20230025_RECOR_MCU Engineers Letter_20.12.24

            site will be required to achieve the following design objectives for operational stormwater
            quality.

                                    Table 1 - Operational Water Quality Objectives

              Pollutant                                            Percentage Reduction Target (%)

              Total Suspended Solids (kg/yr)                       80

              Total Phosphorus (kg/yr)                             60

              Total Nitrogen (kg/yr)                               45

              Gross Pollutants (kg/yr)                             90



            Water Quality Modelling

            Details of the proposed treatment train are provided in RECOR’S SWMP. Further details of
            the proposed devices and preliminary sizing are provided below. Locations of the
            proposed devices are shown on the revised civil drawings.

            Bioretention Basin

            Table B in Appendix 2 of the State Planning Policy (2017) states that “In lieu of modelling,
            the default bio-retention treatment area to comply with load reduction targets for all
            Queensland regions is 1.5 per cent of the contributing catchment area”. MUSIC modelling
            has not been undertaken for sizing of the proposed bioretention basin. The proposed
            bioretention basin has been sized at 1.5% of the contributing catchment area in lieu of
            MUSIC modelling.

            It is proposed to provide a bioretention basin design for this project generally in
            accordance with the following typical section.




                               Figure 1 -Typical Cross Section of a Bioretention Basin




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