Ballarat South Waste Water Treatment Plant, Victoria

GHD was contracted by Central Highlands Water to undertake an odour emissions survey of the Ballarat South Waste Water Treatment Plant (WWTP) in order to assess the buffer distances required around the plant.

EPA recommended buffer guidelines are not available for a WWTP the size of Ballarat South, and therefore two methods can be adopted to determine the appropriate buffer: extrapolate the existing radial buffers with respect to plant capacity, or define nonradial buffers using dispersion modelling.

Three plausible upset/malfunction scenarios were identified. Odour dispersion modelling was conducted using measured odour emission rate data for two of these scenarios ('digester low pH' and 'sludge lagoon cleanout') to determine the minimum nonradial directional buffer distances required to avoid odour nuisance.

As representative meteorological data was not available, GHD used the three-dimensional models TAPM and CALMET to develop a time varying wind field over the site. Dispersion modelling using CALPUFF was used to determine buffer separation as a function of direction from the WWTP using methodology developed by GHD. The predicted extent of the criterion odour level under all possible meteorological conditions is analysed in conjunction with the upset event return interval to determine the appropriate buffer distance.

The direction-dependent nonradial buffers were determined for four fan sectors with respect to Ballarat South WWTP. It is clear that for an impact return interval of five years, the sludge lagoon cleanout buffer is significantly reduced in the eastern segment and a significant intrusion onto existing residences is visible only in the western segment. A radial buffer is clearly inappropriate for Ballarat South WWTP. This work was also carried for Ballarat North WWTP for Central Highlands Water.

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