Storm water is the result of rain or snow melt that collects in an area that can drain from into a nearby body of waters such as a lake or river. The water can collect on roof tops, parking lots, saturated ground, roads, etc. The problem is that many of the pollutants of our modern living such as oil, grease, pesticides, sediment, salt, and animal waste are washed away within the storm water and enters the storm drain system or flows directly into any adjacent bodies of water carrying the pollutants with it. Even following a moderate rainfall, the storm water pollution can be significant enough to cause the water quality in the adjacent public water areas to violate federal and state standards for swimming and boating as defined by the environmental protection agency and state health departments.
Storm water best management practices are methods designed to control storm water runoff incorporating sediment control, and soil stabilization. They also define management practices that can prevent or reduce non-point source pollution. The EPA defines storm water BMPs as a 'technique, measure or structural control that is used for a given set of conditions to manage the quantity and improve the quality of storm water runoff in the most cost-effective manner.'
No single storm water BMP can address all drainage problems. Each one has limitations based on drainage area served, available land, cost, pollutant removal efficiency, and site-specific factors such as soil types, slopes, depth of groundwater table, etc. all of these factors must be taken into consideration before selecting a storm water best management practice methodology or group of BMPs for a particular location.
Goals of Storm Water Best Management Practices (BMP)
The goals of all storm water best management practices is to reduce or eliminate the contaminants collected by storm water from being transported into the natural waterways and other bodies of water so that the quality of the water can be maintained thus protecting both the environment and the public from potential damages caused by exposure to pollutants.
Implementations of Storm Water Best Management Practices (BMP)
There are several implementations to control storm water drain off such as:
- Bio retention areas - these areas are land devoted to using either soil or plants to filter runoff from developed sites. These areas will naturally control hydrology through infiltration and evapotranspiration. These structures are well suited to treat surface runoff from parking lots and other paved areas. The Storm water flows into the area, ponds on the surface, and gradually seeps into the soil bed. The filtered water may be allowed to process naturally through sedimentation or may be collected into an underground drainage area and redirected to the storm drain system.
- Wet Detention (Ponds and Lakes) - natural or man made ponds that can remove water soluble pollutants up to 90% of suspended solids, up to 80% of metals and up to 40% of biochemical compounds through the natural sedimentation process.
- Dry Detention Basin – basically a pond built in areas with a high perk ratio and planted with durable grass that can withstand large amounts of water. The basin collects and hold storm water runoff and will completely empty within 48 hours. It also uses the natural sedimentation process to remove pollutants.
- Filter Strips - are densely planted strips of ground used primarily to contain runoff from paved areas such as roadways, small parking lots, play grounds, etc. This method uses natural sedimentation to filter pollutants.
- Grassed Swales – are simply a shallow channel or depression commonly used in highly developed areas. The storm runoff collects in the swale and natural sedimentation removes the pollutants.
- Green Roofs – are rooftops that have been spread with tops soil and planted with vegetation. These have been used in large urban areas for centuries to reduce the amount of runoff from roof tops. They use natural sedimentation to filter pollutants.
- Infiltration Basin – man made basins planted with hardy vegetation that collects storm water and uses natural sedimentation to remove pollutants. These are commonly seen in parks and other recreation areas. The water will normally drain with 24 to 48 hours.
- Infiltration Planters – are manmade raised areas planted with vegetation to act as strip filters for parking lots, sidewalks and other paved urban areas. They are commonly seen around large buildings.
- Infiltration Trenchs – are man made excavations that are lined with filter material. The trench holds and filters the storm water until it eventually seeps into the surrounding soil. These are used in areas when the natural soil doesn’t drain that quickly.
- Natural/Native Vegetation – this is method of planting natural grasses and other vegetation usually on higher ground adjacent to lowlands. They are designed to reduce and slow runoff and trap sediment. They are normally used in areas where oil, grease and chemical pollution are not present.
- Pervious Pavement - Pervious or porous pavement, when properly maintained can remove from 65% to 95% of pollutants and sediments. Maintenance involves making sure the holes don’t get clogged. These can be used a strips in a parking lot where vehicles can drive over them.
- Rain Barrels and Cisterns – rain barrels are used to prevent runoff from roofs entering the storm drain system and can be used by home owners to provide water for gardens, lawns and flower beds. Businesses usually build cisterns to trap runoff. These methods do not remove pollutants and sediments will have to be removed periodically from the barrel or cistern.
- Rain Garden - A rain garden is a small residential depression planted with native wetland and prairie vegetation designed to collect street runoff. They are small scale version or bio retention areas.
- Wetland – manmade wetlands designed to filer runoff and improve downstream water quality. These are commonly built on the outskirts of large cities as barriers for natural waterways.
Benefits of Storm Water Best Management Practices (BMP)
Selecting the most effective Storm water best management practices can protect your business from lawsuits and expensive clean up, the environment from the effects of unrestrained pollution and the health of community members that could be compromised by exposure to toxic pollutants. To accomplish you need to understand what the water quality requirements of your community are and select the right storm water BMP for your specific project.
Costs of Storm Water Best Management Practices (BMP)
Cost of implementing storm water BMPs can range from as little as nothing if a natural pond is being used to collect the storm water and natural sedimentation is used as the pollutant removal process to more than $100,000 to construct retention basins and man made wetlands. There are also costs associated with maintaining the selected storm water BMP selected. Again, these costs can range from practically nothing to thousands of dollars a year depending on the storm water BMP selected.
Regulations for Storm Water Best Management Practices (BMP)
In 1990, the USEPA created the Phase I National Pollutant Discharge Elimination System (NPDES) storm water rule that regulates storm water discharges from any construction project that disturbs or is a sub project of a project that disturbs 5 or more acres of land.
The Phase II NPDES storm water rule, finalized on December 8, 1999, regulates any construction project that disturbs or is a sub project of a project disturbing between 1 and 5 acres of land.
The Phase I and II rules require operators of large and small construction activities to obtain NPDES storm water Construction General Permit (CGP) if they have a “point source discharge” of storm water associated with construction activity that discharges to waters of the United States either directly or through a municipal separate storm sewer system (MS4). Operators must submit a Notice of Intent (NOI) for coverage under the CGP and prepare and implement a Storm Water Pollution Prevention Plan (SWP3) with appropriate Best Management Practices to minimize the discharge of pollutants from the construction site. The EPA expects to issue the newly revised CGP in May 2003 and has stated that this program will be a low enforcement priority until the new permit is issued. However, the deadline for compliance with the Phase II rule for small construction activity is March 10, 2003