Attachment 7A - Responses to NC Info Request by ADG

 STORMWATER TREATMENT DEVICE DETAILS

 4. Clarify the filter media area          Refer updated SBSMP (ADG Ref: 22366 C R10 Rev04) that
    proposed for the bioretention          provides a preliminary section showing integration with car
    device and provide a preliminary       parking and surrounding.
    section showing how it integrates
    with the proposed car parking
    and surrounding levels
 5. Provide geotechnical borehole          Refer geotechnical borehole and test results for neighbouring
    and test results demonstrating         development “Noosa Sanctuary” (Report No.
    that the proposed ‘pipeless’           GEOTKPAR1178AA/A) that is included as an appendice in
    bioretention will function at the      ADG’s SBSMP. The bio-retention basin is likely to sit
    proposed location by providing         approximately 0.7m – 1.0m beneath existing surface level.
    the following for the bioretention     Geotech borehole logs identify a medium dense silty sand
    location:                              (alluvial) at approximately 1.0m depth beneath existing ground
                                           level (varies).
     5.1. In-situ Soil classification
     5.2. Groundwater level (BGL and       The groundwater was noted at depths of 1.3m below ground
          mAHD)                            surface level and as the subsurface profile is predominately
                                           sands, the water table is likely to fluctuate with tides, flood and
                                           rainfall events.

     5.3. In-situ saturated hydraulic      It is recommended that in-situ saturated hydraulic conductivity
          conductivity test results at     testing is performed during detailed design to confirm the
          proposed level of bioretention   modelling assumptions. Assumptions included in the SBSMP
          base                             are that a silty sand will have a minimum hydraulic
                                           conductivity, k, of 1.0 * 10^-8 m/s and a maximum hydraulic
                                           conductivity of 5.0 * 10^-6. An appropriate hydraulic
                                           conductivity has been assumed between these ranges and it is
                                           recommended that a hydraulic conductivity and permeability
                                           test be conducted by an experienced Geotechnical Engineer at
                                           detailed design stages.
                                           ADG have assumed saturated hydraulic conductivity of 4 × 10−6
                                           m/s which gives a yearly capacity of 3,784 𝑚3 /yr for a 30 m2
                                           bioretention infiltration area.
                                           Please see attached MUSIC modelling which shows the yearly
                                           amount of water required to be infiltrated is 2,900 𝑚3 /yr.

     5.4. Details of proposed planting     Details of proposed planting to be provided by landscape
          within he bioretention device    architect.

We believe the above responses along with the supporting information adequately addresses the items
raised in Council’s recent correspondence. Should you wish to discuss further, please feel free to contact
me on the above details.

Yours sincerely,
ADG ENGINEERS (AUST) PTY LTD


MICHAEL VAN ITALLIE
Associate Director - Civil



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