On January 8, 2013, the U.S. Supreme Court held unanimously in L.A. County Flood Control District v. NRDC that the flow of polluted stormwater from an improved portion of a navigable waterway into an unimproved portion of the same waterway is not a discharge of pollutants under the federal Clean Water Act. The Court’s decision reaffirms its 2004 holding in South Florida Management District v. Miccosukee Tribe of Indians1 and overturns a Ninth Circuit ruling that could have significantly altered the permitting and enforcement scheme for stormwater and flood control, particularly for engineered structures conveying water within a single water body. The Court declined NRDC’s call for it to address broader questions relating to liability for stormwater pollution under Clean Water Act permit terms and focused only on the narrow discharge issue on which it granted review.

The Los Angeles County Flood Control District (“District”) operates a complex and sprawling municipal separate storm sewer system (“MS4”) designed to collect stormwater and control flooding over a 4,500 square mile area within the County. Stormwater flows over paved and developed urban landscapes, often collecting pollutants – including suspended metals, algae-promoting nutrients, pesticides and other toxic contaminants – along its path before entering the MS4 system and ultimately being discharged, untreated, into receiving waters. MS4 stormwater discharges are regulated by EPA under Clean Water Act (“CWA”) Section 402(p).