The networking activities relate to the characterisation and modelling of complex environmental problems, such as encountered in Johannesburg (South Africa), where some landfills lie on old gold mine dumps. There are currently no known studies that have been conducted to assess the complex processes involved in their evolution. Gold mine dumps tend to release acidic water and several chemotoxic elements, whereas landfills tend to release humic substances together with other contaminants. Advanced but robust modelling techniques are required for understanding these complex processes and assessing impacts. The information yielded by modelling techniques such as coupled reactive transport modelling and chemometric modelling is crucial in future studies that will be aimed at designing remediation strategies.