– Copper, with the maximum recorded concentration (330 mg/L) exceeding the default guideline value (0.0014 mg/L) by a factor of 236,000; – Zinc, with the maximum recorded concentration (98.2 mg/L) exceeding the default guideline value (0.008 mg/L) by a factor of 12,000; and ∕ Groundwater at most of the monitoring locations (all except MB9 and MB8-D) was found to be acidic, with pH values ranging from 2.2 to 4.5. Existing Groundwater Model An existing groundwater flow model for the site was prepared by Robertson GeoConsultants during April 2011. Potential changes to the hydrological regime as a consequence of latent tailing excavations and TSF operation are considered immaterial as the hydrological regime is significantly affected by the seepage interception that is maintained by the State and the water treatment system that reduces the standing water level with in the OCP. 6.6.5 This groundwater flow model was used to generate a closed water balance for the Mount Morgan Mine site and enabled a site-wide assessment of contaminant loads to groundwater in the Dee River system under baseflow conditions. Sulphate (SO4), aluminium (Al), copper (Cu), iron (Fe) and zinc (Zn) are the principal COCs at the Mount Morgan Mine site. COC loads generated by mine waste units, removed by the seepage interception system and ultimately bypassing the seepage interception system to reach the Dee River system were estimated by assigning representative seepage and/or groundwater quality data to simulated recharges and flows from the groundwater flow model. Site Wide Conceptual Site Model As committed to through proposed amendments described in Table 5, groundwater monitoring bores are proposed to be installed to better characterise the groundwater regime associated with this amendment. 6.6.6 Most monitoring bores installed to date across the entire site are located between sources of contamination and receiving environment being the Dee River. Installation of groundwater monitoring bores in hydrogeological and topographical upgradient locations has not been warranted by either the State or various EA holders. Groundwater properties specifically within the Upper Mundic Gully TSF area have not been previously investigated, however groundwater properties of the Mundic Creek have. Accounting for some natural variability and acknowledge the modified landform through previous mining activities, reliance on Mundic Creek groundwater characterisation is considered an appropriate representation of the Upper Mundic Gully hydrogeology. Heritage Minerals Project will ultimately result in improved environmental outcomes at the Mount Morgan Mine through the excavation and placement of historical ARD generating mine waste and redeposition into purpose built TSFs, including Upper Mundic Gully TSF. This will result in the removal of the source of ARD generating material from across the site and consolidation where modern capping and closure solutions can be employed reducing recharge of and seepage from mine waste structures. This will reduce impacts from the Mount Morgan Mine to the receiving environment including the Dee River in accordance with the State’s Rehabilitation Plan (Unger et al, 2003) and Phase 3 Agreement. A conceptual site model (CSM) has been developed to describe potential migration pathways between the Upper Mundic Gully area and primary receiving environments being groundwater and the Dee River and is displayed in Figure 44. The CSM has been developed to scale to highlight the topographical reaches of the Upper Mundic Gully area and visualise how topography drives groundwater migration in a south east direction towards the Dee River. This CSM will continual to be refined as further site investigations and modelling is undertaken. When describing the CSM in
Project number: 25B061
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