Stormwater pollution control in urban runoff has been recognised as a major issue for our harbours and waterways and has led to several local Council and State Authority stormwater policies and guidelines. In 1997, the Environment Protection Authority introduced a requirement for the implementation of the principles of ecologically sustainable development (ESD) into Council operations. In 2002, the Water Sensitive Urban Design (WSUD) Program commenced with the aim ‘to enhance the ability and willingness of Council staff and Councillors to promote and implement more sustainable water management practices in their operations and in urban development projects’ in their areas.
Comprising over 1,230Ha spread across the region, Blacktown City Council has the largest area of serviced industrial land in Sydney. With ongoing large industrial development, management and improvement of runoff quality needed to be considered. Through an analysis of runoff from new and existing residential developments, Council prepared and implemented its Stormwater Quality Control Policy (PO1100).
According to the Blacktown City Council Document, each style of development produces a different range of pollutants and as a result the treatment strategies employed on each will vary depending on the size of the catchment, the style of the development and the type of pollutants generated by the activities on the site.
In recent times, Blacktown Council has not only enforced ESD for private development, but has also implemented it into its own projects. A couple of examples are:
- Blacktown Creek at Lancelot Street, Prospect and Bells Creek at Plumpton Park, Plumpton – HumegardTM Gross Pollutant Traps (GPTs) were installed to treat runoff from the large residential catchments prior to discharging into the adjacent wetlands and creeks. They were selected based on low hydraulic head loss, effective removal of gross pollutants and reasonable capital and life cycle costs.
- Blacktown Council Depot, Rooty Hill – The HumeceptorTM at Council’s depot was chosen as the only device available (short of cartridge filtration technology) that could demonstrate capture of fine sediment at the required performance target.
The implementation of WSUD in urban development is changing the way that urban runoff is managed before discharge to our waterways. WSUD is a ‘treatment train’ approach to reducing the pollutants that are readily observed.
GPTs are an essential part of the treatment train capturing gross pollutants, defined by the CRC for Catchment Hydrology as material greater than 5 mm, before it reaches the wetlands or bioretention areas. This is predominantly anthropogenic and organic litter. Some of the better gross pollutant traps, such as HumegardTM, also have the ability to capture coarse sediments, generally greater than about 100 to 150 µm diameter, through their operating processes.
There is a perception that all GPTs are the same and can be interchangeable, however, this has been proven in practice to be incorrect. Specifically, devices such as HumeceptorTM, offer a much higher level of performance in terms of total suspended solids (TSS) removal and have demonstrated performance in terms of retaining hydrocarbon based contaminants through extensive laboratory and field testing.
As a result, the HumeceptorTM is best suited to industrial sites, commercial applications, roads, hardstand areas, pavements and carparks where research has shown high hydrocarbon and fine sediment loads. It can also complement a GPT in catchments where higher TSS removal is desired. HumeceptorTM was developed to target TSS, with a focus on fines down to 20-micron particle size, hydrocarbons/oils and particulate nutrients. Generally GPTs struggle with capturing and retaining these pollutants.
The Rooty Hill Council Depot is a perfect example of a catchment that has a hardstand area unlikely to produce significant quantities of litter, but has many vehicle movements that will produce a fine sediment and hydrocarbons. The key to the HumeceptorTM is its ability to control the velocity inside the treatment zone to 0.007m/s on average to allow sediment to settle and hydrocarbons to float. These low operating velocities reduce the potential for resuspension and scour.
These are also key features of the HumegardTM device, with a design that maintains a velocity through the treatment zone of less than 0.2m/s. This low velocity ensures captured pollutants are retained and not scoured. Further, an effective GPT should have a storage capacity adequate to capture up to 12 months of litter load (approx. 1.5m3/ha/yr) to minimise maintenance costs, as the Prospect Street and Bells Creek devices did.
“Blacktown Council supports the HumeceptorTM and HumegardTM devices, as Humes is one of only a few manufacturers that has funded/facilitated extensive independent field and laboratory research to demonstrate the hydraulic and pollutant removal effectiveness and efficiency of their stormwater quality improvement devices,” said Brian Chapman, Floodplain and Drainage Engineer at Blacktown City Council.
*Copy supplied by Humes Water Solutions www.humes.com.au
