Industrial stormwater is runoff from precipitation (rain or snow) that lands on industrial sites (e.g. manufacturing facilities, mines, airports). This runoff is often polluted by materials that are handled or stored on the sites, and the facilities are subject to regulations to control the discharges.
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Regulation in the United States
In the United States, facilities that discharge industrial stormwater to surface waters must obtain a permit under the National Pollutant Discharge Elimination System (NPDES), pursuant to the Clean Water Act. Stormwater permit regulations issued by the United States Environmental Protection Agency (EPA) govern the permit process. EPA published its "Phase I" stormwater rule, which covers industrial dischargers, in 1990.
Multi-sector general permit
Stormwater permits are issued by EPA and 46 states approved by EPA. EPA published its Multi-Sector General Permit (MSGP) initially in 1995 to govern how industrial stormwater should be managed, and periodically it has updated and reissued the permit. The 2015 MSGP covers 29 industrial and commercial sectors. The permit is applicable to facilities in Massachusetts, New Hampshire, New Mexico, Idaho, the District of Columbia and federal insular areas (territories). Other states have developed their own state-specific industrial stormwater permits (e.g. California's Industrial General Permit).
Construction site stormwater
Under EPA regulations, stormwater runoff from construction sites is also classified as industrial stormwater, however these discharges are covered by a separate set of permits. EPA periodically publishes its Construction General Permit and the approved states publish similar permits, to regulate discharges from construction sites of 1 acre (4,000 m2) or more.