1890 Effluent Disposal Review · MCU20/0022

4.10 Surface irrigation methods of effluent land application are appropriate for this site due
     to:
      Rural residential parcel
             Solar orientation
             Clay subsoil (friable)
             Landscaping opportunities



4.11 In 1993, Beavers and Gardner completed a scientifically based alternative into
     calculating set back distances using the “Viral Die-off Method”, [Beavers, P.D. and
     Gardner, E.A. (1993), Prediction of virus transport through soils, Australian Water
     and Wastewater Association, Technical Papers of the 15th Federal Convention, Gold
     Coast, Australia, 18-23 April 1993 (Volume 2, pp 530-535)]. This applies only to the
     wastewater moving in saturated soils, for example, in shallow groundwater beneath an
     absorption trench or surface irrigation area. “Modified” Advanced Secondary effluent
     is to be excluded 10 metres from a defined watercourse or dam (directional
     separation distance), however, using the Beavers Gardner Viral Die-off Method for
     virus inactivation over distance:


                              =
                                  ∙ ∙




      Where the parameters are as follows:

          t         =     Travel time in days. This is the time required for viruses originating in the
                          wastewater to be inactivated (i.e. reduced t acceptable numbers by
                          natural mortality processes) as they move down gradient in the
                          groundwater. A typical value of 22 days is used.
          K         =     Saturated hydraulic conductivity m/day [Permeability “P” may be used for
                          K]
          i         =     Hydraulic gradient m/m [use surface slope as approximation]
                    =     Effective porosity of the soil [generally use 0.2, or 0.1 for sand free of
                          fines]
          D         =     The seatback distance (metres) that the groundwater has travelled during
                          the travel time (22 days). This refers to the subsurface wastewater
                          movement, and not, for example, to wastewater flowing over the ground
                          surface from irrigation areas of failing absorption trenches.


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