Work to remove soil in a field off Forest Road, Guernsey, that was contaminated by a firefighting chemical will start in the next few months.
Public Services says traces of Perfluorooctane sulfonic acid (PFOS) were found in ground water at the site.
Officials say they want the chemical gone to protect water supplies.
The contamination dates to 1999, when a cargo plane carrying newspapers crashed on approach to Guernsey airport. Two pilots died.