Phase I of NPDES

Medium & Large
Municipal Separate Storm Sewer Systems (MS4s)

In response to the 1987 Amendments to the Clean Water Act (CWA), the U.S. Environmental Protection Agency (EPA) developed Phase I of the NPDES Stormwater Program in 1990. The Phase I program addressed sources of stormwater runoff that had the greatest potential to negatively impact water quality. Under Phase I, EPA required NPDES permit coverage for stormwater discharges from:

• Medium and large municipal separate storm sewer systems (MS4s) with populations of 100,000 or more;
• Companies that fall with one of the eleven categories of industrial activity, which includes construction activity that disturbs five or more acres of land

Requirements for Phase I
Industrial Facility Operators

The Stormwater Phase I Rule requires all operators of regulated industrial facilities to:

• Obtain a National Pollutant Discharge Elimination System (NPDES) permit, and;

• Develop a stormwater management program designed to prevent harmful pollutants from being washed by stormwater runoff into receiving water bodies or from being dumped directly into the MS4.

Large & Medium MS4 Permits

Operators of MS4s regulated under the Phase I NPDES Stormwater Program must obtain permit coverage for stormwater discharges under their control.  The most significant portion of the application was the development of a proposed stormwater management program that would meet the standard of "reducing pollutants to the maximum extent practicable (MEP)." Stormwater management programs for medium and large MS4s include measures to:

• Identify major outfalls and pollutant loadings;
• Detect and eliminate non-stormwater discharges to the system;
• Reduce pollutants in runoff from industrial, commercial, and residential areas; and
• Reduce pollutants from construction sites within their jurisdiction
  
  Current Phase I MS4 Permittees Nationwide
  EPA Large & Medium MS4 Permit Requirements
  Overview of NPDES Stormwater Program & Phase I
  EPA Phase I Webpage

Eleven Categories of Activity

EPA 11 Categories of Industrial Activity

Below is a list of categories defined as "stormwater discharges associated with industrial activity" under federal regulations. Any industrial activity that falls within the eleven categories is regulated under Phase I of the NPDES Storm Water Program.

1. Facilities with effluent limitations
2. Manufacturing
3. Mineral, Metal, Oil and Gas
4. Hazardous Waste, Treatment, or Disposal Facilities 
5. Landfills
6. Recycling Facilities
7. Steam Electric Plants
8. Transportation Facilities
9. Treatment Works
10. Construction Activity *
11. Light Industrial Activity

* Construction Activity, is included in the definition of "stormwater discharges associated with industrial activity," construction activities require construction stormwater permits, not industrial stormwater permits, under the NPDES Stormwater Program. (courtesy EPA)