MS4 Permittees are Liable for Clean Water Act Violations as a Matter of Law When Mass Monitoring Showed Exceedances

Natural Resources Defense Council, Inc., et al., v. County of Los Angeles, et al.

2013 DJDAR 10619

In a recent decision, the Ninth Circuit Court of Appeal ruled that pollution exceedances at mass-monitoring stations at the Los Angeles and San Gabriel Rivers conclusively established Los Angeles County’s liability for Clean Water Act violations, although the source of pollutants was not known.

The case involved the County’s municipal storm sewer system (“MS4”). The MS4 collects stormwater from all over the county, which is routed into various channels, including the Los Angeles and San Gabriel Rivers before entering the Santa Monica Bay. After results from seven mass-monitoring stations recorded 140 exceedances of pollutants between 2002 and 2008, environmental groups brought a citizen-suit alleging violations of Section 301(a) of the CWA and the terms of the County’s MS4 Permit.

The County defendants presented two arguments. First, they maintained that the mass-emissions monitoring data was not intended to measure the compliance of any individual permittee, since it could not irrefutably identify whose discharge caused the exceedances. Second, they contended they could not be held liable for the water quality violations, as the monitoring sites sample pollution levels downstream from a myriad of outfalls, controlled by numerous permittees.

The Ninth Circuit found the County’s position to be inconsistent with the terms of the MS4 permit. The court examined the language of permit and found it established a monitoring program with the objective to characterize discharges and assess water quality standards. Ultimately, the court rejected defendants’ arguments, as they would render the monitoring provisions of the permit pointless if the monitoring results could not be used to establish a violation.

The court drew a distinction, however, between liability for violations, and the appropriate remedy for the violations. The court noted that an MS4 permittee was responsible only for those discharges “for which it is the operator.” This according to the court, guided the remedy to be determined for each permittee, which presumably would take into account facts showing that a permitte did not cause or contribute to an exceedance.

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