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
Penalty for Private Use
$300
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                                                            EPA
                                                      PERMIT No. G-35
EPA/600/SV-95/001

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