Response to Stormwater Management Approval Conditions Letter

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65. Stormwater Quality Treatment must be designed in accordance with the Water by Design MUSIC modelling
    Guidelines. Any deviation away from the recommendations of the Water by Design guidelines may only be
    approved where:

   65.1. Letters signed by the authors of the Water by Design MUSIC modelling guidelines and/or eWater
         MUSIC modelling program are provided to confirm that the modelled design is expected to meet the
         required water quality outcomes at the discharge point of the site; and

Response

   As detailed in Section 4 of the SWMP Report No. 16-001014-01A, modelling of the site and design of stormwater
   quality treatment devices have been undertaken in accordance with Water By Design MUSIC Modelling Guidelines
   (2010) and other relevant Water By Design guidelines. The SWMP Report No. 16-001014-01A demonstrates that
   WQOs for the site are achieved without modelling of the Water Quality Control Pond (WQCP). This is conservative
   considering that the proposed pond will capture suspended solids through sedimentation and will treat some
   nutrients. Furthermore, the proposed Gross Pollutant Traps (GPTs) were excluded from the modelling, which are
   also expected to capture gross pollutants and suspended solids. The only treatment devices modelled are the
   Bioretention Basins, which have been configured in accordance with Water By Design’s MUSIC Modelling
   Guidelines (2010). Therefore, since there is no deviation from the recommendations specified in Water By Design
   Guidelines, a letter from the authors of the Water By Design guidelines or eWater MUSIC program is not required.
   For email correspondence with Water By Design and eWater regarding the modelling of the pond, refer to Calibre
   Consulting Letter No. B14158.W-10A dated 5 February 2016.


   65.2. A contingency plan to monitor for and to remove cyanobacterial and algal outbreaks from
         waterbodies, including costs, is provided for approval with the Operational Works application and the
         approved version is implemented throughout the lifetime of the development. All stormwater runoff
         treatment must be undertaken within the development areas of the site. Stormwater likely to contain
         grease and oil (i.e. from all roads and car parking areas) shall be managed via grease and oil
         arrestors prior to treatment within bioretention basins, wetlands and water quality control ponds.

Response

   As discussed above, modelling of the site and design of stormwater quality treatment devices have been undertaken
   in accordance with Water By Design MUSIC Modelling Guidelines (2010) and other relevant Water By Design
   guidelines. As detailed in Section 4 of the SWMP Report, all stormwater treatment is undertaken within development
   areas of the site. Modelling has demonstrated WQO’s can be achieved prior to discharge from the site.

   Stormwater from all significant roads and car parking areas are proposed to be treated with a HumeGard GPT.
   Council specify that runoff from all road and car parking areas is to be pre-treated for grease and oil prior to
   discharging to the downstream Bioretention systems. According to Water By Design Bioretention Technical Design
   Guidelines (2014) Bioretention systems are suitable for treating runoff from roof, ground and road areas. Table 14 of
   the guidelines outlines pre-treatment measures typically proposed upstream of Bioretention Basins based on
   catchment size (i.e. for catchments between 2ha and 5ha vegetated swales, coarse sediment forebays, inlet pond or
   GPT’s are recommended). The condition to pre-treat all runoff from road and car parking area specifically for oil and
   grease prior to discharge into Bioretention Basins is considered to be conservative given the nature of the
   Bioretention treatment device. There are also many examples of urban, commercial and industrial development that
   propose Bioretention Basins without pre-treatment of oil and grease.

   As per details provided in Section 3.1 of the Stormwater Management Construction & Maintenance Plan Report No.
   16-001014-02A, the HumeGard GPT proposed upstream of the proposed Bioretention Basins has the capability of
   trapping floating oil and grease pollutants. As demonstrated on Page 2 of the HumeGard GPT Technical Manual
   provided in Attachment 2, the application of a floating boom provides separation at the surface of the waters
   between the sediment storage chamber and the outlet chamber. This effectively captures pollutants such as oils and
   greases that float to the surface. Based on laboratory and field testing, Table 1 on Page 3 of the Technical Manual
   indicates 90% removal efficiency of Hydrocarbons during emergency spill events.

   Also, the proposed Bioretention Basins and Pond are not to become Council assets, rather this will be operated by
   the retirement community owner who is responsible for the maintenance and management of these treatment
   devices. Managing and replanting of the Bioretention Basins and Pond will be the responsibility of the retirement
   community owner.

   Based on the above, all areas of road and car parking, except for the road areas in the northern catchment
   (Catchment A1 & A2) will be treated by GPT’s. Since Catchment A is only 2.45ha with no significant areas for car
   parking a sediment forebay is appropriate.