application of compound-specific carbon and chlorine...

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

221

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 down-

gradient 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.

Application of Compound-Specific Carbon and Chlorine Stable Isotope... 222

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


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 (Shouakar-

Stash, 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


and 37

Cl/35

Cl or 13

C/12

C is the measured isotopic ratio (R) of both sample

and standard. The δ37

Cl values were calibrated and reported relative to

the reference material, Standard Mean Ocean Chloride (SMOC)

(Kaufman, et al., 1984) while δ13

C 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 (off-

site) 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.


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.


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 13

C and 37

Cl, 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 13

C and

0.30‰ and 1.78‰ for 37

Cl (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 13

C and -0.49‰ for 37

Cl and

another group with δ values of - 31.8‰ and - 32.6‰ for 13

C and 1.08‰

and 2.03‰ for 37

Cl, 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 13

C 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 (δ13

C = - 23.7‰; δ37

Cl = 0.14‰) than the cis-DCE associated to

the off-site TCE plume (δ13

C = - 28.5‰; δ37

Cl = 4.3‰).


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.


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 isotope-

ratio data, Geochim. Cosmochim. Acta., 60: 3359-3360.

Elsner, M., Cwiertny, D.M., Roberts, A.L. and Sherwood-Lollar, B. (2007) 1,1,2,2-

tetrachloroethane 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).


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.


��

�� !� "�� !��

� ��

��

�

�� !�"��

�� . ��

�� !��"� #��$% ��& ��!�� '��

��! ��(�� )��*�� . �� *�� $�� +��,� ��

��- �� '��(�� .�/�� ,�*� �$ 0� 1��

2 �� 3�� 4�� 5�� "��6� �� 3�� '2��!��

��*�� 7��8�� 9�� )�� . '��

��& �� 9�� *�� 3��:�� $�� '��!�� )��5� #$% ��;�

� �� '�� 3��!�� -�� "(�! 0�� +�

7��% �� /�� <��!� �� !�� =��

'��*��)��$�� $ 0�� )��! ��5 ( >�� ?� � +9��,��

��$�� ,� . ��!�� *�� 3��:�� +�� +�� - ��

��*�@� ��! ��*6* <�"�� 5�� !��trichloroethylene (TCE)

.��&�� 3�� $�� 0�� !�� '��*��

�� $��*�� ! )��!� 1��5�� )��5�� )��$�� .��&�� A��

(PCE) perchloroethene . ��$ ��*�� 3��:�� '�� '��9:%�

�� 3�� $�� ? �� =�� /�� 3�:�TCE ��,�

.�&�� $� . �,�� B6��2� ��- �:56� ��!��

�� =��TCE ��$� �� '��9:% �� =��


��$� �% C�8� D3�� TCE �� +-�� - .�&�� A��

��TCE .��&�� )�� . ��!�� '��!�@� D3�� - '��9:%�

�� "�� +��6� Cl37 �C13 '��*�� '��$ �� )3��!

�� 8��.

application of compound-specific carbon and chlorine...

Documents