Appendix B - Amended Biome Consulting Response

    •    Southern Basin (Bioretention System) – Catchment C is to be treated by a bioretention system. 63% AEP
         peak flows will be directed from this basin into the Central WQCP for additional treatment and detention. The
         system has no permanent water. Refer to Drawing No. 16-001014-400 in Appendix G for system details.

    •    Bioretention Pod D2 – A small Bioretention system is proposed to treat the car parking area.

    •    Bioretention Pod D3 – A small Bioretention system is proposed to treat Catchment D3.

    •    Treatment System for Age Care Facility – A treatment system is proposed to treat the Age Care Facility prior
         to discharge towards the Southern Basin.

Note that runoff from Catchment D3 is conveyed to Site Discharge Location B and therefore has been included in the
overall MUSIC model. An estimated breakdown of road, roof and ground area based on Table 3.3 of WBD’s MUSIC
Modelling Guidelines (2010) has been conservatively assumed for this catchment. A Bioretention Pod sized at 0.9% of
the catchment is proposed for this catchment area when it is developed. Further details are provided in Section 4.4.5.

As per Condition 65.2, Council specify that runoff from all road and car parking areas is to be pre-treated for grease and
oil prior to discharging to the downstream Bioretention Devices. According to WBD Bioretention Technical Design
Guidelines (2014), Bioretention Devices are suitable for treating runoff from roof, ground and road areas. Table 14 of the
guidelines outlines pre-treatment measures typically proposed upstream of Bioretention Devices based on catchment
size (i.e. for catchments between 2ha and 5ha vegetated swales, coarse sediment forebays, inlet pond or GPT’s are
recommended). The condition to pre-treat all runoff from road and car parking area specifically for oil and grease prior to
discharge into Bioretention Devices is considered to be conservative given the nature of the Bioretention treatment
device. There are also many examples of urban, commercial and industrial developments that propose Bioretention
Devices without pre-treatment of oil and grease.

It is also noted that the Bioretention Device will not be a Council asset. Hence it will be the responsibility of the developer
to manage and replant the basin in the very unlikely event that extreme oil spillages damage the Bioretention Devices
vegetation.

Apart from the Northern Bioretention Basin, GPT’s are proposed upstream of all Bioretention Devices and subsequently
the proposed pond. GPT’s have the capability of trapping floating oil and grease pollutants and are considered to be an
appropriate pre-treatment to Bioretention Devices, albeit conservative where the catchment is small. Since Catchment A
(Northern Bioretention Basin) is only 2.45ha with no significant areas of car parking a sediment forebay has been sized.

The HumeGard GPT’s proposed upstream of the proposed Bioretention Devices have the capability of trapping floating
oil and grease pollutants. As demonstrated on Page 2 of the HumeGard GPT Technical Manual provided in Appendix C,
the application of a floating boom provides separation at the surface of the waters between the sediment storage
chamber and the outlet chamber. This effectively captures pollutants such as oils and greases that float to the surface.
Based on laboratory and field testing, Table 1 on Page 3 of the Technical Manual indicates 90% removal efficiency of
Hydrocarbons during emergency spill events.

4.4       MUSIC MODELLING
Water quality modelling of the proposed development has been undertaken using the Model for Urban Stormwater
Improvement Conceptualisation (MUSIC) Version 6 developed by the Cooperative Research Centre for Catchment
Hydrology (CRCCH). MUSIC enables the user to conceptualise the transfer of pollutants through a stormwater drainage
system and provides an aid in quantifying the effectiveness of the proposed stormwater quality management strategy.
MUSIC only provides quantitative modelling for Total Suspended Solids (TSS), Total Phosphorous (TP), Total Nitrogen
(TN), and Gross Pollutants (GP).

The MUSIC model was setup generally in accordance with Water by Design MUSIC Modelling Guidelines (2010). The
subsequent sections discuss the model configurations adopted for the analysis.




16-001014-01B | STORMWATER MANAGEMENT PLAN                         COOROY RETIREMENT COMMUNITY, TRADING POST
(SWMP) | PALM LAKE RESORTS                                                                     ROAD, COOROY                 | 17