If you have worked on civil engineering projects in urban areas, you most likely have heard of an MS4. MS4 refers to a Municipal Separate Storm Sewer System. The Storm Sewer System collects rainwater and is separate from the sanitary sewer system. To learn more about the differences between the storm sewer system and the sanitary sewer system check out the previous blog article What is a SWPPP and What Does it Mean for Your Project?
Stormwater that is collected in the MS4 is discharged into a waterway and regulated under the Federal Clean Water Act. In today’s blog posts, we dive into the details of MS4 and some basic MS4 regulations.
A Municipal Separate Storm Sewer System (MS4) is regulated under The Federal Clean Water Act. an MS4 is classified as either Phase I or Phase II. A Phase I MS4 is a municipality with a population of greater than 100,000 people, per the 1990 decennial census whereas a Phase II MS4 is an “urbanized area” as defined by the last decennial census. Historically, there has been some debate and disagreement over this classification system, because the Phase I determination was at a particular point in time, and municipalities that have experienced rapid growth since 1990 (and there are several in the United States!) may be over 100,000 people today but are still a Phase II municipality based on the MS4 definition because the Phase I designation is based on the population in 1990. While there has been a lot of heated discussion on this situation, as of the time of this article, the classification system still remains though some government officials claim it is unfair.
We previously mentioned that an MS4 is regulated under The Federal Clean Water Act. Specifically, an MS4 requires a permit to discharge the stormwater it collects. Each municipality that has an MS4 is required to obtain a National Pollutant Discharge Elimination System (NPDES) Permit. A Phase I MS4 will need an Individual Permit which is tailored to the municipality, while a Phase II MS4 will be covered by the MS4 General Permit. The MS4 General Permit consists of six (6) Minimum Control Measures (MCM) that localities must do to be in compliance with their MS4 Permit and authorized to discharge stormwater. The 6 Minimum Control Measures Include:
1. Public education and outreach on stormwater impacts
2. Public involvement and participation
3. Illicit discharge detection and elimination
4. Construction site stormwater runoff control
5. Post-construction stormwater management in new development and redevelopment
6. Pollution prevention/good housekeeping for municipal operations
A storm sewer manhole access point is marked with a medallion indicating that water that enters drains to the nearby waterway. This is part of public education measures, required by the City’s MS4 Permit.
Each of these could take its own blog post to cover, but the idea is that municipalities are required to educate the public about the stormwater system, screen the stormwater system for pollutants (which is anything that is not stormwater runoff), and take steps to reduce pollution within the stormwater system and ultimately local waterways. However, in many cases, it is the MS4 Permit and associated stormwater regulatory requirements that govern much of the stormwater and erosion control sediment requirements on construction sites today. MCM 4 Construction Site Stormwater Runoff Control is the basis for the requirement that construction sites have an SWPPP (Stormwater Pollution Prevention Plan). You can learn more about an SWPPP in the blog post linked here: LINK While MCM 5 regulates post-construction stormwater runoff and is the basis for the stormwater best management practices (BMP) and retention and detention ponds that are required with development projects today. More on that in a future blog post, so stay tuned!
A silt fence on the construction site is an example of a best management practice to control erosion and sediment and is required by the MS4 Permit and the Construction General Permit.
Diagram of how the storm sewer system is connected at the drop inlet and water enters from the surface into the MS4.
A retention pond is required by MCM 5 of the MS4 Permit to control runoff from the new development. They also provide a habitat for local wildlife: birds, insects, small animals, etc.
Overall, the MS4 system and the MS4 Permit are important in managing municipal stormwater runoff and ensuring clean waterways in our community. The best management practices required by the MS4 Permit have led to reductions of pollutants in discharges and ultimately cleaner waterways in recent years. As time goes on, the goal is to continue to make improvements to MS4 systems, replacing aging infrastructure and determining infiltration points of pollutants which will help communities across the country to continue to trend towards cleaner waterways.
A clogged storm sewer causes water to back up on the surface. This is due to a lack of maintenance of the storm sewer system, most likely a downstream blockage is causing this to occur.
Storm sewers are an essential part of civil engineering and infrastructure in communities across the country. Civil Engineers will be essential to maintaining and upgrading these systems as populations and developments both continue to grow and as environmental regulations continue to become more stringent. A PE License is vital to your career growth and is essential for any civil engineer involved with sewer or wastewater treatment design and construction. Whether you're just starting on your FE or PE journey, or you're in the midst of exam preparation, I invite you to go here to check out the Ultimate Civil PE Exam and Ultimate Civil FE Exam Review Courses. We are here to help you every step of the way towards passing your Civil FE and PE Exams. We’ll see you there!
Do you have a topic or interesting project that you would like us to cover in a future blog post? Submit it to us here. We would love to hear from you!
________________________________________________
Author: Matt Fanghella, PE, CFM
CEA Resources:
The Ultimate Civil FE Review Course – https://civilfereviewcourse.com
The Ultimate Civil PE Review Course – https://civilpereviewcourse.com
FE and PE Practice Exams – https://civilengineeringacademy.com/exams
Free Facebook Community – https://ceacommunity.com
YouTube Channel – https://www.youtube.com/channel/UCPeFLBZ2gk0uO5M9uE2zj0Q
Newsletter – https://civilengineeringacademy.com/newsletter
Instagram – https://www.instagram.com/theceacademy
Twitter – https://twitter.com/civilengacad
Reach out to Isaac – [email protected]