United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-00-004
June 2000
Issue No. 36
vvEPA Ground Water Currants
Treatment
CONTENTS
Monticello Permeable Reactive
Barrier Project Pg. 1
Field Evaluation of SolventExtrac-
tion Residual Biotreatment
(SERB) Pg. 2
Subsurface Biofilm Barriers
Contaminated Ground
Water Containment Pg. 3
About this Issue
This issue highlights field
results of a zero-valent iron
permeable reactive barrrier
and laboratory work on
development of subsurface
biofilm barriers. Also featured
are laboratory and pilot-scale
work using in situ
biotreatment to enhance the
effectiveness of cosolvent
extraction processes.
Monticello
Permeable Reactive
Barrier Project
by Clay Carpenter, MACTEC-ERS
Inc.; Stan Morrison, Roy F.
Weston, Inc.; and Don Metzler,
U.S. Department of Energy, Grand
Junction Project Office
A permeable reactive barrier (PRB)
system, using zero-valent iron (ZVI),
is cleaning up metal-contaminated
ground water at a former uranium
and vanadium ore-processing mill at
Monticello, Utah. The U.S. Depart-
ment of Energy (DOE) Grand
Junction Project Office (GJPO) is
managing the cleanup in coopera-
tion with EPA Region 8 and the
State of Utah. The site is regulated
under the Comprehensive Environ-
mental Response, Compensation,
and Liability Act (CERCLA), and
the project is being funded by the
DOE Office of Science and Tech-
nology Accelerated Site Technolo
gy Deployment Program.
Uranium, selenium, vanadium,
manganese, and arsenic are the major
contaminants of concern in ground
water at the site. Following an
Interim Record of Decision calling for
emplacement of a PRB hydraulically
downgradient of the site, both labora-
tory and field treatability studies
were used to guide design of the
PRB and selection of the most
appropriate reactive materials.
PRB Construction
The remediation system includes a
PRB and impermeable funnel walls
(see Figure on next page). The
barrier was built by driving steel
sheet piling into the bedrock forming
a rectangular box approximately 100
feet long by 8 feet wide. The native
soils inside the box were replaced
with -8/+20 mesh ZVI and gravel
packs upgradient and downgradient
of the ZVI. The ZVI and gravel
packs extend more than 1 foot into
the underlying bedrock aquiclude.
The upgradient gravel pack is
approximately 2 feet wide and is
composed of 13 percent-4/20 mesh
ZVI (by volume) mixed uniformly
with 0.5-inch gravel. The middle
section of the PRB contains 4 feet of
100 percent-ZVI. The downstream
gravel pack is approximately 2 feet
wide composed of 0.5-inch gravel
and includes an air-sparging system
constructed of perforated polyvinyl-
chloride pipe. The air sparging
system will be used to remove
dissolved manganese and iron if the
concentrations increase to unaccept-
able levels. The south impermeable
wall is 240 feet in length and the
north wall is 97 feet in length; the
impermeable walls are composed of
a bentonite and soil slurry mix.
[continued on page 2]
Recycled/Recyclable
Printed with Soy/Canola Ink on paper that
contains at least 50% recycled fiber
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[continued from page 1]
Sth-ematic of at Monti-cello
The impermeable walls funnel
contaminated ground water to the
PRB for treatment. Construction was
completed on June 30, 1999.
Monitoring Results
In the summer of 1999, a monitoring
network of approximately 50 wells
was established centered on the
reactive portion of the PRB. Ground-
water-quality samples and water-level
data were taken in September,
October, and November 1999, and in
January 2000. Results indicated that
initial concentrations of uranium (700
|lg/L), vanadium (400 |lg/L), sele-
nium (40 |lg/L), and arsenic (10 |ig/
L) have been reduced to non-detect-
able levels as ground water exits the
PRB. Concentrations of manganese, a
trace contaminant in ZVI, increase
slightly across the PRB, but these
concentrations are expected to
decrease over time. Iron concentra-
tions exiting the reactive wall were
much lower than expected.
Upcoming Activities
A tracer study will be conducted to
better evaluate the hydraulic
performance of the reactive gate. In
addition, a colloidal borescope will
be used to measure the rate and
direction of ground-water flow in
and adjacent to the PRB. Sampling
and analysis of the ground water
will continue on a quarterly basis.
For more information, contact Don
Metzler (DOE/GJPO) at 970-248-
7612 or E-mail
dmetzler@doegjpo.com.
Field Evaluation of
Solvent Extraction
Residual
Biotreatment [SERB)
Guy W. Sew ell, Susan C. Mravik,
and A. Lynn Wood, U.S.
Environmental Protection Agency,
National Risk Management
Research Laboratory
Laboratory and pilot-scale experi-
ments have demonstrated the
potential of cosolvent-enhanced in
situ extraction to remove DNAPL in
porous media. While this method is
effective for mass removal, residual
amounts of cosolvents and con-
taminants are expected to remain at
levels that could preclude meeting
regulatory requirements. However,
with the bulk of the DNAPL ex-
tracted, in situ biotreatment
becomes a viable "polishing"
procedure transforming the remain-
ing contaminants to non-hazardous
compounds at a rate that may
exceed the rate of dissolution or
displacement. The efficacy of in situ
bioremediation of chlorinated sol-
vents is usually limited by transport
and mixing considerations, i.e., the
availability of electron donors at the
appropriate concentrations relative to
the concentration of chlorinated
solvent (the electron acceptor).
Concurrent exposure of microbes to
an electron donor and electron
acceptor can be facilitated by the
delivery and extraction process as
well as the co-solvency effect.
A test of the Solvent Extraction
Residual Biotreatment (SERB)
technology was conducted in August
1998 at the former Sages Dry Cleaner
site in Jacksonville, FL. The area is
contaminated with tetrachloroethyl-
ene (PCE). The very low levels of
biodehalogenation daughter products
and the levels of dissolved oxygen
suggest that natural attenuation
processes are not protective of the
site. A week-long in situ cosolvent
extraction test with ethanol was
conducted. Pre- and post-treatment
partitioning tracer tests indicated that
the estimated original 72 kg of
DNAPL were reduced to 22.6 kg, or
an approximately 70% removal of
the original PCE. The dissolved mass
of PCE in the treatment zone was
estimated to be about 3.5kg.
Post-test hydraulic containment was
conducted for approximately 10 days
until the ethanol concentration in the
treatment system dropped below
10,000 milligrams per liter (mg/L).
After pumping was ceased, ground-
water monitoring indicated that, over
time, biotransformation of the PCE
was enhanced. After 4 months,
significant levels of cis-DCE (4 mg/
L), a PCE breakdown product, were
detected in areas exposed to residual
[continued on page 3]
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[continued from page 2]
ethanol, and concentrations above
16 mg/L were observed after 10
months.
Ethanol can be anaerobically de-
graded to acetate (incomplete
oxidation) or carbon dioxide (com-
plete oxidation). Depending on the
extent of the oxidation, 1 to 2 moles
of ethanol are required to drive
complete dechlorination of one mole
of PCE. The average post-contain-
ment concentration of ethanol in the
cosolvent treatment zone was
approximated 8,000 mg/L, or about
289 times the amount needed to
remove the 21.1 moles of dissolved
PCE or 38.8 times the amount of
ethanol needed to degrade the
estimated 157.1 moles of dissolved
plus residual source PCE. This
estimate assumes no competing
terminal oxidation processes such as
methanogenesis or sulfate reduction.
Currently the system remains biologi-
cally active, and the dechlorination
products TCE, cis-DCE, ethene, and
chloride are accumulating. High levels
of dissolved methane and hydrogen
have also been detected in the treat-
ment zone. The maximum and
minimum observed rates of dechlori-
nation (based on cis-DCE production)
are approximately 43.6 and 4.2 ug/L/
day, respectively. These rates can be
extrapolated to a multi-step, concur-
rent, dechlorination process to predict
that the dissolved phase PCE could be
removed in 3 to 30 years, and that the
total source zone PCE could be
transformed in 24 to 240 years. For
additional information, contact Guy
W. Sewell (EPA/National Risk Man-
agement Research Laboratory) at
580-436-8566 or E-mail
sewell.guy@epa.gov.
Subsurface Biofilm
Barriers for
Contaminated Ground
Water Containment
Al Cunningham, Center for Biofilm
Engineering, Montana State
University; Randy Hiebert, MSE
Technology Applications, Inc.
Researchers at Montana State
University's Center for Biofilm
Engineering (CBE), in collaboration
with MSE Technology Applications,
Inc. (MSE) of Butte, MT, have
developed a process for building
subsurface biofilm barriers
(biobarriers) to contain dissolved
contaminant plumes.
Biofilm barriers are developed by
injecting large numbers of mucoid
bacteria into permeable strata forma-
tions. The bacteria are mixed with
water and pumped down a series of
injection wells. A suitable growth
substrate and additional nutrients
then are injected to stimulate micro-
bial growth. These mucoid bacteria
are capable of forming large quanti-
ties of extracellular polymer
material (EPS) during their growth
phase. Bacterial growth and EPS
production form microbial biomass
which substantially reduces the free
pore space in the formation and
consequently reduces the hydraulic
conductivity. This zone of reduced
hydraulic conductivity serves as a
novel barrier technology for con-
trolling off-site migration of mobile
contaminants. Biobarrier technol-
ogy also may be a useful means of
funneling contaminated ground
water through subsurface treatment
systems (i.e., zero-valent iron
systems). The main advantages
offered by biobarrier technology
are: 1) biobarrier construction is
achieved without excavation and
therefore will be economically
attractive at many sites; and 2) there
is no obvious depth limitation for
biobarrier technology. Traditional
subsurface barrier technologies
such as slurry walls and grout
curtains are not usually cost effec-
tive at depths more than 50 feet.
Laboratory Investigation
CBE conducted a 4-year laboratory
investigation to understand factors
which promote or retard biofilm
accumulation in porous media with
the intent to apply such understand-
ing toward the manipulation of
permeability and mass transport
properties. Biofilm formation and
persistence experiments were
conducted in porous media columns
and in lysimeters. Accumulation of
biomass in the columns and lysim-
eters resulted in a reduction of
hydraulic conductivity to less than
0.1 percent of original values.
Results indicated that biobarrier
integrity was unaffected by expo-
sure to 300 mg/L of carbon
tetrachloride and heavy metal
contaminants (strontium and ce-
sium) at concentrations of about 1
mg/L for periods up to 120 days.
These laboratory-scale results
indicated that the ability of micro-
bial biobarriers to manipulate the
hydrodynamic properties of porous
media could result in an effective
technology for the containment of
ground-water contaminants.
[continued on page 4]
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[continued from page 3]
Field Demonstration
Working in collaboration with MSB,
the project team constructed a field
demonstration lysimeter facility in
Butte, MT to develop a comprehen-
sive data set for the evaluation of
biobarrier performance. The field test
began in December, 1999 and is still
in operation. A 180-foot long and 20-
foot deep biobarrier was constructed
in a lysimeter that was 130 feet wide,
180 feet long, 20 feet deep, and lined
with impermeable plastic. A highly
mucoid Pseudomonas strain was used
as the microbial inoculum, and
molasses was the primary growth
substrate; nitrate was added to serve
as the primary electron acceptor after
oxygen was depleted. A flow field
was established across the 180-foot
dimension by injecting supply water
at the up-gradient boundary and
simultaneously pumping from a series
of recovery wells located at the
down-gradient boundary, and the
system was operated to maintain a
constant hydraulic gradient across the
barrier. The integrity of the barrier
was determined by measuring the
reduction in hydraulic conductivity
within the barrier region. Hydraulic
conductivity was measured by slug
tests performed in the 11 injection
wells which spanned the 180-foot
dimension. To date, six sets of slug
test data have been measured. As the
180-foot biofilm barrier developed,
the overall hydraulic conductivity
through the lysimeter steadily dimin-
ished. Hydraulic conductivity reduc-
tions of more than 99 percent were
measured across the barrier.
Cost
A cost analysis was performed by
MSB using information obtained from
the 180-foot lysimeter biobarrier
investigation and other field data.
Results indicated a net present cost
for installation and long-term mainte-
nance for biobarriers in the range of
$7 to $10 per cross-sectional square
foot. These costs compare favorably
with alternative barriers such as sheet
piling which has costs in the range of
$25 to $60 per cross-sectional square
foot.
For further information contact Randy
Hiebert (MSB) at 406-494-7233 or E-
mail hiebert@mse-ta.com, or Dr. Al
Cunningham (CBE) at 406-994-6109
or E-mail al_c@erc.montana.edu.
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EPA 542-N-00-004
June 2000
Issue No. 36
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