United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-00-006
September 2000
Issue No. 37
\vEPA Ground Water Garrantt
CONTENTS
In Situ Chemical
Oxidation for
Remediation of
Contaminated Soil
and Ground Water Pg. 1
Phytoremediation of
Ground Water
Contaminants Pg. 4
Enhanced Biological
Reductive
Dechlorination at a
Dry Cleaning Facility Pg. 5
About this Issue
This issue highlights the use of
peroxide, ozone, and
permanganate in remediating
ground water through chemical
oxidation/reduction. In
addition, it includes a
description of results obtained
in field uses of
phytoremediation and
biologically enhanced
reductive dechlorination.
In Situ Chemical
Oxidation for
Remediation of
Contaminated Soil and
Ground Water
by Robert L. Siegrist, Colorado
School of Mines; Michael A.
Urynowicz, ENVIROX, LLC; and
Olivia R West, Oak Ridge
National Laboratory
Introduction
Chemical oxidation/reduction has
proven to be an effective in situ
remediation technology for ground
water contaminated by toxic organic
chemicals. The oxidants most
commonly employed to date include
peroxide, ozone, and permanganate.
These oxidants have been able to cause
the rapid and complete chemical
destruction of many toxic organic
chemicals; other organics are amenable
to partial degradation as an aid to
subsequent bioremediation. In general
the oxidants have been capable of
achieving high treatment efficiencies
(e.g., > 90 percent) for unsaturated
aliphatic (e.g., trichloroethylene
[TCE]) and aromatic compounds (e.g.,
benzene), with very fast reaction rates
(90 percent destruction in minutes).
Field applications have clearly
affirmed that matching the oxidant and
in situ delivery system to the
contaminants of concern (COCs) and
the site conditions is the key to
successful implementation and
achieving performance goals.
Oxidants and Reaction
Chemistry
Peroxide (See Table 1) Oxidation
using liquid hydrogen peroxide (H2O2)
in the presence of native or supple-
mental ferrous iron (Fe+2) produces
Fenton's Reagent which yields free
hydroxyl radicals (OH"). These strong,
nonspecific oxidants can rapidly
degrade a variety of organic com-
pounds. Fenton's Reagent oxidation is
most effective under very acidic pH
(e.g., pH 2 to 4) and becomes ineffec-
tive under moderate to strongly
alkaline conditions. The reactions are
extremely rapid and follow second-
order kinetics. The simplified
stoichiometric reaction for peroxide
degradation of TCE is given by
equation (a).
2CO2 + 2H2O + 3HCl(a)
Ozone (See Table 1) Ozone gas can
oxidize contaminants directly or
through the formation of hydroxyl
radicals. Like peroxide, ozone reac-
tions are most effective in systems
with acidic pH. The oxidation reaction
proceeds with extremely fast, pseudo
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Recycled/Recyclable
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first order kinetics. Due to ozone's high
reactivity and instability, O3 is produced
onsite, and it requires closely spaced
delivery points (e.g., air sparging
wells). In situ decomposition of the
ozone can lead to beneficial oxygen-
ation and biostimulation. The
simplified stoichiometric reaction of
ozone with TCE in water is given by
equation (b).
O3 + H2O + C2HC13 -»
2CO2 + 3HC1 (b)
Permanganate (See Table 1) The
reaction stoichiometry of permanganate
(typically provided as liquid or solid
KMnO4, but also available in Na, Ca, or
Mg salts) in natural systems is complex.
Due to its multiple valence states and
mineral forms, Mn can participate in
numerous reactions. The reactions
proceed at a somewhat slower rate than
the previous two reactions, according to
second order kinetics. Depending on
pH, the reaction can include destruction
by direct electron transfer or free
radical advanced oxidation — permanga-
nate reactions are effective over a pH
range of 3.5 to 12. The stoichiometric
reaction for the complete destruction of
TCE by KMnO4 is given by (c).
2CO, + 2MnO, + 2KC1 + HC1 (c)
Design and Implementation
The rate and extent of degradation of a
target COC are dictated by the
properties of the chemical itself and its
susceptibility to oxidative degradation
as well as the matrix conditions, most
notably, pH, temperature, the
concentration of oxidant, and the
concentration of other oxidant-
consuming substances such as natural
Table 1. Features of Peroxide, Ozone, and Permanganate Oxidants as Used
Features Peroxide Ozone Permanganate
Oxidation Effectiveness
Susceptible organics
Difficult to treat organics
Oxidation of NAPLs
Oxidation in Situ
Dose concentrations
Single/multiple dosing
Amendments
Companion technologies
BTEX, PAHs, Phenols,
akenes
Some alkanes, PCBs
Yes
5 to 50 wt % H2O2
multiple common
Fe+2 and acid
none required
BTEX, PAHs, Phenols,
alkenes
Alkanes, PCBs
Yes
Variable
multiple
often ozone in air
soil vapor extraction
BTEX, PAHs, akenes
Akanes, PCBs
Yes
0.02 to 4.0 wt % KMnO4
single and multiple
none
none required
Notes:
BTEX = benzene, ethylbenzene, toluene, and xylenes
Fe2+ = ferrous iron
HO = hydrogen peroxide
KMnO4 = potassium permanganate
NAPL = non-aqeous phase liquid
PAH = polycyclic aromatic hydrocarbon
PCB = polychlorinated biphenyl
organic matter and reduced minerals as
well as carbonate and other free radical
scavengers. Given the relatively
indiscriminate and rapid rate of
reaction of the oxidants with reduced
substances, the method of delivery and
distribution throughout a subsurface
region is of paramount importance.
Oxidant delivery systems often employ
vertical or horizontal injection wells
and sparge points with forced
advection to rapidly move the oxidant
into the subsurface. Permanganate is
relatively more stable and relatively
more persistent in the subsurface; as a
result, it can migrate by diffusive
processes. Consideration also must be
given to the effects of oxidation on the
system. All three oxidation reactions
can decrease the pH if the system is not
buffered effectively. Other potential
oxidation-induced effects include:
colloid genesis leading to reduced
permeability; mobilization of redox-
sensitive and exchangeable sorbed
metals; possible formation of toxic
byproducts; evolution of heat and gas;
and biological perturbation.
Engineering of in situ chemical
oxidation must be done with due
attention paid to reaction chemistry and
transport processes. It is also critical that
close attention be paid to worker training
and safe handling of process chemicals as
well as proper management of
remediation wastes. The design and
implementation process should rely on an
integrated effort involving screening
level characterization tests and reaction
transport modeling, combined with
treatability studies at the lab and field
scale.
Conclusions
Field tests have proven that in situ
chemical oxidation is a viable
remediation technology for mass
reduction in source areas as well as for
plume treatment (See Table 2 on page 3).
The potential benefits of in situ oxidation
include the rapid and extensive reactions
with various COCs applicable to many
bio-recalcitrant organics and subsurface
environments. Also, in situ chemical
oxidation can be tailored to a site and
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implemented with relatively simple,
readily available equipment. Some
potential limitations exist including the
requirement for handling large
quantities of hazardous oxidizing
chemicals due to the oxidant demand of
the target organic chemicals and the
unproductive oxidant consumption of
the formation; some COCs are resistant
to oxidation; and there is a potential for
process-induced detrimental effects.
Further research and development is
ongoing to advance the science and
engineering of in situ chemical
oxidation and to increase its overall cost
effectiveness.
For more information, contact Dr.
Robert L. Siegrist (Colorado School of
Mines) at 303-273-3490 or E-mail
siegrist@mines.edu.
Table 2. Example Applications of In Situ Treatment Using Peroxide, Ozone, and Permanganate
Location
(Date) Media and
Oxidant Delivery COCs Application method and results
Peroxide
Ozone
Permanganate
Massachusetts
(1996)
Injectors into
ground water (GW)
South Carolina
(1997)
Injectors into GW
Kansas
(1997)
Injectors into GW
California
(1998)
Injectors into GW
Ohio
(1997)
Horizontal well
recirculation
Ohio
(1998)
Vertical well
recirculation
TCA and VC in
GW
Deep GW zone with
PCE and TCE;
DNAPLs in sand
clay aquifer
PCE in GW
PAHs and PCP in
GW and soil
GW with TCE
DNAPLs in thin
sandy aquifer
TCE in silty sand
and gravel GW zone
30 ft. below ground
surface (bgs)
H2O2+Fe+acid via 2 points over 3 days within 30 feet D.W. TCA
reduced from 40.6 to 0.4 mg/L; VC from 0.40 to 0.08 or ND
mg/L.
H2O2+FeSO4 via 4 injectors into zone at 140 feet bgs beneath old
waste basin. 6-day treatment time. Treatment achieved 94%
reduction in COCs with GW near MCLs. TCE reduced from 21 to
0.07 mg/L; PCE from 119 to 0.65 mg/L.
Old drycleaners site. GW at 14 to 16 ft bgs in terrace deposits.
One sparge point at 3 scfrn at 35 bgs. SVE wells in vadose zone.
PCE in top 15 ft of aquifer at 0.03-0.60 mg/L. Reduced 91%
within 10 ft of well. Comparisons with air only indicated 66-87%
reductions.
Wood treater site 300 ft x 300 ft in area. Stratified sands and clays.
4 multilevel ozone injectors at up to 10 cfm SVE wells in the
vadose zone. After 1 month, PAHs at 1 800 mg/kg reduced by 67-
99%; PCP at 3300 mg/kg reduced 39-98%.
KMnO4 (2-4 wt % feed) delivered by horizontal recirculation wells
200 ft. long and 100 ft apart at 30 ft bgs to treat 106 L zone of
GW over 30 days. TCE reduced from 820 mg/L to MCL in 13 of
17 wells. ~300kg TCE destroyed. Some MnO2 particles generated.
Aquifer heterogeneities noted.
NaMnO4 (250 mg/L) delivered by 5-spot vertical well recirculation
system (ctr. well and 4 perimeter wells at 45 feet spacing) for 3
pore volumes over 10 days. TCE reduced from 2.0 mg/L to MCL.
Oxidant gradually depleted in 30 days and no microtox toxicity. No
permeability loss in formation.
Notes:
bgs = below ground surface PCE = tetrachloroethylene
DNAPL = dense non-aqeuous phase liquid PCP = pentachlorophenol
FeSO4 = ferrous sulfate SVE = soil vapor extraction
MCL = maximum contaminant level TCA = 1,1,1 -trichloroethane
MnO2 = manganese (IV) oxide TCE = trichloroethylene
PAH = polycyclic aromatic hydrocarbon VC = vinyl chloride
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Phytoremediationof
Ground Water
Contaminants
by Lee A. Newman, College of
Forest Re sources, University of
Washington; and Milton P. Gordon,
Department of Biochemistry,
University of Washington
Phytoremediation relies on natural
processes associated with plants to
remove contaminants from the environ-
ment. This technology can be used to
remediate an impressive range of
contaminants in a variety of air, water,
and soil matrices. Plants have been used
in artificial wetland systems to clean
surface water and wastewater streams;
to remove soluble contaminants such as
industrial solvents and gasoline addi-
tives that have infiltrated ground-water
streams; and to remove airborne
pollutants. Plants can enhance the
degradation of recalcitrant organic
compounds in soils, and they can either
accumulate or stabilize heavy metals
and radionuclides in the soil.
As part of the Superfund Basic Re-
search Program, researchers at the
University of Washington have focused
on the use of deep-rooted plants such as
the hybrid poplar Populous trichocarpa
x P. deltoides to treat ground water that
has been contaminated with compounds
including industrial solvents (e.g.,
trichloroethylene [TCE] and carbon
tetrachloride [CT]); pesticides (e.g.,
ethylene dibromide [EDB] and
dibromochloro propane [DBCP]); and
gasoline additives (e.g., methyl-f-butyl
ether [MTBE]). To date, the most
extensive laboratory and field studies
have been done with TCE. Hybrid
poplars have proven to be effective in
the degradation of TCE.
Phytoremediation of
Trichloroethylene
Early laboratory studies showed that
hybrid poplar cells were able to trans-
form TCE to carbon dioxide,
trichloroethanol, and di- and
trichoroacetic acid. The formation of
these metabolites indicates that a
complete aerobic degradation pathway
exists in the plant cells. Additional
work to determine the fate of these
compounds in the plants is ongoing.
Studies conducted in the laboratory and
the greenhouse showed that whole
plants were capable of taking up TCE
from soil. However, the absolute uptake
capacity was unclear, and the amount of
metabolites found in the plant tissue
was not sufficient to account for the
loss of TCE from the systems.
Field Studies
In elaborate field trials, plants were
grown in an artificial aquifer system
which was supplied with TCE at
concentrations of 15 -18 parts per
million (ppm). Unplanted control
aquifers received water with the same
concentration of TCE. Over the course
of two years, the maturing poplars
removed 98 percent of the TCE from
the aquifer; 32 percent of the TCE was
removed from the control aquifers due
to soil/microbial interactions. Negli-
gible amounts of TCE were transpired
to the atmosphere, and very low
amounts of metabolites were seen in the
plant tissues. The bulk of the chloride
that was added to the system as TCE
was recovered as free chloride ion in
the upper layers of the soil, well above
the saturated zone created by the
artificial aquifer. Research is being
done to determine the exact mechanism
of chloride deposition. TCE recovery in
the aquifer increased immediately after
the plants' uptake capacity was ex-
ceeded, indicating that TCE removal
from the aquifer directly correlates to
plant uptake.
Application of Technology
The University is working on several
projects to utilize phytoremediation
technology in the field. One site near
Medford, OR demonstrated the first
application of the "pump-and-irrigate"
technology— contaminated water is
pumped and applied to the trees via an
underground drip irrigation system. In
this application, the technology is not
limited by the rooting depth of the
plants, and the number of sites where
phytoremediation can be used is greatly
increased.
At the Naval Undersea Warfare Center
at KeyportNavy Base, WA, two acres
of trees are being used to stop the
movement of a contaminant plume that
is moving toward a sensitive wetland.
At this site conventional technologies
(pump and treat, and excavation and
removal) were considered, but the costs
(approximately $10 M) were deemed
prohibitive. A state-of-the-art, exten-
sively controlled and monitored
phytoremediation system was imple-
mented for $3.5M, resulting in a
significant cost savings. In addition, the
community support for the
phytoremediation project was over-
whelmingly favorable, and community
visits to the site are common.
Conclusions
Careful site selection and the applica-
tion by experienced personnel can
advance the use of phytoremediation
technology. Additional studies are
underway to increase understanding
about the fate of various compounds
within the plant/rhizosphere system,
and to better understand the potential
feasibility of this technology under
various field conditions. At appropriate
sites phytoremediation has the potential
to be a cost-effective, low maintenance,
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and environmentally sound clean up
solution for contaminated ground water.
For further information contact Dr. Lee
Newman at 206-616-2388 or 206-890-
1090 or E-mail newmanla@
u.washington.edu, or Dr. Milton
Gordon at 206-543-1769 or E-mail
miltong@u. washington.edu.
Enhanced Biological
Reductive Dechlorin-
ation at a Dry Cleaning
Facility
by Judie A. Kean, Florida
Department of Environmental
Protection; Michael N. Lodato, IT
Corporation; andDuane Graves,
Ph.D., IT Corporation
The dry cleaning industry uses tetra-
chloroethylene (PCE) as a degreaser
and waterless cleanser for clothes. The
use of PCE has resulted in the release
of this chlorinated solvent at numerous
dry cleaning facilities. In the past,
many dry cleaning businesses were
independently owned with little regula-
tory oversight regarding the disposal
and storage of solvents. As a result,
PCE contamination of both soil and
ground water at dry cleaner sites is very
common.
Under the auspices of the Florida
Department of Environmental Protec-
tion, and in accordance with the State's
Dry Cleaning Solvent Cleanup Pro-
gram, a commercial dry cleaning
facility's soil and ground water was
extensively characterized with state-of-
the art direct-push diagnostic protocols
and statistical data confidence software.
The total scope of work was designed
to include the evaluation of parameters
which give both qualitative and quanti-
tative indications of the occurrence of
reductive dechlorination of chlorinated
solvents. The combined evidence
generated from several different aspects
of this evaluation suggested that natural
attenuation by the process of reductive
dechlorination was occurring, and was
significantly affecting the fate of
chlorinated compounds in the aquifer.
Measurable levels of c/'s-l,2-DCE
(dichloroethylene) and vinyl chloride
supported the conclusion that reductive
dechlorination of PCE and TCE
(trichloroethylene) affected the chemi-
cal composition of a dissolved
contaminant ground-water plume.
Upon evaluation of all assessment data,
it was determined that an area of
approximately 14,600 square feet of
contaminated ground water was situated
within the 1 mg/L isopleth for PCE;
and in some monitoring wells contami-
nant concentrations approached 9 mg/L.
HRC Application and
Monitoring Program
Approximately 6,800 pounds of
Hydrogen Release Compound (HRC)
were injected into the area described via
144 direct-push points spaced 10 feet
apart on centers within an 80-ft by 180-
ft grid. HRC is a proprietary,
environmentally safe, food quality,
polylactate ester made by Regenesis
Bioremediation Products, Inc. It is
specially formulated for slow release of
lactic acid upon hydration. HRC is
applied to the subsurface via push-point
injection or within dedicated wells.
HRC is then left in place where it
passively works to stimulate rapid
contaminant degradation. At the Florida
site, each point received 2.45 gallons of
HRC between a depth of 5 to 30 feet
below the surface in the upper surficial
aquifer.
The effects of HRC on ground-water
geochemistry and chlorinated solvent
concentrations were determined by
periodically sampling and analyzing
ground water from seven monitoring
wells. Analysis included chlorinated
solvents, dissolved oxygen, oxidation-
reduction potential, pH, conductivity,
temperature, ferrous iron, nitrate and
nitrite, sulfate, methane, ethane, ethene,
manganese, and phosphorus.
Ground-water samples were collected
for six months following the HRC
application to monitor progress of the
treatment.
Results
The application of HRC resulted in an
observable change in the concentration
of chlorinated solvents. An area
approximately 240 by 180 feet was
affected by the HRC application. The
mass of PCE and its dechlorination
products before HRC application and at
various time points after the application
is shown in Table 3 on page 6.
The PCE mass increased from the
initial mass to the mass estimated after
43 days. This change was presumably
due to physical desorption related to the
injection activity. Overall the PCE
mass was reduced by 96% after 152
days of treatment. The dramatic
reduction in PCE mass and the less
dramatic reduction of the mass of the
lesser chlorinated ethenes suggests that
the PCE was being dechlorinated to
TCE, DCE, and vinyl chloride. HRC-
stimulated, biologically mediated,
reductive dechlorination of PCE was
confirmed by changes in ground-water
geochemistry that are typically cata-
lyzed by biological activity.
[continued on page 6]
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[continuedfrom page 5]
The overall results from HRC
application and continued monitoring
indicated that HRC appears to be an
effective alternative for remediating
PCE, TCE, c/s-l,2-DCE, and vinyl
chloride in ground water. The cost for
this large-scale demonstration was
favorable and should encourage the
application of the technology at
appropriate sites. The overall cost of
this project was $127,000. HRC
Table 3. Mass of Chlorinated Hydrocarbons at Various Times After HRC
Initial 43 Days 77 Days 110 Days 152 Days
Compound Mass (g) Mass (g) Mass (g) Mass (g) Mass (g)
PCE
TCE
Cis-l,2-DCE
Viryl Chloride
19,183
2,548
6,309
2,350
24,378
1,261
3,144
1,287
17,925
1,108
3,946
670
12,869
1,222
3,705
572
822
1,254
4,012
1,016
product cost was $27,197. Additional
project costs included the preparation of
a detailed work plan, sampling and
analysis plan, health and safety plan,
preparation of an underground injection
permit, hiring of a Geoprobe
subcontractor, labor, monthly reports
and meetings, contractor oversight, and
field and laboratory analyses. This
project represents the successful
collaboration of the Florida Department
of Environmental Protection, Regenesis
Bioremediation Products, and IT
Corporation, the state cleanup
contractor.
For further information about this
specific project, contact Judie Kean
(Florida Department of Environmental
Protection) at 850-488-0190. For
information about the HRC product,
contact Steve Koenigsberg (Regenesis
Bioremediation Products, Inc.) at 949-
366-8000, ext. 106.
Mention of trade or commercial products does not constitute endorsement by the
U.S. Environmental Protection Agency. 1
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