Stormwater Management Program


This page is provided so the public can easily access Amherst's Stormwater-related plans, permits, public educational messages and other useful information about protecting our most precious natural resource.


Municipal Separate Storm Sewer System (MS4)


Local drainage systems, whether natural or constructed, are important features that generally carry stormwater runoff away from developed areas to undeveloped areas, waterbodies, and wetlands. Although these drainage systems help to manage stormwater in our built environment, they are also a primary source of untreated pollutants in receiving waters including bacteria, nutrients oil, trash, and many other pollutants. These untreated pollutants in stormwater runoff are defined by the U.S. Environmental Protection Agency (EPA) as “nonpoint source pollution”, meaning that the source of the pollution is not directly attributable to a single spatial point or polluter. Stormwater runoff from streets, parking lots, and lawns picks up and carries contaminants as it moves across the ground surface before entering into local drainage systems.

A municipal separate storm sewer system (MS4) includes the stormwater collection, conveyance, and outfall structures within a city or town. These structures include (but are not limited to) catch basins, drain manholes, culverts, stormwater basins, and swales. As with approximately sixty other municipalities in NH, the Town of Amherst MS4 is regulated under the EPA Clean Water Act (CWA) and requires a permit for discharges to the environment.


The Stormwater Phase II rule was promulgated in 1999 and was the next step after the 1987 Phase I rule in EPA’s effort to preserve, protect, and improve the nation’s water resources from polluted stormwater runoff. The Phase II program expands the Phase I program by requiring additional operators of MS4s in urbanized areas through the use of a NPDES permit, to implement programs and practices to control polluted stormwater runoff. Phase II is intended to further reduce adverse impacts to water quality and aquatic habitat by instituting the use of controls on the unregulated sources of stormwater discharges that have the greatest likelihood of causing continued environmental degradation. Under the Phase II rule all MS4s with stormwater discharges from census-designated urbanized areas are required to seek NPDES permit coverage for those stormwater discharges.

On May 1, 2003, EPA Region 1 issued its final General Permit for Stormwater Discharges from Small Municipal Separate Storm Sewer Systems (2003 Small MS4 General Permit) consistent with the Phase II rule. The 2003 Small MS4 General Permit covered “traditional” (i.e. cities and towns) and “non-traditional” (i.e. federal and state agencies) MS4 operators located in the states of Massachusetts and New Hampshire. This permit expired on May 1, 2008, but remained in effect until operators were authorized under the 2017 NH Small MS4 General Permit, which became effective on July 1, 2018.

The Stormwater Management Program (SWMP) describes and details the activities and measures that will be implemented to meet the terms and conditions of the 2017 NH Small MS4 General Permit. The SWMP document should be updated and/or modified during the permit term as activities are modified, changed, or updated to meet permit conditions. The main elements of the SWMP are (1) a public education program in order to affect public behavior causing stormwater pollution, (2) an opportunity for the public to participate and provide comments on the stormwater program, (3) a program to effectively find and eliminate illicit discharges within the MS4, (4) a 1 - 2 program to effectively control construction site stormwater discharges to the MS4, (5) a program to ensure that stormwater from development projects entering the MS4 is adequately controlled by the construction of stormwater controls, and (6) a good housekeeping program to ensure that stormwater pollution sources on municipal properties and from municipal operations are minimized. 

Stormwater Management Program 

Notice of Intent (9-28-18)

Stormwater Management Plan or SWMP

Certification (6-28-19)

Authorization to Discharge EPA Letter (5-14-19)

Stormwater Management Program Team

IPAC Determination, Department of Interior Letter (1-8-18)

Receiving Waters 

MS4 Background Presentation 

Every Drop Post Card

Get Pumped Brochure 

Green Grass & Fertilizer Flyer

MS4 Permit Memorandum (5-23-19)

IDDE Presentation

Employee Training 

Baboosic Lake System Map

MS4 Outfall Map

IDDE Plan (6-28-19)

Stormwater Management Plan (9-27-19)

Year #1 Annual Report (9-27-19)

Year #1 Annual Report Certification (9-27-19)