Seepage issues continue for McArthur River mine

THE management of highly combustible waste rock continues to be a concern at the McArthur River Mine site, near Borroloola

THE management of highly combustible waste rock continues to be a concern at the McArthur River Mine site, near Borroloola.

The annual report by the independent monitor for the environmental performance of the mine finds that while McArthur River mining had expended considerable effort on site geochemistry problems, there were still acidic rock and seepage related issues yet to be completely resolved.

The report also says 63 truckloads of potentially acid-forming waste were dumped in the wrong location at the mine’s southern overburden emplacement facility in 2016.

McArthur River mine has been the centre of controversy since stockpiled combustible waste rock ignited in 2013, casting a shroud of smoke over the mine and township for close to a year. There have also been ongoing fears among the Borroloola community that nearby waterways where they fish have been contaminated by acid and metal seepage.

However the report finds that while fish caught at nearby Barney Creek continued to have elevated levels of lead, concentrations of lead in fish had “generally dropped yearly since 2012, due to controls MRM have implemented”.

“Although there is evidence of contamination of fish in the vicinity of the mine site, the majority of biota collected had concentrations of lead and other metals well below the maximum permissible concentration,” the report says.

The report finds that future dump construction would better control seepage during operations but infiltration through the site’s northern overburden emplacement facility (NOEF) would continue and there was uncertainty about the fate of the seepage and whether the ponds near the NOEF would capture it all.

“Failure of the cover system post closure could continue to impact groundwater and terrestrial and aquatic ecosystems in perpetuity,” the report says. However it points out that McArthur River Mining is investigating installing an interception trench and recovery bores to capture contaminated groundwater from the NOEF.

In terms of further venting and noxious smoke the report says despite efforts to improve combustible waste rock controls, the effectiveness of a clay cover to be able to manage the acidic and combustive materials was still being monitored.