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a
/A newsletter about soil, sediment, and ground-water characterization and remediation technologies
Issue 21
November 2005
Zero-Valent Iron PRB Application Expands to Arsenic Removal
The U.S. EPA Office of Research and
Development's National Risk Management
Research Laboratory (NRMRL) and Region 8
have begun evaluating the performance of a
pilot-scale permeable reactive barrier (PRB) to
treat arsenic-contaminated ground water at the
East Helena Superfund site near Helena, MT.
High ground-water flow rates coupled with high
arsenic concentrations required the barrier
design to involve wider dimensions in the path
of ground-water flow than most PRBs currently
in operation. Barrier construction also was
challenged by the presence of some boulders
in the subsurface, requiring use of large
excavation equipment. Preliminary results
indicate that arsenic concentrations as high as
20 mg/L in ground water entering the PRB are
reduced to concentrations below 10 (Og/L within
the barrier. Concentration reductions
downgradient of the PRB are anticipated after
construction impacts on the treatment system
subside and the ambient ground-water flow
system is re-established.
Primarily due to smelting activities over the past
century, arsenic in ground water at the East
Helena site exists in the redox states of arsenite
(As3+) and arsenate (As5+). The target arsenic
plume is approximately 450 feet wide and
extends 2,100 feet downgradient from the
primary source of subsurface contamination.
The site is underlain by alluvial deposits of
cobble mixed with varying proportions of fine-
to coarse-grained sand to a depth of 48 feet
below ground surface (bgs). The water table
is 30 feet bgs. Only ground water within the
the alluvial deposits and not the underlying
volcanic tuff was found to be contaminated.
Ground-water flow varies from about 0.5 to 3.0
ft/day according to the hydraulic properties of
the aquifer materials and the prevailing hydraulic
gradient.
NRMRL conducted batch and column studies
on simulated ground water in 2003 to assess
the effectiveness of zero-valent iron (ZVI) for
arsenic remediation, determine arsenic removal
mechanisms, and evaluate potential use of a
ZVI barrier in long-term remediation of arsenic-
contaminated ground water. Prior to these
studies, ZVI was used more commonly to treat
metals andhalogenated organic solvents. Study
results showed that arsenic removal is a two-
step reaction with an initially rapid removal of
arsenite (10-fold within 50 hours) followed by a
slow removal process that involves formation
of smaller amounts of As5+. Additionally,
analysis of surface precipitates indicated that
As3+ uptake by carbonate green rust and other
iron-corrosion products may play a major role
in the treatment process. The overall removal
capacity of ZVI was estimated at 7.5 mg arsenic/
giron.
Installation of the PRB was completed over five
days earlier this spring. Heavy excavation
equipment was used to construct a 6-foot-wide
and 46-foot-deep trench running 30 feet in
length perpendicular to the plume (Figure 1).
During excavation, biopolymer slurry was used
to stabilize the walls of the trench.
Approximately 175 tons of ZVI filings were
added to the trench through the biopolymer
slurry using tremie equipment to achieve an
(upper) depth of 25 feet bgs, 5 feet higher than
the average ground-water level. The remainder
of the trench was filled with coarse bedding
sand.
A network of fully screened, short-screen, and
multi-level wells, including 25 within the trench
itself, will be used to monitor performance of
the PRB. hi addition, an in-situ flow sensor
was installed to collect information on ground-
[continued on page 2]
Contents
Zero-Valent Iron PRB
Application Expands to
Arsenic Removal page 1
EPA Evaluates
Approaches for
Assessment of Vapor
Intrusion page 2
Tree-Core Analysis
Brings Savings to Site
Assessments page 3
Cleanup Closure
Reached through
In-Situ Bioremediaton of
Ground Water at
Drycleaner Site page 5
Recent Workshop
Increases Understanding
of Environmental Impacts
from Nanotechnologies page 6
CLU-IN Resources
The State Coalition for
Remediation of Drycleaners has
compiled detailed technical
profiles on remediation projects
underway or completed at more
than 100 sites throughout the
U.S. The profiles are available
online, along with related
information on federal policies,
state drycleaner programs, and
technical reports, through
CLU-IN's "Initiatives and Partner-
ships" at http://www.cluin.org or
directly from the coalition at
http://drvcleancoalition.org.
Recy cled/Recy cl able
Printed with Soy/Carrola Ink on paper that
contains at least 50% recycled fiber
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water flow direction and velocity within the
PRB. The first round of monitoring occurred
in June 2005, 30 days after treatment began.
Results showed arsenic concentrations
below 10 |J,g/L in ground water within the
barrier. Analysis of ground water within the
PRB showed expected trends in pH,
oxidation-reduction potential, and ferrous
iron concentrations typical for ZVI systems.
Data analysis is underway for the second
round of monitoring, which was conducted
last month. Evaluation of the pilot-scale PRB
will continue for two years to determine its
long-term success in reducing arsenic
concentrations to levels near the maximum
contaminant level (MCL) of 10 |Ig/L. If
successful, the PRB could be extended an
additional 450 feet in length to capture 100%
of the arsenic plume. The pilot project shows
that the full-scale system likely should
employ variable PRB thicknesses to
effectively deal with variable arsenic
concentrations across the plume width.
Region 8 estimates a construction cost of
$325,000 for the existing pilot-scale system.
Contributed by Richard Wilkin, Ph.D.
NRA'JRL (wilkin. rick®epa.gov or
580-436-8874), Linda Jacobson, EPA
Region 8 (jacobson. linda(a),epa.gov or
303-312-6503), and Elaine Coombe,
The Shaw Group, Inc.
(elaine. coombe&.shawgrp. com or
303-741-7550)
EPA Evaluates Approaches for Assessment of Vapor Intrusion
The U.S. EPA Office of Solid Waste and
Emergency Response developed guidelines
in 2002 for screening the migration of volatile
organic compounds (VOCs) from the
subsurface into buildings, otherwise known
as "vapor intrusion" (VI). The guidance
applies to sites where halogenated organic
compounds constitute the primary risk to
human health. To supplement the guidance
recommendations, EPA currently is evaluating
empirical methods that provide increased
reliability in VI data quality at a reasonable
cost and which address bias caused by non-
environmental anthropogenic conditions.
To assess VI empirically, EPA's Office of
Research and Development (ORD)
recommends concurrent use of sub-slab
sampling and indoor air sampling. This
combined approach helps to differentiate
VOCs potentially originating from
environmental sources from those originating
from non-environmental sources such as
gasoline, paint, or solvents stored inside
buildings. Sub-slab air sampling allows for
sample collection directly beneath living
spaces, thereby eliminating uncertainty posed
by the analysis of data collected from distant
monitoring locations. Sub-slab sampling also
helps to determine whether, and to what extent,
petroleum hydrocarbon biodegradation may
be occurring onsite.
hi the absence of standardized methods for
collecting or interpreting sub-slab air samples,
ORD and Region 1 used the sub-slab approach
to assess VI at 15 homes and one commercial
business near the Raymark Industries
Superfund site in Stratford, CT. Elevated VOC
concentrations in basement air were determined
to be caused by VI if: (1) a VOC was detected
in ground-water or soil-gas measurements
taken in the building's vicinity; and (2) the
results of statistical testing on empirical sub-
slab and indoor-air data indicated VI was the
cause of VOC presence. Basement and sub-
slab air samples were collected at each of the
study locations through use of evacuated
canisters in accordance with EPA Method
TO-15, Determination of VOCs in Air
Collected in Specially-Prepared Canisters
and Analyzed by Gas Chromatography/
Mass Spectrometry. Additional sub-slab air
samples were collected using one-liter Tedlar
bags.
Statistical testing required the use of an
"indicator" VOC known to be associated only
with subsurface contamination. In this case,
1,1-dichloroethene (DCE) and 1,1-
dichloroethane (DCA) were considered
indicator VOCs due to the presence of their
degradation daughter product, 1,1,1-
trichloroethane(TCA).a5-l,2-DCE also was
considered an indicator due to its presence
as a daughter product of trichloroethene (TCE)
and its unlikely association with commercial
products. Statistical testing involved
[continued on page 3]
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[continued from page 2]
comparing each basement/sub-slab
concentration ratio of an indicator VOC with
that of a VOC of concern. Statistical testing
found that detection of 1,1 -DCE, 1,1 -DC A,
and cis- 1 ,2-DCE in indoor air consistently was
caused by VI, but the presence of TCA
occasionally generated false positives and
negatives.
The use of radon as an indicator compound
was evaluated by statistically comparing
basement or sub-slab concentration ratios for
radon against indicator VOCs at six of the
Raymark locations. Comparisons exhibited
statistical similarities at half of the locations
but varied at a level of significance less than
0. 1 at the remaining locations. Based on these
findings, indicator VOCs were relied upon
when basement/sub-slab concentration ratios
for both types of indicators were available,
and radon ratios were used only in the
absence of indicator VOCs. Indoor air radon
sampling was conducted in accordance with
EPA's Home Buyer 's and Seller s Guide to
A significant objective of die Raymark study
was to document the installation and
sampling of 3-5 vapor probes in each of the
16 basements. Generally, one sub-slab vapor
probe was positioned in the center of each
building while two or more probes were placed
within 1 -2 meters of the basement walls (Figure
2). Among odier benefits, this arrangement
helped to ensure detection of vacuum
throughout the entire sub-slab for
implementation of corrective measures (sub-
slab depressurization). hi addition, spatial
variability of sub-slab concentrations of VOCs
and radon was noted across each building's
footprint.
In assessing efficacy of die sub-slab protocol,
ORD considered factors such as rate-limited
mass transport during air extraction, die radius
of perturbation during probe installation, and
the impact of indoor air infiltration into a sample
container during air extraction. Using diree
mediods to evaluate die impact of indoor air
infiltration, for example, die extraction volume
was found to have little effect on sampling
results.
Based on die Raymark study results and other
recent findings, ORD is developing specific
recommendations for sub-slab sample
collection, data interpretation, and probe
installation, including:
> Design of a multi-use sub-slab vapor probe
dial "floats" in a slab, which allows for air
samples to be collected from sub-slab ma-
terial diat is in direct contact with a slab or
from an air pocket directly beneadi a slab;
> Use of a rotary hammer drill to create con-
crete slab holes for probe installation; and
Figure 2. Only a small hole in the concrete
slab was needed to install a multi-use vapor
probe in each basement of the Raymark study
> Sealing of a probe's annular space through
use of quick-drying, lime-based cement
that allows for installation of three probes
within two hours.
A detailed summary of the study will be
available from ORD and Region 1 in early 2006.
EPA's earlier guidance, OSWER Draft
Guidance for Evaluating the Vapor Intrusion
to Indoor Air Patlnvay from Groundwater
and Soils (Subsurface Vapor Intrusion
Guidance) [EPA530-D-02-004] is available on-
line at http://www.epa.gov/epaoswer/
hazwaste/ca/eis/vapor.htm.
Contributed by Ray Cody, EPA Region 1
(cody. ray(a)epa.gov or 617-918-1366) and
Dominic Digiu Ho, Ph.D., ORDNRMRL
(digiulio.dominic(a)epa.gov or
580-436-8605)
Tree-Core Analysis Brings Savings to Site Assessments
The U.S. Geological Survey (USGS)
collaborated with University of Missouri-
Rolla researchers during the past several
years in using tree-core samples to quickly
assess VOC presence in shallow soil and
ground water (20-25 bgs) at the Riverfront
Superfund site in New Haven, MO. Unlike
previous applications of tree-core sampling,
little subsurface data previously existed at
this site- and tree-core sampling was the
primary tool for initial site assessment.
Conventional soil and ground-water sample
analysis later confirmed the results of tree-
core analysis, which suggested the presence
of subsurface VOC contamination in a 600-by-
200-foot area at operable unit 1 (OU1) known
as the "Front Street site" in downtown New
Haven. The site is one of five potential
tetrachloroethene (PCE) source areas in New
Haven under investigation by the U. S. EPA.
The 1 -acre Front Street site is located in alluvial
deposits approximately 400 feet south of the
Missouri River, a regional ground-water
discharge zone. In the late 1980s and early
1990s, steadily increasing concentrations of
PCE were measured in water from two 800-
foot-deep municipal drinking water wells
serving the New Haven community. One of
the wells, Well 2, was taken out of service in
1993 after PCE concentrations reached 140 mg/
L, substantially above the 5 mg/L MCL. Water
from a new well installed die following year
about 1.5 miles farther south and upgradient
from the contaminated wells showed no signs
of PCE contamination. During an expanded
site investigation in 1995, the Front Street
[continued on page 4]
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[continued from page 3]
site was presumed to be the source of PCE
contamination because of its location only
600 feet north of Well 2. Bedrock monitoring
wells installed throughout the city as part of
a remedial investigation in 2000, however,
showed relatively low (less than 20 mg/L)
PCE concentrations between the Front Street
site and the contaminated public supply
wells.
During the USGS site assessment, core
samples generally were collected from trees
with diameters of three inches or more. If
multiple species were present, preference was
given to rapid-growing species with deep root
systems such as mulberry, poplar, and
cottonwood. Samples were collected at a
height of approximately three feet above
ground surface using a 0.169- by 6-inch-long
increment borer. The samples were placed
immediately into standard 40-mL VOC vials
and allowed to equilibrate overnight at room
temperature. Headspace in the vials was
analyzed the following day for VOC content
using a portable gas chromatograph. Over a
course of five years, core samples were
collected from more than 70 trees and from
apples of trees located on or adjacent to the
Front Street site.
Onsite tree-core samples contained PCE and
TCE concentrations reaching 3,850 mg-h/kg
(micrograms inheadspace per kilogram of wet
core) and 249 mg-h/kg, respectively. In
addition, offsite tree-core analyses detected
subsurface PCE contamination on
downgradient residential properties between
the site and the river. Conventional sample
analysis later confirmed the presence of PCE
at the site with concentrations as large as
6,200,000 mg/kg in soil and 11,000 mg/L in
ground water. Tree-core analysis indicated no
detectable PCE or TCE contamination at a
nearby former dry cleaning facility under
investigation as a potential contaminant source,
and these findings were confirmed by later soil
sampling.
PCE generally was detected in cores from trees
growing in soil containing PCE concentrations
of 60 to 5,700 mg/kg or overlying ground water
containing PCE concentrations ranging from 5
to 11,000 mg/L. The lateral extent of PCE
contamination suggested by tree-core analysis
closely agreed with the results obtained by
conventional soil sampling techniques. A
correlation coefficient (r2) of 0.88 was found
between PCE concentration in trees and PCE in
subsurface soil at depths of 4 feet (Figure 3)
and similar correlations were found for soil up
to 12 feet deep. The correlation between PCE
concentrations in trees and ground water was
much lower (0.17). Researchers attribute the low
correlation to a lack of direct contact between
tree roots and ground water or to non-
equilibrium between tree roots and PCE
concentrations in soil and soil vapor. These
results show that the presence of contaminants
in a tree core likely indicates onsite
contamination but that the absence of tree-core
contaminants does not preclude the need for
further evaluation.
Several variables were found to affect the
distribution of VOCs in trees. The loss of PCE
from tree trunks by diffusion usually resulted
in an exponential decrease in contaminant
concentrations with increasing tree height, hi
addition, diffusional loss in small trees (0.5 -inch-
10,000
1,000-
S> 100-
• Soil at 4 feet deep, r2=0.88
OGround water, r2=0.17
1 10 100 1,000 10,000 100,000 1,000,000
PCE Concentration in soil (MQ/kg) or ground water (u.g/L)
diameter cuttings planted in contaminated
soil) occurred at a rate 10-fold higher than in
trees with a diameter of 6.5 inches. Up to five-
fold variations in PCE concentrations around
individual tree trunks were attributed to spatial
differences in contaminant concentrations in
the soil, the natural twisting of tree trunks,
and possible diffusion of PCE vapors from
the unsaturated zone into tree roots.
Comparison of PCE concentrations in core
and sap samples confirmed laboratory
sorption studies indicating that more than
95% of the PCE and TCE mass resided in
wood rather than the transpiration stream.
Ongoing investigations indicated that
samples from bedrock monitoring wells
located between the contaminated public
supply wells and an area farther south (at
what would become another operable unit,
OU4) contained unexpectedly high
concentrations of PCE reaching 350mg/L at
a depth of 465 feet bgs. Reconnaissance
sampling of trees across OU4 during 2004-
2005 identified a new and substantial PCE
source area upgradient from the contaminated
public supply wells.
Results from OU1 indicate that tree-core
sampling can be used to detect subsurface
PCE contamination in soil at levels of several
hundred mg/kg or less. Experimental data from
hydroponic field tests, in which trees were
grown in nutrient solution rather than soil,
suggest that this approach may be able to
identify PCE in ground water at
concentrations as low as 8 mg/L. Additional
experiments on trees growing adjacent to
contaminated creeks at the Riverfront
Superfund site found that the method could
identify PCE in ground water at similarly low
concentrations of 30 mg/L, as long as the tree
roots are in direct contact with the
[continued on page 5]
Figure 3. Correlation analysis of data
collected from individual trees at the
Front Street site indicates that tree cores
accurately predicted PCE concentrations
in the soil but only loosely predicted
ground-water concentrations.
4
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[continued from page 4]
contaminated ground water and the
unsaturated zone is virtually non-existent.
Otherwise, as the depth to ground water
increases, this sensitivity will decrease with
diffusional loss in the unstaturated zone.
Overall, data collected from the site
demonstrate that tree-core sampling is an
effective, quick, and inexpensive method for
determining relative high and low
concentrations of chlorinated solvents and
for optimizing both soil and ground-water
sample locations. The project also showed
that tree-core sampling serves as a valuable
tool for soil screening in residential settings,
which typically involve sensitivities regarding
private property access and difficult sampling
areas.
The initial tree-coring reconnaissance at the
Front Street site, which employed 26 trees,
required the resources of two field staff for one
day at a cost of less than $2,500. In contrast,
the estimated cost for the collection and
analysis of soil samples from an equivalent
number of soil borings at the site is $25,000 and
requires two field staff for four days and a direct-
push drill rig for several days.
EPARegion 7's use of this novel technique for
site assessment, in addition to innovative
strategies for remediation and property re-use,
merited the Agency's 2003 "ROD of the Year
Award." The complete scientific investigations
report [USGS SIR 2004-5049] on this
application is available online from the USGS
at http://pubs.er.usgs.gov/pubs/. Detailed
methods for using tree-core analysis in site
assessment are under development by the
U.S. Department of Agriculture, which
pioneered this approach.. The methods will
be incorporated into an upcoming U.S. EPA
user's guide.
Contributed by John Schumacher, USGS
(jschu&u sgs.gov or 573-308-3667), Joel
Burken, Ph.D. University ofMissouri-Rolla
(burken(a)umr.edu or 573-341-6547), and
Robert Blake, Black and Veatch Special
Projects Corp (blakere(q)bv. com or
913-458-6681)
Cleanup Closure Reached through In-Situ Bioremediaton
of Ground Water at Drycleaner Site
The Florida Department of Environmental
Protection (FDEP) is working with the State
Coalition for Remediation of Dry Cleaners and
private industry to exchange drycleaner-
specific information that will help expedite
assessment and cleanup at drycleaner
facilities. As part of the Florida Dry cleaning
Cleanup Program, the FDEP recently oversaw
assessment and remediation at King of
Cleaners, an operating facility in Orlando, FL.
The site's ground water contained low
concentrations of PCE, TCE, and cis-l ,2-DCE,
as is common at many drycleaning sites.
Monitored natural attenuation was selected
as a remediation strategy in 1998. After five
years of monitoring, however, one well
continued to exhibit concentrations exceeding
MCLs. In-situ bioremediation consequently
was used to increase reductive dechlorination
of chlorinated organics through the
introduction of potassium lactate as a carbon
donor in the aquifer.
During initial site assessments, PCE and TCE
were detected in monitoring wells at
concentrations of 220 |lg/L and 43 |Ig/L,
respectively. C7s-l,2-DCE also was detected
but at concentrations below the 70 |Jg/L MCL.
In addition, direct-push sampling indicated a
low concentration (7.8 |lg/L) of vinyl chloride
in ground water. PCE was detected in soil at
concentrations averaging 170 |lg/kg, but
testing indicated that concentrations did not
exceed the state's leachability criteria. The water
table is located 6-10 feet bgs within a 46-ft layer
of silty, fine- to medium-grained sand. The
ground-water flow rate ranges from
approximately 1 to 24 ft/day within a gradient
of 0.01 ft/ft.
Bioremediation of the 150-by 100-ft ground-
water plume began in October 2003. Two 2-
inch-diameter wells screened at depths of 33-
43 feet were installed for the injection process,
which was monitored using three existing wells.
Approximately 2,000 gallons of native water
were extracted from a monitoring well to help
establish a gradient between the injection wells
and the downgradient monitoring well, and
mixed with 10 gallons of 60% potassium lactate
to enhance reductive dechlorination. The
solution was inj ected into each of the inj ection
wells at a rate of 1.5 gpm. The event concluded
with injection of 100-200 gallons of potable water
to remove residual lactate and prevent
biofouling.
Two months of performance monitoring
showed no major changes in VOC
concentrations, which remained above target
[continued on page 6]
An estimated 20,000 drycleaners
are contaminated across the
country. Based on an average
cleanup cost of $250,000 per site,
$5 billion is needed to address
these sites.
Source: Drycleaner Site Assessment &
Remediation: A Technology Snapshot
(March 2004)
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Solid Waste and
Emergency Response
(5102G)
EPA 542-N-05-006
November 2005
Issue No. 21
United States
Environmental Protection Agency
National Service Center for Environmental Publications
P.O. Box 42419
Cincinnati, OH 45242
Official Business
Penalty for Private Use $300
Presorted Standard
Postage and Fees Paid
EPA
Permit No. G-35
[continued from page 5]
levels. Therefore, a second injection was
conducted in February 2004, again employing
2,000 gallons of water and a 1.5-gpm injection
rate but a larger volume of 60% potassium
lactate solution (50 gallons).
Approximately one month later, a significant
decrease in contaminant concentrations was
achieved. PCE and TCE concentrations had
decreased to non-detect and 4 (Ig/L.
respectively. As a degradation product, cis-
1,2-DCE concentrations had increased 80%
but were not above the 70 (Og/L MCL. Data
collected during the earlier natural attenuation
monitoring period had indicated that conversion
of cw-l,2-DCE to vinyl chloride was unlikely,
and in fact, no vinyl chloride was detected in
any of the monitoring wells during post-
remediation monitoring. Gradual but continued
decreases in VOC concentrations resulted in a
February 2005 determination that no further
remedial action was required.
The FDEP estimates a total cleanup cost of
$ 168,400 for the King of Cleaners site, including
$81,000 for assessment, $3,400 for design of the
limited remedial action plan, $34,400 for the
injection well installations and two injection
events, $4,200 for site restoration, and $45,400
for six years of ground-water monitoring.
Additional technical profiles describing
cleanup at other dry cleaning sites are available
from the coalition at www.dryclean
coalition.org.
Contributed by Judie Kean, FDEP
(judie.l(ean(a)dep.state./!.us or
850-245-8973) and Mike Lodato,
GeoSyntec Consultants
(mlodato&geosyntec.com or
813-558-0190)
\ Recent Workshop Increases Understanding of Environmental Impacts from Nanotechnologies
The U.S. EPAs Office of Solid Waste and Emergency Response and Office of Research and Development partnered with the Federal Remediation
Technologies Roundtable (FRTR) and the U. S. Department of Commerce in sponsoring a Workshop on Nanotechnologyfor Site Remediation
on October 20-21,2005, in Washington, D.C. Presentation and breakout session topics addressed:
> Findings of recent studies using nanomaterials for contaminant destruction or sequestration,
> Results of field tests using nanoscale ZVI for reduction of VOC contamination in ground water,
> Use of dendrimers, functionalized nano-porous ceramic particles, and zeolites for contaminant reduction, and
> Research needs, research barriers, and incentives involved in using new nanotechnologies while minimizing environmental pollutants.
The workshop presentations and summary proceedings will be available online from the FRTR at http ://www.frtr. gov/hotnew.htm.
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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