Project Summary

Natural Bioattenuation of

Trichloroethene at the

St. Joseph, Michigan

Superfund Site

Research and Development EPA/600/SV-95/001 September 1995

National Risk Management

Research Laboratory

Cincinnati, OH 45268

United States

Environmental Protection

Agency

James W. Weaver, John T. Wilson, and Don H. Kampbell

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. For this type

of degradation to occur, another organic

Data from the St. Joseph, Michigan,

Superfund Site were used in a peerreviewed 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
2

LAKE

MICHIGAN

200 0 200 FT.

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 (HC2

Cl3), resulting in the

loss of one chlorine atom:

H + + H C2 Cl3 = H2 C2 Cl2 + Cl - (1)

Three isomers of dicholoroethene, or DCE

(H2

C2Cl2), 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 (H3

C2Cl)

is produced:

H + + H2 C2 Cl2 = H3 C2 Cl + 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;

Figure 1. Site plan showing the location of the sampling transects.

• 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
3

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 that the transects crossed the entire

width of the contaminant plume.

Data were collected from the site in 1991

along transects near the 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 oxygenrich outside the contaminated zone. The

ground water is depleted of oxygen near the

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 near the water table. 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-DCE isomer in the greatest

abundance. At St. Joseph, for example, the

trans-DCE and the 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 under sulfate reducing conditions and

sulfate concentrations should be measured.

The maximum cis-DCE concentration is

128,000 micrograms per liter, 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 transDCE and 1,1-DCE data sets are not shown

in the video tape.

The vinyl chloride distribution follows the

general pattern of highest concentrations

near the 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 of the other degradation 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, Groundwater treatment for chlorinated solvents,

Handbook of Bioremediation, Norris et al.,

pp 5-1 to 5-30, 1994.

McCarty, P.L. and J.T. Wilson, Natural

anaerobic treatment of a TCE plume St.

Joseph, Michigan NPL site, 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 of Trichloroethene at the St. Joseph, Michigan

Superfund Site" (EPA/600/V-95/001), will be available upon request from:

Subsurface Remediation Information Center

National Risk Management Research Laboratory

U. S. Environmental Protection Agency

P.O. Box 1198

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

EPA/600/SV-95/001

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35