The Massachusetts MS4 Phase II permit is a regulatory requirement under the federal Clean Water Act for municipalities with municipal separate storm sewer systems (MS4s) in urbanized areas. MS4s are networks of stormwater infrastructure that collect and convey stormwater runoff from streets, parking lots, and other impervious surfaces to nearby water bodies.

The MS4 Phase II permit applies to smaller MS4s in Massachusetts, which generally serve populations under 100,000. It aims to address stormwater pollution and protect water quality by implementing a comprehensive stormwater management program. The program involves six key components called Minimum Control Measures (MCM).

Six Minimum Control Measures (MCM)

• Public Education and Outreach: The permit requires municipalities to educate residents, businesses, and community members about the impacts of stormwater pollution on water quality. Public outreach efforts aim to promote behaviors and practices that reduce stormwater pollution.
• Public Participation/Involvement: This measure focuses on engaging the public in stormwater management efforts. Municipalities encourage public participation by seeking input on stormwater management plans, organizing community meetings or workshops, and involving citizens in volunteer programs like storm drain stenciling or stream cleanups.
• Illicit Discharge Detection and Elimination (IDDE): The permit mandates municipalities to identify and eliminate illicit discharges into the storm sewer system. Illicit discharges are any unauthorized releases of pollutants or non-stormwater substances into the stormwater infrastructure.
• Construction Site Runoff Control: The permit sets requirements for managing stormwater runoff from construction sites to prevent sediment and other pollutants from entering the storm sewer system during construction activities.
• Post-Construction Stormwater Management: Municipalities are required to regulate stormwater from new developments and redevelopment projects to minimize its impact on water quality. This involves implementing specific measures to manage runoff from these areas.
• Pollution Prevention and Good Housekeeping: The permit necessitates municipalities to adopt pollution prevention practices and good housekeeping measures for municipal operations and facilities. These measures aim to reduce the potential for pollutants to enter the stormwater system from municipal activities.