Wingecarribee Shire Council's deputy general manager corporate, strategy and development services Mark Pepping said operators often targeted areas within easy access of major highways.

"We've had a number of incidents reported recently including properties at Buxton, Bullio, Exeter and Wingello," he said.

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Mr Pepping said many cases stemmed from residents innocently responding to adverts of 'clean fill' only to learn that the soil dumped on their properties was far from pristine.

"The first truckload may appear clean, but the following loads inevitably contain industrial or construction waste contaminated with asbestos and other hazardous materials."

The fill offered is suspected to originate from major construction sites in western Sydney.

"The problem is that once the fill is offloaded the trucks often vanish without a trace," Mr Pepping said.

"Tracking down the vehicles and successfully prosecuting them once they've absconded can be extremely difficult.

"To make matters worse some of these operators often have dubious connections and stories of stand-over tactics are not uncommon."

Mr Pepping said that if the fill was dumped and found to be contaminated the property owner could be responsible for the clean-up costs.

"Remediating a contaminated property is an extremely expensive undertaking with costs often reaching six figures."

Council said the warning specifically targeted illegal or criminal operators.

"We're not talking about your legitimate landscape suppliers," Mr Pepping clarified.

"We're after those shady operators advertising 'Clean Free Fill' on placards or via online marketplaces.

"We encourage all residents, especially those located near the Hume Highway, to remain vigilant and report any suspicious large multiple truck movements off the motorway.

"Our final advice is that if the offer of cheap or free fill sounds too good to be true - then it most likely is."

To dob in a dirt bag, visit www.wsc.nsw.gov.au/stop-the-trucks or phone 4868 0888.