Did you know that the sewer needs to ‘breathe’? The place that quietly deals with all those little pressies we deliver via a quick flush of the toilet need a little fresh air to make sure they are processed effectively and without too much stench.
This little nugget of information came to the fore following the October 26 Tweed Shire Council (TSC) meeting after residents near the intersection of McAllisters Road and Buenavista Ave and surrounding areas in Bilambil Heights sent a petition into TSC ‘to stop all future works from construction’ and for ‘designers to go back to the drawing board to investigate and find alternative locations that is not out the front of someone’s home and other homes where residents are affected by stink pipe’.
According to a spokesperson from TSC there are ‘about 225 vents across the Tweed’s gravity sewer network and another 12 ground-mounted vents’ and they are ‘required under the Plumbing Code of Australia (AS 3500) and in keeping with standards set out by the Water Services Association of Australia. These vents are in addition to the smaller odour vents commonly found on all houses as part of sewerage services to the home’.
Mayor Chris Cherry was quick to explain that ‘when we are providing wastewater services, our sewage services, these kinds of vents where the system can take in fresh air and make sure that what’s transported in the pipes doesn’t become anaerobic is really important. When it doesn’t have enough oxygen then it actually becomes a lot stinkier.
‘It is important to have these kinds of vents everywhere and as the we heard in community access earlier today, every house does have a small vent for exactly the same purpose. There’s only one time when they will produce odours and that is if a system fails, if something goes wrong. Normally they’re taking in and that’s their purpose.’
A spokesperson for TSC confirmed the purpose of the vents telling The Echo that the vents, ‘allow the sewerage network to “breathe” by allowing air to leave the system as well as for air to be sucked into the system. One of the main purposes of these vents is to avoid odour issues, not create them. They also stop the water traps being sucked out in the house such as those in toilets and sinks.’
The Tweed also has 214 sewer pump stations which all have vent poles, the majority located in residential areas.
‘This is a normal part of living in an urban environment that we have these vents,’ said Cr Cherry.
‘They don’t create toxic fumes. The worst that they can give off is sulphuric kind of a thing, but that is then dissipated into the atmosphere. So it’s not going to create a health risk for our residents.’
‘Odour complaints from the sewer network in the Tweed Shire are extremely low and well below industry trends for local water utilities in NSW. Council averages less than one odour complaint per year related to vents,’ the spokesperson explained.
‘Where there is no significant or ongoing impact to the residents from construction of underground sewer networks within public land, Council does not generally undertake formal community consultation. We typically provide residents with notification 1–2 weeks in advance of construction where it may have immediate or temporary impacts.’
After being alerted to residents’ concerns, Council’s Engineering team conducted a review of the design of the 10m vent stack and its placement. Their findings are as follows:
- The manhole selected (located at the corner of McAllister Road and Buenavista Drive) for the 10-metre-high vent is deemed the most appropriate option. Other options increase the risk of sewer overflows or have the potential to impact the operation of residences’ internal plumbing.
- Although a ground-mounted vent is possible, it may pose a higher risk of ongoing odour problems. Such a vent can also have a visual impact on the area.
- The use of the type 2 standard receiving manhole design is recommended. This design discharges into the gravity with a ‘Y’ just downstream of the manhole, creating negative pressure within the manhole, which reduces the occurrence of air discharge from the vent.
- The possible locations for the vent are limited and are constrained due to existing infrastructure and the topography of the area. The review identified it may be possible to consider moving the vent a few meters upslope from the existing manhole while maintaining a negative gradient, pending resident preferences and the location of other services such as power, water, telecommunications, stormwater, etc. However, it is not possible for a significant change to the location. Staff will work with residents to reduce any perceived visual impact as much as possible.
‘Since concerns were first raised with Council, our Construction Engineer has met with residents and a review of the location of the vent undertaken. Unfortunately, for the reasons outlined above, the vent is not able to be moved by much more than a few metres,’ the spokesperson told The Echo.
More details about sewer ventilation, including information about the 10-metre-high vents, can be found on our website at tweed.nsw.gov.au/sewer-ventilation.