BR190571 - BP Noosaville RFI Response Letter

Item 8
Issue: Stormwater quality treatment and bioretention design - The site is very level-
constrained due to low surface levels and high (tidal) tailwater levels. These constraints are
incompatible with the adopted pit-and-pipe approach to conveying runoff to the bioretention
basins. The OPW drawings show the issues being exacerbated by lower outlet levels and
greater level differences between pavement and bio surface levels than presented at the
MCU.
Information Required:
Provide a revised design for the stormwater quality treatment system at the site which
addresses the following issues which are inconsistent with the Bioretention Technical
Design Guidelines (Water by Design, 2012):
           a. Revise the design levels of the bioretention devices such that the
               controlling level for the saturated zone sits within the transition layer and
               not at the base of the filter media
           b. Revise the design levels of the bioretention devices such that the base of
               the filter media is above HAT. In the absence of tidal data for Weyba Creek,
               levels should be based on the secondary port at Munna Pt.
           c. Revise the design levels of the bioretention devices such that level
               differences between the bioretention surface and adjacent pavement is
               <500mm.
           d. Revise the flush grates specified for the bioretention devices for raised
               grates or domed grates.
           e. Consider an alternative concept which drains pavement areas at-grade to
               swales/bioretention and discharges roofwater to bioretention through
               surcharge pits. Consider whether the discharge from the refuelling area
               treatment device needs to be discharged to the bioretention device (also
               refer to the issue item below).
      -     ACOR Response:
ACOR have undertaken a full redesign of the stormwater quality treatment train for
this site. Due to site constraints with the water table the bio basins have been
replaced with Ocean Protect’s StormFilter System which will consist of 7 standard
Psorb cartridges installed inside a DN2250 Manhole. Further the filter system Ocean
Guards with 200 micron mesh bags will be installed in each of the field inlets around
the site. The design package from ocean protect has been provided for council’s
information.




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