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| Titel |
Estimating the groundwater residence time in eskers of the Amos region, northern Quebec by 3H-3He and (U-Th/4He) methods |
| VerfasserIn |
Christine Boucher, Laureline Berthot, Daniele Luigi Pinti, Marie Larocque, Vincent Cloutier, Daniel Blanchette, Maria Clara Castro, Chris M. Hall |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250079153
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| Zusammenfassung |
| An esker is a long winding ridge of stratified sand and gravel. The eskers of the Amos region
(Abitibi-Témiscamingue, Québec) that were deposited during the last deglaciation, are
known to be aquifers containing drinking water of exceptional quality. Yet little
is known about their hydrologic regime and exchanges with other water sources.
A better understanding of these systems is necessary to assess the vulnerability
of these aquifers to contaminants and to implement a management plan for these
resources. A multi-isotopic study of groundwater in the eskers of the Amos region
(Saint-Mathieu-Berry, Barraute and Harricana moraine) was carried out in 2011-2012. Noble
gas isotopes, together with major ions chemistry and stable isotopes were used to
estimate the residence time of waters, to trace fluid flow paths and to determine the
atmospheric temperature at the time of the recharge took place. Measured 3He/4He
ratios were primarily used to identify mixing between different water types carrying
distinct helium components. The 20Ne/4He vs. 3He/4He relationship shows that
waters flowing into eskers have three helium components: atmospheric, tritiogenic
3He-rich and radiogenic 4He-rich. The measured 3He/4He ratios (R) normalized to
the atmospheric one (R/Ra) varies between 0.224±0.012 and 1.849±0.036. Most
radiogenic 4He-rich mineralized waters are those from fractured basement rocks of
Archean age. Freshwater flowing into eskers show mixing between radiogenic helium
and tritiogenic 3He. A clear relationship between the well depths, salinity and the
3He/4He ratios suggests that mixing occurs between these two groundwater bodies.
Tritium measurements allow the calculation of 3H-3He ages varying from 6.7±1.3 yrs
to 9.7±1.3 yrs for waters flowing through the Harricana moraine. Groundwater
from Saint-Mathieu de Berry esker ranges from 11.0±2.1 yrs to 32.5±1.6 yrs. The
3H-3He ages plotted against the wells depth show a linear relationship for both, the
Saint-Mathieu-Berry esker and the Harricana moraine allowing calculation of vertical
infiltration rates varying between 0.9 and 7.0 m/yr. A calibrated 4He production rate
allows estimation of (U-Th/4He) groundwater residence times. The oldest waters are
those from the fractured bedrock and display an age of 8000 years. Intermediate
waters with ages varying from 50 to 800 yrs are likely the result of mixing between
deeper fossil water and freshwater flowing through the eskers. Interestingly, the
oldest ages recorded in the Saint Mathieu Berry esker are located in a fault zone. |
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