The former Willenhall Town Gasworks site, now known as the Stonegate Housing Estate, was identified as contaminated by Walsall Council back in 2007.
Earlier this year, a remediation notice was served on Jim 2 Limited, the firm the authority claims is liable for the contamination.
But the company lodged an appeal with the Planning Inspectorate, which has led to the public enquiry being held at Walsall Council House.
Campaigners hope they will finally get some answers at the end of the inquiry which is due to finish on Friday and that action will soon follow.
Willenhall North Councillor Ian Shires said: "The enquiry will hopefully see the beginning of the end of a very uncertain time for those directly affected.
"It has been a long process just to get to this point but I think there is some light at the end of the tunnel for local people now.
"However, this will not be easy. This is a really ground-breaking case and the details surrounding it are very complex."
Almost 90 homes on the site of the former gas works near Kemble Close, Oakridge Drive and Brookthorpe Drive in Willenhall were officially declared as affected following a three-year investigation, although nobody as yet has accepted responsibility.
The council has previously said Jim 2 Limited had bought, demolished, cleared and prepared the former gasworks site for residential housing and in doing so had 'caused or knowingly permitted the contamination on the site'.
The council claim the clean-up could cost around £2.5 million.
People living in Brookthorpe Drive and Oakridge Drive previously said they were worried about house prices falling and growing vegetables in their gardens after it emerged their gardens were polluted.
The homes were built in the 1970s on the site of Willenhall Town Gas Works, which shut a decade earlier. It is believed the site was not properly cleared before builders moved on site. Heavy metals, tars and a gas manufacturing by-product called Blue Billy is said to be on the land.
Liberal Democrat campaigner for Short Heath, Dan Barker, said: "It is obvious that the outcome of this inquiry will have far reaching effects on other similar situations."