24-7-19 Attachment F Rev Stormwater Mgmt Plan

18 July 2019




5.3.3.7 MUSIC Results
The resulting percentage based load reductions at the outlet are shown in Table 5 below together
with the Water Quality Objectives for the receiving waters.


                                                                            Residual
                                                     Sources                           % Reduction   Target %
                                                                              Load


Total Suspended Solids (kg/yr)                         1,830                   366        80.0         80

Total Phosporous (kg/yr)                                3.93                   1.06       73.2         60

Total Nitrogen (kg/yr)                                  29.5                   12.1       58.9         45

Gross Pollutants (kg/yr)                                199                    7.46       96.3         90
                                 Table 5 – Percentage Based Load Reduction Results

5.3.3.8 POD Pollutant Reduction

5.3.3.8.1        Litter
Rubbish bins will be located within the building and car park for use by staff and visitors. The
carparks will be cleaned regularly. As a result of this and with the installation of the treatment
devices, levels of litter exiting the site via stormwater are expected to be negligible.

5.3.3.8.2      Sediment
The TSS outflow is identified in Table 5 above. As can be seen from the above table the pollutant
load reduction achieves the Water Quality Objectives. The TSS level is therefore considered
acceptable.

5.3.3.8.3       Nitrogen and Phosphorous
The TN and TP loads are identified in the above Table 5. As can be seen the TN and TP loads leaving
the site achieve the Water Quality Objectives. The Nitrogen and Phosphorous residual loads are
therefore considered acceptable.

5.3.3.8.4    Hydrocarbons
Hydrocarbons will become trapped within the bioretention filter media.

When there is a build-up of hydrocarbons within the bioretention basin, the top layer of the filter
media can be removed and replaced ensuring that no hydrocarbons are discharged from the site.

Studies have shown that micro-organisms in the organic mulch layer degrade and break down the
petroleum-based hydrocarbons and hence they will not be discharged from site.

5.3.3.9        Surfactants
Washing of cars is not expected on site for the proposed development, as a result surfactants
should not be an issue for the drainage system.




Excellence with Economy in Engineering                                                                          14
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