United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-01-006
July 2001
Issue No. 40
vvEPA Ground Water Currents
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CONTENTS
Interagency
Demonstrations on
DNAPL Conducted at
Cape Canaveral Pg. 1
Enhanced Reductive
Dechlorination Pilot
Study Completed Pg. 3
ImagingPemieability
Structure through
Acoustic Crosswell
Tomography Pg. 5
About this Issue
This issue highlightsfieldtesting
of innovative technologies for the
cleanup and characterization of
ground water contaminated with
DNAPL. The field tests range
from a large side-by-side
demonstration of technnologies
at Cape Canaveral, FL, to a
smaller pilot study in Ogallala,
NE. In addition, the use of
acoustic crosswell tomography
to produce permeability images
of the subsurface, which can aid
in locatingDNAPL, is highlighted
in this issue.
Interagency
Demonstrations on
DNAPL Conducted at
Cape Canaveral
by Laymon Gray, Florida State
University
The Interagency Dense Non Aqueous
Phase Liquid (DNAPL) Consortium
(IDC), a strategic alliance of several
government agencies, was initiated in
1997. The IDC was formalized in
1999 through the signing of a memo-
randum of agreement between the
participating agencies with the
mission of demonstrating innovative
DNAPL remediation and monitoring
systems. Members of this Consor-
tium include the U.S. Department of
Energy (DOE)/Office of Science and
Technology, U.S. EPA/National Risk
Management Research Laboratory,
National Aeronautics and Space
Administration (NASA), U.S. Navy
(NAVFAC), and U.S. Air Force/45th
Space Wing. As part of this effort,
the IDC is evaluating and comparing
the cost and performance of three
innovative DNAPL remediation
technologies at a former Cape
Canaveral, FL, launch site.
DNAPLs are a common cause of soil
and ground-water contamination at
DOE, NASA, and U.S. Department
of Defense sites. At the Cape
Canaveral site, the primary contami-
nant of concern is trichloroethylene
(TCE), a solvent historically used for
flushing rocket engines and the
cleaning or degreasing of metal parts,
electronics, and heavy machinery.
An early snapshot of two of the
technologies demonstrated thus far
indicates that favorable alternatives
exist for DNAPL remediation.
In side-by-side plots, this project
demonstrates three innovative
DNAPL remediation technologies:
chemical oxidation using potassium
permanganate (conducted by IT
Corporation), Six Phase Heating™
(conducted by Current Environmental
Solutions), and co-air steam injection
(conducted by Integrated Water
Resources, Inc.). Testing in a side-
by-side setting allows the Consortium
to evaluate the cost and performance
of each technology under essentially
identical site conditions. Each test
cell used in this evaluation is approxi-
mately 50 by 75 feet in size, with a
total depth extending to the underlying
aquitard at 45 feet. Data gathered
during the demonstrations will be
used to expedite regulatory accep-
tance and use of the technologies at
other federal and private sites.
[continued on page 2]
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[continued from page 1]
In Situ Chemical Oxidation
with Potassium
Permanganate
This in situ treatment technology uses
potassium permanganate (KMnO4) to
destroy DNAPL through an oxidative
reaction. The KMnO4 reacts with the
carbon-carbon double bonds found in
chloroethenes to produce primarily
carbon dioxide, chloride ions, and
manganese dioxide as byproducts.
The oxidant was delivered using an
array of injection wells with a lance
approach, thereby allowing precise
delivery to target depths within the
treatment area. In September 1999,
the first of three injection phases was
initiated and the third (final) phase
was completed in March 2000. Based
on cores collected before and after
implementation of this technology, an
overall 82 percent reduction of TCE
was achieved, with an 84 percent
reduction of residual DNAPL
saturation. Preliminary results are
shown in Figure 1.
During operation of the system, high
injection pressures were encountered.
It was determined that the high
pressure sand filter used to remove
suspended solids from the permanga-
nate solution was clogging, which
resulted in the need for frequent
backwashing of the filter system. To
overcome this problem, the filter was
replaced with a large settling tank that
allowed for uninterrupted delivery of
the oxidant to the subsurface. In
addition, modifications were made to
the permanganate storage system.
The original design used an automated
hopper system. This system proved
to be ineffective, however, due to high
moisture conditions at the site, which
resulted in frequent maintenance and
system shutdowns. The hopper
system was replaced with portable
bins that solved the humidity-related
issues and resulted in a more efficient
operation.
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Technology
In Situ Thermal Remediation
with Six Phase Heating™
Six Phase Heating™ (SPH) uses an in
situ electrical resistance heating tech-
nique with the potential to remove
DNAPL by heating the subsurface
sufficiently to vaporize the DNAPL.
This technology can be applied to
contamination in both the vadose and
saturated zones. SPH typically heats
the subsurface by using a hexagonal
array of electrodes that are driven into
the ground to the depth of the aquitard.
The steam and chlorinated volatile
organic compound vapors rise to the
vadose zone, where they are recovered
through vertical and/or horizontal vapor
extraction wells. These vapors then are
condensed, and the effluent air stream
is discharged after polishing with
activated carbon.
The SPH technology demonstration
began in August 1999 and continued
intermittently through July 2000. Based
on cores collected before and after
implementation, a 92 percent reduction
of TCE was achieved, with a 96
percent reduction of residual DNAPL
saturation. Preliminary results are
shown in Figure 1.
It was discovered during operations that
the system's monitoring wells were
becoming pressurized, thus creating a
significant health and safety concern for
on-site personnel. To overcome this
problem, the well heads were retrofitted
with pressure gauges and off-gas
pressure relief valves that were piped to
the soil vapor extraction system. This
modification allowed for the wells to be
safely depressurized and ground-water
samples to be safely collected without
turning off the system.
Based on the heating profile observed
[continued on page 3]
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[continued from page 2]
during system operation, it was deter-
mined that the original electrode design
was ineffective. As a result, the
electrodes were redesigned and the
predicted heating profiles were
achieved. It was found that the
electrode design for this technology is
critical, and will vary depending on
site-specific conditions. Continued
research and development should
enhance the performance of this
system and its application at others
sites, and potentially reduce electricity
costs for SPH.
In Situ Thermal Remediation
with Steam and Co-Air
Injection
An alternative thermal treatment
technology uses steam injection and
extraction to remove DNAPL from the
subsurface. DNAPLs such as TCE
with a boiling point below that of water
are removed by a combination of
volatilization, steam stripping, and
oxidation. Introduction of heat to the
subsurface produces a wide variety of
physical and chemical effects that are
beneficial for the breakdown or
removal of DNAPL contaminants in
both saturated and unsaturated subsur-
face materials, including:
• Increased mobility, volatility, and
diffusion rates
• Distillation, and
• Hydrous pyrolysis and oxidation.
The steam stripping system uses
boilers to generate steam that is
pumped into injection wells within the
treatment zone. The resulting steam
front volatilizes and mobilizes the
contaminants as it moves toward a
network of vertical and/or horizontal
vapor extraction wells.
The thermal treatment system in this
demonstration was designed to include
the co-injection of air. This injected
air combines with steam to create a
broader thermal front containing a
larger volume of air saturated with
contaminant, therefore inhibiting
condensation of the contaminant and
reformation of NAPL. An extended
thermal front is produced, creating a
larger volume within which the con-
taminants can be held in vapor phase.
The air/steam mixture reduces injec-
tion temperatures in the subsurface,
and the co-injected air simultaneously
increases the carrying capacity of
contaminant in vapor. The optimal
ratio of air to steam is based on the
expected concentration of contaminant
and its known vapor pressure. Imple-
mentation of this technology is
scheduled to begin in June 2001.
Following completion of this thermal
treatment technology demonstration,
final cost and performance evaluations
will be completed for all three tech-
nologies. In addition to evaluating the
contaminant removal efficiencies, the
IDC is evaluating the effects of these
technologies on indigenous microbial
communities and the long-term im-
pacts of application.
Several innovative sensors for site
characterization also have been
deployed at the Cape Canaveral site,
using DOE's Site Characterization and
Analysis Penetrometer System
(SCAPS). These sensors are used for
lithologic mapping, in situ vadose zone
and saturated zone sampling, in situ
hydraulic conductivity measurements,
and the determination of subsurface
DNAPL locations. Detailed reports
concerning each aspect of the project
can be found at the IDC's Web site,
www.getf.org/dnaplguest. For more
information, contact Laymon Gray
(Florida State University, Institute for
International Cooperative Environmen-
tal Research) at 850-644-5524 or
e-mail lgray@ispa.fsu.edu.
Enhanced Reductive
Dechlorination Pilot
Study Completed
by VickiMurt, U.S. Corps of
Engineers (formerly with Nebraska
Department of Environmental
Quality)
The Nebraska Department of Envi-
ronmental Quality recently completed
a pilot study on the potential for
achieving reductive dechlorination of
perchloroethylene (PCE) under
"geochemically challenged" conditions
of the Ogallala Ground Water Con-
tamination (Superfund) Site in
Ogallala, NE. Treatment of PCE-
contaminated ground water in the pilot
study consisted of substrate injection
into the plume downgradient of a dry
cleaning facility over a period of one
year. This project required significant
changes to the geochemical environ-
ment of the in situ treatment cell in
order to promote sufficient microbial
growth under anaerobic conditions.
Initial geochemical conditions indicated
that the shallow alluvial aquifer was
highly oxygenated; dissolved oxygen
was measured at 3.9 mg/1, and el-
evated levels of nitrate (11 mg/1) and
sulfate (135 mg/1) also were present.
In addition, limited funding (approxi-
mately $135,000) required completion
of the project without the benefit of a
full-scale microbial analysis. Despite
these challenges, the final pilot study
results indicated the achievement of
appropriate reducing conditions that
[continued on page 4]
3
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supported anaerobes capable of
successfully dechlorinating the PCE.
EPA currently is evaluating the pilot
study to determine whether full-scale
application of this technology will be
implemented.
The Ogallala Ground Water Contami-
nation Site was placed on the NPL in
1994 after five municipal drinking
water wells were found to be affected
by contaminants from multiple
sources, including PCE from a nearby
dry cleaning operation. During earlier
site investigations, the area's shallow,
unconfined alluvial aquifer was found
to contain PCE concentrations ranging
from 0.78 ng/lto 1,400 (ig/1. The
aquifer in the pilot study area consists
of fine- to medium-grained sand
overlying channel deposits of coarse
sands, gravels, and cobbles to a depth
of 26 feet below ground surface. The
Ogallala Aquifer lies beneath this
shallow alluvial aquifer. Depth to
ground water is typically 11 feet, with
seasonal fluctuations of up to 2 feet.
The horizontal gradient is approxi-
mately 0.002 feet/foot and ground
water flows at an average linear
velocity of 3-3.5 feet/day.
The 12- by 3 5-foot in situ treatment
cell was located 800 feet
downgradient of the dry cleaning
facility. The semi-passive extraction/
injection system consisted of one
extraction well, two injection wells,
and six sets of nested monitoring
micro-wells. The extraction/injection
wells were aligned perpendicular to
ground-water flow, with the extrac-
tion well centered between the two
injection wells (Figure 2). During
operation of the system, extracted
ground water was pumped at a rate
of 10-12 gallons/minute through a
closed-loop system to minimize
aeration of the water. The filtered
ground water was amended in-line
with a solution containing 60 percent
food-grade sodium lactate to supply
indigenous microorganisms with a
fermentable organic food source, and
then injected back into the aquifer.
The ground water was recirculated
for 7-8 hours after the lactate addi-
tion until equilibration had been
achieved. Extracted ground water
was monitored for conductivity as an
indicator of the amount of lactate
saturation and degree of equilibration
during the recirculation process.
Figure 2. Schematic Diagram of Injection System
To injection Well
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After the system was shut down, the
substrate solution was transported away
from the injection system under natural
ground-water gradient conditions. This
type of system promoted passive
dispersive mixing that enhanced sub-
strate delivery to the microbes in a
continuous supply as it flowed
downgradient with the contaminated
water. It was found that pulsed injec-
tion of the lactate did not result in
biofouling of the injection well screen
interval. Initially, 40 kg of lactate was
injected every four weeks, but these
rates were increased to 75 kg and then
100 kg every three weeks to sustain the
developing anaerobic microbial popula-
tion as reducing conditions continued to
develop.
Several monitoring strategies were
employed throughout the pilot project.
Field chemistry measurements were
collected using various portable
instruments to measure pH,
conductivity, dissolved oxygen, and
oxidation-reduction potential. During
initial stages, the results of weekly
sampling and analysis for potassium
bromide, a geochemical tracer, and total
organic carbon were used to adjust the
frequency and amount of injected
lactate. Analyses for nitrate and sulfate
were performed periodically to monitor
the development of nitrate and sulfate
reducing conditions. (By the fourth
month, a discernible odor of hydrogen
sulfide was noted in most of the wells
throughout the cell, indicating that
sulfate reduction was occurring).
Methane, ethene, and ethane analyses
also were performed periodically to
determine if methanogenic conditions
were present within the treatment cell,
and whether complete degradation of
the daughter products was occurring.
To monitor the efficiency of the
[continued on page 5]
4
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[continued from page 4]
anaerobes in utilizing the substrate,
additional samples were collected and
transferred to the Idaho National
Engineering and Environmental
Laboratory for analysis of volatile acid
constituents.
Pilot observations found that initial
concentrations of PCE flowing into the
treatment cell may have been too low
to allow for the detection of daughter
products, once sulfate reducing and
mild methanogenic conditions had
developed and the microbes had
become more efficient in lactate
fermentation. After nine months of
operation, a more concentrated slug of
PCE had moved into the treatment cell
area. Analytical results for samples
collected as the slug moved through
the cell indicated that PCE concentra-
tions had decreased from 180 (ig/1 in
the upgradient monitoring well to non-
detect levels in the downgradient
monitoring we 11s. During this time,
both trichloroethylene (TCE) and cis-
1,2-dichloroethylene (DCE) were
detected within the treatment cell, with
TCE decreasing and DCE increasing
in the downgradient direction. Analyti-
cal results for the last round of
samples collected from a monitoring
well located 35 feet downgradient of
the injection system indicated that both
PCE and TCE concentrations had
dropped to non-detect levels, and that
the concentration of c/s-l,2-DCE had
decreased to 14 (ig/1. Non-detection
of vinyl chloride within the treatment
cell area may indicate that degradation
of the daughter products was incom-
plete, or that further degradation of
c/s-l,2-DCE occurred downgradient
of the test cell area.
The "geochemically challenged"
ground-water conditions, coupled with
the relatively high average linear
ground-water velocity, initially
suggested that achieving the
appropriate reducing environment to
support lactate fermentation and PCE
biodegradation would be difficult at
this site, at best. Data suggested that
the indigenous microbial population of
nitrate and sulfate reducers was small,
and that acclimation to the lactate
during the first several months of
operation was slow. Adjustments in
the amount and frequency of lactate
injection were required to overcome
carbon limitations and eliminate the
relatively high concentrations of
inorganic electron acceptors. In
general, it was found that
approximately three months were
required for nitrate-reducing conditions
to develop.
The increased frequency and amount
of lactate injection appeared to have a
pronounced effect four months into
the study, when sulfate-reducing
conditions began to develop. At six
months into the study, methane and
volatile acids were clearly detected,
and the microbial community was
found to be capable of degrading PCE
and TCE. Although vinyl chloride was
not detected, it is possible that
bioaugmentation or a return to aerobic
conditions may be required to com-
plete the degradation process. While
initial geochemical conditions sug-
gested that this technology may not be
feasible at the Ogallala site, the results
of this pilot study suggest otherwise.
For more information, contact Vicki
Murt (U.S. Corps of Engineers) at
816-983-3889 or e-mail
vicki .1 .murt@usace .army.mil.
Imaging Permeability
Structure through
Acoustic Crosswell
Tomography
by Tokuo Yamamoto, Ph.D., Hua
Sun, andJunichi Sakakibara,
University of Miami/Geoacoustics
Laboratory and Paul E.
Mattausch, Collier County,
Florida/Water Department
Researchers at the University of
Miami's Geoacoustics Laboratory
have developed new techniques for
using high-resolution images to track
ground-water movement in shallow
and deep sediments. By analytically
inverting acoustic wave velocity and
attenuation fields that have been
measured through acoustic tomogra-
phy, the permeability, porosity, and
shear strength of a site may be
obtained. Earlier studies have found
that other crosswell methods are
capable of producing porosity, but not
permeability, images. Acoustical
images developed with these new
techniques have shown high correla-
tion with data obtained through
conventional, and more resource-
intensive, pumping methods.
In partnership with Kawasaki Steel
Corporation of Tokyo, Japan, this
technology has been used to
characterize aquifers subjected to
contamination from nearby sources
and by salt water intrusion. Acoustic
tomography can be used to produce
permeability images of a wide range
of geologic materials, including near-
surface sediments, andesite, limestone,
tuff, and shallow water sea-bottom,
and complex contaminant scenarios
such as dense non aqueous phase
liquids.
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[continued from page 5]
Acoustic wave velocity and
attenuation fields typically are
measured by covering the area of
interest between two wells with
acoustic wave fields. These fields are
measured by locating a pieso-electric
source in one well and an array of
hydrophone receivers in another, and
then moving the source and receivers
repeatedly in a vertical fashion. The
sources are activated to generate a
continuous pseudo-random binary
sequence (PRBS) to ensure a
maximum signal-to-noise ratio. Using
various tomography systems capable
of imaging target areas at different
ranges and depths of up to 12,000 feet,
numerous acoustic images at
frequencies of 200 to 30,000 Hz can
be taken.
At a deep limestone aquifer site in
Collier County, FL, permeability
images were produced to provide the
South Florida Water Management
District with a better understanding of
contaminant dispersion in the area.
The permeability model developed
with PRBS data taken from field
measurements was found to correlate
highly with the results of pumping tests
conducted at the site. Overall, the
error between acoustically imaged
permeability and pump tests is esti-
mated to be within 50 percent, and the
errors for porosity to be within 10
percent.
Use of this technique at the Collier
County site provided a single, continu-
ous measure at a cost of
approximately $100,000. In contrast,
researchers estimate that total perme-
ability estimates obtained through use
of traditional pumping tests would
have required testing at several
locations, and cost as much as
$200,000 per pumping point. Addition-
ally, it is estimated that conventional
pumping tests would have required
approximately one month to obtain
100-foot deep permeability estimates,
while a 1,800-foot tomographic image
could be obtained in a single day in the
field.
In addition to providing analytical
results within as little as 48 hours, this
technology avoids the testing problems
and potential data inaccuracies in-
volved when using sandy samples to
measure porosity and permeability in
the laboratory. Two- and three-
dimensional images interpreted in this
way have provided more accurate
modeling of contaminant dispersion at
other sites in complex geophysical
settings, including military and air
transportation facilities located in
coastal areas of the U.S. and Japan.
The approach used in this (patented)
technology has been approved by
Kawasaki Steel Corporation for wide-
spread use by cleanup contractors at
contaminated ground-water sites in the
U.S. For more information, contact
Dr. Tokuo Yamamoto (University of
Miami) at 305-361-4637 or e-mail
tyamamoto(2>rsmas .miami .edu.
Clarification
The passive barrier described in the
article "Iron Reactive Barrier Used as
Rocky Flats Site" in the April 2001 issue
of Ground Water Currents was de-
signed and installed by the U. S. Army
Corps of Engineers, Omaha District.
Mention of trade or commercial products does not constitute endorsement by the U.S. Environmental Protection Agency.
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