Olaf A Cirpka, University of Tübingen, Tübingen, Germany, Yan Liu, University of Freiburg, Institute of Earth and Environmental Sciences, Freiberg, Germany, Christiane Zarfl, Eberhard Karls Universität Tübingen, Center for Applied Geosciences, Tübingen, Germany and Nandita B Basu, University of Waterloo, Civil and Environmental Engineering, Waterloo, ON, Canada