5
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Tl
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/A newsletter about soil, sediment, and groundwater characterization and remediation technologies
Issue 50
Z«w mt/e o/Technology News and Trends highlights accelerated remediation of contaminant
source areas containing dense nonaqueous phase liquid (DNAPL). Treatment typically involves
conversion of contaminants, most commonly trichloroethene, from the nonaqueous phase to the
dissolved phase where degradation occurs more readily through chemical or biological processes.
Dual-Reagent ISCO 'fast-Tracks" Cleanup of Orlando Brownf ield
October 2010
The City of Orlando initiated a three-phase plan
in the summer of 2007 to accelerate remediation of
VOC-contaminated groundwater. Contamination
was found beneath a former industrial site
scheduled to reopen in 2010 as the city's events
center. The first phase of the plan employed in
situ chemical oxidation (ISCO) with catalyzed
hydrogen peroxide (CHP) to target the suspected
contaminant source area, located directly below
the center's proposed athletic arena. The second
phase involved additional ISCO using sodium
permanganate to target residual contaminants,
and the third phase focused on offsite disposal
of shallow impacted soil. Sequentially applying
two oxidants, rather than combining single-
oxidant ISCO with a time-intensive polishing
technology such as bioremediation, met the
project's cleanup goals within nine months.
To meet a tight schedule calling for 2008
startup of building construction, field work
was guided by daily rounds of injector and
monitoring well sampling to optimize reagent
and catalyst dosing. Frequent measurements
of off-gases and degradation end products
also were made to quickly determine when
chemical oxidation was complete.
An investigation in early 2007 confirmed source-
area tetrachloroethene (PCE) in concentrations
reaching 14,600 |J,g/L in groundwater above a
clay-confining layer 40 feet below ground
surface (bgs). Concentrations of PCE
degradation products included 57 |J,g/L of
trichloroethene (TCE) and 98 jig/L of as-1,2-
dichloroethene (DCE) without detectable levels
of vinyl chloride. The presence of DNAPL was
suspected due to the high PCE concentrations
in sand and silt zones immediately on top of the
area's dense clay aquitard. Remediation goals
were set at the Florida groundwater cleanup
targetlevels (CTLs) of 3 jig/L for PCE and TCE
and70|lg/LforDCE.
Shallow soil at depths of 2-4 feet bgs also was
contaminated in two discrete areas near a
concrete pad with an underlying sewer from
past operation of a garage and machine shop.
The highest identified PCE concentration in
soil at these areas was 0.49 mg/kg, which
exceeded the 0.03 mg/kg CTL for leachability.
In early November 2007, field preparations for
ISCO began by installing 72 injection wells
spaced on 20-foot centers in an 80- by 130- foot
area of concern (AOC) under the proposed
arena. Each well extended to one of three
intervals between 10 and 40 feet bgs. Shallow
and deep nested injectors were screened from
15 to 20 feet and 35 to 40 feet bgs, respectively,
and interspersed intermediate-depth zone
injectors were screened at 25 to 30 feet bgs. Use
of a direct-push (DP) instead of conventional
drilling rig allowed for construction of the well
network in two weeks. The grout seals were
allowed to cure for two weeks.
CHP was selected as the primary oxidant due to
its efficiency in destroying DNAPL and sorbed-
phase contamination. The first-phase injection
was conducted in January 2008 using two
trailers connected by chemical hoses to inject
low-pressure CHP solution into the full array of
injection wells. Using a top-down injection
approach, each injection rig initially deployed
four inj ectors to fully blanket the AOC.
A photoionization detector (PID) and multi-
gas meter were used to measure VOCs, oxygen,
[continued on page 2]
Contents
Dual-Reagent
ISCO "Fast-Tracks"
Cleanup of Orlando
Brownfield page 1
In Situ Thermal
Desorption
Minimizes Cleanup
Duration at Dunn
Field BRAC Site page 2
Six-Phase Heating
and SVE Used for
Alameda BRAC
Facility Cleanup page 4
ISCR-Enhanced
Bioremediation
Accelerates
Groundwater
Cleanup atActive
Manufacturing
Facility page 5
CLU-IN Resources
Dense Nonaqueous Phase
Liquids is one of several
Contaminant Focus areas of
the U.S. Environmental
Protection Agency (EPA)
CLU-IN web host www.clu-
in. orq/contaminantfocus/.
Information includes introductory
discussion and additional web
links for DNAPL policy and
guidance, chemistry and
behavior, environmental
occurrence, toxicology, and
treatment technologies.
Recyc led/Recycl abl e
Printed wilh Soy/Canola Ink on paper thai
contains at least 50% recycled fiber
-------
[continued from page 1]
and carbon dioxide in the well headspace as
indicators of treatment progress. PID readings
from four monitoring wells in the source area
showed an initial VOC spike related to
contaminant desorption from the aquifer
matrix, followed by subsequent VOC
destruction to non-detectable levels over the
remainder of treatment. CHP injection was
terminated after 23 days, when PID and other
in situ data indicated completed chemical
oxidation. Residual catalyzed peroxide from
the 85,000-gallon injection was allowed to
degrade for another week before the second
injection phase began.
Sodium permanganate was selected as the
secondary reagent due to its ability to treat
residual contaminants that slowly diffuse out
of the fine-grained aquifer matrix after the
peroxide had removed bulk contamination. In
early February 2008, approximately 21,000
gallons of 4% sodium permanganate solution
was injected through the same well network
over 7 days. The volume was anticipated to
again blanket the full AOC. Injection and post-
injection monitoring included groundwater
sampling for visual analysis to ensure uniform
permanganate distribution. Permanganate in
its characteristic purple color was found
throughout the treatment area.
In the third phase of remediation during late
February, approximately 94 tons (1,800 ft3)
of surface soil were excavated to a depth of
4 feet near the concrete pad. The two-day
excavation targeted all vadose zone soil
documented to contain detectable VOCs
during earlier delineation of the AOC. It also
revealed a P VC pipe connected to a former
floor drain system, which contained residual
sludge above the source area. Elevated PID
readings in the pipe vicinity suggested this
jointed sewer was the source of solvent
discharge. Following extraction of the pipe
and associated bedding, the concrete pad
was removed and the area was backfilled.
Confirmatory sampling in early March did
not detect PCE in soil surrounding the
excavated area.
Groundwater was sampled in five treatment-
area monitoring wells beginning four days after
the permanganate injection and in mid- April
and mid-July. Results indicated that total VOCs
immediately decreased after the first injection
(Figure l)andremainedbelowtheCTLsexcept
at one well (MW-5) close to the former pad and
excavation area. The increase in PCE
concentrations at MW-5 prompted injection 7
days later of 150 additional pounds of sodium
permanganate via shallow injectors within 20
feet of the well. Confirmatory sampling in early
August showed a PCE concentration below
1.0 i-ig/L in MW-5, which supported earlier
suspicion that the observed VOC rebound was
caused by the preceding excavation activities.
July and subsequent monitoring events in five
wells within the treatment area showed a total
VOC concentration of less than 3 ug/L,a99.98%
decrease from maximum pre-treatment levels.
More recent investigations by the Florida
Department of Transportation in an adjacent
offsite area documented a presence of
permanganate that likely continues to polish
onsite groundwater and groundwater
downgradient of the AOC.
The injectors and monitoring wells were
abandoned shortly after MW-5 confirmation
sampling and when all treatment-area wells
exhibited non-detectable levels of PCE, within
290 days after the city executed the cleanup
contract. Field work was completed in 101
days, and the remaining project time involved
regulatory review and post-treatment
monitoring. Costs totaled $596,000 for
remediation (approximately $34/yd3) and
$85,395 for soil and groundwater confirmatory
sampling during and after the injections.
Building construction began on schedule in
July 2008 for opening of the city's new events
center this October.
Contributed by Alan Oyler, Orlando
Department of Public Works
(alan. oyler(q),cityoforlando.net or
407-246-3623), Dan Bryant, Geo-
Cleanse International Inc.,
(dbryant&.geocleanse.com or 732-970-
6696), and Ed Kellar, MACTEC
Engineering and Consulting Inc.
(emkellar(a)mactec. com or 352-332-3318)
^10,000.00
14,645
IPre
14 Days
73 Days
164 Days
1177 Days
MW-5
Figure 1. Monitoring
at two onsite wells with
the highest VOC
concentrations prior to
remediation showed
reductions to below
Florida CTLs within
four days after injecting
CHP.
In Situ Thermal Desorption Minimizes Cleanup Duration at Dunn Field DRAG Site
Full-scale in situ thermal desorption (ISTD)
was initiated in 2008 for areas of Dunn Field at
the Memphis Defense Depot Superfund site
to destroy chlorinated VOCs (CVOCs). ISTD
was selected to replace soil vapor extraction
(SVE) in the top 30 feet of soil, a clay-rich
loess, after SVE pilot testing suggested that
its exclusive use in the loess could take up to
235 years to reach remediation goals (RGs).
Thorough delineation of the C VOC hotspots
minimized the areas needing treatment, which
lowered ISTD costs while significantly
reducing the overall cleanup cost and duration.
The Memphis Depot closed in 1997 under the
Base Realignment and Closure Act (BRAC)
after approximately 55yearsofuse for military
material distribution/storage and maintenance
services. Upon closing, the 64-acre Dunn Field
housed multiple areas used for mineral and
waste storage and disposal. The underlying
stratigraphy consists of the relatively low-
permeability loess which grades, with depth,
to a high permeability fluvial unit consisting
of sand, silt, and gravel. Groundwater depth
is approximately 75 feetbgs.
[continued on page 3]
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[continued from page 2]
A 2004 record of decision (ROD) determined
that 41 acres of the site were suitable for
unrestricted use. The remaining acreage
contained varying degrees of CVOC
contamination, including concentrations high
enough to suggest the presence of NAPL. A
passive soil gas survey helped identify
hotspots requiring remediation to meet the
site-specific soil RGs. Based on the results,
the Depot selected SVE as the presumptive
remedy to address subsurface contamination
that had caused an underlying plume of
contaminated groundwater.
The onsite SVE pilot test indicated that full-
scale SVE in the fluvial unit could be
completed in four to five years, but SVE to
address 1,1,2,2-tetrachloroethane (PCA)
contamination in the loess would take
exponentially more time. A subsequent
remedial design investigation was conducted
to better define the extent of contamination,
particularly through use of a membrane
interface probe (MIP) that could provide
higher data density in the loess zone.
Treatment zones were delineated according
to soil cleanup levels established in the ROD.
More than 160 MTPs were pushed on 40-foot
centers, and more than 80 soil samples were
analyzed. MIP data revealed eight widely
separated hotspots encompassing 1.25 acres
shrinking the 5.5-acre hotspot identified in
the remediation investigation. The total VOC
mass was estimated at 1,200 pounds. The
significantly reduced target area demonstrated
the value of thorough site characterization
and triggered selection of ISTD to replace
SVE in the loess.
The ISTD system employed electrically
powered heating elements suspended in 3-
inch-diameter, steel-cased wells. The wells
were installed 15-18 feet apart in different
treatment areas depending on the
contaminant concentration and properties.
For example, wells were installed 15 feet apart
in one area with high PCE and TCE
Figure 2. Concentrations of all primary
COCs at Dunn Field decreased to below the
remedial action objectives after six months of
applied in situ thermal desorption.
concentrations but 18 feet apart in another area
with lower concentrations and PCA as the
primary COC. Prior to system startup, shotcrete
was sprayed over the eight treatment areas to
provide a vapor seal and insulation and to
prevent water infiltration.
Active heating began in May 2008. A total of
367 heaters operating at 600-800°C were used
to propagate thermal energy away from the well
by way of conduction and convection.
Recovered vapor was collected and transferred
to an aboveground treatment unit through 68
2-inch-diameter vapor recovery wells.
ISTD performance was evaluated in terms of its
operating temperature, vapor flow rate, vapor
contaminant concentrations (as measured by a
PID and an offsite laboratory using EPAMethod
TO-15), and CVOC concentrations in soil (as
determined by an offsite laboratory using
Method 8260). To ensure that all areas in the
treatment zone reached a target operating
temperature of approximately 100°C, 63
temperature monitoring strings equipped with
sensors at 5-foot intervals monitored the soil
temperature. The strings were generally
located at the mid-point of equilateral triangles
formed by selected heater wells, which
provided the coldest temperatures (farthest
from the heaters) within the treatment area.
Twenty-six shallow wells with pressure
gauges were used to verify negative pressure
in the target formation during heating.
Aboveground treatment involved two granular
activated carbon (GAC) systems: one
comprised two 200-pound liquid-phase units
to treat liquids from the condensate unit, and
the other comprised two 2,700-pound vapor-
phase units in line with two 3,600-pound vapor-
phase units. Daily samples of vapor were
collected from the wellfield influent, the
treatment area headers, and three other ports in
the treatment train. These samples were tested
using a PID calibrated by an isobutylene
standard. Once each month, vapor samples
also were collected in six-liter Summa
canisters at the GAC influent line and vapor
discharge point and shipped to an offsite
laboratory for VOC analysis. These data
gauged performance progress and provided
the basis for estimating the amount of
contaminants recovered.
Soil confirmation sampling was conducted
in a phased approach. A direct push rig with a
24-inch-long sampler containing a Teflon liner
was used to collect samples. Upon retrieval,
the liner was capped and placed on ice to
minimize degassing. Sampling locations were
chosen based on the MTP data and visual
observations made during well installation.
The first soil sampling event occurred 83-85
days after heating startup, when the
treatment areas reached the target
temperature range. The second event
occurred at completion of the planned
treatment period, 106-108 days after startup.
Continued high concentrations of CVOCs
measured during the second event indicated
several recalcitrant areas, which were
subsequently re-sampled at two- to three-
week intervals until RGs were met (day 174).
During later stages of heating, 10
performance sampling locations within
four treatment areas continued to exhibit
contaminant concentrations above the
RGs, possibly due to excess soil moisture
in the samples. To optimize system
performance, these sampling locations
were converted to SVE wells. Air was
alternately injected and withdrawn from the
wells to facilitate flow and vapor exchange
and, within weeks, RGs were achieved
[continued on page 4]
Contaminant
Carbon tetrachloride
| Chloroform
1,1,2,2-PCA*
I 1 ,2-Dichloroethene
| Trichloroethene
Maximum
Pre-Treatment
Soil Concentration
(mg/kg)
6.8
14.0
2,850
199
Maximum
Post-Treatment
Soil Concentration
(mg/kg)
<0.005
0.053
0,005
0.132
Remediation
Goal
(*mg/kg)
0.215
0.917
0,0112
0.755
0.182
\ *1,1,2,2-PCA is subject to rapid hydrolysis to TCE at elevated temperatures.
-------
[continued from page 3]
throughout the remainder of the treatment
area (Figure 2). RGs were considered to be
achieved in a given treatment area when the
arithmetic average of the verification samples
(taken from the most contaminated interval)
were below the RG and no single sample
exceeded the RG by a factor greater than 10.
The ISTD system was dismantled in January
2009. The system had treated approximately
49,900 yd3 soil and removed an estimated
12,500 pounds of VOCs. About 10.6 million
kWh of electric power had been applied over
the 177 days of active source-area heating.
Project costs totaled approximately
$4,7489,000, or $79 per cubic yard of soil. Of
this total, $1,009,736 was expended for
transformer installation and power usage.
S VE initiated in 2007 for the remainder of the
contaminated soil at Dunn Field is
anticipated to reach RG's in 2012.
Contributed by Turpin Bollard, U.S.
EPA Region 4 (ballard. turpin(a),epa. gov
or 404-562-8553)
Six-Phase Heating and SVE Used for Alameda BRAG Facility Cleanup
The U.S. Navy undertook a removal action in
2006 to address DNAPL in soil and
groundwater at Installation Restoration (IR)
Site 5 at the former Alameda Naval Air Station
in Alameda, CA. The primary objective of
the removal action was to reduce total
CVOC concentrations in groundwater to
below 10,000 Jlg/L, to the extent technically
and economically practicable. Electrical
heating with SVE was selected to remove
VOC mass in a subsurface area affected
by a plume. After 13 months of active
heating, the average total dissolved
CVOC concentration in targeted onsite
groundwater decreased more than 99%.
Early investigations suggested the presence
of DNAPL due to detection of total CVOC
concentrations as high as 1,710,000 |J,g/L.
Contaminants of concern (COCs) included
PCE, TCE, DCE, dichloroethane (DCA),
trichloroethane (TCA), and vinyl chloride.
Subsequent investigations in 2001-2002
indicated a 33,000-ft2 plume originating in
the area of a former plating shop used for
aircraft maintenance until April 1997, when
the base was closed as part of BRAC. Based
on Hydropunch sampling at an average of 13
feet bgs, baseline concentrations of total
CVOCs prior to treatment averaged 82,000
|J,g/L, with an estimated mass of 400
pounds. DNAPL removal was limited to a
maximum depth of 13-20 feet bgs to avoid
creating downward migratory pathways for
DNAPL in the site's bay sediment, which
contains primarily clay, silty sand, and fine-
grained sand with shell fragments
overlying fractured sedimentary rock.
The target plume ("Plume 5-3") was entirely
beneath Building 5, which encompassed more
than 12 acres and once contained a plating
shop. Some of the building walls and internal
structures were removed to allow access to the
entire plume area. Full-scale application of six-
phase heating (SPFI) of this large plume was
designed for three phases to optimize use of
existing equipment (Figure 3). Each phase used
multiple, hexagonal heating cells wired
independently and in parallel to heat areas
within each cell and between cell pairs.
Five treatment cells each were installed for
phases 1 and 2, and two cells were installed
for phase 3. Each cell consisted of six
electrodes and a neutral electrode, and each
electrode consisted of four sheet-piles wired
in parallel. Power for heating was provided
by three tailored control units with a total
output capacity of 2.5 MW, which were
housed with the vapor extraction equipment
inside the remaining building. Two units were
instrumented with switching contactors and
silicon circuit rectifiers to allow variable power
to the field, as well as programmable logic
controllers and personal computers. The third
power supply was used to heat a single
hexagonal array through manual tuning.
Vapor extraction wells were installed on a 17-
foot grid across the treatment area to collect
vapors. Piezometers measured the vacuum
influence and ensured vapor capture inside
and along the perimeter of the treatment area.
Thermowells throughout the treatment zones
measured temperatures achieved below
ground and to gauge SPH progress.
Phase 1 of active heating began in August
2006 with a target soil and groundwater
temperature of at least 90°C to ensure that
the boiling temperature of all COCs was
exceeded. Phases 2 and 3 began in October
2007 and November 2008, respectively, with
approximately eight months needed to
reposition electrodes and steel pipe between
each phase. Overall plume temperatures at 12
feet bgs increased from an average of 20°C to
nearly 100°C during treatment.
Monitoring during each phase of SPH
operation was conducted at 17 groundwater
monitoring wells once when heating began,
approximately two months after start-up, and
at heating shut-down. Groundwater treatment
continued in each phase until asymptotic
conditions were reached, as determined by
specific operation and performance
parameters: an average groundwater
temperature of at least 90°C across the plume
for a minimum of two weeks, vapor VOC mass
in the vapor recovery system approaching
an asymptote, and VOC concentrations
below 10,000 |lg/L in the monitoring wells. A
final sampling event was performed on all
Plume 5-3 wells three months after phase 3 to
measure rebound of CVOV concentrations.
The vacuum applied to vapor
extraction wells averaged 10
[continued on page 5]
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[continued from page 4]
inches of water column but reached as much
as 25 inches during treatment. The flow rate
of vacuum extraction and vapor treatment
systems, as measured at the exhaust stack,
averaged 800 scfm and ranged from 350 to
UOOscfm
Final post-treatment sampling was
conducted in March 2009 on all 17 monitoring
wells three months after the third phase to
measure rebound of CVOC concentrations.
All monitoring wells showed total CVOC
concentrations below 10,000 |J,g/L, with an
average of less than 300 |Ig/L. Concentrations
in individual wells ranged from 400 |J,g/L to
103,000 jig/L after the first phase of
treatment and 10 jig/L to 17,000 jig/L after
the second phase. After the third phase,
concentrations ranged from 200 |J,g/L to
9,000 jig/L with an average below 300 |lg/L.
Based on vapor concentrations, system flow
rates, and operational time, an estimated 253
pounds of VOCs were recovered in the vapor
recovery system.
Plume-wide rebound sampling conducted in
May 2009 to compare performance of the
three treatment phases/areas showed a 78%
average incremental reduction of total CVOC
concentrations in groundwater: 96%
reduction for the first phase (over two years
of progress), 60% reduction for the second
phase (over one year), and 80% reduction
for the third phase (over four months).
Using multiple sheet-pile electrodes allowed for
individual electrode control by increasing the
surface area compared to drilled electrodes. The
additional surface area also allowed energy to
dissipate faster, thus increasing temperature
faster across the treatment area. In addition,
the stand-alone vapor extraction wells proved
to be more effective than earlier applications of
onsite electrical resistance heating (ERH) that
were integrated with SVE due to reduced
entrainment of water and silt. Use of multiple
power supply units instead of a single large
unit was found to enable beneficial variation
in voltage and current for the electrodes.
Project costs totaled approximately $3 million
(excluding equipment), which is equivalent to
approximately $8,400 per pound of mass
removed, or $200 per cubic yard of aquifer
material. Cost comparisons against the site's
earlier projects indicate that SPH-S VE can be
applied more cost effectively to smaller plumes
with higher contaminant concentrations.
A total of more than 5,300,000 kWh of
electricity was consumed by SPH and SVE
operation, which included 2,600,000 kWh,
2,000,000 kWh, and 660,000 kWh for phase
1, 2, 3 operations, respectively. More
electricity was consumed during phase 1
because SPH continued six weeks longer to
achieve asymptotic conditions.
The U.S. Navy completed remedial action
close-out for Plume 5-3 in January 2010. A
feasibility study for remediation of Operable
Unit (OU) 2C, containing IR Site 5 and two
smaller IR sites, is almost complete; treatment
options may include ISCO or in situ
bioremediation. Remediation at OU 2C is
scheduled to begin in 2013 for anticipated
completion in 2018.
Contributed by James Fyfe, CA Department of
Toxic Substances Control (jjyfe&dtsc. ca.gov
or 510-540-3850) and Derek Robinson,
U.S. NayyBRAC Program Management Office
(derek.j.robinsonl&navy.mil or
619-532-0951)
ISCR-Enhanced Bioremediation Accelerates Groundwater Cleanup at Active Manufacturing Facility
In the winter of 2008, full-scale in situ
chemical reduction (ISCR) was implemented
as a removal action at the Siltronic
Corporation site in Portland, OR, to treat a
source area contaminated by releases of TCE.
The source area was considered to be the
portion of the site with concentrations of TCE
in groundwater greater than 11,000 |J,g/L,
suggesting the presence of TCE as DNAPL.
Implementation involved injecting a
controlled-release, integrated carbon and
micro-scale zero valent iron (ZVI) reagent
(EHC™) and selected microbial agents (KB-
1 ™) throughout approximately one-half acre
of the source area accessible to drilling
equipment. The approach was selected
following a comparative bench testing along
with other alternatives, and a successful field
pilot of combined EHC+KB-1 injections.
ISCR enhanced bioremediation was selected
due to its: (1) lower cost when compared to
alternate but resource-intensive technologies
such as electrical resistance heating (ERH);
(2) higher predictability than technologies
such as surfactant flushing or emulsified oil
sequestration; and (3) compatibility with
ongoing manufacturing operations and
facilities. The groundwater RAO set by the
Oregon Department of Environmental Quality
(ODEQ) for the source area was achieved in
less than six months after completion of the
injection, and TCE concentrations decreased
to below the MCL in several onsite locations.
Silicon wafers have been manufactured at the
80-acre Siltronic site since 1980. Solvent
releases during the early 1980s created a CVOC
source area and downgradient plume
approximately 1,100 feet long and greater than
500 feet wide; a portion of the plume extends
under and discharges into the Willamette
River. In 2006 site investigations, TCE was
identified in source area groundwater at
concentrations reaching 592,000 |J,g/L,
suggesting the presence of DNAPL.
Investigations also indicated a roughly half-
acre TCE source area extending
approximately 40-110 feet bgs and located
approximately 500 feet upgradient of the
riverbank. ODEQ established a groundwater
RAO for the removal action of reducing
dissolved-phase TCE concentrations to less
than 11,000 jig/L (i.e., 1% of the TCE
solubility limit) in source zone wells.
Siltronic evaluated cleanup options given the
limited space to operate and proposed a
controlled-release mixture of carbon and ZVI
that yields redox potentials favorable for the
biological reductive dechlorination of
contaminants. Although the presence of 1,2-
DCE, vinyl chloride (VC), ethene, and ethane
in downgradient groundwater indicated
natural biodegradation was occurring, Siltronic
proposed augmenting the source area's
microbial populations with TCE-targeting
microbes and stimulating existing populations
with an additional carbon source. The
[continued on page 6]
-------
Solid Waste and
Emergency Response
(5203P)
EPA 542-N-10-005
October 2010
Issue No. 50
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]
combined effect of the carbon, ZVI, and
augmentation was expected to increase
microbial activity and reduce dissolved phase
TCE concentrations through abiotic and
biotic degradation. In addition, enhanced in
situ bioremediation was expected to increase
concentration gradients near DNAPL, thus
facilitating more rapid chemical dissolution
and treatment once contaminants were in
the dissolved phase.
Starting in January 2009, a 30% carbon and
ZVI slurry was injected to 40-112 feet bgs
using a direct push (DP) drill rig. The
slurry was injected on the downward
push of the rig's tailored injection head
to target 4-foot vertical intervals among
injection point lines at 7-foot spacing.
The microbe culture was emplaced 7-14
days later in the same holes through use
of a peristaltic pump and a standard DP well
screen from the bottom-up. This injection
process continued for six months with
approximately 200 overlapping injection
points advanced within accessible portions
of the source area. Based on the volumes
used in an earlier pilot-scale test,
approximately 594,000 pounds of the carbon
and ZVI fine powder and 1,831 liters of
microbe culture were injected into the
subsurface. Groundwater was monitored at
23 wells located within and upgradient of
the treatment area, with 13 of the wells
indicating TCE above 11,000 jig/L in the
pre-injection sampling event. Through
December 2009, TCE concentrations in all
13 of these wells had decreased to levels
lower than the 11,000 |lg/L goal. By April
2010, TCE concentrations had been reduced
to less than 100 jig/L at 12 of the 13 wells,
and by August 2010 to less than the 5 |J,g/L
MCL in seven of the wells.
Groundwater monitoring will continue within
and downgradient of the source area to
demonstrate the observed TCE reductions
are sustainable and to monitor potential
rebound. Contaminant rebound is considered
a reasonable scenario as the source area is
underlain by unconsolidated fine-grained
sediments, which could represent
contaminant reservoirs and because
DNAPL was likely present in the source
area. Future monitoring will also be used to
assess the effectiveness of ISCR at treating
CVOCs (e.g., 1,2-DCE, and VC) produced in
the source area through TCE dechlorination.
Contributed by Dana Bayuk
(bayuk.dana(q),deq.state.or.us or
503-229-5543) and Henning Larsen
(larsen. henning(a)deq. state.or. us or
503-229-5527), ODEQ, and Rene Fuentes,
U.S. EPA Region 10 (Juentes. rene(q)epa.gov
or 206-553-2599)
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