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Source Assessment to Support Closure Designs for the Western and Central Development Areas at a Site in Central Laos

Claire Linklater, John Chapman, Alison Hendry, Alex Watson, Justin Rowntree, Donna Noonan
Thursday, September 6, 2018
First presented: 
Mine Closure 2018

SRK Consulting assisted with the development of closure plans for the Western and Central Development Areas at a site in Central Laos. These areas include more than 40 pits, some backfilled, and 13 waste rock dumps. To support closure planning, it is important to identify which pits and dumps represent significant contaminant sources, and to understand how effectively contaminant release can be mitigated as part of the closure design.

Available information for the site included drill hole data, geological block models, current topographic surfaces, future pit and dump designs, outcomes from geochemical characterisation studies, surface and groundwater water quality monitoring data.
Conceptual models of the distribution of reactive materials and contaminant sources within key pits and dumps were developed. Post closure, the most significant ongoing sources of solute production are expected to be related to oxidising sulfide minerals present within unsaturated materials in:
• Above ground dumps
• Pit backfill located above the long term water table and
• Pit walls that remain exposed after closure, i.e. are not covered by backfill, or remain above the long
• term pit lake levels.
Field scale solute production rates (inferred from laboratory column test results) were combined with water flows to calculate water chemistry at source and downstream following mixing with other water sources. A companion paper describes development of a site water balance, including representation of surface and groundwater flows at the site.
The water quality calculations were used to examine the range of possible impacted water chemistries for (i) base case flows and solute loadings – to reflect the condition of the site prior to implementation of active closure measures, and (ii) post closure design conditions – to examine the effect of closure measures, such as emplacement of low infiltration covers on dumps.
Using the site wide water and solute load balance approach it was possible identify the optimal closure measures in terms of mitigation of water quality impacts to downstream receptors (drinking water resources).

Feature Author

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.  She is familiar with application of codes such as PHREEQC and Geochemist’s Workbench, and also SRK’s numerical model SULFIDOX (developed to estimate rates of sulfide oxidation in waste rock dumps and ore stockpiles).

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
Alison Hendry

Alison Hendry is a Chartered Geologist with over 10 years’ experience in environmental geochemistry and water quality impact assessments. Alison began her career researching the geochemical soil mineral surface associations of uranium resulting from the use of deplete uranium (DU) munitions in the Balkans, and utilising isotope geochemistry to assess the mobility of uranium from nuclear process plants in the UK. She has worked on a diverse range of geochemical characterisation (acid and metalliferous drainage, AMD) assessments for mine sites, predictive pit lake water quality assessments, water quality compliance reporting, contaminated site investigations, remediation design projects, landfill hydrogeological risk assessments and environmental impact assessments. Alison has extensive field experience of sampling environmental media for assessment, and has gained experience in hydrogeological testing and assessment methods including drilling supervision, well installation design and permeability testing.

Senior Consultant (Geochemistry & Hydrogeology)
PhD (Uranium Geochemistry), BSc (Geology & Environmental Chemistry), CGeol, FGS
SRK Perth
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
SRK North America