Long-term post-closure surface water and groundwater risk management and subsequent water quality trends at the former Sullivan Mine, Canada

Authors: Humphries, SA; Thomson, DG; Unger, ML Download Paper

DOI https://doi.org/10.36487/ACG_rep/1152_105_Humphries

Cite As:
Humphries, SA, Thomson, DG & Unger, ML 2011, 'Long-term post-closure surface water and groundwater risk management and subsequent water quality trends at the former Sullivan Mine, Canada', in AB Fourie, M Tibbett & A Beersing (eds), Mine Closure 2011: Proceedings of the Sixth International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 367-376, https://doi.org/10.36487/ACG_rep/1152_105_Humphries



Abstract:
The former Sullivan Mine was one of the world's largest producers of lead, zinc and silver, officially closing in 2001 after 92 years of active production. The former mine and mill areas contain large impoundments of tailings, waste rock, and other process wastes as a result of historical mining processes. Environmental controls, site assessment and mitigation measures to manage and protect surface water and groundwater quality have been in place since the 1960s. Large-scale characterisation of the surface water and groundwater systems was initiated in the mid 1990s. At the same time, incremental efforts to assess and mitigate mining-related impacts to these resources commenced, including: waste impoundment covers, seepage collection systems, mine de-watering, pumping well networks; and groundwater interception barriers, trenches and sand drains. In addition to these mitigation measures, a comprehensive risk assessment was performed culminating in a site-wide Risk Management Plan with annual surface water and groundwater monitoring programs. Long-term post-closure monitoring at a number of surface water and groundwater monitoring locations since 2001 have provided indicators of improving surface water and groundwater quality across both the former mine and mill areas. These long-term trends have confirmed predictions made through conceptual hydrogeological and geochemical models developed after closure. Monitoring in the tailings impoundments indicated loading to groundwater from acid rock drainage and metal leaching impacts in source areas has been reduced. Monitoring in downgradient areas suggested groundwater capture has been successful in reducing off-site loading. Surface water quality has improved in receiving creeks and rivers. In addition to mitigation measures implemented at the site, natural attenuation mechanisms originally predicted by geochemical modelling have also been confirmed by long-term trends in groundwater quality. The phased implementation of mitigation measures combined with targeted site assessment and a carefully defined Risk Management Plan with long-term monitoring have provided a cost-effective and successful solution for post-closure management of surface water and groundwater. Additional site assessment, mitigation measures and improvements to existing environmental controls will continue to be implemented on an as needed basis. Further improvements to groundwater and surface water quality are expected to be observed with planned long-term surface water and groundwater monitoring.

References: