Appendix E - Wastewater Report

                              PROPOSED RESIDENTIAL SUBDIVISION
                              9A JIRRIMA CRESCENT, COOROIBAH

7.0      WASTEWATER TREATMENT AND DISPOSAL
An assessment of the type and configuration of wastewater system(s) that may be suitable for a proposed
development requires:
       Assumptions to be made regarding the typical building/visitor configuration and probable
        wastewater flow; and
       Evaluation of the terrain-soil combinations to identify distinct units.

7.1       Wastewater Flow Design Allowance
For a typical four bedroom house (or three bedrooms plus study), we have estimated a peak occupancy of
six persons. This assumption is consistent with current Council development standards and has been used
to demonstrate feasibility of onsite effluent disposal. Should the proposed residence exceed this size, it is
the owner’s responsibility to demonstrate feasibility of the design, meeting all relevant regulations.
For each occupant, a typical wastewater flow allowance of 120 L/person/day has been taken from
Appendix H of AS1547:2012. This represents the flow allowance for households with standard water
reduction fixtures (including duel flush toilets, shower flow restrictors, aerator faucets and water conserving
automatic washing machines) with on-site roof water tank supply.
We therefore estimate a typical daily household wastewater flow rate of 720 L/day (6 x 120 L/person/day).
This gives a weekly flow rate of 5,040 L/week.
It should be noted that wastewater flow rates may be further reduced by the adoption of full water reduction
facilities (e.g. reduced flush 6/3 L toilets, shower flow restrictors, aerator faucets, front-load washing
machines and flow/pressure control valves on all water-use outlets, etc.). Conversely, the use of extra
wastewater producing fixtures (e.g. spa baths) has the potential to increase the household wastewater flow
rate.

Final wastewater flow rates must be calculated at the time of detailed design of the wastewater system, at
building stage once the house design is known.

7.2       Terrain-Soil Assessment
The terrain-soil combination(s) encountered at a site are assessed so that an Expected Available Area (EAA)
can be delineated for suitable methods of wastewater treatment and land application.

The terrain across the potential effluent disposal areas is relatively consistent and has been categorised as
Linear Planar in accordance with the slope configurations described in Figure C2 of AS1547:2012, which
also describes the relationship between the shape of the slope and surface drainage. Such slopes have less
effective natural drainage as distance from the crest increases, with no spreading or acceleration of run-off
as it moves down slope.

It has been assessed from the results of the investigation that the soil profile across likely effluent disposal
area on Lot 1 characterised by the borehole is equivalent to Medium to Heavy Clay (Soil Category 6). This
categorisation has been derived via the method described in Table M1 of AS1547:2012.




4 November 2020
Report No. 20333-001-Rev0                                6