Appendix H - Slope Stability Assessment

Brett Hage                                                                                       22328-001-Rev0
                                                                                              14 September 2022

within the proposed development areas. The nominal 500 m2 land application areas, as shown in Figure 1
would therefore be appropriate, and it is assessed that that there is enough room to site the wastewater
irrigation areas with the necessary setbacks.
The need for a reserve area is generally applied to septic tank systems, producing low quality (Primary
Standard) effluent, due to increased potential for fowling and failure of the trenched land application area to
occur. As the use of an aerated wastewater treatment system is proposed, which are capable of delivering
high quality (Secondary Standard or better) effluent, the risk of fouling and system failure is negligible. As
shallow subsurface drip irrigation is proposed which can be easily repaired in-place as required, the addition of
a separate reserve area is not warranted.
5.3.2        System Positioning
Positioning (‘setback’) of the land application system must be in accordance with the horizontal and vertical
setback distances recommended in Tables T2, T3 and T5 of the Queensland Plumbing and Wastewater
Code 2019, as summarised in Tables 5, 6 and 7 below and on the following page.


Table 1: Setbacks for subsurface land application area for on-site sewage treatment plant
                                                                             Horizontal separation distance
  Site Feature
                                                                             Upslope      Downslope       Level

 Property boundaries, pedestrian paths, walkways, recreation areas,
                                                                               2m              4m          2m
 retaining wall, and footings for buildings and other structures.

 Inground swimming pools.                                                                     6m

 Inground potable water tank.
                                                                                              6m
 (Secondary standard effluent or better)


Note:   Distances measured from the edge of trench/bed excavation or subsurface irrigation distribution
        pipework to the nearest point of the feature.



Table 2: Setbacks for surface irrigated land application area for on-site sewage treatment plant


  Site Feature                                                           Horizontal separation distance


 Property boundaries, pedestrian paths and walkways                                      2m

 Water edge of a swimming pool                                                           6m

 Dwellings, recreation areas                                                            10 m


Note:   Distances measured from the edge of the irrigated wetted area to any point of the feature.




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