The High Court is expected to rule on claims for compensation for workers at the Phurnacite factory in the Cynon Valley - once dubbed 'the dirtiest in Europe'.
The claimants allege that working at the Phurnacite plant in Abercwmboi caused them to suffer lung, skin and bladder cancer, as well as respiratory disease.
One hundred and eighty three men have lodged claims with the court. The judgement is expected to rule whether or not their illnesses were caused by working at the plant.
Coal was turned into smokeless fuel at the Phurnacite plant in Abercwmboi up until the end of the 1980s. The plant produced briquettes from the waste steam coal that was too small to sell. The waste was crushed, dried and mixed with pitch and subjected to a heating process to remove most of the smoke content. But since the factory closed, those who worked there claim they've contracted various cancers and respiratory diseases.
In the late 1980s, a decision was taken to close operations at the Phurnacite plant. The site remained contaminated until a £12.5m land regeneration project was carried out to reclaim the land in 2005.
In total, more than 100,000 tons of contaminated waste were removed from the site in one of the biggest reclamation schemes Wales has seen.