Mass. Gen. Laws ch. 21 § 32
A district shall present a plan for abatement of water pollution to the division within one year after its establishment or such greater or lesser period as the division may prescribe. Such plan shall include detail as to the sources of pollution within the district, the means by which and the extent to which such pollution is to be abated, a project or projects for the construction, acquisition, extension or improvement of facilities required by the plan, estimates of the capital outlay costs thereof, the amount of federal grants applicable to such costs for which the district proposes to apply, the method of apportioning among the several cities and towns and parts thereof in the district the amounts required by the district for the payment of capital outlay costs incurred by it for such capital outlays, the method of apportioning among the several cities and towns and parts of towns in the district the maintenance and operating costs incurred by it in maintaining and operating the facilities, as provided in section thirty-six, or, instead of such apportionment, the method whereby the district may provide for the payment in whole or in part of such maintenance and operating costs by establishing and collecting reasonable and equitably classified charges for the use of the services provided by the facilities, and such other information as the division shall require. After approval, a plan may be altered only with the approval of the division.
Plans submitted under this section shall make provision for securing compliance with any applicable requirements of state or federal law concerning payment by industrial users of their proportional shares of the costs of constructing, operating and maintaining treatment works and services to be made available to such users. Every district is hereby authorized to contract, as may be appropriate, with present or prospective users of its facilities concerning terms and conditions of their use, conformably with applicable provisions of law. Every district is hereby further authorized to meet its expenses through assessments of equitable and proportional user charges in the same manner as cities and towns in a district may do under the second paragraph of section thirty-six.
The division shall not approve a plan unless it finds that such plan includes a method or formula for apportioning among the several cities and towns and parts of towns in the district the amounts required by the district for payment of both capital outlay costs and maintenance and operating costs which the division deems just and equitable. Such a formula may consist in whole or in part of fixed percentages assigned to each city, town or part of a town within the district as their respective shares of the amounts required by the district or may be based in whole or in part upon any one or a combination of two or more of the following factors: (a) population; (b) equalized valuation; (c) flow and characteristics of the wastes contributed; (d) any other factor deemed appropriate for the purpose by the division.
Mass. Gen. Laws ch. 21, § 32