NPDES Phase I of the EPA stormwater program was enacted in 1990. This relies on NPDES permits for:
Construction activity disturbing five acres of land or greater
"Medium" and "large" municipal separate storm sewer systems, normally serving populations greater than 100,000
Ten categories of industrial activity
The Focus of Phase I
NPDES Phase I of this program focused on reducing pollutants in industrial process wastewater and municipal sewage. Many of these discharge sources were identified as responsible for poor water quality. Over time, it became evident more diffuse sources of water pollution were causes of water quality degradation. Overall, stormwater runoff is a major cause of water quality impairment.
How Pollution Is Transported
Stormwater runoff is transported through the municipal separate storm sewer systems (MS4s). This simply means stormwater travels through a conveyance system, such as swales, culverts, and storm drains, and ultimately discharged into local bays, bayous, and other bodies of water without treatment.