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| Titel |
Dating of groundwater using anthropogenic gaseous tracers (SF6, SF5CF3, CFC-12, HC-1311): methodological aspects |
| VerfasserIn |
J. Bartyzel, J. Rosiek, I. Śliwka, K. Rozanski |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061546
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| Zusammenfassung |
| Groundwater is an important source of potable water in many countries. Nowadays,
this strategic resource is at risk due to anthropogenic pollutants of various nature
entering shallow aquifers. Proper management of groundwater resources requires
precise understanding of groundwater dynamics on time scales characteristic for the
history of pollutant input to groundwater. Several anthropogenic trace substances
present in the atmosphere, such as freons (CFC-11, CFC-12) and sulfur hexafluoride
(SF6) play an increasingly important role as environmental tracers allowing a better
insight into the dynamic of groundwater systems. The concentration of SF6 in the
atmosphere is increasing steadily, with the growth rate in the order of 5% per year.
Recently, a new trace gas (trifluoromethyl sulphur pentafluoride - SF5CF3) has been
discovered in the atmosphere. The atmospheric concentrations of SF5CF3 reconstructed
from archive air samples have been increasing during the late 1980s and 1990s
with the growth of ca. 6 % per year, with the sings of leveling-off during the last
decade.
We present here a dedicated analytical system capable to determine environmental levels
of several gaseous tracers (SF6, SF5CF3, CFC-12, HC-1311) in air and water, with the
precision and accuracy sufficiently low do use them for groundwater dating. In addition, the
system is capable to measure in the same water sample the concentrations of Ne and Ar.
This allows corrections for excess air to be made and the calculations of recharge
temperatures.
The field sampling system is based on a dynamic head-space method. The analysed water
is pumped continuously through the extraction system where the dynamic head-space is
created. Approximately 100 liters of water has to be pumped through the system
before the dynamic equilibrium is reached in the head-space volume. Then, gaseous
sample is collected from the head-space volume (ca. 200 ml) and transferred to the
laboratory.
The mixing ratio measurements are performed using a dedicated gas chromatograph
(Agilent 6890) equipped with μ-ECD detector. Due to extremely low atmospheric mixing
ratios and poor solubility in water of the analyzed gases, cryogenic enrichment of the gaseous
sample prior to detection is employed. A specially designed, automatic cryogenic trap is used
for this purpose. Before the cryogenic enrichment, a small fraction of the gaseous sample
(5-10 ml) is diverted for measurements of Ne and Ar content in the analysed water
sample.
Analytical performance of the detection system is presented, supplemented by several
examples of field analyses of the discussed gaseous tracers in groundwater systems in
Poland.
Acknowledgements:
This work was supported through funds from the Polish Ministry of Science and High
Education (projects Nr. N N525 362637 and 11.11.220.01) |
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