The respective boards of county commissioners of two or more contiguous counties may merge any combination of their several inactive or activated authorities to form one activated multicounty authority. Upon a determination that the purposes of this chapter will be served by such merger, each board of county commissioners may adopt the resolution providing for such merger. Such resolution shall become effective only when a similar resolution is adopted by the other contiguous county or counties comprising the proposed authority. The boundaries of such authority shall be coextensive with the boundaries of the counties within which it is located.