properly preserved for the court to adjudicate). This is not legally
permissible. Brick MACT, 479 F. 3d at 880-81. EPA thus does not accept
the argument of some commenters that EPA may only amend promulgated
MACT standards by means of the periodic review procedures of section
112(d)(6), which does not include re-determining floor levels. Section
112(d)(6)does not indicate that it is the exclusive means of amending
MACT standards, and in particular does not speak to a situation where
an original floor was palpably short of statutory requirements and
where that floor became the ultimate standard. EPA consequently
believes it has discretion to reconsider and redo the MACT floor
analysis for PM, and to amend the standard as appropriate.
    Other commenters suggested that even if EPA has such discretion, it
would (or should) be limited to a reanalysis of the original database
for the 1999 rule and so should not consider kilns' subsequent
performance. Were EPA to take that approach here, the floor (and
standard) for PM would be more stringent than the floor (and standard)
in this rule.\33\ Because EPA considers the database for the current
rule to be more representative of performance capabilities of best
performing kilns than the sparser 1999 database, EPA is basing its
determination on the more representative data.
---------------------------------------------------------------------------

    \33\ Calculation of PM MACT Floor Based on Data in 1998
Proposal. July 7, 2010.
---------------------------------------------------------------------------

    EPA is setting a PM standard based on MACT for existing and new
area source cement kilns. As noted at proposal, Portland cement kilns
are a listed area source category for urban HAP metals pursuant to
section 112(c)(3), and control of these metal HAP emissions (via the
standard for the PM metal surrogate) is required to ensure that area
sources representing 90 percent of the area source emissions of urban
metal HAP are subject to section 112 control, as required by section
112(c)(3). EPA has determined that this standard should reflect MACT,
rather than GACT, because there is no essential difference between area
source and major source cement kilns with respect to emissions

of either HAP metals or PM. Thus, the factors that determine whether a
cement kiln is major or area are typically a function of the source's
HCl or formaldehyde emissions, rather than its emissions of HAP metals.
As a result, there are kilns that are physically quite large that are
area sources, and kilns that are small that are major sources. Both
large and small kilns have similar HAP metal and PM emissions
characteristics and controls.
    Given that EPA is developing major and area source standards for PM
at the same time in this rulemaking, a common control strategy
consequently appears warranted for these emissions. We thus have
included all cement kilns in the floor calculations for the final PM
standard, and have developed common PM limits based on MACT for both
major and area sources.
    i. Floor Determination. At proposal we had compiled PM stack test
data for 45 kilns from the period 1998 to 2007. EPA ranked the data by
emissions level and the lowest emitting 12 percent, 6 kilns, was used
to develop the proposed existing source MACT floors of 0.085 and 0.08
lb/ton clinker for new and existing sources respectively.
    Commenters noted that we had omitted some of the data already
submitted to EPA in developing the MACT floor. In addition, we noted
for two of the best performing facilities we had only one emissions
test. Therefore we requested these sources to submit additional PM
emission test data and the source sent two additional PM emissions
tests for each kiln to allow us to better characterize emissions
variability. We modified the PM data base to reflect these submissions.
Another change made since proposal is that we have changed the
compliance requirement to require a PM CEMS. This requires that we
establish an averaging period. We chose a period of 30 days (rolling
average) to be consistent with requirements for mercury and THC, and
because PM emissions on a lb/ton basis are affected by raw mill cycles
(typically encompassed within 30-days, see 74 FR at 21144) for kilns
with in-line raw mills. We have converted the concentrations obtained
from 3-hour tests into 30-day values by means of the UPL equation
previously described. It should be noted that due to the longer
averaging periods, the actual limit will be a lower number compared to
the shorter compliance interval in the proposed rule (30 days versus a
three hour test). This damping of variability when a longer averaging
period is used is well established where continuous monitors have been
used to measure emissions, and is also accounted for in the ``m'' term
of the UPL equation. The results of the new MACT analysis are shown in
Table 8.

                         Table 8--PM MACT Floor
------------------------------------------------------------------------
                                                           PM emissions
                          Kiln                               (lb/ton
                                                             clinker)
------------------------------------------------------------------------
1......................................................          0.01
2......................................................          0.01
3......................................................          0.01
4......................................................          0.03
5......................................................          0.04
6......................................................          0.04
------------------------------------------------------------------------
                             MACT--Existing
------------------------------------------------------------------------
Average................................................          0.02
Variance...............................................          0.001
UPL....................................................          0.04
------------------------------------------------------------------------
                                MACT--New
------------------------------------------------------------------------
Average................................................          0.01
Variance...............................................          0.00001
UPL....................................................          0.01
------------------------------------------------------------------------

    EPA proposed use of PM CEMS as an alternative to using a bag leak
detector, and also solicited comment on requiring their use generally.
74 FR at 21157. As we noted there, performance specifications for PM
CEMS are now available, and continuous monitors ``give a far better
measure of sources' performance over time than periodic stack tests''.
After considering the public comments, EPA continues to believe that
this is the case. See also further discussion of this issue at Section
A.3 of this preamble below.
    EPA does not agree with the comment that use of a CEM renders the
standard more stringent and so results in floors (and standards) more
stringent than those achieved by average of the best performing
sources. First, the continuous collection of data used to assess
compliance with this standard does not create a limit more stringent
that otherwise allowed. As discussed in the preamble to the Credible
Evidence Rule, ``* * * continuous monitoring of the standards (has) no
effect on the stringency of the standard * * * '' (62 FR at 8326,
February 24, 1997).
    Further, a statistically-based adjustment to account for emissions
variability, and which, in this case, increases the numerical value of
the standard (and its longer averaging period) by fifty percent, does
not make the standard more stringent. Finally, increasing the averaging
period beyond the duration associated with conducting a performance
test (typically three hours) to 30 days normally makes a standard more
lenient because there is more opportunity to average out individual
results. As mentioned in the description of the Salo and Pederson
memoranda cited in Section <IP_ADDRESS> of the Credible Evidence Rule
Response to Comment Document, ``* * * (t)he effect of the change from a
3-hour averaging time to a 30-day averaging time is to make the
standard more lenient * * * ''.\34\
---------------------------------------------------------------------------

    \34\ Available at http://www.epa.gov/ttncaaa1/t1/fr_notices/
certcfin.pdf.
---------------------------------------------------------------------------

    ii. Beyond the Floor Determination.
    EPA did not propose beyond-the-floor standards for PM. This was
because the cost effectiveness of adopting beyond-the-floor controls
was several orders of magnitude greater than EPA has accepted for PM
reductions in other rules where standards allow consideration of costs,
and because the incremental amount of PM removed was very small (3 tpy
nationwide). Consideration of non-air quality issues did not change
this conclusion. 74 FR at 21155. Commenters did not challenge this
analysis. EPA accordingly is not adopting beyond-the-floor standards
for PM.
    The final PM emissions limit for existing sources is 0.04 pounds
per ton (lb/ton) clinker for and 0.01 lb/tons clinker for new sources
(30-day average). Kilns where the clinker cooler gas is combined with
the kiln exhaust and sent to a single control device for energy
efficiency purposes (i.e., to extract heat from the clinker cooler
exhaust) will be allowed to adjust the PM standard to an equivalent
level accounting for the increased gas flow due to combining of kiln
and clinker cooler exhaust (an action for which EPA received no adverse
comment). See 74 FR at 21156 and 73 FR at 64090-91 (Oct. 28, 2008)
(explaining the equivalency of this standard and the energy efficiency
benefits resulting from combining these gas flows). The PM standard is
a 30-day rolling average and is measured with a CEM.
    iii. Compliance Alternative for Comingled Kiln/Clinker Cooler
Exhaust.
    As we noted at proposal, some kilns combine the clinker cooler gas
with the kiln exhaust and send the combined emissions to a single
control device. There are significant energy savings (and attendant
greenhouse gas emission reductions) associated with this practice,
since heat can be extracted from the clinker cooler exhaust. However,
there need to be different conversion factors from concentration to
mass per unit clinker in these cases to allow for the increased gas
flow, which result in a different PM emissions limit. We proposed
adjustment factors that would account for these differences and create
a site specific PM emission limit

of this situation. See 74 FR 21155-56 and 21184. We received no
comments on these factors and are thus adopting them as proposed,
except that the factors have been changed to account for changes in the
underlying kiln and clinker cooler emissions limits. Note that
adjustments would also be necessary for kilns subject to the NSPS PM
limit. Thus, we are including a cross reference for the NSPS to the
appropriate section of the NESHAP rule.
f. Opacity Standards for Kilns and Clinker Coolers
    We are removing all opacity standards for kilns and clinker coolers
because these sources will be required to monitor compliance with the
PM emissions limits by more accurate means. Although some commenters
requested retention of opacity as a backup standard, and others as an
alternative, none of these comments offered any convincing information
or other justification for perpetuating a less reliable compliance
methodology. Though we have preserved some regulation text, any kiln or
clinker cooler that uses a PM CEMS to monitor compliance with the PM
emission limit is exempt from opacity standards.
g. PM Standard for Clinker Coolers
    In addition to amending the PM standard for kilns we are similarly
amending the PM emissions limit for clinker coolers. Fabric filters are
the usual control for both cement kilns and clinker coolers. As EPA
noted in our proposed revision to the NSPS (73 FR 34078, June 16,
2008), we believe that the current clinker cooler controls can meet the
same level of PM control that can be met by the cement kiln. No
commenter challenged this. One commenter did state that PM limits for
clinker coolers should not be changed, but we disagree with that
comment for the reasons previously discussed on the PM limit for kilns.
Therefore, we are setting the same PM emissions limits and compliance
requirements for both clinker coolers and kilns.
h. Standards for Open Clinker Piles
    At proposal we noted that open clinker piles were currently
unregulated, and that hexavalent chromium emissions had been detected
in fugitive dust from these piles. See 74 FR at 21163. We requested
comment and information as to how common the practice of open clinker
storage is, appropriate ways to detect or measure fugitive emissions
(ranging from open-path techniques to continuous digital or
intermittent manual visible emissions techniques), any measurements of
emissions of hexavalent chromium (or other HAP) from these open storage
piles, potential controls to reduce emissions, or any other factors we
should consider.
    Commenters did not provide data on this practice. Industry
commenters stated emission were de minimis and should not be regulated.
Other commenters noted that the fact that we know these sources emit
HAP is sufficient to necessitate regulation.
    We agree that these operations do emit HAP and that regulation of
these sources is necessary. See National Lime, 233 F. 3d at 640
(upholding EPA position that de minimis exceptions are not to be read
into the MACT standard setting process). Because the emissions in
question are fugitive dust for which measurement is not feasible since
(by definition) the emissions are not emitted through a conveyance or
other device which allows their measurement (see section 112 (h)(1) and
(2)(A)), we are adopting the work practice standards and opacity
emissions limits contained in Rule 1156 as amended by the South Coast
Air Quality Management District on March 6, 2009 and incorporating them
into this rule. There are only two plants which EPA can state
definitively have open storage piles and are complying with Rule 1156,
so these existing regulatory standards would constitute a floor level
of control (and EPA does not believe beyond-the-floor controls are
needed, since utilizing some type of enclosure should well control
fugitive emissions). A summary of the requirements are as follows:
    If clinker material storage and handling activities occur more than
1,000 feet from the facility property-line,
    [cir] Utilize a three-sided barrier with roof, provided the open
side is covered with a wind fence material of a maximum 20 percent
porosity, allowing a removable opening for vehicle access. The
removable wind fence for vehicle access may be removed only during
minor or routine maintenance activities, the creation or reclamation of
outside storage piles, the importation of clinker from outside the
facility, and reclamation of plant clean-up materials. The removable
opening shall be less than 50 percent of the total surface area of the
wind fence and the amount of time shall be minimized to the extent
feasible;
    [cir] Storage and handling of material that is immediately adjacent
to the three-sided barrier due to space limitations inside the
structure shall be contained within an area next to the structure with
a wind fence on at least two sides, with at least a 5 foot freeboard
above the top of the storage pile to provide wind sheltering, and shall
be completely covered with an impervious tarp, revealing only the
active disturbed portion during material loading and unloading
activities;
    [cir] Storage and handling of other active clinker material shall
be conducted within an area surrounded on three sides by a barrier or
wind fences with one side of the wind fence facing the prevailing wind
and at least a 5-foot freeboard above the top of the storage pile to
provide wind sheltering. The clinker shall remain completely covered at
all times with an impervious tarp, revealing only the active disturbed
portion during material loading and unloading activities. The barrier
or wind fence shall extend at least 20 feet beyond the active portion
of the material at all times; and
    [cir] Inactive clinker material may be alternatively stored using a
continuous and impervious tarp, covered at all times, provided records
are kept demonstrating the inactive status of such stored material.
     If clinker material storage and handling activities occur
1,000 feet or less from the facility property-line these activities
must be in an enclosed storage area.
    In the SCAQMD regulation, there are different requirements for
active vs. inactive open clinker piles. An inactive pile is one that
had not been disturbed for 30 consecutive days. In addition, the ACAQMD
rule has different requirements for clinker piles that are 1,000 feet
or less form the facility property-line. This 1000 foot criterion was a
mutually agreed number among the stakeholders (both industry and
environmental groups) involved in developing the regulation.\35\ Given
the lack of additional data, we saw no reason to change these
criterion. More information on this rule is available at http://
www.aqmd.gov/hb/gb_cal95.html.
---------------------------------------------------------------------------

    \35\ Telecon with Tuyet-Le Pham, South Coast Air Quality
Management District. June 29, 2010.
---------------------------------------------------------------------------

    Industry commenters also maintained that regulation of open storage
piles would violate a 2001 settlement agreement between EPA and the
industry in which EPA agreed that the 1999 rule did not apply to
fugitive emission sources. But nothing in that settlement agreement
prevents EPA from amending its regulations if it is appropriate to do
so (nor could EPA legally bind itself in such a way). The agreement in
fact states that ``[n]othing in this Agreement shall be construed to
limit or modify EPA's discretion to alter, amend, or revise, or to
promulgate regulations that supersede, the

regulations identified in section III of this Agreement.''
Consequently, EPA's action today properly amends the current
regulation, and does not violate any provisions of the settlement
agreement.
i. Format of the Normalized Standards in the NESHAP and the NSPS
    Emission limits are typically normalized to some type of production
or raw material input value because this allows comparison (and
ultimately the ability to set a single standard) for different sized
facilities. As we noted at the NSPS proposal, the current NSPS and
limits (and NESHAP limits before today's amendments) for PM are
expressed on a pound of PM per ton (lb/ton) of dry feed input format.
See 73 FR at 34075-76. In this final NESHAP (and NSPS) we are adopting
a new normalizing parameter of lb/ton of clinker--i.e., normalizing
based on kiln output rather than input for both PM and mercury.
    We noted at proposal of the NSPS that adopting an output-based
standard avoids rewarding a source for becoming less efficient, i.e.,
requiring more feed to produce a unit of product, therefore promoting
the most efficient production processes. 73 FR at 34076. EPA therefore
proposed that all of the NSPS (for PM, NOx, and
SO2) be normalized by ton of clinker produced, and later
proposed the same parameter for the two standards in the NESHAP which
are normalized, mercury and PM. 73 FR at 34076; 74 FR at 21140.
    In this final NESHAP (and NSPS) we are therefore adopting a new
normalizing parameter of lb/ton of clinker--i.e. normalizing based on
kiln output rather than input--for mercury and PM in the NESHAP, and
for PM, NOx, and SO2 in the NSPS. Commenters
either supported this proposal, or did not question that normalizing by
output promotes more efficient production. However, commenters from
industry raised technical objections and concerns to the proposal. They
maintained that the measurement of kiln output is not as exact as the
measurement of kiln input, and that many kilns have not installed
clinker measuring equipment. These objections do not necessitate
normalizing by inputs. Most commenters also stated that kiln feed could
be accurately measured and also indicated that most facilities
currently derive reasonable feed-to-clinker conversion factors from
these measurements. Kilns already calculate clinker production in this
way when required to meet emissions limits normalized by clinker
production, as many NSR and PSD permits for cement kilns presently
do.\36\
---------------------------------------------------------------------------

    \36\ RACT/BACT/LAER Clearing house Report for Portland Cement.
November 25, 2009.
---------------------------------------------------------------------------

    Since it appears from comments that the equipment to accurately
measure clinker is not typically installed in this industry, we must
assume these facilities use a feed-to-clinker conversion factor to
calculate clinker production on whatever time basis is necessary (e.g.,
daily, hourly, etc.). Therefore, we have modified the rule language to
more clearly provide the option allowing facilities to measure feed
inputs and to use their site specific feed/clinker ratio to calculate
clinker production (and to make clear that no prior approval from a
regulatory authority is necessary to do so). Facilities would be
allowed to use a constant feed/clinker ratio in accord with their usual
cycles for determining such ratios, typically on a monthly basis when
clinker inventories are reconciled.
    Commenters were nonetheless concerned that because clinker/feed
ratios change somewhat and are only re-determined at the end of a
cycle, a slight change in clinker/feed ratio, determined at the end of
the cycle, could show lack of compliance without even an opportunity to
alter operation. To obviate this legitimate concern, the rule provides
that facilities are not required to retroactively update clinker
production estimates after recomputing feed/clinker ratios. We would
not expect that the clinker/feed ratio will change significantly from
month to month, so we do not see this as creating a situation where
facilities will be able to have large amounts of excess emissions but
still be considered in compliance (especially since the 30-day
standards are all rolling averages).
    So, for these reasons above we are adopting emission limits
normalized by kiln output for PM in both the NESHAP and the NSPS, for
mercury in the NESHAP, and for NOX and SO2 in the
NSPS (the same analysis applying to the limits in the NSPS).
2. What are the final operating limits under subpart LLL?
    EPA is eliminating the restriction, adopted in the 2006 rule, on
the use of fly ash where the mercury content of the fly ash has been
increased through the use of activated carbon once the kiln has
complied with a numerical mercury emissions limit. Given the emission
limitation for mercury, whereby kilns must continuously meet the
mercury emission limits described above (including when using these
materials) there does not appear to be a need for such a provision.
This provision is removed once a kiln is in compliance with the mercury
limitations adopted in this. We are removing the requirement at
compliance, rather than when the rule takes effect, to prevent the
possibility of additional mercury emissions between the rule's
effective date and the required compliance date. However, once the rule
takes effect EPA is removing the requirement to maintain the amount of
cement kiln dust wasted during testing of a control device, and the
provision requiring that kilns remove from the kiln system sufficient
amounts of dust so as not to impair product quality for the same
reasons. In this case, we do not see immediate removal of these
provisions as creating a likelihood of increased mercury emissions
prior to the compliance date.
3. What are the final testing and monitoring requirements under subpart
LLL?
    Kilns will be required to meet the following changed monitoring/
testing requirements:
     CEMS (PS-12A) or sorbent trap monitors (PS-12B) to
continuously measure mercury emissions, along with Procedure 5 for
ongoing quality assurance.
     CEMS meeting the requirement of PS-8 to measure THC
emissions for existing sources. (New sources are already required to
monitor THC with such a CEMS). Kilns meeting the organic HAP
alternative to the THC limit will still be required to continuously
monitor THC (based on the results of THC monitoring done concurrently
with the Method 320 test), and will also be required to test emissions
using EPA Method 320 or ASTM D6348-03 every 30 months to identify the
organic HAP component of their THC emissions.
     Installation and operation of a PM CEMS that meets the
requirements of PS-11.
     CEMS meeting the requirements of PS-15 will be required to
demonstrate compliance with the HCl standard for all kilns except those
using a caustic scrubber. If a facility is using a caustic scrubber to
meet the standard, EPA Test Method 321 and ongoing continuous parameter
monitoring of the scrubber may be used in lieu of a CEMS to demonstrate
compliance. The M321 test must be repeated every 30 months.
    Raw material dryers that are existing sources will also be required
to install and operate CEMS meeting the requirement of PS-8 to measure
THC emissions. (New raw material dryer sources are already required to
monitor THC with a CEMS). Raw material dryers

meeting the organic HAP alternative to the THC limit will still be
required to continuously monitor THC (based on the results of THC
monitoring done concurrently with the Method 320 test), and will also
be required to test emissions using EPA Method 320 or ASTM D6348-03
every 30 months to identify the organic HAP component of their THC
emissions.
    New or reconstructed raw material dryers and raw or finish mills
will be subject to longer Method 22 and, potentially, to longer Method
9 tests. The increase in test length duration is necessary to better
reflect the operating characteristics of sources subject to the rule.
EPA has included the costs associated with increased test duration in
its estimates of the rule's costs.
    The requirements above are the same as those proposed with the
following exceptions.
    For kilns and clinker coolers, EPA proposed to require bag leak
detection systems for fabric filters and an ESP predictive model to
monitor performance of an ESP. In this final rule we are requiring the
use of a PM CEMS for all PM control devices. We did receive comments on
technical issues associated with PM CEMS, which we have addressed in
the Comments and Responses Document in the docket to this rulemaking.
As explained earlier, we continue to believe that these devices provide
the most positive indication that a facility is actually complying with
the PM emissions limit. We also note that we promulgated a requirement
for PM CEMS in the 1999 final rule but deferred the compliance date
until the establishment of performance specifications. These
specifications have now been established as EPA Performance
Specification 11.
    In the proposed rule we specified that THC CEMS must meet the
requirements of performance specification 8A. Commenters correctly
pointed out certain deficiencies of the 8A method as applied to this
source category. In response to those comments we have changed the
requirement to PS-8.
    Where periodic performance tests are required for HCl we changed
the test frequency to 30 months because a commenter noted both chlorine
inputs and scrubber performance may change significantly over five
years. For similar reasons we changed the testing frequency for the
organic HAP option to 30 months. We believe aligning the test schedules
for all pollutants (dioxin furan, organic HAP, and HCl) to the same
testing schedule will allow for more efficient use of testing
resources.
4. Standards for Startup and Shutdown
    As noted above, the United States Court of Appeals for the District
of Columbia Circuit vacated portions of two provisions in EPA's CAA
section 112 regulations governing the emissions of HAP during periods
of SSM. Sierra Club v. EPA, 551 F.3d 1019 (DC Cir. 2008), cert. denied,
130 S. Ct. 1735 (U.S. 2010). Specifically, the Court vacated the SSM
exemption contained in 40 CFR 63.6(f)(1) and 40 CFR 63.6(h)(1), that
are part of a regulation, commonly referred to as the ``General
Provisions Rule,'' that EPA promulgated under section 112 of the CAA.
When incorporated into CAA section 112(d) regulations for specific
source categories, these two provisions exempt sources from the
requirement to comply with the otherwise applicable CAA section 112(d)
emission standard during periods of SSM.
    The effect of the vacatur is that the cross-reference to 40 CFR
63.6(f)(1) and 40 CFR 63.6(h)(1) in Table 2 to subpart LLL no longer
operates to incorporate an SSM exemption.
    In light of the Sierra Club decision, EPA proposed to require that
sources be in continuous compliance with emissions limits at all times,
even during startup, shutdown, and malfunction. 74 FR at 21161-62. We
proposed that these sources meet the same standards at all times. Id.
We also specifically asked for information on emissions during startup,
shutdown, and malfunction.
    In these final amendments we have eliminated the cross-reference to
the vacated General Provisions' exemptions contained in Table 1 of
current subpart LLL. In establishing the standards in this rule, EPA
has taken into account cement kilns' operating properties during
startup and shutdown periods and, for the reasons explained below, has
established different standards for those periods. EPA is not setting
separate standards for malfunctions so that, for the reasons explained
below, the standard that applies during normal operations applies
during periods of malfunctions. We have also revised Table 2 (the
General Provisions table) in several respects. For example, we have
eliminated the General Provisions' requirement that the source develop
an SSM plan. We have also removed certain recordkeeping and reporting
requirements related to the SSM exemption. EPA has attempted to ensure
that we have not incorporated into the regulatory text any provisions
that are inappropriate, unnecessary, or redundant in the absence of the
SSM exemption.
    Startup is the period of time between when fuel is first introduced
into a cement kiln that is not firing fuel, and when the kiln
temperatures are within normal operating limits, the kiln is using its
normal operating fuel, and the kiln is producing clinker. During kiln
startup, fuel is first introduced into the kiln to raise the kiln to
the appropriate operating temperatures. In the case of a cold start the
fuel is typically a natural gas or distillate fuel. Once the kiln
reaches certain temperatures, the normal operation fuel is introduced.
After the kiln reaches stable operating temperatures, kiln feed is
introduced in low amounts which are gradually increased. Because the
kiln feed is a significant source of most kiln emissions (HAP and
otherwise) we would consequently expect that kiln emissions, on a
concentration basis, would not be any higher during startup than during
normal operations, with any potential short-term emission spikes due to
transient conditions or release of emissions from materials left in the
kiln from the last operating period being accommodated through an
averaging period. Indeed, on a pure concentration basis, kiln emissions
over time would likely be lower than during normal operation given the
lesser volume of inputs being processed, and (at startup) the cleaner
fuel being used to heat the kiln to normal operating conditions.
    Notwithstanding that stack concentrations over time would likely be
the same or less than during normal operation, in some cases, the
manner in which the standard is expressed is not appropriate during
startup. Most particularly, the mercury and PM standards are normalized
to kiln production (amount of pollutant allowed being linked to a ton
of clinker produced). During startup, production is by definition
either non-existent or very low. Even where there is a modest amount of
production during startup, relationships between HAP concentration and
amount of product are skewed so as to make this means of measurement
inappropriate. In addition, normalized standards require accurate
measurements of kiln volumetric flow rate (used to convert
concentration into mass) and kiln flow rate, which changes in important
ways from normal values during startup. When considered along with such
phenomena as varying kiln stack moisture contents and flow rate, flow
rate measurements are significantly less accurate during startup than
during normal operation.
    For these reasons, we are establishing standards for mercury and PM
by converting the normal operation standards to a concentration basis.

These conversions are as follows: 55 lb mercury/MM tons clinker is
equivalent to 10 micrograms per dry standard cubic meter (ug/dscm); 21
lb mercury/MM tons clinker is equivalent to 4 ug/dscm; 0.04 lb PM/ton
clinker is equivalent to 0.004 grains per dry standard cubic foot (gr/
dscf); and 0.01 lb PM/ton clinker is equivalent to 0.0008 gr/dscf.
Mercury and PM would be measured during startup with a CEMS (as during
normal operation) and the concentration standard would be met on the
basis of 7-day averages. We do not believe a 30-day average is
appropriate for these periods because they are of short duration, and
it might take a period of 1 year or more to accumulate 30 days of
startup operation. We considered an averaging period equal to the time
period of each startup, but that would have meant different averaging
periods for each event. Therefore, we chose 7 days as a period short
enough to accumulate the data necessary to calculate the average over a
reasonable period (certainly less than a year) but long enough to allow
averaging out any transient spikes that may occur. In this way, short-
term spikes which occur during startup would be averaged against the
lower concentrations which otherwise typically maintained. A
consequence of this compliance regime (as for the standards which apply
during normal operation), is that a source (at least initially) cannot
determine compliance based on any single startup (or shutdown) event.
Seven days of data will need to be averaged.
    All of the discussion above applies to THC emissions during
startup: Feed (the main source of THC emissions) is introduced
gradually so THC emissions should ordinarily be lower, cleaner fuels
are initially used to heat the kiln to normal temperatures, etc. The
difference is that the THC standard is already expressed as a
concentration, so the measurement difficulties with a normalized
standard do not exist. However, during normal operation the THC
standard is corrected to a specified oxygen concentration to avoid the
situation where a facility uses dilution air to lower the measured
concentration. At startup, oxygen concentrations may be higher than
during normal operation, and may also fluctuate more. This could have
the effect of actually making the standard more stringent during
startup. Consequently, EPA is adopting the same concentration standard
for THC during startup as applies during normal operation, but is
removing the oxygen concentration correction factor. The standard is
measured with a CEMS and is based on a 7-day average so, that, again
the lower concentrations which ordinarily maintain at startup should
balance out any transient events that occur because the kiln is not yet
in steady state mode.
    HCl is also expressed as an un-normalized stack concentration
corrected to a specific oxygen concentration. Where measured with a
CEMS, EPA knows of no reason the same standard as applies during normal
operation should not be met during startup, except that the averaging
period would be 7 days and the oxygen correction factor would be
removed for the reasons noted above. However, for those units equipped
with wet scrubbers, sources may choose to demonstrate compliance by
means of stack testing and parametric monitoring. See Section IV.A.3.
In such a circumstance, there are no parameters to measure because HCl
will not be emitted. This is because HCl is emitted only as kilns begin
burning normal fuel, not the natural gas or distillate used as a fuel
during startup. Consequently, EPA is providing that emissions of HCl
shall be zero at all such times as distillate or natural gas is used to
fire the kiln (and that is the parameter which would be measured).
    The current standard for dioxins and furans is expressed either as
a concentration, or a combination of concentration and temperature
control at the inlet to the PM control device. Continuous compliance is
determined based on demonstrating the measured temperature at the inlet
to the PM control device does not exceed the limit established during
dioxin compliance testing. This is because higher PM control inlet
temperature can increase dioxin emissions. See 63 FR 14196, March 24,
1998. Based on a comment indicating that there can be an increase in
short-term temperature fluctuations during startup (and shutdown), EPA
is indicating in the startup standard that temperature measurements can
increase by 10 percent during these periods.
    Shutdown is the period of time between when kiln raw material feed
is shutoff and gas flow through the kiln ceases. Shutdown operations
are in many ways a mirror image of startup. During shutdown, the same
transient conditions and low product production rates occur as during
startup. Cement kilns cannot be immediately shut off. Even after the
feed is stopped, gas flow must be continued through the kiln and the
kiln continues to rotate to prevent kiln overheating and/or warping.
Moreover, the concerns about inability to have normalized standards or
standards with oxygen correction factors, air pollution control inlet
temperature variability, and lack of measureable HCl emissions when the
kiln is fired with distillate or natural gas and is not HCl CEM-
equipped, all apply at shutdown for the same reasons as at startup. For
this reason, we are setting the same limits for kilns during shutdown
operations as during startup.
    Periods of startup, normal operations, and shutdown are all
predictable and routine aspects of a source's operations. In the
proposed rule, EPA expressed the view that there are different modes of
operation for any stationary source, and that these modes generally
include startup, normal operations, shutdown, and malfunctions. 74 FR
at 21162. However, after considering the issue of malfunctions more
carefully, EPA believes that malfunctions are distinguishable from
startup, shutdown and normal operations. Malfunction is defined as a
``sudden, infrequent, and not reasonably preventable failure of air
pollution control and monitoring equipment, process equipment or a
process to operate in a normal or usual manner * * *'' (40 CFR 63.2).
EPA has determined that malfunctions should not be viewed as a distinct
operating mode or condition and, therefore, any emissions that occur at
such times do not need to be factored into development of CAA section
112(d) standards, which, once promulgated, apply at all times. In
Mossville Environmental Action Now v. EPA, 370 F.3d 1232, 1242 (DC Cir.
2004), the court upheld as reasonable standards that had factored in
variability of emissions under all operating conditions. However,
nothing in section 112(d) or in caselaw requires that EPA anticipate
and account for the innumerable types of potential malfunction events
in setting emission standards. See, Weyerhaeuser v Costle, 590 F.2d
1011, 1058 (DC Cir. 1978) (''In the nature of things, no general limit,
individual permit, or even any upset provision can anticipate all upset
situations. After a certain point, the transgression of regulatory
limits caused by `uncontrollable acts of third parties,' such as
strikes, sabotage, operator intoxication or insanity, and a variety of
other eventualities, must be a matter for the administrative exercise
of case-by-case enforcement discretion, not for specification in
advance by regulation.'')
    Further, it is reasonable to interpret section 112(d) as not
requiring EPA to account for malfunctions in setting emissions
standards. For example, we note that Section 112 uses the concept of
``best performing'' sources in defining MACT, the level of stringency
that major source standards must meet. Applying the concept of ``best

performing'' to a source that is malfunctioning presents significant
difficulties. The goal of best performing sources is to operate in such
a way as to avoid malfunctions of their units.
    Moreover, even if malfunctions were considered a distinct operating
mode, we believe it would be impracticable to take malfunctions into
account in setting CAA section 112(d) standards for this (or any other)
source category. As noted above, by definition, malfunctions are sudden
and unexpected events and it would be difficult to set a standard that
takes into account the myriad different types of malfunctions that can
occur across all sources in the category. Moreover, malfunctions can
vary in frequency, degree, and duration, further complicating standard
setting.
    In the event that a source fails to comply with the applicable CAA
section 112(d) standards as a result of a malfunction event, EPA would,
of course, determine an appropriate response based on, among other
things, the good faith efforts of the source to minimize emissions
during malfunction periods, including preventative and corrective
actions, as well as root cause analyses to ascertain and rectify excess
emissions. EPA would also consider whether the source's failure to
comply with the CAA section 112(d) standard was, in fact, ``sudden,
infrequent, not reasonably preventable'' and was not instead ``caused
in part by poor maintenance or careless operation.'' 40 CFR 63.2
(definition of malfunction).
    In response to comments urging that EPA not apply the same
standards to malfunctions as to normal operation, EPA recognizes that
even equipment that is properly designed and maintained can sometimes
fail and that such failure can sometimes cause (or in the case of 30-
day averages, contribute to) an exceedance of the relevant emission
standard. (See, e.g., State Implementation Plans: Policy Regarding
Excessive Emissions During Malfunctions, Startup, and Shutdown (Sept.
20, 1999); Policy on Excess Emissions During Startup, Shutdown,
Maintenance, and Malfunctions (Feb. 15, 1983)). EPA is therefore adding
to the final rule an affirmative defense to civil penalties for
exceedances of emission limits that are caused by malfunctions. See 40
CFR 63.1341 (defining ``affirmative defense'' to mean, in the context
of an enforcement proceeding, a response or defense put forward by a
defendant, regarding which the defendant has the burden of proof, and
the merits of which are independently and objectively evaluated in a
judicial or administrative proceeding). We also added other regulatory
provisions to specify the elements that are necessary to establish this
affirmative defense; the source must prove by a preponderance of the
evidence that it has met all of the elements set forth in 63.1344. (See
40 CFR 22.24). The criteria ensure that the affirmative defense is
available only where the event that causes an exceedance of the
emission limit meets the narrow definition of malfunction in 40 CFR
63.2 (sudden, infrequent, not reasonable preventable and not caused by
poor maintenance and or careless operation). The criteria also are
designed to ensure that steps are taken to correct the malfunction, to
minimize emissions in accordance with section 63.1348(d) and to prevent
future malfunctions. In any judicial or administrative proceeding, the
Administrator may challenge the assertion of the affirmative defense
and, if the respondent has not met its burden of proving all of the
requirements in the affirmative defense, appropriate penalties may be
assessed in accordance with Section 113 of the Clean Air Act (see also
40 CFR Part 22.77).
5. What are EPA's final actions on compliance dates?
    For existing sources we proposed a compliance date of 3 years after
the promulgation of the new emission limits for mercury, THC, PM, and
HCl to take effect. This is the maximum period allowed by law. See
section 112(i)(3)(A). We continue to believe a 3 year compliance period
is justified because most facilities will have to install emissions
control devices (and in some cases multiple devices) to comply with the
proposed emissions limits. Therefore, we have retained a 3 year
compliance data in this final rule.
    For new sources, the compliance date will be the effective date of
this final rule or startup, whichever is later. Because this is a major
rule as defined by the Congressional Review Act, the effective date of
the rule is 60 days after publication of the Federal Register.
    In determining the proposal date that determines if a source is
existing or new, we have decided to select the proposal date of these
final amendments, which is May 6, 2009, for all the standards.
    At proposal, we considered three possible dates, including March
24, 1998; December 5, 2005; and the proposal date of these final
amendments, which was May 6, 2009. As we noted at proposal, Section 112
(a)(4) of the Act states that a new source is a stationary source if
``the construction or reconstruction of which is commenced after the
Administrator first proposes regulations under this section
establishing an emissions standard applicable to such source.'' ``First
proposes'' could refer to the date EPA first proposes standards for the
source category as a whole, or could refer to the date the agency first
proposes standards under a particular rulemaking record or first
proposes the particular standards at issue. The definition is also
ambiguous with regard to whether it refers to a standard for the source
as a whole, or to a HAP-specific standard (so that there could be
different new source standards for different HAP which are regulated at
different times).\37\ At proposal we chose the date of December 5,
2005, as the proposal date that determines if a source is new or
existing for the mercury, HCl, and THC, and the May 6, 2009, date for
PM.
---------------------------------------------------------------------------

    \37\ See also 74 FR at 21158 n. 41 citing other statutory
provisions indicating that the phrase ``first proposes'' can have a
number of meanings.
---------------------------------------------------------------------------

    After consideration of comments on the selection of the date for
mercury, THC, and HCl, we believe that the May 6, 2009, date for all
pollutants is more in keeping with the evident intent of Section
112(a)(4) that source should have sufficient notice that new source
controls requirements can be considered in the initial design. We
accept commenters' argument that sources coming into existence between
the proposed date of the 2006 standards and the May 6, 2009, proposal
date of these amendments would have no reasonable means of ascertaining
the standards' final content and so lacked notice of what controls and
strategies to adopt. Since this is antithetical to the policy
underlying new source standards, EPA is adopting May 6, 2009, as the
date which determines if a source is existing or new.
    We note that there are currently sources subject to new source
limits for mercury and THC contained in the December 20, 2006, rule.
However, the mercury the new source standards in this final rule are
significantly different than the limits in the December 20, 2006, rule,
and we do not see how the affected sources could have anticipated this
change prior to proposal of these amendments. Accordingly, we have
selected a date that allows these facilities to design and install the
required control equipment.

B. What are EPA's final actions on 40 CFR part 60, subpart F?

1. What are the final kiln and clinker cooler emissions limits under 40
CFR part 60, subpart F?
    For ``new'' affected facilities constructed, modified, or
reconstructed after June 16, 2008, the final emission limits amend the
existing rules as follows:
     Change the format of the PM emission limits from lb/ton of
dry feed to lb/ton of clinker product;
     Reduce the PM emission limit for kilns from 0.3 lb/ton of
dry feed to 0.01 lb/ton of clinker;
     Set a limit on NOX emissions from kilns of 1.50
lb/ton of clinker; and
     Set a limit on SO2 emissions from kilns of 0.4
lb/ton of clinker, or, as an alternative, demonstrate a reduction in
SO2 emissions from the kiln of at least 90 percent; and
     Reduce the PM emissions limit for clinker coolers from 0.1
lb/ton dry feed to 0.01 lb/ton of clinker.
    The emission limits for affected facilities constructed, modified,
or reconstructed before June 16, 2008, remain unchanged in this
subpart. The rationale for these actions is discussed below.
a. NOX Limits for Kilns
    EPA proposed an NOX limit of 1.5 lb/ton of clinker based
on application of Selective Non-Catalytic Reduction (SNCR) to a new
precalciner kiln. At proposal we also considered a level of 1.95 lb/ton
clinker based on the use of SNCR control technology, and a limit of 0.5
lb/ton clinker based on the use of selective catalytic reduction (SCR)
technology.
    After evaluation of the comments, we have decided to adopt the
level of 1.5 lb/ton clinker in this final rule, as proposed. In
general, commenters agreed with the selection of SNCR as the basis of
the standard (i.e., it represents the performance of BDT). However,
there was disagreement over the appropriate emission limit that
represents BDT.
    Industry commenters requested a higher limit, claiming that site
specific properties of raw materials could create a situation where
application of SNCR technology to a well designed preheater/precalciner
kiln could not achieve the level of 1.5 lb/ton clinker without high
ammonia injection rates that would result in significant ammonia
emissions. To support their arguments they noted that EPA based the 1.5
lb/ton clinker level on the assumption that a well designed new
preheater/precalciner kiln could meet a level of 3.0 lb/ton clinker
without SNCR, so that this 3.0 lb/ton clinker should be the baseline
from which performance of SNCR is evaluated. 73 FR at 34079. They
pointed to several newer kilns that had difficulty meeting a level of
3.0 lb/ton clinker without SNCR, and attributed this difficulty to
``hard to burn'' raw materials at certain sites.
    We have rejected the industry argument that 1.5 lb/ton clinker is
not achievable for all new kilns using SNCR technology for the
following reasons. First, the commenters note some kilns without SNCR
cannot meet an NOX level of 3.0 lb/ton clinker. However,
they did not provide the actual levels of NOX emissions the
sources were designed to meet. The NOX emissions for a new
preheater/precalciner kiln are primarily a function of precalciner
design. Though two kilns may have the same basic precalciner design,
certain site specific design parameters will also affect NOX
emissions. A precalciner designed to meet a level above 3.0 lb/ton
clinker, will not necessarily be designed exactly the same way as one
designed to meet 3.0 lb/ton clinker. We are also aware that there are
kiln precalciner designs that were installed that do not represent best
design. We thus do not believe that these kilns' performance alters the
baseline from which performance of SNCR is evaluated. In addition, we
have enough examples of new preheater/precalciner kilns in various
locations in the country to indicate to us that an NOX limit
of 3.0 lb/ton clinker is generally achievable, regardless of location,
if the precalciner is properly designed. For example, several kilns in
Florida and a kiln in California have NOX emissions below
2.0 lb/ton clinker with no add-on controls. According to our
information, raw materials in Florida can be considered ``hard to
burn'' because of the significantly different hardness of Florida
limestone and silica (limestone being soft which create a fine grind,
the silica being harder which creates a more coarse grind) creates
problems with size distribution for the raw material necessitating more
fuel use and higher kiln temperatures with a consequent increase in
NOX emissions. Additional test data for two plants with
reported ``hard to burn'' mix were 1.89 and 2.4 lb/ton. Given these
facts, we believe the assumption that a new kiln without add-on
controls can meet a level of 3.0 lb/ton clinker over the long term is
very reasonable and so should represent a baseline for application of
SNCR performance. See also 73 FR at 34079 noting many other examples of
kilns without end-of-stack controls burning hard-to-burn inputs meeting
a level of 2.5 lb/ton of clinker.
    Second, although we based our 1.5 lb/ton clinker level on an SNCR
emission reduction of 50 percent, there are numerous examples of SNCR
systems achieving emission reductions greater than 50 percent and as
high as 80 percent or more. Id. These reductions were achieved without
appreciable ammonia slip. So even if a new kiln were to emit at levels
above 3.0 lb/ton clinker without end-of-stack controls, application of
SNCR would allow such a kiln to meet the 1.5 lb/ton clinker level. For
example, a new kiln emitting at 4.0 lb/ton clinker would only need an
emission reduction of 63 percent to meet the 1.5 lb/ton clinker level
for NOX.
    Finally, the NOX limit is based on a 30-day averaging
period to be consistent with the averaging periods for other regulated
kiln pollutants, and to allow for averaging of raw mill on and off
emissions. See 74 FR at 21144. Compared to other averaging options
(hourly or daily), this longer averaging time allows additional
operating flexibility to meet the limit.
    Based on comments received, we also considered setting an
NOX limit lower than 1.5 lb/ton clinker based on performance
of SNCR. However, we also rejected that option. We do have data that
indicate that some cement kilns are below 1.5 lb/ton clinker, but we do
not believe the current data support that any new kiln, regardless of
location (and consequent raw material inputs), could meet a level that
low.
    At proposal we also considered an NOX emissions level of
0.5 lb/ton clinker based on performance of SCR. We rejected that option
because at that time we did not believe that SCR was sufficiently
demonstrated technology for this industry. We are aware that there have
been three cement kilns in Europe that have successfully used SCR, and
that SCR technology is a demonstrated control technology for
NOX control for other source categories, such as utility
boilers. We also are aware that that one domestic cement company has
agreed to install SCR technology on one kiln as part of a settlement
agreement. However, we continue to question if SCR technology would be
effective at all locations where new kilns might be installed. The main
concern is the potential for dust buildup on the catalyst, which can be
influenced by site specific raw material characteristics present in the
facility's proprietary quarry, such as trace contaminants that may
produce a stickier particulate than is experienced at sites where the
technology has been installed. This

buildup could reduce the effectiveness of the SCR technology, and make
cleaning of the catalyst difficult resulting in kiln downtime and
significant costs. We were unable to estimate these costs and did not
include these costs in our overall cost estimates for SCR. For these
reasons, we have not selected SCR technology as the basis of BDT. We
will continue to follow this technology as it is applied in the U.S.,
and will reconsider this decision in the next review of this standard.
    Kilns equipped with alkali bypasses cannot be expected to meet the
NOX limit for the portion of the exhaust that goes to
bypass. Bypass gases are quickly cooled and do not remain at a
temperature long enough to treat using an SNCR system. For that reason,
we have revised the rule to clarify that for kilns with an alkali
bypass, only the main kiln exhaust gases are subject to the
NOX limit. Because all kilns do not require an alkali bypass
and the bypass gas stream is a small fraction of the total kiln exhaust
gas flow, any additional NOX emission resulting from this
exclusion will be minimal.
b. SO2 Limits for Kilns
    EPA proposed an emissions limit of 1.33 lb/ton clinker or 90
percent emissions reduction SO2 based on the performance of
a limestone wet scrubber applied to a kiln with high sulfur raw
materials. 73 FR at 34080. Commenters noted that this level was
considerably above the level of many of the recent best available
control technology (BACT) determinations, and was also above the level
actually achieved by the facility EPA used as the basis of this
proposed standard.
    At the time EPA proposed the 1.33 lb/ton clinker limit, we also
considered a limit of 0.4 lb/ton clinker based on the average of recent
BACT determinations for cement kilns. We chose the higher limit at
proposal because the 0.4 lb/ton limit would have resulted in new kilns
with moderate sulfur content raw materials experiencing a cost per ton
of SO2 removed of $6,000. However, we have changed our
proposed decision for two reasons. First, as a result of the NESHAP
requirement to meet a HCl emissions level of 3 ppmvd, we estimate that
all new kilns will have to install wet scrubbers for HCl control. See
section VI below. Hence, the cost of meeting the 0.4 lb/ton clinker
limit in the NSPS is minimal, only the cost of the SO2 CEM.
Second, since proposal we have revised our costs for dry lime
injection, which is the most cost-effective control technology for
controlling a moderate sulfur raw material kiln to the 0.4 lb/ton
clinker level. Based on our revised information, the cost of meeting a
0.4 lb/ton clinker emission limit now ranges from $470 to $1430/ton
SO2 for a kiln with high or moderate sulfur raw materials,
even if these costs are attributed to the NSPS rather than to the
NESHAP. Kilns with low sulfur raw materials can meet the 0.4 lb/ton
clinker level with no add-on controls. We consider these to be
reasonable costs, comparable with other costs for SO2
control EPA has deemed reasonable such as those in the Clean Air
Interstate Rule. See 70 FR at 25201 (May 12, 2005). So, even if a new
facility is able to meet the NESHAP HCl limit without any acid gas
controls, the cost per ton to meet a 0.4 lb/ton SO2 NSPS
limit is still reasonable.
    In the proposal, we considered a SO2 emissions level of
0.2 lb/ton clinker. However, this level adds little environmental
benefit beyond the 0.4 lb/ton limit, and for many facilities would not
be achievable based on the use of wet scrubber technology, which means
these facilities would opt for the 90 percent emission reduction
alternative (discussed below). For these reasons, we did not choose
this level as BDT.
    We also proposed a 90 percent reduction as an alternative limit to
the 1.33 lb/ton emissions limit. We are retaining this alternative in
the final rule.\38\ The alternative 90 percent reduction is to account
for situations where the sulfur content of the raw materials is so high
that, even with the most efficient SO2 control, a kiln
cannot meet the 0.4 lb/ton of clinker emissions limit. Design and
performance data indicate the 90 percent control is continuously
achievable for a well designed and operated wet scrubber.\39\
Compliance with the 90 percent reduction would be determined by
continuously monitoring SO2 at the control device inlet and
outlet. Continuous monitoring of SO2 at the inlet and outlet
is a positive demonstration that the standard is being continuously
met.
---------------------------------------------------------------------------

    \38\ Section 111(b) specifically indicates that standards may be
expressed as numerical limits or as percent reductions.
    \39\ Summary of Cement Kiln Wet Scrubber and Lime Injection
Design and Performance Data, May 29, 2008.
---------------------------------------------------------------------------

c. PM Emissions Limits for Kilns and Clinker Coolers
    We proposed a PM emissions limit of 0.86 lb/ton clinker based on
fabric filters using membrane bags. This specific level was chosen
because it is representative of the performance of this technology and
was equivalent to the new source limit contained in the Hazardous Waste
Combustor (HWC) NESHAP for cement kilns burning hazardous waste. This
rationale is no longer applicable, since EPA is reassessing the PM
limit in the HWC NESHAP. See USEPA Motion for Voluntary Remand in
 05-1441 (DC Circuit, August 29, 2008).
    As previously discussed in section IV.A., in this action we are
setting PM limits under the Portland Cement NESHAP of 0.04 lb/ton
clinker for existing sources and 0.01 lb/ton clinker for new sources
based on a 30 day rolling average. We project that new cement kilns
meeting the 0.01 lb/ton clinker limit will be using the same technology
which formed the basis of the proposed NSPS PM limit, namely fabric
filters and membrane bags. It should also be noted that we estimate
that many new facilities will need to install fabric filters in series
as part of mercury controls. This means that a new kiln will install PM
controls required to meet the 0.01 lb/ton limit in any case, so
establishing the same limit for PM in the NSPS not only is technically
justified, but has no cost. We also assessed the costs of installing
and operating fabric filters with membrane bags at proposal, and found
this to be a cost-effective control technology in any case. 73 FR at
34077. The technology would now be evaluated as more cost-effective
than at proposal, since greater PM reductions will result from its use.
Therefore, we are establishing an NSPS PM limit of 0.01 lb/ton clinker
in this final NSPS, averaged over 30 days (rolling average) and
measured with a CEM. For reasons previously discussed, we are setting
the same limit for clinker coolers. See section IV.A.g of this preamble
above. See section V for a discussion on measuring compliance with a PM
CEM.
d. Change in Format of the Standard From lb/ton Feed to lb/ton Clinker
    The change in format of the standard from feed to lb/ton clinker
was actually proposed in the NSPS. However, this issue was also raised
in response to the proposed PM and mercury limits in the NESHAP, and
was previously discussed in section IV.A.1.i.
e. Applicability of NSPS Limits to Modified Kilns
    At proposal we had one set of emission limits for PM,
SO2 and NOX that were applicable to all new,
reconstructed, and modified kilns. Commenters expressed concerns of the
ability of a modified kiln to meet the same limits as a newly
constructed kiln.
    The PM and SO2 limits are based on control technologies
that can be applied

to any kiln type and achieve the same control levels that would be
expected with a new kiln at similar costs. We see no issue here as to
technical feasibility. However, this is not necessarily the case with
NOX. New preheater/precalciner kilns with staged combustion
achieve NOX levels in the 2.0 to 3.0 lb/ton clinker range.
As discussed above, in developing the NOX limit, we assumed
this level as baseline in assessing the level achievable with SNCR,
which is the technology basis of BDT. However, older kiln designs can
have much higher NOX levels, ranging from 2.0 to 8.0 lb/ton
clinker. Kilns in the higher end of the range might need to achieve an
80 percent emissions reduction to meet the 1.5 lb/ton clinker
NOX limit. Industry commenters requested that EPA either
exempt modification from the NSPS, or set separate limits.
    In this final rule we are still including modified kilns as an
affected source. The suggestion that modified kilns be outright
exempted from these NSPS revisions appears legally strained, given that
modified sources are a type of new source for which EPA is obligated to
develop, and review and revise as appropriate. Moreover, if we were to
exempt modified kilns, then such sources would be free to increase
emissions without application of BDT, a particular concern with respect
to pollutants like NOX which are not presently regulated by
the NSPS. This would undermine the basis of section 111 standards,
where Congress wanted to assure that BDT was applied to modified
sources qualifying as ``new.'' The purpose of the Act is to enhance the
Nation's air quality (CAA section 101 (b)(1)), and new source
performance standards under section 111 serve that goal. Asarco v. EPA,
578 F. 2d 319, 327 (DC Cir. 1978). Commenters had also claimed that
other regulatory programs, most notably new source review, would result
in a site specific BACT determination if emissions increased. Though we
are always mindful of the interrelationship of different EPA regulatory
programs and their effects, we do not see this as sufficient reason not
to establish a NOX emissions limits for modified kilns.
    We further investigated whether we should set a different
NOX emissions limit for modified kilns. However, we believe
the BDT is the same, and are therefore establishing the 1.5 lb/ton
clinker as the limit for modified kilns. We have two reasons for doing
so. First, we note that there are kilns of older design that meet
levels below 1.5 lb/ton clinker, and in some cases below 1.0 lb/ton
clinker, with SNCR control. Therefore, modified kilns would not
necessarily be unable to meet the 1.5 lb/ton clinker limit. However,
sources always have the option of adding sufficient NOX
control to avoid an hourly emissions increase and avoid thus triggering
the modification provision. Cf. Asarco, 578 F. 2d at 328 (``the
operator of an existing facility can make any alternations he wishes in
the facility without becoming subject to the NSPS as long as the level
of emissions from the altered facility does not increase. Thus, the
level of emissions before alterations take place, rather than the
strict NSPS, effectively defines the standard that an altered facility
must meet''; the Court did not rule on the validity of these
unchallenged provisions (id. at n. 32)). The NOX controls
available to cement kilns which could be utilized to prevent an
increase in NOX emissions, in addition to SNCR, are
conversion to indirect firing, mid-kiln fuel injection, mid-kiln air
injection, and substitution of steel slag for some limestone.
f. Regulation of VOC/CO
    We are not establishing limits for CO or volatile organic compound
(VOC) emissions from cement kilns. VOC emissions from new cement kilns
will mainly result from organics in the raw materials. Organic
constituents in the raw materials can be driven off in the kiln
preheater prior to reaching temperature zone that would result in
combustion. All new cement kilns will be subject to a continuous 24
ppmvd THC emissions limit by the Portland Cement NESHAP previously
discussed. Because most of the THC are also VOC, the THC limit also
directly limits VOC, and serves as the baseline for the NSPS analysis.
This limit is also the new source limit based on the best performing
source. Therefore we determined that no additional regulation of VOC
emissions is necessary or feasible.
    Emissions of CO can come from two sources, unburned fuel from the
precalciner and CO evolved from the raw materials by the same mechanism
as the THC emissions. Unburned fuel represents an economic loss to the
facility. Therefore, new precalciners are designed to combust fuel as
efficiently as possible, and CO emissions from fuel combustion are
minimized, regardless of any potential emission limit.
    Emissions of CO evolved from raw materials can be significant if
there are substantial levels of organics in the raw material. As noted
at proposal, the only control technology identified to reduce CO
emissions is a RTO (which also would concurrently reduce any VOC
emissions). However, we believe application of an RTO as BDT for CO
would result in significant cost and adverse energy impacts. Therefore,
we determined that no additional regulation of CO emissions is
feasible.
    We also noted that in no cases had add-on controls for CO (or VOC)
been required as BACT under new source review.
g. Regulation of Greenhouse Gases (GHGs)
    In the proposal we did not propose standards of performance
covering GHGs due to concerns about ``issues related to the regulation
of GHGs under the CAA'' and noted that we were in the process of
evaluating avenues for addressing such concerns. See 73 FR at 34,084.
These concerns were specifically related to the Prevention of
Significant Deterioration and Title V permitting programs and the
unmanageable permitting burden that we anticipated would arise should
GHGs become subject to these programs as a result of regulation under
the Act.
    Since that time, we have issued regulations for GHG emissions under
the CAA through the light duty vehicle rule (75 FR 25324, (May 7,
2010)) and have finalized the greenhouse gas ``tailoring'' rule (75 FR
31514 (June 3, 2010)) and the Johnson memo reconsideration (75 FR 17004
(April 2, 2010)). As a result of these actions, as of January 2, 2011,
GHGs will become ``subject to regulation'' under the Act. Accordingly,
the Agency has now finalized a framework addressing the concerns that
were the basis of our decision not to propose standards of performance
for GHG emissions from this industry at the time we proposed this 8-
year review action.
    Today's final rule does not include a standard of performance for
GHG. There are two reasons for this. First, we did not propose such a
standard. Promulgating such a standard without providing opportunity to
comment on it would not be a logical outgrowth of the proposal and
would, accordingly, violate the norms of notice and comment rulemaking.
Second, we do not yet have adequate information about GHG emissions
sufficient to set a standard. This information forms the basis of
standards of performance, which must take into account achievability
and cost of such controls.
    This is not the end of the matter. To the contrary, based on our
current knowledge we believe that it may be appropriate for the Agency
to set a standard of performance for GHGs. We have historically
declined to propose standards for a pollutant where it is emitting in
low amounts or where we

determined that a BDT analysis would result in no control. National
Lime Assoc'n v. EPA, 627 F.2d at 426. Based on current information we
do not believe such circumstances are present here. Without prejudging
the outcome of a future regulatory process, we note the following
considerations.
    First, Portland cement is one of the largest stationary source
categories of GHG emissions, ranking as the third highest U.S. source
of CO2 emissions. Second, based on our initial evaluation it
appears that there are cost-effective control strategies for this
source category that would provide an appropriate basis for
establishing a standard of performance for GHG emissions. See 73 FR
44491, July 30, 2008. These control strategies include, for example,
energy efficiency measures, reductions in cement clinker content, and
raw materials substitution. There may be other cost-effective controls
as well.
    Based upon this preliminary evaluation, the Agency is working
towards a proposal for GHG standards from Portland cement facilities.
We are not, however, proposing such standards at this time because in
order to develop proposed standards we need additional information on
site specific factors that affect performance of these controls, where
they are currently applied, and control costs. We would also solicit
information on overall facility energy management practices. To this
end, the Agency will be sending out information requests to fill these
information gaps so that we are able to propose a standard addressing
GHGs in a timeframe that would allow the regulated community to make
sound investment decisions in response to these MACT and NSPS
requirements.
2. What is our final action on the other emission limits in the NSPS?
    We did not propose changes to the other emissions limits in the
NSPS, such as materials handling operations. We received one comment
recommending that we promulgate NSPS limits for clinker storage piles,
raw materials handling, and baghouse fall-out. Open clinker piles are
being regulated as part of the NESHAP as previously discussed.
Materials handling operations are currently regulated under NESHAP. We
believe baghouse fall out would be regulated as part of materials
handling standards.
3. What other changes are being promulgated?
    As previously noted, cement kilns are potentially subject to both
the NSPS and the Portland Cement NESHAP (40 CFR part 63, subpart LLL).
In Sec.  63.1356 of subpart LLL, we exempt any source subject to that
subpart from applicable standards under the NSPS and the Metallic
Minerals Processing NSPS (subpart OOO). That language was appropriate
because the NSPS only regulated PM, and the PM limits in the NSPS and
NESHAP were identical. At proposal, where the proposed new source PM
limits in the NSPS and NESHAP were different, we proposed to add
language in both the NSPS and the NESHAP to state that when there are
emissions standards for a specific pollutant that apply to an affected
source in both the NESHAP and the NSPS, the source should comply with
the most stringent limit, and is not subject to the less stringent
limit.
    This proposed language is still applicable even though in this
final rule we are setting identical new source PM standards in the NSPS
and NESHAP rule. For example, a cement kiln that is an existing source
under NESHAP subject to the 0.04 lb/ton clinker emissions limit could
potentially become modified under NSPS and also be subject to the 0.01
lb/ton clinker emissions limit. In addition, there is always a
possibility that other situation may occur where a source is subject to
differing emission limits under NSPS and NESHAP as a result of rule
changes.
4. What are the final testing requirements under subpart F?
    There are no PM, NOX or SO2 compliance
testing requirements; compliance is based on the use of a continuous
emissions monitor (see below).
5. What are the final monitoring requirements under subpart F?
    To demonstrate compliance with the PM emission limits, we are
amending the monitoring requirements to require the installation and
operation of a PM CEMS. The reason for this decision was previously
discussed. Because this requirement is also part of the Portland Cement
NESHAP, it will also apply to existing kilns currently subject to the
NSPS. Consequently, affected facilities under this rule are not subject
to an opacity standard to monitor compliance with the final PM
standard. The PM CEMS must be installed and operated in accordance with
the requirements of Sec.  60.63(g).
    We are also adding monitoring requirements for all emission sources
that are subject to the 10 percent opacity standard--that is, emission
sources other than the kiln and clinker cooler. We are requiring that
they meet the monitoring requirements for these same emission points
contained in the Portland Cement NESHAP, 40 CFR part 63, subpart LLL in
order to make the two rules consistent.
    Under the final amendments, compliance with the emission limits for
NOX and SO2 are also determined using continuous
emissions monitoring systems (CEMS). The requirements for the
installation, operation, and calibration of each CEM, including minimum
data requirements, are specified in the requirements in Sec.  60.63(k)
and (l). Under the final amendments, the owner or operator of kilns
that elect to comply with the alternative SO2 emission limit
of 90 percent reduction are required to continuously monitor
SO2 emissions at the scrubber inlet as well as the outlet.
These are the same requirements proposed. We received no comments on
the NOX monitoring provisions. Commenters objected to the
SO2 monitoring requirement for facilities that do not
require SO2 controls, suggesting stack tests every five
years instead. However, in these cases, it is possible that a source
might change a raw material and significantly increase SO2
emissions beyond the standard. If monitoring is not in place, these
excess emissions could be unchecked for five years before they were
discovered. We believe the cost of the SO2 monitor ($56,000)
is reasonable to prevent these excess emissions. These monitors are
well established technology that are already installed on over 30
cement kilns, including those without SO2 controls.

C. What is EPA's sector-based approach?

    Sector-based approaches are based on integrated assessments that
consider multiple pollutants in a comprehensive and coordinated manner
to manage emissions and CAA requirements. One of the many ways we can
address sector-based approaches is by reviewing multiple regulatory
programs together whenever possible. This approach essentially expands
the technical analyses on costs and benefits of particular
technologies, to consider the interactions of rules that regulate
sources. The benefit of multi-pollutant and sector-based analyses and
approaches include the ability to identify optimum strategies,
considering feasibility, costs, and benefits across the different
pollutant types while streamlining administrative and compliance
complexities and reducing conflicting and redundant requirements,
resulting in added certainty and easier implementation of control
strategies for the sector under consideration.

    In order to benefit from a sector-based approach for the cement
industry, EPA analyzed how the NESHAP under reconsideration relates to
other regulatory requirements currently under review for Portland
cement facilities. In this analysis we looked at how the different
control requirements that result from these requirement interact,
including the different regulatory deadlines and control equipment
requirement that result, the different reporting and recordkeeping
requirements, and opportunities for States to account for reductions
resulting for this rulemaking in their State implementation plans. The
requirements analyzed affect HAP and/or criteria pollutant emissions
from cement kilns and cover the NESHAP reconsideration, area source
NESHAP, and the NSPS revision and their collateral impacts on other
programs such as New Source Review (NSR), Regional Haze and the
National Ambient Air Quality Standards (NAAQS).
    As a result of the sector-based approach, this rulemaking will
reduce conflicting and redundant requirements by setting the same PM
emission limit requirement for both the Cement NESHAP and the Cement
NSPS. Also the sector-based approach facilitated the streamlining of
monitoring, record keeping and reporting requirements on both rules
reducing administrative and compliance complexities associated with
complying with both regulations. In addition, the sector-based approach
promotes a comprehensive control strategy that maximizes the co-control
of multiple regulated pollutants (i.e., mercury and HCl) while
obtaining SO2 and PM2.5 emission reductions as
co-benefits. These collateral SO2 and PM2.5
emission reductions may be considered for ``netting'' and ``offsets''
purposes under the major NSR program or as credits that could help
areas around the country with attainment of the SO2 or
PM2.5 NAAQS.
    For more information on our sector's analyses, its benefits and
interaction with NSR, NAAQS and Regional Haze please refer to the
preamble of the proposal of this rule (74 FR 21159-61).

V. Responses to Major Comments

    This section presents a summary of responses to major comments. A
summary of the comments received and our responses to those comments
may be found in Docket ID No. EPA-HQ-OAR-2007-0877 for subpart F and
Docket ID No. EPA-HQ-OAR-2002-0051 for subpart LLL.

A. What are the significant comments and responses on 40 CFR part 63,
subpart LLL?

    Comment: Many industry commenters (2830, 2832, 2836, 2841, 2844,
2845, 2858, 2859, 2863, 2864, 2874, 2890, 2908, 2910, 2914, 2915, 2916,
and 2917) stated that setting MACT floors on a pollutant-by-pollutant
basis violates the law and results in MACT floors that bear no relation
to emission limits that are being achieved at the best performing
existing sources. According to industry commenters, this method
violates the plain language and intent of section 112(d) of the Clean
Air Act (CAA) and its effect is a MACT floor that reflects a standard
that no one plant in existence currently achieves. Industry commenters
2832, 2841, 2844, 2845, 2846, 2910, 2914, 2915, and 2916 stated that
section 112(d)'s use of the terms best-performing and existing clearly
means that sources in a category or subcategory that are used to set
the MACT floor are to be real, not theoretical or hypothetical, sources
(42 U.S.C. 7412(d), 2006 and Northeast Maryland Waste Disposal
Authority, 358 F.3d at 954). They further contend that the phrase
achieved in practice can only mean that Congress intended actual
sources, performing under real-life conditions, to be the benchmark for
determining the MACT floors. Furthermore, the language of the statute
does not speak in terms of the best-performing source or sources for
each listed pollutant or group of pollutants (42 U.S.C. 7412(d)).
Rather, the focus is on the best existing source or sources for all
pollutants, and what these sources truly can achieve on an overall
basis. Industry commenters argue that EPA's pollutant-by-pollutant
methodology is also at odds with the legislative history underlying
section 112(d) (S. Rep. No. 228, 101st Cong., 1st Sess. 169, 1989).
    According to the industry commenters, the focus on overall
performance is not surprising because in the 1990 CAA Amendments
Congress abandoned section 112's previous focus on individual pollutant
standards, and adopted the technology-based multi-pollutant approach to
regulating toxics in use under the Clean Water Act (CWA). See S. Rep.
No. 228, 101st Cong., 1st Sess. 133-34 (1989). Thus, if one source can
achieve a firm degree of control for one pollutant but not for another,
there may be no justification for including it in the set of sources
from which the floor is calculated (Tanners' Council of America v.
Train, 540 F.2d 1188, 1193 (4th Cir. 1976) deeming CWA effluent
limitations guidelines not achievable where plants in EPA's database
were capable of meeting the limitations for some, but not all, of the
pollutant parameters).
    Some industry commenters (2845, 2910) stated that EPA's previous
use of a pollutant-by-pollutant analysis was based on authorities not
applicable to the CAA. EPA attempted to defend its practice of
establishing pollutant-by-pollutant MACT standards by citing Chemical
Mfr. Ass'n. v EPA, 870 F.2d 177, 239 (1989), clarified 885 F.2d 253,
264 (5th Cir. 1989), cert. denied, 495 U.S. 910, (1990), a case where
the Court held that, under the CWA, best available technology (BAT)
referred to the single best-performing plant on a pollutant-by-
pollutant basis.
    According to industry commenters 2845 and 2910, EPA's reliance on
Chemical Mfr. Ass'n is misplaced as the CAA's procedure regarding the
selection of MACT technologies differs on a textual basis from the
CWA's procedure for identifying best available technology. Under the
CWA, BAT standards are to be set based on the best practicable control
technology currently available. 33 U.S.C. 1311(b)(1)(A)(i)(2006). This
has led to pollutant-by-pollutant determinations. The CAA more narrowly
limits the basis for MACT designation to what has been achieved at
existing sources, not what could be hypothetically achievable on a per-
pollutant basis.
    One industry commenter (2890) stated that EPA appears to be
forgetting that the floor is only the first step in the process. Once
EPA has established a floor based on physical sources, it is directed
to go back and look at options beyond the floor. Those beyond the floor
options would include the best control for each pollutant on every
source. By correcting the floor approach, EPA would also correct the
issue identified by Judge Williams in his concurring opinion to the
Brick vacatur, where a floor that is designed to represent what has
been achieved is more stringent than what would be deemed achievable
under a MACT.
    Response: We disagree with the commenters who object to setting
MACT floors on a pollutant-by pollutant basis. Contrary to the
commenters' suggestion, section 112(d)(3) does not mandate a total
facility approach. A reasonable interpretation of section 112(d)(3) is
that MACT floors may be established on a HAP-by-HAP basis, so that
there can be different pools of best performers for each HAP. Indeed,
as illustrated below, the total facility approach not only is not
compelled by the statutory language but can lead to results so
arbitrary that the approach may simply not be legally permissible.

    Section 112(d)(3) is ambiguous as to whether the MACT floor is to
be based on the performance of an entire source or on the performance
achieved in controlling particular HAP. Congress specified in section
112(d)(3) the minimum level of emission reduction that could satisfy
the requirement to adopt MACT. For new sources, this floor level is to
be ``the emission control that is achieved in practice by the best
controlled similar source.'' For existing sources, the floor level is
to be ``the average emission limitation achieved by the best performing
12 percent of the existing sources'' for categories and subcategories
with 30 or more sources, or ``the average emission limitation achieved
by the best performing 5 sources'' for categories and subcategories
with fewer than 30 sources. This language does not address whether
floor levels can be established HAP-by-HAP or by any other means. The
existing source MACT floor achieved by the average of the best
performing 12 percent can reasonably be read as referring to the source
as a whole or to performance as to a particular HAP. The reference in
the new source MACT floor provision to ``emission control achieved by
the best controlled similar source'' can mean emission control as to a
particular HAP or emission control achieved by a source as a whole.
    Industry commenters also stressed that section 112(d) requires that
floors be based on actual performance from real facilities, pointing to
such language as ``existing source'', ``best performing'', and
``achieved in practice''. EPA agrees that this language refers to
sources' actual operation, but we repeat that the language says nothing
about whether it is referring to performance as to individual HAP or to
single facility's performance for all HAP. Industry commenters also
said that Congress could have mandated a HAP-by-HAP result by using the
phrase ``for each HAP'' at appropriate points in section 112(d). Doing
so would have removed ambiguity from section 112(d), but does not
compel any inference that Congress was sub-silentio mandating a
different result when it left the provision ambiguous on this issue.
The argument that MACT floors set HAP-by-HAP are based on the
performance of a hypothetical facility, so that the limitations are not
based on those achieved in practice, just re-begs the question of
whether section 112(d)(3) refers to whole facilities or individual HAP.
All of the limitations in the floors in this rule of course reflect
sources' actual performance and were achieved in practice.
    The reason EPA has long adopted the interpretation that the
existing and new source MACT floors are to be applied on a HAP-by-HAP
basis are that a whole plant approach likely yields least common
denominator floors--that is floors reflecting mediocre or no control,
rather than performance which is the average of what best performers
have achieved. See 61 FR at 173687 (April 19, 1996); 62 FR at 48363-64
(September 15, 1997) (same approach adopted under the very similar
language of section 129(a)(2)). For example, if the best performing 12
percent of facilities for HAP metals did not control organics as well
as a different 12 percent of facilities, the floor for organics and
metals would end up not reflecting best performance. For new sources,
not only would the floor reflect unoptimized control, but EPA would
have to make some type of value judgment between control of organics
and metals just to decide which source was best controlled.\40\
---------------------------------------------------------------------------

    \40\ Another industry commenter (2859) stated that it had three
sources which were best performers for mercury and three other
sources which were best performers for PM but that each would need
to make upgrades for the pollutant not currently fully controlled.
EPA views this as another least common denominator example whereby
each of the floors would be diluted due to the coincidence that
facilities are not optimizing control of all their emitted
pollutants. See also Petitioners Brief in Medical Waste Institute et
al. v. EPA, No. 09-1297 (DC Cir.) pointing out, in this context,
that ``the best performers for some pollutants are the worst
performers for others'' (p. 34) and ``[s]ome of the best performers
for certain pollutants are among the worst performers for others.''
---------------------------------------------------------------------------

    Commenters provided no description of how their total facility
approach would work in practice. Would a source that is a best
performer for PM and worst for other HAP be in the pool? Would there be
some overall summing of where the kiln fell for each pollutant? Would
there have to be value judgments made among pollutants (is being a best
performer for mercury worth more than for PM in a ranking process)? EPA
evaluated an approach whereby every kiln was ranked for performance for
each HAP and the results were summed with the lowest overall score
being the best performer, and next lowest the second best, etc. (among
other things yielding a tie for best performer with no non-arbitrary
way to break the tie). Using this approach, and with the three lowest
ranked kilns as the average of the best performers, standards (after
applying the UPL equation) would be approximately 65 lb/MM tons of
clinker for mercury, 90 ppm for THC (nearly four fold increase), and
0.12 for PM (over an order of magnitude increase). All but one kiln in
the data base already meets the THC standard, 21 of 89 kilns would meet
the mercury limit, and 27 of 46 kilns have stack test measurements less
than the 30-day value for PM. See memorandum, ``Total Facility Approach
for Setting MACT Floors'', August 6, 2010.\41\ These inflated values,
and especially the drastically inflated THC and PM values, simply do
not reflect best performance.
---------------------------------------------------------------------------

    \41\ This example could have been more extreme. One of the
ultra-high mercury emitting sources is nearly a best performer for
HCl (it is just outside the pool of three best performers).
Inclusion as a best performer, under some methodologies, would have
added these mercury emissions to the pool of ``best performers'',
even though, for mercury, performance is the worst.
---------------------------------------------------------------------------

    These types of results are at odds with Congress' purpose in
adopting MACT floors. The central purpose of the amended air toxics
provisions was to apply strict technology-based emission controls on
HAPs. See, e.g., H. Rep. No. 952, 101st Cong. 2d sess. 338. The floor's
specific purpose was to assure that consideration of economic and other
impacts not be used to ``gut the standards. While costs are by no means
irrelevant, they should by no means be the determining factors. There
needs to be a minimum degree of control in relation to the control
technologies that have already been attained by the best existing
sources.'' A Legislative History of the Clean Air Act Vol. II at 2897
(statement of Rep. Collins). An interpretation that the floor level of
control must be limited by the performance of devices that only control
some of these pollutants effectively ``guts the standards'' by
including worse performers in the averaging process, whereas EPA's
interpretation promotes the evident Congressional objective of having
the floor reflect the average performance of best performing sources.
Since Congress has not spoken to the precise question at issue, and the
Agency's interpretation effectuates statutory goals and policies in a
reasonable manner, its interpretation must be upheld. See Chevron v.
NRDC, 467 U.S. 837 (1984).\42\
---------------------------------------------------------------------------

    \42\ Since industry commenters argued that the statute can only
be read to allow floors to be determined on a single source basis,
commenters offered no view of why their reading could be viewed as
reasonable in light of the statute's goals and objectives. It is not
evident how any statutory goal is promoted by an interpretation that
allows floors to be determined in a manner likely to result in
floors reflecting emissions from worst or mediocre performers.
---------------------------------------------------------------------------

    It is true that legislative history can sometimes be so clear as to
give clear meaning to what is otherwise ambiguous statutory text. As
just explained, EPA's HAP-by-HAP approach fulfills the evident
statutory purpose and is supported by the most pertinent legislative
history. A few

industry commenters nonetheless indicated that a HAP-by-HAP approach is
inconsistent with legislative history to section 112(d), citing to page
169 of the Senate Report. Since this Report was to a version of the
bill which did not include a floor provision at all (much less the
language at issue here), it is of no relevance. National Lime II, 233
F. 3d at 638.
    Other industry commenters pointed out correctly that the section
112(d) air toxic provisions were modeled on the technology-based
control scheme for water toxics in the Clean Water Act. S. Rep. No.
228, 101st Cong. 2d sess. 133-34. However, a HAP-by-HAP approach to
standard setting has actually been adopted and upheld under the Clean
Water Act. Section 301(b)(2)(A) of the Clean Water Act requires plants
to control discharges of toxic pollutants to a degree reflecting
performance of ``best available technology economically achievable.''
In Chemical Manufacturers Ass'n v. EPA, 870 F. 2d 177, 238 (5th Cir.
1989) the Court held that this requirement could permissibly be applied
on a pollutant-by-pollutant basis:

    The legislative history of the CWA indicates that the ``best
available technology'' refers to the single best performing plant in
an industrial field. The EPA urges that because the Act and the
legislative history do not provide more particular guidance, it was
free to determine the ``best'' plant on a pollutant-by-pollutant
basis. The Supreme Court has stated that ``it is by now commonplace
that `when faced with a problem of statutory construction, this
Court shows great deference to the interpretation given the statute
by the officers or agency charged with its administration.''' This
Court defers to the EPA's interpretation of the Act. The EPA's
interpretation of the Act is rational and is not precluded by the
legislative history'' (internal citations omitted).

The Court reaffirmed its holding on this issue at 885 F. 253, 264 (5th
Cir. 1989).
    Industry commenters stated that the Clean Water Act requirement of
Best Available Technology Economically Achievable and Best Practicable
Technology is not the same as the Clean Air Act's requirement of
maximum achievable control technology. These distinctions do not seem
pertinent to the issue at hand. Both statutes require technology-based
performance to control all toxics discharged or emitted, and both
require standards to be achievable. The legislative history to section
112(d) makes clear that the CAA provisions are modeled after those in
the Water Act (as industry commenters correctly noted). EPA does not
see any more certainty in the CWA than in the Clean Air Act on this
point and believes its interpretation that a pollutant-by-pollutant
approach is justified is as reasonable under section 112(d)(3) of the
CAA as it is under section 301(b)(2) of the Clean Water Act.\43\
---------------------------------------------------------------------------

    \43\ One industry commenter cited Tanners' Council of America v.
Train, 540 F. 2d 1188, 1193 (4th Cir. 1976) for the proposition that
technology-based effluent limitation guidelines under the Clean
Water Act are not considered achievable ``where plants in EPA's
database were `capable of meeting the limitation for some, but not
all, of the pollutant parameters' ''. Tanners' Council involved a
situation where EPA established standards for one source category
based on a transfer of performance information from a different,
unrelated source category. 540 F. 2d at 1192-93. Since the
wastewater from the category from which the limits were transferred
was easier to treat than tannery wastewater, the court was skeptical
of EPA's undocumented assertions that the transfer of performance
data (with certain upward adjustments) was permissible. Id. None of
these circumstances apply here. EPA is not transferring performance
from another category, but basing limits on documented performance
of cement kilns. In addition, as noted in earlier preamble text, all
of the kilns in the pool of best performers for each HAP is meeting
the limit for that HAP, a strong showing of technical feasibility
and technical achievability. Cf. CPC International v. Train, 540 F.
2d 1329, 1333 (8th Cir. 1976); American Meat Inst. v. EPA, 526 F. 2d
442, 458, 459 (7th Cir. 1975). Further, as discussed in the final
part of this comment response, EPA has closely examined and is
unaware of any situation whereby optimized performance for one HAP
interferes with or otherwise precludes or impedes optimized
performance for another.
---------------------------------------------------------------------------

    Industry commenters also noted that EPA retains the duty to
investigate and, if justifiable, to adopt beyond the floor standards,
so that potential least common denominator floors resulting from the
whole facility approach would not have to ``gut the standards.'' That
EPA may adopt more stringent standards based on what is ``achievable''
after considering costs and other factors is irrelevant to how EPA is
required to set MACT floors. MACT floors must be based on the emission
limitation achieved by the best performing 12 percent of existing
sources, and, for new sources, on the level achieved by the best
controlled similar source, and EPA must make this determination without
consideration of cost. At best, standards reflecting a beyond-the-floor
level of performance will have to be cost-justified; at worst,
standards will remain at levels reflecting mediocre performance. Under
either scenario, Congress' purpose in requiring floors is compromised.
    EPA notes, however, that if optimized performance for different
HAPs is not technologically possible due to mutually inconsistent
control technologies (for example, metals performance decreases if
organics reduction is optimized), then this would have to be taken into
account by EPA in establishing a floor (or floors). The Senate Report
indicates that if certain types of otherwise needed controls are
mutually exclusive, EPA is to optimize the part of the standard
providing the most environmental protection. S. Rep. No. 228, 101st
Cong. 1st sess. 168 (although, as noted, the bill accompanying this
Report contained no floor provisions). It should be emphasized,
however, that ``the fact that no plant has been shown to be able to
meet all of the limitations does not demonstrate that all the
limitations are not achievable.'' Chemical Manufacturers Association v.
EPA, 885 F. 2d at 264 (upholding technology-based standards based on
best performance for each pollutant by different plants, where at least
one plant met each of the limitations but no single plant met all of
them).
    All available data for cement kilns indicate that there is no
technical problem achieving the floor levels for each HAP
simultaneously, using the MACT floor technology. For most kilns,
compliance with the mercury limits will be accomplished using activated
carbon injection followed by a second PM control consisting of a fabric
filter. There is no technical impediment to using this same system for
control of THC (or organic HAP). Note that the ACI system would have to
be installed downstream of the existing PM control, therefore there
would be no effect on the cement kiln dust collected in the existing PM
control. One industry commenter claimed that carbon is not effective on
mercury and THC at the same time. However, we see no basis for that
statement as long as the correct type of carbon is used. Another
industry commenter claimed ACI increases dioxin emissions. Considering
the fact that ACI can actually be used to remove dioxins from kiln
exhaust gas, we see no basis for that statement either.
    After the ACI system, a wet scrubber can be used for HCl control.
We would expect the wet scrubber to be the downstream control because
it creates a moisture laden exhaust that would require reheating to
then apply ACI. Again, there is no technical impediment to adding a wet
scrubber after the ACI system, and the two control devices should not
interfere with each other's performance. If the facility required an
RTO to meet the THC limit, the RTO would be installed downstream of the
wet scrubber in order to protect the RTO from any acid gases in the
kiln exhaust. The wet scrubber/RTO combination has been demonstrated in
cement kiln applications.
    In order to meet the PM standard a facility could choose to modify
their

existing PM control to meet the new limit, or design the baghouse
downstream of the ACI injection point to meet the PM limit.
    Though we have described some fairly complicated control scenarios,
there are simpler applications of control technology that would likely
be utilized successfully. One example would be simultaneous injection
of alkaline materials (lime or sodium compounds) and activated carbon
downstream of the existing PM control device followed by collection
with a fabric filter. This type of injection scheme would potentially
control acid gases (HCl and SO2), THC (or organic HAP)
mercury, and PM.
    Industry commenters made much of the fact that no single facility
is presently achieving all of the HAP limits proposed. But this only
shows that plants will need to reduce their emissions of certain HAP to
meet standards reflecting average of best industry performers for that
HAP.
Impacts of Pollutant-by-Pollutant Approach
    Comment: Industry commenters 2831, 2844, 2845, and 2874 stated that
in evaluating the economic cost of achieving emission reductions,
looking at one plant's emission control of only one pollutant to the
exclusion of all other emission controls produces a disjointed view of
cost implications and compliance feasibility. While an individual MACT
floor for one pollutant might not appear cost-prohibitive, when
combined with all of the other MACT floors for other pollutants, the
total cost implications could become especially onerous. While the CAA
was authored with the intent of reducing air pollution, Congress did
not intend to disrupt the productive capacity of the United States
through the promulgation of economically unachievable standards. 42
U.S.C. 7401(b)(1)(2006). By setting MACT floors individually and
ignoring the collective cost implications of the entire NESHAP, EPA
would effectively disregard the CAA's requirement that air pollution
control be advanced while promoting the nation's productive capacity.
Id.
    Response: EPA is forbidden by law from considering costs in
determining MACT floors. NRDC v. EPA, 489 F. 3d 1364, 1376 (DC Cir.
2007); National Lime, 233 F. 3d at 640. Although one of the overall
goals of the Act is to protect and enhance the quality of the Nation's
air and resources so as to promote the public health and welfare and
the productive capacity of the population,'' CAA section 101 (b) (1),
this overall goal does not somehow authorize EPA to adopt floors that
either consider costs (overall or otherwise) or to base floors on other
than what best performers achieve.
2.3.3 Lowest Emitters as Best Performers
    Comment: One industry commenter (2834) stated that the Brick MACT
ruling of the DC Circuit Court reinforces earlier holdings in National
Lime Association vs. EPA. The Court again held that floors are to be
based on the emission level actually achieved by the best performers
(those with lowest emission levels), not the emission level achievable
by all sources.
    Response: In this rule, EPA is choosing as best performers those
sources with lowest emissions of each HAP, on a normalized basis, with
sources' variability taken into account in assessing which had the
lowest emissions.
    Comment: Many industry commenters (2841, 2844, 2845, 2846, 2858,
and 2914) stated that EPA established its proposed floors equating best
performing sources with those that have the lowest emissions for
particular HAPs even though there are other ways to measure performance
and, in some cases, other methodologies may comply with the statute
where the ``lowest emitter'' approach does not. Industry commenter 2845
noted that equating best performer with lowest emitter contravenes a
Congressional directive that, in developing MACT standards, EPA cannot
require substitution of raw materials in mineral processing industries,
such as cement manufacturing, quoting the Joint Explanatory Statement
of the Committee of Conference for the 1990 CAA Amendments stated: For
categories and subcategories of sources of [HAPs] engaged in mining,
extraction, beneficiation, and processing of nonferrous ores,
concentrates, minerals, metals, and related in-process materials, the
Administrator shall not consider the substitution of, or other changes
in, metal- or mineral-bearing raw materials that are used as feedstocks
or material inputs * * * in setting emission standards, work practice
standards, operating standards or other prohibitions or requirements or
limitations under this section for such categories and subcategories.
H.R. Rep. No. 101-952, at 339 (1990). According to the industry
commenters, enormous amounts of limestone are fed into a kiln to
manufacture clinker, and it is cost-prohibitive to import limestone
from further away. If the plant's quarry contains limestone with high
concentrations of mercury or high concentrations of organics, the kilns
will emit more mercury or THC and potentially more organic HAPs.
Because limestone with high mercury or organic emissions will result in
higher HAP emissions, and it is not cost-effective to import limestone
from far away, equating the lowest emitters with the best performing
sources makes no sense in the context of cement facilities. It also
would be squarely in opposition to the Joint Explanatory Statement.
    Response: The industry commenter is citing to the ``Joint
Explanatory Statement'' that accompanied the Conference Committee
Report to the 1990 Clean Air Act Amendments. This legislative history
is of limited utility here. As explained at 353 F. 3d 388: ``The Joint
Explanatory Statement describes how the differences between the Senate
and House were resolved in the Conference Committee * * *. The Joint
Explanatory Statement may be helpful in determining Congress's intent,
but does not carry the same weight as the Conference Committee Report
itself.'' See id. at 236-37. If there were some ambiguity in the
statute, the Joint Conference Committee Report could shed some light on
Congress' intent, but there is no exception to section 112(d)(2)(A)'s
requirement that EPA consider ``substitution of materials'' for each
source category. Thus, the statement cannot be read to negate the
express statutory command that MACT is to be based on, among other
things, measures, processes, or systems which reduce the volume of
pollutant emissions through substitution of materials or other process
modifications. Indeed, EPA's attempts to identify best performers by
ignoring the contribution of raw material inputs have been soundly
rejected. Brick MACT, 489 F. 3d at 882-883. In fact, brick and ceramic
production, like Portland cement production, involves extraction of
mined material from a quarry located proximate to the production
facility because transport of raw material over long distances is
``infeasible''. 489 F. 3d at 879. The language from the Joint
Explanatory Statement no more allows EPA to ignore raw material
contribution to Portland cement plants' HAP emissions than it did raw
material HAP contributions to brick and ceramic plants' HAP emissions.
    Comment: Industry commenter 2844 stated that EPA could interpret
section 112(d)(3) as Brick MACT appears to do, as one unitary concept
meaning sources with the lowest emission levels, or EPA can interpret
it as a more complex concept that EPA may determine the emission
control (using any of the various definitions in the CAA) that

sources have achieved in practice (as estimated by reasonably
predictive variability factors) and rank them according to their
relative emissions levels (i.e., a quantitative measure of
achievement). Having done so, the Agency can then evaluate each of the
lowest emitters in terms of whether they meet the Agency's criteria for
best controlled similar source. With regard to best controlled, EPA may
evaluate this from a purely quantitative angle (lowest emissions) or
from more qualitative aspects, reduction efficiency, environmental and
health (or cross-media) impacts, cost-effectiveness of reductions
achieved, impacts on other HAP or pollutant emissions, and so on.
    Industry commenter 2845 provided several examples of judicial MACT
decisions endorsing a technology approach to setting the standards, in
which EPA selected the best performing sources based on the relative
performance of air pollution control technology.
    Industry commenter 2844 stated that EPA also has the discretion to
define best performers as sources other than those with the lowest
achieved emission levels. In the current proposal, the many
difficulties associated with evaluating the impact of HAP content in
the raw material inputs to mercury emission control and other factors
could support a decision by the agency to establish a standard based on
efficiency (i.e., a percent reduction standard) if not for the source
category as a whole, then such a standard might be established for a
particular subcategory as relevant, or as an alternative compliance
strategy. EPA's discretion is sufficiently broad to encompass many
reasonable decisions identifying and estimating the emission control of
best performing sources on bases other than lowest emissions data,
assuming the floor for the standard is based on a reasonable
methodology estimating the percent reduction achieved in practice by
the best performing sources under the reasonably foreseeable worst
operating conditions.
    Industry commenter 2844 stated that before EPA can determine a
floor, EPA must define the following terms in regard to the selection
of a best performer for new sources: Emission control; Achieved in
practice; Best controlled; and Similar source.
    To set the floor for existing sources, the industry commenter
stated that EPA should define the following terms: Average emission
limitation; Achieved; and Best performing.
    Response: EPA must make determinations in each standard as to each
of these terms and has done so here. In this rule, EPA is determining
that the best controlled similar source is the source with the lowest
emissions of the HAP in question on a normalized basis (for mercury and
PM), and on a concentration basis (for THC and HCl) considering
variability in determining both which source is best controlled and in
estimating its achieved performance. EPA is adopting the same approach
for existing sources in determining which are the 12 percent of best
performing sources and the performance they achieve. This approach
accounts for all HAP inputs and outputs (i.e., accounts for HAP in all
raw material and feed inputs as well as all emission controls), and is
consistent with the case law.
    With regard to the comment stating that the standard could be
expressed as a per cent reduction, the industry commenter did not
explain how this can be done without negating the contribution of HAPs
in feed and fuel input into plant performance. Most particularly, for
HAP which are uncontrolled, mercury being the chief example in this
rule, there is no removal efficiency to evaluate. Moreover, even for
HAP which are controlled, plants with higher removal efficiencies may
also be the highest emitters if the levels of the inputs to the control
device is high. For these reasons, EPA is not evaluating best
performers based on removal efficiencies in this rule.
    Comment: Industry commenters 2832, 2846, and 2890 stated that
rather than selecting sources with the lowest emissions for particular
HAP as best performing sources, EPA could use the relative performance
of air pollution control technology to select the best performing
sources, applying the best reasonable method for determining best-
performers, which does not necessarily have to equate to lowest
emissions.
    Response: EPA discussed this issue at some length at proposal. See
74 FR at 21149. The problem with equating best performance with
performance of pollution control alone is that it ignores the
contribution of raw materials and fuels to HAP emissions. Basing
standards exclusively on performance of control technology is legally
permissible when the control technology is the sole factor influencing
performance, which is not the case here. National Lime, 233 F. 3d at
633-34. EPA thus is not adopting these industry commenters' approach.
See previous response as well.
    Comment: Several industry commenters (2845, 2846, 2874, and 2915)
stated that EPA is proposing to calculate MACT floors by averaging the
top 12 percent of sources for which CEMS data are available (even if
that amounts to less than 30 sources), rather than by considering the
top 12 percent of sources for which EPA has emissions information. As a
result, EPA is proposing to establish the MACT floor based on data from
only 2 sources. The industry commenters stated that CAA section 112(d)
obligates EPA to set the MACT floor looking at no fewer than 5 sources,
recognizing the value of relying on the maximum amount of data
available.
    Industry commenter 2841 stated that the use of a minimum of five
facilities should be adopted in the establishment of THC standards as
well as the other standards in this proposed regulation. The
establishment of requirements based on a small amount of data would run
counter to the intent of the CAA in utilizing data that is truly
representative of the best-performing facilities throughout an entire
industry.
    Industry commenter 2841 stated that in previous MACT rulemakings,
EPA used the five best performing facilities if the number of
facilities was less than 30. Consistent with these prior rulemakings,
the industry commenter stated that this approach should be used for
this proposed Portland Cement NESHAP rule and that EPA needs additional
data points in order to appropriately set limits for the industry as a
whole.
    Response: EPA believes that it has discretion to use the data which
most accurately measure sources' performance, which for THC case are
data obtained from CEM-equipped sources. EPA also believes that it has
a reasoned technical basis for not combining CEMS data with non-CEM
data, since this would be a classic apples-to-oranges comparison due to
the difference in measuring times and methods. EPA does not agree that
section 112 (d)(3) mandates a minimum of 5 sources in all instances,
notwithstanding the incongruity of having less data to establish floors
for larger source categories than is mandated for smaller ones. The
literal language of the provision appears to compel this result.
    Comment: One environmental advocacy group commenter (2898)
supported EPA's decision to not rank best performers based on their
relative mercury removal efficiency. Relying on mercury removal
efficiency in setting the MACT floor for the Portland cement
manufacturing industry would downplay the role of HAP inputs on
emissions. EPA characterizes Brick MACT's statement that best
performers are those emitting the least HAP as appearing arguably in
dicta. However, the Brick MACT Court itself

characterizes the statement as the holding of the Cement Kiln case.
Brick MACT, 479 F.3d at 880 (relying on Cement Kiln's holding that
Sec.  7412(d)(3) requires floors based on the emission level actually
achieved by the best performers or those with the lowest emission
levels). The proposed alternative of setting the MACT floor on the
basis of percentage of emission reduction achieved by sources would
minimize, if not eliminate, the consideration of cleaner inputs in
setting MACT floors, as EPA acknowledges, and is therefore contrary to
statutory dictates and case law.
    Response: EPA agrees that the chief legal issue with a percent
reduction approach for expressing floors is that it undervalues the
role of HAP inputs. EPA is not adopting that approach in this
rulemaking.
    Comment: Several industry trade association commenters (2831 and
2901) stated that EPA retains considerable discretion on how to set
MACT floors. The commenters supported the Agency's authority to set
floor standards based on control efficiency, or any method as long as
their method reasonably estimates the performance of the relevant best
performing plants. There is nothing in the Court's decisions that
requires EPA to use the straight-emissions approach favored in this
rule. The commenter stated that the Court has expressly decided that a
straight emissions or arithmetical methodology is not required. EPA's
technology based approach that estimated performance rather than
deriving the standards through an arithmetic-straight emissions
approach is supported by the Courts, as long as it results in a
reasonable estimate of the performance of the best controlled units.
According to the commenter (2901), Brick MACT does not endorse a
straight emissions approach; nor could it. To do so would mean that the
Brick MACT Court was overturning the Chevron step one holding in Sierra
Club and National Lime II, something that it cannot do.
    Response: EPA is adopting the straight emissions (so-called)
approach in this rulemaking and believes that the approach is
permissible under the statue and case law. Commenters also did not
convincingly address the issue of how the alternative approaches they
mention account for HAP inputs. Moreover, Sierra Club and National Lime
II make clear that a straight emissions approach may not be mandated
under the language of the statute, but also make clear that there must
be a reasoned basis for estimating which performers are best. National
Lime II, and later Brick MACT further make clear that contribution of
HAP inputs in raw materials and fuels must be accounted for in making
best performer determinations. See 233 F. 3d at 634, 639; 479 F. 3d at
882-83. Each panel viewed these holdings as consistent with the Chevron
analysis in Sierra Club. 233 F. 3d at 631-32, 633-34; 479 F. 3d at 878.
    Comment: One industry commenter (2844) stated that the CAA requires
that lawfully promulgated NESHAP standards must be achievable. Section
112(d)(2) of the Act requires EPA to establish emission standards for
HAPs that require the maximum degree of reduction in emissions taking
into consideration the cost of the emission reduction and non-air
quality health and environmental impacts and energy requirements, that
the EPA Administrator determines is achievable for new or existing
sources. Further, House Rep. 101-490, Part 1 (328) stated that ``The
Committee expects MACT to be meaningful, so that MACT will require
substantial reductions in emissions from uncontrolled levels. However,
MACT is not intended to require unsafe control measures, or to drive
sources to the brink of shutdown.'' The commenter noted that the
proposed Portland cement proposed NESHAP standards do not comply with
Sec.  112's achievability requirements.
    Response: The industry commenter refers to legislative history to
versions of the 1990 amendments which did not include floor
requirements, so it is not directly applicable in interpreting the
enacted provisions. Moreover, as held repeatedly by the DC Circuit, the
``achievability'' requirement in section 112 (d)(2) does not alter the
minimum level of stringency requirements mandated by section 112
(d)(3)'s requirements. See, e.g., Cement Kiln Recycling Coalition, 255
F. 3d at 861-62.
    Comment: Industry commenter 2844 stated that EPA's conclusion that
section 112(d)(3) and/or Brick MACT requires or even permits the Agency
to ignore the achievability requirements of section 112(d)(2) is an
unreasonable reading of the statute and of Brick MACT. The Agency
retains more than sufficient discretion to devise NESHAP standards that
successfully bridge the tension between achieved and achievable in
section 112's standard-setting provisions by appropriately using both
subcategorization and variability methodologies.
    Response: EPA believes that variability needs to be assessed in
order to accurately measure both which performers are best and what
their performance is. However, authority to subcategorize is
discretionary and need not be exercised where there are rational
grounds not to do so, such as not authorizing emissions of large
amounts of a dangerous neurotoxin. See also previous response.
    Comment: Industry commenter 2844 stated that EPA's floor setting
methodology does not comply with three of Brick MACT's requirements:
Floors must be based on emissions achieved in practice by best-
performing sources; EPA's use of variability factors and methodologies
to adjust reported emissions data must be based on demonstrated
relationships, so that the floor setting methodology serves to
reasonably estimate or predict the performance of the best performing
sources; and EPA must consider the impact of nontechnology factors,
such as raw material and fuel inputs, on a source's emission control
levels.
    Industry commenter 2844 stated that in the Portland cement
proposal, EPA set MACT floor levels that reflect the specific
conditions at the time the data were generated and do not include any
of the operational variability. The commenter suggests that EPA must
look beyond its snap shots of performance to make a reasoned evaluation
and estimation of all operating conditions and factors that might
impact the level of actual emissions from those kilns in practice, and
adjust their reported short term test data appropriately. EPA can and
should adjust raw emissions results to estimate sources' achieved
emissions levels when setting MACT floors and standards. Since Brick
MACT, EPA's methodology now must be able to reasonably estimate the
impacts of variability associated with both technological and
nontechnological factors over the full range of circumstances.
    Response: EPA disagrees that it has based the floors for any of the
HAP on snapshot levels of performance and has not accounted for
potential variability in sources' performance. Each of the floors
reflects a reasonable estimate of what the best performing sources (or
source) will achieve over time. Also, each of the floors considers the
impact of non-technology factors, notably HAP inputs in raw materials
and fuels, on the source's emissions.
    Specifically, for mercury the standard reflects 30 days of data for
all mercury inputs, reasonable estimates of control device performance
(for the few controlled sources), plus a reasonable statistical
methodology to account for variability (including variability of
mercury content of kiln inputs). EPA also used a pooled variability
factor (pooling variability for all kilns in the

MACT pool), which increased variability estimates. Where commenters
provided data showing that kilns' performance was underestimated
because different inputs were used outside the sampling period, EPA
adjusted those emissions estimates. EPA also used data on variability
of kilns quarrying limestone from the same geologic formation as two of
the best performing kilns to estimate intra-quarry variability of those
two best performing kilns, and further applied this variability as part
of the pooled variability. See IV.A.1.c of this preamble and 74 FR at
21142-44.
    The standard for THC reflects hundreds of observations gathered
continuously over time using a CEMS yielding a data set from which
variability can be calculated directly. See IV.A.1.d of this preamble.
    The floors for HCl are set at the minimum reliable quantification
level, which is a factor of three above the actual measured levels, and
are averaged over 30 days as well. EPA believes this fully accounts for
performance variability.
    Floors for PM are based on multiple stack measurements which have