Gates (2013) reported that groundwater helium sources and residence times were investigated using groundwater discharging from springs surrounding Mount St. Helens in the Cascades region of the United States. Significant contributions of mantle helium were found in all samples and are attributable to interaction between groundwater and magmatic gases. Bounding calculations for residence times were made on the basis of helium isotope mixing plots and historical tritium data.
Environmental tracer studies of spring water have yielded insights about groundwater provenance, residence times, and hydrogeochemical processes in a wide range of hydrogeologic settings, including volcanic and geothermal systems. However, investigations in volcanic areas have highlighted several challenges to gas-based residence time indicators of “young” groundwater because of groundwater interaction with magmatic gases and high-temperature water/rock interactions.
In the context of tritium-helium dating, contributions of mantle-derived helium to total dissolved helium in shallow groundwater may be significant in volcanic settings, and must be taken into account in helium source partitioning. The objectives of this work were to examine helium sources to spring water near Mount St. Helens and to examine the implications of magmatic helium inputs for tritium-helium dating of spring discharge.
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