∕ Groundwater contributes to ongoing contaminant loading to surface waters, particularly the Dee River, under both baseflow and wet season conditions.
6.6.3 Hydraulic aquifer properties Hydraulic conductivity values inferred from the historical model calibration and documented testing (Robertson GeoConsultants, 2004, Roberston GeoConsultants Inc, 2011), relevant to the UMG TSF, are summarised in Table 37. Table 37. Hydraulic parameters from existing hydrogeological studies
Hydro stratigraphic units Mine landforms – rock/spoil dumps
Hydraulic conductivity (m/day)
Comments from 2011 modelling report
4.5 to 0.8
Highly variable, moderate to high permeability, promotes rapid infiltration and seepage Transitional unit moderating vertical seepage Primary lateral groundwater flow domain, fracture-controlled
Saprolite
8.6 x 10 -2 to 8.6 x 10 -3
Fractured Palaeozoic bedrock Competent Palaeozoic bedrock
8.6 x 10 -3
Acts as hydraulic basement
6.6.4 Site Wide Groundwater Quality During 2024, GHD completed a review of groundwater quality data obtained from monthly groundwater monitoring and to prepare a report to comply with EA conditions W7, W8 and W9. A copy of this report is provided as Appendix I. The monitoring network comprised of seven EA-listed groundwater monitoring locations (MB2, MB5-D, MB5-S, MB7-D, MB8-D, MB9, and MB14) and an additional two bores (MB4-D and MB11). Heritage Minerals provided groundwater monitoring data collected from August 2022 to September 2024. Tabulated groundwater quality results are too lengthy to replicate in this report but are provided in Appendix I. A description of the groundwater quality is as follows. Groundwater at the site is heavily impacted with acidic conditions resulting in the mobilisation of metal species. Heritage Minerals have not commenced operations at the site and groundwater impacts are due to legacy contamination. An evaluation of the groundwater chemistry compared to groundwater quality guidelines identified multiple exceedances and based on the statistical analysis, identified trends for selected analytes in certain monitoring locations. The main outcomes of this assessment included: ∕ Exceedances of toxicant and physicochemical indicators were observed at all monitoring bore locations; ∕ Metal concentrations exceeded the published water quality guidelines for all metal species. The most notable exceedances were: – Aluminium, with the maximum recorded concentration (3,590 mg/L) exceeding the default guideline value (0.055 mg/L) by a factor of 65,000; – Cadmium, with the maximum recorded concentration (0.605 mg/L) exceeding the default guideline value (0.0002 mg/L) by a factor of 3,000; – Cobalt, with the maximum recorded concentration (12.3 mg/L) exceeding the default guideline value (0.001 mg/L) by a factor of 12,000;
Project number: 25B061
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