Municipal Separate Storm Sewer System (MS4) Phase II Program

What is an MS4?
The acronym MS4 stands for Municipal Separate Storm Sewer System. This system is made up of ditches, curbs, gutters, storm sewers, and similar means of collecting or conveying runoff collected from impervious surfaces. The Village of Ossining's MS4 is subject to the EPA's regulations for Phase II Small MS4s and is permitted through the New York State Department of Environmental Conservation (NYSDEC). The Village is responsible for the maintenance of the MS4 as well as ensuring that all development taking place within the Village complies with NYSDEC regulations. The MS4 does not connect with a wastewater collection system or treatment plant eventually, the stormwater is discharged directly into surface waters, which include streams, rivers, lakes, and reservoirs.

The National Pollutant Discharge Elimination System (NPDES) Stormwater Program regulates stormwater discharges from three potential sources: municipal separate storm sewer systems (MS4s), construction activities, and industrial activities.  A federal regulation, commonly known as Stormwater Phase II, requires permits for stormwater discharges from Municipal Separate Storm Sewer Systems (MS4s) in urbanized areas and for construction activities. To implement the law, the New York State Department of Environmental Conservation has issued two general permits, one for MS4s in urbanized areas and one for construction activities.

Under Phase II, operators of regulated small municipal separate storm sewer systems (MS4s) are required to develop and implement a stormwater management program.

Each MS4 municipality is also required to submit a stormwater management plan and an annual stormwater report.

Current & Past Stormwater Plans and Reports