25 Stormwater Facts on the 25th Anniversary of MS4

It’s been 25 years since the Environmental Protection Agency began the Phase I Municipal Separate Storm Sewer System (MS4) permit program in November of 1990.

The NPDES MS4 permit is designed to protect our rivers, lakes and streams from polluted stormwater runoff. In honor of the anniversary, we connected with SEH MS4 specialist April Ryan, PE, who shared some key facts about stormwater, stormwater pollution, permitting and MS4.

1. Stormwater is precious and powerful.

Stormwater is precipitation (rain or snowmelt) that falls to the ground then flows over land instead of percolating into the ground. In essence, it is the combination of earth’s most precious resource, water, and its most ubiquitous force, gravity. An inch of rain on an acre of land is equivalent to 27,154 gallons of water. It weighs about 113 tons. That’s powerful.

2. Stormwater affects the water you drink.

When precipitation hits the ground, some water trickles down into groundwater aquifers, while the rest flows on the surface to lakes, streams and rivers. Depending on where you live, your drinking water comes from either surface water (lakes and rivers) or a groundwater aquifer.

3. Today’s stormwater moves faster than ever.

Before urbanization, the majority of precipitation was naturally and slowly filtered by soil and grasses. As development occurred and pavements became widely used, stormwater conveyance systems (ditches, gutters, storm sewers) were constructed to quickly transport water from streets to surface waters, like lakes, rivers, wetlands and streams. The NPDES permit program controls water pollution by requiring MS4s to treat stormwater before discharging into surface waters.

4. Polluted stormwater runoff is the number one water pollutant.

As stormwater moves across developed areas, it picks up garbage, debris, sediment, chemicals, automotive fluids, fertilizers, leaves and other pollutants from parking lots, yards, streets, roofs and other hard surfaces. If untreated, these pollutants enter our waterways.

5. Stormwater pollution is classified in two ways.

Water pollution comes either from “point” or “nonpoint” sources. A point source is identifiable, such as a pipe or drain discharging a pollutant directly into a body of water. A nonpoint source is more difficult to define. It includes all the polluted stormwater within a certain geography, like a watershed, for example.

6. An MS4 battles against stormwater pollution.

MS4 refers to conveyance or system of conveyances (including roads with drainage systems, streets, catch basins, curbs, gutters, ditches, man-made channels, and storm drains) which is owned or operated by a state, city, town, county, district, association, or other public body (created by or pursuant to state law).

7. There are many stormwater pollution culprits.

Significant stormwater pollutants include:

  • Sediment
  • Oil, grease, and toxic chemicals from motor vehicles
  • Fertilizers and pesticides used on lawns, gardens, roadways, etc.
  • Viruses and bacteria from pet waste and failing septic systems
  • Litter and trash from motorists, pedestrians and businesses

8. MS4s were born out of the Clean Water Act.

MS4s are regulated by the National Pollutant Discharge Elimination System/State Disposal System (NPDES/SDS) permit program. The NPDES permit was enacted in 1972 as part of the pivotal Clean Water Act.

9. There are over 7,450 MS4s in the country.

As populations continue to grow, so will the number of MS4s.

10. Population and location determine the regulated MS4s.

Although large communities are generally associated with the MS4 program, a regulated MS4 includes smaller public entities located in urbanized areas and/or located near specific water resources.

A stormwater feature slows down fast-moving water flows while filtering debris in Oakdale, Minnesota.

11. There are two kinds of MS4s.

Phase I, issued in 1990, requires medium and large cities or certain counties with populations of 100,000 or more to obtain NPDES permit coverage for their stormwater discharges. There are approximately 750 Phase I MS4s in the United States. Phase II, issued in 1999, requires regulated small MS4s in urbanized areas, as well as small MS4s outside the urbanized areas that are designated by the permitting authority, to obtain NPDES permit coverage for their stormwater discharges. There are approximately 6,700 Phase II MS4s in the United States.

12. Permitting is different for Phase I versus Phase II MS4s.

Each regulated MS4 is required to develop and implement a stormwater management program (SWMP) to reduce the contamination of stormwater runoff and prohibit illicit discharges. Generally, Phase I MS4s are covered by individual permits and Phase II MS4s are covered by a general permit.

13. An MS4 is above and below ground.

Not always just a system of underground pipes, an MS4 can include roads with drainage systems, gutters, and ditches.

14. MS4s are often misinterpreted and misunderstood.

The term MS4 does not solely refer to municipally-owned storm sewer systems. The term has a much broader application that can include, State departments of transportation, universities, counties, townships, local sewer districts, hospitals, military bases, and even prisons.

15. An MS4 reduces stormwater pollution in six ways.

Once classified as an MS4, an entity must meet requirements outlined in six minimum control measures to minimize stormwater pollution. They are:

  1. Public education and outreach
  2. Public involvement and precipitation
  3. Illicit discharge detection and elimination
  4. Construction site stormwater runoff control
  5. Post-construction stormwater management
  6. Pollution prevention/good housekeeping for municipal operations

16. Education is one of the most important tools against stormwater pollution.

It takes individual behavior change and proper practices to control stormwater pollution. The following common individual behaviors have the potential to negatively impact our water resources:

  • Littering
  • Disposing of trash and recyclables
  • Disposing of pet-waste
  • Applying lawn-chemicals
  • Washing cars,
  • Changing motor-oil on impervious driveways
  • Household behaviors like disposing leftover paint and household chemicals

17. Clean stormwater needs many voices.

MS4s are required to provide opportunities for the public to provide input on development, implementation, and review of an MS4's stormwater management program.

18. Illicit discharges occur every day and are 100% preventable.

An illicit discharge includes any discharge to the municipal separate storm sewer system that is not composed entirely of storm water.

19. Sediment-laden stormwater runoff endangers fish and aquatic vegetation.

Stormwater from construction sites can often contain large amounts of sediment. If allowed to enter the MS4 system and waterbodies without proper treatment, sediment can reduce the amount of sunlight reaching aquatic plants, clog fish gills, smother aquatic habitat and spawning areas, and impede navigation.

Ducks on the recently rehabilitated Kinnickinnic River near urban Milwaukee, Wisconsin.

20. Development is outpacing population growth.

Over the last 20 years, the rate of land development has been twice the rate of population growth. This has increased stormwater volume and degraded water quality, which can harm lakes, rivers, streams, and coastal areas. To help mitigate stormwater impacts from development, the MS4 program requires the use of stormwater treatment practices to treat, store, and infiltrate stormwater before entering our valued water resources.

21. When we can’t stop it, we offset it.

Regulated MS4s conduct numerous activities that can create potential stormwater pollution, including winter road maintenance, minor road repairs and other infrastructure work, automobile fleet maintenance, landscaping and park maintenance, and building maintenance. MS4s are required to offset these potential pollution generating activities by implementing practices such as parking lot and street sweeping and storm drain system cleaning.

22. A city block creates five times mores runoff.

Due to hard surfaces like pavement and rooftops, a typical city block generates five times more runoff than a woodland area of the same size.

23. Cleaner stormwater means cleaner surface water.

About 77 percent of the freshwater used in the United States comes from surface-water sources. The other 23 percent comes from groundwater. Surface water is an important natural resource used for many purposes, the most important is drinking water and food growth.

24. Stormwater begins in your yard.

The rainwater or snowmelt from your roof, sidewalks and driveways are the beginning of the stormwater system. From there it flows through a system of conveyances (ditches, hidden pipes and drains) into our local waterways.

25. Everyone can help battle stormwater pollution.

There a dozens of ways all of us can help reduce stormwater pollution. Don’t overwater your lawn. Wash your car in the grass, not in the driveway. Use fertilizers sparingly. There are many others. For more information, visit www.epa.gov.

About the Expert

April Ryan

April Ryan is a Senior Water Resources Engineer with experience assisting clients on a range of municipal and water resources projects. April is located in SEH’s St. Cloud office and serves as SEH’s lead water resources engineer for project needs throughout SEH’s northern and western Minnesota offices including St. Cloud, Hutchinson, Grand Rapids, Duluth, Virginia, and Brainerd. She has a bachelor’s degree in Civil Engineering with a minor in Mathematics from the University of North Dakota and is a licensed professional engineer in Minnesota. April is a current board member for the Minnesota Erosion Control Association (MECA). Contact April

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