5
\
a
/A newsletter about soil, sediment, and ground-water characterization and remediation technologies
Issue 15
December 2004
Biopolymer Slurry Proves Effective for PRB Installation and Performance
Contents
In April 2002, the Air Force Center for Environmental
Excellence (AFCEE) constructed a 1,100-foot long,
zero-valent iron (ZVI) permeable reactive barrier
(PRB) at the former Carswell Air Force Base in Texas
to demonstrate the feasibility of using this technology
to degrade chlorinated ethenes in ground water. The
untreated ground water contains trichloroethene
(TCE) in concentrations reaching 1,500 ng/L, cis-
1,2-dichloroethene (DCE) in excess of 480 |.ig/L, and
trace amounts of /raras-1,2-DCE and vinyl chloride.
Ground water flowing through the PRB experiences
a 99% reduction in TCE concentrations, resulting in
an effluent value of 5(ig/L.
The PRB consists of a 2-foot thick, equal-proportion
mixture of ZVI and sand that extends from a depth of
2-3 feet above the high water table to the top of a
bedrock aquitard. The top of bedrock exists at an
average depth of 38 feet, and the saturated thickness
of the surficial aquifer is 10-12 feet. Preliminary
evaluation of the treatment area and a focused
feasibility study considered various PRB
configurations prior to construction. To prevent the
plume from bypassing the PRB, the selected design
entailed a single, continuous trench housing a 300-
and an 800-foot long section of reactive material.
Use of giiar gum as a biodegradable biopolymer
slurry was an innovative technique for shoring the
trench sidewalls. The slurry method allowed for
rapid installation of the PRB within a small area and
in a "zigzag" pattern to accommodate a landfill, an
overhead power line, a high-pressure water line, and
a maintenance building. Liquid shoring also
eliminated the need for deeper (up to 20 feet) and
more costly trenching. After the trench was
backfilled, the guar gum slurry was degraded by
adding a liquid enzyme breaker within the ZVI, and
recirculating the ground water through the trench
using a system of 22 recirculation wells for a
minimum of three pore volumes. Soil microbes
completed the guar gum degradation process.
Quarterly sampling is conducted at four transects
across the PRB, each consisting of an upgradient well,
a downgradient well, and a well within the reactive
media. Analytical results demonstrate that the PRB
has maintained a TCE removal efficiency of 99.5%
since sampling began in June 2002. Based on an
estimated ground-water velocity of 2 ft/day, it is
estimated that the PRB removes 980 pounds of TCE
each year. Results also indicate that the PRB is reducing
TCE concentrations in the distant and downgradient
residual plume (Figure 1) from a maximum of 2,500
(.ig/L to less than 1,000 ng/L.
Downgradient concentrations of cis- 1,2-DCE also have
decreased, but not to the same extent. Treatment
efficiencies for cis- 1,2-DCE and vinyl chloride have
varied over time and among transects within a single
sampling event. Monitoring suggests that these
variations are attributable to the activity of anaerobic
microbial populations (Dehalococcoides) that were
enhanced by the use of biopolymer slurry. These
findings suggest that the high rate of TCE removal is
due to not only to abiotic degradation by the ZVI but
by anaerobic biodegradation as well.
Ground-water elevations within and adjacent to the
PRB are measured as part of each quarterly monitoring
event. Ground-water flow in the vicinity of the PRB
was disrupted temporarily during construction due
to the liquid shoring, but contouring of ground-water
elevations demonstrated that flow returned to normal
by the second monitoring event.
Several lessons were learned during construction of
the PRB. When the mixing of reactive media in small,
skid-mounted mixers was found to be time-
consuming, a cement mixer was employed. Additions
of ZVI and sand to the cement mixer were made on
an alternating basis to ensure uniform distribution.
During placement of the reactive media in the trench,
the ZVI and sand began to plug the tremie pipe. This
[continued on page 2]
Biopolymer Slurry Proves
Effective for PRB
Installation and
Performance
page 1
Air Force Uses Electrical
Resistance Heating for
TCE Source Removal
and Plume Reduction page 2
Accelerated Cleanup
Follows Fenton's ISCO
and Substrate Addition page 3
SEAR and
Bioaugmentation
Demonstrated for PCE
Source Treatment and
Plume Control page 5
CLU-IN Resources
The Technology Focus area on
CLU-IN (http://www.clu-in.org/
techfocus/) bundles information
on cleanup technologies that
can be used in a variety of
applications. Technology Focus
currently highlights 19 technolo-
gies, including four on which
site-specific applications are
covered in this issue: permeable
reactive barriers (PRBs),
electrokinetics, in-situ oxidation,
and bioremediation. Each
technology-specific information
bundle provides direct access to
relevant guidance materials,
application summaries, training
opportunities, and additional
resources.
Recycled/Recyclable
Printed with Soy/Canola Ink on paper that
contains at least 50% recycted fiber
-------
[continuedfrom page 1]
problem was solved by cutting slots into the
bottom of the pipe and discharging the media
directly from the concrete mixer into the pipe at
a constant rate.
hi addition, use of the site's readily available,
fine-grained sand for backfill unexpectedly plugged
the recirculation wells allowing sand to migrate
across the reactive media. The backfill sand also
decreased the pH of the biopolymer slurry, which
needed to remain high for shiny stability. To
prevent plugging, as well as promote recirculation
of the enzyme used to degrade the biopolymer
slurry, a coarse-grained sand should be used as
backfill. Use of a sand containing limestone would
help maintain the necessary pH.
The biopolymer slurry method proved to be an
effective technique for PRB construction at the
former Carswell Air Force Base, which is now
known as Naval Air Station (NAS) Fort Worth,
Joint Reserve Base (JRB). Project results suggest
that using a series of 300- to 400-foot overlapping
trenches may increase the technology's efficiency
at similar sites with a large contaminant plume.
Operation of the PRB is anticipated to continue
until 2012 or when TCE maximum contaminant
levels for ground water are met.
Contributed byH. DonFicklen, AFCEE (210-
536-5290 or holmesficklen(a),brooks.af.mil),
Cynthia Crane, Ph.D., and Lynn Morgan,
HydroGeologic (703-478-5186 or
ccrane@hgl. com or lmorgan@hgl. com)
Figure 1. Ground-water treatment
by the PRB is significantly reducing
TCE concentrations in the
downgradient toe of the
contaminant plume at the former
Carswell Air Force Base.
- - - NAS Kurt Worth JRB (CaKwell Field)
^^^ permeable reactive tamer
n\
Air Force Uses Electrical Resistance Heating for TCE Source Removal and Plume Reduction
.Performance monitoring indicates that
contaminant concentrations in soil and ground
water at the Air Force Plant 4 in Fort Worth, TX,
have remained low following implementation of
electrical resistance heating (ERH) technology in
2002. Full-scale ERH operations were designed
to reduce residual-phase, dense nonaqueous
phase liquid (DNAPL) in soil; remove
contaminated free-phase DNAPL to the extent
possible; and prevent offsite migration of ground
water with trichloroethene (TCE) concentrations
exceeding the maximum contaminant level. ERH
was used as part of a comprehensive program to
reduce contaminant concentrations and reduce
offsite migration from the entire facility. Analysis
of vapor recovery data upon system shutdown
indicated that ERH treatment resulted in the
removal of more than 1,400 pounds of volatile
organic compounds (primarily TCE) during 9-
months of operation. Monitoring results
compiled this past summer confirm that TCE
levels in soil and ground water remain below the
target levels of 11.5 mg/kg and 10 mg/L,
respectively.
Pretreatment site investigations detected maximum
TCE concentrations of 2,770 mg/kg in soil and
285 mg/L in ground water. Residual DNAPL was
identified in the vadose zone, which consists of
heterogeneous interbedded clay, silt, and poorly
to moderately sorted sand and gravel extending
approximately 35 feet below ground surface (bgs).
The top of the shallow aquifer is located 27-35
feet bgs, with a thickness of 5 feet and hydraulic
conductivity of 4.6 x 10"2cm/s. Tracer tests and
site conceptual models suggested the presence of a
DNAPL source area near Building 181.
ERH was selected as a cleanup remedy due to its
efficiency in removing volatile and semi-volatile
contaminants from both the vadose and saturated
zones, regardless of soil permeability or
heterogeneity, and its past success in treating
DNAPL. The technology uses common (60 Hz)
electricity to generate in-situ resistance heating and
steam stripping, thereby serving as a heat
enhancement to vapor recovery. In typical
remediation applications, ERH electrodes and
vapor recovery wells are co-located in the same
boring.
A pilot-scale six-phase heating test was
performed in 2001 to evaluate the efficacy of
ERH technology at this site and expanded to
full-scale operation the following year. The full-
scale ERH system targeted approximately
27,000 cubic yards of contaminated soil in a
0.5-acre area inside Building 181. The system
involved a network of 63 electrodes and co-located
vapor and steam recovery wells installed on
approximate 17-foot centers directly above the
suspected source area. Fifteen of the electrodes
and co-located vapor recovery wells were
installed on 10-30° angles to remediate the soil
and ground water directly beneath large chemical
bath tanks and piping racks inside Building 181
(Figure 2). Installation and operation of the ERH
system occurred without interruption to ongoing
manufacturing activities, which operate 24
hr/day, 7 days/wk.
Electrical voltage, vacuum pressure, and vapor
flow rates were monitored throughout ERH
operations and analyzed weekly to determine
which adjustments were needed to optimize the
[continued on page 3]
-------
[continuedfrom page 2]
system. Indoor air quality of Building 181 also
was monitored to ensure that no TCE vapors
were emitted. The system was designed to shut
down if any air samples, which were collected
and analyzed every five minutes, exhibited
detectable concentrations of TCE. Over the full
course of ERH treatment, indoor air
concentrations of TCE did not exceed the
detection limit (1 ppmv).
Ground-water samples were collected from a
network of 12 monitoring wells, three of which
were located roughly 75 feet downgradient of the
treatment area. Soil samples were collected from
the ground-water monitoring wells, temperature
monitoring points, and soil borings during
installation and after shutdown of the ERH
system. Approximately 150 soil vapor samples
were collected from the vapor recovery wells and
vapor monitoring wells for analysis before and
after heating to evaluate the ERH effects on TCE
soil vapor concentrations. Results showed a 93%
reduction in the mean TCE concentration of the
vapor plume and significant reduction in the
plume's areal extent. Soil analyses indicated that
the mean TCE concentration had decreased by
90% and the target concentration of 11.5 mg/kg
was met at all sampling locations. Ground-water
samples were collected from the 12 ERH
monitoring wells before, during, and after heating.
Analytical results showed an 87% reduction of
the mean TCE concentration in ground water, to
below the target cleanup level of 10 mg/L in the
vapor phase.
Figure 2. The ERH system constructed at Air
Force Plant 4 was designed to address
residual-phase dense DNAPL, free-phase
DNAPL, and off-site migration of the TCE
plume.
ERH treatment resulted in a total TCE mass
removal of approximately 1,417 pounds of vapor
from the subsurface. Limited chloride monitoring
suggests additional TCE mas reduction due to
biodegradation effects. Review of the overall project
indicated that several factors affected ERH
performance at this site:
> Additional days of operation were required
to achieve the needed energy input because
downhole electrode cables could not support
the system's designed amperage. The same
electrode design was used for both the pilot
test and full-scale application, but electrodes
with higher energy efficiency were used in
the later application in order to increase heat
generation in the vadose zone.
> Ground-water monitoring would be enhanced
by placing well screens at locations that in-
tercept the alluvium/bedrock interface and
possibly extend into the underlying limestone
bedrock.
> Heating targets in the vicinity of one moni-
toring well could not be met, despite vari-
ous efforts.
> Although significant heat was generated in
the low permeability soil, a number of ex-
traction wells produced low flows.
Soil and ground-water monitoring at Building
181 will continue indefinitely. The site's overall
treatment strategy will be revisited during the
next five-year review of the site's record of
decision, which is scheduled to occur in 2007.
Contributed by George Walters, Aeronautical
Systems Center/Engineering Directorate (93 7-
255-1988 or george. walters@wpafb. af.mil),
Derek Peacock, URS Corporation (512-419-
6180 or derek_peacock@urscorp. com), and
David Fleming, Thermal Remediation
Services, Inc. (425-396-4266 or
dfleming@thermalrs. com)
ERH Subsurface Cross Section
Co-Located Temperature
Perimeter Electrode Monitoring
with Deep and Shallow Point with
SVE Wells Thermocouples
Co-Located
internal Electrode
with Shallow SVE
Angled Co-Located
Electrode and SVE
Accelerated Cleanup Follows Fenton's ISCO and Substrate Addition
JVlonitoring data collected by the U.S. of the contaminant source area using in-situ chemical determined that the associated contaminant
Geological Survey (USGS)overthepastsixyears oxidation (ISCO). Concentrations of perchloro- plume contained vinyl chloride (VC), a PCE
show that a plume of chlorinated ethene- ethene (PCE) prior to treatment exceeded 4,500 biodegradation product, in concentrations
contaminated ground water in Kings Bay, GA, J-ig/L in the source area, which is located in an exceeding 800 ng/L. ISCO treatment using
has contracted significantly following treatment abandoned municipal landfill. Investigations [continuedon page 4]
-------
[continuedfrom page 3]
Teuton's reagent reduced the source-area PCE
concentrations to less than 100 ng/L. Since the
time of treatment, PCE concentrations have not
rebounded above this level, and VC
concentrations have decreased progressively.
The U.S. Department of Energy had performed
earlier pilot testing of ISCO at the Savannah
River Site, SC. Based on the promising test
results, which were communicated to the Naval
Facilities Engineering Command (NAVFAC), a
decision was made to implement full-scale ISCO
at the Kings Bay Naval Submarine Base in 1998.
The water table aquifer underlying the Kings Bay-
site is approximately 30-feet thick and comprises
fine-grained sand deposited by a prograding barrier
island. The aquifer has a hydraulic conductivity
of 30 ft/day in the relatively permeable 30- to
35-foot depth interval.
Pretreatment site investigations and modeling
indicated that natural attenuation of PCE, VC,
and other chlorinated ethenes was relatively
efficient. Natural attenuation was insufficient,
however, to meet remedial obj ecti ves focused on
the prevention of chlorinated ethene migration
to a residential development located 600 feet from
the source area.
The USGS partnered with NAVFAC by first
locating the contaminant source area, including
pooled dense non-aqueous phase liquid
(DNAPL), through use of direct-push
technology and field gas chromatography. After
the injections of Fen ton's reagent were complete,
the USGS monitored contaminant degradation
and microbial populations (as indicators of
contaminant degradation) throughout the proj ect.
Monitoring was accomplished through a network
of eighteen 30- to 34-foot monitoring wells
installed downgradient of the contaminant source
area. The wells were placed in three transects
perpendicular to the direction of ground-water
flow. Downgradient sulfate concentrations served
as tracers of treated ground water.
Figure 3. Analytical data show how vinyl chloride
concentrations decreased as sulfate concentrations
increased over the past six years as a result of ISCO
treatment of the source area.
ISCO treatment at Kings Bay employed 23
injectors that targeted chlorinated ethenes in the
source area, initially concentrating on the 20- to
35-foot portion of the aquifer. A mixture of ferrous
sulfate and 50% diluted hydrogen peroxide was
injected during three events over nine months. A
low pH of the injectant, which is needed to optimize
the Fenton's reaction, was maintained throughout
the treatment period. An almost immediate emission
of carbon dioxide was observed at two recovery
wells located farther downgradient, indicating the
desired chemical reactions were occurring.
PCE concentrations in the source area decreased
52-87% within three weeks of the initial injection
and 99% following the second. Similarly, VC
concentrations immediately downgradient of the
source area decreased from more than 800 to less
than 2 ng/L within six months. Researchers
anticipated that additional reduction of the VC
concentrations to the 2-|ig/L maximum contaminant
level could be reached through natural attenuation.
While in-situ oxidation briefly decreased the
abundance and activity of microorganisms in the
source area, microbial activity rebounded within
six months. Six years later, sulfate measurements
now indicate that the treated water has reached the
second (75-ft distanced) line of monitoring wells,
where VC concentrations have decreased
significantly (Figure 3).
The results of this study indicate that source-area
removal actions, particularly when applied to
ground-water systems with a significant natural
attenuation capacity, can be effective in decreasing
the areal extent and contaminant concentrations
of chlorinated ethene plumes. Results also
suggest, however, that the shift from sulfate-
reducing to Fe (Ill)-reducing conditions induced
by Fenton's treatment may have decreased the
efficiency of reductive dechlorination in the
injection zone.
To replenish the organic matter content of the
treatment area, which allowed for continued
microbial contaminant degradation, a consumer-
grade vegetable oil emulsion was injected into
the treated zone of the aquifer during 2002.
Increased concentrations of methane generated
downgradient of the oil injection zone, indicating
increased levels of microbial activity due to
vegetable-oil injection, became evident in 2004.
The pump-and-treat system originally selected
as the interim remedy was terminated two
months after the second ISCO injection.
NAVFAC estimates that removal of
contaminated DNAPL at Kings Bay has lowered
the remediation time from 35 years to
approximately 7 years and the cost from $30
million to $5 million.
Contributed bv Frank Chape lie, USGS
(803-750-6116or chapelle@usgs.gov), Paul
Bradley, USGS (803-750-6125 or
pbradley@,usgs.gov), and Clifton Casey,
NAWAC, at843-820-5561 orcasey@navy.mil
Initial
Fenton's Reagent
Injection
1800
100
CT
1/1/1998 1/1/1999 1/1/2000 1/1/2001 1/1/2002 1/1/2003 1/1/2004 1/1/2005
Date
4
-------
SEAR and Bioaugmentation Demonstrated for PCE Source Treatment and Plume Control
The Great Lakes Mid-Atlantic Center for
Hazardous Substance Research and the Michigan
Department of Environmental Quality are
sponsoring a two-phased effort to address
ground-water contamination at the "Bachman
Road" site in Oscoda, MI. Phase I involved a
demonstration to evaluate the technical
feasibility of using in-situ surfactant enhanced
aquifer remediation (SEAR) for removal of a
DNAPL source zone, and bioaugmentation to
control migration and toxicity of a dissolved
chloroethene-contaminated ground-water plume.
Phase II, which will begin in 2005, will focus on
implementing a full-scale SEAR to remediate a
source area containing high concentrations of
PCE.
Chlorinated solvents released from past dry
cleaning operations have reached residential water
supply wells in the project area. The water table
is 8-24 feet bgs. Site characterization indicates
that the surficial aquifer is composed of medium-
to fine-grained glacial outwash sand of low
organic content and is underlain by a clay
confining layer. Hydraulic conductivity of the
sand is estimated at 10-50 ft/day, and the ground-
water velocity is estimated to be 0.43 ft/day.
The demonstration was conducted in two parallel
and geochemically-similar contaminated ground-
water zones involving two adjacent chlorinated
solvent plumes that were identified during earlier
field studies. Both plumes stretch downgradient
from the suspected source area for approximately
800 feet before discharging into Lake Huron.
The bioaugmentation component of the Phase I
demonstration was designed to characterize
spatial distribution of dechlorinating organisms,
to provide evidence that the organisms are
responsible for observed dechlorination of
contaminants, and to evaluate the need for and
efficacy of bioaugmentation compared to
biostimulation. Genetic tests of ground-water
and soil samples indicated the presence of
dechlorinating bacteria, including
Dehalococcoides species, which can generate
energy during reductive dechlorination of PCE.
Suppressed methanogenesis, depressed redox
conditions, and dissolved hydrogen
concentrations in microcosm studies suggested that
microbial reductive dechlorination is a significant
process. Laboratory studies on soil and ground-
water samples showed that bioaugmentation with
aZ)e/«7/ococco/'fife,s-containing culture would result
in faster and more complete dechlorination to a
nontoxic end product (ethene) than biostimulation
alone.
Bioaugmentation field studies concentrated on the
Phase I dissolved-phase plume, which contains
PCE and TCE at concentrations of 437 and 100
Hg/L, respectively, as well as low concentrations
of cis- and trans-DCE and VC. The microbial
culture used to bioaugment the site contained
Dehalococcoides species. In the field test, over
95% of the chlorinated solvents were transformed
to ethene within 65 days of lactate injection and
within 36 days of inoculation with halorespiring
bacteria. A single inoculation was sufficient, and
State of Michigan cleanup goals were met in the
test area. In addition, degradation of chlorinated
solvents correlated to growth of Dehalococcoides
bacteria in the test plot.
In the source area, ground water contains PCE
concentrations reaching 88,000 ng/L. SEAR was
selected for treatment of the source area plume
due to the technology's ability to enhance solubility
of residual DNAPL through micellar solubilization
and/or to mobilize entrapped organic liquid through
reductions in interfacial tensions. Phase I of the
demonstration's SEAR component was designed
to characterize the DNAPL source region to
evaluate and select surfactant formulations that
would promote solubilization and/or mobilization
of residual-phase contaminants, and to develop
site-specific performance models for the selected
surfactant formulations.
The demonstration confirmed the presence of
residual DNAPL at approximately 11 feet below
the water table and at a depth of approximately 24
feet bgs, just above the clay confining layer.
Estimates of the total PCE volume in the source
area range from 5 to 50 gallons. Due to the absence
of DNAPL pools, surfactant-enhanced
solubilization rather than mobilization was used
in a pilot testing of SEAR. "Tween 80" was selected
as the target surfactant based on the results of
micellar solubilization experiments, measurement
of interfacial tension between the organic liquid
and surfactant solutions, sorption studies, and
experiments in small-scale two-dimensional sand
tanks. Ground-water models were developed to
predict the fate and transport of PCE and Tween
80 and to design the pilot-test flow scheme.
In the pilot test, surfactant was delivered to the
subsurface over a 10-day period. Extracted ground
water was treated using air stripping and vapor-
phase carbon and then discharged to a publicly-
owned treatment facility. Ground-water data
indicated that PCE concentrations in the source
zone were reduced by two orders of magnitude
[continued on page 6]
Contact Us
Technology Ne\vs and Trends
is on the NET!
View, download, subscribe, and
unsubscribe at:
http://www.epa.gov/tio
http://cluin.org
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
Ariel Rios Building
1200 Pennsylvania Ave, NW
Washington, DC 20460
Phone:703-603-7199
Fax:703-603-9135
-------
Solid Waste and
Emergency Response
(5102G)
------- |