The breaches by Consolidated Mining and Civil Pty Ltd (CMC) and Consolidated Broken Hill Holdings Pty Ltd (CBHH) involved separate pollution incidents around Broken Hill sites in 2017 and 2018.

The incidents related to the transport and deposit of lead-laden material.

The NSW Environment Protection Agency alleged CMC broke rules around land pollution and waste transportation after sourcing crushed rock material and moving it to a site 40 kilometres south of Broken Hill.

CBHH, meanwhile, allegedly transported sand waste residues and crushed rock material to a site in Broken Hill without permission.

The EPA said these materials contained elevated levels of lead. Both breaches were not deliberate, it said in a statement.

However the two companies will be obliged to pay the clean-up bill, which is estimated to cost more than $1.2 million, and also pay a combined $200,000 to a local greening project.

"The breaches occurred, in part, due to an error in lab test results and our investigation has revealed that a fault in a machine measuring lead under-reported the levels," the EPA's Carmen Dwyer said on Tuesday.

"This Enforceable Undertaking means CMC will clean up and remediate the area where the material was delivered, and CBHH will remove and correctly dispose of the sand and waste soil residues."

Australian Associated Press