Executive summary
The Mount Morgan Mine (MMM) is a former copper and gold mine located in Central Queensland which operated between 1882 and 1990. The mining activities have left a significant legacy of soil and water contamination, and the site is currently managed by the Queensland Government as a legacy mine site. Heritage Minerals Pty Ltd (Heritage Minerals) plans to commence operations at MMM through reprocessing of tailings produced from former gold and copper mining, following the construction of the processing plant and associated mine infrastructure and water management activities. GHD Pty Ltd (GHD) was commissioned by Heritage Minerals to complete a review of groundwater quality data obtained from monthly groundwater monitoring and to prepare a report to comply with Environmental Authority (EA) conditions W7, W8 and W9. The Heritage Minerals MMM 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). No monitoring was completed from MB3 as required under the EA. GHD understand that MB4-D and MB11 were included in the monitoring program in place of MB3 as this location was dry. Monthly monitoring commenced in August 2022. Heritage Minerals provided groundwater monitoring data collected from August 2022 to September 2024. 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. 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. – 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. – The Mann-Kendall statistical trend analysis identified 15 increasing trends, 15 decreasing trends, 9 probably increasing trends, and 13 probably decreasing trends. These results indicate that parameter concentrations are changing within the local groundwater system. This water quality review considers the current groundwater monitoring to be generally compliant with the conditions prescribed in W7, W8 and W9 of the EA, in terms of monitoring locations chosen, monitoring frequency and analytes assessed. Monitoring bore locations MB4-D and MB11 are currently not included in the MMM EA and were monitored in place of MB3 which was dry. Monitoring was initially completed from MB4-D (six events), with subsequent monitoring completed from MB11 (18 events) as MB4-D became unreliable. It is recommended that future monitoring be completed at MB11 in place of MB3 and this and this approach is confirmed as suitable with DETSI.
GHD | Heritage Minerals Pty Ltd | 12638246 | Groundwater Quality Review 2024
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