Stormwater Management Plan

SC5551 - 28 Elkhorn Dr, Tewantin                                                                        9




3.3.2.2 Treatment Nodes
The following devices have been used in the treatment train to reduce these pollutant loads to achieve WQO’s.


    Bio-Retention Basin – An area of 95m2 of designated Bio-retention to treat road, landscape, and roof
    catchments to achieve the WQO’s was modelled. An extended detention depth of 200mm with a filter
    media of 180mm/hr sandy loam hydraulic conductivity has been modelled. The location of these
    devices is shown on the attached Appendix A.


    Rainwater Tanks – A combined volume of 55,000L rainwater harvesting was modelled to receive 50%
    roofwater areas. This volume is to be re-used for irrigation purposes (excluding road reserve areas).
    Re-use rates for irrigation were calculated as follows: 5,167m 2 ground areas x 75% (areas to receive
    irrigation) x 0.548m annual irrigation, equating to 2,124kL/yr per the MUSIC Modelling Guidelines



3.3.3    Effectiveness in Pollution Reduction
The water quality development model was set up with the incorporation of the above devices to reduce
pollutant export to WQO levels. Table 3.5 indicates the predicted pollutant mean values of stormwater
discharged from the site as calculated by MUSIC:


                                   Pollutant              Percentage Load Reduction

                        Total Suspended Solids (TSS)                  83.2%

                            Total Phosphorus (TP)                     60.3%

                              Total Nitrogen (TN)                     56.2%

                           Gross Pollutants (>5mm)                    100%

                                   Table 3.5 - Flow Based Pollutant Load Reduction



The MUSIC modelling results shown above indicate that the treatment train will adequately treat TSS, TP
and TN generated by stormwater runoff in accordance with the targets required under the water quality
objectives stated previously.