Stormwater is just what it sounds like, water from a storm. Any precipitation that falls from the sky, including rain, hail, and snow is considered stormwater. It either soaks into the soil or remains on top of impervious surfaces like pavement and rooftops. Stormwater will eventually evaporate off of a surface, but most often it flows as runoff to other locations (ponds, wetlands, lakes, streams, and the bay).
When it rains, water flowing over the surface of the land is part of the natural water cycle. However, in areas that are developed (houses and businesses), the soil is often covered with sidewalks, roads, buildings, or other materials that do not allow water to infiltrate into the ground. These hard, impervious surfaces change how water interacts with the land and increases the quantity and rate at which water flows over land straight into our waterways. This can lead to flooding, increased pollution in our water, and land erosion.
One common problem is that as stormwater flows over land or pavement, it can collect pollutants (trash, oils, fertilizer, pet waste, sediment, etc.) and carry them downstream. The polluted runoff flows across the ground or into the County’s stormwater drainage system (ditches, street inlets, streets), also known as a Municipal Separate Storm Sewer System (MS4) where it empties – without filtration or cleaning – into the rivers, lakes, and Tampa Bay. It is a significant source of water pollution that is increasing in Hillsborough County. Developed watersheds require rigorous polluted runoff management programs because they have:
The United States Environmental Protection Agency (EPA) recognizes stormwater pollution as a significant impact to surface waters. To minimize pollution discharged into MS4s and Waters of the State, EPA National Pollutant Discharge Elimination System (NPDES) municipal stormwater program regulations were published in 1990. The NPDES Stormwater Program regulates point source discharges from three potential sources: MS4, construction activities and industrial activities. These regulations were implemented in two phases. EPA’s first round of MS4 regulations in 1990 introduced Phase 1, which covered Large and Medium MS4s based on the total population within the geopolitical boundaries of municipalities (populations of 100,000 or greater). In 1999, EPA issued a second round of MS4 regulations known as Phase II, which requires small MS4s in U.S. to obtain NPDES permit coverage for their stormwater discharge. Small MS4s include but are not limited to smaller cities, towns, and counties (less than 100,000 people), and some other institutional entities. Additional information about Phase I and II is located on the Florida Department of Environmental Protection’s website.
In October 2000, EPA authorized the Florida Department of Environmental Protection (DEP) to implement the NPDES stormwater permitting program in the state of Florida. The authorization that MS4 communities get from DEP to legally discharge stormwater into local stream and rivers is called a NPDES MS4 permit. Hillsborough County operates under a Phase I NPDES MS4 Permit. This grants Hillsborough County the authorization from the DEP to legally discharge stormwater into local streams, rivers, lakes, and the bay.
MS4 is short for “Municipal Separate Storm Sewer System”, where the word “Municipal” refers to a unit of local government, but may also refer to an organization responsible for the administration of a developed area. The number 4 refers to the four words that start with the letter “S”: “Separate”, “Storm”, “Sewer”, “System”.
A separate storm sewer system is a collection of structures, including retention basins, ditches, roadside inlets and underground pipes, designed to gather stormwater from built-up areas and discharge it into local streams, rivers, lakes, and eventually the bay. It’s called a separate system because it’s not connected to the sanitary sewer system, which means the stormwater is NOT treated via a wastewater plant before it enters our ponds, lakes, rivers, and bay.
An NPDES MS4 permit is a general permit issued by DEP under the authority of Section 403.0885, Florida Statutes (F.S.), which is the provision authorizing the state to implement the NPDES program. The NPDES MS4 Permit requires compliance with all applicable water quality regulations related to stormwater runoff, and assurance that all the County’s MS4 infrastructure is functioning and well-maintained. Certain requirements for the program are highlighted below:
