5
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o
/A newsletter about soil, sediment, and ground-water characterization and remediation technologies
Issue 25
July 2006
This issue o/Technology News and Trends looks back to find lessons learned from projects described in earlier issues of the
newsletter. These site-specific updates encompass expanded field operations, the results of longer-term monitoring, techniques
for system optimization, and progress toward cleanup closure.
Biological PRB Application Expanded to Accelerate Perchlorate
Degradation in Ground Water
The success of biological permeable
reactive barriers (PRBs) in treating
contaminated ground water at the Naval
Weapons Industrial Reserve Plant in
McGregor, TX, led to construction of a
second PRB system comprising 7,000
feet of treatment trenches in 2004-2005.
[For more information on the initial PRB
system, see the February 2004 Technology
New sand Trends.] Each PRB system targets
one of three contaminated ground-water
plumes migrating within separate drainage
areas toward drinking-water reservoirs that
serve 500,000 people in central Texas. The
treatment systems are designed to reduce
the mass of commingled contaminants in
the source area, prevent contamination from
exfiltrating to surface water, remediate
shallow ground water on offsite property
within 15 years, and prevent further
migration of contaminated ground water
offsite.
Burn pads and material burial sites of the
facility's former open burning/open
detonation area were identified during early
site investigations as the source of ground-
water contamination. Contaminants include
perchlorate in concentrations up to 1,500
parts per billion (ppb) and trichloroethene
(TCE) with its associated daughter products
in similar concentrations. Field studies show
that perchlorate is the only contaminant
migrating offsite. As part of the facility-wide
remediationplan, contaminated soil from the
burial sites was excavated for offsite disposal
and a RCRA landfill cap was constructed
over the burn pad in 2002.
Both PRB systems involved placement of
2.5-foot-wide barriers (operating in series)
in the area's shallow, weathered limestone,
which keys into a non-water-bearing zone
10-25 feet below ground surface (bgs).
Trenches were constructed using atrackhoe
and/or rock trencher and backfilled with
coarse gravel, wood chips saturated with
vegetable oil, and compost. Slotted polyvinyl
chloride piping was installed six inches above
the trench bottoms to facilitate eventual
replenishment of organic substrates. The
initial PRB system, which was completed
in 2002 to address the first fully delineated
plume, employs seven trenches totaling
4,500 linear feet. The second system
employs 54 trench segments and totals
7,000 feet.
From the onset of operations, perchlorate
and volatile organic compound (VOC)
concentrations in ground water exiting the
final barrier of each PRB system have been
reduced to non-detect levels. By the end of
the second year of operation, in Fall 2004,
the perchlorate mass in ground water
decreased approximately 50%, and offsite
cleanup was 5-8 years ahead of schedule.
Extensive ground-water sampling in January
indicated that perchlorate concentrations in
many locations are below 0.43 ppb,
[continued on page 2]
Contents
Biological PRB
Application Expanded
to Accelerate
Perchlorate
Degradation in
Ground Water page 1
Aquifer Monitoring
Shows Complex-Sugar
Flushing Increases
Potential for
Enhanced
Biodegradation page 2
Combined Treatment
Technologies for TCE
Removal Approach
Cleanup Closure page 4
Pilot Tests Lead to
Expanded ISCO for
Vadose-Zone
Remediation page 5
Anacostia River
Demonstration Finds
Active Caps
Effectively Contain
Sediment
Contaminants page 6
Recycled/Recyclable
Printed with Soy/Canola Ink on paper thai
contains at least 50% recycled fiber
-------
[continued from page 1]
significantly below the State of Texas 17-
ppb residential cleanup standard for
perchlorate.
Concurrent to startup of the initial PRB
system, the Navy initiated a multi-year
study at the McGregor facility to identify
geochemical parameters indicating when
rejuvenation is needed and to establish
engineering protocols for rejuvenation. The
study found that:
> Total organic carbon (TOC) is the most
reliable indicator of perchlorate break-
through. At most sampling locations
where breakthrough appeared immi-
nent, diminishing TOC concentrations
(to below 10,000 ppb) were identified.
> At several locations where nitrate con-
centrations began increasing (to
above 100 ppb), perchlorate concen-
trations began increasing from non-
detect levels to above site cleanup
goals. This correlation suggests that
nitrate breakthrough is a precursor to
perchlorate breakthrough.
> As long as oxidation-reduction poten-
tial (ORP) remained below
-50mV, perchlorate usually existed at
non-detect levels. When ORP in-
creased above this critical value, per-
chlorate concentrations began to ex-
ceed site cleanup goals.
> Several sampling locations also
showed an increase in perchlorate con-
centrations when methane concentra-
tions exceeded 2,000 ppb, which sug-
gests that methane at specific thresh-
old values indicates sufficient reduc-
ing conditions exist for perchlorate
biotreatment.
> Dissolved oxygen (DO) concentrations
did not correlate highly with the onset
of perchlorate breakthrough and are
unlikely indicators of potential break-
through or rejuvenation needs.
> Concentrations of humic, fulvic, and
volatile fatty acids were more useful
for understanding organic substrate be-
havior rather than signaling perchlor-
ate breakthrough and the need for re-
juvenation.
Based on the study findings, the Navy
issued an operations and maintenance
(O&M) manual last year for the McGregor
PRB systems. The O&M process includes
a matrix-based decision tool that scores
geochemical parameters indicating when
rejuvenation of organic substrate is needed.
To ensure that rejuvenation occurs prior to
any breakthrough, the decision matrix
includes a safety factor.
Monitoring of PRB and geochemical
parameters indicate that the initial system
now requires its first organic-substrate
replenishment after 3.5 years of operation.
Fresh carbon sources will be injected into
the piping of each of the seven trenches
this summer in accordance with the new
O&M manual. Engineering protocols
during the rejuvenation process will
address the use of perforated piping,
manifold, and substrate feed systems;
installation of permanent injection ports;
ease of injection; applicability and
frequency of vegetable oil emulsions; and
evaluation of costs.
At locations where topographic conditions
prevented installation of PRB trenches,
relatively inexpensive bioborings were
installed to furtherprevent offsite migration
of contaminated ground water.This
technology employs 10- to 12-inch-
diameterboreholes that extend into the non-
water-bearing zone and contain
biologically reactive media. At McGregor,
these borings were drilled on 10-foot
spacing in three parallel but offset rows.
The boreholes were backfilled with the
same gravel/organic media used in the
trenches, and capped at 2 feet bgs. Nearly
1,300 bioborings currently complement
the biological PRBs. Performance
evaluation of 200 early bioborings that were
installed during a 2000 pilot study suggests
a minimum lifespan of six years.
Contributed by Mark Craig, U.S. Navy/
NAVFAC South Division
(mark, craig&navy. mil or
843-820-5517), Alan Jacobs, EnSafe
(ajacobs&ensafe.com or 901-372-
7962), and Ronnie Britto, EnSafe
(rbritto&.ensafe.com or 901-372-7962)
Aquifer Monitoring Shows Complex-Sugar Flushing Increases Potential for Enhanced Biodegradation
Aquifer flushing was conducted on a
site at the Naval Amphibious Base Little
Creek (NABLC) in Virginia Beach, VA,
in 2002 to remove dense non-aqueous
phase liquid (DNAPL). The flushing
system employed a solution containing
cyclodextrin (CD) to increase solubility
and removal efficiency of chlorinated
solvents. The extracted CD solution was
treated through air stripping and reused
in a subsequent flushing event. Within
six months of the injections, preliminary
results indicated a 50% removal of
DNAPL, which contained primarily
trichloroethene (TCE). [For details on
this application, view the January 2003
Technology News and Trends.} More
complete analysis of contaminant levels
in the extracted solutions now confirms
that cyclodextrin-enhanced flushing
(CDEF) resulted in a 19-fold
improvement in the volumetric rate at
which chlorinated solvents could be
extracted from a DNAPL-contaminated
aquifer.
Researchers from Louisiana State
University (LSU) and the University of
Rhode Island (URI) conducted a
ground-water monitoring program over
the last three years to evaluate the long-
term impact of residual CD in the
[continued on page 3]
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[continued from page 2]
aquifer. The unconfined aquifer consists
primarily of sorted sand with an average
porosity of 31%, and the average ground-
water flow velocity is 9 cm/day. Ground-
water geochemistry parameters and
contaminant concentrations were tracked
for 14 months during three sampling
rounds after the final flushing event, on
days 210, 342, and 425.
During each round, conditions were
measured at eight wells in the CD
treatment zone and at another eight
wells located within 100 meters of the
treatment zone. Geochemical
parameters that were measured in the
field using portable equipment included
temperature, pH, electroconductivity,
ground-water flow velocity, depth, and
terminal electron acceptors (TEAs)
(DO, sulfate, nitrate, and total iron).
Laboratory analyses of ground-water
samples was conducted to determine
TOC content and the concentrations of
target compounds, primarily TCE and
1,1,1-trichloroethane (TCA) and its
degradation product 1,1 -dichloroethene
(DCE).
TOC was used as a cost-effective
measure of the effective concentration
of CD and its metabolites because
residual CD concentrations exceeded
naturally occurring organic-carbon
concentrations (0.25 g/L) by more than
two orders of magnitude. In the three
sampling rounds, TOC analysis showed
that average concentrations within the
CD treatment zone were 6.32 g/L, 3.55
g/L, and 2.07 g/L, respectively. Data
showed that only one-third of the CD
remained in the aquifer 425 days after
the final flushing event, but that TOC
remained in average concentrations
eight-fold above background.
Persistence of TOC in the CD injection
zone also was associated with lower
levels of DO, nitrate, and sulfate
(respectively 46%, 81%, and 98% lower
than background). At the beginning of
the post-flushing monitoring period, DO
averaged 0.44 mg/L in the wells outside
the treatment zone and 0.24 mg/L within
the zone. During the two later sampling
rounds, DO levels within the treatment
zone increased to 0.27 mg/L and then to
0.38 mg/L. These levels were considered
insufficient to support effective aerobic
biodegradation of the CD, since typical
carbon sources require a minimum DO
concentration near 2 mg/L.
Nitrate analysis on samples from the
second and third rounds of sampling
showed that concentrations were below
the detection limit (0.1 mg/L) within the
treatment zone and ranged from 0.1 to
0.8 mg/L with an average of 0.48 mg/L
outside the zone. Sulfate concentrations
also inversely related to TOC. At the 10
sample locations where TOC levels
exceeded 1 g/L (averaging 4.24 g/L),
sulfate concentrations ranged from
below 0.1 to 2.0 mg/L with an average
of 1.14 mg/L. At the 12 locations where
TOC levels were below 1 g/L (averaging
0.32 mg/L), sulfate concentrations
ranged from 0.4 to 51.3 with an average
of 13.7 mg/L. Unlike the other TEAs,
iron showed no correlation with TOC
or other ground-water quality
parameters. These findings suggest that
subsurface injection of CD provided an
effective carbon source for increased
bioactivity in the aquifer and produced
anaerobic conditions, thereby producing
a favorable environment for microbial
degradation of the highly chlorinated
contaminants.
Over the monitoring period, aqueous
concentrations of 1,1-DCE, 1,1,1-TCA,
and TCE within the injection zone
decreased 38%, 81%, and 94%,
respectively. Reduction of contaminants
in monitoring wells outside the injection
zone could not be estimated with high
confidence because those concentrations
were at or below analytical detection
limits. As such, the outside monitoring
wells served as poor experimental
controls and could not provide
circumstantial evidence that residual
CD solutions acted as secondary
means of remediation for highly
chlorinated organic solvents.
Monitoring of aquifer temperature,
pH, and ground-water flow
indicated no biofouling and
suggests that CD concentrations
will decrease to pre-flushing
concentrations in approximately two
years. Although CD-enhanced
biodegradation was not the primary
treatment objective at this site, the
CDEF process apparently benefited
from the presence of residual CD
solution. Additional research is needed
to evaluate the feasibility of injecting
CD solely for the purpose of enhanced
biodegradation.
The U.S. Department of Defense's
Environmental Security Technology
Certification Program (ESTCP)
completed a cost and performance
analysis of CDEF implementation at
the NABLC. (The full report is
available at http://www.estcp.org/
documents/techdocs/cu-0113 .pdf.)
When comparing CDEF to alternate
remediation technologies, the analysis
indicates CDEF capital costs (totaling
$296,000) were 150% more than
conventional pumping and treatment
but only 33% of the potential cost
for surfactant-enhanced aquifer
remediation (SEAR). Significant
differences also were identified in
O&M costs, which were estimated at
$498,000 for SEAR, $1,197,000 for
CDEF, and $1,385,000 for pumping
and treatment.
While total implementation costs for
these technologies are comparable,
both CDEF and SEAR technologies
significantly reduce the time needed for
complete remediation. CDEF also
offers the benefit of introducing only
nontoxic and degradable material into
the subsurface. ESTCP analysis of
[continued on page 4]
-------
[continued from page 3]
CDEF performance indicates that the
technology is most suited to removal
of residual NAPL; its use for free-
moving NAPL should follow other
technologies such as free-product
skimming. The technology is
appropriate for use in lowering
contaminant concentrations sufficiently
to allow otherwise unfeasible remediation
approaches such as enhanced
bioremediation.
Contributed by William Blanford, LSU
(blanford&geol.Isu.edu or 225-578-
3955), Thomas Boving, Ph.D., URI
(boving&.uri.edu or 401-874-7053),
and Roy Wade, U.S. Army Engineer
Research and Development Center
(roy.wade&erdc. usace. army.mil or
601-634-4019)
Combined Treatment Technologies for TOE Removal Approach Cleanup Closure
Use of soil vapor extraction (SVE)
partially enhanced by electrical
resistance heating (ERH) at the Air Force
Plant 4 (AFP4) in Forth Worth, TX, over
the past 13 years has resulted in
successful removal of volatile and semi-
volatile contaminants in the site's vadose
and saturated zones. Treatment of the
contaminated soil and ground water
posed unique challenges due to the
presence of TCE in the vadose zone
directly below the plant's "Building 181."
In one of the building's monitoring wells,
TCE concentrations were as high as
1,400 mg/L.
The area under Building 181 is the
primary source of the AFP4's operable
unit 1 (OU1) ground-water contaminant
plume. As part of the OU1 source-area
remediation plan, vadose-zone treatment
was needed to prevent TCE migration
into the alluvial ground-water system,
which in turn threatened the regional
aquifer. The vadose-zone TCE under the
building serves as a source of ground-
water contamination under an adjacent
parking lot. Alluvium in this area consists
of clayey fill and gravelly clay with low
permeability, conditions shown in the
past to be amenable to SVE applications.
In 1993, the U.S. Air Force (USAF)
constructed an SVE pilot system. The
system employed eight extraction wells,
seven of which extended up to five feet
bgs and one which extended 35 feetbgs
into the alluvial terrace. It also included
19 soil-gas monitoring probes, a 7.5-
horsepower blower for vapor
extraction, and two 3,000-pound carbon
vessels for TCE removal. The first 90
days of SVE operations resulted in
removal of 4,400 pounds of TCE.
Following three years of successful pilot
operations, SVE was selected as the final
remedy for AFP4 and major system
upgrades were initiated. The full-scale
system included 36 soil-gas extraction
wells, three dual-phase extraction wells,
and numerous soil-gas probes and
piezometers to measure system
performance. An additional vacuum
blower, expanded piping network, and a
new semi-permanent operations building
also were added. Instead of the vapor-
phase carbon adsorption used during the
pilot, catalytic oxidation vapor treatment
technology (COVTS) was installed to
treat recovered TCE vapors.
The full-scale SVE system began
operating on a continuous basis in March
2000. During its six-month startup, the
system removed 1,521 pounds of TCE.
As influent concentrations declined, the
COVTS equipment became uneconomical
to operate and was replaced in May 2002
with activated carbon adsorbers. At that
time, analytical sampling indicated TCE
concentrations in source-area soil were
slightly above the 11.5-mg/kg cleanup
goal, and higher TCE concentrations were
detected at some locations near the original
release area. A review of the system's
long-term performance indicated that the
application of an additional treatment
technology in the source area would likely
accelerate cleanup and achieve the
remedial action objectives.
Based on the site characteristics,
technology screening, and pilot-test
results, a full-scale ERH system was
installed in 2002 to enhance source-area
treatment efficiency. ERH technology
employs electrical resistance to heat
contaminated soil, thereby helping to
vaporize residual contaminants, ground
water, vadose-zone moisture, and
perched water. The system targeted
27,000 cubic yards of contaminated soil
in a 0.5-acrea area under the floor of
the building. A total of 63 ERH electrodes
and co-located vapor and steam
recovery wells operated continuously
over nine months. [See the December
2004 Technology News and Trends for
details on this application.] Existing SVE
pipes, wells, and auxiliary equipment
were used for ERH implementation.
The combined SVE-ERH treatment
approach removed 1,743 pounds of
TCE. The ERH system was shut down
in December 2002 when cleanup goals
for both soil and ground water in the
target area were met at 11.5 mg/kg and
10 mg/L, respectively. (One well (MV-
10) could not be heated due to equipment
failure and still contained elevated TCE
concentrations; the USAF will apply a
localized treatment if monitoring does
not indicate a trend of decreasing TCE
concentrations in the well.) The
aboveground ERH system and ancillary
equipment were removed in 2003, while
[continued on page 5]
-------
[continued from page 4]
the SVE and monitoring systems
continued to operate. Temporary
shutdowns of the SVE system occurred
periodically to evaluate soil-vapor
rebound, and only minimal rebound was
detected.
Monitoring throughout 2004-2005
showed an average mean TCE
concentration in soil of 0.184 mg/kg,
significantly below the 11.5-mg/kg target
for OU1. The mean TCE concentration
in ground water also was far below its
10-mg/L target, and averaged 4.1
mg/L. Downgradient dual-phase
extraction wells with concentrations
exceeding 20 mg/L before SVE-ERH
treatment now exhibit TCE
concentrations below 1 mg/L, well
below the remediation target (Figure 1).
As a result, the USAF currently is
shutting down the SVE system,
evaluating the MW-10 well area, and
conducting any final remedial actions in
preparation for OU1 clean-up closure
later this year.
Contributed by George Walters,
Aeronautical Systems Center/
Engineering Directorate
(george.walters&wpafb.af.mil or
937-255-1988)
5-50 og/l
50-500 ug/l
500-5,000 ijg/1
• 5000-10,000 ug/l
• >10,000 ug/l
Carswel! Landfills 4 & 5
Interim Ground-water
Treatment System
Parking Lot
Interim Ground-water
Treatment System
Building 181
Electrical Resistive
Heating 2002
Carswell Landfills 4 & 5
Permeable Reactive
Barrier
TCE Concentrations
5-50 ug/l
50-500 ug/l
500-5,000 ug/l
5000-10,000 ug/l
> 10,000 ug/l
Parking Lot
Final Ground-Water
Remedial Action
Pilot Tests Lead to Expanded ISCO for Vadose-Zone Remediation
Following successful pilot-scale field
testing of in-situ chemical oxidation
(ISCO) in 2001, the USAF began an
expanded-scale application in 2003 to
remove chlorinated solvents from an
upgradient source area at Air Force Plant
44 in Tucson, AZ. [For information on
site conditions and details concerning the
pilot test, see the January 2003 issue of
Technology News and Trends.} During
both the pilot and expanded operations,
potassium permanganate solutions were
injected to remove residual high
concentrations of TCE from fine-grained
alluvial sediments in the upper part of
the regional aquifer.
The expanded-scale treatment area,
known as IRP Site 2, covers
approximately 12 acres and is the most
upgradient and heavily contaminated
[continued on page 6]
-------
[continued from page 5]
source area for a two-square-mile
plume of TCE-contaminated ground
water. A pump-and-treat system has
operated since 1987 for plume
remediation, and a former SVE system
removed more than 75,000 pounds of
TCE from vadose-zone soil. Despite
SVE success, TCE concentrations in
ground water remained elevated in
vadose soil extending to a depth of 150
feet. Injection of potassium
permanganate in a single well during
the August 2001 pilot test produced a
localized, temporary decrease in TCE
concentrations.
In January 2003, the USAF began the
large-scale ISCO effort involving single
injections of potassium permanganate
in multiple wells across IRP Site 2.
Sixteen former SVE wells were used
to inject into the lower vadose zone,
and eight ground-water wells were used
to inject directly into the upper part of
the regional aquifer. To reflect 2001
pilot-test results suggesting that the use
of greater volumes of more dilute
solutions may increase effectiveness,
potassium permanganate was injected
in concentrations of 0.3-0.5% rather
than the 2% solution previously used.
A total of 16,000 pounds of potassium
permanganate were injected. To
enhance operation ease and reduce
intrusive activities, the 20,000-gallon
batch-tank system used in the pilot test
was replaced by a portable flow-through
system tailored for potassium
permanganate delivery in the expanded
injection program. Both vertical and
horizontal flooding techniques were
used.
Monitoring methods and frequencies
were optimized to reflect University of
Arizona research findings from the pilot-
scale application. Monitoring was
conducted quarterly rather than weekly
due to the slow changes occurring in
subsurface conditions. In addition, the
large-scale application focused on key
ground-water monitoring parameters that
included ORP, temperature, pH and
conductivity, and color (purple
indicating the presence of potassium
permanganate). Quarterly monitoring
also included laboratory analysis of
ground-water samples collected within
and downgradient of the treatment
area to determine changing TCE
concentrations.
Three years after the large-scale
injections, active (based on observed
color) potassium permanganate remained
in the injection wells to varying degrees
and for varying durations. This
persistence was attributed to the
aquifer's low TOC content, which was
estimated at 0.1%. TCE concentrations
in the treatment wells began to rebound
over time at differing rates. As a result,
an additional 4,600 pounds of potassium
permanganate were injected last fall
using the same field methods in 10
selected wells: three previously-treated
regional aquifer wells, two previously-
untreated regional aquifer wells, and
five previously-untreated vadose-zone
wells.
To measure treatment effectiveness, pre-
and post-injection TCE concentrations
were compared in ground-water
samples collected from 17 wells for
which complete data were available.
Laboratory analysis of samples
collected in November 2001, before the
initial injection, indicated TCE
concentrations averaging 297 ug/L.
Post-treatment samples collected this
past February (two months after the
final injection) contained TCE
concentrations averaging 18.4 ug/L,
demonstrating a 94% reduction. The
USAF anticipates continued operation
of the IRP Site 2 pump-and-treat
system, and additional ground-water
treatment, if needed. ISCO field-testing
(but without the same degree of
research activities) also was performed
at IRP Site 3 in 2001 and expanded to a
large-scale system in 2004-2005.
Contributed by George Warner, USAF
(george.warner&wpafb.af.mil or
937-255-3241) and Timothy J. Allen,
Raytheon (tjallen&raytheon.com or
520-794-9450)
Anacostia River Demonstration Finds Active Caps Effectively Contain Sediment Contaminants
In March 2004, innovative cap materials
were placed in the Anacostia River in
Washington, DC, to demonstrate their
applicability for management of
sediment contaminants. Conventional
sand caps are designed to reduce
contaminant release from sediments by
physically isolating contaminants from
organisms and the water column. The
active capping process underway at the
Anacostia, however, involves covering
contaminants with layers of alternative
materials that offer treatment and/or
sequestration of contaminants.
Following extensive site characterization
studies and two years of laboratory
treatability studies, three alternative cap
technologies were included in the
demonstration: AquaBlok™, apatite, and
coke breeze in a laminated mat [see the
May 2004 Technology News and Trends
for details on the technology selection
process]. Six-inch layers of AquaBlok
and apatite were emplaced and covered
by 6 inches of sand. The 1-inch layer
of coke breeze in a laminated mat was
also covered with 6 inches of sand. The
[continued on page 7]
-------
Figure 2. A recent vertical profile for
PAHs in the coke breeze-laminated
capping area shows a high degree of
containment of sediment contaminants
and recontamination from
unremediated areas of the Anacostia
River at the surface.
[continued from page 6]
control area consisted of 1 foot of sand.
Monitoring approximately one month
after placement confirmed that each of
the materials was placed effectively in
the river despite a relatively crude
placement approach and the thin target
thickness. The average variation in
layer thickness was approximately
30%, with less than one to two inches
of intermixing with underlying
contaminated sediments.
AquaBlok, apatite, and sand were
placed using conventional clamshell
bucket techniques. Placement was
monitored through use of a high-
resolution digital global positioning
system attached to the arm of the
crane. Coke breeze in the laminated mat
was emplaced by tacking one end of a
10-foot-wide, 100-foot-long roll of mat
and unrolling it through use of a crane.
Divers then ensured proper placement
of each roll, with small overlaps.
Laminated mat was selected for the
coke placement due to the low density
of coke and the relatively high fraction
(10-20%) of non-settleable material that
likely would result if coke were placed
through conventional techniques.
Performance monitoring was
conducted at six and 18 months after
cap placements. Geophysical
parameters were used to evaluate any
changes in bathymetry and to identify
changes in surficial site characteristics
such as the deposition of new fine-
grained sediments. Sediment coring
also was conducted to determine
vertical profiles of contaminant
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concentrations. Innovative monitoring
approaches employed on the low-
permeability AquaBlok cap included the
use of seepage meters to evaluate any
reductions in ground-water flow and an
inclinometer to detect small vertical
deflections that may occur due to tides
or gas movement.
The influence of AquaBlok, for which
the primary objective is permeability
control, could be measured immediately.
Seepage meters during the two
monitoring events showed significant
reductions in ground-water flows, from
1-5 cm/day to significantly less than 1
cm/day. The low permeability of
AquaBlok also led to accumulation and
irregular release of gas from this cap
material, although without apparent
enhancement of contaminant migration
or decrease in long-term cap
performance.
Monitoring results confirm that extensive
time is needed for polycyclic aromatic
hydrocarbons (PAHs) and metal
contaminants to migrate within the
materials, which allows for extended
intermixing of the cap material and
underlying sediment. Results also
indicate that all of the cap materials,
including the sand control plot, are
effectively containing contaminants.
For example, data indicate that the coke
breeze mat efficiently contains PAHs
near the surface (Figure 2), particularly
due to movement of new contaminated
sediment onto the surface of the cap.
[continued on page 8]
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Solid Waste and
Emergency Response
(5203P)
EPA 542-N-06-004
July 2006
Issue No. 25
United States
Environmental Protection Agency
National Service Center for Environmental Publications
P.O. Box 42419
Cincinnati, OH 45242
Presorted Standard
Postage and Fees Paid
EPA
Permit No. G-35
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Penalty for Private Use $300
[continued from page 7]
Long-term effectiveness of the active
cap materials and performance relative
to the sand control will be evaluated
again this Fall for 2006,30 months after
placement. The demonstration
continues to show that alternative cap
materials can be placed effectively in
a riverine environment and that all of the
caps are efficiently containing
contaminants. Monitoring will continue
for a minimum of one additional year to
better quantify the cap performance and
to help identify the performance benefits
of active caps over conventional sand
caps.
Contributed by Danny Reible, Ph.D.
University of Texas
(reible(q)mail.utexas.edu or 512-471-
4642)
EPA is publishing this newsletter as a means of disseminating useful information regarding innovative and alternative treatment techniques and
8 technologies. The Agency does not endorse specific technology vendors.
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