United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5I02W)
EPA/542/N-93/OII
December ) 993
Tree Buffers Protect Shallow Ground Water
at Contaminated Sites
By L. A. Licht and J.L. Schnoor, University of Iowa
Tvesearchers at the GreaT
Plains/Rocky Mountain Haz-
ardous Substances Research
Center (HSRC) are confirm-
ing that vegetation—specifi-
cally poplar trees (Populus
spp.)—can help keep toxic
herbicides, pesticides and fer-
tilizers out of rivers, streams,
creeks and ground water. In
addition to agricultural pesti-
cides and nitrate removal, the
vegetation is being studied at
Superfund sites with other or-
ganic .contaminants and met-
als. Trees serve to decrease
vertical migration of contami-
nants to, and in, shallow
ground water.
At an agricultural test site
on an Iowa farm, a poplar crop,
planted by a University of
"Iowa research" team, was"found '
to significantly reduce nitrate
levels in the ground water. The
trees were planted along a
stream bank between a corn
field and the stream.
One objective of the project
was to reduce the nitrate-nitro-
gen that was leaching out of
fertilized fields into surface wa-
ter. The test buffer clearly met
this objective. In 1990, when
the trees were three years old,
researchers recorded the aver-
age nitrate content of ground
water leaving the corn field at
150 milligrams per liter (mg/L),
more than three times EPA's
permissible limit of 45 mg/L
for nitrate in drinking water.
In the ground water in the
midst of the trees between
the field and the stream, the
readings were 8 mg/L. Along
the creek bank, the nitrate
level in the ground water had
dropped to only 3 mg/L.
Poplar trees were chosen
because they consume such
large amounts of nitrogen.
The trees take up soluble in-
organic nitrogen or ammoni-
um-nitrogen through their
roots, converting nitrates into
protein and nitrogen gas. Af-
ter five growing seasons, the
average tree contains 33
grams of organic nitrogen in
its stem. On land planted
T"withll ,000'treespe;fTiectare,
this amounts to 363 kilo-
grams of nitrogen per hect-
are. The researchers
calculated that this means
that the trees planted on a
hectare of land have tran-
spired, and therefore biore-
mediated 8.07 million liters
of water.
Licht and Schnoor have
used poplar trees in a variety
of toxicity studies in both
controlled chamber and
field experiments. In cham-
ber experiments, atrazine la-
.beled with carbon-14 was
transformed into CO2both in
soil and through plant uptake
and metabolism. In field stud-
ies, the researchers observed
that deep-rooted poplars i
slowed the migration of volsi-
tile organic chemicals.
Trees can serve a variety of
other functions at a polluted!
site. They can serve as a wild-
life habitat, as a wind screen.,
as a filter strip to trap sedi- I
ment and prevent erosion and
as a renewable resource that
can be harvested for products
such as fuel and lumber. At
the Iowa farm test site, a sec-
ond objective was to produce
a cash crop, a strategy likely
to increase consumer accep-:
tance of the technology, since
farmers would be asked to give
up land that would normally
be planted in crops. Poplar
wood can be converted into
plywood, lumber or clean-
burning wood pellets. Licht
has calculated that farmers
could grow the equivalent of
9,250 liters of fuel per hectare
of poplars per year.
For more information, call
L. A. Licht (319-335-5050)
or J.L. Schnoor (319-335-
5649) at the University of
Iowa. The Great Plains/Rocky
Mountain HSRC also has
several initiatives involving
the use of vegetation in biore-
mediation; for more informa-
tion, call the HSRC's
Director, Larry Erickson
(913-532-6519).
This month's Currents features news
from the Army's Waterways Experiment Station
Tree Buffers
Innovative Oxidation
PCE Bioremediation
Complex Mixtures
Printed with Soy/Canola ink on paper that contains at (east. 50% reacted fiber
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Innovative Oxidation Technologies
By Mark Zappi, U.S. Army Corp of Engineers'Waterways Experiment Station
Advanced oxidation process-
es (AOPs) are ground water
remediation techniques that
use powerful chemical oxidiz-
ers under catalyzing condi-
tions to produce hydroxyl
radicals which in turn can de-
stroy a wide variety of organic
compounds. The U.S. Army
Corps of Engineers' Water-
ways Experiment Station
(WES) has been evaluating
both traditional and non-tra-
ditional AOPs. This article
addresses two non-traditional
AOPs—peroxone and ultra-
sonically (sonolysis) catalyzed
oxidation—for treatment of
trinitrotoluene (TNT) con-
taminated ground water. In
addition to TNT remediation,
peroxone has already been
used successfully for treatment
of a wide variety of organic
contaminants and is being
evaluated for additional or-
ganic contaminants.
The results of these studies
indicate much promise for
treating TNT contaminated
ground water at a potential
cost savings over more tradi-
tional AOPs. Although ultra-
sonically catalyzed oxidation
is still in the early stages of
development, we do know
that peroxone oxidation costs
are estimated to range from
$0.10 to $1.00 per thousand
gallons treated. This is signifi-
cantly lower than traditional
U V based AOP costs which
typically range from $1.00 to
$5.00 per thousand gallons
treated.
Until recently peroxone
had been limited to drinking
water treatment. However,
bench and pilot studies indi-
cate a high potential for
utilization of peroxone for
treatment of contaminated
ground water. Peroxone in-
volves the generation of hy-
droxyl radicals through
reaction of ozone with hydro-
gen peroxide. Optimal stoi-
chiometric ratios of hydrogen
peroxide to ozone are in the
0.25 to 1.5 range, indicating a
low dosage_of hydroger^perox-
ide to ozone. Although perox-
one have a slower TNT
removal kinetics (four times
slower) than traditional
AOPs, removal is effective
and at potentially much lower
cost. For the WES study the
test influent was a 100 ug/1
TNT contaminated ground
water. A 10 mg/L hydrogen
peroxide dose in the peroxone
system indicated potential to
remove all of the TNT within
30 minutes of treatment. Sub-
sequent studies indicated that
a 100 mg/L dose was able to
achieve similar treatment
within less than 20 minutes of
batch treatment. The addition
of ultrasound to the peroxone
system substantially enhanced
the rate of TNT jemqyal at
both the 20 and 40 watt/HteT
dose.
Ultrasound are soundwaves
produced from 20 khz to 100
khz frequency range by elec-
trical devices. Ultrasound is
commonly used for cleaning
small objects where extremely
clean conditions are required
in hard to reach areas. Ultra-
sound has also been used to
catalyze slow chemical reac-
tions. Using a directional ul-
trasonic probe along with one
liter, glass reactions, WES has
evaluated the feasibility of us-
ing ultrasound to increase the
reaction rate of TNT during
ozonation as well as peroxone
oxidation. Much like the per-
oxone data, as the level of ul-
trasonic power into the
ozonation system is' increased,
so does the overall TNT oxi-
dation rate. Mechanisms re-
sponsible for increasing
reaction rates are improved
mass transfer, production of
hydroxyl radicals and localized
pockets of high pressure and
temperatures. Because of the
paucity of cost information
and the absence of large scale
ultrasonic chemical reactors
to evaluate pilot scale ultra-
sonic catalyzed oxidation,
WES has initiated a collabora-
tive research and develop-
ment agreement (CRADA)
effort with a manufacturer of
large scale ultrasonic systems
to address these issues.
WES has several other on-
going research activities for
both traditional and non-tradi-
tional AOPs. As. knowledge of
the mechanisms involved in
contaminant destruction are
better understood through cur-
rent WES research efforts,
then treatment costs associat-
:ed witjxUy based-system^ are _
expected to decrease while the
range of applications increases.
Of significant note is the defi-
nition of oxidation pathways
of explosives compounds
(TNT, RDX and HMX) during
AOP treatment which is cur-
rently under investigation by
WES in collaboration with
Howard University and the
University of North Carolina,
Chapel Hill. WES is running
(See AOPs, page 4)
A Word About WES
I he U.S. Army Corp of En-
gineers' Waterways Experi-
ment Station (WES) ,jhrough_
its Hazardous Waste Research
Center, offers a full service
testing and evaluation facility
with safety equipment, a
high-bay testing area and a
fully equipped analytical lab
including GC/MS. In addi-
tion to extensive analytical
equipment and facilities,
WES has technical personnel
with research experience in a
variety of hazardous waste
treatment technology types.
WES has been involved in
best demonstrated available
technology development
work for the EPA and has
conducted treatability testing
at Federal facility sites.
In addition, WES is capable
of conducting and assistinfin
treatability testing for other
Federal agencies on a cost
reimbursement basis and is
currently investigating the
possibility of government/in-
dustry cost sharing for testing
and evaluation of hazardous
waste treatment technologies.
WES has a Resource Conser-
vation andRecovery ActPart B
permit for testing hazardous
waste treatment technologies.
For more information, call
Norman Francinques, Jr. at
601-634-3416.
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F ELDiSTUDY:
Canadian Field Study Assesses Biodegradation of PCE
By Alex Lye, GASReP, Environment Canada
Approximately 15 years ago,
at a storage and transfer facili-
ty in North Toronto, Ontario,
releases of tetrachloroethene
(PCE) occurred during the
coupling and uncoupling of
railway tanker cars transport-
ing this chemical. Recent
studies revealed that free and
dissolved PCE was present in
the ground water below the
facility but that the PCE was
being dechlorinated to ethene
and ethane. Laboratory micro-
cosm studies, conducted with
aseptically retrieved aquifer
sediments from the PCE
source area, confirmed that
methanol stimulated the
anaerobic dechlorination of
PCE to ethene. Additionally,
the presence of methanol,
which was metabolizing to ac-
etate, led to the conclusion
that acetogenic microorgan-
isms (or other hydrogen con-
suming microorganisms) were
involved in the bio transforma-
tion of PCE to ethene at the
site. A field study was con-
ducted to evaluate the specific
conditions that contributed to
the natural in situ PCE biodeg-
radation at this site and to de-
termine if either unenhanced
or enhanced anaerobic bio-
degradation could success-
fully remediate the site. The
field study was financed by
Environment Canada, the
Ontario Ministry of Environ-
ment and Energy, ICI Canada,
Celanese Canada, AT&T and
General Electric Company.
To evaluate the specific
conditions contributing to the
in situ PCE biodegradation,
five in situ microcosms (ISMs)
were installed in the subsur-
face at the site, at a depth of
approximately seven meters.
Each ISM consists of a cylin-
drical stainless steel test
chamber and a detachable
equipment chamber that con-
tains and protects the sam-
pling and injection
equipment. The test chamber:;
is open at the bottom and sep-
arated from the equipment
chamber by a set of coarse and
fine mesh stainless steel
screens. The screens allow
even flow of injected test solu-
tions into the test chamber
through the injection equip-
ment during experiments.
Ground water in the ISM can
be sampled through the tip of
a stainless steel spike which
protrudes approximately 125
centimeters (cm) into the test
chamber of the ISM.
Two of the five ISMs were
installed in aquifer materials
in which high concentrations
of PCE and methanol had
been detected. The remaining
three ISMs were installed
downgradient of the PCE and
methanol source area in
anaerobic aquifer materials
which contained trace con-
centrations of PCE breakdown
products of cis-l,2-dichlo-
roethene (cis-l,2-DCE), vinyl
chloride (VC) and ethene, but
no detectable PCE, trichlo-
roethene (TCE), methanol or
acetate. Two of the ISMs in
each study location were used
for anaerobic treatments and
received amendments of
methanol (1,500 mg/L) in
addition to PCE [10 to 130
micromoles per liter (jiM/L)]
and bromide (100 mg/L asi a
tracer). The remaining ISM in
the downgradient location
would serve as a live control;
so, only bromide and PCE;—
but no methanol—were added
to this ISM. Any PCE loss in
this ISM would be due to
jjorbtiqn. JPCEbiotransforma-
tion in the four anaerobic and
single unamended control
ISMs was monitored at given
times over a period of up to
29 days.
It was expected that a por-
tion of the injected PCE
would sorb to the soil matrix
in the ISMs; and, the study
calculated the amount of soil
sorption in determining the
mass loss of PCE by biodegra-
dation. The observed mass
loss in the unamended control
ISM was approximately 60%.
PCE mass loss in the four
anaerobic treatment ISMs av-
eraged approximately 90%. In
the amended ISMs, methanol
depletion was accompanied
with the production of acetate
and methane and an increase
in chloride concentrations.
These changes were not ob-
served in the control ISM.
Further, the concentration of
PCE continued to decreasie as
long as methanol or acetate
was present. These results; sug-
gest that a continuous supply
of methanol (or suitable alter-
nate electron donor) would be
required to completely de-
chlorinate all of the PCE mass
to ethene or carbon dioxide
(CO2) at this site. j
The production of TCE,
cis-l,2-DCE and VC was
observed in several of the
anaerobic ISMs. However,
these dechlorination products
were only detected at trace
concentrations; and VC did
not accumulate in any of the
anaerobic ISMs during the
study, thus confirming that
PCE can be biotransformed at_
this site without the accumu-
lation of VC. Ethene and
ethane were detected at low
concentrations in the ISMs
but did not accumulate during
the study. CO2 was not quan-
tified, but was assumed to be
the end product, based on the
results of similar studies (Cox
and Major, 1993; Vogel and
McCarty, 1985).
This field study demonstrat-
ed that the depletion of meth-
anol in the anaerobic ISMs
was accompanied by the pro-
duction of acetate and meth-
ane in several of the anaerobic
ISMs. These results provide
evidence that a consortia of
acetogenic (acetate-produc-
ing) and methanogenic micro-
organisms were likely
involved in the observed PCE
mass loss. Methanol was likely
converted to acetate and an
intermediate pool of hydrogen
by the acetogenic microorgan-
isms in the anaerobic ISMs.
This hydrogen pool then
served as a supply of electron
donors for the rapid dechlori-
nation of PCE and its daugh-
ter products.
For more information, call
Alex Lye, Manager, GASReP,
Environment Canada at 905—
336-6438.
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NEW^FOPL
Complex
Mixtures
The occurrence of organic
chemicals in soil and ground
water has become an issue of
great interest and importance.
Research on the transport and
fate of organic contaminants
in subsurface environments
has expanded greatly in re-
cent years. Much of this re-
search has been focused on
dissolved constituents in
aqueous systems. However,
the behavior of "complex
mixtures" is beginning to re-
ceive increased attention. By
complex mixture we mean
any system other than die
simple system of water con-
taining a single solute. Exam-
ples of pertinent problems
involving complex mixtures
include the transport of oxy-
genated gasoline in the sub-
surface, the dissolution of
diesel fuel and coal-tar and
die use of chemical agents
such as surfactants or solvents
to enhance die removal of
contaminants by pump-and-
treat remediation.
M. L. Brusseau of the Uni-
versity of Arizona has pre-
pared an "Environmental
Research Brief" for EPA on
complex mixtures and ground
water quality. As discussed in
the brief, these mixtures may
affect contaminant behavior
through a variety of mecha-
nisms.-Because many c
mechanisms are not we
derstood, approaches for u
ing with complex mixtures m~
die subsurface often involve
direct application or untested
extrapolation of knowledge
derived from relatively simple
aqueous systems.
The primary purpose of
Brusseau's brief is to identify
and discuss, in a generic
sense, some of the important
processes which must be con-
sidered when dealing with
complex mixtures in die sub-
surface, and to illustrate how
these may impact ground wa-
ter quality. From the discus-
sion, it is apparent that
complex mixtures may play a
role in ground water reclama-
tion as well as degradation of
ground water quality. Equally
apparent, however, is the
need for improved scientific
understanding of the process-
of complex mixtures and
che influence that chemi-
cal mixtures have on the be-
havior of specific
contaminants.
A copy of the "Environ-
mental Research Brief;
Complex Mixtures and
Groundwater Quality" can be
ordered from EPA's Center
for Environmental Research
Information (CERI) at 513-
569-7562. When ordering,
please refer to the Document
Number: EPA/600/S-93/004.
AOPs, from page 2
three pilot studies on three
contaminated ground water
sites at Rocky Mountain Ar-
senal in Colorado with a
WES designed and construct-
ed Peroxone Oxidation Pilot
System (POPS). POPS has a
0.5 to 15 gallons per minute
flow rate and is completely
mobiler:WES-is also.develop
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