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/A newsletter about soil, sediment, and ground-water characterization and remediation technologies
Issue 27
This issue of Technology News and Trends highlights various techniques used to design,
construct, and operate permeable reactive barriers containing organic reactive media. Imple-
mentation of these "biobarriers" (PRBs) involves amending the aquifer with relatively inex-
pensive and readily available carbon-donor materials capable of enhancing biological degra-
dation of contaminants. Several federal agencies are evaluating this technology particularly
for treatment of ground water contaminated with perchlorate or volatile organic compounds.
November 2006
Emulsified-Oil Biobarrier Provides Long-Term Treatment
of Perchlorate/VOC Plume
The U.S. Department of Defense (DOD)
has nearly completed an Environmental
Security Technology Certification Program
(ESTCP) evaluation of a PRB containing
emulsified oil substrate (EOS®). The pilot
study was initiated in 2003 at the Alliant
Techsystems, Inc., facility inElkton, MD,
to evaluate effectiveness of EOS
technology for enhancing biodegration of
perchlorate and chlorinated solvents. A
single dose of low solubility, low viscosity,
and slowly biodegradable edible-oil
emulsion was injected directly into the
contaminated aquifer. Post-treatment
monitoring indicates that introduction of
this reactive medium provided sufficient
organic carbon to support biological
degradation of target contaminants and
consistently maintain contaminant
concentrations below target levels for
nearly three years.
Historical activities at the site include
manufacturing of solid propellant rocket
motors. In the 1980s, routine ground-
water monitoring revealed ground-water
contamination resulting from a permitted
hazardous waste surface impoundment.
Site conditions amenable to an EOS PRB
included a shallow aquifer located 5-15 feet
below ground surface (bgs) consisting of
silty sand and gravel with moderate
permeability (-29 ft/day), and a ground-
water flow velocity of approximately 100
ft/year. Demonstration ease was enhanced
by well-defined distribution of
contaminants in a commingled plume
emanating from a closed surface-water
impoundment. Average concentrations of
target contaminants in the treatment area
were 9,000 mg/L perchlorate, 11,000
mg/L 1,1,1-trichloroethane (TCA), 50
mg/L perchloroethene (PCE), and 90
mg/L trichloroethene (TCE).
The demonstration was designed to
evaluate distribution of the emulsified oil
sufficiently to form a PRB perpendicular
to ground-water flow, injection impacts on
aquifer permeability and ground-water
flow paths, and changes in contaminant
concentrations and biodegradation
indicators during ground-water flow
through the biobarrier. The technology
employs emulsified-oil concentrate
consisting of food-grade soybean oil,
surfactants, amino acids, and vitamins
blended to form a stable emulsion with
small, uniformly sized oil droplets. Once
injected, the oil droplets adhere to sediment
surfaces and form a residual oil phase that
provides a carbon source and electron
donor for long-term in-situ anaerobic
biodegradation of contaminants.
[continued on page 2]
Contents
Emulsified-Oil
Biobarrier Provides
Long-Term Treatment
of Perchlorate/VOC
Plume page 1
DOD Compares
Benefits of Active
and Semi-Passive
Biobarriers page 3
Alternate Strategies
Used to Implement
Mixed-Substrate
Biobarriers at
Defense Facilities page 4
CLU-IN Resources
The U.S. EPA Technology
Innovation Program (TIP)
continues to develop compre-
hensive information sources
on key issues related to the
use of innovative technologies
for site characterization and
cleanup. TIP's primary web
site, CLU-IN, includes infor-
mation currently bundled into
nine "Contaminant Focus"
categories of chemical
groups: arsenic, chromium VI,
1,4-dioxane, mercury, MTBE,
perchlorate, persistent organic
pollutants, PCBs, and TCE.
Related guidance, technical
reports, and training opportu-
nities for these focus areas
are available at: http://clu-
in.org/contaminantfocus/.
Recycled/Recyclable
Printed with Soy/Canola Ink on paper that
contains at least 50% recycled fiber
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[continued from page 1]
In October 2003, the biobarrier was
constructed approximately 150 feet
downgradient from a former source
area. A Geoprobe® was used to install
ten injection wells 5 feet on center to a
depth of 15 feet bgs. Each well was
constructed with 10 feet of 0.02-inch
slotted screen and casing to the surface,
and finished with a sand pack and
bentonite seal. The injection setup
included minimal equipment: a
temporary solution mixing/holding tank,
a gasoline-powered transfer pump,
injection hoses, flow meters, pressure
gauges, and valves. Over two days, a
two-person crew injected a total of 55
gallons of diluted emulsion (1:4 EOS
and water) into each of the 10 wells,
followed by 165 gallons of chase water
to distribute and immobilize the
emulsion. Soil sampling showed that the
oil was distributed between the injection
wells and up to 10 feet downgradient,
forming a uniform PRB approximately
50 feet wide and 10 feet thick along the
direction of ground-water flow.
Ground-water conditions upgradient of
the barrier generally were oxidative with
elevated dissolved oxygen (DO >2 mg/L),
positive oxidation/reduction potential
(ORP >100 mV), and measurable nitrate
(9.5 mg/L) and sulfate (35 mg/L).
Emulsion injection resulted in anaerobic
conditions within and immediately
downgradient of the barrier, with a rapid
decline in ORP, DO, nitrate, and sulfate.
Dissolved manganese and iron increased
shortly after emulsion injection followed
by slower production of methane.
Within five days of the injection,
perchlorate concentrations in injection
Figure 1. Perchlorate concentrations
decreased to below the detection limit,
and 1,1,1-TCA concentrations
decreased more than 95% in ground
water 20 feet downgradient of the
Alliant Techsvstems biobarrier.
wells and monitoring wells 12 feet
downgradient decreased more than 99%.
One monthafterthe injection, 1,1,1-TCA
concentrations in the injection and
downgradient wells began to decrease
with concurrent production of
1,1-dichloroethane (1,1-DCA) and
chloroethane.
Though implemented on only a pilot scale,
this ground-water treatment approach
continues to promote contaminant
degradation, and additional injections have
not been required. Two and a half years
after the only emulsion injection,
monitoring wells 20 feet downgradient
of the barrier show perchlorate
concentrations remaining below the
analytical detection limit (<4 |J,g/L) and
1,1,1-TCA concentration reductions
exceeding 95% (Figure 1). Hydraulic
conductivity measurements indicate
emulsion injection has resulted in some
decline in hydraulic conductivity due to
biomass growth and/or gas production.
Tracer tests and detailed mapping of the
perchlorate distribution indicate, however,
that the change in hydraulic conductivity
has not adversely impacted barrier
performance or caused significant flow
around the barrier. Monitoring will
continue until late 2007 to obtain
additional information on barrier
longevity.
Installation of the pilot-scale PRB,
including two drums of EOS
concentrate, cost approximately
$23,000 ($46/ft2 of barrier). Significant
economies of scale are anticipated for
installation of larger barrier systems
involving wider well spacing. For
example, the total cost of a 200-foot PRB
at the same site with 10 injection wells
spaced 20 feet on center is estimated at
$38,000 ($19/ft2). A final cost and
performance report detailing this
evaluation will be issued in late 2007.
Additional information on this project,
detailed procedures for designing
emulsified-oil biobarriers, and other
applications of this technology for
source-area treatment can be found at
www.estcp.org.
Contributed by Andrea Leeson,
Ph.D., SERDP/ESTCP
(andrea.leeson(a).osd.mil or 703-696-
2118), Robert C. Borden, Ph.D., and
M. Tony Lieberman (Solutions-IES,
Inc. (rcborden&solutions-ies.com or
tlieberman(q).solutions-ies.com,
919-873-1060)
15,000
J! 10,000-
o
o
O
5,000
Perchlorate
1,1,1-TCA
1,1-DCA
Chloroethane
200 400 600 800
Days Since EOS Injection
1,000
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DOD Compares Benefits of Active and Semi-Passive Biobarriers
Current ESTCP demonstrations are
examining design, construction, and
performance elements of a semi-passive
barrier at the Longhorn Army
Ammunition Plant (AAP) in Karnack,
TX, and those of an active barrier at the
Navy Industrial Reserve Ordnance Plant
(NIROP) in West Valley City, UT.
DOD's upcoming guidance manual for
characterizing and remediating
perchlorate-contaminated ground water
will reflect site applicability, benefits,
and disadvantages identified through the
demonstrations.
The evaluation focuses on developing
optimal strategies for delivering and
distributing soluble ground-water
amendments serving as organic
substrates (the electron donor), thereby
creating an in-situ biobarrier. The active
approach relies on continuous
recirculation of ground water into which
amendments are injected, while the semi-
passive approach uses intermittent
recirculation of amendments (Figure 2).
Both approaches employ an electron
donor in soluble form that allows easy
Plan View of Semi-Passive Barrier
Ground-Water Recirculation with Intermittent Operation
During Active (pumping) Phase
Plan View of Active Barrier
Ground-Water Continuous Recirculation
distribution in the subsurface target zone.
This strategy relies upon addition of
electron donor in quantities high enough
to achieve target perchlorate reductions,
but low enough to avoid negative
impacts on secondary water-quality
characteristics. In contrast, a fully
passive system involves injection of large
quantities of electron donor during a single
injection event, which maintains reducing
conditions for several years but can more
adversely affect secondary water-quality
characteristics.
The Longhorn AAP semi-passive
biobarrier was constructed down-
gradient of a former landfill, where earlier
investigations identified a 250-foot-wide
perchlorate plume with concentrations
exceeding 3,000 |J,g/L. A shallow aquifer
extends to a depth of 35 feet bgs within
interbedded sand, silt, and clay, and
ground-water velocity in the treatment
zone is approximately 37 ft/yr.
Five recirculation wells with 10-foot
screens were installed in 35-foot
spacing along a line perpendicular to
ground-water flow. The
wells were designed for
use as either injection
or extraction wells,
depending upon selected
ground-water recirculation
patterns. The top of each
well screen generally
coincides with the area's
water table, at 14-17 feet
bgs. Following pump
tests and ground-water
Figure 2. Semi-passive
and active biobarriers
relv on the same
ffl injection well
H extraction well
electron donor in ground-water
but involve contrasting
engineering factors and
electron distributions in
the subsurface.
modeling, two intermediate injection
wells with 15-foot screens were installed
between each of the adjacent
recirculation wells to enhance substrate
distribution. Incorporation of
intermediate wells resulted in an
estimated 33% reduction in time needed
for ground-water recirculation and
associated distribution of electron donor
across the full barrier. Ground-water
travel time between injection and
extraction points ultimately ranged from
one to several months, depending on
flow regimes across the treatment area.
Prior to amending the aquifer, ground-
water extraction pumps in two of the
recirculation wells began operating at
extraction rates of 1.7 and 1.0 gpm.
After five weeks of recirculation and a
tracer test, soluble (60%) sodium lactate
was added as an electron donor through
three injection wells and eight
intermediate wells on a batch basis three
times each week. Over a three-week
period beginning in late March 2004, a
total of 273 gallons of sodium lactate
were injected into the aquifer. The
recirculation system was turned off, and
the system was allowed to operate in a
passive mode for eight months, after
which a second amendment (using 443
gallons of sodium lactate) was
conducted.
Ground-water sampling indicated
perchlorate concentrations within the
biobarrier had decreased from an
average of 450 |j,g/L to approximately
13 |J,g/L within approximately three
months after the second injection cycle.
Only minimal impacts on secondary
water-quality characteristics such as
increased sulfide or manganese
concentrations were noted. Ground-
water sampling after the second
amendment also indicated variability in
contaminant reductions within different
[continued on page 4]
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[continued from page 3]
areas of the biobarrier. Subsequent
tracer tests suggested that one portion
of the barrier received less electron
donor than the remainder. A third
injection cycle was conducted 11
months later, in November 2005, using
an alternate ground-water recirculation
pattern. This system modification
resulted in successful distribution of
electron donor across the biobarrier and
more consistent reductions in
perchlorate concentrations.
In contrast, an active rather than semi-
passive biobarrier was selected for use
at NIROP due to greater concern
regarding potential impacts on
secondary water-quality characteristics.
The active system also was anticipated
to more effectively degrade perchlorate
existing in a deeper (120 feet bgs)
aquifer within sandy lithology. A dual-
well extraction system began operating
in late 2005, using ethanol as an electron
donor delivered into a central injection
well. After 2-3 months of operation, initial
field results suggested that the use of
ethanol may accelerate fouling of the
injection well due to site-specific
geochemical conditions.
System operation was temporarily
suspended in order to complete
modifications that would allow use of
citric acid as an electron donor, and
operations resumed last summer. Ground
water currently is extracted from the two
extraction wells at rates of 10 and 50 gpm,
amended with citric acid, and re-injected
into the central injection well on a
continuous basis. Concentrations of citric
acid are controlled closely, with only small
increases being made to approach but not
exceed the stoichiometric demand of 7.3
mg/L.
Previous applications of active and semi-
passive approaches for electron delivery
suggest that the active approach more
effectively distributes and controls
ground-water amendments and is less
likely to impact ground water.
Implementation of an active system
involves higher costs, however, due to
increased infrastructure and field
operations. Although an active system
may require fewer wells, continuous
operation of the wells and associated
fouling-prevention measures additionally
increase costs for operations and
maintenance (O&M).
A final cost and performance report on
the two demonstrations will be
available in early 2007 on DOD's
ESTCPweb site (http://www.estcp.orgX
DOD anticipates publication and ESTCP
posting of the guidance manual,
including field and laboratory protocols,
later next year.
Contributed by Andrea Leeson, Ph.D.,
SERDP/ESTCP
(andrea.leeson&.osd.mil or 703-696-
2118), Evan Cox, and Tom Krug,
Geosyntec (tkrug&geosyntec. com or
519-822-2230)
Alternate Strategies Used to Implement Mixed-Substrate Biobarriers at Defense Facilities
The U.S. Navy and U.S. Air Force are
testing various approaches to the design,
construction, and operation of
biobarriers for enhancing anaerobic
bioremediation of chlorinated volatile
organic compounds (CVOCs) and
perchlorate found at many military
facilities. Comparison of systems at the
Naval Weapons Industrial Reserve Plant
(NWIRP) in McGregor, TX, and
Whiteman Air Force Base (AFB)
southeast of Kansas City, MO, indicate
that the technology may be implemented
for short-term use (as at Whiteman AFB)
or long-term use involving engineering
elements incorporated during barrier
construction to facilitate carbon
rejuvenation (NWIRP McGregor).
Applications at these facilities and other
sites illustrate that factors such as media
availability, restoration objectives, and
budgetary factors play significant roles
in biobarrier design and construction, and
confirm earlier findings that the
technology is best suited to shallow ground
water.
Nearly 2.5 miles of a biobarrier were
installed in segments within shallow
weathered limestone at NWIRP
McGregor in 2002 to reduce source-area
perchlorate plume mass, remediate
contaminated ground water before
discharge into surface water, and
expedite offsite property cleanup. (For
background information, view the
February 2004 issue of Technology
News and Trends online at http://
www.cluin.org). Prior to construction,
extensive bench- and pilot-scale studies
were conducted to evaluate organic
media and potential construction
methods. Full-scale construction involved
excavation of more than 13,000 linear feet
of trenches and backfilling with a
mixture of mushroom compost, 3/4-inch
pine wood chips, soybean oil, and 1-
inch crushed limestone. Horizontal
sections of perforated polyvinyl chloride
piping were installed along the trench
bottoms for future biobarrier
rejuvenation. Construction costs
averaged $200/ft2 per linear foot or less
than $15 per vertical foot.
Periodic monitoring of geochemical
indicators such as ORP, total organic
content (TOC), and nitrate suggested
that carbon rejuvenation eventually
would be required to sustain long-term
effectiveness of the biobarrier. In August
2006, nearly 22,000 pounds of an
emulsified oil substrate (EOS) solution
were injected into 15 onsite and offsite
biobarrier segments about four years
[continued on page 5]
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[continued from page 4]
after installation. Follow-on analytical
sampling will be conducted this month
to assess carbon-substrate injection
effectiveness.
Sample analysis indicates that the
biobarrier continues to effectively treat
perchlorate-contaminated ground water,
reducing concentrations within the
barrier from 1,000 ug/L to below the
laboratory detection limit of 2 u,g/L.
Effective use of the biobarrier and other
remedial measures resulted in gaining
"operating properly and successfully"
approval for the entire remedial system
in June 2006. Accomplishing this
milestone facilitates upcoming transfer
of 3,700 acres of the NWIRP property
to the City of McGregor for
redevelopment.
The alternate biobarrier strategy at
Whiteman AFB (in an area known as
"Site DP-32") employed lessons learned
at NWIRP McGregor, many of which
involved a streamlined design, more
conventional construction equipment,
and a simpler reactive media mix. The
Whiteman AFB biobarrier was installed
in the vicinity of a site disposal pit that
was part of a former water treatment
plant and possibly also used as a hospital
burn pit. After the treatment plant was
relocated to the west side of the base in
the 1960s, military family housing
(including a playground) was placed in
the area. The housing units and
playground were demolished in 2005,
and the area is expected to be used for
future training activities.
In 2002, field investigations identified
CVOCs (primarily TCE) in the area's
ground water at concentrations reaching
1,000 u,g/L. In addition, surface water in
a downgradient creek contained TCE
concentrations approaching 200 u,g/L.
During remedy selection, a biobarrier was
selected over a ZVI PRB and a ground-
water recovery/treatment system due to:
> Successful biobarriers at Offutt Air
Force Base, NE, and Altus Air Force
Base, OK, showing that organic-mulch
biobarriers effectively remediate shal-
low TCE-contaminated ground water;
> Ready availability of no-cost organic
media;
> Significant savings in construction
costs compared to a ZVI PRB and in
O&M costs compared to a ground-
water recovery and treatment system;
> Absence of aboveground system ele-
ments interfering with ongoing site
operations; and
> Limitations posed by minimal
hydrogeologic data (particularly related
to ground-water residence time) that
would not impact biobarrier design and
implementation.
A full-scale 270-foot-long, 10- to 20-foot-
deep biobarrier was constructed at
Whiteman AFB in March 2004 as part of
a treatability study. The system was
installed in a 5- to 10-foot-thick clayey
gravel (weathered bedrock) layer using
conventional excavators (Figure 3).
Keying into an underlying and competent
shale layer, the barrier trenches were
constructed in approximate 40-foot
sections to minimize side-wall sloughing
and facilitate ground-water management
during field activities. Trenches were
backfilled with a 1:1 mixture of organic
mulch and clean sand. To minimize
material and transportation costs,
[continued on page 6]
Contact Us
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and Technology Innovation
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Phone:703-603-7198
Fax:703-603-9135
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Solid Waste and
Emergency Response
(5203P)
EPA 542-N-06-006
November 2006
Issue No. 27
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
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EPA
Permit No. G-35
[continued from page 5]
recycled vegetation from the facility was
selected as the organic mulch instead
of ground corn (despite slightly higher
organic carbon and nutrient
concentrations) from a local grain
elevator. Due to the short-term
use anticipated for this system, no
injection piping was installed during
construction to facilitate organic-
substrate replenishment.
Costs for installation of the Whiteman
AFB biobarrier, which involved minimal
collection of new hydrogeologic data
and condensed design planning, totaled
approximately $74,000 (about $275 per
linear foot or less than $20 per vertical
foot). Despite these budgetary limitations,
nearly two years of monitoring show that
significant CVOC degradation is occurring
within the biobarrier and CVOC
concentrations in downgradient wells are
88% lower than in upgradient wells.
Sampling results also show indirect
evidence of enhanced reductive
dechlorination in ground water passing
through the barrier, including increased
ferrous iron concentrations and decreased
ORP, dissolved oxygen, and nitrate levels.
Pre- and post-construction gradient
measurements suggest that the biobarrier
has not impacted ground-water flow.
Based on the results of a revised human-
health risk assessment conducted after
biobarrier installation, the Air Force and
Missouri Department of Natural
Resources determined that potential site
risks were within acceptable risk
thresholds. As a result, additional
biobarrier monitoring to determine its
longer-term effectiveness is not
anticipated.
Contributed by Mark Craig, U.S.
Navy/NAVFAC Southeast
(mark, craig&navy. mil or 843-820-
5517), Marvin Eaves, Whiteman AFB
(marvin.eaves&whiteman.af.mil or
660-687-6263), and Mike Perlmutter,
CH2M HILL (mperlmut&ch2m. com
or 770-604-9095)
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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