Contaminant Load Balance Study for Mount Morgan Mine, QLD,

The Mount Morgan Mine is a historic mine site located in Central Queensland, Australia which has heavily impacted portions of the adjacent Dee River. As part of overall closure planning a chemical load balance study was performed for the Mt. Morgan mine site. The contaminants of concern (COC) included in this analysis are sulphate (SO4), aluminum (Al), copper (Cu), iron (Fe) and zinc (Zn). The load balance model was developed based on detailed groundwater quality monitoring at the site (since 2003) and used groundwater flow estimates obtained from a 3D groundwater flow model calibrated for the site. The analysis indicates that seepage from the flooded Open Cut/Sandstone Gully represents the single largest source of contaminants on the site exceeding all other contaminant sources by a wide margin (except for the Lower Mundic Waste, which contributes the highest iron loading). Seepage from the Western Dump and Shepherds Dump represent other dominant sources of contaminant loads, in particular with respect to sulphate, aluminum, and copper. The load balance further suggests that the Mundic West and Frog Hollow sumps intercept nearly 90 % of the contaminant load that is generated by the Open Cut/Sandstone Gully and downstream waste units. Seepage interception is less efficient in the Shepherd’s catchment, where the interception system removes only 20-40 % of the contaminant load supplied by seepage from the Shepherd’s Tailings Dam and the Shepherd’s Outer Dump. The load balance study also identified several data gaps which resulted in the installation of additional monitoring wells on site and along the Dee River. This new monitoring data is currently being used to refine the load balance model for the site and to assess the contaminant loading to the upper Dee River. Additional Key Words: mine closure, acid rock drainage, groundwater modeling