RFI Eng response notice items 4-19 MCU150111

                                                                                                                          6 of 8




Item 12 Provide calculations for “Developed site only with Mitigation”.

Our Response

It is our view that inclusion of external catchments in the MUSIC model provides a more accurate assessment of the
treatment performance. A revised version of Table 4-6 of Report B14158.W-03A is presented below. Note the MUSIC
model was revised to account for a change to carpark areas in Sub-catchment F5, as per Palm Lake Resort Drawing C0-
000-2014 Rev H.

From the Table below, the pollutant load reduction targets have been calculated for the developable area of the site.
MUSIC modelling indicates that the proposed treatment train provides a reduction of pollutant loads greater than what is
required. Since the load retained on site is in excess of the targets, the treatment train is considered to be meeting the
water quality objectives.

Table 4-6 MUSIC Modelling Results


 Description                                                                     Pollutant Load (kg/year)
                                                                     TSS            TP            TN                GP
 Developed Site Only (Without Mitigation)                           23200           57.3            406            3910
 WQOs (Percentage Reduction)                                         80%            60%             45%            90%
 Load Reduction Target                                              18560          34.38           182.7           3519
 Developed Site plus External Catchment (Without Mitigation)        29700          69.20            456            4150
 Developed Site plus External Catchment (With Mitigation)           10200          34.60            269             381
 Load Retention Achieved                                            19500           34.6            187            3769
 Load Retention Achieved as % of Developed Site Load                 84%            60%             46%            96%
 Water Quality Objective Achieved (SPP 4/10)                         YES            YES             YES             YES
 Developed Site without External Catchment (With Mitigation)        15370          29.10           177.0           3529




Item 13 To reduce pressure on the pond, demonstrate whether there is any opportunity to retrofit a water quality
treatment facility within the road reserve or other location within the development so that any activities on the
road system will not be attributed directly to any issues within the pond system.

Our Response

Flows are to be pre-treated prior to entering the central WQCP via bioretention basins. It appears that a flow split pit on
Drawing B14158.W Sheet SK101 was not recognised. This plan has been updated for clarity.

Item 14 Provide the Music Model and Auto Cad files or other mechanism to demonstrate that proposed nodes
and impervious areas are consistent with development plans.

Our Response

The areas of imperviousness was reviewed for each park node in the MUSIC model. The park node for catchment F3 has
15% imperviousness. The park nodes for catchments E1, F1, F2, F3, F5 have 0% impervious, however these catchments
are relatively small and do not need additional imperviousness as this area is captured in separate nodes. Refer attached
plan B14158.W Sheet SK112 which indicates areas of imperviousness.