THE WHITESIDE COUNTY LANDFILL IS A MUNICIPAL SOLID WASTE LANDFILL THAT IS ADJACENT TO AN CONTIGUOUS WITH ANOTHER PIECE OF PROPERTY KNOWN AS THE PRAIRIE HILL RECYCLING AND DISPOSAL FACILITY (RDF). BOTH THE WHITESIDE COUNTY LANDFILL AND PRAIRIE HILL RDF ARE OWNED BY THE COUNTY OF WHITESIDE. PRAIRIE HILL RDF IS OPERATED AS A WASTE DISPOSAL FACILITY BY WASTE MANAGEMENT OF ILLINOIS. THE WHITESIDE COUNTY LANDFILL HAS A DESIGN CAPACITY OF 1.42 MILLION MEGAGRAMS, WHILE PRAIRIE HILL RDF HAS A MAXIMUM DESIGN CAPACITY OF 19.268 MILLION MEGAGRAMS AND 21.638 MILLION CUBIC METERS. TOGETHER, THE TOW HAVE A DESIGN CAPA- CITY IN EXCESS OF 2.5 MILLION MEGAGRAMS AND 2.5 MILLION CUBIC METERS. IN SEPTEMBER OF 1993, THE WHITESIDE COUNTY LANDFILL CLOSED THE OPENING OF PRAIRIE HILL RDF, WHICH BEGAN ACCEPTING MUNI- CIPAL SOLID WASTE IN AUGUST 1006, WAS A LATERAL EXPANSION OF THE WHITESIDE COUNTY LANDFILL THAT RESULTED IN AN INCREASE IN THE DESIGN CAPACITY OF THE WHITESIDE COUNTY LANDFILL, AND HENCE WAS A MODIFICATION OF THE WHITESIDE COUNTY LANDFILL WITHIN THE MEANING OF 40 C.F.R. 60.2. THEREFORE, PRAIRIE HILL RDF AND THE WHITESIDE COUNTY LANDFILL CONSTITUTE A SINGLE MSW LANDFILL WITHIN THE MEANING OF 40 C.F.R. 60.751 IN 1997, PRAIRIE HILL RDF HAD AN NMOC EMISSION RATE OF 35.22 MEGAGRAMS PER YEAR IN 1997. WHITESIDE COUNTY, THE OWNER OF THE