2016-07-12 - Item 14 - Att 1 - Effluent Disposal Planning Study

The study found there was a large body of water quality sampling results, but that the absence of a
methodology behind collection and testing prevented any useful interpretation of long term
changes in water quality. With ‘little information’ for much of the shire, a conservative approach
was adopted. Recommendations about future water testing of key areas were included. (P.8)

A further significant challenge arose in the resolution of ‘acceptable’ run-off quality – defined in the
study as ‘sustainable, conservative and practical’. This is broad terminology and does not offer
specific parameters for determining preferred actual outputs for differing terrain.

The Shire was divided into 8 catchments (refer Figure 1). Run-off from these catchments was
modelled using a daily time-step water balance for a number of defined land uses for each
catchment. Estimates of runoff (with an allocated nutrient export rate) were performed for each
catchment. Separate studies referred to above were important inputs to support this work.
Predicted water quality accounted for residential use together with various rural uses existing in the
catchments.

The modelling results suggested Lake Macdonald, Maroochy and Stumers catchments already had
more dwellings than was desirable. Lake Weyba was close to a recommended maximum. Kin
Kin, Mary River East and Lake Weyba had a reliance on off-site dilution to achieve suitable stream
water quality. The remaining catchments Cooroibah and Mary River West exhibited sustainability
of water quality. (P.3&4)




On-Site Effluent Disposal in Noosa Shire 2016                                                     Page 4