Alcoa operates the Kwinana Refinery to produce alumina from bauxite mined at Huntly in the Darling Range. Alcoa is licensed to take 5.4 GL/annum of groundwater from the Superficial Aquifer for ore processing, about half of which is recovered seepage at the refinery and residue storage areas.
In 2010, Rockwater completed an H3 Level of Hydrogeological Assessment of the Superficial Aquifer. As part of the assessment, we considered obtaining water from the Kwinana Wastewater Treatment Plant (WWTP), where the infiltration of treated waste-water had led to artificially elevated water levels in the Spectacles Wetland an important conservation significant wetland on the Swan Coastal Plain.
Rockwater was commissioned by Alcoa to determine the effects that reduced infiltration from the WWTP would have on the Spectacles Wetland. We completed a hydrogeological and environmental assessment of the wetland, involving the use of a groundwater model. The rates and magnitude of drawdowns predicted by the model were used to assess impacts on the vegetation communities.
A risk matrix was used to determine the level of risk for each category of groundwater-dependent vegetation. It was determined that the majority of the wetland communities are at a low risk of impact, and that the key environmental values could be maintained by the reduced infiltration from the WWTP.
