1. Faculty of Natural and Agricultural Sciences; Institute for Groundwater Studies, University of the Free State; Bloemfontein 9300 South Africa
2. CONACyT-Centro Nacional de Investigación y Desarrollo Tecnológico, Tecnológico Nacional de México; Interior Internado Palmira S/N, Col. Palmira, C.P. 62490, Cuernavaca Morelos México