198 F.3d 275 (D.C. Cir. 1999)
American Petroleum Institute and National Petrochemical & Refiners Association, Petitionersv.U.S. Environmental Protection Agency and Carol M. Browner, Administrator, U.S. Environmental Protection Agency, RespondentsValero Energy Corporation, Intervenor
No. 98-1561
United States Court of AppealsFOR THE DISTRICT OF COLUMBIA CIRCUIT
Argued October 26, 1999Decided January 4, 2000

On Petition for Review of an Order of the Environmental Protection Agency
Michael F. McBride argued the cause for petitioners. With him on the briefs were Bruce W. Neely, G. William  Frick, John E. Reese and Maurice H. McBride.
Mary F. Edgar, Attorney, U.S. Department of Justice,  argued the cause for respondents. With her on the brief was  Lois J. Schiffer, Assistant Attorney General, and John T.  Hannon, Attorney, Office of General Counsel, U.S. Environmental Protection Agency.  Christopher S. Vaden, Attorney,  U.S. Department of Justice, entered an appearance.
Sam Kalen and Howard Bleichfeld were on the brief for  intervenor.
Before:  Silberman, Williams and Randolph, Circuit  Judges.
Opinion for the Court filed by Circuit Judge Williams.
Williams, Circuit Judge:


1
Automobile engines emit volatile  organic compounds ("VOCs"), which together with nitrogen  oxides ("NOX") form ozone.  Reformulated gasoline ("RFG")  can reduce VOCs emissions compared to levels associated  with ordinary gasoline;  but it costs more, and there is some  concern about the nation's current RFG production capacity. See 42 U.S.C. § 7545(k)(6)(B) (1994) (creating special provisions that operate in the event of insufficient capacity).  In  guiding the efforts of the Environmental Protection Agency  to limit ozone concentrations, Congress in the Clean Air Act  (the "Act") authorized limited reliance on RFG.  It directed  that RFG should initially be mandatory in the nine worst  ozone areas with populations over 250,000, with any area later  classified as "Severe" to be added as well.  See 42 U.S.C.  § 7545(k)(1), (5), (10)(D).  And it also provided for "opt-in,"  i.e., for election by a state to demand an EPA ban on the sale  of non-RFG in specified areas.  But Congress carefully limited the eligible areas:


2
Upon the application of the Governor of a State, the Administrator shall apply the prohibition [on the sale of non-reformulated gasoline] in any area in the State classified ... as a Marginal, Moderate, Serious, or Severe Area....


3
Act § 211(k)(6)(A), 42 U.S.C. § 7545(k)(6)(A) (emphasis added).  There is a fifth category, "Extreme," to which only Los  Angeles belongs;  there was no need to include that category because it was automatically covered by Congress's direct  mandate.


4
Apart from Los Angeles, most areas of the United States  that are not in "attainment" for EPA's ozone standards  belong to one of the four specified categories.  But for several  reasons--mainly the interaction between Congress's (1) rules  limiting the ability of a nonattainment area to break into the  broad sunlit uplands of attainment, and (2) provisions governing the treatment of missing data--an area may be in "nonattainment" but not in any of the four specified classes.  In  interpreting the opt-in provision EPA decided that Congress  meant to include not only "Marginal, Moderate, Serious, or  Severe" areas, but also any other areas that either were  currently out of attainment or had ever been.  The American  Petroleum Institute ("API") has petitioned for review of the  rule, arguing that the agency exceeded its statutory authority;  we agree.


5
* * *


6
The Act requires EPA to establish and periodically revise a  primary national ambient air quality standard ("NAAQS") for  each air pollutant that the agency identifies as meeting  certain criteria.  See 42 U.S.C. §§ 7408-7409.  The primary  NAAQS for each pollutant is the maximum concentration  "requisite to protect the public health" with "an adequate  margin of safety."  42 U.S.C. § 7409(b)(1).  In 1979 the EPA  administrator set a primary NAAQS for ozone at 0.120 parts  per million ("ppm"), averaged over intervals of one hour.  See  44 Fed. Reg. 8202.  That level was upheld by this court in  American Petroleum Inst. v. Costle, 665 F.2d 1176 (D.C. Cir.  1981), and remains in effect today.1


7
In approaching this case the most critical distinction is  between "nonattainment" and "design value" as measures of  compliance.  A maximum concentration, without more, leaves  open the question of how often an area's hourly reading can  exceed 0.120 ppm without causing the area to be out of  compliance.  Congress adopted EPA's answer to this question.  It decreed, "by operation of law," that each area's  attainment status would be based on the regulatory standards  "in effect immediately before November 15, 1990."  42 U.S.C.  § 7407(d)(1)(C).  Under those standards (also still in effect),  an area is allowed no more than one day a year in which its  maximum hourly ozone concentration is greater than 0.120  ppm.  But the exact formula is more complicated because it  recognizes that many areas will not have data for every hour  of the year;  it therefore uses estimates to fill this gap.  See  40 CFR pt. 50, App. H.  The formula generates an "expected  number of days per calendar year with maximum hourly  average concentrations above 0.12 parts per million," id.  § 50.9(a), and if the expected number of exceedances for a  three-year period is greater than one, the area is in nonattainment.


8
In 1990 Congress also introduced, for ozone, a refinement  based on how far each nonattainment area was from attainment status, establishing different dates for compliance according to the severity of the existing violations.  See 42  U.S.C. § 7511(a)(1).  To group areas according to the various  deadlines, Congress used a concept already in use by EPA,  known as "design value," and once again adopted EPA's  method for calculating this number.  See id. ("The design  value shall be calculated according to the interpretation methodology issued by the Administrator most recently before  November 15, 1990.").  Much like the calculation of attainment, EPA's method for determining design values also excuses one exceedance per year (e.g., the first three exceedances in a three-year period have no effect on the design  value).  But it has no mechanism for generating data to fill gaps in monitoring:  Here, the design value is simply the  fourth-highest daily maximum ozone concentration in an area  over three consecutive years for which there are sufficient  data.  See American Trucking Ass'ns v. EPA, 175 F.3d 1027,  1046 n.6 (D.C. Cir. 1999) ("ATA"), modified on reh'g, 195 F.3d  4 (D.C. Cir. 1999);  EPA, The Clean Air Act Ozone Design  Value Study:  Final Report 1-3 to 1-5 (1994).


9
In § 181(a)(1) of the Act Congress used design value to  create five categories of nonattainment, with varying compliance deadlines for each category:


10
                        Margina                 l0.121 to 0.138 ppm
                        Moderate                0.138 to 0.160 ppm
                        Serious                 0.160 to 0.180 ppm
                        Severe                  0.180 to 0.280 ppm
                        Extreme                 0.280 ppm and above


11
See 42 U.S.C. § 7511(a)(1) tbl.1.  But because Congress  treated missing data differently for purposes of design value  and attainment status, while every area with a known design  value above 0.120 ppm is in nonattainment, an area may be in  nonattainment even though its design value is 0.120 ppm or  below.  EPA called such areas "submarginal."  See 56 Fed.  Reg. at 56,697/2 (1991).


12
Similarly, § 107(d)(1)(C)(i) of the Act, 42 U.S.C.  § 7407(d)(1)(C)(i), requires areas designated nonattainment  under portions of the previous standards, see 42 U.S.C.  § 7407(d)(1)(C) (adopting provisions of the Clean Air Act  Amendments of 1977, § 103, Pub. L. No. 95-95, 91 Stat. 685,  687-88), to remain so classified because of inadequate data .EPA called such areas "incomplete data areas."  56 Fed. Reg.  at 56,697/3;  cf. 42 U.S.C. § 7511e (allowing areas that can  demonstrate compliance with the ozone NAAQS for the years  1987-89 to have a special, "transitional," status).


13
The key issue here is the application of the RFG program  to these two types of areas, "submarginal" and "incomplete  data."


14
*  *  *


15
In the disputed rule, EPA stated that any "area currently  or previously designated as a nonattainment area for ozone  under 40 CFR 50.9 ... or any time later, may be included on  petition of the governor."  40 CFR § 80.70(k);  63 Fed. Reg.  at 52,104.  Largely because of the divergence between the  concepts of nonattainment and design value, this rule swept  into "opt-in" a variety of areas not belonging to the four  categories specified by Congress--Marginal, Moderate, Serious or Severe.  We assess the validity of the rule under the  familiar two-step process in Chevron U.S.A. Inc. v. NRDC,  467 U.S. 837, 842-43 & nn.9 & 11 (1984).


16
Chevron requires us to determine whether Congress spoke  "to the precise question at issue."  Id. at 842.  It is hard to  imagine how Congress could have done so more clearly. Acting within a universe where nonattainment and the four  categories overlap but are distinct, Congress chose the four  categories.  If it meant to express "nonattainment," its wording was not merely a long-winded but a positively obtuse way  of doing so.  As we said in Michigan Citizens for an Independent Press v. Thornburgh, 868 F.2d 1285 (D.C. Cir.), aff'd  by an equally divided court, 493 U.S. 38, 39 (1989), if Congress makes an explicit provision for apples, oranges and  bananas, it is most unlikely to have meant grapefruit.  Id. at  1293.


17
Despite the text, EPA argues that the scope of § 211(k)(6)  is ambiguous, thus opening the door to "reasonable" interpretations by EPA.  It notes that § 181(a)(1) of the Act states  that "[e]ach area designated nonattainment for ozone ...  shall be classified at the time of such designation ... as a  Marginal Area, a Moderate Area, a Serious Area, a Severe  Area, or an Extreme Area based on the design value for the  area."  42 U.S.C. § 7511(a)(1).  From this it infers that,  despite the different methods for calculating design value and  attainment status, Congress thought that no nonattainment  area would be classified as other than Marginal, Moderate,  Serious, Severe, or Extreme, and thus the reference to the  first four categories in § 211(k)(6) was Congress's way of making the RFG program available to all nonattainment  areas.  Because § 211(k)(6) does not prohibit the inclusion of  nonattainment areas with design values below 0.121 or areas  whose design values are unknown, EPA argues, it is at least  ambiguous as to whether they may join.


18
EPA seems to think that the possibility that Congress was  unaware of the nonattainment-design value divergence suggests that, had it been aware, it might have wanted EPA to  allow nonattainment areas with incomplete data or design  values below 0.121 ppm to require RFG.  There are two  problems here:  the assumption of congressional ignorance is  farfetched, and even if correct would not get EPA where it  wants to go.


19
In the normal case Congress is assumed to be conscious of  what it has done, especially when it chooses between two  available terms that might have been included in the provision in question.  See BFP v. Resolution Trust Corp., 511  U.S. 531, 537 (1994) ("[I]t is generally presumed that Congress acts intentionally and purposely when it includes particular language in one section of a statute but omits it in  another.").  Sometimes (e.g., where the pieces of legislation  are not closely linked in either codification or time of enactment) this assumption may be a stretch, justifiable in part  because its effect is to push toward coherent interpretations  of law.  See West Virginia Univ. Hosps., Inc. v. Casey, 499  U.S. 83, 100 (1991).  But here the assumption that Congress  was aware of the law is sound:  the divergence between  nonattainment and design value is the direct product of  distinctive definitions explicitly adopted by Congress.  To  suppose that Congress was ignorant of the divergence is to  impute sleepwalking to the legislators.


20
We have already explained how Congress expressly  adopted differing formulae.  These formulae generate the two  problematic categories at issue here.  First, as we recognized  in ATA, the stringent criteria for changing an area's designation from nonattainment to attainment ensures that there can  and will be nonattainment areas with design values below 0.121 ppm (submarginal areas).  ATA, 175 F.3d at 1047;  42  U.S.C. § 7407(d)(3)(E) (noting that an area cannot be redesignated to attainment status until it shows compliance with the  relevant NAAQS and that the improvement in air quality is  due to permanent and enforceable reductions in emissions).Second, "incomplete data areas" have no hope of leaving  nonattainment until they generate enough data to prove that  they comply with the ozone NAAQS.  See id.  Thus, they  must remain in nonattainment, but can secure the RFG  option if they generate data placing them in the four congressionally specified categories.  Quite sensibly, the literal reading of § 211(k)(6)(A) provides RFG as an option when the  need is clear, and only then.


21
But even the ignorance assumption, were it true, would not  support EPA's inference.  Having used words of art to  describe areas eligible for opt-in, a hypothetically ignorant  Congress would likely have assumed that if some areas  turned up partly resembling the areas it specified--areas out  of attainment but less clearly so--they would not be subject  to RFG in the absence of new congressional action.  More  specifically, even if Congress had thought that, as of 1990, all  nonattainment areas under the 0.120 ozone NAAQS would  have a recorded design value of at least 0.121 ppm, it knew  that the formula for nonattainment status (unlike the fixed  values for design value) was likely to change over time.  EPA  has a continuing obligation to review and revise the NAAQS  every five years, see 42 U.S.C. § 7409(d)(1);  ATA, 175 F.3d  at 1049, and to redesignate attainment status accordingly, see  42 U.S.C. § 7407(d)(1)(B).  In ATA, we noted that Congress  had locked the categories of § 181(a)(1) into place, presumably to avoid having its ozone enforcement scheme administratively overridden by EPA as a result of such revision.  175  F.3d at 1049-50.  The same is true here.  By basing the optin provisions in § 211(k)(6) on the statutorily imposed categories in § 181(a)(1), Congress could limit the scope of the RFG  program to areas that clearly fall within the categories of its  choosing.2


22
On this record we are reluctant even to mention the  legislative history.  "[W]e do not resort to legislative history  to cloud a statutory text that is clear."  Ratzlaf v. United  States, 510 U.S. 135, 147-48 (1994);  see also Sutton v. United  Air Lines, Inc., 119 S. Ct. 2139, 2146 (1999);  United States v.  Bost, 87 F.3d 1333, 1336 (D.C. Cir. 1996).  But it scarcely  helps EPA.  The conference report observed, "States could  elect to have the [RFG] requirements apply in other cities  with ozone pollution problems."  H.R. Conf. Rep. No.  101-952, at 336, reprinted in 1 A Legislative History of the  Clean Air Act Amendments of 1990, at 1449, 1786 (1993)  [hereinafter Leg. Hist.].  But this is said simply to distinguish  the statute's mandate of RFG for specified regions, and  certainly does not claim that every other city with any ozone  pollution would qualify for opt-in.  The floor debates add little  clarity.  True, there are statements of the authors of the  provision in question, and sponsors of the amendments generally, to the effect that "any" or "all" non-mandated ozone  nonattainment areas could join the RFG program;  but none  shows enough attention to the problem presented here to  overcome the plain language of the text.  See Senate Debate  on the Clean Air Act Amendments of 1990 Conference Report, reprinted in 1 Leg. Hist. at 731, 1024;  House Debate on  the Clean Air Act Amendments of 1990 Conference Report,  reprinted in 1 Leg. Hist. at 1177, 1266;  House Debate on  H.R. 3030, reprinted in 2 Leg. Hist. at 2667, 2690.  Interestingly, all the statements contain inaccuracies on another  issue, asserting that the area makes the election, not the state  or governor, a position with no support in the statute.  The  colloquial language of debate is at best a rough guide to the  intricacies of technical statutory wording.


23
Similarly, the Senate and House committee reports that list  the likely classification of nonattainment areas under  § 181(a)(1) do not show that Congress meant to base RFG participation on attainment status.  Both lists classify the  areas according to their design values.  The Senate list does  not even mention attainment status, and is thus no evidence  at all of congressional determination that it should control. See S. Rep. No. 101-228, at 35-37 (1989), reprinted in 5 Leg.  Hist. at 8375-77.  Nor does the House Report speak of  nonattainment.  It uses the looser term "areas violating the  ozone NAAQS" and then lists areas by design value.  H. Rep.  No. 101-490, at 230-32, reprinted in 2 Leg. Hist. at 3254-56.EPA would have us believe that the list demonstrates acceptance of its view that Congress really meant nonattainment  because the table includes two areas, Jacksonville, FL and  Waldo Co., ME, as likely to be classified as marginal areas  despite their design values of only 0.120 ppm.  But the likely  explanation is that the compiler mistakenly thought that  because 0.120 was the cut-off point for "Marginal," an area  with exactly that reading should be so classified.  Moreover,  these lists can shed no light on the proper classification of  areas that lack sufficient data to calculate a design value or  even to confirm their nonattainment status.


24
EPA next argues that even if the text is clear, this case  presents one of the rare instances "in which the literal  application of a statute will produce a result demonstrably at  odds with the intentions of its drafters."  R.G. Johnson Co. v.  Apfel, 172 F.3d 890, 895 (D.C. Cir. 1999) (internal quotations  omitted).  The agency appears to find absurdity because  under the direct reading of the statute it denies opt-in to  some areas with "continuing ozone problems."  But the argument assumes away all trade-offs.  Given the acknowledged  cost and supply drawbacks associated with RFG, it seems  entirely sensible to confine opt-in to areas experiencing nonattainment with the comparative clarity implied by belonging  to one of the four specified categories.  We see no absurdity.


25
EPA offers a special argument under which it could reach  back into history to allow opt-in for an area that once was-but is no longer--classified as Marginal, Moderate, Serious,  or Severe.  The statute allows opt-in for "any area in the  State classified ... as a Marginal, Moderate, Serious, or Severe Area."  As a matter of sheer linguistic possibility,  either of two explicit phrases could be understood to precede  the word "classified":  it could read (1) "any area in the state  [that is presently] classified ... as a Marginal, Moderate,  Serious, or Severe Area," or (2) "any area in the state [that  has ever been] classified as a Marginal, Moderate, Serious, or  Severe Area."  EPA favors the second reading, but it seems  utterly implausible.  If an area is in attainment, its historical  design value has no relationship to its need for RFG.  If it is  in nonattainment, but lacks sufficient data to be classified  under § 181(a)(1), then RFG will be an option if, in the  process of generating sufficient data to prove itself in attainment, it is shown to have a design value of 0.121 ppm or  above.  See 42 U.S.C. § 7407(d)(3)(E).


26
In § 211(k)(6) Congress provided for opt-in only for areas  classified as Marginal, Moderate, Serious or Severe.  It  meant what it said.  Accordingly, API's petition for review is


27
Granted.



Notes:


1
  In 1997 the EPA adopted a revised ozone NAAQS of 0.08 ppm  averaged over an eight-hour period.  See 62 Fed. Reg. 38,856  (1997).  But in American Trucking Ass'ns v. EPA, 175 F.3d 1027,  1038 (D.C. Cir 1999) ("ATA"), modified on reh'g, 195 F.3d 4 (D.C.  Cir. 1999), we granted a petition for review of that order and  remanded to the EPA with instructions to provide an intelligible  principle guiding its interpretation of the relevant sections of the  Act.  See ATA, 175 F.3d at 1038-40.  Thus, the 0.12 ppm, 1-hour  standard remains in place.


2
  In the rulemaking the EPA expressed its belief that areas in  nonattainment for the new, more stringent ozone NAAQS, would be  allowed to opt into the RFG program.  See 63 Fed. Reg. 52,094,  52,101 (1998).  The issue is temporarily moot in the light of ATA,  but on its face such a claim seems even less well-founded than  EPA's core position.


