RFI engineering - 20230504 RFI response

            b. demonstrate the lid type of proposed stormwater structure 1/A and how the structure
            will be constructed to avoid trip hazards in the road reserve; and

            The pit within the road reserve has been updated to a closed manhole lid to minimise
            potential trip hazards.

            c. demonstrate that the existing services along the Myall Street frontage will not be
            impacted by proposed stormwater lines 2/A – 1/A and 1/A – EX/A (including vertical
            clearances).

            Sewer main depths from Unity Water and indicative water service levels have been added
            to the stormwater longsections to demonstrate clearance. The sewer main invert is located
            at a level of between 110.35m and 110.74m with approximate I.L. at the crossing point
            110.52m. The lowest invert for the proposed drainage line is 112.5m therefore the required
            cover over sewer is achieved.

            Water main depth has been assumed and may vary between 600mm and 1.5m along the
            frontage in accordance with the SEQ Water and Unity Water standards. The actual depth
            will require potholing by the contractor to confirm final levels prior to any future operational
            works commencing. An annotation has been added to the stormwater long sections noting
            that the contractor will be required to adjust the water services in accordance with Unity
            Water requirements levels to achieve the required cover should there be a service conflict
            within the road reserve with the proposed stormwater line.

            Issue: Stormwater Quality
            7. Provide updated plans, SWMP and MUSIC model which only applies nutrient removal
            rates for proprietary products if they have been verified through SQIDEP.

            Proprietary products have been removed from the treatment line. Modelling has been
            revised to take into account treatment from the proposed rainwater reuse tanks, as well as
            the treatment from the bioretention area which was found to achieve the required level of
            stormwater quality pollutant reduction for the site. Please refer to the updated SWMP for
            further details.

            8. Provide survey of the downstream existing pit in Myall St in order to demonstrate that
            the bioretention sub-soil drains can freely discharge.

            The configuration of the proposed bioretention area makes use of a drop pit to which the
            subsoil drains will discharge. Subsoil drains will have an invert of approximately 114.4,
            and the outlet invert from the pit will be at nominally RL 113.6. The surface level of the
            downstream kerb inlet pit has been identified as 113.13m from LiDAR topography being
            below the level of the outlet pipe from the site. The bioretention sub-soil drains will
            therefore remain free draining under the proposed conditions as the elevation of the
            pipes above the downstream levels prevents water being able to back up to the proposed
            design levels.



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