Open cut mining creates significant challenges with respect to rehabilitation of open pits, tailings storage facilities (TSF) and above-grade waste rock dumps (WRD). In many jurisdictions, after closure and rehabilitation of a site, the operator is required to continue monitoring receiving streams to assess if the site is coming into equilibrium with the surrounding catchment. That is, in broad terms, is stream water quality meeting closure criteria and unaffected by surface flows and site seepage, is groundwater unaffected, is revegetation establishing itself and similar to vegetation in undisturbed areas of the catchment, is the rehabilitated landform aesthetically pleasing to stakeholders and is the site geomorphologically stable with respect to the surrounding catchment. Geomorphic stability can be assessed by regular measurement of gully development and sediment deposition. However, research by our principal consultant using high quality stream monitoring data, has found that measuring turbidity as a surrogate for fine suspended sediment (FSS) and stream discharge can be used to show that an elevated landform is returning to equilibrium with the undisturbed catchment. The research showed that during times of disturbance such as earthworks to form a final landform, stream FSS loads during a rainfall/runoff event are elevated relative to pre-disturbance conditions. Once the rehabilitation earthworks are completed and vegetation is establishing itself, it has been found that the elevated FSS loads return to pre-disturbance levels. This may take several years but after this time, the research shows, that FFS load return to per-disturbance levels.
ECAust consultants are at the forefront of this technology both in development and application. The methods have been peer-reviewed and published in international journals and are currently being applied as closure criteria for the Ranger Mine.
ECAust can provide a wide range of services in this field including:
• Designing monitoring programs to assess post-mining landform stability,
• Collation and analysis of collected FSS and stream discharge data, and
• Reporting to stakeholders and regulatory officials to present results and advise on landform stability.
150A/45 Malak Cres, Malak NT 0812
P: 08 89 280 380
M: (0)4 7519 8875
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