Derivation of Site-Specific Water Quality Guidelines

National water quality guidelines (ANZECC/ARMCANZ 2000) provide default trigger values for the protection of aquatic ecosystems from the impacts of stressors and toxicants.

However, toxicity is influenced by many environmental factors that vary between locations. As such, site-specific water quality trigger values (SSTVs) often need to be developed for mining projects, using baseline water quality and local biological effects data, such as field biological data.

In collaboration with the Environmental Research Institute of the Supervising Scientist (eriss), WRM developed SSTVs to protect the current ecological values of creeks impacted by mine tailings seepage enriched with magnesium sulphate (MgSO4). To account for the diluting effects of wet season flows on MgSO4 concentration, the relationship between daily flow and electrical conductivity (EC, as an indicator of MgSO4) was modelled using telemetered data. Under the model, if the flow-EC relationship for a given year were to fall outside the upper 95% prediction interval of the “reference” relationship, then this would indicate water quality has deteriorated [Van Dam et al. (2014)].

This project provided the client with a flow-dependent trigger value to assess changes in water quality as a result of their operation.