Electrical Conductivity and Magnesium (i) Undertake continuous monitoring of electrical conductivity and event-based sampling for magnesium. (ii) When the electrical conductivity Investigation Trigger (42 S/cm for > 6 hours) is exceeded, convert continuous electrical conductivity data to magnesium concentration data. (ii) Report and act on Trigger Value exceedances at the downstream compliance sites. (iii) Minimise mine derived magnesium at the downstream compliance sites to the greatest extent practicable. 18 S/cm 1 mg/L 30 S/cm 2 mg/L - Derived from exposure Guideline for exposures < 72 hours) - 3 mg/L (Chronic exposure for exposures ≥ 72 hours) (i) Electrical conductivity is monitored accurately and continuously. (ii) Electrical conductivity Investigation Trigger is not exceeded at downstream compliance sites (without accompanying exceedances at upstream control sites) without reasonable cause. (iii) Sufficient magnesium data are collected to enable reliable and accurate estimation of magnesium concentrations from electrical conductivity data. (iv) Magnesium pulse exposure Guideline Trigger Values are not exceeded at downstream compliance sites (without accompanying exceedances at upstream control sites) without reasonable cause. (v) Magnesium Limit is not exceeded at the downstream compliance sites without accompanying exceedances at upstream control sites. (vi) All Trigger Value exceedances are investigated and reported as outlined in Section 4 of the Revised Water Quality Objectives for Magela Creek and Gulungul Creek (2015) “Actions Invoked by Trigger Value Exceedances”. (vii) Electrical conductivity and magnesium concentrations will not deteriorate compared to those measured in previous wet seasons, without reasonable cause.
Radium-226 (i) Undertake routine sampling for Radium-226. (ii) Report and act on Trigger Value exceedances at the downstream compliance sites. (iii) Minimise mine derived radium-226 at the downstream compliance sites to the greatest extent practicable. - - - 3 mBq/L (wet season geometric mean difference between compliance and upstream sites) (i) The wet season geometric mean total activity concentration measured at the downstream compliance sites minus that measured at the upstream control sites is not greater than the Limit. (ii) All Trigger Value exceedances are investigated and reported as outlined in Section 4 of the Revised Water Quality Objectives for Magela Creek and Gulungul Creek (2015) “Actions Invoked by Trigger Value Exceedances”. (iii) Radium-226 activity concentrations will not deteriorate compared to those measured in previous wet seasons, without reasonable cause. 6 Guidance for continuous monitoring and event-based sampling methods. Methods Purpose Control Event-based Sample Collection Event-based sampling should be implemented to ensure that each EC pulse recorded by the continuous monitoring system is sufficiently chemically characterised to allow effective assessment against the relevant Trigger Values. Total concentrations of metals and major ions should be measured by acidifying unfiltered samples to 5 per cent nitric acid and digesting them at 100-110 ºC for a minimum of six hours, prior to analysis. ERA should provide details of their sample collection methodology in the Annual Water Management Plan for stakeholder approval. Total metal concentrations should be converted to equivalent dissolved metal concentrations by use of the appropriate concentration conversion factor prior to comparison with the Ranger Water Quality Objectives. Details in Section 3.5 of the Revised Water Quality Objectives for Magela Creek and Gulungul Creek (2015) “Data Interpretation and Reporting”. Continuous Monitoring Data Continuous monitoring data for EC, turbidity and pH should be recorded at a frequency that provides assurance that the full magnitude of a given pulse will be captured to an environmentally relevant resolution. ERA should provide details of their data recording methodology in the Annual Water Management Plan for stakeholder approval.