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.