United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SV-95/001
September 1995
4>EPA Project Summary
Natural Bioattenuation of
Trichloroethene at the
St. Joseph, Michigan
Superfund Site
James W. Weaver, John T. Wilson, and Don H. Kampbell
Data from the St. Joseph, Michigan,
Superfund Site were used in a peer-
reviewed video entitled "Natural
Bioattenuation of Trichloroethene at the
St. Joseph, Michigan Superfund Site."
Computer visualizations of the data set
show how trichloroethene, or TCE, can
degrade under natural conditions. The
purpose of the tape is to present
sampling results from the site to a
technical audience. Although the
visualizations show the general
distribution of chemicals at the site, it is
not possible to determine the precise
concentrations from the tape. Thus the
data set itself is available in a companion
document. The following text is an
amplified version of the narration on the
video.
This Project Summary was developed
by the National Risk Management
Research Laboratory's Subsurface
Protection and Remediation Division,
Ada, OK, to announce key findings of the
research project that is documented in a
video of the same title (see video ordering
information at back).
Site History
The site is located four miles south of St.
Joseph and one-half mile east of Lake Michigan
(Figure 1). Since the 1940s, the site has
supported auto-parts manufacturing, including
a foundry, as well as machining and painting
operations. Because of past activities, ground
water at the site is contaminated with
industrial wastes that include trichloroethene
(TCE). A plume of contamination reaches
from its source near the industry, toward
Lake Michigan to the west (Tiedeman and
Gorelick, 1993).
The aquifer is primarily composed of
medium, fine, and very fine sands that are
of glacial origin. The base of the aquifer is
defined by a clay layer that lies between 21
and 29 meters below the ground surface.
Since the ground water flows toward Lake
Michigan, the contamination underlies
residential and shoreline property. This
water eventually discharges directly into
the lake.
Although the TCE contamination is moving
toward the lake, evidence indicates that the
contaminants are degrading naturally along
the way (McCarty and Wilson, 1992).
Reduction in concentration alone does not
necessarily indicate bioattenuation, because
concentrations can decline from the effects
of advection, dispersion and sorption.
Rather, bioattenuation of TCE is indicated
here by the presence of daughter products
and certain geochemical conditions.
Degradation of TCE
Chlorinated organic compounds such as
TCE can be biodegraded in the subsurface,
but not because the microorganisms oxidize
these compounds as a food source. On the
contrary, the degradation of TCE under
anaerobic conditions occurs through a
reductive transformation where the TCE
molecule serves as an electron acceptor. In
a loose analogy, we could say that the
microorganisms "breathe" TCE. Forthistype
of degradation to occur, another organic
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Figure 1. Site plan showing the location of the sampling transects.
compound must be present to serve as an
oxidizable carbon source, or "food" for the
microorganisms. Under this condition, and
in the absence of oxygen, TCE can be
transformed through a series of intermediate
chemical compounds to ethene. The
intermediates are hazardous, and therefore
incomplete degradation of TCE is potentially
undesirable.
TCE may undergo a reductive
transformation in an anaerobic environment.
An enzyme or cofactor catalyzes the
reduction of TCE (HC2CI3), resulting in the
loss of one chlorine atom:
H * + H C7 Cl = H, C7 CL +
(1)
Threeisomersofdicholoroethene.orDCE
(H2C2CI2), can result: 1,1-DCE; cis-1,2 DCE
and trans-1,2 DCE. Of these, cis-DCE is
usually produced in the greatest abundance.
The presence of the DCE isomers is
significant, because these chemicals have
rarely been used on a large scale for
industrial purposes. Therefore their
presence is an indication of transformations
occurring in the subsurface.
With the loss of another chlorine atom
from a DCE isomer, vinyl chloride (H3C2CI)
is produced:
H2C2CI2 = H3C2CI
Cl-
(2)
The production of vinyl chloride is
undesirable because it is a known
carcinogen. However, ethene, which is not
a compound of regulatory concern, can
result from the loss of the chlorine atom
from the vinyl chloride:
H * + H3 C2 Cl = H4 C2 + Cl-
(3)
For further information on TCE
biodegradation see McCarty and Semprini,
1994, and Semprini et al. 1995.
Field Evidence for TCE
Bioattenuation
At a field site, natural bioattenuation of
TCE is indicated
• by the presence and degradation of an
oxidizable substrate;
• by the absence of oxygen and the
presence of strongly reducing conditions
(i.e., the abundance of methane);
• by the presence of the intermediate
products (the DCE isomers and vinyl
chloride); and,
• by the presence of ethene, the end
product.
Specific site conditions determine the
rate at which the transformations occur and
the likelihood of producing a harmless end
product. Each site must be evaluated
individually for its potential to degrade TCE.
There are sites where TCE either does not
degrade or is only partially degraded. Thus
the results from St. Joseph show the
possilbilty of degradation of TCE, but do not
indicate that degradation will occur at all
sites.
Representation of the Data
In the visualizations, each data set is
displayed as a set of colored cubes that
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surround the borings. Each boring appears
as an elongated, colored stack of cubes.
This approach was taken so that the data
was not smoothed, interpolated, nor
extrapolated. The representations of the
data, therefore, show the variation in
concentration that occurs over small
intervals at the site, and the irregularity of
the distributions. The top of each set of
cubes roughly corresponds to the water
table; and the bottom corresponds to the
clay layer that forms the base of the aquifer.
Narration on the tape makes it clear that
the views have been exaggerated in the
vertical direction in order to better illustrate
the distribution of the chemicals over the
thickness of the aquifer. The lengths of the
borings were indicated by noting that each
cube in the on-shore borings is 1.5 meters
tall, and that the borings contain from five to
eleven cubes. Thus the borings represent
aquifer thicknesses varying from 7.5 to 16.5
meters. This scale is also noted by the
distance (16.5 meters) between the top of
the bluff and the shore line. The exaggerated
veritcal distances contrast with the distance
across the site from the industry's parking
lot to the shore of Lake Michigan (730
meters); and the width of the contaminant
plume (110 meters). These features of the
visualizations indicate that the views
emphasize vertical variations in the
contaminant distribution. In actuality the
contaminant plume is a long and thin object.
The color scale that is used to indicate
concentration ranges from blue to red,
indicating low to high concentrations,
respectively. A logarithmic scale was used
to discriminate between concentrations that
range over six orders of magnitude.
The St. Joseph Data Set
Data were collected at St. Joseph in sets
of borings that form transects across the
site. The borings were made with a 1.5
meter long slotted auger from which water
samples were taken. A gas chromatograph
was used to detect the pollutants as the
borings were made. These procedures
assured thatthe transects crossed the entire
width of the contaminant plume.
Data were collected from the site in 1991
along transects nearthe source region, and
in 1992 along two transects lying between
the source and the lake (Semprini et al.,
1994). In August 1994, a set of samples
were taken from a barge anchored in Lake
Michigan. These samples determined the
contaminant concentrations in the ground
water immediately before it discharges into
the lake.
Features of the St. Joseph Data
Set
In the vicinity of the plume, dissolved
oxygen is depleted from the ground water,
even though the ground water is oxygen-
rich outside the contaminated zone. The
ground water is depleted of oxygen nearthe
bottom of the aquifer. Oxygen at
intermediate and high concentrations, from
two to ten milligrams per liter, is found in
some locations near the water table. The
methane data show a pattern that is almost
exactly opposite that of the dissolved
oxygen. Methane concentrations are highest
near the bottom of the aquifer and are
lowest nearthe watertable. This distribution
shows that the aerobic and anaerobic zones
in the aquifer are clearly separated.
At St. Joseph, there is a decrease of COD
from the source area to the lake. This is
indicative of anaerobic degradation of the
oxidizable carbon source, which remains to
be specifically identified.
The highest TCE concentration at the site
is 89,000 micrograms per liter and is found
near the source area. The contaminants
tend to move toward the lake in the deeper
part of the aquifer, as noted by the absence
of TCE near the water table. By the time
TCE reaches the lake, however, the
concentrations are reduced to levels that
are mostly undetectable. There are a few
TCE concentrations of one to two
micrograms per liter in the lake transect.
These concentrations are below the EPA
drinking water standard of 5 micrograms
per liter.
The pattern of declining concentration as
the chemicals flow toward the lake is
repeated in both the DCE and vinyl chloride
data sets. Dechlorination of TCE usually
produces the cis-DCEisomer in the greatest
abundance. At St. Joseph, for example, the
trans-DCE andthe 1,1-DCE concentrations
are generally lower than the cis-DCE
concentrations by at least a factor of 10.
The transformation of TCE to DCE may
occur undersulfate reducing conditions and
sulfate concentrations should be measured.
The maximum cis-DCE concentration is
128,000 micrograms perliter, occurring near
the bottom of the aquifer in the source region.
cis-DCE concentrations decline toward the
lake and the compound is undetectable in
the lake transect. Because the cis-DCE is
the dominant isomer at St. Joseph, the trans-
DCE and 1,1-DCE data sets are not shown
in the video tape.
The vinyl chloride distribution follows the
general pattern of highest concentrations
nearthe bottom of the aquifer and declining
concentrations toward the lake. No vinyl
chloride concentrations above the drinking
water standard of two micrograms per liter
were detected from samples taken in the
lake.
The presence of ethene is evidence for
the complete dechlorination of the TCE.
Ethene is present throughout the
contaminant plume; its distribution follows
the pattern oftheotherdegradation products.
Summary
In summary, the intermediate products of
TCE bioattenuation are found in oxygen
depleted portions of the aquifer that are
also rich in methane. Ethene is found in
significant concentration, indicating some
of the TCE is degraded to a compound that
is not of regulatory concern. The
concentrations of TCE and the degradation
products significantly decline toward the
lake. The off-shore data show that only
minute concentrations of these chemicals
exist in the ground water that discharges
into the lake.
Analysis of data from the St. Joseph,
Michigan Superfund site indicates that
natural bioattenuation of TCE is occurring
as the contaminants flow toward Lake
Michigan. Depletion of oxygen, the presence
of methane and the appearance of
degradation products indicate that the
reduction in TCE concentrations is not solely
due to volatilization or dilution. Rather, they
are indicative of microbial processes helping
to reduce the contaminant concentrations
below EPA drinking water standards before
the water is discharged into Lake Michigan.
Continued monitoring of the site is necessary
to demonstrate that contaminant levels
remain below accepted standards and that
the flux of chemicals into the lake remains
low.
REFERENCES
McCarty, P.L. and L. Semprini, Ground-
water treatment for chlorinated solvents,
Handbook of Bioremediation, Norris et al.,
pp5-1 to 5-30, 1994.
McCarty, P.L. and J.T. Wilson, Natural
anaerobic treatment of a TCE plume St.
Joseph, Michigan NPLsite, Bioremediation
of Hazardous Wastes, US EPA, EPA/600/
R-92/126, 47-50, 1992.
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Semprini, L, P.K. Kitanidis, D. Kampbell
and J.T. Wilson, Anaerobic transformation
of chlorinated aliphatic hydrocarbons in a
sand aquifer based on spatial chemical
distributions, Water Resources Research,
31(4), 1051-1062, 1995.
Tiedeman, C., and S. Gorelick, Analysis
of uncertainty in optimal groundwater
contaminant capture design, Water
Resources Research, 29(7), 2139-2153,
1993.
The EPA authors, James W. Weaver (also the EPA Project Officer, see below), John T.
Wilson, and Don H. Kampbell, are with the National Risk Management Research
Laboratory's Subsurface Protection and Remediation Division, Ada, OK 74820.
The video, entitled "Natural Bioattenuation ofTrichloroethene at the St. Joseph, Michigan
Superfund Site" (EPA/600A/-95/001), will be available upon request from:
Subsurface Remediation Information Center
National Risk Management Research Laboratory
U. S. Environmental Protection Agency
P.O. Box1198
Ada, Oklahoma 74820
Telephone: 405-436-8651
FAX: 405-436-8503
The EPA Project Officer can be contacted at:
Subsurface Protection and Remediation Division
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Ada, OK 74820
United States
Environmental Protection Agency
National Risk Management Research Laboratory (G-72)
Cincinnati, OH 45268
Official Business
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$300
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EPA/600/SV-95/001
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