ON WRITS OF CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE TENTH CIRCUIT. ON WRITS OF CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE TENTH CIRCUIT
Stevens, J., delivered the opinion for a unanimous Court.
JUSTICE STEVENS delivered the opinion of the Court.
Pursuant to the Clean Water Act, 86 Stat. 816, as amended, 33 U.S.C. § 1251, et seq., the Environmental Protection Agency (EPA) issued a discharge permit to a new point source in Arkansas, about 39 miles upstream from the Oklahoma state line. The question presented in this litigation is whether the EPA's finding that discharges from the new source would not cause a detectable violation of Oklahoma's water quality standards satisfied the EPA's duty to protect the interests of the downstream State. Disagreeing with the Court of Appeals, we hold that the Agency's action was authorized by the statute.
In 1985, the City of Fayetteville, Arkansas, applied to the EPA, seeking a permit for the City's new sewage treatment plant under the National Pollution Discharge Elimination System (NPDES). After the appropriate procedures, the EPA, pursuant to § 402(a)(1) of the Act, 33 U.S.C. § 1342(a)(1), issued a permit authorizing the plant to discharge up to half of its effluent (to a limit of 6.1 million gallons per day) into an unnamed stream in northwestern Arkansas.*fn1 That flow passes through a series of three creeks for about 17 miles, and then enters the Illinois River at a point 22 miles upstream from the Arkansas-Oklahoma border.
The permit imposed specific limitations on the quantity, content, and character of the discharge and also included a number of special conditions, including a provision that if a study then underway indicated that more stringent limitations were necessary to ensure compliance with Oklahoma's water quality standards, the permit would be modified to incorporate those limits. App. 84.
Respondents challenged this permit before the EPA, alleging, inter alia, that the discharge violated the Okla-homa water quality standards. Those standards provide that no degradation [of water quality] shall be allowed" in the upper Illinois River, including the portion of the River immediately downstream from the state line.*fn2
Following a hearing, the Administrative Law Judge (ALJ) concluded that the Oklahoma standards would not be implicated unless the contested discharge had something more than a mere de minimis impact" on the State's waters. He found that the discharge would not have an undue impact" on Oklahoma's waters and, accordingly, affirmed the issuance of the permit. App. to Pet. for Cert. in No.90-1262, pp. 101a-103a (emphasis deleted).
On a petition for review, the EPA's Chief Judicial Officer first ruled that § 301(b)(1)(C) of the Clean Water Act requires an NPDES permit to impose any effluent limitations necessary to comply with applicable state water quality standards."*fn3 Id., at 116a-117a. He then held that the Act and EPA regulations offered greater protection for the downstream State than the ALJ's undue impact" standard suggested. He explained the proper standard as follows:
[A] mere theoretical impairment of Oklahoma's water quality standards -- i.e., an infinitesimal impairment predicted through modeling but not expected to be actually detectable or measurable -- should not by itself block the issuance of the permit. In this case, the permit should be upheld if the record shows by a preponderance of the evidence that the authorized discharges would not cause an actual detectable violation of Oklahoma's water quality standards." Id., at 117a (emphasis in original).
On remand, the ALJ made detailed findings of fact and concluded that the City had satisfied the standard set forth by the Chief Judicial Officer. Specifically, the ALJ found that there would be no detectable violation of any of the components of Oklahoma's water quality standards. Id., at 127a-143a. The Chief Judicial Officer sustained the issuance of the permit. Id., at 145a-153a.
Both the petitioners in No. 90-1262 (collectively Arkansas) and the respondents in this litigation sought judicial review.*fn4 Arkansas argued that the Clean Water Act did not require an Arkansas point source to comply with Oklahoma's water quality standards. Oklahoma challenged the EPA's determination that the Fayetteville discharge would not produce a detectable violation of the Oklahoma standards.
The Court of Appeals did not accept either of these arguments. The court agreed with the EPA that the statute required compliance with Oklahoma's water quality standards, see 908 F.2d 595, 602-615 (CA10 1990), and did not disagree with the Agency's determination that the discharges from the Fayetteville plant would not produce a detectable violation of the those standards. Id., at 631-633. Nevertheless, relying on a theory that neither party had advanced, the Court of Appeals reversed the Agency's issuance of the Fayetteville permit. The court first ruled that the statute requires that where a proposed source would discharge effluents that would contribute to conditions currently constituting a violation of applicable water quality standards, such [a] proposed source may not be permitted." Id., at 620. Then the court found that the Illinois River in Oklahoma was already degraded," that the Fayetteville effluent would reach the Illinois River in Oklahoma, and that that effluent could be expected to contribute to the ongoing deterioration of the scenic [Illinois R]iver" in Oklahoma even though it would not detectably affect the River's water quality. Id., at 621-629.
The importance and the novelty of the Court of Appeals' decision persuaded us to grant certiorari. 499 U.S. (1991). We now reverse.
Interstate waters have been a font of controversy since the founding of the Nation. E. g., Gibbons v. Ogden, 9 Wheat. 1 (1824). This Court has frequently resolved disputes between States that are separated by a common river, see, e. g., Ohio v. Kentucky, 444 U.S. 335 (1980), that border the same body of water, see, e. g., New York v. New Jersey, 256 U.S. 296 (1921), or that are fed by the same river basin, see, e. g., New Jersey v. New York, 283 U.S. 336 (1931).
Among these cases are controversies between a State that introduces pollutants to a waterway and a downstream State that objects. See, e. g., Missouri v. Illinois, 200 U.S. 496 (1906). In such cases, this Court has applied principles of common law tempered by a respect for the sovereignty of the States. Compare id., at 521, with Georgia v. Tennessee Copper Co., 206 U.S. 230, 237 (1907). In forging what may not improperly be called interstate common law," Illinois v. Milwaukee, 406 U.S. 91, 105-106 (1972) (Milwaukee I), however, we remained aware that new federal laws and new federal regulations may in time pre-empt the field of federal common law of nuisance." Id., at 107.
In Milwaukee v. Illinois, 451 U.S. 304 (1981) (Milwaukee II), we held that the 1972 Amendments to the Federal Water Pollution Control Act did just that. In addressing Illinois' claim that Milwaukee's discharges into Lake Michigan constituted a nuisance, we held that the comprehensive regulatory regime created by the 1972 Amendments pre-empted Illinois' federal common law remedy. We observed that Congress had addressed many of the problems we had identified in Milwaukee I by providing a downstream State with an opportunity for a hearing before the source State's permitting agency, by requiring the latter to explain its failure to accept any recommendations offered by the downstream State, ...