FurtherAdviceResponse_2020.09.07 (002) · 132008.1128.04

Our ref: PR132983-1

Water quality

Issue
In regards to water quality, the changed application states:
The proposed redesign does not fundamentally affect the proposed stormwater management for the site.
Importantly, the stormwater network and treatment systems have been approved under OPW19-0020. This
approval included a 50m2 bio basin and 45m2 infiltration basin located along the northern boundary of the
site. These basins have been retained in the proposed design, albeit with minor reshaping of the bio basin.
The stormwater network is shown on drawing 5002-106(B) and 5002-400(B). A change application for
OPW19-0200 will be required in the future to reflect the changes to the stormwater basins.
Assessment documentation for the sizing of the water quality treatment systems for the RAC site
(OPW19/0047) and the Retirement Living Sites (OPE19/0020) identified that the water quality treatment
provided to serve the RAC site were undersized (56% deficit) and the Retirement living site were oversized,
but that combined they allowed for the required water quality treatment to be achieved. The current
approved staging whereby part of the Retirement Living was to be constructed first meant that when the
RAC was built – the pollution reduction targets would be achieved for the overall development.
The new proposed staging whereby the RAC is proposed to be built first, means that the situation no longer
exists whereby the overall pollution reduction will be achieved when the RAC is first built. The unknown
timeframe of delay between proposed commencement of use of the RAC and the now delayed construction
commencement for the Retirement Living also means that the overall development will not achieve the
required pollution reduction targets until such time as the Retirement Living development commences.
Advice Required
3.    Demonstrate how the required pollution reduction targets will be achieved for the development during
      the timeframe where the RAC site is operational prior to development of the Retirement Living stage.

Response

Refer to Attachment C - Stormwater Quality Engineering Response (Calibre).



MUSIC Model

Issue
A rerun of the previously supplied MUSIC model with the additional 1,298m2 site cover (coarsely added to
the RAC site as roof area, with no other adjustments made) identified that the TSS pollution reduction for
the combined site would fall short of 80% reduction in total suspended solids.
Advice Required
4.    Demonstrate that the overall development will still achieve the required pollutant reduction targets by:
      –      Provision of an updated MUSIC model that reflects the proposed changes;
      OR
      –      Provision of a table that lists the area and corresponding impervious pervious fractions that should
             apply to each source node of the MUSIC model [18-001942-Sunrise_Beach-080420]. This will
             facilitate for assessment officers to interrogate the existing model and proposed changes with
             correct information.

Response

Refer to Attachment C- Civil Engineering Response (Calibre). We understand that the ‘additional’ 1,298m2
is as a result of a change to the way the Site Coverage areas are calculated and this does not represent an
actual increase in the site coverage (roof area) for the purposes of stormwater as indicated by Council. The
catchment areas within the MUSIC model represents the actual (measured) catchment areas. The
‘additional’ 1,298m2 is not an actual increase in site coverage from a water quality catchment area
calculation perspective.



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