Appendix E - Geotechnical Report

                             PROPOSED RECONFIGURATION OF A LOT
                             216 BLACK MOUNTAIN ROAD, BLACK MOUNTAIN

7.5      Drainage
Adequate site drainage must be installed to ensure that surface water runoff is directed away from
pavements and footings.

All excess stormwater collected around the residence (including overflow from rainwater tanks) must be
directed to discharge at least 10 m down slope of any building or fill embankment and towards the gully north
of the proposed building envelope. This should be handled by pipes or lined channels to discharge into a
rock-lined contour drain, stacked rock weir, or similar.



8.0      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/worker configuration and probable
        wastewater flow; and
       Evaluation of the terrain-soil combinations to identify distinct units.

8.1      Wastewater Flow Design Allowance
For a typical four bedroom house (or three bedrooms plus study), we have estimated 6 Equivalent Persons
(EP) total. For each EP, a typical wastewater flow allowance of 115 L/person/day has been taken from
Appendix 4.2D of AS1547:2000. This represents the flow allowance for households with standard water
reduction fixtures and on-site roof water tank supply. We therefore estimate a typical daily household
wastewater flow rate of 6 x 115 = 690 L/day. This gives a weekly flow rate of 7 x 690 L/Day = 4,830 L/week.

It should be noted that 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.

8.2      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.

Possible areas for on-site effluent disposal on Lot 2 include the areas of mature trees adjacent to the
nominated building envelope (provided set-backs can be maintained), and on the grassed slope below. The
terrain on the slopes below the house has been categorised as Linear Planar in accordance with the slope
configurations described in Figure 4.1B2 of AS1547:2000, 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 profiles across the likely effluent
disposal area on Lot 2 are equivalent to Strongly Structured Medium to Heavy Clay (Soil Category 6),
based upon a typical soil profile encountered. This soil classification has been derived via the method
described in Table 4.2A4 of AS1547:2000. The indicative soil permeability rate (Ksat) for a soil of this
category is 0.06 to 0.05 m/d.

8.3      Recommendations
8.3.1        System Type
Having consideration for the terrain-soil assessment and environmental constraints of the site, we have
made an assessment of suitable methods of wastewater treatment for the site. The sewage treatment plant
(STP) connected to the house on Lot 2 must be licensed to produce at least Secondary standard effluent
and verified under the Plumbing and Drainage Act 2002. It is recommended that the STP is connected to a
surface or shallow subsurface drip irrigation system.




19 June 2018
Report No. 17427-001-Rev0                             12