Transport-based source tracking of contaminants in a karst aquifer: Model implementation, proof of concept, and application to event-based field data

Ferry Schiperski; Johannes Zirlewagen; Claudia Stange; Andreas Tiehm; Tobias Licha; Traugott Scheytt

doi:10.1016/j.watres.2022.118145

Transport-based source tracking of contaminants in a karst aquifer: Model implementation, proof of concept, and application to event-based field data

Water Res. 2022 Apr 15:213:118145. doi: 10.1016/j.watres.2022.118145. Epub 2022 Feb 1.

Authors

Ferry Schiperski¹, Johannes Zirlewagen², Claudia Stange³, Andreas Tiehm³, Tobias Licha⁴, Traugott Scheytt⁵

Affiliations

¹ Technische Univerinfromt Berlin, Dept. of Applied Geosciences, Applied Geochemistry, Ernst-Reuter-Platz 1, 10587, Berlin 10587, Germany. Electronic address: schiperski@tu-berlin.de.
² Technische Univerinfromt Berlin, Dept. of Applied Geosciences, Applied Geochemistry, Ernst-Reuter-Platz 1, 10587, Berlin 10587, Germany.
³ DVGW-Technologiezentrum Wasser (TZW), Karlsruher Straße 84, Karlsruhe D-76139, Germany.
⁴ Hydrochemistry Group, Institute for Geology, Mineralogy and Geophysics, Ruhr-University Bochum, Universitatsstr. 150, Bochum 44801, Germany.
⁵ Technische Universität Bergakademie Freiberg, Dept. of Geology, Hydrogeology, Freiberg 09596, Germany.

PMID: 35151087
DOI: 10.1016/j.watres.2022.118145

Abstract

Identification and location of contamination sources is crucial for water resource protection - especially in karst aquifers which provide 25% of the world´s population with water but are highly vulnerable to contamination. Transport-based source tracking is proposed and verified here as a complementary approach to microbial and chemical source tracking in karst aquifers for identifying and locating such sources of contamination and for avoiding ambiguities that might arise from using one method alone. The transport distance is inversely modelled from contaminant breakthrough curves (BTC), based on analytical solutions of the 1D two-region non-equilibrium advection dispersion equation using GNU Octave. Besides the BTC, the model requires reliable estimates of transport velocity and input time. The model is shown to be robust, allows scripted based, automated 2D sensitivity analyses (interplay of two parameters), and can be favourable when distributed numerical models are inappropriate due to insufficient data. Sensitivity analyses illustrate that the model is highly sensitive to the input time, the flow velocity, and the fraction of the mobile fluid region. A conclusive verification approach was performed by applying the method to synthetic data, tracer tests, and event-based field data. Transport distances were correctly modelled for a set of artificial tracer tests using a discharge-velocity relationship that could be established for the respective karst catchment. For the first time such an approach was shown to be applicable to estimate the maximum distance to the contamination source for coliform bacteria in karst spring water combined with microbial source tracking. However, prediction intervals for the transport distance can be large even in well-studied karst catchments mainly related to uncertainties in the flow velocity and the input time. Using a maximum transport distance is proposed to account for less permeable, "slower" pathways. In general, transport-based source tracking might be used wherever transport can be described by the 1D two-region non-equilibrium model, e.g. rivers and fractured or porous aquifers.

Keywords: 2RNE non-equilibrium transport model; Environmental forensics; STANMOD CXTFIT; Sensitivity analyses; Water resources.