On-Site Sewerage Systems
What are we monitoring?
The number of licences for on-site sewage systems in the Blue Mountains.
An on-site sewage system is a mechanism for storing or treating sewage. The owner of an on-site sewage system is required by law to have a licence for its use, authorised by Blue Mountains City Council.
| On-site sewage systems | 1999-2000 | 2000-2001 | 2001-2002 | 2002-2003 | 2003-2004 | 2004-2005 | 2005-2006 | 2006-2007 |
|---|---|---|---|---|---|---|---|---|
| Aerated wastewater treatment systems | 315 | 415 | 420 | 482 | 460 | 483 | 434 | 444 |
| Septic tank and absorption trenches | 1433 | 1940 | 2200 | 2200 | 2200 | 2200 | 1333 | 1299 |
| Pump-out | 784 | 836 | 800 | 708 | 800 | 670 | 646 | 641 |
| Alternative technologies | 40 | 37 | 47 | 47 | 40 | 46 | 46 | 32 |
| Total | 2572 | 3228 | 3467 | 3437 | 3500 | 3399 | 2459 | 2416 |
What is the trend?
The number of operating on-site sewage systems increased until 2001 but has remained relatively stable until 2004/05. During the last financial year the number of on-site sewerage systems decreased significantly to reflect the number of on-site systems connecting to the sewer network.
Why is monitoring this trend important?
In towns and cities the bulk of sewage is piped through sewers to sewage treatment plants and treated off-site. On-site sewage systems store or process toilet waste at the place where it’s generated. There are a lot of on-site systems in the Blue Mountains, largely due to the difficulty of building sewers across mountainous geography for relatively small numbers of people. These systems are prone to high failure rates and to deliberate misuse. Such problems sometimes lead to human health issues. They also lead to excessive nutrients in the local environment. Most Blue Mountains soils are low in nutrients. High nutrient levels in these soils lead to the introduction of weeds and reduce water quality. Poor on-site sewage treatment is one reason why water in Blue Mountains streams are considered not fit to drink.
The amount of decommissioning is heavily influenced by provision and promotion of new sewerage networks in areas not previously serviced. By connecting to these networks, more residents are able to pipe their sewage to treatment plants. Sydney Water has been extending the sewage network in the Blue Mountains.
Some types of systems work better than others. Overall, inspections by Council staff reveal that more than 50% of on-site systems are failing to meet basic operational requirements. A large portion of these systems generate pollution. Hence, there is a strong link between the number of systems and the amount of pollution.
Source
This data comes from Blue Mountains State of Environment reports (published by Blue Mountains City Council). These reports have records of the number of on-site sewage licences issued by the Council. The data is shown in the table above.