concurring:
I agree with my colleagues that the petition for review should be granted because the EPA’s construction of the 1990 Clean Air Amendments is not acceptable. But I do not agree that Congress directly addressed the precise issue presented. The language of the relevant provisions is, at least in part, ambiguous, which requires us to proceed to Chevron’s second step and ask whether the agency’s construction is a permissible or reasonable one. Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837, 843, 104 S.Ct. 2778, 2782, 81 L.Ed.2d 694 (1984). It is sometimes thought that Chevron really imposes only a one step analysis — that if the statutory language is ambiguous, affir *94manee of the agency's interpretation is a foregone conclusion. I believe that notion misreads the “plain language” of the Chevron opinion (if I may be pardoned the pun), Chevron, 467 U.S. at 842-43, 104 S.Ct. at 2781-82; which has troublesome consequences. Judges who accept that premise explicitly or implicitly can be led to find clarity in an ambiguous statute in order to avoid Chevron's second step. To be sure, there are relatively few cases in which a reviewing court has held an agency’s interpretation of ambiguous language unreasonable, see, e.g., Public Employees Retirement Sys. v. Betts, 492 U.S. 158, 171, 175, 109 S.Ct. 2854, 2863, 2865, 106 L.Ed.2d 134 (1989); Abbott Laboratories v. Young, 920 F.2d 984, 988 (D.C.Cir.1990), cert. denied, 112 S.Ct. 76 (1991); but that is all the more reason, in my view, to be careful in identifying those cases when they arise. This is such a case.
As the majority opinion ably demonstrates, prior to the 1990 Clean Air Amendments it was exceedingly doubtful whether the EPA had the authority to “stay” a proposed regulation establishing emission standards. With that backdrop, Congress, in the 1990 Amendments, focused on the general problem of the regulation of radionuclide emissions by both the Nuclear Regulatory Commission, which licenses nuclear facilities, and the EPA.
Section 112(d)(9) looks to the future and sets forth the procedure and standards the EPA Administrator must use in determining whether to promulgate new regulations for facilities regulated by the NRC:
No standard for radionuclide emissions from any category or subcategory of facilities licensed by the Nuclear Regulatory Commission (or an Agreement State) is required to be promulgated under this section if the Administrator determines, by rule, and after consultation with the Nuclear Regulatory Commission, that the regulatory program established by the Nuclear Regulatory Commission pursuant to the Atomic Energy Act [42 U.S.C.A. § 2011 et seq.] for such category or subcategory provides an ample margin of safety to protect the public health. Nothing in this subsection shall preclude or deny the right of any State or political subdivision thereof to adopt or enforce any standard or limitation respecting emissions of radionuclides which is more stringent than the standard or limitation in effect under section 7411 of this title or this section.
42 U.S.C. § 7412(d)(9) (West Supp.1992). If the Administrator is inclined to defer to the NRC’s regulations, § 112(d)(9) obliges him to proceed by rule to allow interested parties to comment. That provision also requires him to assume the responsibility of making formally the sobering determination that the NRC’s regulation promises an “ample ” margin of safety to protect the public health.
Section 112(q), on the other hand, entitled “Savings provision,” is directed to past EPA regulatory proceedings. Paragraph (4) of that section is specifically directed to medical facilities:
[N]o standard promulgated under this section prior to November 15, 1990 with respect to medical research or treatment facilities shall take effect for two years following November 15, 1990, unless the Administrator makes a determination pursuant to a rulemaking under section 7412(d)(9) of this title. If the Adminis- . trator determines that the regulatory program established by the Nuclear Regulatory Commission for such facilities does not provide an ample margin of safety to protect public health, the requirements of section 7412 of this title shall fully apply to such facilities. If the Administrator determines that such regulatory program does provide an ample margin of safety to protect the public health, the Administrator is not required to promulgate a standard under this section for such facilities, as provided in section 7412(d)(9) of this title.
42 U.S.C. § 7412(q)(4) (West Supp.1992). As is apparent, Congress was so concerned about the dual regulation of medical facilities that it imposed a two-year stay itself on the EPA’s regulations covering those facilities that had been promulgated, but were not yet effective. If the Administrator determined by rule that the NRC regu*95lations provided an “ample margin of safety,” EPA’s standards would never become effective. In the meantime (but not to exceed two years), while the Administrator was pondering that question, Congress mandated a stay on the promulgated regulations. The EPA, in effect, wishes to extend similar treatment to non-medical facilities.
The majority concludes that application of the common sense maxim of statutory construction expressio unius est exclusio alterius indicates that the EPA Administrator did not have authority to impose a stay on promulgated, but not yet effective, regulations applying to anything other than medical facilities. Although I favor the maxim as an aid to statutory construction, see Michigan Citizens for an Indep. Press v. Thornburgh, 868 F.2d 1285, 1292-93 (D.C.Cir.1989), aff'd by an equally divided court, 493 U.S. 38, 110 S.Ct. 398, 107 L.Ed.2d 277 (1989) (per curiam), I think my colleagues stretch it a bit too far here. Paragraph (4) does not speak about the Administrator’s discretion to grant a stay. If it did, the majority would be on firmer ground. Instead, it refers to a stay mandated by Congress for medical facilities, and, therefore, does not preclude clearly the Administrator from exercising his discretion to grant a stay regarding other facilities. That is not to say paragraph (4) is irrelevant; it is only to say that it is not dispositive. See, Silberman, Chevron — The Intersection of Law & Policy, 58 Geo. Wash.L.Rev. 821, 827 (1990) (“Of course the Step I analysis informs a court’s approach to the second step”).
Furthermore, paragraph (1) of that section directly addresses regulations promulgated (but not yet effective) other than those directed at medical facilities:
Any standard under this section in effect before the date of enactment of the Clean Air Act Amendments of 1990 shall remain in force and effect after such date unless modified as provided in this section before the date of enactment of such Amendments or under such Amendments. Except as provided in paragraph (4), any standard under this section which has been promulgated, but has not taken effect, before such date shall not be affected by such Amendments unless modified as provided in this section before such date or under such Amendments.
42 U.S.C. § 7412(q)(1) (West Supp.1992) (emphasis added).
Congress, by using the emphasized words, certainly would appear to have addressed specifically the regulations which are at issue in this case. The difficulty arises because of the ambiguity of the phrase: “unless modified as provided in this section.” That language could not refer to paragraph (4) dealing with medical facilities, because the sentence starts with the phrase “except as provided in paragraph (4).” In other words, the emphasized sentence would appear to contemplate that promulgated, but not yet effective, standards (other than those applying to medical facilities), could be modified pursuant to another subsection of § 112.1
The only other subsection of § 112 that either petitioner or respondent point to as arguably relevant is subsection (d)(9). But that subsection speaks only to the Administrator’s authority before promulgation, so facially it appears inapplicable. The ambiguity thus created is whether or not a promulgated regulation can be stayed pursuant to subsection (d)(9).2 Petitioner assumes arguendo that the EPA can use that subsection for that purpose, but only if it follows the procedures the Administrator would use if he did not wish to promulgate the regulation in the first place. Thus, according to petitioner, the Administrator *96must proceed by rulemaking to grant a stay, and he must determine before issuing a stay that the regulatory program established by the NRC provides an ample margin of safety for the public.
The EPA, on the other hand, would use the ambiguity to reshape subsection (d)(9) to allow the agency to grant a stay without adopting a rule and without making the determination called for in that subsection. I think that interpretation is flatly unreasonable. It fails the second step of Chevron because the agency seeks to exploit the ambiguity rather than to resolve it, and to advance its own policy objectives rather than Congress’.
The agency’s interpretation does not fit within the statute’s structure. If the agency were authorized to use subsection (d)(9) to stay regulations already promulgated, but not yet effective (which I think is a reasonable although not obvious interpretation), it is implausible to claim that the Administrator is not obliged to make the same determination as to public safety (by rule) that he would be required to make before promulgation. The Administrator must take subsection (d)(9) as he finds it, not as he would refashion it.
The EPA argues that its interpretation is justified because rulemaking imposes no compliance costs in the pre-promulgation period. In the post-promulgation period, by contrast, stay authority is needed to prevent unnecessary regulations from forcing higher compliance costs during the rulemaking process. The EPA’s argument, although it may reflect sound policy, is not well-grounded in the legislation. The statutory language focuses on providing the public with an ample margin of safety, not on avoiding double regulation. While Congress did not insist on dual regulation, the language it chose makes it rather obvious that it preferred to risk overregulation rather than underregulation.
The only exception to that general policy is embodied in paragraph (4), where Congress limited the mandatory stay it imposed to two years. During that time the Administrator must make the public safety determination — and the determination again must be made by rule. It seems to me quite anomalous to argue that Congress intended to authorize the Administrator to issue stays of other promulgated regulations without the openness of rule-making, without making a determination of public safety, and with no apparent limit to the stay.
In sum, I believe that a careful reading of the statute, allowing for its ambiguities, reveals that the EPA’s interpretation is unreasonable.
. I do not understand the majority’s statement, that while § 112(q)(1)’s "modified as provided in this section” is "imprecise, the EPA does not claim that any of the standards has been modified.” Maj.Op. at 93. The agency argues that it has the right to modify a standard by using the procedures defined in other provisions of § 112 — particularly subsection 112(d)(9) — and that the authority to stay the promulgated regulation is such a "modification.”
. The EPA does not point to any legislative history which shows that Congress intended to grant this authority free from the requirements of rulemaking.