Under the Clean Water Act, the National Pollutant Discharge Elimination System, or NPDES Program, is aimed at reducing and eliminating pollution from discrete sources of wastewater, known as "point sources", to waters of the United States. According to the act, all point sources must obtain an NPDES permit which regulates the facility's discharge of pollutants into water of the United States.
Point sources are generally divided into 2 types: industrial and municipal. Under the NPDES Program, industrial point sources which include commercial and manufacturing facilities discharging wastewater directly into a receiving stream, are required to be covered by a permit which specifies the monitoring and reporting provisions and establishes limits on the pollutants that are discharged.
If an automotive service/repair shop discharges wastewater directly from its facility (such as from a holding pond) to waters of the United States, that shop is considered an industrial point source and is subject to NPDES regulations.
Wastewater (domestic waters from households and indirect discharges of industrial wastes from manufacturing and commercial activities) discharged into rivers or streams from municipal sources (also know as public owned treatments works (POTWs)), are governed by the NPDES program, as well. Stormwater from municipal separate storm water sewers and storm water associated with industrial activity, including automotive service/repair shops, are also considered point source discharges and are addressed by the NPDES program.