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A newsletter about soil, sediment, and ground-water characterization and remediation technologies
February 2004
Issue 10
Steam Injection Combined with Electrical Resistance Heating at
the Young-Rainey STAR Center
The U.S. Department of Energy (DOE)
completed the first phase of a full-scale
remediation project this past fall to remove non-
aqueous phase liquid (NAPL) at a comer of the
Young-Rainey STAR Center (formerly the Pinellas
Plant) in Largo, FL. A combination of steam
injection and electrical resistive heating was used
in an area covering 10,000 ft2 and extending to a
depth of 35 ft. Final analysis of the project
indicates considerably higher success than
anticipated, with all cleanup targets for both soil
and ground water being met.
NAPL containing principally trichloroethene
(TCE) and dichloroethene (DCE) was discovered
at the STAR Center in 1998. Field investigations
revealed an estimated mass of 5,500 Ibs of NAPL
and volatile organic compounds within the target
area. Concentrations of TCE and DCE were as
high as 360 mg/L and 450 mg/L, respectively.
Cleanup goals for TCE were set at 20.4 mg/kg in
soil and 11 mg/L in ground water. DCE cleanup
goals were set at 71 mg/kg in soil and 50 mg/L in
ground water.
The site is located in a swampy area with silty
clay and sandy silt overlaying a clay aquitard
30 ft below ground surface. Dense NAPL pools
were identified directly above the aquitard (Figure 1),
and were suspected to exist atop the sandy silt
layer within the alluvium. Previous research
indicated that contaminant concentrations were
too high to use bioremediation, but that
conditions favored using thermal technologies
to remediate both soil and ground water.
Figure 1: Steam was injected directly through
alluvial deposits to reach NAPL pools 30 feet
below ground surface.
Construction of the treatment systems
began in May 2002 with the installation of
21 steam injection wells placed at 20-ft
intervals along the perimeter of the
treatment area. Anetwork of 28 ground water
extraction wells with 20-ft screens was
installed in the center. To provide additional
heat to the underlying confining area, 30
electrodes spaced at 20-ft intervals were
installed on the confining layer and an
additional 21 electrodes were installed in
steam injection wells within the treatment
zone.
Contents
Steam Injection
Combined with Electrical
Resistance Heating at
the Young-Rainey
STAR Center page 1
Biological PRB Used for
Perchlorate Degradation
in Ground Water page 2
Integrated Methods
for Characterizing a
Fractured-Rock Aquifer page 3
Prior to the commencement of steam
injection, soil around the perimeter of the
treatment area and the aquitard itself were
heated to a temperature of 160°F using five
400-kW power generators to pass electrical
current through the soil. Steam generated
by two 6-million-BTU boilers was
distributed on a pulsed basis through the
injection wells at rates of 100-5,000 Ibs/hr.
The combined technologies converted
contaminants to vapor that could move
more readily through the soil. The resulting
steam front pushed vapors toward the
central network of extraction wells for
eventual removal and treatment at an
existing above-ground facility. Treatment
of the extracted vapor with regenerative
granular activated carbon was required
prior to atmospheric discharge.
[continued on page 2]
ground surface
surficial aquifer sil
and fine sands
DNAPL
/A
clay lens
clay layer
zone of
vaporized
contaminants
Recycled/Recyclable
Printed with Soy/Catwla Ink on paper that
contains at least 50% recycled fiber
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[continued from page 1]
After four and a half months of operation,
preliminary sampling indicated that the target
cleanup levels for both soil and ground
water had been met. The systems were shut
down at that point and allowed to cool for
six months. Confirmatory sample analysis
conducted six months after operations had
stopped showed that TCE and DCE
concentrations decreased approximately
99% in ground water and soil. Only 4 of more
than 400 samples revealed contaminant
concentrations exceeding their maximum
contaminant levels. Sample analysis also
showed that thermal treatment had not
increased movement of NAPL to outlying
areas.
The total project cost (including design,
construction, operations, demobilization, and
preparation of the final report) was
approximately $3.8 million. DOE's complete
project report, Northeast Site Area A Final
Report, is available at http://www.gjo.doe.gov.
EHie to the success of the first phase of NAPL
removal, DOE now is planning to apply the
combined technologies at a 1-acre area
nearby. Construction of the second thermal
system is expected to begin in July 2004,
with operations scheduled to begin in July
2005.
Contributed by David Ingle, DOE Office
of Legacy Management/LM-50 (727-541-
8943 or David.Insle(a)sio. doe. eov)
Biological PRB Used for Perchlorate Degradation in Ground Water
Ihe U.S. Navy is evaluating performance
of a full-scale, in-situ permeable reactive
barrier (PRB) constructed in 2002 at the Naval
Weapons Industrial Reserve Plant McGregor
(NWIRP McGregor) to biologically degrade
perchlorate plumes in ground water. Project
monitoring indicates that the perchlorate
concentration consistently decreases to a
non-detect level in ground water that has
passed through the PRB system. Based on
this success, the U.S. Navy anticipates
implementing biological PRB systems over
the next two years at additional areas of the
installation.
The 9,700-acre NWIRP McGregor is located
in an agricultural region approximately 20
miles southwest of Waco, TX. Until the
facility closed in 1995, the site was used to
manufacture and test rocket motor propulsion
systems. Operations involved the use of
ammonium perchlorate, which is highly
soluble in water and disassociates readily
into ammonia gas and perchlorate ion (C1O4~)
upon contact with water. Investigations
conducted at that time revealed perchlorate
concentrations in ground water exceeding
91,000 ppb. The contaminant plumes are
located primarily in the upper portions of an
unconfined 5- to 35-ft-thick bedrock aquifer
exhibiting decreased (limestone) fracturing
and weathering with increased depth.
Ground water in this region seasonally varies
from depths of 2-10 ft below ground surface,
with a flow velocity ranging from 0.13 to 3.0
ft/day.
An in-situ pilot study was conducted in early
2002 to evaluate efficacy of a biological PRB
in treating perchlorate at one of the NWIRP
McGregor source areas. The pilot system
consisted of five 10- to 15-ft-deep trenches of
lengths of 75-100 ft and widths of 18-24 in.
Earlier testing indicated that both vertical and
horizontal migration of the amendments would
occur.
The trenches were filled with a mixture of
gravel and carbon material (wood chips) in a
7:1 ratio. Microbial consumption rates of
various forms of wood chips were tested:
alone, with the addition of acetate, and soaked
with soybean oil or a soybean oil/mushroom
compost mixture. The addition of carbon
sources acting as electron donors changed
ground-water conditions from aerobic to
anaerobic. Through this process, indigenous
bacteria were enabled to use perchlorate (ion)
as respiratory oxygen until it was depleted
and only (non-toxic) chloride remained.
Perchlorate concentrations in ground water
entering the pilot trenches were 700-800 ppb
prior to treatment, while ground water exiting
the trenches contained concentrations below
the laboratory detection limit (0.43 ppb).
Exiting ground water also had high total
organic content and low oxygen/reduction
potential (ORP), which indicated microbial
activity was occurring within the trenches.
Sample analysis of exiting ground water
showed that the concentration of TCE, a co-
contaminant, also decreased from 300 ppb to
a non-detect level as a result of treatment.
Seasonal rainfall variations influencing
ground-water flow were not found to affect
trench performance adversely. Sample
analysis of ground water entering and exiting
the trenches will continue on a quarterly
basis in order to acquire long-term
performance data.
The unexpected presence of floating edible
oil after an oil pump test required the PRB
design to be modified to include stand-alone
sampling ports, which helped to avoid oil
during sampling. The pilot study indicated
that the highest rate of perchlorate
degradation was achieved in trenches where
oil-saturated wood chips were added, with
or without mushroom compost. Monitoring
data collected over the year-long pilot study
test suggest that carbon rejuvenation of a
full trench (using a soluble carbon source
such as vegetable oil or molasses) should
occur in a single event on an annual or
biennial basis. The onsite pilot trenches were
designed with internal piping systems that
will allow for injection of liquid carbon when
ORP data indicate that trench rejuvenation
is necessary. Rejuvenation will occur until
perchlorate concentrations drop below the
state's drinking water standard of 4 ppb. EHie
to the extent of ground-water contamination
(7 plumes encompassing 2,800 acres),
reaching this standard may take 30 years.
Based on early results of the pilot study, a
full-scale PRB system employing 3,500 linear
feet of trenches was constructed in late 2002
[continued on page 3]
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[continued from page 2]
to address a perchlorate plume migrating
off site. To eliminate the potential for water
to seep to the surface under high ground-
water conditions, segments of trenches were
installed in a pattern alternating with non-
trenched segments along the plume
pathway. Piezometric contours were used
to select the length of each trench, which
range from 100 to 750 ft long. Seven trench
segments were installed on 1,000-ft centers
in a gallery fashion (Figure 2), and each was
backfilled with a mixture of gravel (70%),
mushroom compost (20%), and soybean oil-
soaked woodchips (10%). Approximately
4,200 tons of material were used to backfill
the trenches.
Ground water entering the trench located
closest to the source area contains an average
perchlorate concentration of 13,000 ppb.
Upon exiting the trench, however, the
concentration decreases to a level below the
detection limit. System monitoring over the
first three months of PRB operation indicated
that the treatment envelope of a single trench
had traveled a distance of 400 ft
downgradient, where it reduced the
perchlorate concentration in a monitoring well
by 99% from a pre-treatment concentration
of 1,000 ppb.
Offsite trenches were designed to remediate
the contaminant plume in 15 years or less,
thereby avoiding the need for institutional
controls. Due to a projected PRB lifespan of
8-15 years, replacement of the solid organic
material (woodchips and mushroom
compost) may be required. The cost of
constructing and operating the trenches in
both scales of operation is approximately
$150/linear foot. Overall, the Navy estimates
a capital cost avoidance of $3 million as a
result of using this technology instead of
conventional ex-situ options such as ground
water pumping and treatment.
Contributed by Mark Craig, U.S. Navy/
NAVFAC South Division (843-820-5517
or craigm(Sigfdsouth.navfac.navy.mil) and
Alan Jacobs, EnSafe (901-372-7962 or
aiacobs(a)ensafe.com)
Integrated Methods for Characterizing a Fractured-Rock Aquifer
In 1990, the U.S. Geological Survey (USGS)
began developing and testing field
techniques and interpretive methods to
characterize ground-water flow and chemical
migration in the fractured-rock aquifer of the
Mirror Lake watershed in central New
Hampshire. Investigation results showed
that data from multiple hydrogeologic
disciplines were required to identify
fractures, their hydraulic significance, and
their hydraulic connectivity. An integrated
approach using data from geologic and
fracture mapping, surface and borehole
geophysics, ground water modeling,
hydraulic testing, and geochemical and
isotopic methods is needed to develop a
defensible site conceptual ground water
model for a fractured-rock aquifer.
In 1998, the University of Connecticut
assembled a multidisciplinary team
including USGS researchers to use this
approach in characterizing the nature and
extent of contamination in soil, ground water,
and surface water in the area of a landfill and
former chemical-waste disposal pits in Storrs,
CT Sampling of domestic wells in the mid-1980s
had indicated the presence of volatile organic
compounds in area ground water. To
characterize the fractured-rock aquifer and help
assess remediation alternatives, the team
developed a conceptual model using integrated
multidisciplinary data.
> Resistivity soundings were used to define
the orientation of geologic features. Results
indicated a dominant bedrock fracture strike
direction consistent with local geologic
maps. Additional soundings verified by
aerial photography helped to interpret the
orientation of waste disposal cells in the
landfill.
> Two-dimensional (2-D) resistivity profiles
indicated a landfill thickness of 10-15 meters.
> Conductivity profiles combined with 2-D
resistivity surveys detected conductive
anomalies interpreted to be leachate plumes
near two surface-water discharge areas: (1)
a shallow plume dissipating about 45
meters north of the landfill, and (2) a
deeper plume existing in overburden and
shallow bedrock along an intermittent
drainage area southwest of the landfill.
Eleven bedrock boreholes were installed at
35- to 90-meter depths to further character-
ize anomalies detected with surface-
geophysical methods and to obtain hydrau-
lic data, ground-water samples, and frac-
ture characteristics.
Heat-pulse flowmeter logging collected
under ambient and pumped conditions iden-
tified several transmissive fractures and
ambient vertical flow between some of the
fractures. These results indicate a hydrau-
lic potential for cross contamination within
boreholes open to multiple fractures.
A multifunctional bedrock aquifer trans-
portable testing tool (BAT3) (Figure 3),
recently developed by the USGS, was used
temporarily to isolate sections of the bore-
hole to collect discrete-interval ground-
water samples, identify hydraulic head as
[continued on page 4]
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Technology
News and Trends
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-04-001
February 2004
Issue No. 10
United States
Environmental Protection Agency
National Service Center for Environmental Publications
P.O. Box 42419
Cincinnati, OH 45242
First Class Mail
Postage and Fees Paid
EPA
Permit No. G-35
Official Business
Penalty for Private Use $300
[continued from page 3]
a function of depth, and conduct single-
hole hydraulic tests that helped identify hy-
draulic properties of fractures.
> Discrete-zone monitoring systems were
installed soon after well drilling and bore-
hole logging to provide a method for
long-term discrete-interval sampling and
to determine hydraulic head, connections
between transmissive zones within frac-
tured rock, and the extent of connection
between fractured rock and surficial aqui-
fers. These systems prevented cross con-
tamination between borehole fractures.
Hydrogeologic characterization of the Storrs
landfill area demonstrates the importance of a
multidisciplinary approach for characterizing
contamination in a fractured-rock aquifer. The
project also highlights the need for collect-
ing discrete-interval hydraulic-head and
water-chemistry data, which were used to
produce a conceptual ground-water model
for designing final site remediation.
Figure 3: The multifunction BAT3 contains two
inflatable packers for isolating the test interval,
pump, and injection ports, and three pressure
transducers for monitoring fluid pressure in,
above, and below the test interval.
Additional information on approaches for in-
tegrating these and other characterization
tools is available from the USGS Toxic Sub-
stances Hydrology Program web site at http://
toxics.usgs.gov, and the USGS Office of
Ground Water, Branch of Geophysics web site
at http://water.usgs.gov/ogw/bgas/.
Contributed by Carole Johnson, USGS (860-
487-7402 or cjohnson&usgs.gov), P.P. Haeni,
USGS Emeritus, and Allen Shapiro, USGS
(703-648-5884 or ashapiro(a)usgs.gov)
surface borehole
casing
bottom
packer
(not to scale)
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