Introduction to Stormwater
Stormwater runoff is generated when precipitation from rainfall and snowmelt flows over top of the land because it is not able to infiltrate into the ground. Runoff can occur on land that is compacted, bare (no trees or vegetation), sloped (hills or mountains), or covered by impervious surfaces (manmade surfaces). Impervious surfaces can consist of paved streets, parking lots, building rooftops, decking, driveways, etc. The precipitation that runs off can flow into storm drains that lead to nearby water bodies and eventually to the ocean.
Runoff can accumulate pollution such as debris, chemicals, sediment, nutrients (nitrogen and phosphorus), oil and grease, pesticides and herbicides, or pathogens (bacteria or viruses).Stormwater runoff can also lead to erosion, flooding, and other environmental and health issues if not properly managed.
One way that stormwater runoff is managed is through the federal Clean Water Act (CWA), which prohibits the discharge of pollutants into waterways without the appropriate permits. These permits are managed under the National Pollutant Discharge and Elimination System (NPDES) by the US Environmental Protection Agency (EPA) and Pennsylvania Department of Environmental Protection (DEP). More information on Stormwater Regulations can be found on our Regulations page.
Explore the requirements of the PA Stormwater Management Act 167 and the Municipal Separate Storm Sewer System (MS4) Program in the pages below, along with methods to meet these requirements through stormwater best management practices (BMPs), case studies and initiatives for stormwater management, and planning for stormwater management.
Discover stormwater best management practices (BMPs) based on type and land use.
TMDLs and PRPs
TMDLs and PRPs
Understand Total Maximum Daily Loads (TMDLs) and Pollutant Reduction Plans (PRPs) requirements.