For the purposes of this Article “regional sewage disposal? system” is defined as a public sewage disposal system of a municipality, county, sanitary district, or other political subdivision of the State, or combination thereof, which provides, is intended to provide, or is capable of providing adequate collection, treatment, purification and disposal of sewage to a substantial portion of the population within a county, or a region composed of all or parts of two or more counties, or to a metropolitan area in two or more counties. “Comprehensive planning” is defined as that planning which is a prerequisite for qualifying for receipt of federal and/or State grant funds for preparation of plans and specifications and for actual construction of regional sewage disposal systems. (1971, c. 870, s. 1; 1975, c. 251, s. 1.)