Over the last six to eight months, a "foul odour" has been seeping through their homes, wrecking everything from their sleep to their busineses, dust has coated their cars and washing, and plastic and paper have been blown through their gardens.

And they believe the Bowral Waste Centre, situated just across the railway tracks on Kiama Street, is to blame.

"We can't sit outside," said Stephane Bourrigaud, who operates a vehicle repair shop behind his family home on Railway Parade.

"My clients say when they pick up their cars, the smell of s-t lingers all day.

"And the value of our house is pretty much worthless - if no one will buy here, it's really worth nothing."

He notes that most Southern Highlands residents don't know the tip exists, so have been mystified about the odour in the southern part of the town.

"They just come in and say, 'What is that smell'," he said.

Bowral Waste Centre admits there is an odour problem and blames "wet Gyprock" for the smell, following a damper than average year, although it rejects any suggestion that the smell is methane-related, saying it does not accept putrescible waste (food waste or organics), which typically can cause odour issues.

The Environmental Protection Authority (EPA) also confirmed the presence of odours from the site and said they will "shortly formalise" new regulatory requirements with the owner.

But fellow Railway Parade resident Margaret Woods has gathered 64 names to add to a letter to Wingecarribee Shire Council, sent yesterday, questioning the recent approval of an increase in waste to 75,000 tons each year.

"The DA no 11/1041.05 that was submitted by the Waste Centre on November 16, 2020 and approved in April 2021 sought, and was granted, an increase of 25,000 tonnes additional rubbish," reads the letter, which goes on to ask what community consultation was conducted in relation to the DA.

"No residents recall any such consultation. We ask the council to provide the evidence of this consultation...what form did it take, to whom.

"The recommendation to increase the amount of rubbish did not consider the potential for increased odour to the surrounding areas. Why was this not considered?"

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The letter also calls on the council to address the matter of the waste centre's proximity to the nearby water catchment area.

Ernest Dupere, director of Benedict, one of Bowral Waste Centre's owners, said an odour specialist visited the site on June 18, 2021.

"The specialist has recommended several data gathering actions (like water and gas bores) that will allow us to ascertain the exact cause and thus arrive at the most effective solution," he said.

"It should be noted there has also been reports of a sewer odour as well. The sewer odour is not caused by Bowral Waste Centre and is a separate odour issue."

Mr Dupere added that during May 2021, Bowral Waste Centre's onsite weather station recorded 213mm of rainfall.

"This heavy rainfall has possibly saturated the actual landfill, although our leachate generation rate is low," he said.

"The combination of the saturated landfill and cooler temperatures during May has slowed the time for the landfill to dry out completely and could be the main cause contributing to the reported odour complaints."

He said the centre applies clay or soil to all exposed landfill working surfaces, which is the EPA required method used at landfills to manage odours.

"Since the heavy rain Bowral Waste Centre has increased the thickness of the cover," he said.

"Bowral Waste Centre had re-capped the entire landfill in an attempt to further mitigate any odour issues and has brought in extra machinery to increase the thickness of this capping as we speak.

"Bowral Waste Centre is also working to find particular spots from within the landfill where odour seems to be more of an issue and placing extra cover material on those particular spots."

They also use fixed sprinker systems to damp suppress dust.

Regarding concerns about the large bodies of water in the tip, Mr Dupere said they had "no impact on the water table", and the largest ones contain "only stormwater produced by rainfall that has not come into contact with waste and is tested to ensure that this is the case".

"Bowral Waste Centre sincerely apologises for this inconvenience and will continue to work closely with the council and EPA to ensure that all license and consent conditions are followed," he said.

In a statement to the Southern Highland News, the EPA said they had also inspected the Bowral Waste Centre on June 3 and again on Friday, June 18.

"During the inspections EPA officers confirmed the presence of odours," said the statement.

"The EPA has discussed immediate and longer-term solutions with the operator to address the odour issue, including changes to operations at the site.

"These actions will be shortly formalised as regulatory requirements for the operator.

"The EPA has received 25 odour complaints in relation to the Bowral Waste Centre since May 11, 2021, including six on June 18.

"Residents who experience odour issues are encouraged to make a report to the EPAs 24-hour Environment Line on 131 555 with as much detail as possible. Information on how to report odours can be found on the EPA website."

But residents question the effectiveness of the methods being used to suppress dust and solid pollution.

"I have collected bucketloads of rubbish from my property," said resident Chris Hurditch.

"I've written to council and had no answer."

They also question why the site was ever approved in the first place, with the EPA's own guidelines being disregarded in relation to the centre's "proximity to residences (many residences within 100m of the landfill); businesses (including food and medical businesses within 100m); the Mittagong creek (draining into the Sydney catchment)."

The residents have called on the council to increase surveillance of the tip, and develop a "detailed, transparent plan as to mitigation steps", with close monitoring of such, and closure of the tip as a last resort.

Finally, independent local government candidates from the 'Let's Get it Right' Group have joined the fray, raising concerns they would like council to address.

"It is the role of our local council and the EPA to ensure waste facilities such as this do not have an adverse impact on the local community," said candidate Aaron Neill-Stevens.

"This facility is too close to residences and businesses.

"Residents are entitled to ask 'how did this facility, which allows people to dump asbestos, get approved to operate in such close proximity to the centre of Bowral?"

"A major concern is how rainfall and runoff are managed on this site given that runoff feeds into Mittagong Creek, and into the Wingecarribee River, which is part of the Water NSW catchment area for drinking water.

"We also need to be assured that correct measurement has been taken to stop the resulting toxins leaching through the fractured shale at the base of the quarry and into the underlying aquifers?"

In commenting about water contamination, Mr Dupere provided further detail regarding the centre's practices.

"The smallest pool is plastic lined and contains leachate which evaporates from the pond or is irrigated back on to the active tipping face, as per the licence requirements," he said.

"Additionally, we have a spare lined pool for excess leachate storage if needed but it currently has only a small amount of rainwater in it."

Wingecarribee Shire Council have been contacted for a response.