Information response · MCU15/0005

There are also concerns with the location of the existing stormwater drainage structures
and the proposed “built to boundary” wall and its associated foundations. The
stormwater pit located about mid-way along the southern site boundary appears to be
either straddling the boundary or be very close to the boundary line.

Information Required
Provide a preliminary stormwater disposal design for the proposed development. The
design must include:
    a) Collection and treatment of the runoff from the building and hardstand areas
    b) A treatment area that is in generally accordance with the higher order approval
       and modified, where necessary, to cater for the proposed development.
    c) The connection points to the existing common property drainage system
    d) A system that demonstrates consistency with the requirements of the approved
       Stormwater Management Plan and as detailed on Approved Drawing BM080320
       B10 by VDM Consulting, dated 17 November 2011.

Response:
The development layout has been updated with a conceptual stormwater quality
management system to reflect the requested information above.
   a) Please refer to the attached annotated document for information on the size,
      position, and levels of the proposed bioretention basin.
   b) The treatment area of the proposed basin is approx. 9m2 which is in accordance
      with the approved stormwater Management Plan by VDM Consulting for the
      higher order development. It is noted that the approved VDM stormwater quality
      management plan had achieved superseded treatment targets of 90% reduction
      in concentration of TSS, 70% reduction in concentration of TP, and 50%
      reduction in concentration of TN. Current legislation of stormwater pollutant
      removal targets requires load-based (kg/yr) reductions of 80% TSS, 60% TP and
      45% TN. In appendix B of the Stormwater Management plan for the higher order
      development, the load based reductions over the whole development are listed
      as 98.5% TSS, 78.5%TP, and 50% TN. Therefore, the greater development is
      performing above the current legislated requirements in terms of quality of
      frequent storm runoff. The proposed bioretention basin of 9m2 (in accordance
      with the VDM report) treats approx. 85% of the Lot 11 development site.
   c) The bulk of the development is connected to the higher order development
      drainage system via the outflow from the proposed bioretention basin. The small
      portion of site runoff not flowing to the bioretention basin will be received via the
      grated inlet of the field inlet pit in the eastern site corner.
   d) The proposed bioretention system is compliant in area with the approved VDM
      drawing BM080320- B10, the conditions (in the change to existing approval (ref:
      142009.42.2) dated 10-01-2011, and the Approved Stormwater Quality
      Management Plan by VDM Consulting (Ref: M3048). Please refer to the
      attached drawing for details.




1259-01 KHA Development Managers                                                          2
PB/cl