Metropolitan Collieries Pty Ltd (MCPL), a wholly owned subsidiary of Peabody Energy Australia Pty Ltd, has developed a method to emplace coal mine rejects underground. The rejects are processed to form high density slurry which is pumped into underground workings. The technology will eliminate the transport of rejects by truck through the township of Helensburgh, thereby significantly reducing the environmental impacts of dust, noise, and visual amenity as well as improving road safety. MCPL conducted a range of investigations from initial laboratory studies, field trials and a pilot underground emplacement facility. Key flow characteristics of the high density slurry include a pumping distance of up to 8 km, non-settling; and a drained strength that eliminates the liquefaction risk.