In reviewing, commenting upon, and approving or disapproving integrated waste management plans and the elements thereof, the board shall take into account both of the following:
(a) The shared responsibility which exists under law between the board and local agencies for activities such as the development of markets for materials diverted from disposal facilities, public education and information, and source reduction.
(b) The importance of promoting regional cooperation among local agencies, and cooperation between local agencies and the board in achieving the objectives of this division, to the extent that cooperation will result in more cost-effective and efficient implementation of this division.