Natural Resources Defense Council, Inc. v. County of Los Angeles, 725 F.3d 1194

Stormwater runoff from Los Angeles County MS4 discharges into navigable waters; District monitoring data shows multiple exceedances of water quality standards.
Plaintiffs NRDC and Baykeeper allege permit violations under the CWA arising from County Defendants’ MS4 discharges; district court granted summary judgment to defendants.
On appeal, the Ninth Circuit previously reversed in part, then the Supreme Court reversed and remanded; on remand, the Ninth Circuit reconsidered the liability issue.
The district court had held that liability required proof that pollutants actually passed through a defendant’s specific outfall; data from monitoring stations downstream was insufficient.
The Ninth Circuit now holds that pollutant exceedances detected by mass-emissions monitoring at downstream stations can establish liability for permit violations under the permit, remanding for remedy assessment.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether monitoring data alone proves liability under the permit	NRDC/Baykeeper rely on monitoring data to show permit violations	County Defendants argue data cannot attribute exceedances to any specific permittee	Yes; monitoring data can establish liability
Whether the permit’s language allows using mass-emissions data to assess compliance	Data assess compliance with Part 2 of the Permit	Mass-emissions monitoring not intended to measure individual permittee compliance	Yes; mass-emissions data assess compliance and support liability
Whether the clause stating each permittee is responsible only for its own discharges precludes liability from joint sources	Reading favors liability based on shared system monitoring	Clause limits liability to operator discharges	No; interpretation should assign monitoring data a remedial, system-wide meaning for liability
Whether the court may reconsider its prior position on remand given finality concerns	Panel may reconsider prior ruling	Decision may be final and law of the case	Yes; judgment not final until mandate issues; court may reconsider on remand
Whether permit shield bars liability when discharges comply with permit terms	Liability arises from exceedances regardless of permit compliance	Shield protects from liability if compliance with permit is shown	Remand for remedy; the data showing exceedances supports liability consistent with permit interpretation

Arkansas v. Oklahoma, 503 U.S. 91 (1992) (authority on NPDES permit delegation and compliance)
S. Fla. Water Mgmt. Dist. v. Miccosukee Tribe of Indians, 541 U.S. 95 (2004) (discharge within same water body not a CWA discharge)
Nw. Envtl. Advocates v. City of Portland, 56 F.3d 979 (9th Cir. 1995) (permit obligations and data considerations under CWA)
Piney Run Pres. Ass’n v. Cnty. Comm’rs of Carroll Cnty., 268 F.3d 255 (4th Cir. 2001) (permit shield and contract-like interpretation)
In re Crystal Props., Ltd., L.P., 268 F.3d 743 (9th Cir. 2001) (interpretation of contract-like permit provisions)
Klamath Water Users Protective Ass’n v. Patterson, 204 F.3d 1206 (9th Cir. 1999) (interpretation of permit terms and obligation to give effect to all provisions)
L.A. Cnty. Flood Control Dist. v. Natural Res. Def. Council, 133 S. Ct. 23 (2012) (Supreme Court on whether discharge from one part of a river to another part is a pollutant discharge)
Mastrobuono v. Shearson Lehman Hutton, Inc., 514 U.S. 52 (1995) (contract interpretation principles)
City of Burbank v. State Water Res. Control Bd., 108 P.3d 862 (Cal. 2005) (state-law framework for basin plans and water quality objectives)