Post-Closure Groundwater Impact Assessment for the Underground Mining Operation at Olympic Dam

The current BHP Billiton Olympic Dam (OD) operation comprises underground workings (tunnels, stopes) and a number of surface facilities including the TSF and processing plant.  Mined out stopes in the underground workings are backfilled using cement aggregate fill which includes a portion of process tailings. Current life-of-mine plans indicate that the underground operation will continue for at least another 45 years.  At the end of mine life, dewatering will cease, and the underground workings will re-flood.  An assessment of the potential impacts that the Olympic Dam underground operation could have on the regional hydrogeology and groundwater quality in the intermediate and long term is required to support development of closure plans for the mine site.

During the period 2007 to 2011, OD considered the option of developing a large-scale open pit mine operation.  Groundwater modelling and TSF source term assessments were conducted (SWS, 2010; SRK 2010) to support the environmental impact assessment of that proposed development (BHP Billiton 2009; 2011). The current assessment utilised material from these previous assessments where possible; however, modifications were necessary, in particular to the groundwater model, to reflect the change from an open pit to an underground operation