Application of stable isotopes in geotechnical settings - Examples from current projects

Description

The intended functions of constructional components in (geo)technical settings often suffer from the formation of unwanted carbonate and accessory mineral precipitates. Widespread examples are chemical-sedimentary deposits (scaling) clogging deep wells, thermal water pipelines and heat exchangers in the course of hydrogeothermal energy production or impaired water flows in drainages of railway and highway tunnels. In all of these cases disturbed natural (hydro)chemical equilibria (e.g. in the aquifer), as well as technically altered physicochemical gradients and substrate materials result in the occurrence and variable growth dynamics of unwanted scale deposits. Multi-parameter (proxy) approaches and environmental monitoring of the geotechnical infrastructure and spatiotemporally evolving precipitates target an advanced process understanding of changing fluid-solid interaction and envisage tailor-made (site-specific) countermeasures and optimization. In this context, traditional stable isotope tracers (e.g. H, C, O) and new isotope systems (e.g. clumped isotopes) are applied to fluid and solid phases based on elaborated sampling and monitoring strategies in the field (in-situ) and experimental laboratory. Stable O (δ18O) and clumped isotopes (Δ47) are recognized as sensitive tracers of natural and operational temperature changes and for fluid provenance tracing. Stable C and O isotopes further reflect variable outgassing of CO2 and H2O (steam) intimately coupled to variable CaCO3 precipitation rates based on the aqueous carbonate chemical (dis)equilibrium, e.g. separated two-phase (water & gas) fluid flows in geothermal pipelines. Considering different types and locations of tunnel drainages, these stable isotope ratios capture information on varying CO2 outgassing versus CO2 absorption from the (tunnel) atmosphere, evaporation towards complete desiccation, and possible microbial influences affecting the carbonate mineralogy, compact to porous fabrics and the scale material consistency. Results and new insights from current research and consulting projects involving carbonate dominated scale materials from geothermal installations in Hungary and Germany, as well as from Austrian railway and highway tunnels will be presented.

Period	8 Nov 2019
Event title	17th Stable Isotope Network Austria (SINA) Meeting ·
Event type	Conference
Location	Innsbruck, AustriaShow on map