Closure planning, water quality, remediation.
Hydrobiology can provide assessment of the geochemical and biological processes of mine pit lakes and work with mining companies to explore remediation and closure options. These services can be utilised in the production of mine closure plans and contaminated site remediation. These services can be combined with traditional effluent discharge studies to assess mine pit lake dewatering options and impacts to receiving environments.
Skills and Techniques
This capability focus sheet provides specific information on the mien pit lake assessment methods and applications utilised by Hydrobiology.
Existing mine pit lake assessment
Hydrobiology can bring together its range of expertise and experience in the aquatic sciences to provide multiple lines of investigation into the present
condition and processes occurring in mine pit lakes.
Mine pit lake waters can be highly variable in quality from the surface to bottom waters. Due to the physical structure of the typical mine pit lake, they often have multiple layers (stratification) of differing water quality based on density differences. Each layer can have its own suite of contaminants of concern and a highly variable concentrations. Knowing the physical, biological and chemical structure of your pit lake water column is a key step in identifying remediation and management options.
Methods employed in pit lake research include:
- High resolution vertical profiles of “field” parameters including pH, temperature, conductivity, turbidity, dissolved oxygen, chlorophyll (phytoplankton/algae) and Photosynthetically Active Radiation (PAR);
- Laboratory analysis of a reduced number of vertical samples depending on the water column structure identified by field parameter profiling;
- Bathymetry and bottom hardness mapping using GPS referenced boat mounted sonar. Useful for determining the total volume of each lake layer as well as location of hard substrate and recent sedimentation/slumping that might not be present on mine plans;
- Geochemical modelling to assess the likely form (e.g. complexed or free ions) of contaminants and major ions in the pit lake waters. Modelling of mixing of receiving waters or other sources of water available to the mine (e.g. underground dewatering discharge);
- Experimental application of remediation options including “limnocorrals” or fencing off small areas (~3 m2) of the lake to test additives/options before expanding to full lake scale works.
Mine Closure Planing
As many open pit mines operate below the water table, mine closure often means
that a pit lake will form once active dewatering stops. The shape of the final void, the depth to the water table, evaporation rates and the host rock geology can be used to estimate to likely water quality within the pit lake upon closure. Understanding the water quality is critical to understanding remediation and discharge options, particularly if a positive water balance is possible. Hydrobiology has internal resources as well as links to academic groups to provide assessment of mine closure options with respect to mine pit lakes.