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Backfilled Pits – Laboratory-scale Tests for Assessing Impacts on Groundwater Quality

Alex Watson, Claire Linklater and John Chapman
Thursday, October 13, 2016
First presented: 
AusIMM Life-of-Mine Conference, 28-30 September, 2016
Water Management

Closure options under consideration at some sites include backfilling mined-out pits with waste rock. Backfill may include mineralised and non-mineralised waste rock. Following groundwater rebound, flow-through conditions may develop in the pit post- closure. The backfill located in the saturated zone below the water table may release solutes under such conditions. It is therefore important to understand the potential impacts that backfilled pits could have on postclosure groundwater quality.

Geochemical characterisation programs are the foundation for assessing the potential chemistry of water that has contacted mined wastes. Such programs must be designed to obtain data relevant to the closure options under consideration. To complement standard testing techniques, SRK utilises saturated column testing designed to generate data on leaching rates under anoxic conditions that could be encountered within submerged backfill.

This paper presents the findings of saturated column test work carried out on waste rock samples from an iron ore mine in the Pilbara.

Feature Author

Alex Watson

Alex Watson has 20 years’ experience in environmental projects gained from working in the UK, South Africa and Australia. While his main area of expertise is geochemistry, he also has experience in water and waste management, mine closure planning, environmental impact and management and due diligence studies. Alex has experience in site investigation, characterisation and assessment (mine site/mineral waste and contaminated land). He has provided consulting expertise to both the private and public sectors on projects concerning mining, industrial and waste management issues in order to achieve legal compliance, improve environmental performance or manage risk.

Principal Consultant (Environmental)
MSc (Analytical Chemistry), BSc Hons (Physics and Chemistry), MAusIMM
SRK Sydney
Claire Linklater

Claire Linklater has 22 years’ experience in interpretation of geochemical data, building conceptual models of processes which control in situ geochemical behaviour and the application of geochemical modelling codes.  Her early career was focused on management of radioactive wastes; understanding and quantifying the geochemical behaviour and mobility of radionuclides in the ‘geosphere’ surrounding a proposed underground repository and assessing the long-term stability of engineered and natural barriers.  More recently, she has focused on sulfidic materials management: acid/alkaline rock drainage (ARD) assessment and prediction; water quality and pollutant mobility from waste rock dumps, tailings storage facilities, underground workings and pit walls; assessing the effectiveness of potential mine closure strategies.

Principal Consultant (Geochemistry)
PhD (Geology), FGS, FAusIMM
SRK Sydney
John Chapman

John Chapman has more than 26 years of relevant experience and has developed multi-disciplinary skills relating to mining environmental impacts assessment and environmental controls.  He is a recognised expert in ARD assessment and prediction, mine waste characterisation and management, and mine closure with recent project experience in Australia, South East Asia, Canada, USA and Europe.  John has facilitated enterprise-wide risk assessment workshops, undertaken due diligence and environmental risk assessments for a wide range of mining projects.  Recent projects include detailed geochemical assessment of the tailings properties for the Olympic Dam Project in SA, design and development of the geochemical characterisation program for the Cannington Life Extension project in QLD as well as for the Yeelirrie Project in WA.

Principal Consultant (Geochemistry and Environment)
MSc (Chemical Engineering), P Eng (British Columbia), P.Eng (Yukon Territory)
SRK Brisbane
SRK Kazakhstan