From the Commissioner's Overview
Stockton mine is the largest coal mine in New Zealand and it is located in an area which presents huge challenges to any environmental manager. The discovery of the endangered giant snail, Powelliphanta augusta, and the subsequent relocation programme, have dominated media coverage about the impact of the mine on the environment. That issue is not recanvassed in this report; rather the focus is on the physical environment as the cradle of the ecosystem.
Average rainfall on the Stockton Plateau exceeds six metres per year. The streams in the area are naturally acidic, and mining exacerbates this because sulfide minerals exposed through mining are oxidised and sulfuric acid is formed. This ‘acid mine drainage’ is one of the most significant environmental effects of coal mining in general, and for Stockton mine in particular. And it is of special interest, since water quality is a major environmental issue in New Zealand.