Pollution Traps
The City of Sydney owns and operates many stormwater pollution control devices, also known as gross pollutant traps (GPT), stormwater quality improvement devices (SQID) and trapped gully pits.
Indicator |
2003/04 |
2004/05 |
2005/06 |
2006/07 |
Trend |
Rubbish from Council stormwater pollution traps (t) |
1,011 |
1,366 |
1,249 |
1,290 |
~ |
City of Sydney gross pollutant traps
Figures may include water removed in the process of cleaning
Gross pollutant traps treat around 5% of our Local Government Area (LGA). The numerous trapped gully pits treat a far greater proportion of the catchment.
In 2004, the City together with Sydney Water, engaged the Manly Hydraulics Laboratory (MHL) to quantify the amount of sediment and larger pollution entering the stormwater system. The results are summarised in the tables below:
Materials |
Pits (method 1) |
Enviropods (method 2) |
|---|---|---|
Course sediment |
36.8% |
46.6% |
Organics |
46.3% |
37.1% |
Litter |
17.0% |
16.4% |
Composition of materials from stormwater pollution traps
Source: Manly Hydraulics Laboratory
The study also conducted qualitative analysis of stormwater sediments which is summarised below:
Course Sediment Quality |
Minimum |
Maximum |
|---|---|---|
Grain size (microns) |
350 |
2,800 |
Copper (mg/kg) |
39 |
628 |
Lead (mg/kg) |
91 |
12,500 |
Zinc (mg/kg) |
292 |
10,200 |
Nitrite and Nitrate (mg/kg) |
1 |
40 |
Total Nitrogen (mg/kg) |
625 |
8,790 |
Total Phosphorus (mg/kg) |
410 |
2,120 |
Organic matter (%) |
27 |
Mean sediment quality from stormwater pollution traps
Source: Manly Hydraulics Laboratory
The study concluded that the City's trapped gully pits are very efficient at retaining gross solids and sediment pollution, always greater than 70% efficiency.
It is also estimated the City's street cleansing program removes between 1 and 12 kilograms per hectare per day (kg/Ha/day) of material that could otherwise enter the stormwater system.
The executive summary can be downloaded here.
NSW Maritime Authority
Maintenance, cleaning and enforcement of water pollution offences below the mean high tide mark are the jurisdiction of the NSW Maritime Authority.
The authority also maintains litter booms at Blackwattle Bay, Rozelle Bay and Rushcutters Bay. The waste is mostly large organic matter and litter and probably only represents a small proportion total pollution.
Solid waste removed from Blackwattle Bay and Rozelle Bay
Source: NSW Maritime Authority
Downloads
- City Sediments Executive Summary | PDF 3.7Mb
