Myra Falls Mine
The Myra Falls Mine is located on Vancouver Island in western Canada. The mine has produced zinc, copper, and lead concentrates by underground methods since 1993. Before then, mining was done by open pit methods. Sulfidic tailings are used to backfill the underground workings and are deposited at surface in one of two Tailings Disposal Facilities (TDFs). Waste rock is currently used to construct one of the TDF embankment berms. The groundwater system at Myra Falls is highly transient and characterized by strong interaction of groundwater and surface water. Groundwater and surface water at Myra Falls is impacted by ARD/ML from mine water and seepage from tailings and waste rock.
RGC was retained in 2013 to help manage current ML/ARD impacts by characterizing the physical and geochemical characteristics of tailings and waste rock at surface and by developing a site-wide seepage control plan for the site. RGC has also been assisting Nyrstar in managing their expanding surface and groundwater monitoring programs and has prepared the Annual Effluent Report and Annual Reclamation Report for the site since 2019.
RGC completed hydrogeological investigations at Myra Falls in 2013, 2014, 2015, 2017, and 2018 to characterize the complex hydrogeology of the mine site and to assess the impacts of seepage from the waste rock and tailings on the local groundwater and nearby Myra Creek. Since 2013, RGC has installed over 60 monitoring wells in the valley sediments and underlying bedrock to delineate the contaminant plume in the Myra Valley Aquifer. In 2018, RGC updated the Site-Wide Water and Load Balance Model (WLBM) for the site, which incorporates a transient numerical flow model and solute transport model developed in MODFLOW/MT3D. Borehole logs from over 150 geological, geotechnical, and hydrogeological boreholes were interpreted using the software GMS to develop a three-dimensional model of the Myra valley aquifer system. This hydrostratigraphic model was then imported into MODFLOW/MT3D to parameterize the 3D groundwater flow model. The model covers a surface area of 2.6 km2 and includes the Myra Valley aquifer and lower side hills where tailings and waste rock are stored. This model update involved an in-depth analysis of the interaction of groundwater and surface water and associated contaminant loading to Myra Creek. Of particular interest was the assessment of a Seepage Interception System (SIS) that consists of a fence of pumping wells downgradient of the Lynx TDF.
- ARD and geochemical characterization of tailings and waste rock
- Development of a site-wide seepage control plan and routine performance assessment of installed seepage interception systems
- Design and management of surface and groundwater monitoring programs
- Development of a water and load balance
- Supervision of drilling, installation and development of pumping and monitoring wells
- Numerical modelling of groundwater flow & solute transport