GEOSS undertakes contamination assessments for clients in various industries. For a power station, GEOSS assessed the potential impacts to groundwater from alternative ash disposal techniques. This allowed for an assessment of the risks, and the subsequent motivation for the preferred option along with relevant cost-benefit consideration. To any contamination study, development of a conceptual model for the site is critical to the necessary understanding and assessment of risk. Numerical modelling provides a tool for simulating various scenarios.