Appendix H - Slope Stability Assessment

Brett Hage                                                                                     22328-001-Rev0
                                                                                            14 September 2022

Table 3: 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 agriculture,          10 m                     30 m
     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. Boreholes indicate adequate unsaturated soil depths are
available.
Individual site layout shall be decided at building stage, in conjunction with a design provided by a NC
registered evaluator.
5.3.3 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 elements given below shall be implemented:
       Shallow subsurface drip systems must be installed at 100 mm to 150 mm depth into 150 mm to
        250 mm of good quality sandy 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 shall be imported to the site.
       Receiving native soils will be prepared by undertaking deep ripping / shallow cultivation combined
        with the addition of organic matter (10 kg/m² raw mulch) and gypsum (1 kg/m²) to ‘break up’ any
        relatively hard clay subsoils and improve overall drainage characteristics.
       Shallow subsurface irrigation lines will run parallel to slope contours. To evenly distribute
        wastewater throughout the irrigation areas, pressure equalisation systems (i.e. pressure
        compensating drip emitters) should be installed.
       Surface diversion drainage shall be installed on the up-slope sides of the land application areas to
        divert surface water and shallow subsurface seepage flows away. Such drainage should penetrate
        to a minimum depth of 0.3 m BGL.
       A low earthen bund shall be constructed, down slope of the effluent disposal areas up to 0.3 m high
        to retain run-off and promote sheet flow.
       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”).
       Erect barriers where necessary to restrict access to public which may interfere or damage the
        irrigation system.




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