Stormwater is qualified as any rain or snowmelt that is unable to soak in to the ground and instead "runs off" into gutters or storm drains, and into rivers, bays and other waterways. As the runoff flows over impervious surfaces, such as parking lots, streets and rooftops, it accumulates chemicals and other pollutants that can adversely affect waterways. While many technologies exist to treat and control stormwater discharges, most modern methods focus on the use of best management practices, according to the U.S. Environmental Protection Agency (EPA).
????? A Significant Threat
Increased urbanization causes rain and snowmelt to run directly in to storm drains, ditches and waterways without the benefit of treatment. And that stormwater, which has likely picked up bacteria, pathogens and chemicals, can present human health risks. Nutrient-laden stormwater may sound like a good thing, but it's not: It reduces dissolved oxygen levels, stimulates algae growth in lakes and rivers and increases erosion and sedimentation. It threatens the quality of aquatic habitats.
Add to that the increase in volume of water runoff, and stormwater containment systems can be easily overwhelmed, causing flooding and raw sewage releases. Stormwater pollution also threatens waterway aesthetics, recreation and tourism.
????? Stormwater Pollutants
A variety of harmful pollutants are found in stormwater. Substances associated with urban activities include heavy metals, oil, pesticides and herbicides that wash off streets, lawns and fields. Stormwater frequently contains nutrients like phosphorous and nitrogen, from landscaping, agriculture and leaking sanitary and septic sewers. Sediment, the largest pollutant load that often stems from construction activities, increases water turbidity and harms aquatic life. Other pollutants include organic matter and bacteria.
????? "Point" and "Nonpoint" Sources
Different regulations help control stormwater runoff. One focuses on "nonpoint source" (NPS) pollution, defined by the federal Clean Water Act (CWA) as water pollution without well-defined discharge points. State and local agencies oversee treatment and control programs designed specifically for NPS pollution, including urban runoff.
"Point source" discharges like those found at industrial and wastewater treatment plants are overseen by the National Pollutant Discharge Elimination System (NPDES) permit program under the CWA. Site-specific programs are designed in accordance with regulatory requirements and to address pollutant and other parameters of concern.
????? Best Management Practices
Compliance with NPDES, state and local stormwater programs revolves around the use of "best management practices" (BMPs) to manage stormwater runoff volume and prevent or reduce the release of pollutants. BMP methods fall into the general categories of treatment and control, and preventive measures.
Treatment and control technologies can reduce levels of oil, suspended solids, dissolved metals and phosphorus. Stormwater flow is captured and pollutants removed through filtering, infiltration, detention and other techniques. Such measures typically require a long-term operation and maintenance commitment, according to the North Carolina Division of Water Quality (DWQ).
????? Prevention Techniques
Preventive measures reduce the negative effects of stormwater runoff through design, operation and or management techniques that include land use management practices and source reduction practices. Land use management practices focus on the best way to locate land uses within a project site to avoid environmental damage.
Source reduction practices focus on locating the sources of pollutants and introducing design and operational changes that minimize, or remove, these sources. Preventive measures are generally thought to be more efficient and cost-effective than control measures, according to the DWQ.
????? Public Education
Educating citizens about the importance of stormwater management and how to prevent pollution from entering waterways is one of the most effective BMPs. The EPA recommends that commercial establishments cover and clean grease storage containers to prevent leaks, for example, and that construction companies install silt fences, vegetative cover and other sediment and erosion controls, especially after rainstorms. The agriculture, forestry and automotive industries are among those whose BMPs can help to significantly control stormwater runoff.
????? What You Can Do
There are countless ways residents can help reduce polluted stormwater runoff. Avoid pouring household products such as insecticides, pesticides, paint and used motor oil onto the ground or into storm drains. Properly maintain your vehicle to prevent oil and antifreeze leaks. Use fertilizers and pesticides only when necessary or seek non-chemical solutions.
Deice your driveway with sand instead of salt and chemicals. Not least, volunteer for local stormwater management programs. Public initiatives include riparian planting, volunteer monitoring, storm drain marking and stream cleanup. For more information, see the EPA's National Menu of BMPs.
?