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Closure Water Balance Model to Support Closure Designs for a Mine in Laos

Brian Luinstra, John Chapman, Alison Hendry, Alex Watson, Russel Staines, Justin Rowntree, Donna Noonan
Thursday, September 6, 2018
First presented: 
Mine Closure 2018


SRK Consulting (Australasia) Australia Pty Ltd (SRK) are currently assisting with the development of closure plans for portions of a mining Development Area located in Central Laos. 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.

A catchment delineation process was undertaken in which flow paths and catchment areas were defined to reflect the Life of Mine (LOM) topography, landforms and features within individual precincts. A closure water balance model (CWBM) was constructed to allow assessment of impacts for closure options at the precinct, sub catchment and catchment scale.
Stochastic rainfall was developed based on the available climatic data for the years 1994 2015 and showed good correlation with long term averages. Runoff from natural (i.e. non mining) areas for the CWBM was developed using the Australian Water Balance Model (AWBM). Unique calculations of hydrologic fluxes were conducted within GoldSim for mine pits, backfilled pits, water management structures, waste rock landforms and non mining areas. Within the CWBM, flows from natural areas and precincts were aggregated at nominated water quality assessment points to provide flow estimates for water quality predictions.
In general, pit voids and water management structures follow a distinct seasonal pattern, with ephemeral outflows during the wet season, and no outflow during the dry season. The assessment predicts that this seasonal pattern will be maintained after closure, such that the pit voids and water management structures maintain perennial lakes through the dry season, and overflow during the wet season. In addition, most pit lakes will be gaining water bodies, i.e. receiving significantly more seepage from groundwater than they are losing to groundwater and will spill.

Feature Author

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
Brian Luinstra

Brian Luinstra has 19 years of experience in the field of geology and hydrogeology working primarily in Canada.  He has executed and managed a wide scope of hydrogeological assessments.  These include regional scale water budgets; water supply assessments; well head protection studies; aquifer hydraulic testing; groundwater monitoring network establishment and program implementation; aquifer conceptualisation and impact assessment; karst investigations and hydrological and hydrogeological modelling.  He is experienced working in remote locations, and has varying levels of proficiency with specialised geological and groundwater modelling packages.  Brian provides technical direction and review on hydrogeological projects, and has been project manager for several key clients.

Principal Consultant (Hydrogeology)
PhD (Earth Science), BSc (Geology)
SRK Perth
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