RFI - Attachment 5 - Amended Stormwater Management Plan · MCU22/0094

 31 March 2023



 Land Use – Commercial                    Log10 TSS (mg/L)                     Log10 TP (mg/L)         Log10 TN (mg/L)


                                          Base            Storm               Base          Storm      Base       Storm
                                          Flow             Flow               Flow           Flow      Flow        Flow

 Roof                Mean                   0              1.30                 0            -0.89      0          0.37

                     Std. Dev.              0              0.38                 0            0.34       0          0.34

 Roads               Mean                 0.78             2.43               -0.6           -0.30     0.32        0.37

                     Std. Dev.            0.39             0.38                0.5           0.34      0.30        0.34

 Ground              Mean                 0.78             2.16               -0.6           -0.39     0.32        0.37
 Level/Open
 Space               Std. Dev.            0.39             0.38                0.5           0.34      0.30        0.34
                                Table 2 – Pollutant Export Parameters (Commercial)

5.4.3.5 Water Quality Objectives
The Water Quality Objectives of the receiving waters for the proposed development have been
obtained from State Planning Policy July 2017. The State Planning Policy load reduction targets are
summarised in Table 3 below.


                                              WATER QUALITY OBJECTIVES


 Total Suspended              Total Nitrogen                  Total                     Litter/Gross
  Solids (TSS) %                 (TN) %                   Phosphorous                   Pollutants %        Oils/Grease
    Reduction                   Reduction               (TP) % Reduction                 Reduction

                                                                                                         No visible films
           80                          45                             60                       90
                                                                                                           or odours
                                            Table 3 – Water Quality Objectives

5.4.3.6 Treatment Plan
In order to achieve the Water Quality Objectives for the proposed development, it is proposed to
use natural treatment methods to treat the runoff prior to discharge from the site.

Stormwater runoff from the roof will be captured in a series of new gutters, downpipes and pits,
which will discharge along with the remaining on ground catchments to the bioretention basin,
where Q1 flows will receive treatment while additional flows will discharge into the external
stormwater network.

Approximately 140m2 of the access driveway, footpath and landscaped areas will bypass the
bioretention basin. This bypass has been compensated for in the model so the overall net water
quality objectives are achieved for the development.

Stormwater collected from the roof will be harvested within the proposed 1.5kL slimline rainwater
tank. This volume will have the capacity for year-round toilet flushing reuse, meeting the water



 Excellence with Economy in Engineering                                                                                     10
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