Among the many big cases awaiting decision from the Supreme Court are Rapanos v. United States and Carabell v. U.S. Army Corps of Engineers - two companion cases that challenge the scope of federal regulatory jurisdiction under the Clean Water Act (CWA). Argued in February (on Justice Alito's first day), decisions are expected soon. According to some, the future of water pollution control is at risk. Such hyperbole aside -- and it is hyperbole -- these two cases are easily the most important environmental cases of the term and merit close attention. (I previewed both in an NRO column here; the "Rapanos blog" is here.)

The CWA applies to all "navigable waters of the United States" (which the Act defines simply as "waters of the United States"). As interpreted in prior cases, this jurisdiction extends to cover wetlands adjacent to navigable waterways (but does not reach isolated, intrastate waters). At issue in each case is how far the CWA's jurisdiction extends beyond navigable waters and adjacent wetlands, specifically whether the Act applies to wetlands adjacent or hydrologically connected to tributaries of navigable waters. In one case, the wetlands are adjacent to a ditch that drains into a creek that in turn drains into a tributary that is connected to a navigable waterway many miles away. In the other, the wetland is directly adjacent to a tributary, but it is hydrologically separated by a man-made berm.

The federal government argues that jurisdiction under the CWA extends to all wetlands with any hydrological connection to navigable waters, no matter how small or insignificant. "One drop" is enough, according to Solicitor General Paul Clement at oral argument. Rapanos' attorneys at the Pacific Legal Foundation make an equally ambitious argument, that the CWA does not apply past those wetlands truly adjacent to navigable waters -- and that if it did it would press against the limits of the federal government's Commerce Clause power.

Either argument, taken to its fullest extent, would have significant repercussions. Yet the Supreme Court is unlikely to accept either side's case in unadulterated form. While there are four justices who seem willing to adopt the government's position, I doubt they could get a fifth vote without making some concessions. On the other side, I also doubt there are five votes to curtail federal regulations as far as PLF suggests -- particularly since such an amibitious claim is not necessary for either petitioner to prevail on his underlying claim.

In the end, more important than who "wins" this case -- the government or the petitioners -- is how either side wins. In these cases, the devil will be in the details. For instance, the Court could side for the petitioners and remand their cases, yet do so on such narrow terms that they are certain to lose again in the lower courts. The Court could also side for the government largely by deferring to agency expertise without swallowing the heart of the government's argument (and without resolving some of the legal uncertainty that led to these cases in the first place). In other words, how they win is more important than who wins. We'll know soon . . . perhaps as early as today Thursday, when the Court is expected to next issue opinions.