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Ground Water Currents
^ter Treatment
CONTENTS
Permanganate
Chemical Oxidation
Used in Fractured
Bedrock Pg. 1
Performance of Dual
Reactive Walls
Monitored at
Watervliet Arsenal Pg. 2
Phytoremediation
Field Demonstration
Conducted at Naval
Air Station Pg. 3
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Permanganate Chemical
Oxldadon Used In
Fractured Bedrock
by Dan Morgan, NASA, Dan
Bryant, Geo-Cleanse International,
and Kimberly Coleman, Earth Tech
The U.S. National Aeronautical and
Space Administration (NASA) recently
conducted a treatability study of in situ
chemical oxidation (ISCO) using
permanganate to destroy trichloroethene
(TCE) in a fractured bedrock aquifer.
The study took place at NASA's Dry den
Flight Research Center (Dryden) on
Edwards Air Force Base (AFB), which is
located north of Los Angeles, CA.
Project researchers believe this study is
the first to demonstrate the effectiveness
of permanganate ISCO in fractured
bedrock.
Located on approximately 800 acres
bordering Rogers Dry Lake, Dryden
comprises laboratory, service, and
storage buildings that support aeronauti-
cal research operations. The treatability
study was conducted in a 100- by
50-foot area of "Site N7," at a treatment
depth reaching 100 feet. This area
contains approximately 5 feet of silty
sand overlaying granitic bedrock. The
first 10 feet of bedrock is moderately
weathered, with fracture dips of 60-90
degrees and apertures of 0.08-0.77
inches. Ground water, which is at a
depth of approximately 10 feet, is
alkaline and slightly saline. Volatile
organic compounds (VOCs) such as TCE
and its natural degradation product, cis-
1,2-dichloroethene (DCE), were detected
at this area in maximum concentrations
of 7,000 //g/L and 790 //g/L,
respectively.
Field operations involved the use of six
existing screened wells and two newly
constructed boreholes for injection. At
each of the 8 locations, approximately
1,000 gallons of a 1.8-percent potassium
permanganate (KMnO4) solution were
injected into the bedrock. A 40:1 ratio
of KMnO4 to VOC was selected to
ensure complete delivery and oxidation
of the solution. Injection rates ranged
from 0.25 to 2 gallons per minute, at
pressures ranging from 5 to 70 pounds
per square inch (psi). In addition, air
was introduced to the system at pressures
up to 70 psi and flow rates up to 4 cubic
feet per minute.
Field injections were conducted for four
days in August 2000. A total of 7,450
gallons of the KMnO4 solution, equiva-
lent to 1,102 pounds of solid KMnO4,
was injected. Offgas monitoring for
carbon dioxide, oxygen, volatile organ-
ics, and lower explosive limit was
discontinued after initial data indicated
they were not produced in measurable
quantities. Daily ground-water samples
were analyzed to determine manganese,
chloride, pH, and permanganate levels,
but only permanganate concentrations
were found to be useful indicators of the
oxidation rate or reagent distribution.
VOC and metals analyses occurred
during packer testing, to evaluate the
vertical distribution of VOCs; prior to
injection, to establish baseline condi-
tions; and in three post-injection rounds
(at 5, 30, and 60 days) to evaluate
performance of the technology. Moni-
toring locations were selected based on
the known release location, pre-existing
ground-water monitoring wells, and
major fracture locations identified by a
three-dimensional seismic survey.
Destruction of TCE and DCE in the
treatment zone was complete after 60
days, and concentrations remain below
detection limits (Figure 1). Following
injection, however, acetone at concentra-
tions reaching 3,000 //g/L was detected,
which suggested it formed as an oxida-
tion product. Although acetone has
attenuated to concentrations below 460
//g/L, researchers noted that it generally
has not been reported as a permanganate
oxidation product of chlorinated ethenes,
and was not detected in pre-injection,
bench-scale studies at Edwards AFB.
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[continuedfrom page 1]
Additionally, concentrations of most
metals (possibily colloidal materials
associated with the permanganate or
liberated from the formation) were
elevated during and following the period
of injections.
With the exception of chromium, metal
concentrations have fallen to pre-injection
levels. Since the injection event, chro-
mium concentrations have continued to
decrease due to metal precipitation as the
ground water returns to alkaline condi-
tions.
Permanganate concentrations in nearby
wells and field observations of ground-
water mounding near the injection wells
were used to estimate the radius of
influence (ROI) for the injection process.
In some cases, the achieved ROI was
better than the expected ROI of 30 feet.
Data indicated a horizontal ROI of 30-55
feet and a vertical ROI of at least 28 feet.
Implementation costs for permanganate
ISCO at Site N7 are estimated at $72,000
(excluding project management, well
installation, and reporting). No further
treatment at Site N7 is anticipated as post-
injection chlorinated solvent
concentrations in targeted "hot spots"
have remained below laboratory detection
limits. Based on these study results,
permanganate ISCO will be considered at
other sites to remove chlorinated sol-
vents dissolved in the fractured bedrock
aquifer at Edwards AFB. For more
information, contact Dan Morgan (NASA
Dry den) at 661-276-3 976 or
dan.morgan@dfrc.nasa.gov, Dan Bryant
(Geo-Cleanse International) at 908-206-
1250 ordbryant@geocleanse.com, or
Kimberly Coleman (Earth Tech) at
916-971-8705 orkimberly_coleman@
earthtech.com.
Performance of Dual
Reactive Walls Monitored
at Watervliet Arsenal
by Steve Wood and Curtis
Heckelman, U.S. Army Corps of
Engineers, and Kenneth Goldstein,
Malcom Pirnie, Inc.
In 1998, the U.S. Army Corps of Engineers
installed an in situ permeable reactive wall
system at the Watervliet Arsenal (WVA)
near Albany, NY, to remediate ground
water contaminated with chlorinated
hydrocarbons (CHCs). Monitoring data
collected over the past three years
indicates that CHC concentrations remain
below detection levels and/or regulatory
standards within and upon exiting the
Figure 1: Pre- and Post-Injection VOC Concentrations at site N7
8000
7000
6000 -
~ 5000
Injection Period (August 22-25)
- Pre-lnjection Sampling *'*'* Post-lnjectio
5/12/1999 8/12/1999 11/12/1999 2/12/2000 5/12/2000 8/12/2000 11/12/2000 2/12/2001
-TCE
DCE
Time
reactive walls. In addition, researchers
estimate that a cost savings of over $3
million in operation and maintenance costs
will be realized over the 30-year life cycle of
the project, when compared to the conven-
tional alternative of a pump and treat
system.
WVA contains a 14-acre unit known as the
Siberia Area used since the early 1940s for
the storage, handling, and shipping of raw
materials and hazardous wastes or sub-
stances. One area of the site was used to
burn combustible material such as scrap
lumber, liquid wastes, and various solid
wastes. The site contains three saturated,
unconsolidated deposits overlying shale
bedrock with an average porosity of 3-4
percent. These deposits comprise an upper
4-foot fill unit, a 2- to 6-foot unit of clayey
silt extending to weathered bedrock, and a
lower unit of fluvial sand and gravel.
Ground water in this area is at a depth of
approximately 3-6 feet below ground
surface.
During site investigations, a wide range of
CHCs in high concentrations was found
migrating along the shallow ground-water
flow paths in the overburden and weath-
ered bedrock. Contaminants of concern
included trichloroethylene (1,500//g/L), cis-
1,2-dichloroethene (4,200 //g/L),
tetrachloroethene (1,100//g/L), and vinyl
chloride (1,700 //g/L). The contaminant
plume is estimated to be approximately 450
feet long and 200 feet wide.
Bench-scale testing indicated that, at a flow
velocity of 0.15 feet per day and a required
residence time of 2.5 days for CHC degrada-
tion, optimal treatment would require a
0.82-foot-thick reactive wall consisting of
100 percent reactive iron filings. In addi-
tion, extensive ground-water modeling
indicated that a continuous reactive wall,
rather than a funnel and gate design, would
prevent the escape of contaminated ground
water under the wall.
Design planning of the system found that
conventional excavation or trenching with
[continued on page 3]
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[continuedfrom page 2]
backfilling would result in excavation of
2.5-foot trenches, which were wider than
the 0.82 feet required. To reduce the
expense of placing extra reactive iron in the
walls, iron filings were mixed with clean
washed sand in a (1:1) ratio sufficient to
maintain the required amount of iron.
Ratios of the iron/sand mixture were
controlled at an offsite cement mixing
batch plant and sampled periodically
throughout the construction process.
The reactive system installed at WVA
consists of a 200-foot-long reactive wall
adjacent to the source area. A second 83-
foot-long wall is positioned 175 feet
downgradient of the first and approxi-
mately 300 feet from the source area. Each
wall is set into the top of competent
bedrock at a depth of 12 feet below ground
surface. Inside each wall, wells at three
locations are used to monitor chemical
reactions and the production of precipi-
tates. The complete system contains a
total of 326,360 pounds of sand and
330,940 pounds of reactive iron. Construc-
tion costs for the reactive walls totaled
approximately $280,000, which was
estimated to be one-third of the cost for
establishing a conventional pump and
treat system for this site.
Semi-annual hydraulic monitoring over the
past three years shows that the ground-
water flow is directed through both
reactive walls without any short-circuit-
ing, and that no head buildup exists on
the upgradient side of the walls. Analyti-
cal monitoring shows that the zero-valent
iron continues to reductively
dehalogenate the CHCs through the
natural corrosion process into non-toxic
chloride ions and ethenes/ethanes. The
most recent analytical results, which were
obtained in May 2001, indicate that
ground water exiting the walls contain
concentrations below maximum contami-
nant levels for all targeted CHCs (Figure
2). WVA workers also have found that
implementation of this technology has not
disrupted ongoing activities at the Siberia
Area, which involve primarily shipping of
equipment and supplies for the manufac-
ture of cannons.
Currently, WVA researchers are planning
the installation of diffusion bag samplers
in the reactive wall wells to improve CHC
sampling and analysis. For more
information, contact Stephen Wood (U.S.
Army Corps of Engineers) at
410-962-3506 or stephen.c.wood@
nab02.usace.army.mil, or Kenneth
Goldstein (Malcolm Pirnie, Inc.) at
914-641-2615orkgoldstein@pirnie.com.
Figure 2: Concentrations of Chlorinated VOCs as Ground Water
Passes through Reactive Wall
Ground-Water Flow Direction
reactive wal!
Phytoremediation Field
Demonstration Conducted at
Naval Air Station
by Steven Rock, U.S. EPA/National
Risk Management Research
Laboratory, and Gregory Harvey,
U.S. Air Force
The U.S. Air Force (USAF) initiated a
field demonstration in 1996 involving the
use of eastern cottonwood trees to
remediate shallow ground water contami-
nated with trichloroethene (TCE) at the
Naval Air Station (NAS) near Fort Worth,
TX. Monitoring data indicate that TCE
concentrations during the first three years
after planting remained nearly constant
due to a continuous influx of contaminated
ground water. The mass flux of TCE out of
the site, however, decreased by 11 percent
due to transpiration of contaminated water
directly from the aquifer. These conditions
resulted in an overall decrease in contami-
nated ground water flowing from the site.
By the end of the fifth growing season, in
situ biodegration of the TCE had occurred
locally beneath and immediately
downgradient of the trees.
The demonstration is taking place in a
1-acre area of the NAS, which was formerly
known as Carswell Air Force Base. Earlier
site investigations indicated a TCE plume
in the shallow alluvial aquifer located 6-11
feet below ground surface. This extensive
ground-water plume contains TCE concen-
trations within a range of low parts per
billion. The sand and silt aquifer receives
appoximately two inches per year in
recharge from precipitation.
Phytoremediation was selected at the NAS
due to its low cost, minimal disruption, and
general aesthetics. The tree plantings
resemble a well-tended park, and blend
seamlessly with the adjacent golf course
(Figure 3). The technology is expected to
serve as a natural pump and treat system
[continued on page 4]
3
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[continuedfrom page 3]
involving any or all of three mechanisms:
• Stimulation of microbial activity in the
rhizosphere and enhanced in situ
biodegration of contaminants as a
result of root dieback and exudation;
• Metabolism or mineralization of
contaminants within tree tissues as a
result of root uptake of contaminated
water; and
• Transpiration of water by tree leaves,
with non-detect levels of contaminant
released to the air.
Approximately 700 eastern cottonwood
trees were planted at the NAS during the
spring in rows 10 feet apart at a spacing
of 4 and 8 feet. Irrigation of the trees was
conducted during the first two years of
growth. TCE concentrations in the
ground water, rhizosphere soil, and tree
tissues are monitored on a semi-annual
basis, as are ground-water levels and tree
sap flow.
At full-system performance, the
reduction in TCE mass
flux due to transpiration
directly from the aquifer
has been modeled at 20-
30 percent. The
reduction in the TCE
mass flux due to in situ
biodegration has yet to
be determined.
Research and Development under its
Superfund Innovative Technology (SITE)
Program and the U. S. Department of
Defense under its Environmental Security
Technology Certification Program
(ESTCP), will be published later this year.
The USAF anticipates full-scale imple-
mentation of phytoremediation at the
NAS through the planting of additional
trees during 2003. For more information,
contact Steven Rock (National Risk
Management Research Laboratory) at 513 -
569-7149 or rock.steven@epa.gov, or
Greg Harvey (USAF) at 937-255-7716 x302
or gregory.harvey@wpafb.af.mil.
Current results of the
demonstration, which
was funded jointly by the
U.S. EPA Office of
Figure 3: Tree Plantings at the NAS
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