Stormwater Basics

Stormwater is the water that falls during wet weather events. As the water falls onto streets, roofs, construction sites, parking lots, etc., it collects and flows off the sites. This is called “runoff”. When precipitation falls onto trees, lawns, and other vegetation, some is absorbed into the soils that support the plants. These areas are called “pervious surfaces“. However, roofs, parking lots, sidewalks, etc. cannot absorb any water, and 100% of what falls on those “impervious surfaces“ runs off, making its way into our storm sewer system. You see components of these systems when you pass roadway or parking lot inlets, ditches, and detention ponds. The runoff from rain or snow events flows through these systems, called a Municipal Separate Storm Sewer System (MS4), often picking up pollutants like litter, sediment, fertilizers, animal waste, and oils along the way. The water in the MS4 system is eventually discharged directly into creeks, streams, and rivers with no treatment. Stormwater programs like those at MTSU aim to minimize the pollutants being discharged into our waterways through education, maintenance, and regulations.

By law, municipalities that operate an MS4 must obtain and comply with the National Pollutant Discharge Elimination System (NPDES) permit. This permit is renewed every five years and is audited by the Tennessee Department of Environmental Conservation (TDEC) – Water Resources Department. MTSU partners with the City of Murfreesboro as a co-permittee to implement the requirements of our NPDES permit and keep the City and the University in compliance. The NPDES permit is made up of six components.

1. Public Education and Outreach
2. Public Participation and Involvement
3. Illicit Discharge Detection and Elemenation
4. Construction Site Stormwater Runoff Control
5. Post-Construction Stormwater Management
6. Pollution Prevention and Good Housekeeping for Municipal Operations

What is an illicit discharge?

An illicit discharge is disposal of anything other than storm water into the storm water drainage system. This includes illegal connection or tie-ins to the storm sewer system.

Examples of illicit discharge to storm sewer system:

• Trash
• Sanitary wastewater (sewage)
• Septic tank waste
• Car wash, laundry or industrial wash water
• Concrete truck washout
• Improper disposal of automotive fluids and household toxics
• Soapy water used to wash parking lots, sidewalks,buildings and loading docks
• Grease trap overflows
• Sump pump with contaminated water flowing into storm drain
• Dirty water from mopping being dumped to a storm drain