The NSW Environment Protection Authority (EPA) issued Maas with a clean up notice on Friday after its inspectors discovered white asbestos at the residential estate.

The EPA's report said on February 19 it became aware that Maas trucks were taking building waste, possibly containing asbestos, from Millers Point in Sydney and dumping it at Southlakes.

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Six days later, its inspectors witnessed grey coloured waste material being dumped onto the residential development.

During an inspection on March 2 by EPA officers, where Dubbo Regional Council staff attended, 28 stockpiles of demolition waste were discovered at the site.

"Which contained foreign materials comprising brick, concrete, render, plastic, rubber, PVC pipe, glass, tiles and terracotta pipe," the EPA's report said.

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One of these stockpiles was located alongside a water channel that runs through the estate.

Debris from the site tested positive as white asbestos, while more was taken for analysis.

"EPA officers saw suspected asbestos pipe and fragments of suspected asbestos containing materials within a number of pieces of concrete," the EPA said.

When contacted by the Daily Liberal, Maas Group managing director Wes Mass said the EPA's accusations were incorrect and residents were safe.

"This is a false accusation, there were no truckloads of fill from Sydney," he said.

"We can assure residents in the estate that the estate is completely clear of any contaminants.

"This has been verified by an independent EPA accredited auditor."

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Mr Maas said clean up works had not been conducted prior to the independent auditor's report.

"The site is completely clear, there is no work to be done," he said.

Mr Maas said he was "very disappointed" in the situation and had passed on the auditor's report to the EPA.

"They've responded verbally, but they've got their processes to follow," he said.

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Meanwhile the EPA's clean up notice has ordered Mass to cease dumping waste materials and not to remove any materials from the site until further testing could be conducted.

An EPA spokesman was unable to provide any further information as the matter was still under investigation.

Maas were ordered to pay $563 for the issue of the clean up notice.