Effluent Impact on Receiving Streams: A Cost Effective Basis for Study

In deriving the requirements for discharge from point sources, regulatory authorities are placing more emphasis on the achievement of water quality objectives within the receiving water. Such an approach was adopted in the assessment of discharge requirements for both the current situation and for the future with increased plant loadings. The receiving waters under study form part of the catchment for Lake Burragorang (50 kms downstream) and pass through the semi wilderness area which provides catchment protection to the lake. The major nutrient inputs to the system were found to be the sewage treatment effluent and a horticultural enterprise, but during wet weather diffuse sources from the urban areas became significant. The study identified not only the chemical and nutrient contents but also the diversity of the in-stream ecosystem. The combination of these two indicators enabled a comparatively short term study to determine the appropriate nutrient balance for the stream and hence the future requirements for discharges so as to maintain the in-stream ecosystem.