RFI - Attachment 4 - Updated Stormwater Management Plan

                                       STORMWATER MANAGEMENT PLAN
Client: Devcon Capital 9                                                     Location: 11 Leo Alley Road, Noosaville


3.2.3 Proposed Stormwater Treatment Train
The stormwater runoff from each catchment will be treated by bioretention basins. Two (2)
bioretention basins are proposed for the development (Bioretention Basin A and B). The filter media
of each bioretention basin was modelled using a total nitrogen content of 400 mg/kg and an
orthophosphate content of 30 mg/kg. This is in accordance with the MUSIC Modelling guidelines
(consultation draft) by Water by Design (2018). Refer to Table 4 for the bioretention basin
characteristics.

                                   Table 4 – Bioretention Basin Characteristics
                                          Bioretention Basin A              Bioretention Basin B
      Extended Detention (m)                      0.30                              0.30
          Filter Depth (m)                        0.50                              0.50
        Surface Area (m2)                        35.00                             10.00
          Filter Area (m2)                       35.00                             10.00


3.2.4 MUSIC Model Results

MUSIC modelling of the proposed catchments was performed to ensure the nominated treatment
strategy achieves the required pollutant reduction objectives. The target reductions in stormwater
pollutants are based on a comparison of an unmitigated scenario, having no treatment on site, and
the mitigated scenario, which has stormwater treatment measures incorporated onto the site. Tables
5 and 6 provide the results of the modelling for catchment and Table 7 provides the modelling results
for the development in its entirety. The MUSIC modelling demonstrates that compliance has been
met or exceeded for the objectives required by NSC and the SPP (2017) for Total Suspended Solids
(TSS), Total Phosphorus (TP), Total Nitrogen (TN) and Gross Pollutants (GP).

                                 Table 5 - MUSIC Model Results for Catchment A
                  Unmitigated           Mitigated       Reduction           Target
 Pollutant                                                                                     Compliance
                    (kg/yr)              (kg/yr)       Achieved (%)      Reduction (%)
    TSS               949                  178              81                80                       Y
     TP              1.91                 0.498            73.9               60                       Y
    TN               11.8                 5.82             50.7               45                       Y
    GP                114                   0              100                90                       Y

                                 Table 6 - MUSIC Model Results for Catchment B
                  Unmitigated           Mitigated       Reduction           Target
 Pollutant                                                                                     Compliance
                    (kg/yr)              (kg/yr)       Achieved (%)      Reduction (%)
    TSS               378                   63             83.4               80                       Y
     TP              0.651                0.15              77                60                       Y
    TN                3.1                  1.5             52.7               45                       Y
    GP               29.2                    0             100                90                       Y

                           Table 7 - MUSIC Model Results for Overall Development Area
                  Unmitigated           Mitigated       Reduction           Target
 Pollutant                                                                                     Compliance
                    (kg/yr)              (kg/yr)       Achieved (%)      Reduction (%)
    TSS              1360                  272              80                80                       Y
     TP              2.64                 0.728            72.4               60                       Y
    TN               15.4                 7.82             49.3               45                       Y
    GP                143                   0              100                90                       Y




Covey Associates Pty Ltd                                  4                                   Project No: 192297
Consulting Engineers                                                                            26719Rpt, Issue E