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Municipal Separate Storm Sewer System 

What is MS4?


M = Municipal

S4 = Separate Storm Sewer System


An MS4 is a surface water drainage system or system of drainage conveyances (ditches, pipes, culverts, etc.) that is:


  •  owned by a state, city, town, village, or other public entity that discharges to waters of the U.S.,

  • designed or used to collect or convey stormwater (e.g., storm drains, pipes, ditches),

  • not a combined sewer, and

  • not part of a sewage treatment plant, or publicly owned treatment works (POTW). 


To prevent harmful pollutants from being washed or dumped into specific types of MS4s, operators might be required to obtain NPDES permits and develop stormwater management programs (SWMPs).



Stormwater runoff is water from rainfall or snowmelt that does not soak directly into the ground. As this water washes over rooftops, parking lots, buildings, and other paved areas, it often carries harmful pollutants such as bacteria, chemicals, sediments, petroleum products, trash, pet wastes and heavy metals and deposits them into nearby waterways. Stormwater runoff is one of the leading causes of water pollution in New Hampshire. However, there are many ways that we can all do our part to help prevent water pollution in local waterways. The following resources offer information and tips for everyday practices that will help keep our water clean. These messages help Raymond meet educational and outreach requirements of the USEPA NPDES stormwater permit.


Information on Fertilizer and lawn care: Some lawn care practices create local water quality problems. Excess nutrients (including nitrogen and phosphorus found in fertilizers) that run off our properties into nearby waterbodies can trigger harmful algal blooms. It's possible to have a healthy, green lawn that is both attractive and safer for the environment. Visit the link below for simple and easy home lawn care tips, that can lead to Green Grass & Clear Water.


Pet waste: We love our dogs. But dog waste carries harmful microorganisms that can make our waters unsafe for swimming and drinking. Picking up our dog’s waste and throwing it out properly is a small effort that can make a bid difference in keeping our waters clean.


Yard waste: Leaves, grass clippings, and other yard waste contain organic nutrients such as phosphorus and nitrogen. When yard waste is dumped near waterways, these nutrients disrupt the water body ecology, stimulating excess algae growth and depleting the water of oxygen. Visit: for more information.


Septic systems information and maintenance: Help protect New Hampshire’s drinking water resources and ensure your continued enjoyment of all the benefits our surface waters offer, such as swimming, fishing, boating, eating seafood and enjoying a walk beside clear waters, by taking care of your system.

In September of 2012, the Town of Raymond was notified by the U.S. Environmnental Protection Agency that it was "considered a regulated small Municipal Separate Storm Sewer System (MS4) in accordance with 40 CFR § 122.32(a)(l). Being a regulated small MS4 makes your municipality subject to the permitting requirements of Phase II storm water program which was promulgated in 1999." 


Click Here to Read Official Notice

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