Aquifers : properties roles and research An overview of aquifer vulnerability Saheed A. Oke Civil Engineering Department Central University of Technology Bloemfontein South Africa Hydrochemical analysis of groundwater from Brazilian aquifers by TXRF analysis Daniel Marcos Bonotto and Gabrielle Roveratti Departamento de Petrologia e Metalogenia Universidade Estadual Paulista (UNESP) Rio Claro (SP) Brazil and others The water quality evaluation of aquifer systems on human health : a case study of northern Sri Lanka Pankaj Kumar Chitresh Saraswat Binaya Kumar Mishra and Srikantha Herath United Nations University Institute for the Advanced Study of Sustainability (UNU IAS) Tokyo Japan