United States Court of Appeals
FOR THE DISTRICT OF COLUMBIA CIRCUIT
Argued November 9, 1998 Decided March 2, 1999
No. 97-1686
Sierra Club and
Natural Resources Defense Council,
Petitioners
v.
United States Environmental Protection Agency
and Carol M. Browner, Administrator,
United States Environmental Protection Agency,
Respondents
Integrated Waste Services Association and
Pharmaceutical Research and Manufacturers of America,
Intervenors
On Petition for Review of an Order of the
Environmental Protection Agency
James S. Pew argued the cause for petitioners. With him
on the briefs was Howard I. Fox.
Steven Edward Rusak, Attorney, U.S. Department of Jus-
tice, argued the cause for respondents. With him on the brief
were Lois J. Schiffer, Assistant Attorney General, and Mi-
chael W. Thrift, Counsel, United States Environmental Pro-
tection Agency.
Michael B. Wigmore argued the cause for intervenors.
With him on the brief were Charles H. Knauss, Tracy N.
Zlock and David M. Friedland.
David P. Novello was on the brief for amicus curiae
Cement Kiln Recycling Coalition.
David S. Biderman was on the brief for amicus curiae
Medical Waste Institute.
Before: Wald, Williams and Henderson, Circuit Judges.
Opinion for the Court filed by Circuit Judge Williams.
Williams, Circuit Judge: Section 129 of the Clean Air Act,
added by the 1990 amendments, directs EPA to establish
performance standards for new and existing medical waste
incinerators ("MWIs"), including "emissions limitations and
other requirements" for new units and "guidelines ... and
other requirements" for existing units. 42 U.S.C.
s 7429(a)(1). In general, the standards1 are to
reflect the maximum degree of reduction in emissions of
air pollutants ... that the Administrator, taking into
consideration the cost of achieving such emission reduc-
tion, and any non-air quality health and environmental
__________
1 The EPA explains that the rules for existing units are "guide-
lines," while those for newly constructed units are "standards."
The difference between the two appears to be that standards are
federal requirements that apply directly to newly built MWIs, while
guidelines do not directly govern MWIs, but are given effect
through a requirement that states adopt rules that are at least as
strict as the guidelines. See 62 Fed. Reg. 48,348, 48,351/1 (1997)
[J.A. 976/1]. Since the distinction is not important for purposes of
this case, for convenience we refer to both sets as "standards."
impacts and energy requirements, determines is achiev-
able for new or existing units in each category.
42 U.S.C. s 7429(a)(2). The EPA explains that this level of
control is commonly referred to as "maximum achievable
control technology," or "MACT." See 62 Fed. Reg. 48,348,
48,351/3 (1997).
The statute supplements this general directive with specific
requirements, detailed below, that dictate minimum levels of
stringency below which EPA may not go (using the phrase
"shall not be less stringent than"). See 42 U.S.C.
s 7429(a)(2). The parties refer to these requirements as
"floor" provisions. (The nomenclature can be confusing be-
cause these sentences in fact establish maximums on the
emissions that EPA's standards may permit.) The statute of
course authorizes EPA to establish still stricter standards if it
finds them "achievable." In its rulemaking, the EPA first
established each floor (i.e., addressed the "not less stringent
than" provisions) and then considered whether to set the
standard at a stricter level. See 62 Fed. Reg. 48,348, 48,353/2
(1997). In some cases EPA found greater stringency achiev-
able, in others not.
The petitioners, the Sierra Club and the Natural Resources
Defense Council (both referred to here simply as the Sierra
Club), challenge EPA's rule establishing MWI standards,
complaining principally that EPA failed to comply with the
specifications of s 7429(a)(2) for the floors. Although we
reject the Sierra Club's statutory construction challenge, we
conclude that there are serious doubts about the reasonable-
ness of EPA's treatment of the floor requirements, and
remand the rule for further explanation. The Sierra Club
also claims that EPA should have required MWIs to use
pollution prevention measures, such as programs to reduce
waste streams, and that it unlawfully failed to consider cer-
tain "non-air quality" effects of MWI pollution on health and
the environment. We reject both these claims.
I.Floors for Existing Units
The Clean Air Act contains the following floor requirement
for existing MWIs:
Emissions standards for existing units in a category may
be less stringent than standards for new units in the
same category but shall not be less stringent than the
average emissions limitation achieved by the best per-
forming 12 percent of units in the category. The Admin-
istrator may distinguish among classes, types, ... and
sizes of units within a category in establishing such
standards.
42 U.S.C. s 7429(a)(2).
The EPA's first step was to divide the MWI population into
three subcategories, based on waste-burning capacity: small,
medium, and large. 61 Fed. Reg. 31,736, 31,740/2 (1996).
Setting standards for nine pollutants in each of these three
subcategories, EPA went on to make 27 separate floor deter-
minations.
To do so, it surveyed the emissions limits imposed by state
regulations and permit requirements, reasoning that each
such limit was an "emissions limitation" within the meaning of
the Clean Air Act. Then, for each of the nine pollutants
covered by the standards, EPA ranked the incinerators by
the stringency of the control provisions to which they were
subject, from strictest to laxest. Finally, it selected the 12
percent of the incinerator population subject to the strictest
controls and set the floor level for the subcategory by averag-
ing the emissions limitations governing those incinerators.
See 61 Fed. Reg. 31,736, 31,744-45 (1996).
For 17 out of the 27 floors to be established, however, EPA
found that the share of the MWI population covered by any
regulatory requirement was less than 12 percent. See Pat-
rick Chang, Letter to Jim Pew, June 4, 1998, at 1. (Questions
about the validity of this finding are discussed below.) So for
these 17 EPA supplemented the regulatory data with "uncon-
trolled" data--data from its test program recording the per-
formance of incinerators with no pollution controls. See 61
Fed. Reg. 31,736, 31,745/2 (1996); Suzanne Shoraka Blair,
"Determination of the Maximum Achievable Control Technol-
ogy (MACT) Floor for Existing Medical Waste Incinerators,"
Jan. 31, 1996, at 2 ("Blair Mem."). For instance, EPA
estimated the total population of small MWIs at 1,118, so that
12 percent amounted to 135 units. Id. But it found that
state limitations covered 135 or more MWIs only with regard
to two of the nine pollutants. Its solution for the other seven
pollutants is illustrated by its treatment of hydrogen chloride
(HCl). Estimating that only 91 small MWIs were actually
subject to state HCl limits, EPA assumed that the last 44
units in the top 12 percent were not subject to emissions
control at all. To calculate the HCl standard it averaged the
state ceilings (evidently weighted for the number of units
covered), together with the highest (i.e., worst) of the results
from its own testing of uncontrolled small MWIs, weighted 44
times. Id. at 2-4.
A.Challenge to Statutory Construction
The Sierra Club argues that EPA's use of regulatory
permit data rather than performance data violated the stat-
ute's requirement to base the floors on "emissions limita-
tion[s] achieved." s 7429(a)(2). The EPA defends itself
principally with a tortured argument that 42 U.S.C.
s 7602(k), which defines an "emission limitation" solely as a
type of regulatory requirement, applies here in the sense of
allowing the use of regulatory data, but not in the sense of
requiring the use of such data exclusively. The Sierra Club's
arguments to the contrary lead off with the claim that
s 7602(k) cannot apply here because it defines an "emission
limitation," while s 7429(a)(2), the provision calling for these
standards, refers to an "emissions limitation."
The parties beckon us into a labyrinth, but in this case,
unlike the hapless Athenian youths and maidens given in
tribute to King Minos, we are not compelled to enter. The
permissibility of EPA's approach does not turn on the appli-
cability of s 7602(k), but on whether using the state regulato-
ry data is a reasonable means of estimating the performance
of the top 12 percent of MWIs in each subcategory. If using
the state data is reasonable for this purpose, EPA does not
need s 7602(k); if using the state data is unreasonable, then
EPA has conceded that s 7602(k) will not save its position.2
__________
2 The EPA found in its response to comments that reasonable-
ness requires the use of data that allow the agency to conclude
We first reject the Sierra Club's claim that EPA's decision
to base the floors on regulatory data fails the first step of the
Chevron test. None of the Sierra Club's arguments establish
that Congress has "directly addressed" and rejected the use
of regulatory data. See Chevron v. NRDC, 467 U.S. 837, 843,
845 (1984).
The Sierra Club argues that the plain meaning of
s 7429(a)'s words, "average emissions limitation achieved by
the best performing 12 percent of units," precludes the use of
regulatory data. But this phrase on its own says nothing
about how the performance of the best units is to be calculat-
ed. And the Sierra Club has disavowed any interpretation
that would require measuring the performance of every last
unit--it stated in its brief and confirmed at oral argument
that the statutory language "does not preclude EPA from
relying on a representative sample of the units in each
category." The phrase does not by its plain meaning exclude
estimation, either by sampling or by some other reliable
means.
The Sierra Club also claims that the legislative history of
s 7429(a)(2) reflects Congressional intent to prohibit EPA
from relying on regulatory data. The Sierra Club cites an
earlier version of the 1990 Clean Air Act Amendments that
would have required emissions standards to "reflect the
greatest degree of emission reduction achievable ... which
... (A) has been achieved in practice ..., or (B) is contained
in a State or local regulation or any permit ..., whichever is
more stringent." S. 1630, 101st Cong., 2d Sess. s 306 (1990)
("Senate Bill"). The Sierra Club argues that the disparity
between the language of the Senate Bill and that of the
enacted amendments establishes Congress's intent to prohibit
the use of regulatory data. Obviously Congress was deliber-
ate in dropping the Senate Bill's mandate that EPA use state
or local regulatory limits whenever they were more stringent
than the results achieved in practice. But it seems to us
__________
"what the best performing 12 percent of existing HMIWI were able
to achieve," EPA Response to Comments ("RTC"), July 1997, at 3-
28. [J.A. 736].
quite a stretch to infer that in thus reducing the mandated
degree of stringency Congress expressed an intent to ban use
of regulatory data as a proxy for what firms have achieved.
The Sierra Club offers two additional arguments that the
use of regulatory data fails the first step of Chevron. Nei-
ther, it turns out, has any bite so long as EPA used the
regulatory data merely to generate a reasonable estimate of
the actual performance of the top 12 percent of units. First,
the Sierra Club says that using regulatory data is impossible
because such data exists for fewer than 12 percent of units.
But if the regulatory data provide a good proxy for the
performance of the units they do cover, then it is irrelevant
that the coverage is incomplete. (The issue of how well the
units work as proxies is addressed below.) Second, the
Sierra Club argues that using regulatory data would imper-
missibly "import an achievability requirement" into the unit
floor computation. A premise of the argument is the counter-
intuitive proposition that an "achieved" level may not be
"achievable," or, as Sierra Club puts it, may be better than
"EPA's notions about what is 'achievable.' " Again we need
not enter the thicket. The distinction is irrelevant if (as here)
the permit data are used only to approximate what actually is
"achieved" in practice.
Addressing the second step of Chevron, we find nothing
inherently impermissible about construing the statute to per-
mit the use of regulatory data--if they allow EPA to make a
reasonable estimate of the performance of the top 12 percent
of units. Indeed, the Sierra Club conceded at oral argument
that "a reasonable sample" may be used "to find out what the
best 12 percent are doing." Oral Arg. Tr. at 11. To be sure,
the Sierra Club did not concede that permit data may be
used. But neither has it provided any basis for believing that
state and local limitations are inherently such weak indicators
of performance that using them is necessarily an impermissi-
ble stretch of the statutory terms.
EPA typically has wide latitude in determining the extent
of data-gathering necessary to solve a problem. We general-
ly defer to an agency's decision to proceed on the basis of
imperfect scientific information, rather than to "invest the
resources to conduct the perfect study." See American Iron
& Steel Inst. v. EPA, 115 F.3d 979, 1004 (D.C. Cir. 1997) (per
curiam). Although the agency's choice of model will be
rejected if it "bears no rational relationship to the reality it
purports to represent," Columbia Falls Aluminum Co. v.
EPA, 139 F.3d 914, 923 (D.C. Cir. 1998), the necessary
relationship seems quite possible here. Indeed, it seems
likely that any jurisdiction bothering to impose limits would
not knowingly set them below what it found firms to be
achieving in practice. And there seems no reason to think
that underachieving firms would be overrepresented in juris-
dictions making this effort. Of course those jurisdictions may
have proceeded in error, may have outdated limits, and may
have contained unrepresentatively high shares of bad actors,
but we address the evidence of possible infirmities below in
our discussion of the Sierra Club's challenge to EPA's meth-
odology as arbitrary and capricious. We note that since EPA
had data on only one percent of about 3000 MWIs, RTC at 3-
28, the data-gathering costs of any non-sampling method may
well have been daunting.
The Sierra Club complains that EPA never used the rea-
sonable-estimation rationale in explaining its decision to use
regulatory data, but instead rested on its interpretation of
s 7602(k). Although much of EPA's explanation during the
rulemaking was indeed devoted to s 7602(k), the agency did
state that use of the regulatory data was permissible because
the agency "could conclude from these data what the best
performing 12 percent of existing [MWIs] were able to
achieve." RTC at 3-28. Similarly, it characterized the
MACT floor as "a measure of the level of air pollution control
currently used by a relatively small fraction of the MWI."
RTC at 3-30. In its 1995 rulemaking proposal, EPA ex-
plained that it examined the state regulatory data "to deter-
mine the emission limitations achieved by the best-performing
12 percent of units in each subcategory," and further defend-
ed its decision by observing that "[i]t was assumed that all
MWI's are ... achieving their [regulatory] limits." 60 Fed.
Reg. 10,654, 10,674/2-3 (1995). This link between the regula-
tory requirements and actual performance undergirded
EPA's decision to use regulatory data when it first proposed
MWI standards in 1995, and the agency certainly did not
disavow that rationale when it adopted the standards in the
present rulemaking.
We therefore reject the Sierra Club's argument that the
Clean Air Act forbids the use of permit and regulatory data,
and hold that the use of such information is permissible as
long as it allows a reasonable inference as to the performance
of the top 12 percent of units. Similarly, as long as there is a
reasonable basis for believing that some of the best perform-
ing 12 percent of units are uncontrolled, EPA may include
data points giving a reasonable representation of the perfor-
mance of those units in its averaging.
B.Challenge as Arbitrary and Capricious
We now examine whether EPA was justified in using its
combination of regulatory data and uncontrolled values to
approximate the performance of the top 12 percent of MWIs.
The Sierra Club argues that EPA has not pointed to evidence
supporting the reasonableness of the approximation, and we
agree that at a minimum further explanation is needed. We
outline the problems that need to be resolved on remand.
Although EPA said that it believed the combination of
regulatory and uncontrolled data gave an accurate picture of
the relevant MWIs' performance, it never adequately said
why it believed this. We refer to two specific areas to
illustrate the deficiencies in EPA's explanation.
First, EPA has said nothing about the possibility that
MWIs might be substantially overachieving the permit lim-
its.3 If this were the case, the permit limits would be of little
value in estimating the top 12 percent of MWIs' performance.
__________
3 Although the agency conceded in its response to comments
that "actual emission data routinely fall below the State and permit
emission limits," RTC at 3-27, the context makes reasonably clear
that the EPA was referring to data on "actual emissions" during
tests; EPA implied that "these levels are not routinely achieved in
practice." Id.
Data in the record suggest that the regulatory limits are in
fact much higher than the emissions that units achieve in
practice. For 13 of the 27 cases EPA considered, the floor,
which is the weighted average of the regulatory limits and the
uncontrolled data, is higher than the value used for the
uncontrolled data.4 For instance, in the case of the HCl floor
for small MWIs, the value for uncontrolled emissions was
2,770 parts per million volume, and the floor (the weighted
average of the regulatory and uncontrolled data) was 4,426
ppmv. Blair Mem. at 2. Thus, unless EPA made a mathe-
matical error (or we have), the average of the regulatory data
must have been 5,227 ppmv5, or 89% higher than the uncon-
trolled emissions.
Even under the most deferential standard, it is difficult to
accept a method under which the emissions of the best-
performing 12% of units are hypothesized to pollute nearly
twice as badly as the worst of test units that lacked any
emissions controls. Our observations are based on our own
analysis of EPA's data, and we may have omitted some
crucial step in the process, but the exercise highlights the
need for additional explanation even if our calculation is
wrong.
Second, EPA never gave any reason for its apparent belief
that MWIs that were not subject to permit requirements did
not deploy emission controls of any sort. Unless there is
some finding to this effect, it is difficult to see the rationality
in using the "uncontrolled" data for the units that were not
subject to regulatory requirements.
Furthermore, data on which EPA relied strongly suggest
that it was irrational to suppose that any of the incinerators
__________
4 Such at least is our reading of the Blair Memorandum. It
lists what appear to be the test results used (evidently with no
breakdown for size category), and the floor emission levels selected.
See id. at 3.
5 We know the data for the uncontrolled 44 and the average of
all 135, with only the figure for the permit data unknown (X):
((2,770 * 44) + 91X)/135 = 4,426. Solving for X we get 5,227.
in the top 12 percent were uncontrolled--at least for the six
pollutants that wet scrubbers control.6 Data submitted by
the American Hospital Association in 1995 indicate that over
55% of MWIs in each category were controlled by wet
scrubbers.7 See Comments and Recommendations of the
American Hospital Association, April 28, 1995, Exhibit 3.
Particularly since the AHA data were the starting point for
EPA's estimate of the number of MWIs,8 see 61 Fed. Reg.
31,736, 31,739/3, it is difficult to see how it was rational to
include any uncontrolled units in the top 12 percent, at least
with respect to pollutants that wet scrubbing controls.
With these numbers, EPA's method looks hopelessly irra-
tional. Moreover, assuming the regulatory data was a good
proxy for the better controlled units and that there were
shortfalls in reaching the necessary 12 percent, EPA has
never explained why it made sense to use the highest of its
test run data to make up the gap. Nonetheless, we do not
vacate the standard. It is possible that EPA may be able to
explain it, and the Sierra Club has expressly requested that
we leave the current regulations in place during any remand,
rather than eliminate any federal control at all. We therefore
remand the floor determinations for existing units for further
explanation by EPA.
__________
6 These pollutants include particulate matter, dioxin precursors,
HCl, lead, cadmium, and mercury. See Brian Strong, Memoran-
dum to Rick Copland, March 20, 1996, at 2.
7 The exact figures are 690 of 1,214 small units (56.8%), 365 of
589 medium units (62.0%), and 281 of 430 large units (65.3%). AHA
Comments, Exhibit 3.
8 The EPA added about 400 MWIs to the AHA data and
deleted about 200 from that total. See 61 Fed. Reg. at 31,739/3.
Even in the unlikely event that all the added MWIs lacked scrub-
bers and all the deleted ones had them, more than 12 percent of
MWIs in these subcategories would as a matter of mathematical
necessity have to be controlled. Yet in each subcategory the EPA
used uncontrolled data points for at least some of the pollutants
that scrubbers control. See Chang Letter at 1.
II.Floors for New Units
The Clean Air Act prescribes that standards for newly
constructed MWIs "shall not be less stringent than the
emissions control that is achieved in practice by the best
controlled similar unit, as determined by the Administrator."
42 U.S.C. s 7429(a)(2).
To implement this provision, EPA examined each subcate-
gory and identified the most effective technology in use by an
incinerator in that subcategory. That technology became the
basis for the new unit standard for incinerators in the subca-
tegory. For instance, the most effective technology that it
identified as in use by a small MWI was a so-called moderate-
efficiency wet scrubber, so the floor for new small MWIs is
based on the performance capability of such a scrubber. If
EPA had identified any small MWIs employing high-
efficiency wet scrubbing, the new small MWI floor would
presumably reflect the performance of that technology. See
61 Fed. Reg. 31,745-46 (1996).
To determine the performance of a given technology, EPA
consulted the data from its own testing program and data
provided by private parties and identified the highest level of
emissions recorded in any test of an incinerator using the
technology in question. It then increased that value by 10
percent and rounded up to "an appropriate round number" to
arrive at the emissions performance figure it ultimately used
for that technology. See Mark B. Turner & Katie Hanks,
Memorandum to Richard A. Copland, May 20, 1996, at 10
("Turner/Hanks Memo").
The Sierra Club, pointing to the statutory reference to the
"best controlled similar unit," 42 U.S.C. s 7429(a)(2), pur-
ports to find two deficiencies in EPA's approach. First, it
argues that EPA should have identified the single best-
performing unit in each subcategory and based the new unit
floor for that subcategory on that particular unit's perfor-
mance, rather than considering the performance of other
units employing the same technology. Next, it argues that
EPA compounded its error by basing the floor on the emis-
sions of the worst-performing unit employing the technology
in question. We address the Sierra Club's claims in the
reverse of the order of presentation.
First, EPA would be justified in setting the floors at a level
that is a reasonable estimate of the performance of the "best
controlled similar unit" under the worst reasonably foresee-
able circumstances (we use the subjunctive because it is not
clear from the record whether the agency was doing this). It
is reasonable to suppose that if an emissions standard is as
stringent as "the emissions control that is achieved in prac-
tice" by a particular unit, then that particular unit will not
violate the standard. This only results if "achieved in prac-
tice" is interpreted to mean "achieved under the worst fore-
seeable circumstances." In National Lime Ass'n v. EPA, 627
F.2d 416, 431 n.46 (D.C. Cir. 1980), we said that where a
statute requires that a standard be "achievable," it must be
achievable "under most adverse circumstances which can
reasonably be expected to recur." The same principle should
apply when a standard is to be derived from the operating
characteristics of a particular unit. Although this potential
rationale for EPA's method was made clear in the briefs for
the agency and the parties intervening on its behalf, it does
not appear in the rulemaking record with enough clarity for
us to say that the agency's "path may reasonably be dis-
cerned." Bowman Transportation, Inc. v. Arkansas-Best
Freight System, Inc., 419 U.S. 281, 286 (1974).
The Sierra Club also claims EPA erred in considering the
emissions of units other than the best controlled unit. The
EPA simply has not explained why the phrase "best con-
trolled similar unit" encompasses all units using the same
technology as the unit with the best observed performance,
rather than just that unit itself, as the use of the singular in
the statutory language suggests. We do not mean to say that
EPA's interpretation is impossible. 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. Or perhaps EPA reasonably considered
all units with the same technology equally "well-controlled,"
so that each unit with the best technology is a "best-
controlled unit" even if such units vary widely in perfor-
mance. But we do not know what interpretation the agency
chose, and thus cannot evaluate its choice.
A similar analysis applies to the agency's choices to add 10
percent to the observed emission levels and to further round
up the result, often in ways that seem contrary to ordinary
principles of rounding. See, e.g., Turner/Hanks Memo at 11
(rounding from 0.0198 to 0.03). Each of these may be
justifiable as a means of reasonably estimating the upper
bound of the best-controlled unit's performance, but in the
absence of agency explanation of both the decision to increase
the levels and the choice of method for determining the
increases, we are in no position to decide.
III.Other Sierra Club Claims
The Sierra Club's remaining claims are directed not to the
floors EPA established for the various types of facilities, but
to the emissions standards themselves. The floor provision
require only a minimum level of stringency, and the emissions
standards themselves are to "reflect the maximum degree of
reduction in emissions of air pollutants ... that the Adminis-
trator, taking into consideration the cost of achieving such
emission reduction, and any non-air quality health and envi-
ronmental impacts and energy requirements, determines is
achievable." 42 U.S.C. s 7429(a)(2). The Sierra Club argues
that EPA failed to consider two separate factors in moving
from the floors to the standards themselves: the effectiveness
of pollution prevention measures and non-air quality health
and environmental effects arising from water, soil, and food
contamination by MWI pollutants. We reject both of these
claims.
A.Pollution Prevention Measures
The Sierra Club starts its argument with the observation
that emissions standards are to be based on "methods and
technologies for removal or destruction of pollutants before,
during, or after combustion," 42 U.S.C. s 7429(a)(3), and
focuses on the "before" in that requirement. It claims that
EPA wrongly failed to require MWIs to undertake programs
to reduce the mercury and chlorinated plastics in their waste
streams.
The EPA does not deny that the waste stream reductions
the Sierra Club calls for would reduce pollution. The less
mercury in, the less mercury out, and the less chlorinated
plastic in, the less HCl out. But the EPA has consistently
argued in its response to comments and here that it does not
have evidence that allows quantification of the relevant output
reduction. For mercury, the only quantitative evidence be-
fore EPA was that a pollution prevention program aimed at
mercury could reduce mercury emissions from very high
levels to typical levels. See RTC at 7-14 to 7-15. For
chlorinated plastics, there was no quantitative evidence before
the agency. See RTC at 7-16, 7-18. The Sierra Club does
not contest the adequacy of EPA's data-gathering with re-
spect to these measures.
There also doesn't appear to be any evidence in the record
about the costs of the pollution prevention measures the
Sierra Club advocates. In the absence of any type of quanti-
fication of benefits or costs, the Administrator had no basis
for finding that, "taking into account the cost," emissions
reductions from pollution prevention programs were "achiev-
able" as the statute uses the word.
B.Non-Air Quality Health and Environmental Effects
Finally, the Sierra Club observes that EPA failed to consid-
er the fact that dioxin and mercury from MWIs can contami-
nate water, sediment, and soil, and can bioaccumulate in food.
The Sierra Club argues in a paragraph that this omission was
improper because the Clean Air Act directs EPA to consider
"any non-air quality health and environmental impacts" in
setting the MWI emissions standards. But the Sierra Club
has made no serious effort, either in its briefs or in its
comments to the agency, to show that the problems about
which it complains are actually "non-air quality" effects within
the meaning of s 7429(a)(2). Because this threshold step is
unbriefed, and because the Sierra Club's argument is present-
ed in such a conclusory manner, we decline to consider the
challenge. See Texas Rural Legal Aid, Inc. v. Legal Servs.
Corp., 940 F.2d 685, 697 (D.C. Cir. 1991).
* * *
The case is remanded to EPA for further explanation of its
reasoning in determining the "floors" for new and existing
MWIs. Petitioners' claims are otherwise rejected.
So ordered.