Attachment 3 - Revised Engineering Report (rec. 7.04.2025) MCU24-0165 & OPW24-0222

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5.6.2.7 MUSIC Model Results
The model's minimum load-based pollutant reduction efficiencies are achieved, shown in Table 6, and
in accordance with the QLD SPP (July 2017), Table B: Post Construction Phase - stormwater
management design objectives.
TABLE 6: MUSIC MODEL RESULTS

 Parameter                             Required Load            Music Results                    Result
                                         Reduction
 Total Suspended Solids (TSS)                80%                    82.2%                      Compliant
 Total Phosphorous (TP)                      60%                    73.6%                      Compliant
 Total Nitrogen (TN)                         45%                    52.3%                      Compliant
 Gross Pollutants >5mm                       90%                     100%                      Compliant

5.7      Stormwater Quality Asset Maintenance
Vegetation plays an important role in the healthy and effective operation of the bioretention basin.
Maintenance in the initial establishment period (up to two years) is crucial to the ongoing performance
of the bioretention basin, where weed removal and re-planting may be required.
There are several typical maintenance elements for bioretention basins, as follows:
    •   Routine inspection of the bioretention basin profile to identify any obvious areas of increased
        sediment deposition, scouring from storm flows, rill erosion of the batters from lateral inflows,
        damage to the profile from vehicles and clogging of the bio-retention basin (evident by a 'boggy'
        filter media surface);
    •   Routine inspection of inflows systems, overflow pits and under-drains to identify and clean any
        areas of scour, litter build-up and blockages;
    •   Removal of sediment where it is smothering the bio-retention basin vegetation;
    •   Where a sediment forebay is adopted, removal of accumulated sediment.
    •   Repair any damage to the profile resulting from scour, rill erosion, or vehicle damage by
        replacing appropriate fill (to match onsite soils) and revegetating.
    •   Regular watering/irrigation of vegetation until plants are established and actively growing; and
    •   Removal and management of invasive weeds (herbicides should not be used);
Routine inspections shall be undertaken on the bioretention after every significant rainfall event (30mm
or more of rainfall within a 24 hr period) or on a three-monthly basis within the first two (2) years during
the establishment of the planting media. After that, inspections can be reduced to a six (6) monthly
basis.

The following minimum requirements for inspection should be undertaken:
    •   Check for a build-up of sediment at pipe inlet/outlet structures, and remove as required;
    •   Check all concrete structures for damage and deterioration;
    •   Check for the build-up of vegetation matter on the bioretention basin surface and removal of
        the excess build-up to ensure minimal blockage to filter media;
    •   Check health of planting and ensure establishment has occurred;
    •   Check bioretention basin during rainfall events to ensure stormwater is filtering through media
        and operating according to the design intent.
5.7.1 Maintenance Schedule
Outlined below in Table 7 are the recommended maintenance schedules for the treatment types.




 15 November 2024                                                                                          Page 15