Section 22. The department shall, after hearing, determine the amount which shall be assessed upon each city or town which is included in a district established under the provisions of section twenty-one to meet the costs, including capital costs, of operating such district. The amount so assessed shall be based upon the amount and category of solid waste originating within such city or town, or the part thereof included in such district, which is disposed of at a facility established under the provisions of this chapter in proportion to the total amount of solid waste originating within such district which is so disposed.

Cities or towns or parts thereof designated as new members of such a solid waste disposal district subsequent to the establishment of such a district will not be assessed costs under this section until such disposal service is actually rendered to that member. Assessments under this section will include a fair and equitable share of capital costs incurred by the district provided such costs can currently be allocated to such member under accepted cost accounting practices. The proportion in which each participating city and town shall annually pay money into the treasury of the commonwealth to meet expenses incurred under sections eighteen through twenty-four, inclusive, and any deficiency in the amounts previously paid in shall reflect appropriate adjustments which take into account fees paid by users other than cities and towns.