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October 08, 2013
Establishing liability for stormwater discharges

Courts take multiple cuts at SoCal case

In a case that is making several circuits through the federal judiciary, the U.S. Court of Appeals for the 9th Circuit has issued an opinion that may result in many small local governments with municipal separate storm sewer systems (MS4) being forced to either cease discharging pollutants into those systems or obtain National Pollutant Discharge Elimination System (NPDES) permits. 

MS4 pollutants are generated by stormwater running off streets, parking lots, commercial sites, and other developed parcels of land.  Currently, elimination of pollutants from such surfaces is not economically or technically feasible virtually anywhere on earth.  But with the 9th Circuit opinion, the prospect of tens of thousands of small governments being compelled into the NPDES permitting system and state environmental agencies being forced to shoulder a universe of new enforcement responsibilities is closer to reality.

That prospect is causing great alarm among organizations that speak up for counties, cities, and towns facing new regulatory programs.  One group of organizations, which filed an amicus brief in the case, argues that it was not the intention of the Clean Water Act (CWA) to hold local governments to the same type of end-of-pipe NPDES requirements to which industrial facilities are subject.  According to the groups, this view is espoused by the U.S. EPA, which has stated:

“Congress was aware of the difficulties in regulating discharges from [MS4s] solely through traditional end-of-pipe treatment and intended for EPA and NPDES States to develop permit requirements that were much broader in nature than requirements which are traditionally found in NPDES permits for industrial process discharges or POTWs.”

The “broader” nature of requirements for local governments comprise “practices that are highly effective in reducing pollutants in stormwater, even though they may not always eliminate the pollutants altogether,” say the organizations.   “The CWA’s more practical and limited goal is not to prohibit MS4s from discharging stormwater pollutants altogether but instead to encourage local governments to improve their MS4 facilities by best management practices and reduce stormwater pollution to the extent feasible.”

While that position may prevail in municipal governments and even with regulatory agencies, it was found wholly inadequate to several environmental plaintiffs concerned about pollutants in several rivers in Southern California (SoCal) that were falling short of water quality standards.  According to the groups, the Los Angeles County Flood Control District (District) bore responsibility for pollution that originated with many smaller municipalities that released stormwater into the District’s MS4. 

Specifically, the plaintiffs—the Natural Resources Defense Council (NRDC) and Santa Monica Baykeeper—contended that the District’s NPDES permit makes it responsible for controlling all pollutants that are conveyed into the rivers via its MS4, which comprises 2,800 miles of storm drains and 500 miles of open channels and collects the stormwater discharges of 84 municipalities in LA County’s water district.  The principal evidence presented by the groups is that pollutant monitoring stations owned and operated by the District showed pollutant discharges in excess of those allowed in the District’s NPDES permit.  

Missing evidence

The case began in district court, which dismissed the complaint against LA.   According to the district court, the plaintiffs did not present the evidence needed to establish the District’s liability—specifically, which local government(s) were responsible for the water quality violations.  The District contended that the pollutants the plaintiffs charged it caused were, in fact, already in the MS4 upstream of the District’s own monitoring stations and outfalls.  The argument, derived from a previous U.S. Supreme Court ruling (South Florida Water Management District v. Miccosukee Tribe of Indians), is that the flow of water from one portion of river through an engineered improvement to a downstream portion of the same river does not constitute a regulated discharge of pollutants under the CWA.

The plaintiffs appealed their defeat to the 9th Circuit, which reversed the lower court’s ruling.  According to the 9th Circuit, the District was discharging pollutants into waters of the United States in violation of its NPDES permit.  “Although the District argues that merely channeling pollutants created by other municipalities or industrial NPDES permittees should not create liability because the District is not an instrument of ‘addition’ or ‘generation,’ the Clean Water Act does not distinguish between those who add and those who convey what is added by others – the Act is indifferent to the originator of water pollution,” stated the 9th Circuit. 

The District appealed to the U.S. Supreme Court, which agreed to review one aspect of the case—whether the flow of water from an improved portion of a navigable waterway into an unimproved portion of the same waterway qualifies as a discharge of pollutants under the CWA.  The Court found that such a flow could not be considered a discharge of pollutants.  The opinion of the 9th Circuit was therefore reversed and remanded to the 9th Circuit.  However, the Supreme Court emphasized that its ruling was limited to that single “narrow” aspect of the case.  Not addressed was the plaintiffs’ claim that exceedances detected at the District’s monitoring stations are by themselves sufficient to establish the District’s liability under the CWA for upstream discharges.  Through the remand, that issue was thrown back into the hands of the 9th Circuit and is the crux of that court’s more-recent decision. 

Exceedances not disputed

In its second cut at the case, the 9th Circuit focuses on two aspects of the District’s NPDES permit.  One, that limits are placed on the type and amount of pollutants the District may discharge from its MS4.  Two, that the District must monitor the impacts of the MS4 discharges on water quality and publish the results of all pollution monitoring at least annually.  The purpose of monitoring is to assess the District’s compliance with its permit, says the 9th Circuit.  The plaintiffs alleged that between 2002 and 2008, mass-emissions data collected at the monitoring stations indicated 140 separate exceedances of the permit’s water quality limits, including excessive levels of aluminum, copper, cyanide, zinc, and fecal coliform in the Los Angeles and San Gabriel rivers. 

The plaintiffs argued that this information was sufficient to establish the District’s liability.  Furthermore, the District did not dispute that data from the monitoring stations indicated pollution levels in excess of those allowed in the permit.  However, the defendants also contended that the plaintiffs needed to provide more evidence than just the pollution reports to hold any individual defendant liable for the pollution excesses.  According to the District, the monitoring data were insufficient to establish liability because these data were “neither designed nor intended” to measure the compliance of any permittee and the monitoring data cannot parse out precisely whose discharge(s) contributed to any given exceedance.  The 9th Circuit responded that this defense is “belied by the text of the permit and is rejected.” 

Following are the main points put forth by the 9th Circuit.


The District’s NPDES permit establishes a monitoring and reporting program with the stated objectives of both characterizing stormwater discharges and assessing compliance with water quality standards. “The permit language could not be more explicit in this regard, stating that ‘[a]ssessing compliance with this [permit]’ is one of the “primary objectives of the monitoring program,” says the 9th Circuit.  “Consequently, we decline to embrace the District Defendants’ initial argument that ‘the mass-emission monitoring stations, as a matter of fact, do not assess the compliance of any permittee with the Permit.’” 

Moreover, says the 9th Circuit, the District itself chose the locations of the monitoring stations specified in the permit because they were representative of the monitored activity (the permittees’ discharges of stormwater runoff into the navigable waters of the United States).  “Now, however, District Defendants claim that their compliance with the Permit cannot be measured using the results of the representative monitoring they themselves agreed to, that the Regional Board approved, and that the Permit itself contemplates is to be used to assess compliance with its terms,” says the 9th Circuit.  “We take this opportunity to reevaluate and reject District Defendants’ arguments.”


The District pointed to a clause in the permit that states: “[each] permittee is responsible only for a discharge for which it is the operator.”  The District contends that this clause precludes the use of monitoring data to assess compliance with the permit.  The 9th Circuit responds that this reading would render the monitoring provisions of the permit “largely meaningless.” 

Under the District’s interpretation, individual permittees could discharge an unlimited amount of pollutants from the MS4 but never be held liable for those discharges based on the results of mass-emissions monitoring, even though monitoring is explicitly intended to assess whether permittees are in compliance with the discharge limits.  “Limiting a permittee’s responsibility to discharges that result from its own operators applies to the appropriate remedy for the violations, not to liability for the violations,” stated the 9th Circuit. 

Permitting authority

The defendants’ position has been explicitly rejected by the California State Water Resources Control Board for the Los Angeles Region (Regional Board), the entity that issued the permit.  “This is important,” says the 9th Circuit, “because one of our obligations in interpreting an NPDES permit is to determine the intent of the permitting authority. . . .”  In a case “nearly identical to this one,” the Regional Board filed an amicus brief in which it stated: 

“The Permit recognizes that the interconnected nature of the system means that it may be difficult to determine exactly where [pollutants] originated within the [LA] MS4. This does not mean, however, that the Permit assumes only one permittee may be responsible.  Instead, it recognizes that in such an integrated storm sewer system, one or more Permittees may have caused or contributed to violations. . . .  Having constructed a joint sewer system that, by design, co-mingles the [Permittees’] discharges, they cannot avoid enforcement because one cannot determine the original source of pollutants in the waste stream.”

The Regional Board also noted that “the monitoring program that the permittees requested (and were granted) does not readily generate the permittee–by–permittee outfall data that the District would require as a precondition to enforcement.”  As a result, the Regional Board disagreed with any construction of the Permit that would require individualized proof of a Permittee’s discharges to establish liability.

“Simply put, the Regional Board indicated that it ‘does not agree’ that the ‘burden [of proving Permit violations] rests upon the enforcing entity,’” says the 9th Circuit.  “Although we do not defer to the Regional Board’s interpretation of the Permit, its rejection of the District Defendants’ position is clearly instructive.”


As the 9th Circuit notes, stormwater runoff is one of the most significant sources of water pollution in the nation, at times producing effects more detrimental to the environment than contamination from industrial and sewage sources.  As such, this case will probably be central to how environmental agencies use their permitting authority under the CWA to regulate stormwater discharges from currently unregulated sources, similar to the small municipalities that discharge into LA District’s MS4.  The 9th Circuit’s opinion returns the case to the point where it started—the District Court, which may, or may not, have the final word in this important debate on MS4 permitting.

NRDC v. Los Angeles County  Flood Control District

William C. Schillaci