6.6 Site Hydrogeology Groundwater at the site is contaminated as a result of previous mining activities. The long-term exposure of sulphide-bearing mine waste to atmospheric conditions has led to the widespread occurrence of ARD in mine waste units across the Mount Morgan Mine site (Robertson GeoConsultants 2011). As a result of seepage from these mine waste units, groundwater and the nearby Dee River are generally acidic and characterised by high concentrations of ARD products such as sulphate, magnesium, and various dissolved metals (Robertson GeoConsultants 2011). As with surface water, groundwater EVs and WQOs within Mount Morgan Mine receiving environment are outlined within the Callide Creek Catchment Environmental Values and Water Quality Objectives (DEHP, 2013). The environmental values of the Callide groundwaters (including Dee River) are the same as surface water with the exclusion of human recreation values. The WQO for aquatic ecosystem protection states that where groundwaters interact with surface waters, groundwater quality should not compromise identified environmental values and WQOs for those waters. GHD (2017) provided a detailed summary of groundwater flows at the Mount Morgan Mine following review of previous RGI (2003, 2005, 2010 and 2011) groundwater reports. Inferred groundwater flow contours for dry season groundwater levels are shown on Figure 41, and the monitoring bores locations shown on Figure 42. The hydraulic gradients and inferred groundwater flow contours correlate well with pre-mining topography (GHD, 2017). Overall, the interpreted groundwater flow direction is towards the southeast and flow to the Dee River and is not anticipated to change significantly due to seasonal variations in groundwater levels (GHD, 2017). the groundwater flow direction from the Upper Mundic Gully TSF footprint is expected to mimic the contours represented on Figure 39 being towards the Dee River, given the pronounced topography of the Upper Mundic Gully footprint (refer to the conceptual site model in Figure 44). On a regional scale, groundwater is recharged via infiltration from direct rainfall recharge and previously by seepage from the No. 8 Dam (GHD, 2017). Seepage from No. 8 dam has since been rectified through DNRMMRRD rehabilitation and remediation works completed in 2021. Recharge to groundwater is also enhanced at the site due to seepage from the overlying tailings dams to the underlying bedrock (saprolite and/or fractured bedrock), seepage of water held in OCP / Sandstone Gully TSF to the adjacent mine waste and bedrock, and seepage of water held in some of the mine waste dumps to the underlying bedrock (GHD, 2017). Much of the shallow groundwater flow through saprolite and fractured bedrock and sub surface flow through mine waste and tailings is intercepted by the seepage interception system at the various sumps, before being pumped back to the OCP. Contaminated water seepage and runoff from the Mount Morgan Mine is currently managed by the State via the seepage interception system, and will continue to be managed by the State.
Project number: 25B061
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