Selection of active and passive treatment systems for AMDflow charts for New Zealand conditions

Treatment of acid mine drainage can be accomplished by either active or passive treatment systems. Choice between active and passive treatment and appropriate selection of systems within each category is critical for treatment success. In general, active treatment is more commonly used at operational mines whereas passive treatment is typically considered for closed and abandoned mines. Operational mines often have limited space for remediation systems and have large and fluctuating flow rates with changing drainage chemistry as mining proceeds, factors that are addressed more easily with active than passive treatment. In the long term, passive treatment could offer more economic options than active treatment. Various flow charts have been prepared by previous researchers to help select among the passive systems but little work has been done to help select between active and passive treatment or to select appropriate active treatment systems. Furthermore, the passive treatment flow charts have often not included variables important for application to New Zealand sites: topography, climate and available land area. Very steep topography, dense and often protected vegetation, and a high-rainfall climate may result in acid mine drainage with high flow rates in locations with limited space for remediation. This paper presents flow charts specific to New Zealand which have been prepared to accommodate topography and available land area.