McArthur River Mine is a world-class zinc-lead mine located 970 km South East of Darwin, Northern Territory, in the Gulf of Carpentaria. The open cut mine has been in operation since 1995 and is operated by Glencore, one of the world’s largest global diversified natural resource companies. To achieve an open cut mine, material is required to be excavated in order to reach the mineral deposits below ground, this is known as overburden. The additional waste products generated by the mine are stored onsite in an area called a tailings dam. A tailings dam contains mining waste, predominantly in liquid form, and is left open to the atmosphere to evaporate providing a solid concentrate to be disposed of. The tailings dam at McArther River Mine is located in an area that poses a possible threat of leaching the contaminates into a nearby watercourse, Surprise Creek. Menard were contracted to mitigate this seepage by constructing two impermeable grout curtains adjacent to the creek, to prevent possible ingress of the pollutants.

The ground conditions consisted of slightly weathered rock overlain by alluvial soils. The rock showed signs of cracks and fissures which presented the issue of subsurface flow of liquids from the tailings dam into the groundwater and Surprise Creek. The alluvial overburden was to be excavated post construction to expose the weathered rock, creating an interception trench for the tailings contaminants to be diverted elsewhere onsite.

Menard Oceania were tasked with the construction of two grout curtains to seal the fissured rock and mitigate the seepage from the tailings dam. This was achieved by drilling inclined holes at 10m centres to depths up to 30m, high pressure grout was then introduced to each bore at 5m intervals, penetrating the fissures and creating an impermeable ‘grout curtain’. Further bores were opened at 5m and 2.5m spacings along the curtain alignment to ensure the high-pressure grout had impregnated the rock mass sufficiently. The project was completed within a four-week timeframe during the wet-season, well within predicted estimates, to high quality standards and within budget.

The primary objective of the overall project was to mitigate the risk of leachate from the tailings dam entering the groundwater and ultimately the watercourse, Surprise Creek.