Sealed Judgement

4.3          Stormwater Quality Treatment Measures
The following stormwater quality treatment devices were modelled.


4.3.1        Bioretention Basin

It is proposed to incorporate a bioretention basin with a filter area of 50 m2. The properties of the
modelled bioretention basin are as follows:

x   Extended detention depth:300 mm;
x   Surface Area:              50m2;
x   Filter Area:               50 m2;
x   Hydraulic Conductivity:    200 mm/h;

x   Filter Depth:              0.4 m;
x   TN content of filter media:400 mg/kg;

x   Orthophosphate:            30 mg/kg; and
x   Exfiltration Filtration Rate: 0.0 mm/hr (initial run) 115 mm/h (sensitivity).


4.3.2        Rainwater Tank

As noted in Section 3.4, it is proposed to use part of the rainwater tank volume for detention. It is
also expected that a trickle top-up system will be used to supply water when the collected rainwater
supply is exhausted. This gives rise to the potential for rainfall to occur when the tank has been
topped up and for rainfall otherwise collected for reuse to drain from the tank.

To account for this, the assessment has assumed that the lowest part of the tank is not effective for
the capture of runoff and its reuse.

Subject to detailed design, a 10kL tank would provide the following:

x   Low segment- 2kL for trickle top up;

x   Middle segment- 5kL for capture and storage of roof runoff for reuse; and

x   Upper segment- 3kL for detention storage, which is drained via a pipe set at the top of the
    middle segment.

To calculate expected internal demand, the following assumptions were made:

x   Toilet requires 25 L/day (per person) in accordance with Table 4.4 of the MUSIC Modelling
    Guidelines 2010;

x   Laundry requires 21 L/day (per person) in accordance with Table 4.4 of the MUSIC Modelling
    Guidelines 2010;

x   Peak occupancy of two (2) people per dwelling for the proposed 16x 2-bedroom units for the
    holiday accommodation in accordance with Table 4.3 of the MUSIC Modelling Guidelines 2010.




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