at lower

operating and maintenance costs than pump-and-treat technology. In

contrast to funnel-and-gate or continuous permeable wall

technologies, the GeoSiphon Cell could be constructed using an

existing foundation and well drilling techniques. In addition, there is

potential for accelerating cleanup through the use of induced flow
86

rates greater than natural flow. With a maximum siphon lift of 25 ft,

application of the GeoSiphon Cell technology was found to be

limited to areas of shallow ground water such as that existing at the

TNX Area.
87

Radionuclides
88
89

Fry Canyon Site, UT

Installation Date: 

August 1997 

Contaminants: 

U 

Reactive Media: 

Fe0, AFO, PO4

Design Cost: 

$30,000 

Installation Cost: 

$140,000 

Construction: 

Funnel and Gate 

Points of Contact:

Ed Feltcorn 

U.S. EPA/ORIA 

401 M St., SW 

Washington, DC 20460 

Tel: 202-564-9422 

Fax: 202-565-2037 

E-mail:

feltcorn.ed@epa.gov 

David Naftz, Ph.D. 

U.S. Geological Survey 

1745 W. 1700 South 

Salt Lake City, UT

84104 

Tel: 801-975-3389 

Fax: 801-975-3424 

E-mail:

dlnaftz@usgs.gov

A field-scale demonstration of a permeable reactive barrier (PRB)

system is underway at an abandoned uranium upgrader site in Fry

Canyon, UT. The U.S. Environmental Protection Agency (EPA) is

the lead agency on the site. 

Site Background

The ultimate goal of the demonstration is to determine the

technological and economic feasibility of using permeable chemical

or biological obstacles, placed in the flow path, for removing

dissolved metals and radionuclides from contaminated ground

water. This project is testing the performance of three permeable

reactive barriers at the Fry Canyon site. Anticipated results of the

research for each of the PRBs tested will include long-term removal

efficiencies for uranium and an evaluation of the commercialization

potential for each. Specific objectives of the field demonstration

project include: (1) hydrologic and geochemical characterization of

the site prior to emplacement of barriers; (2) design, installation, and

operation of three PRBs; and (3) evaluation of barrier performance

and commercialization potential. 

At the Fry Canyon site, the water table is approximately 8-9 ft

below ground surface, and the underlying aquifer ranges from 1-6 ft

deep. Estimated hydrologic properties and measured hydraulic

gradients indicate that ground water in the alluvial aquifer moves at

a rate of about 1.5 ft/day nearly parallel to the direction of stream

flow. The uranium (U) concentration in the shallow colluvial aquifer

ranges from 60 μg/L in water from a background well to 20,700

μg/L in water beneath the tailings. The hydraulic conductivity of the

barriers is approximately 1,500 ft/day, while that of the surrounding

native material is 1 to 2 orders of magnitude smaller. Native material

consists of poorly sorted fine- and medium-grained sand. 

Technology Application

The funnel-and-gate system, installed in August 1997, is comprised

of three barriers, each constructed of different reactive materials.

One is bone char phosphate (PO4), another is foamed zero-valent

iron (Fe0) pellets, and the third is amorphous ferric oxide (AFO).

Each barrier is approximately 7 ft wide, 3 ft thick, and 4 ft deep.

Approximately 110 ft3 of material was used in each barrier. Each

contains 22 monitoring points, a water-quality mini-monitor, four

pressure transducers, and a flow-sensor port. According to

steady-state modeling results, ground-water velocities in the reactive

walls are about 4.5 ft/day. 
90

Cost

The EPA and U.S. Geological Survey have estimated that the

design cost (engineering design and planning for the funnel-andgate construction) for this system totals $30,000. The installation

cost, including construction, materials, and the reactive materials,

totals $140,000. These estimates do not include bench-scale testing

of the candidate barrier materials. 

Results

Overall, results to date show that the system is controlling uranium

migration in Fry Canyon. One year of uranium-concentration data

have been collected from the three PRBs installed using funnel-andgate designs. The input uranium concentrations are significantly

different for each PRB, ranging from less than 1,000 mg/L in the

PO4 PRB to higher than 20,000 mg/L in the AFO ZVI. The input

uranium concentrations to each of the PRBs also vary seasonally by

approximately 4,000 to 7,000 mg/L. During the first year of

operation, the PRBs are removing the majority of incoming

uranium; however, the percentage of uranium removal varies with

time and barrier material. The ZVI PRB has consistently removed

greater than 99.9 percent of the input uranium concentration in

flow-path 1. The percentage of uranium removed in the PO4 and

AFO PRBs is slightly less than the ZVI PRB. Except for two

monitoring periods, over 90 percent of the input uranium

concentration was removed in the PO4 barrier. The AFO PRB

removed over 90 percent of the input uranium concentration through

November 1997. From January 1998 through September 1998 the

uranium removal percentage was reduced to less than 90 percent.

Studies will continue to evaluate the barriers under varying

hydrologic and geochemical conditions. Final results will be

presented after peer review in the report to be issued by end of fiscal

year 1999. 

Lessons Learned 

The Fry Canyon project has shown continued promise for use of

PRB technology at appropriate sites (as determined by

characterization). Uranium reduction ratios were calculated for all

water samples collected from each reactive wall from September

1997 through January 1998. These calculations indicate that the Fe0

reactive chemical wall has been most efficient in removing uranium

from ground water; however, uranium removal efficiencies in the

PO4 and AFO walls also have been high. Other lessons learned to

date include the following: 

Project results thus far indicate that the PO4 binder system can be

used to customize reactive materials effectively.
91

Data also suggest, however, that the dissolution of Fe0 and its

associated clogging could present problems, while the AFO is less

subject to clogging and iron release. Although the possibility

exists for elevated iron concentrations downgradient of the PRB

(which could cause degradation in water quality not present before

barrier installation); to date, iron concentrations in downgradient

wells do not seem to present a large water-quality problem. 

Numerous geochemical, hydrological, and other factors that affect

uranium removal efficiencies and processes in each of the PRBs are

currently being evaluated. These factors include:

Changes in the amount and velocity of water flowing through the

PRBs

Type and quantities of minerals forming within the PRBs

Leakage between underlying “no-flow” paths through the PRBs 

The following potential problems also are being assessed: 

In a low-gradient system like Fry Canyon, it is difficult to 

estimate mass of treated water and, at times, whether there is

even flow through some of the gate structures. This presents an

unknown to regulators in estimating total mass of contaminant

that will be cleaned up per unit of time since PRB deployment.

Seasonal changes are apparent in the PRBs’ efficiency in 

removing uranium. The processes causing these changes need to

be identified in order to effectively determine long-term clean-up

goals.

PRBs that are placed adjacent to ephemeral channels could be

destroyed or have their long-term function significantly 

compromised during intense thunderstorm events in the Fry 

Creek drainage basin without proper erosion control measures.

Ground settling could compromise the lack of visual impact that

PRBs have in future remediation applications and could impact

monitoring wells.
92

Y-12 Site, Oak Ridge National Laboratory, TN 

Installation Date:

December 1997

November 1997

Contaminants: 

U, Tc, HNO3

Reactive Media: 

Fe0

Installation Cost: 

$1,000,000

Construction: 

Funnel and Gate 

Continuous Trench

Point of Contact:

Baohua Gu

Oak Ridge National 

Laboratory

Environmental 

Sciences Division 

Oak Ridge, TN 

37831-6036 

Tel: 423-574-7286 

Fax: 423-576-8543 

E-mail: b26@ornl.gov

Permeable reactive barrier (PRB) systems have been constructed in

two different ground-water pathways through the Y-12 site at the

U.S. Department of Energy’s (DOE) Oak Ridge National

Laboratory, TN. 

Site Background

Liquid wastes, including nitric acid (HNO3) with uranium (U), and

technetium (Tc), were placed in disposal ponds on the site from

1952 to 1981. The site was capped in 1983. Leached wastes have

contaminated both ground and surface water. 

The site is underlain by unconsolidated clay and regolith overlying

fractured shales. The permeability of the clay is very low

(approximately 4 x 10-7 in/sec), but the weathered bedrock above

the shales generally has a higher permeability (locally as high as 4 x

10-4 in/sec). The depth to ground water is 10-15 ft, and the shallow

unconsolidated unit aquifer is 10-20 ft thick. The PRBs are focused

on capturing ground water in this shallow unconsolidated zone. 

Technology Application

Pathway 1 PRB

A funnel-and-gate system was installed in the area designated

Pathway 1 in December 1997. The system is approximately 220 ft

long and consists of two wing walls designed to funnel ground

water to a concrete vault containing treatment canisters for

evaluating different treatment media. The treatment vault consists of

five vertically stacked reactors. An advantage of vertical reactors is

the ease of cleaning and replacing used or clogged iron. The wing

walls were installed to a depth of approximately 25 ft. The natural

ground-water gradient and permeability contrast between the gravel

backfill in the trench and surrounding native silt and clay is designed

to generate flow through the treatment zone. Barriers were installed

using a guar gum slurry for support to reduce slumping in the

trench. An enzyme breaker was used to digest the guar which was

recycled down the trench as construction progressed. 

Pathway 2 PRB

A continuous trench system was installed in the area designated

Pathway 2 in November 1997. It is 225 ft long, 2 ft wide, 22-30 ft

deep, and filled with gravel except for a 26-ft section in the middle

that is filled with 80 tons of zero-valent iron (Fe0). Guar gum was

added during excavation to keep the trench walls from collapsing.
93

The trench was installed parallel to the direction of ground-water

flow. 

Although total iron and ferrous iron concentrations were initially

high after installation, concentrations have decreased as the pH

within the iron has increased over time (to as high as 9 or 10). This

initial spike is likely a result of enhanced microbial activity from the

guar used in the barrier installation. Due to the effect of the guar on

ground-water chemistry, nitrate concentrations increased in the

upgradient wells over time. Sulfate levels in the ground water have

decreased as sulfate is reduced to sulfide. Additionally, a decreased

concentration of calcium in ground water was observed and may be

attributed to the precipitation of calcium carbonate within the iron

barrier. Continued monitoring and performance evaluation is in

progress to better understand the flow paths through the PRB, the

potential for clogging due to mineral precipitation, and the long-term

effectiveness for uranium removal. 

The total installation cost for the two walls was approximately

$1,000,000. This includes the cost of design, construction, materials,

and the reactive material.

Results

The goals of the project were to investigate the feasibility and

effectiveness of passive in situ treatment systems to remove the

contaminants in the ground water that are migrating to Bear Creek

from the disposal ponds. Early results indicate that Fe0 is an efficient

and cost-effective method of simultaneously removing certain

radionuclides, such as U and Tc, as well as HNO3. Sampling to

monitor performance is occurring on a monthly basis. 

Lessons Learned 

Pathway 1 PRB

The use of guar increased biological activity in the system. 

Pathway 2 PRB

Preliminary evaluation of hydraulic and chemical data suggests that,

under wet-season hydraulic conditions, contaminated ground water

may migrate across the trench instead of down the trench as

designed. Vertical gradients at the site appear to have a significant

impact on ground-water flow and capture. The data suggest that to

effectively operate passively in all hydraulic conditions, the trench

needs to be longer and discharge at a lower hydraulic head

downgradient. The following modifications are planned for the

Pathway 2 PRB in fiscal year 1999 to enhance treatment efficiency: 
94

The trench will be extended an additional 100 ft to increase the

ground-water capture zone.

Guar will not be used to excavate the trench extension because of

potential geochemical impacts on the iron media, native soil, and

ground water observed during initial trench construction.

Ground water from the trench extension will be siphoned

approximately 800 ft to a second Fe0 treatment zone deployed in

subsurface concrete boxes.

The treated water will flow into an infiltration trench

downgradient of the second treatment zone.
95

Other Organic Contaminants
96
97

Marzone Inc./Chevron Chemical Company, Tifton, GA

Installation Date:

August 1998

Contaminants:

BHC, beta-BHC, DDD,

DDT, xylene,

ethylbenzene, lindane,

and methyl parathion

Reactive Media:

Activated carbon

Design Cost:

$230,000

Installation Cost:

$520,000

Construction:

Funnel and Gate

Point of Contact:

Annie Godfrey

U.S. Environmental

Protection Agency,

Region 4

61 Forsyth Street

Atlanta, GA 30303

Tel: 404-562-8919

Fax: 404-562-8896

E-mail:

godfrey.annie@epa.gov

A permeable reactive barrier (PRB) was installed in August 1998 at

Operable Unit 1 of the Marzone site in Tifton, GA, to remediate

ground water contaminated with pesticides and volatile organic

compounds (VOCs).

Site Background

A 1994 Record of Decision originally selected a pump-and-treat

system to remediate the ground water. During remedial design

activities, however, it was determined that an in situ treatment

system such as a funnel-and-gate system may be a more appropriate

technology for the specific site conditions. The Marzone facility was

used as a pesticide formulation facility from 1950 until the 1980s.

Ground-water contaminants of concern and their initial maximum

concentrations are: alpha-hexachlorobenzene (BHC) (60 mg/L),

beta-BHC (98.5 mg/L), DDD (7.6 mg/L), DDT (9.3 mg/L), xylene

(94,000 mg/L), ethylbenzene (6,100 mg/L), lindane (54.6 mg/L)

and methyl parathion (47 mg/L). A shallow aquifer is located at a

depth of 7 ft and a deeper aquifer exists at approximately 25 ft.

Hydraulic conductivity is estimated at 2.9-4.6 ft/day. Soils in this

area consist of a mixture of sand, sandy clay, and clay. 

Technology Application

The modified funnel-and-gate system comprises a 400-ft barrier wall

that was installed using a vibrating beam technology. A collection

trench lined with geotextile and filled with granular drain material

was constructed upgradient of and parallel to the barrier wall.

Ground water collected in this trench moves by way of a slotted

well screen and associated piping into treatment vaults containing

approximately 1,800 pounds of activated carbon located between

the collection trench and barrier wall. From the treatment vaults,

ground water moves slowly (1-2 gal/min) by way of piping through

the barrier wall and into a distribution trench of similar construction

as the collection trench but running perpendicular to the barrier wall. 

Cost

Design costs for the Marzone PRB system were $230,000.

Installation costs, including construction, materials, and reactive

material, are estimated at $520,000. 

Results

Cleanup goals for the contaminants of concern are: 0.00003 mg/L

for alpha-BHC, 0.0001 mg/L for beta-BHC, 0.00077 mg/L for
98

DDD, 0.00054 mg/L for DDT, 10 mg/L for xylene, 0.7 mg/L for

ethylbenzene, 0.0002 mg/L for lindane, and 0.0039 mg/L for methyl

parathion. Sampling of the treatment vault effluent is conducted on a

monthly basis. Preliminary sampling indicates contaminant

concentrations that are below detection levels. 

Lessons Learned

The funnel-and-gate system was selected for use because if offered

less impact to the surrounding community than other treatment

technologies, while being partially self-operational. Flushing of the

system is required every 3-4 weeks in order to reinitiate flow; as a

result, costs for operation and maintenance are higher that

anticipated.
99

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100
101

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