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

The government, as at April 2016, had approved many systems. Secondary -35, advanced
secondary - 25 and advanced secondary with nutrient removal - 7.

For this Planning Study, the above systems are of primary interest. The use of holding tanks,
common collection systems, greywater treatment or chemical, composting, incinerating or
waterless toilets are not considered due to their lesser potential for adverse impacts.

Figure 4 - Aerated treatment plant




3.3      Environmental Impacts
The primary purpose of on-site wastewater treatment is to enable the safe use of land for housing
and other purposes in circumstances where there is no sewerage for collection of unwanted liquid
wastes. Those liquids entering the treatment system primarily contain contaminants of nitrogen,
phosphorus and faecal coliforms. Both nitrogen and phosphorus are potentially adverse to the
receiving environment being nutrients. Faecal coliforms are dangerous to human health.

On-site wastewater treatment is an effective means of dealing with these potentially hazardous
wastes provided the conditions are suitable. Inappropriate discharging is unfortunately far more
common than would be desirable. Given the range of factors that can impact on satisfactory
operations, including occurrence of adverse weather conditions, it is not the case that all systems
can be made to work all the time.

Understanding the potential impacts of the systems on the receiving environment is a complex and
evolving issue. Treatment systems can be audited and an understanding of their failings is
currently possible. However, the effects of failing systems on receiving environments are another
matter entirely. Studies and the technical understanding of these impacts are limited and
potentially quite varied depending on the local circumstances of soil, weather, terrain and
vegetation.

Various studies have been published following investigations around Australia. These mainly relate
to assessing areas which are predominantly employing septic tanks. This planning study does not
propose an overview of those efforts. What is clear though is that there is a variety of findings and
conclusions in attempting to determine the general suitability of on-site treatment systems. More
research and sampling will contribute to an improvement to a technical understanding of the issue.
Modelling capability is also progressing as demonstrated by some initiatives in south east
Queensland that are attempting to predict water quality processes throughout an entire catchment.

On-Site Effluent Disposal in Noosa Shire 2016                                                 Page 8