EPA
United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-R-99-002
April 1999
www.epa.gov/tio
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Field Applications of In Situ
Remediation Technologies:
Permeable Reactive Barriers
permeable
reactive
barrier
direction of ground water flow
permeable
reactive
barrier
clean
ground water
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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
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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.
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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-and-
treat 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
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IV
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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 Dry cleaning 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
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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
VI
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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.
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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 (Fe°) as the reactive media for
converting contaminants to non-toxic or immobile species. For example, Fe° 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 funnel-
and-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.
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Chlorinated Solvents
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Aircraft Maintenance Facility, OR
Installation Date:
March 1998
Contaminants:
TCE
Reactive Media:
Fe°
Installation Cost:
$600,000
Construction:
Funnel and Gate
Point of Contact:
James Romer
EMCON Associates
HSOKnutsonRoad
Suite 5
Medford, OR 97504
Tel: 541-770-6977
Fax: 541-770-7019
E-mail:
j romer@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 |ig/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 (Fe°). 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.
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Caldwell Trucking, NJ
Installation Date:
April 1998
Contaminants:
TCE
Reactive Media:
Fe°
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 ng/L in the ground water to below 50 |ig/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/see. 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 (Fe°)
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 Fe°
down a well into the fractured bedrock through an open borehole).
Cost
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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 |ig/L to a downgradient concentration of less than 400 |ig/L.
TCE ground-water concentrations, affected by variable ground-
water 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.
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Federal Highway Administration (FHA) Facility, Lakewood, CO
Installation Date:
October 1996
Contaminants:
TCA; 1,1-DCE;TCE;
cDCE
Reactive Media:
Fe°
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 cis-
dichloroethylene (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 (Fe°). 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 |ig/L of
TCE and 700 |ig/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 |ig/L reporting level is
1,1-dichloroethane, which has been measured up to 8 jig/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
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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.
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Former Drycleaning Site, Rheine, Westphalia, Germany
Installation Date:
June 1998
Contaminants:
PCE, 1,2-DCE
Reactive Media:
Fe°, 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
Garb sen, 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 (Fe°) mixed with gravel at a 1:2 volume ratio (34.5
tons each of Fe° 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
|ig/L. There has been only a low level of metabolite production. No
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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.
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Former Manufacturing Site, Fairfield, NJ
Installation Date:
September 1998
Contaminants:
1,1,1-TCA, PCE, TCE,
DNAPL
Reactive Media:
Fe°
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(S)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 water-
table 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 |ig/L. Key contaminants included
1,200 |ig/L trichloroethane (1,1,1-TCA), 19 |ig/L
tetrachloroethylene (PCE), and 110 |ig/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 (Fe°) 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
12
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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 |ig/L for PCE, 1 |ig/L for TCE,
and 30 |ig/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 jig/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.
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Industrial Site, Belfast, Northern Ireland
Installation Date:
December 1995
Contaminants:
TCE, 1,2-cDCE
Reactive Media:
Fe°
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
NIK 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 (Fe°). 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 |ig/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-l,2-dichloroethylene
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(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
|ig/L) of cDCE have been detected. Vinyl chloride, a common
breakdown product of this process, has not appeared in appreciable
quantities.
15
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Industrial Site, Coffeyville, KS
Installation Date:
January 1996
Contaminants:
TCE, 1,1,1-TCA
Reactive Media:
Fe°
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 |ig/L of TCE and 100 |ig/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 (Fe°) 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).
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Industrial Site, NY
Installation Date:
December 1997
Contaminants:
TCE, cDCE, VC
Reactive Media:
Fe°
Installation Cost:
$797,000
Construction:
Continuous Trench
Point of Contact:
Diane Clark
Stearns & Wheler, LLC
One Remington Park Dr.
Cazenovia,NY13035
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-l,2-dichloroethylene (cDCE), and
vinyl chloride (VC) are the primary contaminants of concern at this
facility. Initial concentrations ranged from 200-1,280 |ig/L for TCE,
300-1,800 |ig/L for cDCE, and 26-53 |ig/L for VC. Total volatile
organic compounds (VOC) concentrations ranged from 300 |ig/L-
900 |ig/L. The goal of this project is to clean the site to New York
ground-water standards, 5 |ig/L for TCE, 5 |ig/L for cDCE, and 2
|ig/LforVC.
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 (Fe°) 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
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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 |ig/L TCE, 4,900 |ig/L 1,2-DCE, and 260 |ig/L VC.
Downgradient results showed only 5 |ig/L 1,2-DCE and 23 |ig/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.
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Industrial Site, SC
Installation Date:
November 1997
Phase 1 of a full-scale permeable reactive barrier (PRB) was
installed at a former industrial site in Manning, SC, in November
1997.
Contaminants:
TCE, cDCE, VC
Reactive Media:
Fe°
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
Site Background
Trichloroethylene (TCE), cis-l,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% zero-
valent iron (Fe°) by volume in the form of iron filings. The 400 tons
of Fe° 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
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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 cost-
effective 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 Fe°.
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.
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21
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Intersil Semiconductor Site, Sunnyvale, CA
Installation Date:
February 1995
Contaminants:
TCE, cDCE, VC,
Freon 113®
Reactive Media:
Fe°
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 |ig/L of trichloroethylene (TCE),
450-1,000 |ig/L of cis-l,2,-dichloroethylene (cDCE), 100-500 |ig/L
of vinyl chloride (VC), and 20-60 |ig/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 semiconfmed aquifer that is 2-4 ft
thick. It is composed of interfmgering 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 (Fe°) 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
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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 |ig/L for TCE, 6 |ig/L for cDCE, 0.5 |ig/L for VC,
and 1,200 |ig/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.
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Kansas City Plant, Kansas City, MO
Installation Date:
April 1998
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.
Contaminants:
1,2-DCE, VC
Reactive Media:
Fe°
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
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 jig/L of 1,2-DCE and 291 jig/L
ofVC.
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 (Fe°). The
remainder of the trench was filled with 2 ft of Fe° 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 |ig/L for 1,2-DCE and 2 |ig/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
24
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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
25
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created by the use of "Z" piles; and uniform, continuous placement
of iron was visually verified.
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Lowry Air Force Base, CO
Installation Date:
December 1995
Contaminants:
TCE
Reactive Media:
Fe°
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
|ig/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
(Fe°) 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
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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.
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U.S. Coast Guard Support Center, Elizabeth City, NC
Installation Date:
June 1996
Contaminants:
Cr+6, TCE
Reactive Media:
Fe°
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 |ig/L for TCE and more than 3,430 |ig/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 (Fe°) 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 |ig/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
29
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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 |ig/L within
the wall, but exceed 50 jig/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.
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Area 5, Dover Air Force Base (AFB), DE
Installation Date:
January 1998
Contaminants:
PCE, TCE, DCE
Reactive Media:
Fe°
Installation Cost:
$800,000
Construction:
Funnel and Gate
Point of Contact:
ILt. 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 |ig/L of PCE, 549 |ig/L of TCE, and 529 |ig/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 (Fe°) 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
-------
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.
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Borden Aquifer, Ontario, Canada
Installation Date:
1991
Contaminants:
TCE, PCE
Reactive Media:
Fe°
Installation Cost:
$30,000 (not including
Fe° 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: 519-885-1211x3159
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 |ig/L TCE and 43,000 |ig/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
(Fe°) 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.
33
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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.
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Cape Canaveral Air Station, FL
Installation Date:
October-November 1997
Contaminants:
TCE, DCE, VC
Reactive Media:
Fe°
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 7823 5
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 (Fe°) 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 Fe° with
guar gum and a binder. About 107 tons of Fe° 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
35
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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.
36
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Industrial Site, NY
Installation Date:
May 1995
Contaminants:
TCE, cDCE, VC
Reactive Media:
Fe°
Installation Cost:
$250,000
Construction:
Funnel and Gate
Point of Contact:
Diane Clark
Stearns & Wheler
One Remington Park
Drive
Cazenovia,NY13035
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 |ig/L existed at this former plating facility. As
a result of reductive dehalogenation of TCE, 100-500 jig/L of cis-
1,2-dichloroethylene (cDCE) and 80 |ig/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
(Fe°). 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 |ig/L for TCE and
cDCE and 2 |ig/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 Fe° 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.
37
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The PRB system was destroyed following completion of the
pilot-scale demonstration to make way for a full-scale installation in
1997.
38
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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(S)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, unconfmed 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.
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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.
40
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Massachusetts Military Reservation CS-10 Plume, Falmouth, MA
Installation Date:
June 1998
Contaminants:
PCE, TCE
Reactive Media:
Fe°
Installation Cost:
$160,000
Construction:
Hydraulic Fracturing
Point of Contact:
Robert W. Gillham
University of Waterloo
2400 University Avenue
West
Waterloo, Ontario
Canada N2V1T4
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 |ig/L and 15 |ig/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 (Fe°) (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.
41
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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 permeability-
increasing 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 Fe° 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.
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Moffett Federal Airfield, Mountain View, CA
Installation Date:
April 1996
Contaminants:
TCE, 1,2-DCE, PCE
Reactive Media:
Fe°
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 |ig/L (TCE), 280 |ig/L (1,2-DCE), and 26
|ig/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, semiconfming
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 (Fe°). 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
43
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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.
44
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Savannah River Site TNX Area, Aiken, SC
Installation Date:
July 1997
Contaminants:
TCE, cDCE, CT, NO3
Reactive Media:
Fe°
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 |ig/L, cis-l,2-dichloroethylene
(cDCE) at 20-50 |ig/L, carbon tetrachloride (CT) at 15-45 |ig/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 (Fe°) 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 Fe° 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
45
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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 jig/L of TCE could be treated, while
maintaining the average discharge TCE concentration below 5 |ig/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
46
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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.
47
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SQL 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
NIK 1S6 Canada
Tel: 519-824-0432
Fax: 519-763-2378
E-mail:
j vogan@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 |ig/L,
perchloroethylene (PCE) at concentrations ranging from
4,100-13,000 |ig/L, and cis-l,2-dichloroethylene (cDCE) at
concentrations ranging from 35-1,600 |ig/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
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characterization, bench-scale studies, permitting, and installation of
ground water extracton/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 |ig/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.
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Somersworth Sanitary Landfill, NH
Installation Date:
1994
Contaminants:
TCE, VC
Reactive Media:
Fe°
Installation Cost:
To be determined
Construction:
Funnel and Gate
Point of Contact:
Roger Duwart
U.S. Environmental
Protection Agency
Region 1
JohnF. 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 jig/L and 1,900 |ig/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 (Fe°) 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).
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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 (\igfL}
Benzene* 5
1,1-Dichloroethylene 7
Methylene chloride* 5
Tetrachloroethylene 5
Trichloroethylene 5
Vinyl chloride 2
cis-l,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.
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A continuous trench of reactive material should allow for flow through
the PRB which more closely emulates flow through the aquifer.
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U.S. Naval Air Station, Alameda, CA
Installation Date:
December 1996
Contaminants:
cDCE, VC, TCE, BTEX
Reactive Media:
Fe°, O
Installation Cost:
$400,000
Construction:
Funnel and Sequenced
Treatment Gate
Point of Contact:
Michaye McMaster
Beak International Inc.
42 Arrow Rd.
Guelph, Ontario
NIK 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 (CC14) and toluene. The technologies were: (1)
abiotic reductive dechlorination using zero-valent iron (Fe°),
followed by oxygen releasing compound (ORC™) 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 Fe° followed by oxygen
biosparging in a funnel-and-gate system to remediate
trichloroethylene (TCE); cis-l,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
lOmg/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% Fe°, 5 ft of Fe°, a 3-ft pea gravel
transition zone, a 3-ft biosparge zone, and a 2-ft pea gravel zone.
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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 jig/L and 217 jig/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-and-
gate area and for monitoring to continue on a quarterly basis.
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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.mars'
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 |ig/L;
trichloroethylene (TCE), 1,500 |ig/L; cis-dichloroethylene (cDCE),
4,200 |ig/L, trans-dichloroethylene (trans-DCE), 11 |ig/L; and vinyl
chloride (VC), 1,700 |ig/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
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Cleanup goals for the contaminants of concern are: PCE, 5 |ig/L;
TCE, 5 |ig/L; cis-DCE, 5 |ig/L; trans-DCE, 5 |ig/L; and vinyl
chloride, 2 |ig/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.
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X-625 Groundwater Treatment Facility,
Portsmouth Gaseous Diffusion Plant, Piketon, OH
Installation Date:
March 1996
Contaminants:
TCE
Reactive Media:
Fe°
Installation Cost:
$4,000,000
Construction:
Horizontal Well
Point of Contact:
Thomas C. Houk
Portsmouth Gaseous
Diffusion Plant
3 930 US Route 23 S
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 |ig/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 (Fe°). 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 Fe° in
the form of foamed pellets. Electrochemical enhancement by
passing a current through the iron media also is being considered.
Results
Testing of Fe° filings was conducted from March 1996 through
March 1998. Results indicated a reduction of TCE concentrations to
less than 5 jig/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
Fe° corrosion rates influenced by the high sulfate levels in the
ground water.
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Future sampling plans will be developed during conversion to the
higher flow rate, which is expected to be completed by October
1998.
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Metals and Inorganics
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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
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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
bi annually.
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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 |ig/L of Pb, 77 |ig/L of Cd, 313
Hg/L of As, 1,130 ng/L of Zn, and 140 |ig/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.
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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.
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U.S. Coast Guard Support Center, Elizabeth City, NC
Installation Date:
June 1996
Contaminants:
Cr+6, TCE
Reactive Media:
Fe°
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 |ig/L for TCE and more than 3,430 |ig/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 (Fe°) 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 |ig/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
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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 |ig/L within
the wall, but exceed 50 jig/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.
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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, WA99352
Tel: 509-376-3937
Fax: 509-372-1704
E-mail:
j ohn. 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 jig/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.
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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(S)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, unconfmed 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.
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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.
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Fuel Hydrocarbons
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East Garrington, (Near Olds), Alberta, Canada
Installation Date:
September 1995
Contaminants:
BTEX
Reactive Media:
O,
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 OM6
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-and-
gate 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.
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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 |ig/L at the
treatment gate, and no contaminants have been detected off site.
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.
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U.S. Naval Air Station, Alameda, CA
Installation Date:
December 1996
Contaminants:
cDCE, VC, TCE, BTEX
Reactive Media:
Fe°, O
Installation Cost:
$400,000
Construction:
Funnel and Sequenced
Treatment Gate
Point of Contact:
Michaye McMaster
Beak International Inc.
42 Arrow Rd.
Guelph, Ontario
NIK 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 (CC14) and toluene. The technologies were: (1)
abiotic reductive dechlorination using zero-valent iron (Fe°),
followed by oxygen releasing compound (ORC™) 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 Fe° followed by oxygen
biosparging in a funnel-and-gate system to remediate
trichloroethylene (TCE); cis-l,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
lOmg/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% Fe°, 5 ft of Fe°, a 3-ft pea gravel
transition zone, a 3-ft biosparge zone, and a 2-ft pea gravel zone.
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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 jig/L and 217 jig/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-and-
gate area and for monitoring to continue on a quarterly basis.
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Nutrients
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Y-12 Site, Oak Ridge National Laboratory, TN
Installation Date:
December 1997
November 1997
Contaminants:
U, Tc, HNO3
Reactive Media:
Fe°
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 (Fe°). Guar gum was
added during excavation to keep the trench walls from collapsing.
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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 Fe° 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:
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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 Fe° treatment zone deployed in
subsurface concrete boxes.
The treated water will flow into an infiltration trench
downgradient of the second treatment zone.
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Public School, Langton, Ontario, Canada
Installation Date:
August 1993
Contaminants:
P043-, N03-
Reactive Media:
Fe/Ca oxides,
high-Ca limestone,
organic carbon
Installation Cost:
$5,000
Construction:
Funnel and Gate
Points of Contact:
Will Robertson (NO30
David W. Blowes (PO430
University of Waterloo,
Department of Earth
Sciences
200 University Avenue
West Waterloo, Ontario
N2L 3G1 Canada
Will Robertson
Tel: 519-888-4567x6800
Fax: 519-746-7484
E-mail: wroberts@
sciborg.uwaterloo. ca
David Blowes
Tel: 519-888-4567x4878
Fax: 519-746-7484
E-mail: blowes@
sciborg.uwaterloo. ca
A pilot-scale demonstration of a funnel-and-gate system designed to
remediate phosphate (PO43") 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 PO43" 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 unconfmed.
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
PO43" 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. PO43" 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
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One lesson learned from this demonstration is that if walls are not
keyed into a underlying impermeable material, underflow must be
carefully considered.
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Savannah River Site TNX Area, Aiken, SC
Installation Date:
July 1997
Contaminants:
TCE, cDCE, CT, NO3
Reactive Media:
Fe°
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 |ig/L, cis-l,2-dichloroethylene
(cDCE) at 20-50 |ig/L, carbon tetrachloride (CT) at 15-45 |ig/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 (Fe°) 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 Fe° 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
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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 jig/L of TCE could be treated, while
maintaining the average discharge TCE concentration below 5 |ig/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
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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.
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Radionuclides
87
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Fry Canyon Site, UT
Installation Date:
August 1997
Contaminants:
U
Reactive Media:
Fe°, 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 |ig/L in water from a background well to 20,700
Hg/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 (Fe°) 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.
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Cost
The EPA and U.S. Geological Survey have estimated that the
design cost (engineering design and planning for the funnel-and-
gate 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-and-
gate 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 Fe°
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.
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Data also suggest, however, that the dissolution of Fe° 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.
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Y-12 Site, Oak Ridge National Laboratory, TN
Installation Date:
December 1997
November 1997
Contaminants:
U, Tc, HNO3
Reactive Media:
Fe°
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 (Fe°). Guar gum was
added during excavation to keep the trench walls from collapsing.
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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 Fe° 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:
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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 Fe° treatment zone deployed in
subsurface concrete boxes.
The treated water will flow into an infiltration trench
downgradient of the second treatment zone.
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Other Organic Contaminants
95
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Marzone Inc./Chevron Chemical Company, Tifton, GA
Installation Date:
August 1998
Contaminants:
BHC, beta-BHC, ODD,
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), ODD (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
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ODD, 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.
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Bibliography
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