Risk assessment of chemical contaminants from Ranger uranium mine via the surface water pathway

Modelling of risk pathways is an essential component of ERA. A conceptual model for identifying transport modes of contaminants, off-site from Ranger mine was determined involving an internal and external technical expert panel to identify and agree on the relevant details within model elements. The model is a useful communication tool and places off-site contaminant issues at Ranger in a risk management context (Figure 1).

To characterise off-site exposure probabilities for key contaminants, the surface water sub-model (Figure 1) was populated with monitoring data from Magela Ck (downstream of Ranger mine) for the key solutes: uranium; manganese; magnesium; and sulfate. Effects probabilities for these solutes were derived from ecotoxicological endpoints for native aquatic species or, where data were absent, data from the Australian Water Quality Guidelines. Initial results of this assessment indicate that the mean minesite risk probability (from all solute contaminants combined) is very small at 0.00027, with uranium making an extremely small contribution. More detailed information relating to this project can be found in the Supervising Scientists Annual Report 2005-2006.