RIPDES Stormwater Municipal Separate Storm Sewer Systems (MS4s)
In December 2003, the Rhode Island Pollutant Discharge Elimination System (RIPDES) Program issued the first General Permit for Stormwater Discharge from Small Municipal Separate Storm Sewer Systems (MS4s) and from Industrial Activity at Eligible Facilities Operated by Regulated Small MS4s. Under the General Permit MS4s are required to submit an Annual Report documenting progress made towards achieving the requirements of the program, as well as reporting on ongoing maintenance of their stormwater system. MS4s are required to make their Annual Report available to the public, and many choose to post it on their website. The permit expired in 2008, and has since been administratively continued until a new permit is issued. For updates on the status of the MS4 General Permit reissuance, go to the For Permittees/MS4 Operators Page.
Who is regulated under Phase II?
Under the Phase II Stormwater Rules adopted in 2003, 33 municipalities were regulated based on urbanized or densely populated area, 1 municipality was regulated due to the issuance of a TMDL, and 7 non-municipal/non-traditional entities were regulated based on the size of the population served. For
Municipalities:
Municipalities are automatically designated if their small MS4 is located either completely or partially within an urbanized area (UA) or densely populated area (DPA). The following twenty-five municipalities have populations greater than 10,000 persons within urbanized areas (UA) and will require permits by March 10, 2003 (not eligible for waivers).
Municipalities in UA with populations greater than 10,000 people
Require permits by March 10, 2003 (not eligible for waiver).
(C)- Located completely within "urbanized area" | (P)- Located partially within "urbanized area"
- Barrington (C)
- Bristol (C)
- Central Falls (C)
- Coventry (P)
- Cranston (C)
- Cumberland (P)
- East Greenwich (P)
- East Providence (C)
- Johnston (P)
- Lincoln (P)
- Middletown (P)
- Narragansett (C)
- Newport (C)
- North Kingstown (P)
- North Providence (P)
- Pawtucket (C)
- Portsmouth (P)
- Providence (C)
- Smithfield (C)
- South Kingstown (P)
- Tiverton (P)
- Warren (P)
- Warwick (C)
- West Warwick (C)
- Woonsocket (C)
Municipalities in UA with populations greater than 1,000 and less than 10,000 people
Require permits by March 10, 2003 unless a waiver is granted. May be eligible for 1-10K waiver in UA.
(P)- Located partially within "urbanized area"
- Burrillville (P)
- Glocester (P)
- Jamestown (P)
- North Smithfield (P)
- Scituate (P)
- Exeter (P)
MS4s with > 1K but less than 10K population
Regulated small MS4s that serve a population under 10,000 may be eligible for a waiver if all waters that received a discharge from the MS4 have been evaluated through a Total Maximum Daily Load (TMDL) or TMDL-like analysis, and, stormwater controls are not needed based on a TMDL for those waters, and future discharges from the MS4s are evaluated.
The following one (1) municipality has a population of less than 1,000 persons within an urbanized area and will require a permit by March 10, 2003 but may be eligible for a waiver.
Require permits by March 10, 2003 unless a waiver is granted. May be eligible for <1K waiver in UA.
(P)- Located partially within "urbanized area"
- West Greenwich (P)
(P)- Located partially within "urbanized area"
MS4s with < 1K population
Regulated small MS4s that serve a population of less than 1,000 may be eligible for a waiver if the MS4s are not contributing substantially to the pollutant loadings of a physically interconnected MS4, and if discharging to an impaired water body, stormwater controls are not needed based on a TMDL that addresses the pollutants of concern.
The following two (2) municipalities are located within densely populated areas and will require permits by March 10, 2003 but may be eligible for a waiver.
Require permits by March 10, 2003 unless a waiver is granted. Population > 10,000 in DPA. Density > 1,000 per square mile
(P)- Located partially within "densely populated area"
Note: South Kingstown has both UA and DPA areas
- South Kingstown (P)
- Westerly (P)
MS4s located in DPAs:
Small MS4s that meet the criteria of a densely populated area (DPA), may be eligible for a waiver if the small MS4s are not contributing substantially to the pollutant loadings of a physically interconnected MS4, and if discharging to an impaired water body, stormwater controls are not needed based on a TMDL that addresses the pollutants of concern.
The remaining six (6) municipalities will require permits by March 10, 2008 unless demonstrate effective protection of Special Resource Protection Waters (SRPWs), Outstanding National Resource Waters (ONRWs), and Impaired Waters.
Require permits by March 10, 2008 (unless demonstrate effective protection of SRPWs and Impaired Waters)
- Charlestown
- Foster
- Hopkinton
- Little Compton
- New Shoreham
- Richmond
Federal, State, Quasi-State Facilities:
Federal, State, and Quasi-State facilities serving an average daily population of equal to or greater than 1,000 persons regardless of location will require permits (not eligible for a waiver).
Department of Transportation (DOT):
Department of Transportation (DOT) MS4s in urbanized areas, densely populated areas, and areas qualifying as a divided highway (not eligible for a waiver).
Construction activities:
Construction activities that disturb one (1) or more acres of land will require a permit.
Industrial activities:
Federal, State and municipally-owned facilities (exempted under Phase I) will be required to apply for permit coverage by March 10, 2003 or submit a "no exposure" certification. The no exposure certification has been expanded to all categories of industrial activities. All industrial categories must submit a no exposure certification or apply for permit coverage by March 10, 2003.
Designated on a Case-by-Case Basis:
Operators of MS4 that are designated on a case-by-case basis either through:
- Total Maximum Daily Load (TMDL)
- Significant contributor of pollutants
- Public petition
- Physically interconnected
- Change of circumstance
- Ineffective program
The Phase II Rule automatically covers all small MS4s located in "urbanized areas" (UAs) as defined by the Bureau of the Census. As U.S. Census data changes the applicability of the program also changes. The RIPDES Program is required to reevaluate who is regulated following each census and designate any additional MS4s as the urbanized areas (UAs) and densely populated areas (DPAs) change. View the most recent map of stormwater regulated areas in RI based on census data. For more detail, view EPA's Urban Areas Map.
The 2010 census places a portion of the Town of Hopkinton in a category that will require coverage under the MS4 program. This designation becomes official when the RIPDES Regulations are amended to include the 2010 U.S. Census data and the MS4 permit is re-issued.
Note that there are other ways that the stormwater regulated area can be expanded, including Special Resources Protection Waters (SRPWs) and impaired waterbodies with approved TMDLs. These areas are not indicated on the census-based map above.
Each municipality/MS4 has designated one person to be their Stormwater Coordinator. For a list of contacts, please visit MS4 Stormwater Coordinators List.
Historical Overview of Stormwater Phase II
The National Pollutant Discharge Elimination System (NPDES) Phase I stormwater program, initiated in 1990, required operators of "medium" or "large" Municipal Separate Storm Sewer Systems (MS4s) (MS4s that serve a population of 100,000 or greater), to obtain permits and implement a stormwater management program as a means to control polluted discharges from these activities. On December 8, 1999, the NPDES Stormwater Program was expanded (Phase II) to require operators of small MS4s (MS4s serving populations of less than 100,000, located within Urbanized Areas,) to obtain permits and establish a stormwater management program that is intended to improve waterbodies by reducing the quantity of pollutants that can enter storm sewer systems during storm events.
The Phase II rule described six minimum control measures, which regulated small MS4s needed to implement. These minimum control measures were typically implemented by applying one or more Best Management Practices (BMPs) appropriate to the source, and/or necessary to address problems specific to the MS4. To assist MS4s with the development of their programs, EPA developed a National Menu of Stormwater Best Management Practices. The menu was intended to provide guidance to regulated small MS4s as to the types of practices they could use to develop and implement their stormwater management programs. The menu was intended as guidance only. More information about Phase II requirements can be found on the Requirements: Six Minimum Control Measures page.
Why Manage Municipal Stormwater Systems?
In Rhode Island there is a strong correlation between the amount of impervious area in a watershed and the waterbody within that watershed being listed as impaired by the RIDEM. Increased volume, temperature, and rate of runoff from impervious surfaces, and the concentration of pollutants in the runoff can cause changes in hydrology and impact water quality.
At greater than 10% impervious area, we begin to see:
- Water quality issues
- Impacts to biological communities
- Increased flooding
- Stream erosion
- Loss of recreational uses
- Shellfish bed closures
- Beach closures
- Reduced baseflow and recharge
Effective management of stormwater runoff offers a multitude of benefits, including protection of wetlands and aquatic ecosystems, improved quality of receiving waterbodies, conservation of water resources, protection of public health, and flood control.