How do companies in Massachusetts know which regulations apply to their wastewater sewer discharge? It's interesting how much separation there is between a local authority, such as the Massachusetts Water Resource Authority, and the state authority, the MassDEP. Unfortunately the lack of outreach by either entity typically results in something being missed with respect to compliance.
In fact, no matter which sewer authority a facility in Massachusetts discharges to, wastewater treatment system plans and descriptions must be submitted to the MassDEP along with a staffing plan. Also, facilities are required to have an Operations & Maintenance Manual specific to their system. And depending on the volume discharged, you may need a MassDEP permit as well.
On the other hand, the MWRA (and most local authorities) are most concerned about the characteristics of the wastewater being discharged. They care only that it meets compliance with the sewer use ordinance, local limits, and/or specific permit limits. That is because they have a biological treatment system to protect and their own discharge limits to meet. In most instances you will be required to apply for a discharge permit. However, some of the smaller communities and sewer authorities may not require a permit if your discharge volume is low or you have no chemicals of concern in use.
So my best advice is to do your due diligence before starting up or relocating. Companies need to look into their regulatory obligations prior to moving and understand just what is required. And those already in operation, to be on the safe side, check to make sure that you have made the proper submittals to the MassDEP and/or local sewer authority. (A final word of caution - don't assume that the contractor that installed your treatment system took care of this for you.)