Authorized by the Clean Water Act, the National Pollutant Discharge Elimination System (NPDES) permit program controls water pollution by regulating point sources that discharge pollutants into waters of the United States.
The NPDES Municipal Storm Water Permitting Program regulates storm water discharges from municipal separate storm sewer systems (MS4s). NPDES Municipal Permits were issued in two phases.
Phase I, which started in 1990, permit coverage for medium (serving between 100,000 and 250,000 people) and large (serving 250,000 people) municipalities.
Phase II requires General Permit coverage for the discharge of stormwater from small MS4s, including non-traditional Small MS4s such as governmental facilities like military bases, public campuses, prisons and hospitals.
The MS4 General Permit requires the discharger to develop and implement a Storm Water Management Plan/Program (SWMP) with the goal of reducing the discharge of pollutants to the maximum extent practicable.
Stormwater discharges are generated by runoff primarily from disturbed land and impervious areas during rainfall and snow events that often contain pollutants in quantities which could adversely affect water quality and beneficial uses of water bodies. Sources of stormwater pollution include driveways, streets, parking lots, lawns, construction sites, agricultural activities, failing septic or sewer systems, and illicit discharges such as dumping of waste motor oil. Pollutants found in stormwater runoff include heavy metals, oil, grease, sediment, fertilizers, pesticides, herbicides, bacteria, and trash. When it rains, these pollutants are washed through our streets and storm drains directly into creeks and into Clear Lake.
Many stormwater discharges are considered point sources for pollution and require coverage by a National Pollutant Discharge Elimination System (NPDES) permit. The primary method for control of stormwater discharges is through the use of Best Management Practices(BMPs). BMPs include scheduling of activities, prohibition of practices, pollution prevention and education practices, maintenance procedures, and other management practices to prevent or reduce to the maximum extent practicable the direct and indirect discharge of pollutants to the County storm drainage system and to natural surface waters.