Question: How is stormwater regulated?

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stevie asked on February 09, 2017 22:11
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I'm interested in understanding how stormwater is regulated. I'm also curious to know if there are places that treat stormwater before it is discharged into waterways.

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stormwater answered npdes

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2 Answers

One way stormwater is regulated is through the National Pollutant Discharge Elimination System (NPDES).

See NPDES wiki "NPDES only applies to “point sources” of water pollution, specifically a “discernable, confined, discrete conveyance” into waters of the United States (CWA section 502(14)). Point sources include direct effluent pipes and conduits, ditches, tunnels, and more. Stormwater is included as a point source of pollution, due to stormwater drain discharges, culverts, and other infrastructure that channel stormwater to a receiving surface water. Industrial sources and stormwater sources are regulated differently due to the reasonable control over pollutant input (e.g. direct effluent from a facility versus urban runoff), where stormwater permits are based more on “best management practices” rather than numeric water quality limits. There are also specific exemptions of industrial and stormwater point source pollution, and non-point sources of pollution like agricultural operations are not subject to NDPES permits."

While some places do treat stormwater, many times stormwater drains directly into waterways.

Many older cities treat stormwater before it is discharged. Quoting Kate Asher in Anatomy of a City (2005), "New York is one of only 800 or so cities in the [United States] that rely on what's known as a "combined sewer system"—one that mixes storm water with wastewater, and sends them both on to the same treatment plant." Page 174.

Combined sewer systems have "combined sewer outfalls" -- i.e., the ends of pipes that discharge treated water into waterways. These outfalls are well documented, have publicly visible signage and each have a permit. During times of high volumes of rain when treatment plants can't handle it all, "combined sewer overflow" (CSO) events release untreated stormwater AND untreated sewage directly into waterways. See

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