Appendix D - Geotechnical Report

Table 8: Setback distances for on-site sewerage facilities (Protection of surface and groundwater)
                                                                                         Separation distance
    Site Feature
                                                                            Advanced Secondary
                                                                                                       Secondary Effluent
                                                                                 Effluent
    Surface Waters:
    ▪ Top of bank of permanent or intermittent water course,
         lake, bay or estuary;
    ▪ Top water level of a surface water source used for                             10 m                      30 m
         agriculture, aquaculture or stock purposes;
    ▪ Open stormwater drainage channel or drain;
    ▪ Bore or a dam.
    Unsaturated soil depth to a permanent water table (vertically)                   0.3 m                     0.6 m
Note:     Distances measured from the edge of the irrigated wetted area to any point of the feature.

Unsaturated soil depths of 0.6 m (i.e. depth to rock or wet soil) and 0.3 m are recommended for
Secondary and Advanced Secondary effluent, respectively. The test pits indicate that adequate
unsaturated soil depths are available across the proposed development area.
A conceptual wastewater layout plan has been prepared (attached as Figure 1) which demonstrates that
a new STP and wastewater irrigation area can be positioned within each proposed allotment. It is noted
that this plan demonstrates conceptual layout only for the purpose of demonstrating feasibility.
Individual site layouts shall be decided at building stage.

8.4.3          System Construction
Construction of wastewater land application areas must be carried out in accordance with Appendix M of
AS1547:2012 and NC requirements. In order to prevent any adverse impacts on the water quality from
effluent disposal, the following shall be implemented:
▪      For shallow subsurface drip irrigation, systems must be installed at 100 mm to 150 mm depth into
       150 mm to 250 mm of good quality topsoil, in grassed of other suitably vegetated areas. Any sandy
       topsoil material won from site works may be used to supplement the soil within the respective
       disposal fields or alternatively may be imported to the site.
▪      Shallow subsurface irrigation lines will run parallel to slope contours. To evenly distribute
       wastewater throughout the irrigation area, a pressure equalisation system (i.e. pressure
       compensating drip emitters) should be installed.
▪      Surface diversion drainage shall be installed on the up-slope sides of the land application area(s) in
       order to divert surface water and shallow subsurface seepage flows away. Such drainage should
       penetrate to a minimum depth of 0.3 m BGL, to capture and divert any seepage which may develop
       between the topsoil and underlying soils.
▪      Plant and maintain grasses, reeds and/or small shrubs within the land application areas. Preference
       should be given to native plant species endemic to the local area, which are suitable for mostly wet
       soils and are tolerant of nutrient loads (e.g. native riparian vegetation)
▪      Erect signage at the boundaries of the area in at least two places in accordance with Council
       requirements to warn people regarding the presence of wastewater pipes (e.g. “Sewage Effluent
       Pipework Installed Below – DO NOT DIG” or “Recycled Water – Avoid Contact - DO NOT DRINK”).




Geotechnical Investigation
10 June 2026 | 26073-001-Rev0                                                                                           24