Helium-isotope data and groundwater ages of 700 shallow and deep groundwater sites in and around the Austrian Eastern Alps

Groundwater ages provide valuable insights for water managers and users, helping them understand the timeframe required for water quality improvement measures to become effective and the timeframe in which groundwater bodies are renewed. To estimate groundwater ages in important shallow Austrian aquifers more than 700 tritium/helium-3 analyses and some tracer gas (CFC, SF6) investigations were conducted within the national groundwater monitoring and additional research projects. Noble gases ³He, ⁴ He and ²⁰Ne were measured at the Institute of Environmental Physics (IUP), University of Bremen, Germany and some at the Isotope Hydrology Section of the IAEA in Vienna, Austria. Groundwater ages vary across Austria and within groundwater bodies due to hydrogeological heterogeneities and depending on gradients of precipitation amounts and recharge rates. They range generally between 0 – 25 yrs. Tritium/helium-3 analyses are an essential tool for groundwater age estimation and the respective piston flow model ages of the shallow aquifers are mostly in the range of 0 – 15 years. However, the missing correlation with the sampling depth indicate partly an internal mixing in the observation wells due to large screen lengths.

The existent of elevated ⁴He-concentrations in aquifers with low background U and Th-content are good indicators of the admixture of old groundwater or just increased ⁴He-fluxes. The ⁴He concentrations range from air-equilibrium up to 1.6E-03 (cm³ STP /kg).  The ³He/⁴He- ratio decreases down to 8.0E-08. Preliminary studies of increased ⁴He-data with major tectonic fault zones indicate a positive correlation. Clear indications of the admixture of mantle helium were discovered at the end of Eastern Alps toward the western border of the Pannonian Basin.

 

[1]        Kralik, M., Humer, F., Fank, J., Harum, T., Klammler, D., Gooddy, D., Sültenfuß, J., Gerber, C., Purtschert, R. (2014): Using ¹⁸O/²H, ³H/³He, ⁸⁵Kr and CFCs to determine mean residence times and water origin in the Grazer and Leibnitzer Feld groundwater bodies (Austria). Applied Geochemistry, 50 (2014), 150-163 http://dx.doi.org/10.1016/j.apgeochem.2014.04.001

[2]        Bundesministerium für Land- und Forstwirtschaft, Regionen und Wasserwirtschaft, Grundwasseralter 2009-2021, Wien (2022).

 (https://info.bml.gv.at/themen/wasser/wasserqualitaet/grundwasser/grundwasseralter2019-2021.html)