(a) On or before July 1, 1991, each county or regional solid waste authority shall prepare and complete a commercial solid waste facilities siting plan for the county or counties within its jurisdiction: Provided, That the Solid Waste Management Board may authorize any reasonable extension of up to one year for the completion of the said siting plan by any county or regional solid waste authority. The siting plan shall identify zones within each county where siting of the following facilities is authorized or prohibited:
(1) Commercial solid waste facilities which may accept an aggregate of more than ten thousand tons of solid waste per month.