JKAU: Met., Env. & Arid Land Agric. Sci., Vol. 22, No. 3, pp: 221-232 (2011 A.D. /1432 A.H.)
DOI: 10.4197/ Met. 22-3.12
Application of Compound-Specific Carbon and Chlorine
Stable Isotope for Fingerprinting Sources of Chlorinated
Compounds in Groundwater
Orfan Shouakar-Stash, Ramon Aravena, Daniel Hunkeler1 and
Brian Bjorklund2
Department of Earth Sciences, University of Waterloo, 200 University
Ave. W., Waterloo, Ontario, Canada N2L 3G1, 1University of Neuchatel,
Neuchatel, Switzerland, and 2ERM, Environmental Resources
Management, Walnut Creek, CA, USA
Abstract. Groundwater contamination by hazardous substances
including chlorinated solvents has become a serious widespread
problem, representing a substantial liability. Evaluation of
contaminant sources in groundwater plumes, which has significant
relevance for assignment of responsabilities for groundwater
remediation, is one of the key aspects that consultants and
environmental agencies have to deal with in contaminated
groundwater. In recent years, compound-specific stable isotope
analysis have become a valuable methodology that is employed as an
indicator of chemical and biological degradations of chlorinated
solvents in groundwater and as a tool to distinguish different plumes
(fingerprinting) and trace them back to the release source point. In this
study, chlorine and carbon stable isotopes were used to identify the
origin of trichloroethene (TCE) in a co-mingled plume that can be
associated to a primary in-site source and an off-site TCE source link
to biodegradation of perchloroethene (PCE). The stable isotope data
showed a very distinct and significantly different isotopic fingerprint
for the primary source of TCE compared to the off-site source. This
difference can be observed in the co-mingled TCE plume downgradient from the two TCE sources clearly showing that the off-site
TCE source is contributing to the in-site TCE plume. These results
showed the great potential of the combined use of 37Cl and 13C for
fingerprinting organic contaminant sources in groundwater.
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Application of Compound-Specific Carbon and Chlorine Stable Isotope...
1. Introduction
In the last two centuries, the impact of human activities on nature has
been growing dramatically. Many natural resources show some degree of
anthropogenic impact, including the widespread contamination of
groundwater aquifers by hazardous materials (Alvarez and Illman, 2006).
Groundwater contamination is an important problem since groundwater
represents 98% of the available fresh water on the earth. According to a
1982 EPA survey, 20% of drinking water wells showed contamination by
synthetic organic compounds. Approximately 30% of the 48,000 public
drinking water systems that serve population in excess of 10,000 people
were contaminated. There are 300,000-400,000 sites in the United States
that are highly contaminated by toxic chemicals and require remedial
action. The estimated cost of environmental cleanup and management is
in the order of one trillion dollar in the United States and it is expected to
be over 1.5 trillion dollar in Europe (ENTEC, 1993, La Grega, et al.,
1994, NRC, 1994, 1997).
2. Contamination Sources
Groundwater and soil contamination can be generated from
different sources and processes. The most common sources of
groundwater contamination includes leaking from underground storage
tanks, municipal solids and hazardous landfills, house hold septic
systems, pesticide application areas, abandon petroleum wells, seawater
salt intrusion, surface waste discharge or accidental spills.
3. Common Groundwater Contaminants
The most common classes of groundwater contaminants include
aromatic hydrocarbons, chlorinated solvents and pesticides. Common
inorganic contaminants include nitrate, arsenic, selenium, and heavy
metals such as lead, cadmium and chromium.
3.1 Petroleum Hydrocarbons
The extensive use of petroleum hydrocarbons has resulted in
widespread soil and groundwater contamination. The most common
sources for this type of contaminants are leaky underground tanks,
pipelines and refining wastes. Petroleum hydrocarbons consist of a large
Orfan Shouakar-Stash, et al.
223
variety of chemicals compounds exceeding 300 different compounds
(e.g. Benzene, toluene, ethylbenzene, xylene). Benzene is considered to
be one of the most important petroleum hydrocarbon contaminants due to
its high solubility which makes it highly mobile in aquifers and its
carcinogenic effect on human. Hydrocarbons are generally lighter than
water and tend to float on the water table.
3.2 Chlorinated Compounds
Chlorinated compounds make up an important group of organic
contaminants that are both widespread and relatively persistent in
aquifers. Chlorinated ethenes are chemically stable compounds that are
resistant to combustion and explosion, therefore they were widely used as
degreasers in a variety of industries such as instrument manufacturing,
aerospace, electronic, printing and dry cleaning for most of the twentieth
century (McCulloch and Midgley, 1996). The combination of extensive
use, volatility, spills and chemical stability has led to their widespread
contamination of groundwater and soil by these compounds. Chlorinated
compounds are occupy 12 out of the top 20 places in the 2007 Priority
List of the Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA) of organic hazardous substances frequently
encountered at superfund sites (CERCLA Priority List, 2007). The most
common chlorinated solvent contaminates are tetrachloroethylene (PCE),
trichloroethelyene (TCE), dichloroethelyene (DCE) and vinyl chloride
(VC), all of which are potential carcinogens.
Chlorinated solvents generally have higher specific gravity than
water and tend to sink to the bottom of the aquifer when present in a
separate organic phase. Reductive dechlorination generally decreases the
toxicity and enhances the solubility (and bioavailability) of pollutants,
but there are exceptions where the toxicity can be enhanced (e.g.,
trichloroethene (TCE) reduction to VC). Vinyl chloride is classified as a
known human carcinogen by the International Agency for Research on
Cancer and is considered as one of the most toxic groundwater
contaminants (IARC, 2007).
3.3 Pesticides
Agricultural applications of pesticides represent an important
source of soil and groundwater contaminants. Pesticides that contaminate
aquifers are often insecticides and herbicides. Pesticides are problematic
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Application of Compound-Specific Carbon and Chlorine Stable Isotope...
because they are designed to be persistent. There are two main classes of
pesticides, organochlorides (e.g. DDT and Aldrin) and organophosphates
(e.g. Malathion and Diazinon). Pesticides account for eight top twelve list
of persistent organic contaminants identified by the United Nations
Environmental Programme (UNEP, 1999).
3.4 Newly Emerging Contaminants
In the last decade, a wide variety of organic compounds have
become identified potentially important contaminants. These include
endocrine disrupting products by pharmaceutical and personal care
product industries. Furthermore, pharmaceuticals, hormones, and other
wastewater contaminants are being detected in water resources
throughout the United States (Kolpin, et al., 2002).
4. Compound-Specific Stable Isotope Analyses
In the last 10 years, compound-specific carbon stable isotopes have
been increasingly used in chlorinated solvent contamination studies
(Hunkeler, et al., 1999; Sherwood-Lollar, et al., 1999; and Elsner, et al.,
2007). More recently, compound-specific chlorine stable isotopes were
introduced in investigating the behavior of these compounds (ShouakarStash, et al., 2006; Shouakar-Stash, et al., 2009; and Aby, et al., 2009).
The information provided by the isotopic signatures of organic compounds can
be employed to distinguish between different sources of contamination
“Isotopic Fingerprinting”. Chlorinated compound plumes can originate from
more than one source or during different episodes of release from one source.
Research that was conducted on chlorinated solvents over the last ten years (van
Wormerdam, et al., 1995, Beneteau, et al., 1999; and Shouakar-Stash, et al.,
2003) showed that commercially available chlorinated solvents are
characterized by a large isotopic variation which allows us to use isotopes as
fingerprinting tools. Furthermore, compound-specific stable isotopes can be
used in monitoring the fate of contaminant compounds in the groundwater (i.e.
evaluating processes such as biodegradation, sorption, dispersion and diffusion)
The isotopic compositions are reported in permil (‰) deviation
from isotopic standard reference material using the conventional δ
notation, where:
δ = [(Rsample/Rstandard) -1] × 1000
Orfan Shouakar-Stash, et al.
225
and 37Cl/35Cl or 13C/12C is the measured isotopic ratio (R) of both sample
and standard. The δ37Cl values were calibrated and reported relative to
the reference material, Standard Mean Ocean Chloride (SMOC)
(Kaufman, et al., 1984) while δ13C values are reported relative Vienna
Peedee Belemnite (VPDB) (Coplen, 1996).
5. Fingerprinting Case Study
5.1 Study Site
The study site is in Pleasant Hill, California. There is a primary
source of TCE near the southwest corner of the site and a separate (offsite) source of PCE located west of Vincent Road (Fig. 1). The
contamination is present in two aquifer zones. The A-Zone represents
relatively thin unconfined to semi-confined sand stringers within a fairly
tight silty clay matrix, and is generally found from the water table surface
(20- 25 ft bgs) to a depth of approximately 30 feet bgs. The B-Zone is a
confined aquifer, consisting of a fairly continuous sand bed found
between approximately 30 to 70 feet bgs.
A
B
Fig. 1. Distribution of TCE in aquifers A and B.
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Application of Compound-Specific Carbon and Chlorine Stable Isotope...
5.2 Sampling
The sampling approach for the isotope fingerprinting application
focused on the isotope characterization of the primary TCE source, the
TCE originated by biodegradation of PCE and the TCE at the hot spot
(MW-14A). The approach also included collection of samples along
the flow system in the plume associated to the plimary TCE source,
the off-site source and samples that seem to be in a commingled
plume. Samples were also collected down gradient of the hot spot.
5.3 Chemical Data
The concentration data showed an off-site PCE plume in aquifer A
ranging in concentration from 2,400 µg/L (well MW 20A) representing
the source to 740 µg/L (well MW-01) down gradient within the property.
The PCE in the aquifer B showed values between 10,000 µg/L at the
source and 1,500 µg/L in the down-gradient wells but it does not reach
the property (Fig. 2).
A
B
Fig. 2. Distribution of PCE in aquifers A and B.
Orfan Shouakar-Stash, et al.
227
The TCE data at aquifer A within the property showed values that
vary between 2,800 µg/L representing the source to values that varies
between 1,800 µg/L and 19 µg/L in the down-gradient areas. In case of
Aquifer B, the TCE concentration range between 11,000 to 1,900 µg/L in
the down-gradient areas (Fig. 1). The TCE plume associated with the
PCE plume show concentration values of 150 and 48 µg/L in aquifer A
and 790 and 98 µg/L in aquifer B (Fig. 1). The hot spot off-site of the
property showed TCE ranging between 5,300 µg/L (MW-14A, aquifer
A) and 780 µg/L (MW-14B, aquifer B) to values of 440 and 550 µg/L in
down-gradient areas of aquifer A and B, respectively (Fig. 1).
5.4 Isotope Data
The isotope data showed δ values ranging between - 24.4‰ and 22.7‰ and -0.70‰ and -0.31‰ for 13C and 37Cl, respectively, at and
near the TCE source in both aquifers (Fig. 3). A very different isotopic
composition is observed in the TCE in the off-site TCE plume that is
characterized by δ values between - 33.3‰ and - 31.5‰ for 13C and
0.30‰ and 1.78‰ for 37Cl (Fig. 3). Two set of δ values are observed in
the proposed commingled plumes with one group showing δ values
similar to the TCE source, - 23.9‰ for 13C and -0.49‰ for 37Cl and
another group with δ values of - 31.8‰ and - 32.6‰ for 13C and 1.08‰
and 2.03‰ for 37Cl, representing the off-site TCE plume (Fig. 3). The
plume associated to the hot spot (well MW 14-A) is characterized by δ
values between - 24.2‰ and - 25.7‰ for 13C and 0.3‰ and - 0.07‰ for
37
Cl (Fig. 3). These data are very different than the isotope composition
of the TCE source inside the property.
The isotope data on cis-DCE also showed that the cis-DCE
produced by biodegradation of the in-situ TCE source is isotopically
different (δ13C = - 23.7‰; δ37Cl = 0.14‰) than the cis-DCE associated to
the off-site TCE plume (δ13C = - 28.5‰; δ37Cl = 4.3‰).
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Application of Compound-Specific Carbon and Chlorine Stable Isotope...
A
B
Fig. 3. Isotopic Composition of TCE in aquifers A and B.
6. Conclusion
The compound-specific carbon and chlorine stable isotope data
show very significant isotopic differences between the TCE associated to
the study site TCE source located near the southwest property corner and
the off-site TCE source linked to biodegradation of PCE. The different
isotopic signature makes it possible to evaluate the origin of TCE in the
commingled area of the plume. It is clear that the TCE present in well
MW-07 and MW-0l is associated to the off-site plume and the TCE
present in wells MW-08A and MW-03 is related to the on-site TCE
source.
References
Abe, Y., Aravena, R., Zopfi, J., Shouakar-Stash, O., Roberts, J.D. and Hunkeler, D. (2009)
Carbon and chlorine isotope fractionation during aerobic oxidation and reductive
dechlorination of vinyl chloride and cis-1,2-dichloroethene, Environmental Science &
Technology, Environmental Science and Technology, 43: 101-107.
Orfan Shouakar-Stash, et al.
229
Alvarez, P. and Illman, W.A. (2006) Bioremediation and Natural Attenuation: Process
Fundamentals and Mathematical Models, John Wiley & Sons.
Beneteau, K.M., Aravena, R. and Frape, S.K. (1999) Isotopic characterization of chlorinated
solvents laboratory and field results, Journal of Organic Geochemistry, 30: 739-753.
Cercla Priority List (2007) Priority List of Hazardous Substances that Will Be the Subject of
Toxicological Profiles and Support Document, U.S. Department of Health and Human
Services, Agency for Toxic substances and Disease Registry - Division of Toxicology, In
Cooperation with the: U.S. Environmental Protection Agency, December 2007.
Coplen, T.B. (1996) New guidelines for reporting stable hydrogen, carbon and oxygen isotoperatio data, Geochim. Cosmochim. Acta., 60: 3359-3360.
Elsner, M., Cwiertny, D.M., Roberts, A.L. and Sherwood-Lollar, B. (2007) 1,1,2,2tetrachloroethane reactions with OH-, Cr(II), granular iron and a copper-iron bimetal:
Insights from product formation and associated carbon isotope fractionation, Environ. Sci.
Technol. 41: 4111-4117.
ENTEC (1993) Directory of Environmental Technology, Earthscan Publications and Lewis
Publishers/CRC Press, Ann Arbor, MI.
Hunkeler, D., Aravena, R. and Butler, B.J. (1999) Monitoring microbial dechlorination of
tetrachloroethene (PCE) in groundwater using compound-specific stable carbon isotope
ratios: Microcosm and field studies, Environ. Sci. Technol., 32(16): 2733-2738.
IARC (2007) Biennial Report 2006-2007 of the International Agency for Research on Cancer,
IARC, World Health Organization, Lyon, France.
Kaufmann, R.S., Long, A., Bentley, H. and Davis, S. (1984) Natural chlorine isotope variations,
Nature, 309: 338-340.
Koplin, D.W., Furlong, E.T., Meyer, M.T., Thurman, E.M., Zaugg, S.D., Barber, L.B. and
Buxton, H.T. (2002) Pharmaceuticals, hormones, and other organic wastewater
contaminants in U.S. streams, 1999-2000: A national reconnaissance, Environ. Sci.
Technol., 36: 1202-1211.
La Grega, M. D., Buckingham, P.L. and Evans, J.C. (1994) Hazardous Waste Management,
McGraw-Hill, Inc. Publishers, New York, NY.
McCulloch, A. and Midgley, P.M. (1996) The production and global distribution of emissions of
trichloroethene, tetrachloroethene and dichloromethane over the period 1988–1992,
Atmospheric Environment, 30: 601-608.
National Research Council (1994) Alternatives for Ground Water Cleanup, National Academy
Press, Washington, DC.
National Research Council (1997) Innovations in Ground Water and Soil Cleanup: From
Concept to Commercialization, National Academy Press, Washington, DC.
Sherwood-Loller, B., Slater, G.F., Ahad, J., Sleep, B., Spivack, J., Brennan, M. and
MacKenzie, P. (1999) Contrasting carbon isotope fractionation during biodegradation of
trichloroethylene and toluene: Implications for intrinsic bioremediation, Org. Geochem.,
30: 813-820.
Shouakar-Stash, O., Drimmie, R.J., Zhang, M. and Frape, S.K. (2006) Compound-specific
chlorine isotopes ratio of TCE, PCE and DCE isomers by direct injection using CF-IRM,
Applied Geochemistry, 21: 766-781.
Shouakar-Stash, O., Frape, S.K. and Drimmie, R.J. (2003) Stable hydrogen, carbon and
chlorine isotope measurements of selected chlorinated organic solvents, Journal of
Contaminant Hydrology, 60: 211-228.
Shouakar-Stash, O., Frape, S.K., Gargini, A., Pasini, M., Drimmie, R.J. and Aravena, R.
(2009) Analysis of Compound-Specific Chlorine Stable Isotopes of Vinyl Chloride by
Continuous Flow-Isotope Ratio Mass Spectrometry (CF-IRMS), Environmental Forensics
Journal (Under Publication).
230
Application of Compound-Specific Carbon and Chlorine Stable Isotope...
United Nations Environmental Protection Programme (UNEP) (1999) Inventory of
Information Sources on Chemicals: Persistent Organic Pollutants, UNEP Chemicals,
Geneva, Switzerland.
van Warmerdam, E.M., Frape, S.K., Frape, Aravena, R., Drimmie, R.J., Flatt, H. and
Cherry, J. A. (1995) Stable chlorine and carbon isotope measurements of selected
organic solvents, Applied Geochemistry, 10: 547-552.
231
Orfan Shouakar-Stash, et al.
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