(1) The boundaries of such authority shall include said city and the area within 10 miles from the territorial boundaries of said city, but in no event shall it include the whole or a part of any other city unless a resolution shall have been adopted by the governing body of such other city declaring that there is a need for such authority to exercise its powers within that city.
(2) After the creation of an authority, the subsequent existence within its territorial boundaries of more than one city shall in no way affect the territorial boundaries of such authority.