Glossary of Terms

Best Management Practices (BMP)

Any activities, structural solutions, maintenance procedures, prohibition against certain activities, and other management practices intended to prevent or reduce the pollution of surface waters or the County’s MS4. BMPs include but are not limited to: treatment facilities to remove pollutants from stormwater; operating and maintenance procedures; facility management practices to control runoff, spills or leaks of non-stormwater, waste disposal, and drainage from raw materials storage; erosion and sediment control practices; the prohibition of specific activities, practices, and procedures; and other such actions as the County or City determines appropriate and necessary for the control of pollutants.

Illicit Discharge

Any direct or indirect discharge to the County’s MS4, Waters of the U.S., or Waters of the State that is not composed entirely of stormwater, unless exempt pursuant to City or County Ordinance (some discharges, such as firefighting activities, are unavoidable, and are not prohibited.) Any discharge in violation of a NPDES permit also constitutes an illicit discharge.

Municipal Separate Storm Sewer System (MS4)

A conveyance or system of conveyances designed for conveying stormwater

  • including, but not limited to, roads with drainage systems, streets, catch basins, curbs, gutters, ditches, manmade channels, or storm drains,
  • owned or operated by a local government,
  • that discharges to Waters of the United States, Waters of the State, or connects to other MS4s (of other cities or counties).

The word “separate” distinguishes most local government storm sewer systems from some of the older systems that were combined with “sanitary” sewers. These systems (called “combined sewers”) often experienced overflows of untreated sewage during storms, and are no longer built or permitted.

The legal definition of MS4 also includes any detention ponds, inlets, and other structures that are part of the stormwater conveyance system.

Nonpoint Source Pollution

Nonpoint source (NPS) pollution, unlike pollution from industrial and sewage treatment plants, comes from many diffuse sources. NPS pollution occurs when rainfall, snowmelt, or irrigation runs over land or through the ground, picks up pollutants throughout the watershed, and deposits them into rivers, lakes, and coastal waters or introduces them into ground water. Imagine the path taken by a drop of rain from the time it hits the ground to when it reaches a river, ground water, or the ocean. Any pollutant it picks up on its journey can become part of the NPS problem. Essentially, anything we put on the ground will eventually find its way into our surface waters.

NPS pollution is widespread because it can occur any time activities disturb the land or water. Septic systems, urban runoff from streets and yards, construction, recreational boating, agriculture, forestry, grazing by livestock, physical changes to stream channels, and habitat degradation are all potential sources of NPS pollution. Careless or uninformed household waste management also contributes to NPS pollution problems.


National Pollutant Discharge Elimination System. This is the name given to the United States Environmental Protection Agency’s water permitting programs (including stormwater, domestic wastewater, and industrial wastewater discharges).

For complete information on the Florida NPDES Stormwater Program including Rules, Forms and more, visit the FDEP website.