(4) The real property contains a hazardous substance, hazardous waste, or underground storage tank that would require cleanup or other removal under any federal, State, or local law, ordinance, or regulation, only if the tax purchaser purchased the property without actual knowledge of the hazardous substance, hazardous waste, or underground storage tank. This paragraph (4) applies only if the owner of the certificate of purchase has made application for a sale in error at any time before the issuance of a tax deed. If the court declares a sale in error under this paragraph (4), the court may order the holder of the certificate of purchase to assign the certificate to the county collector if requested by the county collector. The county collector may, upon request of the county, as trustee, or upon request of a taxing district having an interest in the taxes sold, further assign any certificate of purchase received pursuant to this paragraph (4) to the county acting as trustee for taxing districts pursuant to Section 21-90 of this Code or to the taxing district having an interest in the taxes sold.
Whenever a court declares a sale in error under this subsection (b), the court shall promptly notify the county collector in writing. Every such declaration pursuant to any provision of this subsection (b) shall be made within the proceeding in which the tax sale was authorized.