A TERRIBLE “rotten egg” stench coming from the WestConnex St Peters interchange construction site has neighbouring residents fearing the smell may be affecting their health.

Dozens of locals have complained to authorities that the noxious odour is causing headaches, breathing difficulties, nausea, itchy skin and insomnia.

The site, where tunnelling is under way for the New M5 section of the $16.8 billion motorway, is on the former Alexandria landfill dump.

One resident described the stench as an “overwhelming hideous methane/sulphur smell”. Another said it smelled like rotten egg.

I smelt this yesterday and today in Newtown. What are they doing @GladysB? They have no concern for anyone in the area. #NoWestCONnex https://t.co/II5wGLOOti — Elizabeth Brown (@lizibrown) March 28, 2017

Householders said that for the past two weeks they have had to keep their windows and doors closed and had to cancel backyard barbecues because the smell was unbearable.

The strongest odours are coming from near the corner of Canal Rd and the Princes Highway, close to where tunnelling began in November.

The St Peters 2044 community Facebook page has been inundated with entries calling on authorities to immediately investigate the source of the smell.

media_camera A tunnel drilling machine at the St Peters interchange construction site just prior to tunnelling starting on the New M5 section of WestConnex.

A resident told the Facebook page they had to sleep with a T-shirt over their nose to block out the smell.

People complained the odour had woken them up and that they could detect the smell as far away as Sydenham and Tempe.

A resident said he received a call from the Environment Protection Authority (EPA) which told him that nitrogen sulphide was being emitted from the site, but that emission levels were “thousands of points below where the gas is toxic”.

Today the EPA issued a “prevention notice”, requiring the toll road’s builders to take immediate action to minimise the odours going beyond the worksite and to ensure local residents are no longer impacted by odours.

When residents phoned a WestConnex community helpline, they were told that gas detection equipment had not detected any readings for dangerous gases such as hydrogen sulphide, methane, carbon monoxide or ammonia as well as volatile organic compounds.

media_camera An artist’s impression of the completed WestConnex interchange at St Peters.

In an email to residents the WestConnex community relations team said the odour was caused by the recent heavy rain.

“There is a high amount of leachate and standing water within the landfill. (Leachate refers to water that has been in contact with waste),” the email said.

It said an “odour-suppressing foam” was being applied and that an “odour suppression cannon” was constantly spraying mist over the site.

“While the odour can be very irritating, please be assured that it does not pose a risk to human health,” the email said.

“Individuals can be highly sensitive to the odour of certain gases even though their concentration in the atmosphere may be very low.”

media_camera Tunnelling work at the WestConnex St Peters interchange.

Resident Jo McAlister, who has an eight-year-old daughter, said children could not go outside to play.

“As a mother of a young daughter I have real concerns that the toxins in the area are unsafe and I believe that building such an infrastructure on the unstable, toxic landfill can’t be good for the residents surrounding the project,” Ms McAlister said.

“As residents we feel completely ignored and overwhelmed by this massive intrusive project.

“WestConnex keep telling us that their work practice is safe but the lack of transparency through the entire project to date, forces us to feel mistrustful and apprehensive.”

WestConnex Action Group spokeswoman Pauline Lockie said the smell was another example of the botched planning process that inevitably leads to things going wrong.

“As with everything to do with WestConnex, residents are suffering as a result,” Ms Lockie said.

The EPA said it issued the prevention notice to CPB Contractors after numerous calls to the EPA’s Environment Line about a “rotten egg gas” smell. EPA officers attended the site between March 23 and 28 to investigate.

At end of day impact on people's lives in case #WestCONnex is continuing traffic congestion, sick making odours and dust, cracked walls etc https://t.co/0tmgdCM9zM — Wendy Bacon (@Wendy_Bacon) March 29, 2017

The EPA requested Fire and Rescue NSW to undertake testing in the area on Tuesday night. No detectable levels of methane or hydrogen sulphide were found.

EPA regional director (metropolitan) Giselle Howard said heavy rainfall over recent weeks was the most likely trigger for the smell.

“The rain has pushed water through the landfill and the resulting liquid has then flowed into the on-site dam,” she said.

“The smell mainly occurs because the dam doesn’t have enough oxygen circulating.

“Our main community concern is to address the odour, which is very unpleasant, however the liquid is contained on site and the dam has not spilled over.”

M4 widening complete M4 widening complete

By this Friday, the contractor must ensure offensive odours do not leave the boundary of the premises and that the site is managed appropriately.

A Sydney Motorway Corporation spokesman said it and the New M5 contractor have been working with the EPA to manage the odour.

“While the odour is strong, testing by the EPA has confirmed it does not pose a risk to human health or the environment,” the spokesman said.

“We will continue to carry out regular inspections to ensure odours are managed in line with our requirements. The local community is thanked for their patience and understanding at this time.”