Developing Site-Specific Water Quality Limits for Stockton Mine

The streams draining the Brunner Coal Measures on the West Coast are unusual. They are naturally acidic (pH 4–5) and enriched in metals due to the surrounding geology, climate, and soils, yet they support diverse and adapted aquatic life, including macroinvertebrates and the distinctive blue-tinged kōura (freshwater crayfish).

The unusual water chemistry in these streams can exceed national guidelines, prior to any mine water reaching them. This means that site-specific criteria are required for assessing environmental effects when consenting operations.

To develop site-specific thresholds, we compiled and analysed more than 20 years of macroinvertebrate and water quality monitoring data from streams draining the Brunner Coal Measures. We used multiple statistical approaches to examine relationships between stream chemistry and ecological condition across gradients of exposure.

The analyses identified ecological response thresholds for the key variables – pH and dissolved aluminium – and allowed the mine operator to move forward with mine planning and consenting.