 |
| Titel |
Halon-1301, a new Groundwater Age Tracer |
| VerfasserIn |
Monique Beyer, Rob van der Raaij, Uwe Morgenstern, Bethanna Jackson |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250102190
|
| Publikation (Nr.) |
 EGU/EGU2015-1495.pdf |
|
|
|
|
|
| Zusammenfassung |
| Groundwater dating is an important tool to assess groundwater resources in regards to
direction and time scale of groundwater flow and recharge and to assess contamination risks
and manage remediation. To infer groundwater age information, a combination of different
environmental tracers, such as tritium and SF6, are commonly used. However ambiguous age
interpretations are often faced, due to a limited set of available tracers and limitations of each
tracer method when applied alone. There is a need for additional, complementary
groundwater age tracers.
We recently discovered that Halon-1301, a water soluble and entirely anthropogenic
gaseous substance, may be a promising candidate [Beyer et al, 2014]. Halon-1301 can be
determined along with SF6, SF5CF3 and CFC-12 in groundwater using a gas chromatography
setup with attached electron capture detector developed by Busenberg and Plummer [2008].
Halon-1301 has not been assessed in groundwater.
This study assesses the behaviour of Halon-1301 in water and its suitability as a
groundwater age tracer. We determined Halon-1301 in 17 groundwater and various modern
(river) waters sites located in 3 different groundwater systems in the Wellington Region, New
Zealand. These waters have been previously dated with tritium, CFC-12, CFC-11 and SF6
with mean residence times ranging from 0.5 to over 100 years. The waters range from oxic
to anoxic and some show evidence of CFC contamination or degradation. This
allows us to assess the different properties affecting the suitability of Halon-1301 as
groundwater age tracer, such as its conservativeness in water and local contamination
potential.
The samples are analysed for Halon-1301 and SF6simultaneously, which allows
identification of issues commonly faced when using gaseous tracers such as contamination
with modern air during sampling.
Overall we found in the assessed groundwater samples Halon-1301 is a feasible new
groundwater tracer. No sample indicated significantly elevated concentration of Halon-1301,
which indicates absence of local anthropogenic or geologic sources (contamination), despite
some samples showing CFC contamination. We found agreement of 71% of mean age
estimates with ages inferred from tritium and SF6 within +/- 2 years, for samples where direct
age comparison could be made. The remaining sites showed reduced concentrations
of Halon-1301 along with reduced concentrations of CFCs. The reasons for this
need to be further assessed, but are likely caused by sorption or degradation of
Halon-1301.
Further Halon-1301 studies are planned covering various hydrogeologic situations, land
use practises, and redox conditions to evaluate the potential of Halon-1301 as groundwater
tracer, and to elucidate the causes for reduced Halon-1301 concentrations.
Acknowledgements
Greater Wellington Regional Council, especially S. Tidswell, is thanked for support and
organisation of the sampling of the groundwater wells. This study is part of a PhD supported
by GNS Science as part of the Smart Aquifer Characterization program funded by the New
Zealand Ministry for Science and Innovation (http://www.smart-project.info/).
References
Beyer, M., van der Raaij, R., Morgenstern, U., Jackson, B. (2014) Potential groundwater
age tracer found: Halon-1301 (CF3Br), as previously identified as CFC-13 (CF3Cl), Water
Resources Research.
Busenberg, E. and Plummer, L.N. (2008) Dating groundwater with trifluoromethyl
sulfurpentafluoride (SF5CF3), sulfurhexafluoride (SF6), CF3Cl (CFC-13) & CF2CL2
(CFC-12), Water Resources Research 44 |
|
|
|
|
|
|