HOW IS STORMWATER TREATED?

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 How Are Stormwater Contaminants Removed?


It may seem like rainwater just hits the ground, flows down the street  and out to the nearest river, lake or ocean. But stormwater collection and treatment systems are more complicated than that. 

Rainwater that falls gently on lawns or in woods, may percolate into the soil. But, as stormwater flows over impervious surfaces like roofs, driveways, parking lots, roads, highways, construction sites and more, it picks up contaminants that could end up in our natural waters:
  • Sediment
  • Oil, grease, antifreeze, metals
  • Detergents
  • Microplastics
  • Lawn clippings, leaves, yard waste and other organics
  • Fertilizers, herbicides and pesticides
  • Bacteria from pet waste and wildlife 
  • Trash/Litter

These contaminants affect water quality and may harm aquatic plants and animals. And in some parts of Florida, the affected waters are drinking water sources. While drinking water must go through a highly regulated treatment process, contaminants from stormwater could make it more difficult and expensive to treat.

Stormwater Regulations

EPA, the Florida Department of Environmental Protection (FDEP), and the Water Management Districts regulate conveyance and treatment of stormwater. Each city stormwater system,  must have a National Pollutant Discharge Elimination System (NPDES) Permit.  This permit requires the city to develop and implement a Storm Water Management Program (SWMP) to reduce the discharge of pollutants from the stormwater system. (LOTS of acronyms with these regulations). These NPDES Permits also regulate stormwater discharge from industrial sites and construction activities. Contractors must obtain permits before starting construction.

Stormwater Conveyance

Unlike wastewater, stormwater is not transported to a single site for treatment. Stormwater flows into a varied network of storm drains and piping, ditches, basins,  ponds and swales. Some of it may flow through various structures or pumping stations. 

In the past, stormwater systems were only designed to prevent flooding. As contamination became a concern, we've improved the systems to provide treatment and protect receiving waters.

In some states, stormwater and wastewater systems are combined--but not in Florida. Stormwater and wastewater systems must be separate per FDEP.


Stormwater Treatment

Some stormwater treatment methods mimic nature, by allowing the stormwater to percolate slowly through the soil, providing a natural filtration. Contaminants may also be absorbed by natural plant material and soil. Other treatment methods use various structures. These treatment methods include:

Wet Detention Ponds 

Photo: St. Johns River WMD

You'll see these everywhere in Florida, as they are often required for developments, homeowners associations, or office parks. These ponds are designed to let material settle and be absorbed - with water draining through an outflow pipe. A certain level of water is kept in the pond, and it may be surrounded with plants. Some have fountains installed, which provides aeration and helps prevent algae growth.

Stormwater Retention Basins

These are larger basins, designed to hold stormwater and let it percolate for about 4 days. Retention basins are closed systems that do not allow stormwater to reach natural waters.

Swales
Photo: Southwest Florida WMD

Swales are depressed areas usually located along roadways, often grassed. The stormwater may be absorbed or transported to natural waters.

Dry Retention Systems

These systems are designed to hold water for about 4 days while it percolates through the ground until it dries out. Dry retention systems include a "popoff valve" that allows water to overflow if a storm is heavier than the system can handle.

Stormwater Treatment Structures

Several types of structures can be installed in the stormwater system to remove pollutants. Some include baffles that trap sediment, while others include filtration devices or separators that use swirl action to remove particles.

Here are a couple examples from Oldcastle Infrastructure:

Perkfilter® Media Filtration Vault

Nutrient Separating Baffle Box®:


How You Can Help Prevent Stormwater Pollution

There are a number of ways to help keep pollutants from being carried away by stormwater. Some are easy, and others take more effort or cost more. 

Lawn and Garden:

  • Use fertilizers, herbicides and pesticides only when necessary and at the amount and times recommended. Avoid applying these chemicals close to water or before a rainstorm. 
  • Store or dispose of unused chemicals properly.
  • Don't overwater lawns and gardens. 
  • Plant native shrubs and flowers that use less water.
  • Install a rain barrel to collect water from your roof, and use the collected water for lawn and garden irrigation.
  • Re-direct downspouts to water plants or lawn.
  • Use yard waste as mulch, or properly bag for disposal.
  • If possible, incorporate a grass swale or other depression in the yard to hold water and let it percolate into the ground.
  • Sweep driveways and walkways instead of hosing them down.
  • Use pervious pavers for walkways and other hardscape.

Vehicles:

  • Keep your car well maintained - repair any leaks as soon as possible.
  • Wash your vehicle on gravel or a pervious surface. Even better, use a car wash, as most of them recycle the water.
  • Walk, bike, or do ride-sharing as much as possible. 

Other Important Items:

  • If you have a septic tank, maintain it properly.
  • Pick up pet waste.
  • Do not litter.
  • Adopt a street to pick up litter. Cigarette butts are some of the worst - they're everywhere.
  • Use non-toxic, environmentally friendly chemicals outdoors. 
  • Pick up spills that may have occurred during garbage or recycle collection.
  • NEVER put anything down a storm drain or manhole. (From my time in Public Works, I've seen people pushing yard waste or the results of pouring chemicals down a storm drain).



Geek Out

Here's an excellent 1-hour video on how the stormwater system works in Florida - Stormwater 101: Understanding Drainage, Ponds, & How Florida Manages Rainwater:



Like all important infrastructure, stormwater pipes and structures need to be inspected and maintained. We pull some strange things out of drainage pipes - yes, even alligators end up there!




Contractors must obtain a permit for construction projects. These projects must be inspected by a qualified inspector. Here is information on the:



Read about Florida's NPDES Stormwater Program, pertaining to cities, construction sites, and industrial facilities.






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