6.6.2 Upper Mundic Gully Hydrogeological Conceptualisation Based on the information derived from the recently installed groundwater monitoring bores and information ascertained from developing the seepage management plan, the key aspects relevant to the hydrogeological conceptualisation of UMG TSF are as follows: Groundwater occurrence ∕ Groundwater in the Mount Morgan mine area occurs predominantly within fractured Paleozoic volcanic and intrusive rocks that have negligible primary porosity and transmit groundwater through fractures, joints, and weathered zones. Fractured Paleozoic bedrock represents the primary groundwater flow domain, with hydraulic behaviour governed by fracture density and connectivity rather than lithology. ∕ Site investigations define a layered hydrostratigraphy at the site, comprising mine waste and tailings, saprolite, fractured bedrock, and deeper competent bedrock with very low permeability. Groundwater elevation and flow ∕ At the regional scale, groundwater flow is topographically controlled, with recharge occurring on elevated areas and regional discharge directed toward major surface water features, particularly the Dee River, which functions as the principal hydraulic sink within the mine area. ∕ Groundwater elevations broadly follows land surface topography, with higher heads beneath uplands and progressively lower heads toward gullies and the Dee River valley. Groundwater flow from the mine area is interpreted to be radially outward, converging toward local drainage features and ultimately discharging to the Dee River. ∕ Groundwater levels underlying the proposed TSF area shown in groundwater modelling studies range between 300 m AHD and 209 m AHD, while groundwater level measurements taken by Heritage Mineral at monitoring bores WGMB01, WGMB02 and WGMB03 indicates levels ranging sits between 307 m AHD and 315 m AHD in February 2026. ∕ Long term monitoring indicates that groundwater levels and flow directions are relatively stable over time, rehabilitation measures. Groundwater and surface water interaction ∕ East of the OCP, historic gullies, drainage lines, and zones where fractured bedrock intersects the surface act as preferential seepage pathways, locally expressing as seeps, pools, or sustained baseflow. ∕ Groundwater surface water interaction is significant, particularly during dry periods, when baseflow conditions in the Dee River are sustained by groundwater discharge and mine ‑ related seepage. ∕ The pit lake in the OCP sit at approximately 271 m AHD and considered to be hydraulically connected to the groundwater system, acting as a sink to the west of the OCP, where groundwater sits at higher elevations, and as a source east of the OCP towards the Dee River where the groundwater table gradually slopes toward the Dee River. Groundwater quality ∕ Groundwater quality in proximity to the mine site is strongly affected by historic mining activities, with widespread acid and metalliferous drainage conditions resulting from sulphide oxidation within mine wastes and altered bedrock. ∕ Elevated acidity and high concentrations of dissolved metals are recorded in groundwater across mine waste, saprolite, and fractured bedrock. Historical and recent monitoring indicate acidic conditions typically in the range of approximately pH 2.2 to 4.5 while groundwater electrical conductivity (EC) is generally greater than 10,000 µS/cm.
Project number: 25B061
Page 111
Powered by FlippingBook