Abstract:

A number of active and historical coal mines are located on the Stockton and Denniston plateau areas of New Zealand. These West Coast sites have high rainfall, with some mine sites experiencing > 5 m of rainfall per year, which recently included > 1.5m in a single month.

Rainfall can be a key driver of acid and metalliferous drainage (AMD) loads for historic opencast operations (e.g., waste rock dumps) and underground mine working (where there is direct ingress of rainfall due to overlying strata collapse). However, many current operations recognise this risk, and are using best practicable AMD management approaches to minimise the generation of sulfide oxidation products within engineered landforms, which even with high net percolation rates, have acidity loads that can be managed by passive treatment systems at closure.

This paper investigates the management approaches at two West Coast coal mining operations that have utilised or are planning to utilise best practicable AMD management techniques to reduce contaminant loads at closure. This includes backfill opportunities and engineered landforms. Although net percolation rates are expected to remain high, the overall acidity load is forecast to be low, suitable for passive treatment technologies.

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Tim Mulliner