"Release of mine-affected water is a common practice across Queensland. This activity is typically managed through a range of management and monitoring requirements in line with industry standards prescribed under the Environmental Protection Act 1994 and regulated by the Department of Environment and Science (DES)."
"Macroinvertebrate data supports the distinction of a ‘Slightly Disturbed’ aquatic ecosystem condition under the EPP Water. The management intent for this water type is to gradually improve water quality and to aim to achieve a Highest Ecological Value (HEV) waterway classification, however HEV Water Quality Objectives (WQOs) may not be achievable in the Copperfield River asthere are a number of regionally based negative influences on water quality."
"For toxicants in the <0.063 mm fractions, exceedances reported around the potential release sites (e.g., W1 and W2) are also reported in the upstream and downstream monitoring sites (e.g.,WB and W3, respectively) suggesting that there are no widespread impacts from historical mining activities evident within the Copperfield River and that the concentrations of metals found are a result of the overall catchment drainage. Additional sampling and monitoring is recommended inaccordance with the REMP."
"Proposed releases are subject to initial mixing within the near field and predicted water quality within the mixing zone reaches the HMTV for dissolved zinc (the constituent of most concern), within a maximum (worst-case) distance of 625 m. Other modelled scenarios indicate a much smaller mixing zone of between 50 and 70 m downstream."
"Mixing zone modelling has indicated that the use of a diffused discharge outlet structure will facilitate rapid near field mixing at the outlet such that the WQO for the contaminant of most concern (dissolved zinc) will be met within 625m for the range of scenarios and outlet configurations assessed (most modelled scenarios suggest a mixing zone of between 50 and 70m downstream). There are no known permanent or semi-permanent pools within 625m downstream of the release location which could provide refuge for aquatic ecology. There are no other known sensitive receptors within this mixing zone."
"During the operations phase, the simulated releases are well in excess (200:1) of the minimum dilution ratio for toxicity-related impacts in the receiving environment (9:1).
Concentrations of parameters relevant to other EVs (including drinking water, irrigation, farm supply, stock watering, human consumption, industrial use and recreation) are all modelled to be below the specified WQO."
As far as I can tell the impact appears to be minimal, and localised to the immediate downstream (up to 625m worst case scenario, at 200:1 dilution, which is more than 10x the minimum dilution required (9:1 minimum)).
IMO DYOR etc etc. Read the report, it's all there.
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