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/A newsletter about soil, sediment, and ground-water characterization and remediation technologies
Issue 17
March 2005
Nanoscale ZVI Injection Rapidly Reduced Source CVOCs
in Redrock Ground Water
Pilot-scale testing at a RCRA-regulated
facility in Research Triangle Park (RTF), NC,
was conducted in 2002 to test the
effectiveness of in-situ injections of nanoscale
zero-valent iron (NZVI) in removing
chlorinated hydrocarbons from bedrock
ground water. Pre- and post-treatment sample
analysis indicated a 90% reduction of total
chlorinated volatile organic compound
(CVOC) concentrations within seven days
of the injection. During the following five
weeks, concentrations of trichloroethene
(TCE), as the primary contaminant of
concern, decreased more than 99%.
Ground-water contaminants consist mainly
of CVOCs that were released during industrial
activities conducted by the former property
owners. The pilot test was conducted in an
area downgradient from a past waste disposal
area with the highest TCE concentrations
(14,000 ug/L) and a high hydraulic
conductivity (approximately 10~3 cm/s).
Ground water is approximately 30 feet below
ground surface (bgs) within Triassic-aged
interbedded siltstone and sandstone. NZVI
technology rather than in-situ chemical
oxidation was selected due to the site's low
to moderate oxidation/reduction potential
(ORP) and evidence that NZVI would not
destroy the native microbial populations.
Earlier testing also demonstrated the
technology's capability to increase
concentration gradients and contaminant
mass transfer from dense nonaqueous phase
liquid (DNAPL) to the dissolved phase.
The injection well was installed into shallow
bedrock approximately 125 feet from the
disposal area, and two downgradient
observation wells were drilled in similar
subsurface environments approximately
22 feet and 43 feet from the disposal area. An
existing monitoring well located 63 feet
downgradient served as a third monitoring
point. NZVI was injected into ground water
as a slurry suspension prepared onsite using
potable water and bi-metallic (palladium-
doped) nanoscale particles (BNPs) ranging in
size from 1 to 100 nm. A total slurry volume
of 1,600 gallons, at a BNP concentration of
1.9 g/L, was injected into the subsurface over
two days. Electronic monitoring was
conducted continuously during the NZVI
injection to ensure a flow rate averaging
0.6 gpm.
Ground-water quality was monitored before
and after the injection to evaluate changes in
CVOC concentrations, ORP, dissolved
oxygen, pH, specific conductance, and
temperature. In addition to a 90% reduction
in total CVOCs in the injection well and the
nearest observation well within the first week,
TCE concentrations decreased from
14,000 ug/L to below the 2.8 ug/L cleanup
target (specified by State ground-water
standards) within six weeks (Figure 1).
Concentrations of 1,2-dichloroethane,
benzene, toluene, ethylbenzene, and xylenes
also declined significantly, by over 50% within
2-3 months.
Prior to treatment, the test area exhibited
primarily moderate oxidative conditions with
an ORP of +50mVto -100 mV The injection
created highly reducing methanogenic
[continued on page 2]
Contents
Nanoscale ZVI Injection
Rapidly Reduced Source
CVOCs in Bedrock
Ground Water pagel
Deep PRB Installed by
Vertical Hydrofracturing
Demonstrates Long-Term
Success page 2
Mass Flux Evaluation
Finds SEAR Continues
to Reduce Contaminant
Plume page 4
EPA Recommends a
New Approach for
Accelerating Landfill
Biodegradation page 5
CLU-IN Resources
CLU-IN's "Alternative Landfill
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cluin.org/products/altcovers/)
describe more than 80 site-
specific demonstrations and
full-scale applications of
alternative design covers at
disposal sites containing solid,
hazardous, and/or radioactive
wastes. With a focus on
evapotranspiration (ET) covers,
capillary barrier ET covers, and
bioengineering management,
the searchable profiles provide
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Recycled/Recyclable
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contains al least 50% recycled fiber
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[continued from page 1]
conditions with an ORP of -700 mV in
the injection well and -450V in the nearest
monitoring well. These lower ORPs
persisted for a minimum of 28 weeks in
the injection well and the two closest
observation wells. Monitoring for potential
mobilization of ORP-sensitive metals such
as manganese, barium, and arsenic
identified no concentration increases in the
test area.
Measurements of VOC concentrations
indicated a 20- to 40-foot radius of
influence around the injection well.
Samples collected at the beginning and end
of the purge cycle indicated that treatment
distribution was relatively uniform within
20 feet of the injection well but more
heterogeneous at greater distances.
Microbiological testing of ground-water
samples from the monitoring wells
indicated that BNP injection had no
detrimental effect on the total biomass and
community structure at the injection well,
suggesting that bioremediation may serve
as a final cleanup step.
Reactivity of the NZVI particles was
exhausted and contaminant rebound was
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observed after three months. Extension of
the effective particle lifetime could be
achieved by conducting repeat injections
under the lower ORP conditions already
established by an initial injection. Design
of a full-scale NZVI system for the RTF
site is underway, with anticipated startup
in 2006. Remediation of the TCE plume
will be further evaluated following these
source control efforts.
Contributed by Rob McDaniel, NC
Department of Environment and Natural
Resources (919-733-2178 or
robert. mcdaniel@ncmail. net), Lindsey
Walata, GlaxoSmithKline, Wei-xian
Zhang, Ph.D., Lehigh University (610-
758-5318 or wez3@lehigh.edu), and
Florin Gheorghiu, Colder Associates,
Inc. (856-616-8166 or
florin@golder. com)
Deep PRB Installed by Vertical Hydrofracturing Demonstrates long-Term Success
A 240-foot continuous permeable reactive
barrier (PRB) was constructed in 1999 at
the former Toastmaster Superfund site in
Centerville, IA, to remediate ground water
containing concentrations of TCE and
c/5-l,2-dichloroethene (DCE) reaching
810,000 ug/L and 1,000 ug/L, respectively.
Vertical hydrofracturing was used to inject
115 tons of zero-valent iron filings
extending from 25 to 75 feet bgs, a depth
often limiting the use of a trenched PRB.
Monitoring results collected over the past
five years show an average contaminant
reduction of up to 99.7% in ground water
exiting the barrier.
The site formerly was used for electrical
appliance manufacturing processes
involving the use of TCE-based solvents.
Field investigations in 1988 revealed TCE
concentrations of 14,000 ug/L in ground
water near the source area, which led to
the selection of a pump-and-treat remedy.
The ROD later was amended for use of an
in-situ PRB for ground-water remediation,
a fracture-enhanced dual phase soil vapor
extraction (SVE) system for source
removal in the vadose zone, and monitored
natural attenuation for the residual
downgradient plume.
Site ground water is approximately 30 feet
bgs with an estimated flow rate of 0.4 ft/day.
The aquifer consists of medium- to fine-
grained, loose-flowing, channel sands
between layers of over-consolidated, stiff
to very stiff till. Hydraulic pulse interference
tests (HPITs) showed the average hydraulic
conductivity of the aquifer to range from
0.4 to 115 ft/day. These conditions were
optimal for the medium sand-size PRB
iron filings, which have a hydraulic
conductivity of approximately 150 ft/day
and a porosity of about 55%. This is double
the porosity of the majority of the
surrounding soils, hence, the average
residence time of contaminated ground
water in the PRB is doubled.
The PRB was installed 10 feet
downgradient of a building directly above
the contaminant source area (Figure 2).
Installation of the PRB involved drilling
sixteen 6-inch boreholes at 15-foot
intervals and depths ranging from 45 to
75 ft bgs. The PRB was constructed from
the "bottom up" by placing packers to
isolate the target frac casing, which was
[continued on page 3]
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[continued from page 2]
used to propagate the fracture and inject
iron filings. This formed panels
approximately 20 feet high by 15 feet
wide. Due to relatively slow ground-water
movement and the higher porosity of the
iron filings, a PRB thickness of only
3 inches was considered necessary.
The iron filings were mixed with a
hydroxypropylguar biodegradable gel
containing a cross-linking agent and
enzyme. The mixture was injected at low
pressure (5 psi higher than the
surrounding horizontal stress at depth)
directly into the aquifer through the
downhole frac casing systems. Each
gallon of gel contained approximately
10 pounds of iron filings. The cross-
linking agent immediately caused the gel
to become highly viscous, with the
strength to carry iron filings to their
designed destinations. Within hours of
injection, the enzyme broke the gel into
water and non-toxic sugars to leave a
continuous coalesced wall of permeable
iron filings between neighboring frac
casings.
Use of a "trenchless" PRB construction
technique required a suite of QA/QC tools:
> bench-scale column tests to determine
primary and secondary contaminants,
daughter products, and respective half-
lives;
> pre-construction HPITs to determine
hydraulic conductivity and to establish
benchmarks for post-construction
comparisons;
> probabalistic design involving integra-
tion of column test data, HPIT results,
a multi-species VOC model for degra-
dation within the PRB, and a fate and
transport model for downgradient
natural attenuation;
> active resistivity imaging to monitor
PRB construction; and
> post-construction inclined profile sam-
pling to verify PRB thickness.
The PRB influent and effluent were analyzed
quarterly over the first four years and semi-
annually thereafter. Due to the low ground-
water flow velocities, downgradient
monitoring wells were not expected to
experience significant reductions in VOC
concentrations for three years. However, the
analytical results indicate that TCE and
cis-l,2-DCE concentrations decreased to near
non-detect levels within 21A years. Results
indicate that TCE concentrations have
decreased from810,000 ug/L to an average
of 27 ug/L and cis-1,2-DCE concentrations
have decreased from 1,000 ug/L to an
average of 160 ug/L.
No signs of iron reactivity loss or PRB
fouling have been observed. Recent
infiltration of surface water seeping
from a pile of road salt into one of the
downgradient monitoring wells, as
evidenced by unusually high sodium
and nitrate levels, may have caused
minor increases in VOC concentrations.
Following replacement of the monitoring
well, VOC concentrations appear to be
decreasing.
Use of the PRB is anticipated to achieve
ground-water cleanup in 2009,10 years
after placement. Design and
construction of the PRB was estimated
to cost $938,000. The vertical hydraulic
fracturing technique has since been used
to install PRBs extending to greater
depths ranging from 95 to 115 feet at
four other sites, including Tinker Air
Force Base, Sierra Army Depot, and two
commercial sites in California.
Contributed by John Cook, EPA
Region 7 (913-551-7716 or
cook.john@epa.gov) and Grant
Hocking and Jim Ortman, GeoSierra
(678-514-3300 or
ghocking@geosierra. com and
jortman@geo sierra, com)
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Mass Flux Evaluation Finds SEAR Continues to Reduce Contaminant Plume
Measurements of contaminant mass flux
at HillAirForce Base Operable Unit2 (OU2)
show that aggressive source zone
remediation using surfactant-enhanced
aquiferremediation (SEAR) technology has
resulted in a 67-90% decrease in mass flux
from the contaminant source zone. Under
the Strategic Environmental Research and
Development Program (SERDP),
researchers from the U.S. EPA Robert S.
Kerr Environmental Research Center and
University of Florida conducted two rounds
of post-treatment measurements following
the 2002 SEAR treatment. An updated site
conceptual model and contaminant fate and
transport modeling suggest that flux from
the source zone now is less than the
assimilative capacity of the aquifer. Over
time, decreases in the area! extent of the
dissolved plume and the lifetime of the
contaminant source are expected to occur.
SEAR at OU2 was designed to generate
and propagate in-situ foam to divert
surfactant from the upper, uncontaminated
portion of the aquifer into the lower
DNAPL-contaminated zone. To generate
the foam, air was injected with surfactant
in a two-hour alternating mode. The
21-day SEAR process consisted of three
days of pre-surfactant brine flooding using
a 1.0 wt% sodium chloride (NaCl) solution;
seven days of surfactant flooding with
4.0 wt% sodium dihexyl sulfosuccinate
(MA-80I) and 1.0 wt% NaCl; and 11 days
of post-surfactant brine/water flooding.
Surfactant/foam flooding resulted in recovery
of approximately 220 gallons of DNAPL.
Mass flux was measured immediately
downgradient of an area of DNAPL
contamination outside a bentonite-slurry
containment wall that surrounds most of the
OU2 source zone. Pre-treatment ground-
water contaminant concentrations in the flux
monitoring wells ranged from 9 to
150 mg/L. Following SEAR application, only
one confirmation soil sample exhibited residual
DNAPL in the source zone, with a saturation
of 2%. No mobile or pooled DNAPL has
been observed since SEAR treatment, and
contaminant concentrations in ground-water
samples collected from and immediately
downgradient of the treatment zone have
decreased by 1-2 orders of magnitude.
Monitoring of cumulative flux rather than
contaminant concentrations is allowing for
direct evaluation of the contaminant mass
loading rate and improved decision-making
regarding remedial efforts at OU2. Two
distinct approaches-a static "flux meter"
technique and a dynamic integral pumping
test-were used to assess contaminant flux
immediately priorto SEAR implementation
and in two post-treatment measurement
rounds. Both techniques use forms of
point measurements and derive mass flux
based on spatial integration of the product
of local flux-averaged contaminant
concentration and water flux.
TCE mass flux from the source zone prior
to treatment was estimated to be
107 g/day based on data collected using
the flux meter technique, with flux values
integrated overthe control plane to produce
a mass loading rate. Approximately 10
months after source zone treatment, a flux
of 10 g/day was estimated. Similar results
were obtained with the integral pumping
technique. Initial mass flux estimates ranged
from 52 to 115 g/day, compared to 17 to
29 g/day after remediation. Data reduction
for the most recent (2004) flux
measurements is not yet complete but
preliminary results suggest that the
contaminant flux is similar to thatmeasured
the previous year, with no evidence of
contaminant rebound. Measurements
reflect significant reductions in mass flux
[continued on page 5]
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Figure 3.Compiled data collected through both the flux meter and
integral pumping techniques show similarly significant reductions in
mass flux at OU2 as a result of SEAR application.
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[continued from page 4]
at each of the eight monitoring wells used
for data collection (Figure 3).
Prior to SEAR implementation,
concentrations of c/s-l,2-DCE were below
quantification limits. In post-SEAR flux
measurements, however, c/s-l,2-DCE
contributed 30-35% of the total mass flux.
These data suggest that applicationof SEAR
remedial fluids stimulated transformation
of residual TCE to c/'s-DCE due to
anaerobic reductive dechlorination.
Results also suggest that the MA-80I
surfactant has provided the carbon donor
necessary to stimulate continued reductive
dechlorination. An apparent degradation
product of the MA-80I, methyl isobutyl
ketone (MIBK), was detected last year at
relatively high concentrations (up to
409 mg/L) in the source zone. Continued
monitoring of MIBK concentration indicates
that it is rapidly degrading, with recent
measurements in the source zone showing
maximum concentrations of approximately
60 mg/L. An additional round of
measurements using both of the mass flux
assessment techniques is anticipated.
Contributed by Kyle Gorder, Hill Air
Force Base (801-775-2559 or
kyle.gorder@hill. af.mil), Michael
Brooks, U.S. EPA/Robert S. Ken-
Environmental Research Center (580-
436-8982 or brooks.michael@epa.gov),
and Chuck Holbert, URS Corporation
(801-904-4056 or
chuck_holbert@urscorp. com)
EPA Recommends a New Approach for Accelerating Landfill Biodegradation
EPA began working with Waste
Management Inc. under a cooperative
research and development agreement in
2000 to examine various methods for
improving landfill efficiencies. Related
studies underway at the Outer Loop
Recycling and Disposal Facility in
Louisville, KY, involve two types of
bioreactor-based technology. The Agency
anticipates that bioreactors will enhance
waste containment in unlined landfills and
could accelerate microbial degradation of
hazardous and solid waste contaminants
by 50%. Accordingly, in March 2004 EPA
began allowing states to issue research,
development, and demonstration permits
to large-scale landfill operations for
innovative methods such as bioreactors.
By recirculating landfill leachate through
existing waste material and trenches
constructed outside the waste perimeter,
bioreactors are designed to increase landfill
moisture. This approach contrasts
significantly with previously recommended
and commonly used "dry tomb" methods
relying on reduction of landfill moisture
content.
One of the two bioreactors under evaluation
involves only anaerobic mechanisms, while
the second operates under both anaerobic
and aerobic conditions. Although anaerobic
conditions naturally occur in most landfills,
optimum degradation of solid waste or
CERCL A contaminants requires the addition
of moisture. This type of bioreactor
conceptually lends itself to retrofitting of
existing landfills (Figure 4). In contrast, an
aerobic-anaerobic "hybrid" bioreactor
landfill is designed to cause rapid
biodegradation of easily degradable waste
in the aerobic stage, thus reducing the
production of organic acids in the anaerobic
stage and generating earlier onset of
methanogenesis.
Both types of bioreactor landfills offer
advantages over dry tomb landfills:
> The accelerated degradation of waste
mass can increase settlement, provid-
ing additional years of landfilling
capacity.
> The increased rate of methane genera-
tion caused by biological activity allows
for more effective landfill gas control
and lower costs for onsite electrical
generation.
> Recirculation of leachate lowers the
costs for leachate management.
> Controlled but accelerated degradation
of the waste reduces post-closure care
and future exposure risk.
The Agency currently is seeking sites at
which to demonstrate anaerobic retrofitting
of an existing landfill or construction of a
hybrid bioreactor facility. Under EPA's
Project XL, landfill pilot projects employing
bioreactors are underway in Buncombe
County, VA, King George County, VA, and
Yolo County, CA [see March 2003 issue
of Technology News and Trends for more
information]. In addition to bioreactor
[continued on page 6]
Contact Us
Technology News and Trends
is on the NET!
View, download, subscribe, and
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Technology News and Trends
welcomes readers' comments
and contributions. Address
correspondence to:
Ann Eleanor
Office of Superfund Remediation and
Technology Innovation
(5102G)
U.S. Environmental Protection Agency
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1200PennsylvaniaAve,NW
Washington, DC 20460
Phone: 703-603-7199
Fax:703-603-9135
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Solid Waste and
Emergency Response
(5102G)
EPA 542-N-05-002
March 2005
Issue No. 17
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]
technology, the Agency is evaluating the
use of compost as a landfill cover at the
Outer Loop facility.
Thabet Tolaymat, Ph.D, National Risk
Management Research Laboratory
(513-487-2860 or
tolaymat. thabet@epa.gov)
Leachate
Nitrification
Treatment
Gas
Colled
to Generate
Energy
I Leachate / Liquids Addition
Gas Collection
Figure 4. Conceptual designs for
technology at existing landfills involve
methods for the addition of liquids as w
as the recirculation ofleachate.
In the January 2005 Technology News
and Trends article, "Ultraviolet and
Hydrogen Peroxide Treatment Removes
1,4-Dioxane from Multiple Aquifers,"
measurement units for the State of
Michigan drinking water standards on
1,4-dioxane and bromate were printed
erroneously. The correct standards are
85 ug/L for 1,4-dioxane and 10 ug/L for
bromate. It also should be noted that
maximum 1,4-dioxane concentrations in
the treated plume, as described, are now
less than 10,000 ug/L.
EPA is publishing this newsletter as a means of disseminating useful information regarding innovative and alternative treatment techniques and
technologies. The Agency does not endorse specific technology vendors.
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