Giant mounds of asbestos dug up underneath the M4 motorway are set to be dumped in Western Sydney.

The $470 million transformation of the road into a “smart motorway” saw workers discover a significant amount of asbestos-contaminated material.

In order to continue construction, the asbestos needs to be removed. NSW Roads and Maritime Services made a decision to dump it in a nearby vacant bit of land - only 160 metres from Orchard Hills Public School.

Furious parents confronted RMS representatives at a public meeting last night, demanding it was dumped somewhere else.

"Everyone is quite distressed and annoyed," Resident Vicki Knott told 9NEWS.

"People are threatening to take their children out of the school."

Community pressure, and the prospect of political pain, saw Roads Minister Melinda Pavey reverse the decision, but she insists they still intend to dump the waste somewhere.

"We will try and find another location, I give that commitment but I also make the commitment that is safe." Minister Pavey said.

A memo from RMS to locals, shows a reluctance to send the asbestos to a waste facility.

“Although offsite disposal of the (asbestos) at a licensed waste facility is an option, the Environmental Protection Authority (EPA) prefers that efforts are made to maintain such material on road projects.” RMS said.

The Minister claims asbestos disposal is "world's best practice" with the material buried 50cm underground and covered by a geofabric layer, soil and bush.