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EPA Updates its NPDES Small MS4 Draft Permits


The United States Environmental Protection Agency, through its Region 1 office has issued an update to its Draft Small MS4 Permits in Massachusetts and New Hampshire. The single draft permits for all Massachusetts watersheds are expected to be issued this Spring. 

The MS4 permits are issued under the EPA's National Pollution Discharge Elimination System which is authorized under the Clean Water Act. The MS4 programs designate reporting requirements and encourage municipalities to implement stormwater treatment and management practices. The goals of the permit program are intended to reduced the pollutant loadings into our nation's waterways.

The MS4 programs apply to communities that fit the EPA's definition of an urbanized area. An urbranized area is defined as "a densely settled core of census tracts and/or census blocks that have population of at least 50,000, along with adjacent territory containing non-residential urban land uses as well as territory with low population density included to link outlying densely settled territory with the densely settled core. It is a calculation used by the Bureau of the Census to determine the geographic boundaries of the most heavily developed and dense urban areas." As you will see on the graphic below, MS4 areas can cover part or the whole of a municipality, depending on its population density. 

MA PermitType resized 600

To learn more about Norfolk's stormwater management and municipal engineering services please see the respective pages or contact John B. McAllister at (508) 747-7900 extension 117.  

The incremental evolution of stormwater management and its consequences


For several years, the stormwater field went through different changes that progressively reshaped the way to manage stormwater. Techniques are innovative and scientific understanding is better. And this new trend will continue because the US Environmental Protection Agency (EPA) stormwater rulemaking that is expected to be released this fall is going to bring new changes to stormwater management. The main change could be the attempt to control stormwater at the source, instead of capturing, conveying and storing it.


There have always been many controversies about numeric limits. In 1987 the reauthorization of the Clean Water Act was held and there were many disagreements about EPA’s stormwater permitting program. The EPA wanted a larger use of numeric effluent limits in NPDES permits for Municipal Separate Storm Sewer Systems (MS4s). However, including numeric standards in stormwater permit is a true challenge that the Congress had difficulties dealing with. Congress finally required that MS4s permit holders reduce the discharge of pollutants to the ‘maximum extent practicable’ (MEP). This is a Best Management practice (BMP).

The issue of numeric effluent limits for MS4 permit holder started to become really controversial, especially when the EPA released a memorandum in November 2010 about the Total Maximum Daily Load (TMDL) program.   In this memorandum, the EPA completely changed course stating that permit holders now have to include numeric effluent limitations as part of discharge permits for MS4s, while the EPA was taking the opposite view 8 years ago.  It changed its mind because the stormwater program permit has matured and it realized that ‘the numeric effluent limitations create objective and accountable means for controlling stormwater discharges’.


There are new efficient techniques to manage stormwater by protecting watershed and addressing certain pollutants. These efficient methods are green infrastructure approaches: bioretention, permeable pavers and green roofs. Communities mostly adopt these techniques when regulatory requirements encourage them to do so. For example, communities with combined sewers often use green infrastructures to reduce Combined Sewer Overflows (CSOs) because this technique has many advantages in terms of aesthetics and quality of life. Green infrastructure approaches are clearly preferred by communities and regulators as the traditional approaches to improve water quality.

However, these techniques face significant barriers to implementation because of:

  • The relative infancy of green infrastructure technology, and
  • The corresponding lack of robust information regarding performance and implementation time frames


A recent legal decision in Los Angeles raised questions about liability for pollutants in runoff. Entities responsible for collecting and conveying stormwater could be hesitant about cooperating regionally if they have concerns about liability for pollutants in runoff. In the Los Angeles case, the Los Angeles Flood Control District was accused of water quality violations because the stormwater that discharges into the Los Angeles and San Gabriel rivers contained pollutants.   After the lawsuit, the decision came up: the Los Angeles County discharged pollutants from its MS4 to the two rivers in violation of its NPDES permit.

This decision could have really significant consequences on the efforts to manage stormwater on a watershed basis. Because of such actions, holders of MS4 permits could limit their liability on purpose rather than seeking to cooperate in addressing water quality issues.  It could also have an effect on MS4 permit holders interacting with neighboring permit holders as there may be a shared liability aspect to consider.


If you have any question about stormwater management, please contact John McAllister at or at (508) 747 - 7900 x 117.


Information in this article taken from Sept 2011, article by Jay Landers published in

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