At or prior to the time the principal of and interest on any revenue bonds issued hereunder to provide a particular pollution control facility have been fully paid, the county may execute such deeds and conveyances as are necessary and required to convey its right, title and interest in such pollution control facilities to any person, provided that if such conveyance is made prior to when the revenue bonds are fully paid, the county has determined that adequate provision has been made for the payment of principal and interest on the bonds as they become due.