Appendix E - Stormwater Management Plan

external areas would be difficult in practice as they drain through the site and could not practically be diverted around
treatment measures. Therefore, opportunity to treat stormwater runoff from these areas has been taken to benefit the
water quality of downstream systems. The treatment of external catchments is consistent with the strategy previously
approved by Council (Report No. B14158.W-01A dated December 2014). Refer to Section 4.4 for further details of the
modelling methodology.

As per the approval conditions, grease and oil generated from road and car parking areas, must be managed by
proprietary GPT’s before discharge to Bioretention Basins. This requirement will be identified and incorporated if
necessary during detailed design.

4.3.1     UTILISED TREATMENT SYSTEMS

A treatment train of Gross Pollutant Traps (or sediment forebays), Bioretention systems and a Water Quality Control
Pond (WQCP) is proposed for the site’s stormwater quality management strategy. The details of the treatment systems
are provided below.
    •   Proprietary Gross Pollutant Trap (GPT) Devices (Primary Treatment) – While GPT’s have not been
        modelled in MUSIC, GPT’s are proposed upstream of the Central Bioretention Basin, Northern Bioretention
        Basin and Bio-Pod D2 (these secondary treatment devices receive runoff from a significant catchment, above
        5ha, and/or large car parking areas). As discussed in Section 4.3.2 below, GPT’s will be sufficient for capturing
        oil and grease from car parking areas prior to discharge to the downstream Bioretention System.
    •   Bioretention Systems (Secondary Treatment) – These systems utilise a sandy loam soil based media to filter
        runoff. Sediment particles and suspended solids are trapped on the surface of the filter media, while
        microorganisms and vegetation planted in the filter removes dissolved nutrients (nitrogen and phosphorus)
        through biological uptake processes. Subsoil drainage provided below the filter media allows the treated runoff to
        discharge from the bioretention basin.
    •   Water Quality Control Pond (WQCP) (Tertiary Treatment) –The WQCP reduces stormwater pollutants
        associated with fine particulates such as TSS, metals, nutrients and toxicants as well as soluble contaminants.
        The water bodies/ponds will have enhanced nutrient removal by incorporating macrophyte planting areas and
        open water zones. They will ensure that adequate pollutant retention is achieved before discharging offsite to
        adjacent properties. WQCP have a permanent water storage volume.

4.3.2     PROPOSED END-OF-LINE SYSTEMS

Three end-of-line stormwater quality systems are proposed for the development and are summarised below.

    •   Northern Basin (Bioretention System) - Catchment A is to be treated by a bioretention system. The system
        has no permanent water. Refer to Drawing No. 16-001014-415 in Appendix G for system details.

    •   Central Basin (Bioretention System and WQCP) - The Central Basin will treat Catchment B and C of the
        development. The central basin is proposed to be an open water feature. The basin comprises of a bioretention
        system and WQCP. The open water body will be topped up with treated stormwater from the Southern Basin
        during rainfall events. It is proposed that the macropyhtes are to cover a minimum of 20% of the water surface.
        Due to larger catchment a proprietary Gross Pollutant Trap (GPT) will be included upstream of the Bioretention
        Basin. Refer to Drawing No. 16-001014-405 in Appendix G for system details.

        At Council’s request the WQCP has not been modelled in MUSIC, i.e. the treatment resulting from the WQCP
        has not been modelled or included in the results contributing to the overall reduction in pollutant loads. This is
        conservative, considering that the WQCP will provide treatment by reducing suspended solids through
        sedimentation and is designed to capture some nutrients.




16-001014-01B | STORMWATER MANAGEMENT PLAN                       COOROY RETIREMENT COMMUNITY, TRADING POST
(SWMP) | PALM LAKE RESORTS                                                                   ROAD, COOROY                    | 16