Chemical Distributions and Anaerobic Transformation of Chlorinated Aliphatic Hydrocarbons in a Sand Aquifer

EPA/600/A-95/111
"PREPRINT EXTENDED ABSTRACT"
Presented at the I&EC Special Symposium
American Chemical Society
Atlanta, GA September 19-21, 1994
Chemical Distributions and Anaerobic Transformation of
Chlorinated Aliphatic Hydrocarbons in a Sand Aquifer
Lewis Semprini1. Peter K. Kitanidis2, Don Kampbell3, and John T. Wilson3
* Department of Civil Engineering, Oregon State University, Corvallis, OR 97331
^Department of Civil Engineering, Stanford University, Stanford, CA 94305
3U.S. Environmental Protection Agency, Robert S. Kerr Environmental Research Laboratory,
Ada, Oklahoma 74820
INTRODUCTION
A sand aquifer near the town of St. Joseph, Michigan, was contaminated with trichloroethylene
(TCE). Monitoring well data, indicated dichloroethylene (DCE), and vinyl chloride (VC), were present
as transformation products. A detailed chemical characterization of the subsurface was performed that
demonstrated the anaerobic transformation of TCE to DCE, VC, and ethene. The characterization
permitted zones to be identified where transformations are occurring, and permitted flux estimates of the
contaminants and transformation products.
The potential for anaerobic biological transformations of chlorinated aliphatic hydrocarbons
(CAHs) in the subsurface was demonstrated in 1981 (1). Subsequently, CAHs in general have been
found to be transformed under a variety of environmental conditions in the absence of oxygen. Redox
conditions in the subsurface are often regulated by microbial processes. Common anaerobic electron
acceptors and the associated microbial process, in the order of their redox potential are
nitrate(denitrification); Mn(IV) (manganese reduction); Fe(III) (iron reduction); sulfate (sulfate
reduction); and carbon dioxide (methanogenesis). Many of the CAHs are highly oxidized and have
redox potentials above these common electron acceptors (2), and therefore can be reduced. The
sequential reduction of the double-bonded CAHs, including tetrachloroethylene (PCE) and
trichloroethylene (TCE), is of concern since these compounds are frequently observed at contamination
sites, and there is potential for the formation and accumulation of vinyl chloride (VC), a known
carcinogen. Recently there has been renewed interest in anaerobic transformation of chlorinated
ethenes, with the observations that VC can be further reduced biologically to ethene (3,4).
Reductive dehalogenation depends on the availability of electron donors (5,6,3). At
contamination sites, along with CAHs, other co-contaminants such as fuels, alcohols, ketones, organic
acids, and unidentified forms of Chemical Oxygen Demand (COD), are often present that can serve as
electron donors to drive the anaerobic transformations.
The geologic formation of interest at the St. Joseph site is an unconfined aquifer consisting of a
layer of unconsolidated fine sand with some silt. The aquifer is relatively homogeneous, having been
formed by eolian sorting of glacial deposits, with a hydraulic conductivity of about 10~4 m/s . The site
is bounded by Lake Michigan to the northwest and Hickory Creek to the east. The hydrology of the
sandy aquifer is relatively simple: a high recharge rate {about 55 cm/year) replenishes the aquifer and the
groundwater drains into the lake and the creek, which act as constant-head boundaries, at a nearly steady
rate.
An automotive brake manufacturer disposed of wastewater into unlined lagoons from the mid-
1950's through the mid-1970's. It has not been confirmed whether TCE was directly discharged to the
lagoons. Regional groundwater flow modeling studies indicated that the lagoons were a possible source
of contamination (7).

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METHODS
In August-September, 1991, 155 groundwater samples were collected along three transects
located near the areas of highest concentration. Two transects (1 and 2) were nearly perpendicular to the
groundwater flow and Transect 3 was nearly parallel. The three transects included a total of 17 borings
within the saturated zone. Groundwater samples were collected at five foot intervals between the water
table, located within 35 to 40 feet from the ground surface, and the underlying clay confining bed,
located 65 to 90 feet below the ground surface. The groundwater samples were collected through a five
foot long, 4.25 inch ID. stainless steel drive-point that was slotted with 0.01 inch openings. The drive
point was driven ahead of the drilling augers.
Real-time gas chromatography analyses were performed in the field to aid in selecting the
location of the borings. Water samples were analyzed in the laboratory for TCE and its anaerobic
transformation products using purge and trap with gas chromatography (8). Methane, ethene, and ethane
were determined by a headspace procedure (9). Ammonium ion was measured as Total Kjeldahl
Nitrogen (TKN), and chloride and sulfate were measured by ion chromatography (8)
RESULTS
The characterization showed some pockets of very high contaminant concentration. The
maximum TCE concentration was 133 mg/L. Elevated methane concentrations were present at greater
depth (maximum, 11.3 mg/L). 1,2-cis-dichloroethylene(c-DCE) was the dominant DCE isomer present.
The maximum concentrations of the DCE isomers were as follows: c-DCE, 133 mg/L; trans-DCE, 3.9
mg/L; and 1,1-DCE, 5.3 mg/L. VC and ethene (maximum, 56 mg/L; 6.6 mg/L, respectively) were
associated with the areas of elevated methane concentrations, and depressed sulfate concentrations. The
high methane concentrations indicated methanogenic conditions existed, and the presence of ethene
indicated some of the TCE had been completely dechlorinated. Ethane, however, was not detected.
The transects showed general spatial trends in concentrations of CAHs, ethene, methane, sulfate,
and ammonium ion. The high contaminant concentrations (>10,000 mg/L) of TCE and c-DCE tend to
be at shallower depths (65 to 75 ft), compared to VC (65 to 85 ft) as well as methane and ethene (65 to
85 ft). The high values of VC and ethene were usually associated with high values of methane.
Figure 1 shows a typical distribution of the CAHs, ethene, and methane that was observed in the
borings. The methane concentration increases with depth. The low methane was associated with high
TCE concentrations. The TCE concentration decreased as the methane concentration increased with
depth. The c-DCE profile was similar to that of TCE but shifted to a greater depth. The VC and ethene
increased with depth, consistent with methane. The ethene profile was a subdued version of methane's.
The results show the sequential transformation of TCE, with complete dechlorination to ethene at depth
associated with higher methane concentrations.
Figure 2 shows the distribution of ammonia, chloride, and sulfate in the same boring. The sulfate
concentration decreases with depth as methane concentrations increase. This indicates the preferential
use of sulfate as an electron acceptor at shallower depths. The ammonium profile is similar to that of
sulfate. The decrease in both sulfate and ammonium with depth, and the increase in methane indicates
an increase in anaerobic activity. The decrease in ammonium could be associated with cell synthesis.
TCE rapidly decreases in this zone, while c-DCE increases to a maximum, and then decreases. The
chloride profiles shows no trend with depth, due to high background levels in the groundwater.
2-D contour analysis showed similar spatial trends. TCE was present in zones of low methane
concentration. c-DCE was found between areas of low and high methane concentrations. t-DCE and
1,1-DCE show contours that are similar to c-DCE, but reduced in concentration, indicating similar
processes produced and transformed the DCE isomers. VC and ethene were associated with the zones of
high methane and low sulfate concentrations. The contaminant contours indicate VC production and
complete dechlorination to ethene was associated with zones of methanogenesis. The abrupt decrease in
TCE concentration in the highly methanogenic zones indicates reductive transformation in the zone
surrounding the methanogenic zone, in areas associated with sulfate reduction. The results indicate that
the presence of sulfate could inhibit the further reduction of c-DCE, or perhaps indicate zones where the
electron donor concentrations were lower and thus biological activity was less.

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r
Table 1 presents estimates of mole fluxes of the CAHs, ethene, and methane across Transects 1
and 2. The mole flux of CAHs plus ethene (Total Ethenes) at Transect 2 (upgradient) was 1.9 times
\ greater than at Transect 1 (downgradient). The flux of methane is approximately four times greater
through Transect 2 than through Transect 1. Thus, more highly anaerobic conditions may exist
upgradient. c-DCE represents the greatest mole flux in both transects, indicating significant anaerobic
transformations are taking place. Ethene represents a greater mole flux out of Transect 1 than VC,
possibly indicating more complete dehalogenation with transport downgradient. Ethene represents 8 to
22 percent of the total mole flux. Thus, a significant amount of the CAHs is being completely
dehalogenated to a non-toxic endproduct.
REFERENCES
(1)	Bouwer, E.J., B. E Rittmann, and P. L. McCarty, Anaerobic degradation of halogenated 1- and 2-
carbon organic compounds, Env. Sci. Technol, 15, 596-599, 1981.
(2)	Vogel, T.M., C.S. Criddle, and P.L. McCarty, Transformations of halogenated aliphatic compounds,
Environ. Sci. and Technol., 21,722-736, 1987.
(3)	Freedman, D.L. and J.M. Gossett, Biological reductive dechlorination of tetrachloroethylene and
trichloroethylene to ethylene under methanogenic conditions, Appl. Environ. Microbiol, 55, 2144-
2151,1989.
(4)	DiStefano, T.D., J.M. Gossett, and S.H. Zinder, Reductive dechlorination of high concentrations of
tetrachloroethene to ethene by anaerobic enrichment culture in the absence of methanogenesis, Appl.
Environ. Microbiol, 57,2287-2292, 1991.
(5)	Fathepure, B.Z, and S.A. Boyd, Dependence of tetrachloroethylene dechlorination on
methanogenic substrate consumption by Methanosarcina sp. strain DCM, Appl. Environ.
Microbiol, 54,2976-2980,1988.
(6)	Baek, N.M. and P.R. Jaffe, The degradation of trichloroethylene in mixed methanogenic cultures, J.
Environmental Quality, 18,515-518, 1989.
(7)	Tiedeman, C. and S.M. Gorelick, Optimal hydraulic containment designs under parameter
uncertainty for a vinyl chloride plume in Southwest Michigan, Water Resour. Res., 29, 2139-2153,
1993..
(8)	Standard Methods for the Examination of Water and Wastewater, 18th Edition, American Public
Health Association, Washington, DC, 1992.
(9)	Kampbell, D. H„ J. T. Wilson, and S. A. Vandergrift, Dissolved oxygen and methane water by a
GC headspace equilibration technique, Int. J. Environmental Chemistry, 36, 249-159, 1989.
Table 1. CAH, Ethene, and Methane Flux Estimates for Transects 1 and 2
Transect 1
TCE
c-DCE
VC
Ethene
Total
Ethenes
Methan
Mole Flux
(g mole/yr)
470
730
180
380
1760
3280
Mole Flux
(percent)
27
41
10
22
100
-
Transect 2






Mole Flux
(g mole/yr)
1120
1580
360
280
3340
.. 11750
Mole Flux
(percent)
34
47
11
8
100
-

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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before compl'
1. REPORT NO.
EPA/600/A-95/111
2.

4. TITLE AND SUBTITLE
CHEMICAL DISTRIBUTION AND ANEROBIC TRANSFORMATION
OF CHLORINATED ALIPHATIC HYDROCARBONS IN A SAND
AQUIFER
5. HEPORT DATE
r
6. PERFORMING ORGANIZATION CODE
7. author(s) LEWIS SEMPRINI (1)
PETER K. KITANIDIS (2)
DON KAMPRKT.T, AND JOHN T. WTT.SDN m
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADORESS ' '
DEPT. OF CIVIL ENG.,OREGON STATE UNIV.,CORVALLIS
OR (1)
DEPT. OF CIVIL ENG.,STANFORD UNIVSTANFORD,CA (2
US/EPA, RSKERL, ADA, OK. (3)
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
)
STANFORD U/WRHSRC
12. SPONSORING AGENCY NAME ANO AOORESS
U.S./EPA, NRMRL-ADA
SUBSURFACES PROTECTION & REMEDIATION DIVISION
P.O. BOX 1198
ADA, OK 74820
13. TYPE OF REPORT AND PERIOD COVERED
BOOK CHAPTER
14. SPONSORING AGENCY CODE
EPA/600/15
15. SUPPLEMENTARY NOTES
16. ABSTRACT
We estimated the distribution of chlorinated aliphatic hydrocarbons (CAHs)
from groundwater samples collected along three transects in a sand aquifer.
Trichloroethylene (TCE) leaked and contaminated the aquifer probably more than a
decade before we collected the measurements. The data show significant concentrations of
TCE, cis-l,2-dichloroethylene (c-DCE), vinyl chloride (VC), and ethene. We attributed
DCE, VC, and ethene to the reductive dehalogenation of TCE. The CAH concentrations
varied significantly with depth and correlate with sulfate and methane concentrations. |
Anoxic aquifer conditions exist with methane present at relatively high concentrations at j
depth. High concentrations of TCE correspond with the absence of methane or low j
methane concentrations, whereas pioducts of TCE dehalogenation are associated with
higher methane concentrations and low sulfate concentrations. Indications are that the
dechlorination of TCE and DCE to VC and ethene is associated with sulfate reduction
and active methanogenesis. TCE dechlorination to DCE is likely occurring under the less
reducing conditions of sulfate reduction, with further reductions to VC and ethene
occurring under methanogenic conditions. We estimated that about 20% of TCE has
dechlorinated to ethene. The analysis of the data enhanced our knowledge of natural
in situ transformation and transport processes of CAHs.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. cosati Field.Group
TRICHLOROETHYLENE
GROUND-WATER
TCE
CIS-DICHLOROETIIYLENE
^INYL CHLORIDE
REDUCTIVE DECHLORINATli
)N
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21 NO. OP PAGES
h
20. SECURITY CLASS (This pane;
UNCLASSIFIED
22. PRICE
EPA Farm 2220-1 (8«v. 4-77) previous edition is obsolete
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