The department shall determine the eligible costs of each municipal solid waste landfill completed between fiscal year 1985 and fiscal year 1995 in accordance with the records on file at the department pertaining to each such closure and its eligible costs and for the closure of the waste-to-energy incinerators operated by the Lamprey Regional Solid Waste Co-operative and the city of Portsmouth, and eligible municipal incinerators which ceased operating prior to July 1, 1998. The department shall assume 20 percent of such eligible costs and the interest cost related to that 20 percent on bonds issued on such projects beginning on July 1, 1995 for landfills and July 1, 1998 for incinerators. The department shall determine the amount due for such eligible costs prior to July 1, 1995 for landfills and July 1, 1998 for incinerators and, with prior approval of the joint legislative fiscal committee and the governor and council, reimburse each municipality subject to the funds as appropriated by the legislature for this purpose.