233 F.3d 625 (D.C. Cir. 2000)
National Lime Association, Petitionerv.Environmental Protection Agency, Respondent
No. 99-1325 Consolidated with 99-1326
United States Court of Appeals FOR THE DISTRICT OF COLUMBIA CIRCUIT
Argued September 5, 2000Decided December 15, 2000

[Copyrighted Material Omitted][Copyrighted Material Omitted]
On Petitions for Review of An Order of the Environmental Protection Agency
Hunter L. Prillaman argued the cause for petitioner National Lime Association.  With him on the briefs were Arline  M. Seeger and Kenneth A. Rubin.
James S. Pew argued the cause for petitioner Sierra Club.  With him on the briefs was Howard I. Fox.
Daniel M. Flores, Attorney, U.S. Department of Justice,  argued the cause for respondent.  With him on the brief were  Lois J. Schiffer, Assistant Attorney General, Daniel R. Dertke, Attorney, and Steven E. Silverman, Attorney, Environmental Protection Agency.  Christopher S. Vaden and H.  Michael Semler, Attorneys, U.S. Department of Justice, entered appearances.
William M. Bumpers was on the brief for amicus curiae  the American Portland Cement Alliance.
Before:  Edwards, Chief Judge, Ginsburg and Tatel,  Circuit Judges.
Opinion for the Court filed by Circuit Judges Ginsburg and  Tatel.*
Ginsburg and Tatel, Circuit Judges:


1
In this case we  consider petitions by the Sierra Club and the National Lime  Association challenging the Environmental Protection Agency's hazardous air pollutant emission regulations for cement  manufacturing.  With respect to the Sierra Club petition we  (1) reject its challenge to the emission standards for hazardous metals and dioxin/furan;  (2) find the Agency's failure to  set standards for hydrogen chloride, mercury, and total hydrocarbons contrary to the Clean Air Act's plain language; (3) direct EPA to consider the health impacts of potentially  stricter standards for hazardous metals;  and (4) sustain the  regulation's monitoring requirements.  Concluding that the  National Lime Association has associational standing, we (1)  reject its argument that EPA's use of particulate matter as a  surrogate for non-volatile metal hazardous air pollutants violates the Clean Air Act and is arbitrary and capricious;  and  (2) reject its challenge to the testing method EPA adopted for  determining whether a manufacturer qualifies as a "major  source" of hazardous air pollutants.

I. Background

2
The Clean Air Act requires the Environmental Protection  Agency to establish emission standards for "major sources" of  hazardous air pollutants listed in the statute.  42 U.S.C.  § 7412(d)(1).  The Act directs the Agency to review the list  periodically, and, where appropriate, to revise it by rule.  Id.  § 7412(b)(2).  Hazardous air pollutants are known as HAPs.


3
A "major source" is any stationary source that emits ten  tons per year or more of any single HAP or twenty-five tons per year or more of any combination of HAPs.  Id.  § 7412(a)(1).  Under section 7412(d)(2) of the statute, emission standards must require


4
the maximum degree of reduction in emissions [of HAPs] ... that the Administrator, taking into consideration the cost of achieving such emission reduction, and any nonair quality health and environmental impacts and energy requirements, determines is achievable ... through application of measures, processes, methods, systems or techniques including, but not limited to, ... process changes, substitution of materials or other modifications.


5
In addition to this general guidance, the statute includes  minimum stringency requirements for emission standards  that apply without regard to either costs or the other factors  and methods listed in section 7412(d)(2).  These stringency  requirements differ depending on whether a source is "new"  or "existing."  New sources are defined as "stationary  source[s], the construction or modification of which is commenced after the publication of regulations (or, if earlier,  proposed regulations) prescribing" air pollution standards  that will be applicable to such sources.  Id. § 7411(a)(2).  For  new sources, the statute provides that "[t]he maximum degree of reduction in emissions that is deemed achievable for  new sources ... shall not be less stringent than the emission  control that is achieved in practice by the best controlled  similar source, as determined by the Administrator."  Id.  § 7412(d)(3) (emphasis added).  For existing sources, defined  as all stationary sources other than new sources, id. § 7411(a)(6), the statute provides that standards shall not be  less stringent than "the average emission limitation achieved  by the best performing 12 percent of the existing sources (for  which the Administrator has emissions information)."  Id.  § 7412(d)(3)(A).


6
EPA implements these statutory requirements through a  two-step process.  The Agency begins by setting the minimum stringency standards required by section 7412(d)(3) for  new and existing sources.  Adding confusion to this already  complex statute, EPA calls these minimum stringency requirements "floors," even though they in fact establish maximum emission levels.  See Sierra Club v. EPA, 167 F.3d 658,  660 (D.C. Cir. 1999) ("Sierra").  Once the Agency sets statutory floors, it then determines, considering cost and the other  factors listed in section 7412(d)(2), whether stricter standards  are "achievable."  42 U.S.C. § 7412(d)(2).  The Agency calls  such stricter requirements "beyond-the-floor" standards.


7
This case concerns emission standards for port land cement  manufacturing plants.  See National Emission Standards for  Hazardous Air Pollutants from the Portland Cement Manufacturing Industry, 40 C.F.R. §§ 63.1340-.1359.  Patented in  1824 by Joseph Aspdin and named for its resemblance to  port land stone, limestone from the Isle of Portland, see 9 The  New Encyclopedia Britannica 629 (15th ed. 1998), port land  cement is a fine powder that serves as the key ingredient in  the concrete used in most construction.  See National Emission Standards for Hazardous Air Pollutants;  Proposed Standards for Hazardous Air Pollutants Emissions for the Portland Cement Manufacturing Industry, 63 Fed. Reg. 14,182,  14,185 (Mar. 24, 1998).  The cement manufacturing process  begins by grinding together materials such as limestone, clay,  shale, sand, iron ore, and flyash and heating the mixture in a  kiln.  See 40 C.F.R. § 63.1341;  63 Fed. Reg. at 14,194. Known as "clinker," the heated mixture is then cooled in a  "clinker cooler" and ground to a fine powder in a mill.  See 40  C.F.R. § 63.1341.


8
Prior to setting cement manufacturing emission standards,  EPA estimated that port land cement plants throughout the  country emitted a total of 290 tons of HAPs per year.  63  Fed. Reg. at 14,183.  EPA found that most individual cement  plants released over ten tons of hydrogen chloride ("HCl")  annually, qualifying them as major sources of HAPs for which  the Clean Air Act required the Agency to set emission  standards.  See id. at 14,192-93.  In addition to HCl, EPA  found that cement plants emitted significant levels of HAP  metals, dioxin/furan, mercury, and organic HAPs other than  dioxin/furan.  See id. at 14,195-96.  These HAPs were released by kilns, clinker coolers, and mills, as well as by  storage and transportation of materials within cement plants. See id. at 14,183.  According to EPA, the potential health  effects of these pollutants include inflammation of the respiratory tract, reproductive problems, cancer, nausea, blood disorders, and damage to the immune system.  See id. at 14,184.


9
Acting on this information, EPA began by considering  emission "floors" for each of the five major categories of  HAPs released by cement plants.  For dioxin/furan, the  Agency set emission floors for both new and existing sources. Considering particulate matter ("PM") to be an appropriate  surrogate for non-volatile HAP metals--components of PM  that are difficult to measure directly--EPA established emission floors for new and existing sources for PM as well.  EPA  set no floors--referred to as floors of "no control"--for the  three remaining HAPs, HCl, mercury, and organic HAPs  other than dioxin/furan.


10
The Agency took a technology-based approach to setting  emission floors.  For cement plants qualifying as new  sources, EPA identified the emission control technology used  by the best performing plant for which it had information and  called this the MACT floor technology.  MACT means "maximum achievable control technology."  EPA then looked at  emissions data for all plants using the MACT floor technology  for which it had information, not just data from the best  performing plant, and set the new source emission floor at the  highest emission level reported by a plant using that technology.  To set existing source emission floors, EPA followed a similar procedure.  It identified the technology used by the  median plant out of the best twelve percent of plants for  which it had information and set the existing source emission  floor at the emission level of the worst performing plant in its  database using that technology.  If, as in the case of HCl,  mercury, and organic HAPs other than dioxin/furan, EPA  found an insufficient number of plants in its database (one for  new sources or twelve percent for existing sources) controlling a particular HAP with pollution control technology, it set  no standard at all, i.e., it determined that the emission floor  was "no control."


11
Proceeding to the next stage of the emission standard  setting process, EPA declined (with one exception not relevant to this case) to set beyond-the-floor standards for either  new or existing sources for any of the five HAPs.


12
In addition to requiring EPA to set emission standards, the  Clean Air Act directs the Agency to require owners and  operators of major sources to conduct "enhanced monitoring"  of their emissions and to submit "compliance certifications"  reporting compliance with the emission standards.  42 U.S.C.  § 7414(a)(3).  Acting pursuant to this requirement, EPA directed cement plants to use a technique known as Fourier  transform infrared spectroscopy ("FTIR") to measure their  HCl emissions to determine whether they qualify as major  sources.  See 40 C.F.R. § 63.1352(a);  id. pt. 63, app. A.  Plants qualifying as major sources must conduct performance  tests that measure PM emissions every five years.  See id.  § 63.1349(b)(1), (c).  To test for compliance with PM standards between performance tests, cement plants must monitor opacity either with a continuous opacity monitor or  through visual inspections.  See id. § 63.1350(c).  Cement  plants must also develop site-specific operations and maintenance plans to be submitted to EPA for approval as part of  the permitting process.  See id. § 63.1350(a).


13
Petitioners Sierra Club and National Lime Association  ("NLA") challenge these regulations.  The Sierra Club  mounts four specific challenges:  (1) EPA's approach to setting emission floors for PM and dioxin/furan both violates the  Clean Air Act and is arbitrary and capricious;  (2) the Agency's refusal to set standards for HCl, mercury, and total  hydrocarbons violates the statute;  (3) EPA's rejection of  beyond-the-floor standards for mercury, total hydrocarbons,  and HAP metals (for which PM is a surrogate) is arbitrary  and capricious;  and (4) the monitoring requirements fail to  provide adequate assurance of compliance with the PM standard.  NLA, a trade association representing lime manufacturers, some of which also manufacture cement, argues that  (1) EPA's decision to use PM as a surrogate for HAP metals  violates the statute and is arbitrary and capricious;  and (2)  the Agency's decision to require cement plants to use the  FTIR method to determine their major source status is  arbitrary and capricious.  The American Portland Cement  Alliance, a trade association representing cement manufacturers and marketers, intervenes in support of EPA.  We consider the Sierra Club's challenges in Section II and NLA's in  Section III.

II. Sierra Club Petition
A. PM and Dioxin/Furan Floors

14
Relying on Chevron U.S.A. Inc. v. Natural Resources  Defense Council, Inc., 467 U.S. 837, 842-43 (1984) (establishing that when Congress's intent is clear, "that is the end of  the matter;  for the court, as well as the agency, must give  effect to the unambiguously expressed intent of Congress"),  the Sierra Club argues that the Agency's technology-based  approach conflicts with the Clean Air Act's plain language. According to the Sierra Club, section 7412(d)(3) requires EPA  to set new source floors at the lowest recorded emission level  for which it has data and existing source floors at the average  of the lowest twelve percent of recorded emission levels for  which it has data.  Nothing in the statute, the Sierra Club  argues, permits the Agency to set floors based on the performance of technology as opposed to the recorded performance  of plants.


15
In resolving this issue, we do not write on a clean slate. EPA's technology-based approach to setting new source emission standards has already faced and survived a Chevron one  challenge.  In Sierra, 167 F.3d 658, we reviewed a new source  emission standard for solid waste combustion that EPA promulgated pursuant to section 7429, which establishes emission  requirements virtually identical to section 7412's.  There, as  here, the Sierra Club argued that EPA's MACT technology  approach to setting emission standards is unambiguously  forbidden by the Clean Air Act.  Sierra rejected that argument, holding that EPA may estimate the performance of the  best performing units and that it was not "impossible" that  EPA's methodology constituted a reasonable estimation technique.  See 167 F.3d at 665.  Concluding that EPA could  reasonably interpret the statutory phrase "emissions control  that is achieved in practice" to mean emissions control that is  "achieved under the worst foreseeable circumstances," see id.  (citing National Lime Ass'n v. EPA, 627 F.2d 416, 431 n.46  (D.C. Cir. 1980)), we hypothesized:  "perhaps considering all  units with the same technology is justifiable because the best  way to predict the worst reasonably foreseeable performance  of the best unit with the available data is to look at other  units' performance."  Id. at 665.  But because EPA failed to  explain why it adopted the MACT approach, we remanded to  the Agency for further explanation, thus never needing to  determine whether the MACT approach would have survived  petitioners' Chevron two or arbitrary and capriciousness challenges.


16
EPA has now explained why it adopted the MACT approach.  In the announcement of the regulations challenged  in this case, the Agency, citing Sierra, explains (1) that it  must ensure that emission "standards are achievable 'under  [the] most adverse circumstances which can reasonably be  expected to recur,' " 64 Fed. Reg. 31,898, 31,915 (June 14,  1999) (quoting Sierra, 167 F.3d at 665), and (2) that "evaluating how a given MACT technology performs is a permissible  means" of estimating the actual performance of the top  twelve percent of plants.  Id.  EPA explains further that the  emission standards it set "are based on the emission levels  achieved through the application of MACT floor technologies and account for variation in the process and in the air  pollution control device effectiveness."  Id. at 31,916.


17
The Sierra Club does not challenge EPA's extension of  Sierra to existing source standards.  Instead, it argues that  Sierra's Chevron one analysis does not control this case  because section 7412 (at issue here) differs from section 7429  (at issue in Sierra).  Although the two sections contain identical stringency requirements for new sources, section 7412, the  Sierra Club emphasizes, directs the Agency to base emission  standards for existing sources on those plants "for which the  Administrator has emissions information," 42 U.S.C.  § 7412(d)(3)(A), a limitation appearing nowhere in section  7429.  See id. § 7429(a)(2).  According to the Sierra Club,  section 7412's additional limitation implies that EPA must  directly calculate the average of the best twelve percent from  the data it has, thus precluding the Agency from estimating  emissions based on the use of MACT technology.


18
We do not agree that the difference between the two  sections requires a different result in this case.  Section  7412's additional phrase says nothing about what data the  Agency should use to calculate emission standards.  It says  only that standards must be based on the best performing  "sources (for which the Administrator has emissions information)."  42 U.S.C. § 7412(d)(3)(A).  Following this directive,  EPA set standards for PM and dioxin/furan at the average  emission levels it estimated the best 12 percent (for which it  had information) achieved.  In doing so, the Agency simply  did not limit itself to consideration of data from the best  twelve percent of plants;  instead it used data it had from  other plants that use the same technology as the best twelve  percent to estimate the performance of the best twelve percent.  Sierra found this approach not unambiguously forbidden by the statute.  See 167 F.3d at 665.


19
Thus bound by Sierra's Chevron one analysis, we turn to  the Sierra Club's argument that the MACT approach is both  unreasonable, see Chevron, 467 U.S. at 843 ("if the statute is  silent or ambiguous with respect to the specific issue, the  question for the court is whether the agency's answer is based on a permissible construction of the statute"), and  arbitrary and capricious.  See 42 U.S.C. § 7607(d)(9)(A).  According to the Sierra Club, EPA has never explained why  emission floors set through the MACT approach accurately  estimate the performance of the relevant best performing  plants:  "The Agency provide[d] absolutely no reason to believe that an emission level that is achievable by every source  that uses a particular control technology is necessarily a  reasonable estimate of the actual performance of the best  performing twelve percent of sources."  Sierra Club Br. at  23.


20
We agree that to comply with the statute, EPA's method of  setting emission floors must reasonably estimate the performance of the relevant best performing plants.  See 42 U.S.C.  § 7412(d)(3);  Sierra, 167 F.3d at 665.  Yet the Sierra Club's  brief does not explain why the emission standards EPA set  might not accurately estimate the performance of the best  performing twelve percent of plants.  The brief never even  suggests that the MACT approach in fact fails to predict the  emission levels of the best performing sources.  When we  asked about this at oral argument, it became clear that the  Sierra Club believes that EPA's MACT approach would not  accurately estimate emission levels of the best performing  twelve percent of plants if the best performing plants  achieved their emission levels not just by using technology,  but also by selecting cleaner manufacturing inputs.  For  example, the best performing twelve percent of plants might  perform well because, in comparison to other plants having  the same technology, they use less-polluting fuels or purer  raw materials.  Such plants would have predictably lower  emissions than plants using MACT floor technology alone. Under such circumstances, the Sierra Club argues, because  technology would represent only one of the factors determining emission levels of the best performing plants, EPA could  not assume that emission levels from the worst-performing  plant using MACT floor technology predict the performance  of the best performing plants under the worst conditions.


21
Although this argument may well have merit, the Sierra  Club's failure to include the argument in its opening brief precludes us from considering it.  See Corson & Gruman Co.  v. NLRB, 899 F.2d 47, 50 n.4 (D.C. Cir. 1990).  Claiming only  that the Agency has "never explained" why the MACT approach accurately predicts the performance of the relevant  best performing sources falls far short of alerting EPA to the  argument we now understand the Sierra Club to be making,  thus giving the Agency no opportunity to respond.  The  Sierra Club's failure is particularly serious because the  MACT approach would accurately estimate the performance  of the best performing sources of a particular HAP if pollution control technology were the only factor determining  emission levels of that HAP--in other words, if emissions  were unaffected by the use of either alternative fuels or raw  materials.  To be sure, as the Sierra Club points out in a  letter submitted after oral argument pursuant to Rule 28(j) of  our rules, it did raise its multiple control factors argument  during the rulemaking in a comment regarding emission  standards for mercury.  Record comments, however, cannot  cure a failure to raise a key argument here.  We will therefore deny the Sierra Club's petition for review with respect to  emission floors for PM and dioxin/furan.


22
B. Failure to set floors for HCl, mercury, and total hydrocarbons


23
EPA established emission floors of "no control" for HCl,  mercury, and total hydrocarbons (a surrogate for organic  HAPs other than dioxin/furan) because the Agency found no  cement plants using control technologies for these pollutants. The Sierra Club argues that EPA's failure to set emission  limits for these HAPs violates the statute's requirement that  the Agency establish emission standards for each of "the  hazardous air pollutants listed for regulation."  42 U.S.C.  § 7412(d)(1).  Defending its decision, EPA points to Sierra's  suggestion that the worst foreseeable performance of the best  performing unit might be predictable from the performance  of the worst performing unit using the same technology.  See  64 Fed. Reg. at 31,915 (citing Sierra, 167 F.3d at 665). According to EPA, if no control technology exists, then the  worst foreseeable performance "could vary day by day" and the standard must be no control.  See EPA Response to  Comments (May 7, 1999), at 190.


24
On this issue, we agree with the Sierra Club.  Nothing in  the statute even suggests that EPA may set emission levels  only for those listed HAPs controlled with technology.  To  the contrary, the statute lists over one hundred specific  HAPs, 42 U.S.C. § 7412(b)(1), and requires EPA to "promulgate regulations establishing emission standards for each  category or subcategory of major sources ... of hazardous  air pollutants listed for regulation."  Id. § 7412(d)(1).  The  statute directs the Agency to promulgate these emission  standards by November 15, 2000.  Id. § 7412(e)(1)(E).  Congress added the list of pollutants to be regulated, regulation  deadlines, and minimum stringency requirementsto the  Clean Air Act precisely because it believed EPA had failed to  regulate enough HAPs under previous air toxics provisions. "The [air toxics] law has worked poorly.  In 18 years, EPA  has regulated only some sources of only seven chemicals.... The legislation reported by the Committee would entirely  restructure the existing law, so that toxics might be adequately regulated by the Federal Government."  S. Rep. No.  101-228, at 128 (1989);  see also H.R. Rep. No. 101-490, pt. 1,  at 322 (1990) ("Since 1970, EPA has listed only eight substances as hazardous air pollutants ... and has promulgated  emissions standards for seven of them.").


25
Contrary to EPA's argument, nothing in Sierra relieves it  of the clear statutory obligation to set emission standards for  each listed HAP.  Although Sierra permits the Agency to  look at technological controls to set emission standards, see  167 F.3d at 665, it does not say that EPA may avoid setting  standards for HAPs not controlled with technology.


26
Although we thus believe that section 7412(d)(1)'s language  disposes of this issue, we add that our reading of that section  is reinforced by section 7412(d)(2)(A).  See Martini v. Federal National Mortgage Association, 178 F.3d 1336, 1345-46  (D.C. Cir. 1999) ("Under Chevron's first step ... we have a  duty to conduct an independent examination of the statute in  question, looking not only to the particular statutory language at issue but also to the language and design of the statute as  a whole.") (internal citations omitted).  Section 7412(d)(2)(A)  directs the Agency, in determining the maximum degree of  achievable emission reductions, to consider pollution-reducing  measures including "process changes, substitution of materials or other modifications."  42 U.S.C. § 7412(d)(2)(A).  By  focusing only on technology, EPA has ignored this directive. The Clean Air Act's legislative history confirms that Congress  wanted the Agency to consider more than just pollution  control technology:


27
The technologies, practices or strategies which are to be considered in setting emission standards under this subsection go beyond the traditional end-of-the-stack treatment or abatement system.  The Administrator is to give priority to technologies or strategies which reduce the amount of pollution generated through process changes or the substitution of materials less hazardous.  Pollution prevention is to be the preferred strategy wherever possible.


28
S. Rep. No. 101-228, at 168.


29
For all of these reasons, the absence of technology-based  pollution control devices for HCl, mercury, and total hydrocarbons did not excuse EPA from setting emission standards  for those pollutants.  We thus will remand for EPA to do so.

C. Beyond-the-Floor Standards

30
The Sierra Club presents a number of objections to EPA's  refusal to set general beyond-the-floor emission standards for  mercury, total hydrocarbons, and HAP metals (for which PM  is a surrogate).  Because EPA will now need to initiate new  rulemaking proceedings to establish emission floors for mercury and total hydrocarbons, we need not consider the Agency's refusal to set beyond-the-floor standards for those two  HAPs.  We address only the Sierra Club's challenge to the  Agency's refusal to set beyond-the-floor standards for HAP  metals.


31
When determining whether to set beyond-the-floor standards, the Clean Air Act requires EPA to consider "the cost of achieving such emission reduction, and any non-air quality  health and environmental impacts and energy requirements." 42 U.S.C. § 7412(d)(2).  The Sierra Club argues that EPA  violated the statute by failing to consider the non-air quality  health and environmental impacts of potential beyond-the floor standards for HAP metals.  Again, we agree.  Although  EPA considered costs and energy requirements, nowhere in  the record does it appear to have taken account of any non-air  quality health effects.


32
EPA's analysis of potential beyond-the-floor standards for  HAP metals suffers from a second defect.  As the Sierra  Club points out, EPA, responding to a comment in the  rule making suggesting that stricter emission standards for  HAP metals could be achieved if cement kilns switched to  natural gas, asserted that "[t]here are no data available to  EPA that indicate that [fuel switching] can or has achieved  metals emission reductions."  64 Fed. Reg 31,917.  Yet a  study in the record contains just such information, demonstrating that switching to natural gas would in fact reduce  metal emissions.  See Office of Air Quality Planning and  Standards, U.S. EPA, Study of Hazardous Air Pollutants  Emissions from Electric Utility Steam Generating Units  13-2 (1998).  EPA now tells us that fuel switching is not a  viable alternative because of inadequate supplies of natural  gas.  In support of this proposition, the Agency points to a  handwritten notation on a report in the administrative record. But that note, supposedly written by an EPA employee, is  virtually illegible--even the Agency's counsel was unable to  decipher it at oral argument.  Therefore, the note cannot  supply a basis for EPA's decision.  Although the Agency's  brief cites one other study in support of its assertion that the  supply of natural gas is inadequate, nothing in the rule making  indicates that EPA relied on it.  "[A]n agency's action must  be upheld, if at all, on the basis articulated by the agency." Motor Vehicle Mfrs. Ass'n v. State Farm Mut. Auto. Ins. Co.,  463 U.S. 29, 50 (1983).


33
Thus, because EPA failed to consider non-air quality health  and environmental impacts of potential beyond-the-floor standards for HAP metals, and because it relied on a factually incorrect assertion in rejecting such standards, we will remand the beyond-the-floor determination for HAP metals for  further consideration consistent with this opinion.  In view of  the Sierra Club's request that we not vacate the EPA's  regulations, because "to do so would at least temporarily  defeat [Sierra Club's] purpose, the enhanced protection" of  the environment, Environmental Defense Fund, Inc. v.  Adm'r of the EPA, 898 F.2d 183, 190 (D.C. Cir. 1990), we will  leave the current PM regulations in place during remand.

D. Monitoring

34
In its final challenge, the Sierra Club argues that the  regulation's monitoring requirements fail to provide reasonable assurance of compliance with the emission standards. Specifically, it argues that the opacity monitoring required by  the regulation will not guarantee compliance with the PM  standard.  EPA responds that opacity monitoring promotes  good operation and maintenance, which in turn reasonably  ensure compliance with the PM standard.  Because the Sierra Club has given us no basis for doubting this assertion, and  because analysis of this issue "requires a high level of technical expertise, we must defer to the informed discretion" of the  Agency.  Marsh v. Oregon Natural Resources Council, 490  U.S. 360, 377 (1989) (internal quotation marks omitted).


35
III. Petition of the National Lime Association


36
Petitioner National Lime Association (NLA) claims that  two additional aspects of the portland cement rule are contrary to law and arbitrary and capricious:  the EPA's use of  PM as a surrogate for HAP metals, and its requirement that  cement kilns use a specified technique to measure their HCl  emissions under certain circumstances.  We consider these  arguments only after concluding that the NLA has standing  to raise them.

A. Standing of the NLA

37
The EPA argues that the NLA lacks standing to object to  the port land cement rule because it is a trade association of lime and not of cement manufacturers.  Although the EPA  recognizes that some NLA members manufacture both cement and lime, the agency asserts that the NLA made no  mention of its cement members during proceedings before  the agency, "suggesting only that [the port land cement rule]  could establish adverse precedents ... for the commercial  lime industry."  The EPA also emphasizes that NLA members that manufacture both lime and cement are also members of the American Portland Cement Association (APCA),  which--in the view of the agency--adequately represents  their cement interests.  The APCA, as mentioned above, has  intervened in this case in defense of the port land cement rule.


38
The EPA cites no authority--and we know of none-suggesting that the position taken by one association affects  the right of another to seek judicial review;  and although the  possibility of an adverse precedent is clearly insufficient to  establish the injury necessary for standing under Article III,  an association anxious to avoid an adverse precedent may still  bring a petition if it otherwise meets the requirements for  standing.  Those requirements are straightforward:


39
[A]n association has standing to bring suit on behalf of its members when:  (a) its members would otherwise have standing to sue in their own right;  (b) the interests it seeks to protect are germane to the organization's purpose;  and (c) neither the claim asserted nor the relief requested requires the participation of individual members in the lawsuit.


40
Hunt v. Washington State Apple Advertising Comm'n, 432  U.S. 333, 343 (1977).  That the NLA meets requirement (c) is  unquestioned.  In order to prevail on the standing question,  then, the EPA must show that the NLA fails to meet  requirement (a) or (b).


41
Requirement (a) is met if "any one" of the association's  members can "make out a justiciable case."  Warth v. Seldin,  422 U.S. 490, 511 (1975).  The member must show (i) that it  was injured in fact, (ii) that its injury was caused by the  challenged rule, and (iii) that its injury would likely be  redressed by a favorable decision of the court.  Lujan v. Defenders of Wildlife, 504 U.S. 555, 560-61 (1992).  The NLA  submits an affidavit from the "Environmental Director" of  Blue Circle, Inc. affirming that Blue Circle is an NLA member, stating that it operates both cement and lime manufacturing plants, and asserting facts indicating that it meets all  three elements of requirement (a).  Blue Circle asserts both  that the use of PM as a surrogate and the HCl measurement  requirement impose "significant" monitoring and compliance  costs upon its cement operations, which would be avoided by  this court's favorable decision.  Blue Circle's specific assertions as to harm, causation, and redress-ability are neither  "general" nor "conclusory," as the EPA suggests.  We conclude, therefore, that the NLA has at least one member that  could assert a justiciable claim in its own right.


42
Beyond injury in fact, causation, and redress-ability, requirement (b) of Hunt demands that the interest an association seeks to protect be "germane to the organization's purpose."  432 U.S. at 343.  This requirement of germaneness is  "undemanding";  "mere pertinence between litigation subject  and organizational purpose" is sufficient.  Humane Soc'y v.  Hodel, 840 F.2d 45, 58 (D.C. Cir. 1988).  The subject of this  litigation is the regulation of portland cement manufacturing; that is certainly "pertinent" to the NLA as a trade association  of manufacturers of lime.  Not only do some companies  manufacture both cement and lime, but both industries share  a critical raw material--limestone--and lime itself is sometimes used as an ingredient in portland cement.  See 63 Fed.  Reg. at 14,194/2;  J.A.H. Oates, Lime and Limestone 81, 124 (1998).  The processes underlying the two types of manufacture are also similar, as is made abundantly clear by the  NLA's efforts to introduce into the record in this case data  from the EPA's administrative record regarding the manufacture of lime.  Ct. Op. at 24-25 below.  The two manufacturing processes also emit some of the same pollutants.  The  regulation of portland cement thus falls well within the "specialized expertise and research resources" of the NLA.  Humane Soc'y, 840 F.2d at 56.


43
Our analysis of germaneness is unaffected by the EPA's  argument that the NLA, in advancing its lime interests, has taken a position on the cement rule adverse to the interests of  cement manufacturers.  The NLA is entitled to be an advocate for a subgroup of cement manufacturers whose interests  diverge from those of the run of cement producers--for  example, companies such as Blue Circle that manufacture  both cement and lime.  Cf. National Maritime Union v.  Commander, Military Sealift Command, 824 F.2d 1228, 1234  (D.C. Cir. 1987) (quoted in Humane Soc'y, 840 F.2d at 59  n.25) ("mere fact of conflicting interests among members of  an association does not of itself defeat the association's standing to urge the interests of some members in litigation, even  though success may harm the legal interests of some members").


44
Because the NLA has at least one member that could have  pressed the same claims in its own right, and because those  claims are germane to the organizational purpose of the NLA,  we conclude that the association has standing to petition for  review of the portland cement rule.

B. The Use of PM as a Surrogate

45
The NLA's primary objection to the portland cement rule  is that it limits PM emissions from cement kilns instead of  regulating emissions of HAP metals individually.  The EPA  justifies its decision to regulate PM as "a surrogate for nonvolatile HAP metals" by noting first that PM generated by  cement kilns invariably contains HAP metals, so that preventing the emission of a unit of PM necessarily prevents the  emission of some quantum of HAP metals.  Using PM as a  surrogate thus "achieves exactly the same level of HAP metal  emissions limitation" as would be reached were the metals to  be regulated directly.  The agency also states that "the  MACT floor equipment and level of control for HAP metals  ... is identical to that for PM."  Finally, the agency notes  that the use of a surrogate "eliminates the cost of performance testing to comply with numerous standards for individual metals."  64 Fed. Reg. at 31,916/3.


46
The EPA may use a surrogate to regulate hazardous  pollutants if it is "reasonable" to do so.  See Dithiocarbamate  Task Force v. EPA, 98 F.3d 1394, 1399 (D.C. Cir. 1996) (EPA may attribute characteristics of a subclass of substances to an  entire class of substances if doing so is scientifically reasonable);  NRDC v. EPA, 822 F.2d 104, 125 (D.C. Cir. 1987)  (EPA may regulate pollutant indirectly when its emissions  are controllable by regulation of other pollutants).  Even a  reasonable surrogate, of course, may not be used where doing  so would be otherwise contrary to law.  The NLA does not  challenge the legality of surrogacy in general, but does maintain that in this case the use of PM as a surrogate is both  contrary to law and unreasonable.


47
1. Legality of using a criteria pollutant as a surrogate


48
The NLA argues first that the EPA may not use PM as a  surrogate for HAP metals because PM is a criteria pollutant--one of several ubiquitous pollutants that the EPA  regulates by establishing national ambient air quality standards (NAAQS) under §§ 108-09 of the Clean Air Act.  42  U.S.C. §§ 7408-09.  The provision authorizing the EPA to  regulate HAPs in the Clean Air Act is limited by the qualification that "no [criteria] air pollutant ... may be added to  the list [of regulable HAPs]."  Id. § 7412(b)(2).  The NLA  argues that although surrogates for HAPs are permissible in  general, using a criteria pollutant as such a surrogate has the  effect of regulating that pollutant as a HAP "through the  back door" and thus illicitly supplementing (or even supplanting) the NAAQS applicable to that pollutant.


49
The EPA suggests first that the NLA's interpretation is  inconsistent with the stated expectation of the Congress that  HAP metals might be regulated under the Clean Air Act by  way of a PM surrogate, but the agency's point is not welltaken.  The EPA relies principally upon a report accompanying Senate Bill 1630, a version of which would ultimately  become the Clean Air Act Amendments of 1990.  The report,  in a discussion of the EPA's discretionary authority to lower  the level of emissions that qualifies a facility as a "major  source" of HAPs, see 42 U.S.C. § 7412(a)(1), notes that the  agency may find this power "especially useful in the control of  particulate emissions including metals for some source categories."  S. Rep. No. 101-228, at 151.  The authors of the


50
report thus appear to have contemplated that the regulation  of "metals" could be subsumed by controls placed upon  "particulate emissions."


51
The report, however, was issued in conjunction with Senate  Bill 1630 as it went to the floor of the Senate on December 20,  1989.  In that version of the bill, the passage that would have  become § 7412(b)(2) authorized the Administrator to add to  the list of hazardous air pollutants any additional pollutants


52
which present, or may present, ... a threat of adverse human health effects (including, but not limited to, substances which are known to be, ... carcinogenic [etc.,] but not including effects for which a pollutant has been listed pursuant to section 108 of [the Clean Air] Act).


53
S. 1630, 101st Cong. § 301, at 324 (1989) (emphasis added). The italicized clause in the reported version of Senate Bill  1630 does not appear in the statute as enacted.  The sentence  that appears in the legislation that the Congress ultimately  passed, and upon which the NLA bases its statutory claim,  provides:  "No air pollutant which is listed under section  7408(a) of this title [i.e., § 108 of the Clean Air Act,] may be  added to the list [of HAPs] under this section."  42 U.S.C.  § 7412(b)(2).


54
The italicized clause in the unenacted bill is materially  different from the statutory provision upon which the NLA  bases its claim.  The earlier version would have prohibited  the regulation of a criteria pollutant as a HAP only if such  regulation was based upon the same reason for which the  pollutant was listed as a criteria pollutant under § 108.  The  final statute, by contrast, unqualifiedly prohibits listing a  criteria pollutant as a HAP, that is, regardless of the reason. Because the comment in the Senate Report regarding PM  and metals was made before the blanket prohibition upon  regulating PM as a HAP was added to the statute, the report  is irrelevant to our construction of § 7412(b)(2) as enacted.


55
The enacted statute, to which we now turn, prohibits the  addition of any criteria pollutant to "the list" of HAPs, with a  single exception for certain precursor pollutants not relevant to this case.  See id.  This prohibition extends of necessity  not only to rules that literally list a criteria pollutant as a  HAP but also to any rule that in effect treats a criteria  pollutant as a HAP.  As the EPA shows, however, the  portland cement rule does not treat PM as a HAP generally; it regulates only PM that is emitted from cement kilns.  The  rule does not treat PM, unlike a HAP metal, as a pollutant  the emissions of which determine whether a cement plant is a  "major source" of emissions.  See id. § 7412(a)(1).  Nor does  the EPA suggest in any way that it contemplates broad  regulation of PM pursuant to § 7412.  To the contrary, all of  the evidence upon which the agency relies to justify its use of  PM as a surrogate is particular to the cement industry.  See  Memorandum from Elizabeth Heath, Research Triangle Institute, to Joseph Wood, EPA 2-8 (Feb. 21, 1996);  Memorandum from Michael Benson, Research Triangle Institute, to  Mary Johnson, EPA 1 (June 21, 1993);  Portland Cement  Ass'n, An Analysis of Selected Trace Metals in Cement and  Kiln Dust at 3-4 (1992).  We therefore conclude that the use  of PM as a surrogate for HAP metals is not contrary to law.

2. Reasonableness of the PM surrogate

56
The NLA also contends that PM is an unreasonable surrogate for HAP metals because HAP metals make up a "very  small and variable" portion of cement kiln PM emissions. The NLA faults the EPA both because it did not demonstrate  and quantify a consistent correlation between PM stack emissions and their HAP metal content, and because it selected a  surrogate of which HAP metals make up only "about one  tenth of one percent."


57
The EPA acknowledges both points.  The closest the agency comes to making a numerical estimate of the correlation  between PM and the HAP metals it contains is the statement  that "the total average HAP metal content of kiln exhaust  PM is approximately one weight percent."  63 Fed. Reg. at  14,195/2.  The EPA thus admits that the ratio of HAP metals  to total particulates is small;  and the agency nowhere discusses the variance associated with its estimated average. The EPA contends, however, that it justified the surrogacy adequately by demonstrating that "where there is cement kiln  PM, HAP metals are always in it, and when cement kiln PM  is removed from emissions, HAP metals are always removed  with it."  According to the EPA, as long as it demonstrates  that there is a correlation between HAP metals and PM, it  need not quantify that correlation or assess its variability  because PM control technology is such that each unit of PM  emissions avoided "carries" within it some quantum of HAP  metals.


58
The agency's analysis is not unreasonable.  If HAP metals  are invariably present in cement kiln PM, then even if the  ratio of metals to PM is small and variable, or simply  unknown, PM is a reasonable surrogate for the metals-assuming, as both the EPA and the NLA appear to do, that  PM control technology indiscriminately captures HAP metals  along with other particulates, an assumption about which we  say more in the next paragraph.  The EPA is under no  obligation to achieve a particular numerical reduction in HAP  metal emissions;  it must reduce their emission only to the  level "achieved" by the best performing facility or, for existing sources, to the level achieved by the median of the best performing 12 percent of facilities.  42 U.S.C. § 7412(d)(3). If PM control is the only means by which facilities "achieve"  reductions in HAP metal emissions, then the EPA may  require PM control without quantifying the reduction in HAP  metals thus achieved.


59
We should add, however, that the EPA may need to  reconsider whether PM is an appropriate surrogate for HAP  metals when, upon remand, it considers whether to establish  beyond-the-floor standards for HAP metals (for which PM is  a proxy).  We held above, see Ct. Op. at 14, that the EPA  must consider the potential impact upon emissions of changes  in inputs to the cement manufacturing process, especially the  possibility of fuel switching.  The EPA decided to use PM as  a surrogate for HAP metals because PM control technology  traps HAP metal particles and other particulates indiscriminately.  In considering the role of inputs, the EPA must also  assure itself that fuels and other inputs affect HAP metal  emissions in the same fashion that they affect the other  components of PM.  For example, PM might not be an appropriate surrogate for HAP metals if switching fuels  would decrease HAP metal emissions without causing a corresponding reduction in total PM emissions.


60
3. The NLA's other arguments against PM as a surrogate


61
The NLA offers several other reasons for thinking the  EPA's use of PM as a surrogate for HAP metals might be  unreasonable or contrary to law, but each of them is without  merit.  First, the NLA claims that the use of PM as a  surrogate is incompatible with the agency's own methodology  for setting MACT floors.  According to the NLA, this methodology requires the agency to set a floor of "no control" for  HAP metals because no cement plant intentionally controls  HAP metals;  metal emissions are controlled only incidentally  by controls placed upon PM.  The EPA's response is the  correct one:  "cement plants actually are controlling HAP  metals[,] [i]ntentionally or not."  The Clean Air Act requires  the EPA to set MACT floors based upon the "average  emission limitation[s] achieved," 42 U.S.C. § 7412(d)(3);  it  nowhere suggests that this achievement must be the product  of a specific intent.  Moreover, as we have seen, the EPA's  floor-setting methodology does not permit the agency to set a  MACT floor of "no control" simply because no controls are in  place, see Ct. Op. at 12 above;  a fortiori, the EPA may not  set such a floor when the controls are in place but the cement  kilns have not intentionally deployed them for that purpose.


62
Second, the NLA claims that the EPA, in limiting PM  emissions, failed to meet the statutory requirement to "tak[e]  into consideration the cost of achieving ... emissions reduction[s]" for the underlying HAP metals.  42 U.S.C.  § 7412(d)(2).  According to the NLA, the per unit cost of  preventing HAP metal emissions is prohibitively high.  Cost,  however, may be taken into account only in considering  beyond-the-floor emissions limitations, which in the case of  PM we have remanded to the agency;  cost may not influence  the determination of a MACT floor, which depends exclusively upon the emissions reductions achieved by the best performing sources.  See id. § 7412(d)(3).  Relatedly, the  NLA also claims that in light of both the high costs and the  low quantities of HAP metals to be controlled, the EPA should read a de minimis exception into the requirement that  it regulate all hazardous air pollutants emitted by major  sources.  The EPA reasonably rejected this argument on the  ground that the statute "does not provide for exceptions from  emissions standards based on de minimis principles where a  MACT floor exists."  Response to Comments at 211.

C. Measurement of HCl Emissions

63
HCl is emitted in sufficient quantity from most cement  kilns to qualify each kiln as a "major source," that is, a source  that "emits or has the potential to emit considering controls,  in the aggregate, 10 tons per year or more of any [HAP]," 42  U.S.C. § 7412 (a)(1).  See 63 Fed. Reg. at 14,192-93.  The  challenged rule allows a single technique for measuring HCl  emissions from a cement kiln--Fourier Transform Infrared  Spectroscopy (FTIR)-if the kiln "wishes to claim it is not a  major source."  64 Fed. Reg. at 31,907/2.  The EPA refused  to allow kilns to use two other methods--so-called Method 26  and its variant, Method 26A--to support such a claim because, in the agency's view, these methods "may underestimate HCl emissions by a factor of 2 to 25."  63 Fed. Reg. at  14,193/1.  The NLA claims that this determination was unlawful and arbitrary and capricious.  It also asserts that the  EPA acted unlawfully when it refused to consider NLA's  comments suggesting potential improvements in Method  26/26A.


64
The NLA bases its claim upon data regarding Method  26/26A that it submitted to the EPA but the agency did not  consider.  The EPA was under no obligation to do so, however, because the materials the NLA cites were not part of the  administrative record.  All but one of the letters from the  NLA transmitting the disputed information to the EPA are  dated after June 26, 1998, the close of the comment period. 64 Fed. Reg. at 31,900/1.  Informationsubmitted to the  agency out of time is incorporated into the administrative  record only if the Administrator of the EPA determines that  it is "of central relevance to the rulemaking."  42 U.S.C.  § 7607(d)(4)(B)(i).  Because she did not so determine, the  NLA may not present arguments based upon that information.


65
The one document the NLA proffers that was submitted  within the comment period is a letter dated June 22, 1998,  transmitting a summary of a conference call that day between  officials of the NLA and of the EPA.  See Letter from Arlene  Seeger, Executive Director, NLA, to Joseph P. Wood, EPA 1. The June 22 letter nowhere suggests, however, that it is  being submitted in connection with the proposed portland  cement rule.  Instead, as is also implied in later correspondence between the EPA and the NLA, the conference call  appears to have been part of an ongoing dialogue between the  agency and the NLA regarding a proposed rule affecting the  lime industry.  The EPA is not required to consider in its  deliberations here information apparently submitted in connection with a different rule making proceeding when no one  timely asked it to do so.


66
The NLA also suggests that the EPA unlawfully failed to  consider several pages of handwritten calculations that purport to test whether another approach to measuring HCl  emissions--gas filter correlation infrared spectroscopy  (GFCIR)--generates biased results relative to FTIR.  The  EPA concedes that this test should have been, but was not,  included in the administrative record.  As the EPA points  out, however, the omission is immaterial because the agency  used the calculations only to determine that GFCIR was too  biased to be a usable testing method--and the NLA does not  challenge that determination.  We therefore conclude that the  EPA was not required to consider the data the NLA cites in  deciding that Method 26/26A could not be used to challenge  "major source" determinations.


67
Separately, the EPA concedes that it failed to consider the  NLA's properly submitted comments regarding possible improvements to Method 26/26A.  We therefore remand this  matter to the agency so that it may respond to those comments.

IV. Conclusion

68
In summary, we remand the rule to the EPA to allow the  agency to (1) set "MACT floor" standards for HCl, mercury, and total hydrocarbons;  (2) consider setting "beyond-the floor" standards for HAP metals;  and (3) respond to comments suggesting improvements to Method 26/26A for measuring HCl emissions.  With respect to all other issues discussed herein, the petitions are denied.


69
So ordered.



Notes:


*
 Judge Tatel wrote Sections I and II.  Judge Ginsburg wrote  Sections III and IV.


