North Lanarkshire Council was at the centre of a legal case in which a group of 77 residents of the Watling Street area of Motherwell started legal proceedings with a view to securing remediation of the land on which their homes had been built.
The figure was revealed at the Court of Session in Edinburgh yesterday where a lawyer representing the residents was trying to force the council to allow its results to be made public.
The Evening Times previously revealed that the council was dropped from the action this year, but it still has a responsibility for the land under Part IIA of the Environmental Protection Act.
The houses were built between 1998 and 2001 adjacent to a former landfill site and it is also thought that the estate is near the former site of a factory which made instrument panels for fighter planes during the Second World War and produced harmful waste products.
Earlier this year, in response to a series of tests carried out by experts working on behalf of Collins Solicitors, the council instructed a firm to carry out its own tests and said it would publish the results in due course.
Des Collins, senior partner at Collins Solicitors, said: "We got tired of waiting to see these results so we put in a Freedom of Information request to the council. They gave us the results for tests carried out on land underneath the house at 31 Empire Way, but incredibly they said we could not disseminate that information in any way.
"We were in court to try and have the information made public."
At the Court of Session, Lord Doherty denied the request, however, Andrew Hajducki QC, acting for Collins, claimed in open court that the council's tests showed readings of dense non-aqueous phase liquid (DNAPL) "55 times" - or 5500% - higher than the accepted standards.
Lord Doherty said: "I don't think it is appropriate at this stage to make any order for the production of the defender's reports."
The council was not represented at the Court of Session hearing and would not comment on the test results. A council spokesman said: "North Lanarkshire Council is not a party to the action and was not represented. We will always comply with court orders."