Swmp

Nutrient Runoff:

Nutrients such as Nitrogen and Phosphorus can be mobilised and transported in Stormwater runoff from
the site. This can compromise Water Quality Objectives.

Potential Causes

         •      Runoff from hard surfaces within the site.
         •      Detergents used in car washing and similar activities.
         •      Fertilisers used in propagation of landscaped areas.
         •      Embodied nutrients contained in silt (topsoil) runoff.
         •      Embodied nutrients contained in runoff.

Mitigating Measures

         •      Fall vehicles pavement areas towards landscaping areas and the bioretention bed.
         •      Implement management plan for landscaping propagation. Use stable organically bound
                fertilizers cultivated immediately prior to turf placement. Mulch over areas of exposed
                topsoil.
         •      Construction of silt fences during construction and maintained beyond completion of
                landscaping.
         •      Drain stormwater runoff through the Bio Basin.
         •      Capture roof runoff and store for re-use.

5.3.3    Proposed Treatment Measures
Following the water quality objectives for the site mentioned above, to ensure that on-site stormwater
management facilities can be economically maintained, it was deemed the most appropriate method for
treatment is the use of a small grass swale and an on-site bio-retention basin. Roof and surface runoff
will be collected by an internal drainage network and directed to the on on-site bio retention basin prior
to the lawful point of discharge.

5.3.4    Pollutant Modelling
The impact of the stormwater quality management strategy of runoff discharged from the site has been
assessed using the Pollutant Export Model, Model for Urban Stormwater Improvement
Conceptualisation (MUSIC).

For our model the proposed treatment train has been modelled: -

         1.     Roof water from buildings containing units 601-602, 201-204 and the rear portion of the
                roofs for units 701-704 and 101-105 will be collected by a 14kL rainwater re-use tank
                with overflow to the onsite Bio retention basin located in the north-eastern corner of the
SCG Consulting Engineers                   Page 11                                 SCG Ref: 33132(SWMP)