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Radiogenic 4He as a conservative tracer in buried-valley aquifers

Water Resources Research

By:
, , ,
DOI: 10.1029/2004WR003857

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Abstract

[1] The accumulation of 4He in groundwater can be a powerful tool in hydrogeologic investigations. However, the use of 4He often suffers from disagreement or uncertainty related to in situ and external sources of 4He. In situ sources are quantified by several methods, while external sources are often treated as calibration parameters in modeling. We present data from direct laboratory measurements of 4He release from sediments and field data of dissolved 4He in the Mahomet Aquifer, a well-studied buried-valley aquifer in central Illinois. The laboratory-derived accumulation rates (0.13-0.91 ??cm3 STP kgwater-1 yr-1) are 1-2 orders of magnitude greater than the accumulation rates based on the U and Th concentrations of the sediments (0.004-0.009 ??cm3 STP kgwater-1 yr -1). The direct measurement of accumulation rates are more consistent with dissolved concentrations of 4He in the groundwater. We suggest that the direct measurement method is applicable in a variety of hydrogeologic settings. The patterns of accumulation of 4He are consistent with the conceptual model of flow in the aquifer based on hydraulic and geochemical evidence and show areas where in situ production and external sources of 4He are dominant. In the southwestern part of the study area, Ne concentrations are less than atmospheric solubility, indicating gases have been lost from the groundwater. Available evidence indicates that the gases are lost as groundwater passes by pockets of CH4 in glacial deposits overlying the aquifer. However, the external flux from the underlying bedrock appears to dominate the accumulation of radiogenic 4He in the aquifer in the southwestern part of the study area, and the loss or gain of helium as groundwater passes through the overlying sediments is minor in comparison. Copyright 2005 by the American Geophysical Union.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Radiogenic 4He as a conservative tracer in buried-valley aquifers
Series title:
Water Resources Research
DOI:
10.1029/2004WR003857
Volume
41
Issue:
11
Year Published:
2005
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Water Resources Research
First page:
1
Last page:
13
Number of Pages:
13