The National Pollutant Discharge Elimination System (NPDES)

The National Pollutant Discharge Elimination System (NPDES) program was established by the Clean Water Act of 1972.

Initially, the NPDES program focused on decreasing easily identifiable sources of major pollutants: industrial process wastewater and municipal sewage.  The program tracks individual point sources and requires the discharges of pollutants to be minimized through effluent limits set by water quality standards.

Through time, as the NPDES program was implemented, it became more obvious that other sources of water pollution were also significant causes of water quality impairment.

It is estimated that 46% of the nation’s waters are "impaired" by stormwater runoff, which means these waters cannot be used for drinking, they are not safe to swim in, and the fish living in the waters are not safe to eat.

The Clean Water Act was amended by Congress in 1987 to require the Environmental Protection Agency (EPA) to implement a two-phased program to regulate stormwater discharges under the NPDES permit program. 

The Phase I Stormwater Program

The Phase I program requirements were published in 1990 and covered stormwater discharges from large priority sources including medium and large municipal separate storm sewer systems and several categories of industrial activity including construction activities that disturb over 5 acres of land.

Municipal separate storm sewer systems

Medium and large municipal separate storm sewer systems are located in incorporated cities with populations of 100,000 or more and counties, which have over populations over 100,000 in their unincorporated, urbanized areas.

The Washington State Department of Ecology (Ecology), which is delegated by the EPA to manage the NPDES program in Washington, issued three municipal Phase I permits in 1995, which cover the Cities of Seattle and Tacoma, King, Snohomish, Pierce and Clark Counties, and the Washington State Department of Transportation. 

Industrial activities

Eleven categories of industrial stormwater dischargers require Phase I permits based on Standard Industrial Classification (SIC) codes. These include facilities subject to EPA stormwater effluent guidelines: heavy manufacturing facilities; mining/oil and gas; hazardous waste treatment, storage or disposal facilities; landfills; recycling facilities; steam electric power; transportation facilities; certain sewage treatment plants; and light manufacturing facilities.

Ecology issued the first Phase I stormwater permit for industrial activities in 1995, which covers approximately 1200 industrial facilities.  

Construction sites

Ecology also issued the first Phase I construction stormwater permit in 1995, which covers construction sites disturbing greater than 5 acres.  There are an estimated 800 Phase I construction sites.

The Phase II Stormwater Program

The Phase II requirements were published by the EPA in 1999 and require NPDES permit coverage for small municipal separate storm sewer systems and construction sites disturbing between 1 and 5 acres.  These requirements have been in effect starting in March 2003.

Small municipal separate storm sewer systems

These are defined as being located in “urbanized areas” as defined by the Bureau of Census.  There are approximately 95 small municipal systems in Washington State that will require Phase II permits.

Construction sites

Construction sites disturbing 1 to 5 acres of land are required to have this permit.  It is estimated that 1000-1500 sites per year require Phase II permits.