Attachment D - Stormwater and Water Quality report

                                                                               Callaghan & Toth


6.0 PROPOSED REMEDIATION OF STORMWATER DEVICES

6.1      Biobasins

The two existing biobasins will be accepting the existing stormwater flows from the area as well
as the new hardstand areas. These biobasins and are in need of refurbishment, having been in
use for approximately 14 years. It is also noted that design guidelines have changed since
these biobasins were installed, and they are currently not to best practice standards. It is
proposed to undertake the following maintenance:

Biobasin 1 – in Lot 7 (following completion of the new carpark landscaping):
    Remove debris and litter
    Remove weeds and vegetation around biobasins and on the surface
    Fix erosion of the inlet swale to Biobasin
    Check the pipe inlet
    Check the outlet weir and pipe, fix erosion and clean pipes as required
    Remove filter media
    Remove underdrainage pipes
    Remove drainage layer material
    Line Biobasin with welded poly-liner
    Install drainage layer with replacement pipes
    Install an outlet pit connected to the new underdrainage pipework
    Install transition layer
    Install filter media to design depth
    Landscape planting in filter media

Biobasin 2 – adjacent Mary River Road
    Remove debris and litter
    Remove weeds and vegetation around biobasins and on the surface
    Check the pipe inlet
    Check the outlet weir and pipe, fix erosion and clean pipes as required
    Remove filter media
    Remove underdrainage pipes
    Remove drainage layer material
    Line biobasin with welded poly-liner
    Install drainage layer with replacement pipes
    Install an outlet pit connected to the new underdrainage pipework
    Install transition layer
    Install filter media to design depth
    Landscape planting in filter media




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2001 Lower Mill Carpark Extension SWMP                                      February 2020