United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
<5102G)
EPA-542-N-96-005
September 1336
Issue No. 16
v> EPA Ground Water Currents
Developments in innovative ground water treatment
CHLORINATED SOLVENTS BIODEGRADATION
By John Wilson, National Risk Management Research Laboratory, Ada, OK
The environmental chemistry of
a sitejn part determines the rate
of biodegraclation of chlorinated" ~
solvents at that site. The initial
metabolism of chlorinated sol-
vents such as tetrachloroethylene,
trichloroethylene and carbon tet-
rachloride in ground water usu-
ally involves a biochemical pro-
cess described as sequential re-
ductive dechlorination. The oc-
currence of different types and
concentrations of electron donors
such as native organic matter,
and electron acceptors such as
oxygen and chlorinated solvents,
determines to a large degree the
extent to which reductive dechlo-
rination occurs during the natu-
ral attenuation of a site. For in-
stance, reductive dechlorination
only occurs in the absence of oxy-
gen; and, the chlorinated solvent
actually substitutes for oxygen in
the physiology of the microor-
ganisms carrying out the process.
-•—As-a'resolrofthe use of the chlo-~
rinated solvent during this physi-
ological process it is at least in
part dechlorinated.
The chemical term "reduction"
was originally derived from the
chemistry of smelting metal
ores. Ores are chemical com-
" pounds of metal atoms
coupled with other materials.
As the ores are smelted to the
pure element, the weight of
the pure metal are reduced
compared with the weight of
the ore. Chemically, the posi-
tively charged metal ions re-
ceive electrons to become the
electrically neutral pure metal.
Chemists generalized the term
"reduction" to any chemical
reaction that added electrons
to an element. In a similar
manner, the chemical reaction
of pure metals with oxygen
results in the removal of elec-
trons from the neutral metal
to produce an oxide. Chem-
ists have generalized the term
"oxidation" to refer to any
chemical reaction that re-
moves electrons from a'mate-
rial. For a material to be re-
duced, some other material
must be oxidized.
The electrons required for
microbial reduction of chlori-
nated solvents in ground water
are extracted from native
ABOUT THIS ISSUE
This issue of Ground Water Currents addresses the natural attenuation
of chlorinated solvents In ground water. According to the most recent:
definition proposed by the U,S. Environmental Protection Agency,
"natural attenuation is the biodegradation, dispersion, dilution, sorp-
tion, volatilization, and/or chemical and biochemical stabilization of
contaminants to effectively reduce contaminant toxicity, mobility, or
volume to levels that are protective of human health and the ecosys-
tem." Note that the primary reason for the change in terminology
from intrinsic remediation to natural attenuation is to be consistent
with the language in the National Contingency PJan, which permits
the use of natural attenuation as a remedy fotSuperfimd sites.
organic matter, from other
contaminants such as the ben-
zene, toluene, ethylene and xy-
lene compounds released from
fuel spills, from volatile fatty
acids in landfill leachate or
from hydrogen produced by
the fermentation of these ma-
terials. The electrons pass
through a complex series of
biochemical reactions that
support the growth and func-
tion of the microorganisms
that carry out the process.
To function, the microor-
ganisms must pass the elec-
trons used in their metabolism
to some electron acceptor.
This ultimate electron accep-
tor can be dissolved oxygen,
dissolved nitrate, oxidized
minerals in the aquifer, dis-
solved sulfate, a dissolved
chlorinated solvent or carbon
dioxide. Important oxidized
minerals used as electron ac-
ceptors include iron and man-
ganese. Oxygen is reduced to
water, nitrate to nitrogen gas
or ammonia, iron (III) or fer-
ric iron to iron (II) or ferrous
iron, manganese (IV) to
manganese (II), sulfate to sul-
fide ion, chlorinated solvents
to a compound with one less
chlorine atom and carbon di-
oxide to methane. These pro-
cesses are referred to as aerobic
respiration, nitrate reduction,
iron and manganese reduction,
sulfate reduction, reductive
dechlorination and meth-
anogenesis, respectively.
The energy gained by the
microorganisms follows the
sequence listed above: oxygen
and nitrate reduction provide a
good deal of energy, iron and
manganese reduction some-
what less energy, sulfate reduc-
tion and dechlorination a good
deal less energy and meth-
anogenesis a marginal amount
of energy. The organisms car-
rying out the more energetic
reactions have a competitive
advantage; as a result, they
proliferate and exhaust the
ultimate electron acceptors in
a sequence. Oxygen and then
nitrate are removed first.
When their supply is ex-
hausted, other organisms
(continued on page 3)
This Month in Currents
BIODEGRADATION
p. 1
DOVER
p. 2
CONSORTIUM
p. 3
BOOKSHELF
p. 4
Recycled/Recyclable
Printed with Soy/Canola ink on paper that contains at least 5O% recycled liber
-------
FIELD STUDY
NATURAL ATTENUATION RESEARCH AT DOVER
An extensive four-year re-
search program is in progress at
Dover Air Force Base in Dela-
ware. The Dover study is be-
ing conducted by the
Remediation Technologies De-
velopment Forum's (RTDF)
Biorcmediation of Chlorinated
Solvent Consortium. This
Study will contribute greatly to
a fundamental scientific under-
standing of natural attenuation
as » remedy for chlorinated sol-
vent contamination. To date,
acceptance of natural attenua-
t,ion of chlorinated solvents has
been largely site specific. The
protocol being used at Dover
and the information to be ob-
tained will be applicable for the
assessment and understanding
of other sites. The Dover site
offers the opportunity not only
to assess the contributions of
reductive dehalogenation but
other multiple processes as
ivell, including both aerobic
and anaerobic reactions.
Dover Air Force Base was
chosen over the many other
sites evaluated for the study be-
cause: (1) the plume is well
Characterized; (2) analyses of
ground water chemistry pro-
vided clear evidence that chlo-
rinated solvent contaminants
dre being biodegraded; (3) the
deep zone of the aquifer has
relatively simple geology and is
underlain by a thick confining
layer; (4) access for sampling
and testing is good and the site
is easily reached by offsite per-
sonnel and visitors; (5) the base
has a proactive environmental
program.
The plume contains prima-
rily TCE and dichloroethene
(DCE), with smaller amounts
of vinyl chloride. It occupies
an area north and south of
U.S. Highway 113 approxi-
mately 9.000 feet long and
3,000 feet wide. There are
multiple sources of solvent
contamination in the area
north of the highway, as well as
several minor sources of petro-
leum hydrocarbons. There ap-
pear to be at least three sources
ofTCE.
Based on currently available
information, natural biological
attenuation of PCE and TCE
is occurring in the ground wa-
ter as evident from the pres-
ence of daughter products such—
as cis-DCE, vinyl chloride and
ethylene. Methanogenesis ap-
pears to be the dominant mi-
crobial process in the anaerobic
portion of the aquifer. The rate
and extent of this process is
likely to be controlled by the
geochemistry, particularly the
availability of natural or an-
thropogenic co-substrates
which are needed to drive the
reductive dehalogenation reac-
tion. However, the results ap-
pear to suggest that there are
multiple biodegradation path-
ways involved (i.e., anaerobic
and aerobic). Based on the
distribution of the contami-
nants and the geochemical pa-
rameters, aerobic biodegrada-
tion pathways may also deter-
mine the fate of the chlori-
nated ethenes. The extent of
ground water contamination
by TCE is greater than the size
of the cis-DCE and vinyl chlo-
ride plumes. The cis-DCE and
vinyl chloride can be degraded
in aquifer samples under aero-
bic conditions in the absence
of any additional co-substrate.
Vinyl chloride has been shown
to be used as a carbon source
for growth of aerobic bacteria.
Based on these observations,
cis-DCE and vinyl chloride
may be degraded via aerobic
biodegradation mechanisms.
This conclusion is supported
by preliminary results of
laboratory microcosm studies
conducted using soil from the
Dover site. Under aerobic
conditions, 14-C labeled DCE
and vinyl chloride appear to be
degraded to carbon dioxide.
TCE concentrations in the
ground water range up to 20
milligrams per liter (mg/L).
The TCE concentration de-
clines rapidly near Highway
113. TCE is degraded before
reaching the St. Jones River to
-die-south of the plume.—
DCE concentrations are over
10 mg/L in two areas. The
DCE is primarily cis-1,2-
DCE, the isomer produced by
biodegradation of TCE.
Chemically manufactured
DCE can be distinguished
from biogenic DCE because
chemically manufactured DCE
contains a mixture of isomers,
of which cis-DCE is a minor
component. The DCE plume
overlaps the TCE plume.
DCE concentrations also de-
cline rapidly south of Highway
113.
There is a smaller vinyl chlo-
ride plume with concentra-
tions up to 1 mg/L. Since vi-
nyl chloride was never used on
the base, the Consortium be-
lieves that is present as a bio-
degradation product of DCE.
- If DCE were being-lost -pri-
marily by reduction to vinyl
chloride, we should be able to
detect low, transient concen-
trations of vinyl chloride
throughout the area contain-
ing DCE, regardless of the
relative degradation rates of
the two compounds. The area
containing vinyl chloride,
however, is considerably
smaller than the DCE plume.
Ethylene is also present,
showing that complete reduc-
tive dehalogenation of TCE
does occur in the deep zone.
The amount of ethylene is
small, however, i.e., 50
micrograms per liter or less.
This is much too low to ac-
count for the observed losses of
TCE and DCE.
The project at Dover is in
the second year of the four-
year study. The evidence
clearly demonstrates that active
intrinsic remediation of chlori-
nated solvents is occurring.
The key evidence supporting
this conclusion is as follows.
First, the contaminanr plumes
are "stacked," indicating that
the more mobile contaminants
are being destroyed before they
can move away from the less
mobile contaminants. Second,
the chloride ion concentration
increases as the solvent concen-
tration declines. The increase
is large enough to account for
the entire observed loss of sol-
vents. Third, there is clear
field evidence of reductive
dehalogenation and oxidation,
and possible evidence for
co-oxidation.
In addition to the Dover
study mentioned in this
issue and the St. Joseph Super-
fund Site (see Natural
Bioremediation of TCE in
the September 1993 issue of
Ground Water Currents], natu-
ral attenuation of chlorinated
-solvents is being examined at a
number of sites around the
world. We will be reporting to
you on all of this research as it
comes to fruition.
Information for this article
was, for the most part, ex-
cerpted from Symposium on
Natural Attenuation of Chlori-
nated Organics in Ground Wa-
ter, Dallas, Texas, September
11-13, 1996, pp. 93-97 and
Intrinsic Remediation of Chlori-
nated Solvents in Groundwater,
from Conference on Intrinsic
Bioremediation, London,
England, March 18-19, 1996.
Ground Water Currents
-------
PARTNERS
CHLORINATED SOLVENTS CONSORTIUM
The Bioremediation of Chlo-
rinated Solvents Consortium
(Consortium) is one of the
five Action Teams of the
Remediation Technologies
Development Forum
(RTDF). The RTDF was cre-
ated by EPA in 1992 to foster
collaboration between the
public and private sectors.
The specific mission of the
Consortium, created in May
1993, is to accelerate the ""
development of the most
cost-effective in-situ
bioremediation processes for
degrading chlorinated sol-
vents. The Consortium is
composed of representatives
from various companies (Beak
International, Ciba-Geigy
Corporation, Dow Chemical
Company, DuPont, General
Electric, ICI Americas,
Monsanto Company and
Zeneca, Inc.), universities,
EPA, the Departments of De-
fense (DoD) and Energy
(DOE) and the U.S. Air
Force.
To accomplish their mis-
sion, each of the Consortium
members jointly participates
in the research, development,
demonstration and evaluation
efforts necessary to achieve
public and regulatory accep-
tance of these biological pro-
cesses. Consortium members
contribute personnel, equip-
ment, laboratory facilities and
funding. The companies are
sharing proprietary informa-
tion, patented technologies
and their collective under-
standing and experience in
bioremediation mechanisms
and kinetics, hydrogeology
and nutrient delivery systems
to support development and
testing. The Federal sector
brings substantial bioreme-
diation expertise and labora-
tory experience, tools for mi-
crobial characterization and
site characterization and expe-
rience in the development and
field testing of bioventing
processes.
Shortly after the Consor-
tium was formed, they began
developing a comprehensive
research plan to test and
evaluate the effectiveness of
three complimentary in-situ
bioremediation processes for
degrading chlorinated solvents
— natural attenuation, accel-
erated anaerobic degradation
and cometabolic bioventing.
Three Phase I field tests began
at Dover Air Force Base in
Dover, Delaware in early
1995. (See the article, Natu-
ral Attenuation Research at Do-
ver, in this issue of Ground
Water Currents for a detailed
discussion of the natural at-
tenuation research.) These
Phase I projects will continue
until 1998.
The three technologies have
been identified as the reme-
diation methods of choice in
the Record of Decision
(ROD) for the specific sites at
Dover. Data from the first
year of the Phase I field and
laboratory studies are being
analyzed by Consortium
members. Extensive geologi-
cal and hydrological character-
ization efforts have been com-
pleted to provide significant
insight into the subsurface
conditions. Initial laboratory
biodegradation studies in
batch, column, fed batch and
differential soil bioreactors
have been completed for each
technology. Microbial charac-
terization efforts have been
initiated to determine the na-
ture of the indigenous micro-
organisms responsible for de-
grading chlorinated solvents
at the site. A number of char-
acterization techniques, such
as Most Probable Number di-
rect count, Phospholipid
Fatty Acid Analysis and mo-
lecular approaches (16sRNA)
have been employed to this
end. The Consprtium also
initiated modeling efforts to
develop a tool that will help
predict the performance of
each of the bioremediation
processes at other sites. Plan-
ning is underway to conduct
field studies for each of the
three processes at second sites.
The Consortium is in the
process of gathering and ana-
lyzing characterization data
for sites that might be appro-
priate for the Phase II studies.
The Strother Field Industrial
Park Site in Winfield, Kansas,
has been selected for the
Phase II Accelerated Anaero-
bic Biodegradation Study and
the Intrinsic Bioremediation
Study. Complementary ef-
forts will be undertaken to
validate the conclusions
drawn from Phase I. Efforts
to locate a suitable site for the
Phase II Bioventing Study are
in progress.
In addition, the Consor-
tium has been in contact with
the Western Governors Asso-
ciation (WGA) and the
WGA's Interstate Technology
and Regulatory Cooperation
(ITRC) subgroup. The
ITRC will provide assistance
during the development and
validation of the technology
protocols, which will facilitate
the transfer of the technolo-
gies to other sites. .
For more information on the
Consortium and the other
RTDF Action Teams
(Lasagna™ Partnership, Perme-
able Barriers, Sediments
Remediation and IINERT Soil-
Metals), contact EPA's Robert
Olexsey at 76 West Martin
Luther King Drive, Cincinnati,
OH 45268 (telephone:
513-569-7861; or e-mail:
olexsey.bob@epamail.epa.gov)
or Walter Kovalick, Jr., Ph.D.,
at 401 M Street, S.W. (5102G),
Washington, D.C. 20460 (tele-
phone: 703-603-9910; or e-mail:
kovalick.walter@epamail.epa;gov).
To request copies of RTDF fact
sheets, send a request to EPA/
NCEPI by mail at 11305 Reed
Hartman Highway, Suite 219,
Cincinnati, OH 45241 or by
FAX at 513-670-3815.
(continuedfrom page 1)
are able to proliferate, and manga-
nese and iron reduction begins. If
electron donor supply is adequate,
then sulfate reduction begins,
usually with concomitant iron re-
duction, followed ultimately by
methanogenesis. Ground water
where oxygen and nitrate are be-
ing consumed is usually referred
to as an oxidized environment.
Water where sulfate is being con-
sumed and methane is being pro-
duced is generally referred to as a
reduced environment.
Reductive dechlorination usu-
ally occurs under sulfate-reducing
and methanogenic conditions.
Two electrons are transferred to
the chlorinated compound being-
reduced. A chlorine atom bonded
with a carbon receives one of the
electrons to become a negatively
(continued on page 4)
Ground Water Currents
-------
NEW FORTHE BOOKSHELF
Commonly Asked Questions Re-
garding the Use of Natural At-
tenuation for Chlorinated Sol-
vent Spills at Federal Facilities is
a brochure developed through a
partnership among the U.S.
EPA, Air Force, Army, Navy
and Coast Guard. The
brochure covers a description
of natural attenuation and un-
der what conditions federal,
state and local regulations al-
low natural attenuation as an
option for remediation of
chlorinated solvents. The bro-
chure briefly addresses how
natural attenuation is different
from the "do nothing" ap-
proach and how chlorinated
solvents are different from pe-
troleum products such as fuels
and guidelines on how to tell if
natural attenuation may work
at a site.
To get a copy of the brochure,
mail a. request to: Deborah
Tremblay, U.S. Environmental
Protection Agency (5402W),
401 MStreet, S.W., Washing-
ton, D.C. 20460.
(continuedfrom page 3)
charged chloride ion. The sec-
ond electron combines with a
proton (hydrogen ion) to be-
come a hydrogen atom that re-
places the chlorine atom in the
daughter compound. One
chlorine at a time is replaced
with hydrogen; as a result, each
transfer occurs in sequence. As
an example, tetrachloroethylene
is reduced to trichloroethylene,
then any of the three
dichloroethylenes, then to
monochloroethylerie (corri"-
monly called vinyl chloride)",
then to the chlorine-free car-
bon skeleton ethylene, then fi-
nally to ethane.
This article is, for the most
part, excerpted from Environ-
mental Chemistry and the Ki-
netics ofBiotransformation of
Chlorinated Organic Com-
pounds in Ground Water, John
T. Wilson, Donald H.
«w»fr,^tt,,.rjH.^nf ,-~--^* r\rr-~- '""" •
11 and James w.
, Symposium on Natu-
.t.tenuation of Chlorinated
Orvanics in Ground Water, pp.
124-127.
To obtain a copy of the full
Symposium on Natural Attenua-
tion of Chlorinated Qrvanics in
Ground Water (EPA Document
No. EPAI540IR-96I590) call
Kay Cooper (405-436-8651) at
the R. S. Kerr Environmental
Research Center or call the Cen-
ter for Environmental Research
Information (CERI) at 513-
569-7562. The document will
also be available on the EPA's
Office of Research and Develop-
ment (ORD) homepage, Bio
Site, at: http://wwui.epa.gov/
docs/ord/ in November 1996.
MAILING LIST/ORDER IKFO/ON-LINE ACCESS
To get on the permanent mailing list for Technology Innovation Office publications .pr to, order additional .copies of tteor previqus. issues of Ground Water Currents,
send a fax request to the National Center for Environmental Publications and Information (NCEPI) at 513-489-8p% or send;a; mail request to
NCEPI.P.O. Box 42419, Cincinnati, OH 45242-2419. Please referto thedocument number on. the cover of dteissue if available,; . ...
Ground Water Currents can be obtained by accessing EPA's C!ean-Up Information (CLU-IN) WWWsite (http://clu-w,com) ,W Cttl-IN BBS (by modem at
301-589-8366 or via the Internet by telnet to du-in,epa.gov,or ,134x57.99.13); For voice help call 301-589-8368. , ,;,, ;
Ground Water Currents welcomes readers'comments and contributions,. Address .cprrespondencB to: , , ,...:..;., ..'....
Ground Water Currents, NCEPI, P.O. Box 42419, CincjnnaH,; OH, 45.242-2419 ;X ;.'.'.;. >/,',.' ..'^VU. ..'...,•, '-.I..:.
United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-N-96-005
September 1996
Issue No. 16
vvEPA Ground Watel Cononts
Developments in innovative ground water treatment
------- |