Assessing Environmental Safety of In-pit Disposal of Tailings in Coal Mines

In-pit disposal of tailings can be beneficial because of the stability of tailings storage attained by placing the tailings below the natural ground surface, thereby reducing risk of wall failure. However, there is a potential risk of contaminant release into the surrounding environment through groundwater transport. The main objective of the project was to examine the potential environmental issues arising from the in-pit disposal of coal tailings through a multidisciplinary approach and to suggest a framework to assess in-pit tailings. The assessment of tailings includes physical, hydrological and geochemical techniques.

Several coal mines in New South Wales and Queensland with in pit tailings were visited and relevant site information was collated. To cover a wide spectrum of physical and geochemical properties of tailings, Burton, Mt Arthur and Wambo coal mines were selected for further field measurements and geochemical sampling. The project involves three main parts:

· Hydrological and geochemical characterisation of tailings;

· Long-term behaviour, attenuation and management scenarios of co-disposed reject and tailings; and

· Statistical analysis and modelling.

Hydrological and geochemical characterisation results were used to better define potential release, reactivity and mobility of contaminants from tailings. Possible contaminants from coal tailings include acids, salts and heavy metals.

Long-term behaviour, attenuation and management scenarios of co-disposed reject and tailings accounted for different properties of co-disposed tailings. Therefore, it is important to characterise these factors to determine geochemical consequences of alternative tailings disposal options and to guide tailings management. Statistical analysis of data can alleviate the need for extensive sampling and chemical analysis of tailings to perform a risk assessment, and the modelling approach predicts hydro-geochemical processes controlling the chemistry of seepages from in-pit tailings.

A consistent approach suggested by this study for the assessment of in-pit tailings enables the stakeholders to more easily communicate data and provides necessary information for better management of tailings and planning for mine closure. This study recommends collection of long-term groundwater monitoring data to validate the result of hydro2 geochemical models and reduce uncertainty of long-term consequences of in-pit disposal of tailings.