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/A newsletter about soil, sediment, and ground-water characterization and remediation technologies
Issue 32
TTn's M's-we o/ Technology News and Trends highlights site remediation involving in-situ
application of heat or electrical current to treat soil or ground water containing volatile
organic compounds (VrOCs), including non-aqueous phase liquid. These projects demon-
strate significant cost and time savings gained over conventional remedies such as soil
excavation or ground-water pumpingwith limited aboveground treatment, and suggest methods
to address common difficulties such as treatment of heterogeneous contaminant sources or
verification of system performance.
Innovative E-Barrier Controls Ground-Water Plume
of Energetic Compounds
September 2007
Demonstration of an emerging technology
known as the electrolytic reactive barrier
(e-barrier) is underway at the Pueblo
Chemical Depot near Pueblo, CO. This
technology combines the principles of
electrochemistry with those of permeable
reactive barriers to manage ground-water
plumes contaminated with chlorinated
solvents or energetic compounds. Under
the federal Environmental Security
Technology Certification Program
(ESTCP), evaluation of the Depot's
e-barrier focuses on its performance in
treating RDX, TNT, and 2,4-DNT in ground
water and on the relationships between the
system's power requirements and
performance. Efforts to reduce electricity
costs for powering this already low-energy
treatment method are enhanced by an off-
grid solar photovoltaic (PV) system.
Environmental restoration at the Pueblo
Chemical Depot was initiated in 1988 after
closure of the base under the Base
Realignment and Closure Program. The
demonstration site encompasses a fonner
munitions washout facility where unlined
holding ponds leached RDX, HMX, TNT,
2,4-DNT, 1,3,5-TNB, ammonium, and
nitrate into ground water. The source was
partially excavated in 1997-1998 and
contaminated soil was composted;
however, concentrations of energetic
compounds in ground water remained
high. Source concentrations in the
treatment zone average 35 ug/L for RDX
and 5 ug/L for 2,4-DNT. Based on site-
specific condtions, the State of Colorado
set cleanup goals at 0.55 ug/L for RDX
and 0.0885 ug/L for 2,4-DNT.
The contaminant plume resides within an
alluvial sand and silt matrix with a saturated
thickness of about 3 feet, underlain at 12
feet by a shale aquitard with ground-water
flow rates averaging 6 in/day. The plume
extends approximately two miles
downgradient from the source area. To
address high concentrations of RDX in
off-site irrigation wells, a pump and treat
system employing granular activated
carbon and ion exchange has operated at
the Depot since 2001.
An e-barrier consists of closely spaced
mesh titanium electrodes mounted to rigid,
non-conductive sheet piling. The barrier is
installed vertically to intercept the
contaminated plume and functions as a
penneable reactive barrier (Figure 1). Low-
voltage direct current is applied to the
electrodes to drive electrochemical
oxidation of contaminants at the anode and
reduction of contaminants at the cathode.
DC/DC converters allow adjustment of
voltage to optimize treatment. Depending on
target contaminants, the e-barrier can be
[continued on page 2]
Contents
Innovative E-Barrier
Controls Ground-Water
Plume of Energetic
Compounds page 1
Three-Phase System
Improves ERH Control
in Removing Source-
Area VOCs page 2
Steam Injections
Combined with SVE
Accelerate Cleanup of
Brownfield page 4
ERH Removes VOC
Contaminants Under
Cold and Low-
Permeability
Conditions page 5
CLU-IN Resources
CLU-IN's "Technology Focus"
(http://cluin.org/techfocus/)
provides guidance, cost and
performance reports, and case
studies on in-situ thermal
technologies such as electrical
resistance heating, hot-air
injections, hot-water injections,
steam injections, radio-
frequency heating, thermal
conduction, and vitrification.
Similar material is available for
ex-situ technologies such as
thermal desorption, hot-gas
decontamination, plasma high-
temperature recovery, pyrolysis,
and thermal off-gas treatment.
Recycled/Recyclable
Printed with Soy/Canola Ink on paper that
contains at least 50% recycled fiber
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[continued from page 1]
operated in either a sequential oxidation-
reduction mode or sequential
reduction-oxidation mode. Multiple
sequences may be employed to
completely degrade target contaminants
and any intermediate compounds.
The Depot e-barrier comprises 15
individual electrode modules mounted to
commercially available vinyl sheet pile.
Conventional cranes were used to load
each 2-ft by 8-ft section of electrode
mesh-covered sheet piling into the 4-ft
e-barrier trench. Once emplaced,
modules were linked to form a
continuous barrier with an estimated
ground-water residence time of eight
hours in the vicinity of the electrodes.
The trench was backfilled with clean,
coarse sand obtained from a local quarry.
PV panels are used to power die system
due to the Pueblo area's high solar-energy
rating, averaging 4.5 kWh/mVday. A
single 2-kW, non-tracking PV array
equipped with storage batteries provides
sufficient power to operate all of the
system modules. Though energy
consumption varies according to applied
voltage, current operation of the e-barrier
at an applied potential of 5.3 V results in
an energy demand of 500 W.
Treatment began in March 2006. Tests
using applied voltages of 2.3,3.3, and 4.3
V are complete, and testing of 5.3 V
began in June 2007. Performance is
monitored at 26 monitoring wells
located up- and downgradient from the e-
barrier. To date, degradation of RDX
Mesh Electrodes
Solar Power Supply
and Controller
•^^™ Ground-water Flow
"" Dfesolvwl Cowamifngt...i
Contaminant Plume Saur.ce.2oiw.--
I
Figure 1. Completion
the natural gradient
of contaminated
ground water.
has ranged from 70% at 4.3 V to 40% at
2.3 V, with no apparent formation or
accumulation of known intermediates.
Similar rates of 2,4-DNT and TNT
transformation to compounds more
thermodynamically amenable to treatment
have been observed, supporting previous
experiments that found treatment efficacy
directly relates to applied potential.
Results suggest that a threshold of 5 V is
needed to optimize reactions within the e-
barrier while avoiding undesired reactions.
Extreme redox conditions (pe and pH)
developing at electrode surfaces, even at
low voltages, potentially cause formation
of precipitates on electrode surfaces.
Although this problem may not occur at
sites with more favorable ground-water
geochemistry, it was resolved at the Depot
by reversing polarity for one hour each
day using a programmable logic controller.
A remote data-acquisition system collects
electrical data such as current and
electrode potentials at 15-minute
intervals. In addition, cellular modem
connection provides real-time monitoring
of the electrical system and access to
its data logger.
Project costs are estimated at $24/ft2
for installation and $1,200 for each
e-barrier module, for which a 20-year
lifespan is estimated. Project results
will be detailed in a future cost
and performance summary. Pending
final results of the demonstration
and funding availability, full-scale
operations involving additional
transects at the Depot may begin
in 2009. Earlier demonstration of
e-barrier prototypes at Warren Air
Force Base (see cost and performance
summary at www.estcp.org) and
Canadian Forces Base Borden showed
that simple reversal or shifting of
electrode polarity allows the
technology to treat chlorinated solvent
plumes.
Contributed by David Gilbert,
Ph.D. (gilbert&engr.colostate.edit or
970-491-8880) and Tom Sale, Ph.D.,
Colorado State University
ftsale&.engr.colostate.edu or
970-491-8413), and Chris Pulskamp,
Pueblo Chemical Depot
(Christopher.Pulskamp(q:i:us.army.mil
or 719-549-4252)
Three-Phase System Improves ERH Control in Removing Source-Area VOCs
The U.S. Navy increasingly uses three-
phase electrical resistance heating
(ERH) to remove VOCs from
contaminant source areas on Navy
facilities. One site is the Naval Station
(NS)-Annapolis, MD, where ERH was
conducted in 2006 in a portion of the
area known as "Site 1." As part of a
CERCLA interim removal action, the
primary objective of ERH application
was 95% removal of bulk contaminants
in source-area soil to reduce potential for
contaminant migration to ground water.
After ERH system shutdown, the volume
of VOC mass removed by the system
more than doubled the amount originally
targeted.
Site 1 covers 39 acres along the north shore
of the Severn River and directly across
from the U.S. Naval Academy. From 1944
until 1973, the site was used for metal
storage and salvaging operations. The
Navy commissary/exchange building and
parking areas currently occupy the site's
northwestern portion, and the remainder
is primarily wooded. The ERH treatment
area is located directly behind the
commissary and exchange building's
loading dock.
[continued on page 3]
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[continued from page 2]
A 1988 site investigation identified
elevated concentrations of VOCs in
ground water, likely resulting from past
metal salvaging. Contamination consisted
primarily of 1,1,2,2-tetrachloroethane
(TeCA) and trichloroethene (TCE) at
concentrations reaching 45,000 ug/L and
2,800 ug/L, respectively. Subsequent
investigations identified a 150- by 110-
foot vadose-zone source area
extending in soil from a depth of 10
feet below ground surface (bgs) to
65 feet bgs. Studies showed no direct
exposure to contaminated soil in the
source area, which now is covered
with asphalt or grass.
Remedial alternatives for subsurface soil
included ERH. soil vapor extraction
(SVE), and excavation. Life-cycle costs
for ERH and SVE were comparable, but
SVE was projected to require up to seven
years of operation to remove the target
VOC volume, and ERH was estimated
to remove the same amount in less than
one year. Soil excavation was not a viable
cost option due to the depth of
contamination. To optimize capital and
operating costs, extensive sampling was
conducted to fully delineate the treatment
area and determine the minimum number
of electrodes needed.
ERH technology promotes contaminant
volatilization through a combination
of steam stripping and in-situ
degradation that removes dissolved-
phase contaminants. Its performance
relies on critical spacing of electrodes
for heating the subsurface while
targeting contaminant depths and
concentrations. At NS-Annapolis,
electrodes were placed in vadose- and
saturated-zone VOC recovery wells.
Each electrode boring included a co-
located vapor recovery well. Instead of
using sand to backfill around the
electrodes, as in conventional well
installations, an electrically conductive
material (graphite) was emplaced in the
wells at target depths. Unnecessary heat
conductance and associated electricity
costs at the periphery, where
contamination was shallow, were
minimized through use of shorter spans
of graphite. Five temperature-monitoring
points were used to measure temperatures
at 5-ft intervals from 5 ft to 75 ft bgs.
Two drilling methods were needed to
install wells to a target depth of 72 feet.
An air rotary rig drilled through sand, silt,
clay, and a 10-foot iron layer to reach the
saturated zone located 60 feet bgs. A
hollow-stem auger was used to preserve
integrity of the well walls during drilling
of the remaining 12 feet and for
electrode placement.
The system includes 24 steel
electrodes, a conventional-electricity
power control unit (PCU), a steam
condenser, granular activated carbon
(GAC) filters, and an SVE blower.
Electrodes were installed in a triangular
grid for three-phase, instead of more
common six-phase, heating to achieve
more uniform heating of the
subsurface. All portions of the
electrodes were installed underground
to avoid interference with ongoing
site activities.
Soil vapors and contaminant-laden
steam were transported through the
combined electrode/recovery wells to the
system's aboveground condenser, where
soil vapors and VOCs were separated
from steam. Resulting condensate was
recycled in the condenser system as
supplemental cooling water. Air and
VOC vapors passed from the condenser
through GAC filters to the SVE blower
for atmospheric discharge. Emission
tests during the heating process
showed no VOC concentrations
exceeding air standards.
The selected PCU allowed manual and
fully remote computer-based control of
the ERH system, which required 100-
amp, 13.8 kV power to apply 2,000 kW
of electricity to the source area. Current
was applied to the subsurface for 116
days in February-May 2006. Subsurface
temperatures averaged 99°C throughout
the heating process, reaching a
maximum of 107°C. Pre-treatment tests
suggested a target temperature of
100°C.
Operations were suspended only
once early in the project to address
blower noise affecting a nearby
residential neighborhood. Addition of
a muffler to the inlet and outlet lines
of the blower achieved a 75%
reduction in noise, and operations
resumed four days later.
Daily measurement of VOC concentrations
in vapor streams of the condenser's
outlet indicated a total VOC volume of
1,800 pounds was removed from soil
over the course of treatment. This volume
significantly exceeded a pretreatment
estimate of approximately 850 Ibs,
showing higher than anticipated ERH
performance as well as under-estimate of
the original volume.
Ground-water sampling was conducted
before system operation, immediately
after system shutdown, and at three-
and six-month intervals after shutdown.
At the three-month interval, some
contaminant rebound was observed
in the treatment area, and TCE
concentrations in downgradient wells
exceeded pretreatment measurements.
These concentrations decreased
significantly by the next round of
sampling. Six-month sampling indicated
total VOC concentrations in the well
closest to the treatment area decreased
at least one order of magnitude, with
TeCA and TCE concentrations falling
[continued on page 4]
Call for Abstracts
The U.S. EPA Office of Superfund
Remediation and Technology
Innovation and the Environmental
Institute/University of Massachusetts
Amherst are co-sponsoring a
conference on Triad Investigations:
New Approaches and Innovative
Strategies on June 10-13, 2008, in
Amherst, MA. Abstracts for platform
or poster presentations must be
submitted by November 1, 2007.
Visit http://www.umass.edu/tei/
conferences/triad.html for more
information.
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[continued from page 3]
to levels below 10 ug/L and 1,500
ug/L, respectively.
Over the course of active heating, the
system's electricity consumption totaled
1,710,726 kW-hrs. Electricity costs
comprised 19% of the $1.7M total
project cost, including installation and
operation. Soil sampling to verify ERH
results will occur next year following
complete cooling of the subsurface.
Contributed by Jennifer Melton, U.S.
Navy (Jennifer, melton&.navy. mil or
202-685-3275)
Steam Injections Combined with SVE Accelerate Cleanup of Brownfield
The Port of Ridgefield in Washington
is conducting steam-enhanced
remediation (SER) as an interim/
emergency action to remove a ground-
water contaminant source and control
migration of a free-phase plume into
the Ridgefield National Wildlife Refuge
of the Columbia River basin. The
treatment area comprises four acres of
the Port's 41 -acre Lake River Industrial
Park, a brownfield requiring restoration
before mixed-use redevelopment. In
cooperation with the State of
Washington Department of Ecology,
the Port estimated that cleanup using
conventional ground-water pumping
and aboveground treatment (P&T)
would take up to 90 years. Early results
of SER/SVE treatment confirmed that
significant reductions in cleanup
duration could be achieved through
technologies other than P&T. During
the initial year of its application,
alone, SER/SVE technology removed
the same volume of subsurface
contaminants expected to be removed
by P&T in 6.5 years.
Pacific Wood Treating Corporation
treated wood for approximately 30
years on this Port-owned property
located approximately 10 miles north
of Vancouver. Chemicals used during
wood-treating included creosote,
pentachlorophenol, and water-borne
solutions containing copper, chromium,
and arsenic. These chemicals were
released to the soil and ground water
and eventually threatened to migrate to
Carty Lake, now part of the wildlife
refuge. Investigations indicate that the
site's shallow (20 ftbgs) ground water
contains a plume with more than
100,000 gallons of free-phase
chemicals. Soil in this area consists
of a 50-ft layer of fine to course sand
and cobbles overlaying a cemented
gravel aquitard.
SER implementation began in 2004 with
an initial phase to start hydraulic control
of the plume containing semivolatile
organic compounds, begin mass removal,
optimize the SER system, and fine-tune
a design for expanded operation.
Treatment targeted a one-acre area with
initially one injection well; later during this
initial phase, five more injection wells
were added. Each well received
continuous steam injection over an
average of 180 days, at an average rate
of 2,000 Ibs/lir. Performance information
helped adjust well spacing during
subsequent full-scale installation and
detennine an energy consumption goal
of 500 kW-hr/m3 for each cubic meter
of soil treated. Approximately 4,700
gallons of nonaqueous-phase liquid
(NAPL) were removed during the initial
phase.
In 2006, the full-scale SER system was
installed and operations began to treat four
areas sequentially. Current objectives are
to remove NAPL, the contaminant
source, and mobile contaminants from
both soil and ground water. Based on
first-phase results, the expanded system
generally maintains a 2:1 ratio between
the amount of ground water extracted
and the amount of cold-water equivalent
of steam injected. Each injection is
designed to apply approximately four
pore volumes of steam.
The system employs 51 injection wells
(spaced 86 ft apart) and 40 vapor/
ground-water extraction wells (spaced
50 ft apart) in addition to the pilot
project's 17 combined ground-water and
vapor extraction wells. The 4-inch-
diameter steel injection and extraction
wells have 10-ft and 35-ft screens,
respectively. Each well is grouted in
place with a mixture of silica flour and
Portland cement to provide a good well
seal and prevent steam escape at the
surface.
The system includes a 100-gpm liquid
treatment system and 1,500-scf vapor
treatment system housed in a 100-
by 100-ft aboveground facility.
Treatment of extracted liquid involves
sequential use of two parallel heat
exchangers, two parallel bulk oil/water
separators, coagulation/flocculation
units, an inclined plate clarifier, two
parallel mixed media filtration skids, and
three GAC beds. Extracted vapors are
treated in a separate treatment train using
a "fin-fan" heat exchanger, air/liquid
separators such as knockout pots, air
dryers, and two steam-regenenerated
GAC systems. Treated liquids are
discharged into Lake River, an adjacent
tributary of the Columbia River under
an NPDES permit.
Full-scale enhancements included use of
hammerhead airlift pumps rather than
progressive cavity pumps for better
maintenance of hydraulic control during
extraction and ease of in-field repair;
other pumping methods failed due to heat
build-up and associated chemical
reactions. To increase the rate of
removing light NAPL, a second vacuum
system was added, whereby 1-inch
flexible "slurping" tubing is used to draw
liquids off the ground-water surface.
Full-scale operations began in January
2006 to address the 4-acre treatment
zone in 1-acre increments, each
employing 8-10 injection wells
supported by 20-30 extraction wells.
Each well received continuous steam
[continued on page 5]
4
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[continued from page 4]
injection over an average period of 180
days, at an average rate of 2,000 Ibs/hr.
Approximately 60,000 gallons of
contaminated liquid, averaging about
120°F upon extraction, were treated at
the water treatment plant each day.
Automated systems allow simultaneous
monitoring by the Port and WA
Department of Ecology, which oversees
the cleanup. In contrast to earlier steam-
injection projects based onNAPL removal
from an aquifer, performance monitoring
indicated mat die majority of NAPL floats
on top of the water table.
Treatment in the first 1-acre area was
suspended in June, when approximately
16,600 gallons of NAPL had been
cumulatively removed. The material was
placed in onsite storage tanks pending
offsite incineration. Work focus was
turned to the next 1-acre area in order
to maximize treatment returns on the
NAPL recovery, and begin monitoring of
"polishing" technologies such as
hydropyrolysis/oxidation and natural
bioremediation.
Cleanup costs are anticipated to total
$48M. Use of the Port's existing steam
generator reduced construction costs,
and operation of the system by in-house
Port personnel significantly reduces
operating costs. Approximately $6M and
three years of system operation also
were saved by installing the complete
well field at one time rather than through
four rounds of field mobilization.
Steam injection in the second 1-acre
treatment area began this past July, with
expected completion in 6-9 months. SER
across the entire four acres is anticipated
to be complete by 2013-15. The Port
has begun assessing risk associated with
residual (primarily non-mobile)
contamination in the treatment area as
part of a current remedial investigation/
feasibility study.
Contributed by Brent Grening, Port of
Ridgefield fbgren ing&portridgefield. org
or 360-887-3873), Dan Alexanian, WA
Department of Ecology
(dale461 (Siecy.wa.gov or 360-407-
6249), and Ste\>en Taylor, Maul Foster
& Alongi, Inc. (staylor&mfainc. org or
360-694-2691)
ERH Removes VOC Contaminants Under Cold and Low-Permeability Conditions
The U.S. EPA's Region 8 recently
remediated soil and ground water at a
VOC-contaminated site in West Fargo.
ND, using thermally enhanced vapor
extraction relying on ERH technology.
Though the treatment area encompassed
only 10,300 ft2 of a former dry-cleaner
site, an extensive heating system was
required to reach cleanup goals in the
region's cold climate. Remediation was
further challenged by the presence of
dense NAPL, an extremely low-
permeability subsurface, and the site's
location next to residential and
commercial properties. Acceleration of
this Superfund removal action was
needed to protect the small city's
drinking water source, a municipal well
only one-quarter mile from the site.
Treatment was designed to target five
depths ranging from 0 to 56 ft bgs to
treat a total soil volume of approximately
13,800 yd3. Concentrations of PCE, the
primary contaminant of concern,
reached 2,200 mg/kg in soil consisting
primarily of clay with goethite infilling
Figure 2. Rates of contaminant removal
increased dramatically after additional
DVE wells began operating at the West
Fargo site.
between joints and fractures. The highest
PCE concentration in ground water,
encountered at 3-7 ft bgs, was 89 mg/L.
In contrast to a typical conductivity of
200-1,000 uS/cm, ground water at this
site exhibits a natural conductivity ranging
from 8,000 to 12,000 uS/cm. This
condition required application of extremely
high-current, low-voltage electricity to
heat the subsurface. Based on site-specific
conditions and the technical practicability
of the thermal technology, cleanup goals
were set at 3 mg/kg PCE in soil and
1 mg/L total VOCs in ground water.
The ERH system included 56 multi-
zone electrode/vent assemblies and an
array of horizontal vapor extraction
wells. An additional 74 dual vacuum
extraction (DVE) wells were added
midway through the project to augment
contaminant extraction in the low-
penneability clay. Subsurface temperatures
were monitored with 10 temperature-
monitoring piezometers, and nine multi-
level perimeter monitoring wells were
installed on the site perimeter to evaluate
pre-treatment conditions and monitor any
[continued on page 6]
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Solid Waste and
Emergency Response
(5203P)
EPA542-N-06-011
September 2007
Issue No. 32
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
Official Business
Penalty for Private Use $300
[continued from page 5]
contaminant migration. Extracted vapor
and condensate were treated with
activated carbon. A temporary building
was constructed to cover the entire area,
avoiding the need to winterize individual
components of the treatment system.
Site construction began in June 2004.
Active subsurface heating began the
following March, when average daily
temperatures rose to a high above
32°F and average monthly snowfall
dropped to below nine inches. Three
36,000-amp power supply units
converted conventional electricity to
750 kW of power at voltages ranging
from 70 to 950 V. The target
subsurface steam temperature of
100°C was achieved within three
months (in May), and the system
operated for an additional six months
(until November) (Figure 2). The
DVE system continued to operate for
three more months while the
subsurface cooled.
A total of 5,188 pounds of VOC mass
was removed within one year after
treatment startup. Soil and ground-
water sampling upon ERH shutdown
confirmed target concentrations were
reached at all locations of the treatment
area, except one on the periphery where
contamination was not fully defined.
Some subsidence of clay was observed
during the treatment process.
Over the course of treatment, a total of
2.8 mW-hrs of energy was consumed.
Cleanup costs, including site restoration,
totaled approximately $3M.
Contributed by Joyce Ackerman, EPA
Region 8 (ackerman.joyce®,epa.gov
or 303-312-6822)
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