Breach and decant of an acid mine lake by a eutrophic river: river water quality and limitations of use
Faculty of Health, Engineering and Science
School of Natural Sciences/Mine Water and Environment Research Centre
Surface and ground waters of catchments comprising mining resources often show elevated solute concentrations in baseline conditions due to their unique geologies which may complicate the interpretation of natural differences in regional water quality. Mining lease conditions often specify the use of ecosystem protection guidelines for regulating discharge water quality limits. We present a case study from Collie in south-western Australia, where breaching and subsequent decant of an acidic pit lake by a diverted eutrophic river identified the need for establishing site specific river water quality guidelines in a moderately disturbed catchment. Following the breach of the acidic Lake Kepwari pit lake by the diverted Collie River in August 2011, water quality samples were collected at lake decant and other Collie River monitoring sites above and below the lake discharge on a daily basis for six weeks. Water quality results were compared to Australasian (ANZECC/ARMCANZ 2000) livestock drinking water guidelines, 90% ecosystem protection guidelines and recreational water quality and aesthetic guidelines. Water quality results indicated no significant risk of toxicity to livestock drinking water during the period, however water quality at all sites sampled including a reference site above the discharge exceeded ecosystem protection guidelines for pH and Zn, and recreational water quality and aesthetic guidelines for pH, Fe, Al, Mn and TDS. We conclude that background concentrations in the Collie River are already slightly elevated in various solutes such that site specific water quality guidelines are recommended for future water quality analyses.