The Scottish Environment Protection Agency (Sepa) said it was currently in talks with contractors - the Scottish Roads Partnership joint venture - carrying out the project to see if work was in line with laws designed to prevent avoidance of landfill tax.
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A spokesman said: "We have been investigating a complaint made regarding a deposit of waste, to form temporary roads at Aitkenhead Road, Uddingston, associated with the M73/ M8 upgrade works.
"We are currently in discussion with the operator and assessing whether a breach of environmental legislation has occurred."
Transport Scotland, who commissioned the work, said it believed all materials supplied complied with Sepa guidelines.
It said: "As part of the M8/M73/M74 Motorway Improvements Project, Scottish Roads Partnership has a contractual requirement to maximise the re-use of materials and prevent unnecessary production of waste. SRP is using recycled aggregate and road planings as an engineering fill."