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Delaware Department of Transportation

Stormwater Management

Why Stormwater Is Regulated

Stormwater discharges are generated by precipitation and runoff from land, pavements, building rooftops and other surfaces. Stormwater runoff can accumulate pollutants such as oil and grease, chemicals, nutrients, metals, and bacteria as it travels across land. Heavy precipitation or snowmelt can also cause sanitary sewer overflows which, in turn, may lead to contamination of water sources with untreated human and industrial waste, toxic materials, and other debris. Water pollution from runoff degrades surface waters and can make them unsafe for drinking, fishing, swimming, and other activities, as well as degrading wildlife habitat.

What is NPDES?

EPA controls the water quality of stormwater discharges through its National Pollutant Discharge Elimination System (NPDES). In 1990, the EPA issued the Stormwater NPDES Phase I Regulations as required by the Clean Water Act. The Phase I regulations cover urban areas with a population of 100,000 or more. In 1999, the EPA required some smaller urbanized areas to obtain Phase II Permits for municipal separate storm sewer system (MS4) discharges.

DelDOT has a Phase I Permit that covers all of New Castle County, and a Phase II permit that covers urbanized areas of Kent and Sussex Counties.

The stormwater management programs of Phase I and II are designed to prevent harmful pollutants from being washed by stormwater runoff into the storm sewer system (or dumped) and then discharged from the storm sewer system into local waterbodies.

Phase I Requirements

New Castle County was required by the Environmental Protection Agency (EPA) to obtain an NPDES permit under the Phase I NPDES regulations.

New Castle County, 12 municipalities, and DelDOT are jointly responsible for implementing a Stormwater Pollution Prevention and Management Program covering the following areas:

  • Structural controls and operations
  • Areas of new development & significant redevelopment
  • Roadways
  • Flood control projects
  • Pesticides, herbicides, and fertilizer application
  • Illicit discharges and improper disposal
  • Spill prevention and response
  • Industrial & high risk runoff
  • Construction site runoff
  • Public education
  • Monitoring programs

Phase II Requirements

In addition to the Phase I permit requirements for New Castle County, DelDOT now has a Phase II permit for the urbanized areas of Kent and Sussex Counties. This includes areas of Dover in Kent County and Delmar in Sussex County. There are six required program elements including:

  • Public Education and Outreach on stormwater impacts
  • Public participation/involvement
  • Illicit discharge detection and elimination
  • Construction site stormwater runoff control
  • Post-construction stormwater management in new development/redevelopment
  • Pollution prevention/good housekeeping for municipal operations

DelDOT is required to develop a stormwater management program which includes the six program elements, implement the stormwater management program using appropriate management strategies, develop measurable goals and evaluate the effectiveness of the program.

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