While it sometimes is difficult to discern the immediate effects of any Supreme Court decision, there can be no dispute that the Court's rulings often lead to fundamental changes in the law and broader impacts to society. Consider last term's decision on the constitutionality of the Affordable Care Act and its far-reaching effect on the powers of the federal government.

In early December, the Court is scheduled to hear two cases involving EPA's authority under the Clean Water Act, and these cases promise to set the stage for EPA's regulatory emphasis under the Act for years to come.

We've seen this story before. The Court's environmental decisions in recent years have caused EPA and businesses to shift their focus to new and emerging environmental issues. In Massachusetts v. EPA, 549 U.S. 497 (2007), for example, the Court's holding that the Clean Air Act authorized EPA to regulate greenhouse gas emissions gave birth to an entirely new regulatory program seeking to control such emissions. In American Electric Power v. Connecticut, 131 S. Ct. 2527 (2011), the Court's conclusion—that the Clean Air Act displaced federal common law nuisance claims challenging emissions of greenhouse gas emissions—has cut short what promised to be a spate of climate change tort suits against businesses emitting greenhouse gases. And, in Sackett v. EPA, 132 S. Ct. 1367 (2012), the Court's holding that Clean Water Act administrative compliance orders were final agency action and thus judicially reviewable has already affected EPA's use of administrative orders under many of the statutes that it administers. These decisions thus have resulted in monumental changes in the environmental regulatory landscape.

The two Clean Water Act cases the Court is considering this term could lead to similar changes in EPA's priorities. The first case, Decker v. Northwest Environmental Defense Center, which was consolidated with Georgia-Pacific West, Inc. v. Northwest Environmental Defense Center, involves the issue of whether storm-water runoff from logging roads requires a discharge permit. Previously, the Ninth Circuit dismissed EPA's well-established interpretation that its regulations and the Clean Water Act exempt such runoff from the Act's permitting program, and instead held that runoff from logging roads needs to be permitted.

While it is possible that the Court could avoid the issue entirely by finding the challenge to EPA's interpretation untimely, a decision on the merits could help to define the extent to which EPA can exempt various activities and other wet-weather discharges from the Act's permitting program. This is particularly important given that wet-weather discharges like those at issue in Decker are a regulatory and enforcement priority for EPA and environmental advocacy groups.

The second case, Los Angeles County Flood Control District v. Natural Resources Defense Council, also involves a Ninth Circuit decision regarding wet-weather discharges. This case addresses Los Angeles County's municipal separate storm sewer and raises the issue of whether the flow of contaminated water from one portion of a river through a concrete-lined municipal separate storm sewer system into a lower portion of the same waterway constitutes a "discharge" that requires a Clean Water Act permit. While the matter is of obvious interest to municipalities and other public authorities responsible for managing municipal separate storm sewers, the case has broader implications for the regulated community because it could affect the scope of the Clean Water Act's control over storm-water and other wet-weather discharges.

An interesting aspect of these cases is that they reflect a broader trend of environmental advocacy groups driving EPA's regulatory agenda. Both cases involve enforcement actions brought by environmental groups and, in both instances, the Court granted certiorari in the face of opposition by EPA and the Solicitor General. Moreover, there are numerous other examples of citizen groups bringing enforcement actions where EPA has not, or where the groups sued EPA to demand that the Agency issue new regulations. We can expect that these groups will continue to use litigation to push their issues and thus impact how EPA allocates its limited resources.