The findings were revealed in the final results of an environmental study done for Cheltenham Borough Council by the Environment Agency (EA).
According to the report overall soil contamination was found to be low, but there were traces of asbestos and greater quantities of methane and carbon dioxide than recommended in the site. It was turned into public open space in the 1960s after it was filled, at a time when there was little regulation of domestic rubbish tipping.
The council said further work would be carried out in the Spring to check the boundary of the underground waste and that any problems are confined to the site area.
EA area environment manager Stuart Baker said: “There is nationwide legacy of old landfill sites that were completed many years ago before the tight controls that are in force today.
“This project is an example of how the EA and the local authorities can work together to resolve problems of pollution in our environment.”