In a rare review of a portion of the federal Clean Water Act (CWA), the United States Supreme Court has ruled in favor of a flood control district's defense of discharges of stormwater in its municipal stormwater system (MS4).  The Court held unanimously that a discharge of stormwater containing pollutants from an improved portion of a waterway to an unimproved portion of a waterway was not a violation of the CWA under the precedent of South Florida Water Management District v. Miccosukee Tribe, 541 U.S. 95, 109-112 (2004).  The Miccosukee case involved the transfer of polluted water from one part of a water body to another part of the same water body without a National Pollution Discharge Elimination System (NPDES) Permit.  The Court ruled that under those circumstances, no NPDES permit was required under the CWA.

 Likewise in the Los Angeles case, there was no violation of the CWA because the District did not add any pollutants to the discharge when it flowed from the concrete channel to an unimproved part of a river.  The Court derived the decision from the language of the CWA itself.  Noting that the term "discharge of a pollutant" means "any addition of any pollutant to navigable waters from any point source."  33 U.S.C. section 1362(12).  Thus, concluded the Court, under the common meaning of the word "add" if water is merely transferred between different portions of the same water body no pollutants are added.  It is like taking a ladle of soup from a pot and pouring it back into the same pot.  Nothing is added, the Court analogized.

The decision will assist entities with MS4 permits and any entity that discharges stormwater where there is an allegation of receiving water violations where there is no proof that the pollutants are actually added by the permittee at a point source under its exclusive control.  In the Los Angeles case, the concrete channel where the pollutants were detected received stormwater contributions from hundreds if not thousands of other sources. 

The case is Los Angeles County Flood Control District v. Natural Resources Defense Council, Inc. et al., No. 11-460, January 8, 2013.