United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-98-010
December 1998
Issue No. 30
^er Treatment
CONTENTS
Microbial Precipitation of
JDissolved-Metals
Using Molasses
Pg. 1
FieldDemonstration
of a Surfactant/Foam
Process for Aquifer
Remediation
Waste Paper Mill
Sludges as Reactive
Semi-Permeable
Barrier Slurry Walls
Pg.2
Pg.3
Resources Developed
by the National
Research Council Pg. 4
About this Issue
This issue features
innovative methods of
enhancing conventional
ground-water remediation
technologies for the
treatment of organic and
inorganic contaminants.
lUlicrobial Precipitation of
Dissolved Metals Using
Molasses
by Eugene Dennis, U.S. EPA
Region 3, and Suthan
Suthersan, ARCADIS Geraghty
& Miller, Inc.
Preliminary results of operations at the
Avco Lycoming Superfund site in
Williamsport, PA, indicate that a new
technique for in situ remediation is
enhancing and inducing microbial
reduction of dissolved metals in ground
water. The technology involves the use of
a carbohydrate solution (dilute blackstrap
molasses and water) that is injected into
the aquifer to reduce dissolved metals,
such as hexavalent chromium, to less
soluble states, such as trivalent chromium.
This reduction process yields significant
remedial benefits because trivalent
chromium is less toxic, less mobile, and
precipitates more readily than hexavalent
chromium.
The Avco Lycoming site is a 28-acre
active manufacturing facility where
hexavalent chromium contamination is
located in a shallow, glacially-derived,
silty sand aquifer. A 1991 record of
decision (ROD) for the site called for a
pump and treat system to be used, but the
ROD was amended in 1996 to allow for in
situ precipitation of ground water
contaminated with hexavalent chromium.
Clean-up goals specified in the ROD
include a level of 0.032 mg/L for
hexavalent chromium.
The target area for in situ treatment is a
shallow overburden approximately 25 feet
below land surface covering
approximately two acres. Collection of
samples from monitoring wells indicated
initial ground water concentrations of
hexavalent chromium and cadmium as
high as 3.0 mg/L and 0.8 mg/L,
respectively.
The technology used at this site is based
on the rapid degradation of carbohydrates
(primarily sucrose) present in molasses by
indigenous heterotrophic microorganisms
residing in the aquifer. This metabolic
degradation process utilizes available
dissolved oxygen to create anaerobic
conditions conducive to reduction
processes. As a result, hexavalent chro-
mium is reduced to trivalent chromium,
which then reacts with naturally occurring
hydroxides available in the aquifer to form
chromium hydroxide. Under alkaline to
moderately acidic conditions, chromium
hydroxide readily precipitates out of
solution because of its extremely low
solubility, and is immobilized in the soil
matrix of the aquifer. Conversion of
trivalent chromium back to hexavalent
chromium is expected to occur only under
extremely acidic conditions (pH less than
3.5).
A small-scale field design test was
conducted at the Avco Lycoming site over
a six-month period prior to full-scale use of
this technology. Within approximately 70
days of initiating molasses injections,
analytical results indicated a decrease in
hexavalent chromium from 2.4 mg/L to
less than 0.01 mg/L in a monitoring well
located approximately 5 feet from the
injection wells. Analytical results of
Recycled/Recyclable
Printed with Soy/Canola Ink on paper that
contains at least 50% recycled liber
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samples taken from a second monitoring
well located 12 feet from the injection wells
indicated a decrease in hexavalent
chromium from approximately 3 mg/L to
less than 0.01 mg/L within 155 days.
Overall, hexavalent chromium
concentrations in ground water decreased
to below detection levels during the field
test, and the concentration of total
chromium also decreased.
Full-scale use of this technology was
initiated in January 1997, at which time
daily injection of the molasses solution
began. Analysis of quarterly ground water
samples collected over an 18-month period
indicates that microbial reduction has
occurred in an area encompassing approxi-
mately 12,000 ft2. Substantial reductions in
metel concentrations in ground water have
been observed, including a 90% reduction
in hexavalent chromium.
In situ remediation of hexavalent chromium
using molasses is continuing at the Avco
Lyeoming site. For more information,
contact Eugene Dennis (U.S. EPA, Region
3) at 215-814-3202 or E-mail
dennis.eugene@epa.gov, or Suthan
Suthersan (ARGADIS Geraghty & Miller,
Inc.) at 215-752-6840 or E-mail
ssutliersan@gmgw.com.
Field Demonstration of a
Surfactant/Foam Process
for Aquifer Remediation
by George Hirasaki, Ph.D., Rice
University
The first field demonstration of a surfactant/
foam process for removal of dense non-
aqueous phase liquid (DNAPL) from a
heterogeneous alluvial aquifer was
conducted during the Spring of 1997 at Hill
Air Force Base, UT. Air was injected to form
an in situ "foam" in the zones of highest
permeability that is capable of diverting
surfactant solution to zones of lower
permeability, thus improving removal
process efficiency. This demonstration,
which differed from others utilizing
continuous surfactant injection without
foam generation, proved the process
effective in reducing the average DNAPL
saturation of the swept pore volume to
0.03%.
The surfactant solution was designed to
mobilize and solubilize contaminants
located in the lowest part of the saturated
zone of the aquifer contained in a buried
paleo-channel eroded into thick clay
deposits. The demonstration was
conducted in a 6.1-meter line drive well
-pattern with three-injectiorrandrthree
extraction wells spanning the width of
the buried channel (approximately 3.7
meters). Hydraulic conductivity ranged
from 10"4 m/sec to more than 10'3 m/sec.
The contaminated zones near the bottom
of the channel (approximately 13.7
meters below ground surface) had
hydraulic conductivities in the lower
portion of this range.
Contaminants consisted of 70%
trichloroethene (TCE) and smaller
amounts of other solvents and dissolved
greases. Initial borings and a partitioning
interwell tracer test (PITT) indicated that
approximately 79 liters of contaminant was
present initially. [See the September issue of
Ground Water Currents for more informa-
tion on PITT application.] The
demonstration area did not contain a
DNAPL pool, but instead a migration path
of the contaminants to known nearby pools.
A solution containing 3.5% (by weight) of
the anionic surfactant sodium
dihexylsulfosuccinate was injected over a
period of 3.2 days, for a total amount of 3.2
times the swept pore volume of the aquifer.
During most of this time, air was injected
for two-hourintervals at the three injection
wells on a rotating basis. Monitoring wells
showed that the foam first swept the upper
intervals and thus diverted surfactant to the
lower intervals where DNAPL was present
(Figure 1). Moreover, injection of the
nonpartitioning tracer with the surfactant
indicated that foam reduced the swept
volume by approximately 50%. Subse-
quent water flooding broke the foam and
restored the swept volume to its initial
value, as shown by the final PITT.
Analysis of effluent showed that 140 liters
of DNAPL was produced as a result of
surfactant flooding. Since this DNAPL
Figure 1. Foam Propagation Profile
40 50
Relative Change in Latitude (f
T T
IN-2 MW-1
Legend
Time after first gas injection
at injection well 2 (IN-2):
Si 2 hours
B 12 hours
H 2.7 days
HC hydraulic control
IN injection well
MW monitoring well
EX extraction well
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recovery exceeds the 80-liter estimate of
initial volume present, additional DNAPL
likely entered the pattern from the region
beyond the injection wells. The amount of
DNAPL remaining at the end of the test was
very low based on the final PITT (10 liters)
and post-test borings (6 liters). The average
final DNAPL saturation in the swept
volume based on the higher of these
estimates was only 0.03% (77 mg/kg soil).
These results show that the surfactant/foam
process was successful in reducing the
DNAPL source from the low-permeability
zone at the base of the demonstration area.
This project was sponsored by the Ad-
vanced Applied Technology Demonstration
Facility (AATDF) of the U.S. Department of
Defense located at Rice University.
Researchers currently are conducting
seismic studies to identify other structural
low features in the base of the aquifer where
DNAPL may have accumulated. Contact
Dr. George Hirasaki (Rice University) at
713-285-5416 or E-mail gjh@rice.edu for a
detailed report on this demonstration or
more information.
Waste Paper Mill Sludges
as Reactive Semi-
Permeable Barrier Slurry
by Horace Moo-Young, Jr., Ph.D.,
Lehigh University
Lehigh University researchers are assessing
the feasibility of utilizing paper mill
sludges for active semi-permeable barrier
applications in situ. Paper mill slurry walls
not only serve to contain contaminants
such as heavy metals, but also attenuate the
contaminants as ground water passes
through the barrier system. As a waste
product of the paper industry, mill sludge is
available to users at little or no cost, while
clay materials commonly used in slurry
walls, such as raw sodium bentonite, can
cost $70-100 per ton. In contrast to
alternative slurry systems, the costs for
paper mill sludge systems may be further
reduced by the lack of need for expensive
pump and treat systems to remove contami-
nants from the subsurface slurry.
Figure 2 illustrates a conceptual model for a
reactive semi-permeable barrier, where
contaminants transported by the natural
hydraulic gradient are immobilized by the
sludge. Paper sludge has a low hydraulic
conductivity (1 x 10~7 cm/sec or less),
which makes the material ideal as a
hydraulic barrier. Other properties that
make paper sludge an excellent candidate
for use as a slurry material are a high initial
watercontent (2-5'tifhes1 higher than die;' '
solids, by weight) and a low initial solids
content (15-20%) prior to dewatering. After
dewatering, the solid content is increased to
25-35%. In comparison, most slurry walls
constructed with bentonite have a solid
content of 5-15% before the addition of
backfill soil.
Sequential batch equilibrium tests of heavy
metal aqueous solutions at varying
concentrations of lead and cadmium were
conducted on paper sludge from a local
paper mill. Resulting adsorption isotherms
yielded information on the adsorption
magnitude of contaminants, how much
contaminant is sorbed, and the adsorptive
capacity changes relative to contaminant
concentrations. This information was used
to compare the effectiveness of paper
sludge with other adsorbents commonly
used for lead and cadmium contaminants,
such as sand-bentonite slurry. Conservative
findings indicated that paper sludge has a
comparable or higher sorption capacity
than that of sand-bentonite mixtures.
Paper sludge obtained directly from a mill
wastewater treatment plant typically is
composed of 50-75% organics (cellulose
fibers and tissues) and 30-50% kaolinite
clay. The increased adsorption capacity of
paper sludge in comparisbnf to kaolinite can
be attributed to the higher organics content,
possibly because the organic fibers and
tissues act as electron acceptors in oxida-
tion and reduction reactions. In addition,
the higher organics content provides a
carbon source for supporting microbial
growth needed to enhance natural attenua-
tion.
To estimate the life-time expectancy of a
reactive semi-permeable barrier constructed
of paper sludge, site-specific testing prior to
application is required. As organics in the
barrier anaerobically decay, the barrier will
become more like clay, thus acting like an
impermeable clay barrier that will decom-
pose more slowly over time. Furthermore,
Figure 2. Conceptual Design of Reactive Barrier Using Paper
Sludge
x-v Reactive
Contamination Source ^^ N^ Impermeable
Barrier
Remediated
Groundwater
Impermeable Stratum
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Ground Water Currents is on the NET!
View or download it from:
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Ground Water Currents
welcomes readers' comments and contributions.
Address correspondence to:
Ground Hater Currents
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Fax:301-589-8487
the rate of microbial activity typically is
low because paper sludge is treated
(disinfected) with chlorine or ozone. In
earlier application as a landfill cover
material, a 15% decomposition rate in
organics contained in the paper sludge was
identified after the first two years of use.
Follow-on studies are underway at Lehigh
University to evaluate mineral enhance-
ment of paper mill sludge using fly ash
and steel slag. For further information,
contact Dr. Horace Moo-Young, Jr.
(Lehigh University) at 610-758-6851 or
E-mail hkm3@lehigh.edu.
Resources Developed by
the National Research
Council
New information about protecting and
remediating ground water is available from
the National Research Council. Publica-
tions released during 1997 include:
Innovations in Ground Water and Soil
Cleanup: From Concept to Commer-
cialization, and
Valuing Ground Water: Economic
Concepts and Approaches.
Earlier publications addressing ground
water contamination issues include:
Ground Water Vulnerability Assess-
ment: Predicting Relative Contami-
nation Potential Under Conditions
of Uncertainty,
In Situ Bioremediation: When Does
it Work?, and
Rock Fractures and Fluid Flow:
Contemporary Understanding and
^Applications-. ----- -- ,,, -:,__
To read these books on-line, access the
National Academy Press (NAP) Web site
at www.nap.edu/readingroom. For
copies, contact the NAP at 800-624-
6242 or 202-334-3313.
United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-98-010
December 1998
Issue No. 30
Ground Water Currents
^'teter Treatment
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