Section 44C. The regional refuse disposal planning board, consisting only of the regional refuse disposal planning committees which vote in favor of the establishment of a regional refuse disposal district, shall draw up a proposed agreement. The said agreement shall contain provisions describing the sharing of construction and operating costs, the number, method of selection and terms of office of the members of the regional refuse disposal district committee, the general area in which the refuse disposal facility shall be constructed, the terms by which another city or town may be admitted to the district, the method by which the agreement may be amended, the procedure for the preparation and adoption of the annual budget and any other matters, not incompatible with law, which the said board may deem advisable; provided, however, that all plans for refuse disposal facilities shall be subject to the approval of the state department of environmental protection.