performing source for major sources and nothing that allows EPA to
include area sources as part of a MACT pool.

Commenter 2916 stated that it is unlawful for EPA to group major and
area sources for purposes of setting MACT. By blending area and major
sources together for standard setting purposes, EPA has created a hybrid
major/area source category that is not authorized under §112.

Response: In the final rule, no data from natural or synthetic minor
area sources are being used to establish the standard for HCl.

Establish GACT standards

Comment: One commenter (2887) stated that EPA should develop generally
available control technology (GACT) standards (or management practices)
for area sources under §112(d)(5) for the pollutants listed in
§112(c)(6). EPA could minimize the economic impact on all area sources
by subjecting them to GACT for the §112(c)(6) pollutants.
Alternatively, the EPA could create a subcategory for area sources that
are small entities and subject this smaller number of sources to GACT
(or management practices). This would satisfy the policy behind Small
Business Regulatory Enforcement Fairness Act (SBREFA) as implemented by
EPA policy (to minimize the economic impact on small entities while
still meeting the mandates of the CAA).

Response: EPA explains in the preamble to the final rule its various
dispositions for applying standards to area cement kiln sources.

Comment: One commenter (2887) stated that for HAPs that are not listed
under §112(c)(6), EPA should establish GACT (or management practices)
for area sources under §112(d)(5), and not regulate area sources under
MACT for non-section 112(c)(6) pollutants. The commenter stated that,
specifically, EPA proposed limits for PM emissions as a surrogate for
non-volatile metal HAPs (arsenic, cadmium, beryllium and lead) on cement
manufacturing facilities that are area sources. Alternatively, the EPA
could choose to not regulate area sources or a subcategory of area
sources that are small entities for these pollutants. Emissions from
area sources, and even more so from the subcategory of area sources that
are small entities, are very small.

Response: EPA explains in the preamble to the final rule its various
dispositions for applying standards to area cement kiln sources.

2.3.6	Legal

Removal efficiency standards vs emission limits

Comment: One 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 §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: See response in preamble to final rule.

Comment: Several 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, and EPA’s technology based
approach that estimated performance rather than deriving the standards
through an arithmetic straight emissions approach, as long as they
result in a reasonable estimate of the performance of the best
controlled units, is supported by the courts. 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: See response in preamble to final rule.

Comment: One commenter (2832) stated that EPA has incorrectly focused on
the term emission limitation in proposing a numeric allowable HAP
emissions MACT floor. In fact, EPA is required to set emission
standards, not necessarily numeric emissions limitations in creating a
MACT floor. The Court in the Brick decision did not require otherwise.
In fact, the wording of §112, a reduction in emissions that is achieved
in practice by the best controlled similar source contemplates air
emissions control equipment whose manufacturer’s specified HAP
emissions removal efficiency for all HAPs is the highest percentage
achieved in practice in the industry in question. Inlet and outlet stack
testing that confirms the efficacy of air emissions control equipment is
the legal requirement of the §112(d)(3). The law does not state that
EPA is required to set numeric HAP emissions limits. In identifying the
best performing sources, the Administrator is directed by §l12(d)(3) to
review emissions information, not numeric emissions data or emissions
stack test reports. Sections 112(j)(5) and 1l2(i)(5) also support this
reading of §112(d)(3). Each refers to demonstrations of emissions
reductions of a stated numeric percentage as a means of meeting MACT
requirements. EPA’s discussion of the beyond-the-floor evaluation
confirms this approach as well.

Response: The commenter does not address the issue of how non-numeric
percent reduction standards address the issue of raw material and fuel
HAP levels and their contribution to emissions. EPA cannot ignore such
contributions in determining which sources are best performing, and
their level of performance. At the least, EPA is adopting a reasonable
approach of establishing numerical standards, and using a ranking
methodology based on which sources emit the least of the HAP in
question, on a normalized basis (for Hg and PM) and considering their
performance over time (variability).

Standards must be achievable

Comment: One commenter (2844) stated that the CAA requires that lawfully
promulgated NESHAP standards must be achievable. Section 112(d)(2) of
the Act, 42 U.S.C. §7412(d)(2), required 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 §112’s achievability requirements.

Response: See preamble to final rule for response.

Comment: Commenter 2844 stated that EPA’s conclusion that §112(d)(3)
and/or Brick MACT requires or even permits the Agency to ignore the
achievability requirements of §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 §112’s standard-setting
provisions by appropriately using both subcategorization and variability
methodologies.

Response: See response in preamble.

Comment: One 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.

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: See response in preamble to final rule.

Comment: One commenter (2844) also stated that EPA adopted a floor
setting methodology that is based on using lowest reported emission
results with minimal variability adjustments to estimate emission
control achieved in practice by best performing sources. EPA considered
test-to-test variability, but did not consider the inherent variability
due to raw materials, product mix, fuels, operating conditions and plant
types. The commenter stated that EPA has not evaluated or validated
whether its methodology accurately estimates emissions control achieved
in real world circumstances at sources.

Response: See response in preamble.

Comment: One commenter (2844) stated that EPA cannot evaluate floors
using methodologies that focus exclusively on technology if the
resulting standards do not reflect actual average limitation[s] achieved
(Brick MACT, 479 F.3d at 882). The commenter concludes that Brick MACT
requires EPA to address the role of nontechnological factors that impact
emissions in setting floors and EPA must develop a methodology that
accurately estimates the actual emissions achieved in practice by the
best performing sources under a variety of operating conditions, taking
into consideration testing and technological and nontechnological
variability. As proof that EPA failed to properly account for sources’
variability in setting the standards, the commenter (and commenter 2845)
included a chart purporting to demonstrate that the kilns comprising the
pool of best performers for each HAP could not themselves meet the
proposed standard.

Response: See response in preamble.

Comment: One commenter (2844) stated that the proposed standards cannot
be viewed as assessing the emissions control achieved by best performing
sources, given that there is no single existing source that meets the
standards simultaneously and for two of the pollutants, no existing
units meet the standards without operational changes. The EPA has an
obligation to devise appropriate variability methodologies and to
collect the information necessary to do so.

Response: EPA has responded above and rejected the argument that the
statute unambiguously compels that floors be established on a complete
facility basis.

Worst Reasonably Forseeable Circumstances

Comment: Several commenters (2844, 2846, and 2915) stated that EPA’s
floor methodology does not estimate emission control achieved under the
worst reasonably foreseeable circumstances. EPA must estimate emission
levels achieved under the worst foreseeable circumstances in order to
reasonably estimate achieved in practice control levels. The proposed
portland cement rule proposes that sources must achieve compliance with
the proposed floor standards at all times, including periods of startup,
shutdown and malfunction (SSM) events. Because the data to estimate the
appropriate variability factor for SSM events do not exist and are
technologically impracticable to develop, EPA cannot reasonably set a
floor based on compliance during SSM events.

Commenter 2845 stated that the policy and common sense approach is
recognized and required by the D.C. Circuit. Once the similar sources
category is established, the EPA must identify the lowest emission
limitation that has been achieved in practice by these sources. In
another MACT case, the D.C. Circuit has held that the phrase achieved in
practice refers to the performance of the source under the worst
foreseeable circumstances (Sierra Club v. EPA, 167 F.3d 658, 664, D.C.
Cir. 1999).

Commenter 2845 stated that EPA should follow its own common sense
approach and the directive of the D.C. Circuit and develop MACT
standards that consider the long term emission variations in portland
cement facilities.

Response: First, EPA has established separate standards for startup and
shutdown, so these operating conditions are not part of the performance
EPA is evaluating in developing the main MACT floors. EPA also explains
in the preamble to the final rule why it reasonably did not consider
malfunction events in developing those floors, which reasons include
that EPA is therefore adding to the final rule an affirmative defense to
civil penalties for exceedances of emission limits that are caused by
malfunctions. Since malfunctions, if properly demonstrated, would not be
considered to contribute to an exceedance of the standard (for purposes
of civil penalties), EPA surely need not consider malfunctions in
assessing best performing sources’ performance and establishing MACT
floors.

Second, EPA agrees that long term performance of sources – their
variability – is to be considered both in determining which sources
are best performing and what their level of performance is. EPA has
reasonably done so in establishing this NESHAP.

CAA requires emission reductions by 94 percent of sources

Comment: One commenter (2890) stated that the setting of a MACT floor
requires 94 percent of any population of sources, including those that
had never engaged in any emission reduction techniques, to either add
air pollution control devices or shut down processes, without the
consideration of costs. The floor should identify what the best actual
sources in the category are doing; presuming that if the average of the
top 12 percent was achieving this level of control in the absence of a
rule, achieving that level of control must have been at a reasonable
cost.

Response: The commenter is correct that costs cannot be considered in
establishing MACT floors and that by virtue of the floor process the
statute implicitly assumes that the great majority of plants will have
to upgrade their performance to meet promulgated standards of at least
the designated minimum stringency.

Exclusion of sources engaged in mining

Comment: Several commenters (2890 and 2916) stated that Congressional
intent in the establishment of MACT shows a clear intention to exclude
mined minerals: For categories and subcategories of sources of hazardous
air pollutants 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 materials inputs, or metal- or
mineral-bearing materials processed or derived from such feedstocks or
materials in setting emission standards, work practice standards,
operating standards or other prohibitions or requirements or limitations
under this section for such categories and subcategories. The
prohibition of the preceding sentence shall not apply to the
substitution, modification, or changes of chemicals (not including
metal- or mineral-bearing materials) used in mining, extraction,
beneficiation, or processing of nonferrous ores, concentrates, minerals,
metals and related in-process materials which is necessary to reduce air
emissions of such chemicals and for which substitutes that are safe and
effective in performing the intended function of the chemical to be
substituted are reasonably available [From Joint Explanatory Statement
of the Committee of Conference, H.R. Rep No. 101-952, at 339 (1990)].
EPA used this same quote in a previous court case involving the
secondary copper MACT [Sierra Club v. EPA (No. 02 -1253)].

Commenter 2890 suggested that after mined minerals are eliminated from
consideration for MACT, several options for establishing the best
controlled sources are:

Control of the mercury and other pollutants that are not in materials
other than the limestone typically mined onsite.

Any emission control equipment or other practice that reduces the amount
of emissions that are ultimately emitted from the processing of the
mined material.

Response: See preamble to final rule for response.

Consideration of variability

Comment: One commenter (2845) stated that case law and policy dictate
that the EPA must consider variability in establishing MACT standards,
and the approach used by EPA in Prevention of Significant Deterioration
(PSD) permitting should also apply in establishing MACT standards. To
evaluate the emission limits achieved by existing sources, EPA is
required to develop methodologies for estimating the variability
associated with all factors that impact a source’s emissions,
including process, operational and non-technological variables (see
Nat’l Lime Ass’n v. EPA, 627 F.2d 416, 443, D.C. Cir. 1980). While
courts have affirmed EPA’s authority to choose a methodology designed
to estimate emissions in setting the MACT floor, the courts have also
made clear that EPA’s method must allow a reasonable inference as to
the performance of the top 12 percent of units (Cement Kiln Recycling
Coalition v. EPA, 255 F.3d 855, 862 (D.C. Cir. 2001) (citing Sierra Club
v. EPA, 167 F.3d 658, 663, D.C. Cir. 1999). Accordingly, the Court of
Appeals for the D.C. Circuit has stated that EPA must show not only that
it believes its methodology provides an accurate picture of the relevant
sources' actual performance, but also why its methodology yields the
required estimate (Cement Kiln Recycling Coalition, 255 F.3d at 862).

Response: See response in preamble.

Comment: One commenter (2845) further stated that EPA has a clear policy
of considering long-term variability when establishing enforceable
emission rates. In considering appropriate enforceable emissions rates
in PSD permits under the CAA, the Environmental Appeals Board has held
that a permitting authority is not required to set the Best Available
Control Technology (BACT) emissions limit at the most stringent
emissions rate that has been demonstrated in practice by a facility
using similar emission controls (In re Newmont Nevada Energy Investment,
12 E.A.D. 429, 441-42, EAB 2005 (citing Kendall New Century Dev., 11
E.A.D. 40, 53, EAB 2003). The Board has recognized the use of safety
factor[s] in the calculation of permit limits to take into account both
the variability and fluctuation in the expected performance of pollution
controls and the fact that setting emissions limitations for one
facility at the highest control efficiency demonstrated at another
facility would make violations of the permit unavoidable (Id. at 442,
citing In re Masonite Corp., 5 E.A.D. 551, 560, EAB 1994).

Response: Although BACT determinations under PSD are by no means
analogous to determining MACT floors (cost is considered in determining
BACT, for example), EPA agrees that consideration only of single data
points may not adequately represent sources’ performance over time,
and EPA consequently is not utilizing that methodology in this rule. EPA
also has taken variability into account during the process of
establishing the emission limits for this rule.

Comment: Commenters 2844, 2845, and 2916 objected to EPA’s
interpretation of CAA Sections 112(d)(2) and 112(d)(3) and the Brick
MACT (Commenter 2845 provided a white paper as an appendix to their
comments for the HWIMI MACT proposal, dated December 01, 2008.). The
paper, entitled Implications of the Brick MACT Decision on EPA’s
Discretion in Setting MACT Floors, discusses variability at some length.
The paper’s main points were:

The Agency has chosen to focus on setting MACT floors based on lowest
emitting sources derived from limited test results that are not
appropriately adjusted to account for stack test variability.

The Brick MACT decision holds that EPA must base MACT floors on achieved
emissions control rather than control technology, but it does not
require EPA to ignore operational variability in determining those
floors.

Variability methodologies must reasonably estimate or predict emissions
or variability through a demonstrated relationship between the data used
and the performance intended to be estimated.

Non-technological factors (i.e. raw materials and fuel) must be
considered in determining emission control achieved by best performers.

It is within the EPA’s discretion to define the best performing
sources.

EPA should estimate variability in determining achieved emissions.

The Agency can and must seek appropriate data from regulated entities
and other stakeholders, and to develop appropriate fact-based estimating
methodologies on the data available.

Response: See response in preamble.

Brick MACT

Comment: Several commenters (2834, 2844, 2845, and 2859) stated that the
Brick MACT decision makes the expectations of what is expected by EPA in
regards to setting the floor very clear:

Floors must be based on emission control achieved in practice by the
best performers

Variability methodologies must reasonably be calculated to estimate such
actual performance levels

Nontechnological factors that impact emissions must be considered in
determining the achieved emissions levels

In devising new methodologies to set lawful floors, EPA must ensure that
compliance with §112(d)(2) general standard setting criteria is also
met.

EPA can use discretion to define the factors necessary to establish a
floor under §112(d)(3) that meet the CAA’s statutory intention to be
technology-forcing and require compliance with the best that has been
demonstrated to be achieved in practice while considering costs, other
non-air health and environmental impacts, and energy impacts when
defining achievable MACT standards.

Based on these points, the Brick MACT decision requires that EPA’s
floor analyses include a review of the best performers and consideration
of variable factors that can affect emissions achieved in practice by
the pest performance sources. EPA’s analyses and methodological
choices must be based on facts and records that support its final
determination. It is appropriate that a full review of the existing
records and the development of new data be considered in making a final
decision.

Response: The case law makes overwhelmingly clear that the requirement
in section 112 (d)(2) that MACT standards be achievable after
considering various factors does not supersede the requirement of
section 112 (d)(3) that they be of minimal stringency as determined by
the criteria for establishing MACT floors. See, e.g. Cement Kiln
Recycling Coalition, 255 F. 3d at 861-62. As discussed in the preamble
and in other comment responses, EPA has carefully assessed best
performers’ short- and long-term variability for each HAP in
estimating their performance.

2.3.7	Format of Emission Limits

Use CEMS units as limits

Comment: One commenter (2638) recommends the EPA use plain language and
units that can be related to ambient measurements for its emission
limits. The units currently proposed require modifying the direct CEMS
output with inputs under the control of the plant, which make the
results un-interpretable by anyone wanting to make comparisons with
ambient measurements or health effects; or the CEMS concentration
readings should be required to be posted/reported.

Response: 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 in 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 the 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.

We are currently developing a reporting mechanism for CEMS data. We will
consider these comments as we continue that effort. In concept, the CEMS
data base would be publically available. However, the reporting
frequency has not been developed.

See the preamble discussion under format of the normalized standards in
the NESHAP and the NSPS, for more information on EPA’s decision.

Use of kiln feed vs clinker in emission limits

Comment: Commenters (2830, 2844, 2845, 2859, and 2879) stated that they
supported emission limitations in pounds of pollutant per ton of kiln
feed rather than as pounds per ton of clinker produced. Commenters 2844,
2859, and 2879 noted that clinker conversion factors may vary from plant
to plant and may give erroneous results. According to the commenters,
clinker weigh systems are not common in the cement industry and will not
improve accuracy over a kiln-feed measurement system with an appropriate
clinker factor, as is commonly used. On a short-term basis, clinker
output from the kiln will fluctuate while the kiln feed rate remains
constant. The variable nature of clinker production creates more
inaccuracy in short-term (hourly) clinker weigh data than the +/- 5
percent specified by the EPA. If the standards are based on tons of
clinker, then the kiln owner should have an option to determine clinker
weight from feed that should not require EPA approval of the method and
the averaging time and accuracy requirements should reflect what is
practical, achievable and useful.

Commenters 2844 and 2845 asked for clarification from EPA on proposed
language regarding alternative methods to measuring clinker production
and the need to obtain Administrator approval for such methods. The
Proposal also stated that the use of a system that directly measures
kiln feed rate and uses a conversion factor to determine the clinker
production rate is an acceptable method. The commenter states that it is
unclear whether EPA believes that Administrator approval is required to
utilize such a method when EPA identifies in the regulations that the
method is acceptable. In any event, cement plants should be given the
option of complying with the regulation by either measuring the clinker
production or by measuring kiln feed and developing a clinker factor to
calculate clinker production. Almost all cement plants measure kiln feed
and develop a clinker factor. Such a method requires periodic
adjustments to the clinker factor and justifies a longer time-frame than
hourly for determining clinker production.

Response: See the response to the comment above, regarding the format of
the standards.

Commenters maintain 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.

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 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,
would show lack of compliance without an opportunity to alter operation.
To obviate this concern, the rule provides that facilities are not
required to retroactively update clinker production estimates after
re-computing 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).

See the preamble discussion under format of the normalized standards in
the NESHAP and the NSPS, for more information on EPA’s decision.

Accuracy of determining kiln input or output

Comment: One commenter (2845) stated that kiln feed accuracy should be
established on a longer timeframe than one hour:

Daily clinker production typically is estimated by measuring the kiln
feed rates and utilizing a clinker factor to convert kiln feed rate
(which includes kiln feed and kiln dust returned) to clinker production
rate. Several variables in the calculation are measured are not
determined more frequently than a weekly basis and can vary on a short
term basis. Another variable, dust loss, is estimated, not measured. It
cannot be expected to have a clinker factor in the short term with an
accuracy of better than +/-10 percent. Tracking these variables on a
short term basis is not practical.

Plants typically measure clinker inventory daily, and conduct more
detailed physical inventories on a monthly and/or quarterly basis.

Plants that utilize a single clinker handling system for multiple kiln
lines cannot confirm the clinker factor for each individual kiln.

Response: See the response to the comment above, regarding the accuracy
of determining kiln input or output, and the latitude for determining
site-specific clinker factors. See the preamble discussion under format
of the normalized standards in the NESHAP and the NSPS, for more
information on EPA’s decision.

Grain loading format

Comment: Commenter 2859 stated that as an alternative to basing the PM
standard on pounds per ton dry feed, EPA could use a grain loading
standard (i.e., gr/acf).

Response: See the preamble discussion under format of the normalized
standards in the NESHAP and the NSPS, for more information on EPA’s
decision regarding format of the standard.

2.3.8	Other

Central stack

Comment: Many commenters (2893, 2975, 2990, 2992, 3001, 3003, 3005,
3017, 3022, 3034, 3038, 3045, 3052, 3056, 3059, 3063, 3073, 3074, 3077,
3089, 3098, 3107, 3117, 3124, 3125, 3128, 3130, 3131, 3132, 3160, 3226,
and 3227) stated that EPA should require that all cement kilns have one
central stack. Without a central stack, the emissions from the kiln
cannot be adequately monitored, and the CEM required in the proposed
rule would not be viable for monitoring emissions and confirming
emissions reductions. In addition, necessary scrubbers and/or other
pollution control devices require a central stack for placement.

Response: The majority of cement kilns are equipped with control devices
that are equipped with a central stack. However, those kilns using
positive pressure fabric filters may be equipped with roof monitors
instead of stacks. In the case of PM emissions, such devices can be
equipped with a bag leak detection system, which is a viable monitoring
alternative to PM CEMS and explicitly allowed in the rule as a
monitoring alternative. In other cases, the source may have to retrofit
the control device outlet to install one or more stacks. Finally,
sources can always request EPA approval under the part 63 General
Provisions (§63.7(f)) to use an alternative method to accommodate
site-specific conditions. For example, open-path monitoring may be
viable in some situations.

2.4	General Legal Issues

Comment: One commenter (2901) stated that National Lime II stands for
the principle that as long as the facility is controlling pollution, the
levels achieved can be considered, even if the facility was not
intending to control the specific HAP. The commenter noted that the
major issue in National Lime II was whether EPA could decline to set an
emission standard for HAPs that no facility in the source category was
controlling with technology. The National Lime II court was saying that
if a facility was already controlling its emissions, the fact that it
was not intending to control the HAP in question could not be a reason
for EPA to consider the pollutant uncontrolled.

Response: The commenter correctly describes this portion of the second
National Lime decision.

2.4.1	Subcategorization

Comment: One commenter (2844) stated that subcategorization based on
nontechnical factors may result in opportunities for reasonable beyond
the floor (BTF) standards. It would be appropriate for EPA to base the
NESHAP standard on BTF levels that reflect application of the
nontechnological factor as an intended control strategy under §112.
However, while Brick MACT requires EPA to take into account emissions
data irrespective of whether it was achieved through specific intended
operational choices or control technology, nowhere did the court say EPA
had to or even could simply assume that a source’s emissions in
practice would be invariably equivalent to a particular observed
emission level and that all operational and nontechnological factors
that happen to be in effect on the day of testing could be assumed and
required to be in effect, in the future.

Response: EPA agrees that sources’ variability is unlikely to be
encompassed by a bare single measurement. It is for this reason that EPA
developed all of the standards based on substantial data gathering
augmented where appropriate by statistical estimates of variability.

Comment: One commenter (2844) stated that if EPA determines that raw
material inputs impact the emission control achieved in practice by the
best performing sources, EPA must assess that impact. Given that the raw
material input varies, the commenter stated that EPA’s variability
methodology must include that variability in estimates of emission
control achieved by the sources; further, if the variability in the raw
materials used by the differing units is significant, EPA may determine
that subcategorization is the most reasonable way to regulate the
industry to ensure that each source is subject to the most stringent
floor level of control reasonable to apply to sources utilizing raw
material sources of similar HAP input.

Response: EPA’s reasons for not creating a subcategory for the two
plants with exceptionally high mercury emissions due to limestone quarry
mercury content is set out in the preamble to the final rule.

Comment: One commenter (2846) stated that EPA has authority to establish
subcategories of sources when issuing standards. Subcategorization would
allow for a workable MACT standard and allow sources that are limited in
certain ways to apply the best available control technology for their
facilities and still comply with the standards. The commenter believes
that subcategorization for on the basis of feed material quality is
wholly appropriate and required by law.

Commenters 2832 and 2859 support subcategorization as permitted in the
Concurring Opinion in the Brick decision. This support includes but is
not limited to subcategorization according to process operations (type,
raw materials, chemistry/formulation data, associated equipment and
final products), emission characteristics (amount and type of HAP), and
air pollution control device applicability, opportunities for pollution
prevention, and existing regulations or guidance from states and other
regulatory agencies.

Commenters 2776, 2777, 2810, 2814, 2833, 2859, 2904, 2915, 2920, 2926,
3204, 3212, 3214, and 3215 supported the use of subcategorization in the
proposed rule. Commenter 2915 stated that in allowing EPA to create
subcategories, §112(d)(4) does not restrict subcategorization to only
factors that affect emissions. The provision requires EPA to establish
regulations for each category or subcategory on the schedules set out in
§112. EPA states in the preamble, EPA may create a subcategory
applicable to a single HAP, rather than to all HAP emitted by the source
category. While the commenter disagreed with EPA’s approach to MACT
standard-setting, if EPA continues to follow that HAP-by-HAP approach to
MACT standard-setting, then EPA should create different subcategories
for each HAP rather than one set for all HAPs.

Response: Because EPA is determining not to exercise its discretion to
create a subcategory for a subcategory for kilns with exceptionally high
mercury emissions due to high levels of mercury in their limestone
quarries, it is unnecessary to respond to these comments.

Comment: One commenter (2824) suggested that for the best protection of
human health, create an optimized mercury subcategory by evaluating
increased exposure from foreign plants in response to plants that could
shut down due to technology or economics while varying construction
demand.

Response: This comment does not track the MACT standard setting process
prescribed by law, which requires technology-based determinations based
at a minimum on performance of certain best operated or controlled
domestic plants in the source category.

2.4.2	Fly Ash Ban

Comment: Several commenters (2816 and 2835) stated that it was
appropriate for EPA to remove the prohibition on kilns using fly ash
from utility boilers using activated carbon injection for mercury
control. Given that the mercury emission limit will apply regardless of
fuel or fuel substitutes, this prohibition is no longer needed.

Response: EPA agrees.

Comment: One commenter (2828) suggested that EPA retain a ban on cement
kilns pyroprocessing (or heating) of fly ash from power plants if the
mercury content of the fly ash has been increased above its normal
concentration by mercury capture systems at the power plant. Until there
is certainty on how coal- and oil-fired electric utility steam
generating unit (EGU) will be required to account for mercury
re-emissions from cement plants that acquire their fly ash, the cement
MACT rule should maintain a ban on the use of fly ash with captured
mercury. The commenter encouraged EPA to retain the proposed mercury
emission standard, and supplement it with a continued ban on fly ash
pyroprocessing if the ash has elevated mercury or if the power plant
producing the ash took credit for the reductions. The commenter
suggested that this rule, as well as the upcoming EGU MACT rule, require
coordination between fly ash producers and potential fly ash users so
that re-emission of mercury is properly accounted for, and we do not
have the problem of mercury being emitted to the atmosphere at one
location after being controlled at another.

Response: The technology-based standard for mercury reflects the minimum
level of performance achieved by the average of the best performers, or
the best controlled similar source. If other kilns can meet these limits
while importing fly ash, there is nothing in section 112 (d)(3) which
prohibits them from doing so, since the provision is technology-neutral.
So long as the standards are satisfied, the statute does not dictate
how.

Comment: One commenter (2638) stated that coal ash is enriched in other
urban HAP metals besides mercury. These enrichments of coal are on the
order of 5 to 10 fold. With these enrichments, it will important that
emission limits be developed for each individual urban HAP metal and be
correspondingly monitored. Without this assurance, the EPA should not
allow coal ash to be used in the manufacture of portland cement.

Response: Given that the PM emission limit (as a surrogate for
nonvolatile metal HAP) will apply regardless of fuel, fuel substitutes,
or raw materials, this prohibition is not needed. The standard for PM
reflects the minimum level of performance achieved by the average of the
best performers, or the best controlled similar source. If kilns can
meet these limits while incorporating coal ash, there is nothing in
section 112 (d)(3) which prohibits them from doing so, since the
provision is technology-neutral. So long as the standards are satisfied,
the statute does not dictate how.

2.4.4	Other

Offsets

Comment: One commenter (2898) stated that any netting or offsets
pursuant to NSR must meet all CAA requirements. The CAA only allows
offsets for incidental emissions reductions that are not otherwise
required. 42 U.S.C. 172(c)(2). Federal regulations additionally require
that emissions reductions, in order to qualify as offsets, be surplus,
permanent, quantifiable, and federally enforceable. 40 CFR
51.165(a)(3)(ii)(C)(1)(i). Longstanding agency guidance, including the
General Preamble for State Implementation Plans (57 FR 13498, 13552-54,
dated April 16, 1992), imposes additional restrictions. Per the
foregoing, The EPA’s policy for NSR offsets is that since hazardous
emissions reductions required to meet the MACT standards at 40 CFR 60
and 61 … are required by the Act these emissions are not creditable as
NSR offsets. Memorandum from J. Seitz to B. Hannesschlager re: Crediting
MACT Emission Reductions for New Source Review (NSR) Netting and Offsets
(November 12, 1997).

Response: These comments relate to NSR, which is outside the scope of
this rulemaking.

Comment: Several commenters (2845 and 2874) agreed that EPA correctly
suggests that surplus sulfur dioxide credits could be used for offsets
and netting and commended EPA for this recommendation that surplus
sulfur dioxide emission reductions resulting from the installation of a
wet scrubber (used to satisfy sulfur dioxide offset requirements) can be
used for netting purposes under the CAA new source review program.
Commenter 2874 believed that this is an appropriate position and EPA
should repeat this statement in the preamble to the final rule, making
the point clear to regulators dealing with portland cement new source
review matters.

Response: See above.

2.5	Mercury Standards

2.5.1	Legal Issues

Subcategorization

Comment: Many commenters (2816, 2828, 2834, 2895, 2898, and 2923)
supported EPA’s approach of establishing a single national standard,
rather than weakening the proposed standard through the use of
subcategorization. According to several commenters (2816, 2834, and
2898), EPA properly rejected subcategorizing cement kilns for the
following reasons:

Under §112(d)(1), EPA can only create subcategories based on classes,
types, and sizes of sources. Since limestone mercury content can vary
within a single quarry, kilns with proprietary quarries with sections
that have high mercury content are not sufficiently uniform to be
considered a class or type. Even for those high-mercury quarries
identified by EPA, the Agency is not aware of the mercury content of the
remainder of the quarry. Nor is there any suggestion that a quarry’s
mercury content is related to its size. Further, the lack of a causal
link between limestone mercury content and emission rates makes
subcategorizing by quarry content untenable.

Kilns with more mercury-rich limestone would be favored and those with
lower mercury levels disadvantaged. Kilns would be rewarded for
selecting the highest mercury limestone to test for categorization.
Thus, the category would create an incentive for kilns to concentrate in
areas with limestone formations that just exceed the mercury
concentration cut-off for the category.

Subcategorization is unnecessary because it is not clear that any
outliers exist. EPA separated two facilities as having the highest
quarry mercury contents and identified those sources as potential
outliers. But EPA acknowledges that at one of those kilns it does not
currently have any data on the possibility that this site may have
portions of its existing quarry that have lower mercury content. They
may simply be in sections of their quarries that are particularly high
in mercury. Creation of a subcategory without further evidence it is
justified would be arbitrary.

Creating a subcategory for kilns with quarries that are high in mercury
would be a continuation of the pattern repeatedly rejected by the D.C.
Circuit as violating the CAA- setting emission standards based on a
concern about ensuring that its floor is achievable by all kilns in the
subcategory. If §112 is to meet its purpose of require the maximum
degree of reduction in emissions, then the standards created pursuant to
it cannot be set so as to accommodate the heaviest polluters. EPA must
heed the D.C. Circuit’s previous rejection of efforts to tailor
emission standards so as to ensure all sources can meet those standards.

Commenter 2898 agreed with EPA that none of the bases for
subcategorization discussed in the proposed rule meet the CAA’s
guidelines:

Any basis for subcategorizing must be related to an effect on emissions,
rather than to some difference among sources which does not affect
emissions performance. The commenter agreed that subcategorization on
the basis of the type of kiln or the presence of an inline raw mill is
inappropriate because none of these distinctions affects total mercury
emissions over time.

Subcategorization on the basis of geographic location is inappropriate
because mercury content can vary significantly from quarry to quarry and
even within a quarry, nor does a difference in geographic location
constitute a difference in class, type, or size. Moreover, EPA found no
correlation between geographical distribution of mercury emissions and
total mercury.

Subcategorization based on the practice of wasting cement kiln dust is
inappropriate as it can be considered a control technology and
subcategorization by control technology would defeat the purposes of the
MACT requirement, which is to control the worst HAP pollution.

Subcategorization by total mercury inputs is inappropriate because total
mercury inputs do not differentiate facilities by size, class, or type
because a particular set of inputs are not inherent to the operation of
the cement facility. Because subcategorization on this basis would
result in a situation where facilities with higher total mercury inputs
would have higher total emission limits, it would create the same
problems as subcategorizing by control technology.

Subcategorization on the basis of mercury content of facility’s
proprietary limestone quarry is inappropriate would essentially be
subcategorizing by control technology. As Brick MACT confirmed, inputs
are a means of emissions control. As with total mercury inputs, the
mercury content of the proprietary limestone quarries does not
differentiate facilities by size, class, or type. There is nothing about
the limestone from the proprietary limestone quarry that is inherent to
the process of the cement facility. While it is true that all cement
plants have a limestone quarry located near the facility and that
facilities are often sited based on the location of the quarry, the
proprietary nature of the quarry does not diminish the fact that the
cement facility’s kilns will work equally well with limestone from
other sources. The only operational difference between limestone from
the proprietary quarry and limestone from other quarries is cost (for
transportation or purchase), an impermissible consideration in setting
the MACT floor. Separate standards would unfairly expose communities
near the dirtiest cement facilities to the highest levels of mercury
pollution from cement plants and leave them with the least protection
against such pollution. Subcategorization by the mercury content of the
limestone quarry runs counter to the holding of Brick MACT and other
decisions. Brick MACT holds that EPA must account for raw material HAP
contributions in establishing MACT floors and that the proprietary
nature or proximity of the raw material does not excuse EPA from
considering the HAP emission from the raw material in setting the MACT
floor.

Commenter 2898 disagreed with the Portland Cement Association’s
(PCA’s) (commenter 2845) arguments for subcategorization by mercury
content of proprietary quarries. The commenter provides counterarguments
to (PCA’s) citations and interpretations of case law.

Commenters 2842 and 2911 opposed the use of subcategories. Commenter
2911 stated that setting separate standards for kilns that use high
mercury limestone would be unlawful.

The sentence in §112(d)(1) that allows EPA to distinguish among
classes, types, or sizes of sources within a category or subcategory in
establishing standards does not permit EPA to set separate standards for
cement kilns that merely have limestone quarries containing higher
levels of mercury. The distinctions between class and type must relate
to the source itself and not a distinction between the raw materials
used by the source. Under EPA’s own definition, a quarry is not any
part of an affected source.

EPA states inaccurately that kilns with mercury above a given level
might be considered a different type or class of kiln because their
process necessarily requires the use of that higher mercury input (74 FR
21145). EPA does not and cannot identify any kiln whose process requires
the use of high mercury input. At most, it is merely cheaper for these
kilns to continue using such input.

Although EPA stated that [t]he concurring opinion in Brick MACT supports
subcategorization in situations involving sources’ dependence on
high-HAP raw materials to avoid situations where a level of performance
achieved by some sources proves unachievable by other sources even after
application of best technological controls, viewing such sources as of a
different type than others in the source category (74 FR 21148 and
Sierra Club v. EPA, 479 F.3d 875, 884-885, D.C. Cir. 2007, and 74 FR
21140 [concurring opinion may provide a way out of the situation where
the floor standards are achieved for some sources, but the same floors
cannot be achieved for other sources due to differences in local raw
materials whose use is essential]), those statements are no more than
dicta in a concurring opinion without precedential value or authority.

EPA itself states subcategorizing by control device … is not
permissible, 74 FR 21145. As the CAA and D.C. Circuit precedent both
make clear, the best performing sources are those with the lowest
emission levels, regardless of whether those emission levels are
achieved through the use of end-of-stack control technology or the use
of cleaner fuels or raw materials. Sierra Club (479 F.3d 879-880).
Because there is no relevant distinction for floor purposes between
controlling emissions with an end-of-stack control device and
controlling them through the use of cleaner fuels and raw materials,
setting separate and more lenient standards for sources with high
mercury limestone is just as impermissible as setting such standards for
sources with ineffective or outdated control technology would be.

Commenter 2911 stated that setting separate standards for kilns that use
high mercury limestone would be arbitrary and capricious. Nothing in the
CAA suggests that standards have to be achievable through the use of any
particular control technology or through control technology in general.
Creating a separate subcategory would create a perverse incentive for
other kilns to find high mercury limestone so as to avail themselves of
the same effective exemption from mercury emission standards.

Commenter 2842 states that the decision not to subcategorize is fully
consistent with the language in §112 for setting emission standards.
Congress left the decision of whether to subcategorize based on class,
type, and size of source entirely to the Agency’s discretion. Based on
the record before it, the Agency reasonably concluded that the mercury
emissions data do not readily support a subcategorization approach. The
commenter’s further argued that:

EPA’s technical determination is worthy of deference. See Natural
Resources Defense Council, Inc. v. EPA, 489 F.3d 1364, 1375 (D.C. Cir.
2007) (rejecting industry challenge to EPA decision not to subcategorize
in light of the technical nature of the determination and the agency’s
reasoned explanation).

The argument advanced by certain industry representatives that
subcategorization is required because some kilns with high levels of
mercury in their feedstocks will not be able to achieve the standards in
a cost effective manner finds no support in the statute. The D.C.
Circuit has held that EPA must account for raw material HAP
contributions in establishing MACT floors, and the fact that raw
materials may be proprietary or otherwise not obtainable category-wide
does not relieve EPA of that obligation. 74 FR at 21148 (citing Sierra
Club v. EPA, 479 F.3d at 882-83).

Section 112 does not allow EPA to consider costs in establishing the
MACT floor for HAPs such as mercury. NRDC v. EPA, 489 F.3d at 1375; see
Sierra Club v. EPA, 479 F.3d 875 (D.C. Cir. 2007). Congress envisioned
that the establishment of the MACT floor would be a technical
determination, not an economic one. See Sierra Club v. EPA, 479 F.3d at
875 (rejecting argument that in establishing MACT floors based on what
best performing sources have achieved, EPA may redefine best performing
to mean those sources with emission levels that are achievable by all
sources).

Judge Williams in the Sierra Club case noted, there is not necessarily
any guarantee, even with suitable subcategorization, [that] every source
will be able to achieve standards that meet a lawful application of
§112(d)(3) to reasonably defined subcategories. 479 F.3d at 885.

Response: Because EPA is choosing not to exercise its discretion to
create a subcategory for high mercury emitters with high mercury
limestone quarries, it is unnecessary to respond to these comments.

Comment: Several commenters (2845, 2863, and 2916) stated that case law
under the CAA §111 New Source Performance Standards (NSPS) made it
clear that EPA may establish subcategories that are essentially based on
a pollutant concentration in an input to the process. In its coal-fired
power plant NSPS, EPA essentially distinguished between sources based on
the concentration of a pollutant in an input – the sulfur
concentration in the coal. The D.C. Circuit upheld EPA’s approach,
holding that it had considerable latitude in differentiating between
source types. Sierra Club v. Costle (657 F.2d 298, 318-319, D.C. Cir.
1981). The power plant NSPS required greater sulfur dioxide removal
efficiency for sources with a higher concentration of sulfur dioxide
emissions than for sources with a lower concentration in the emissions.
When challenged, the D.C. Circuit quoted the §111(b)(2) language on how
EPA is authorized to distinguish among classes, types, and sizes of
sources, and concluded that [c]ertainly the text of the statute nowhere
forbids a distinction based on sulfur content.

Examples cited by the commenters of other MACT standards using
subcategorization by pollution concentration in raw materials are:

Proposed National Emissions Standards for Hazardous Air Pollutants for
Refractory Products Manufacturing, 67 FR 42108, 42110, and 42119 (June
20, 2002);

Proposed National Emissions Standards for Hazardous Air Pollutants for
Plastic Parts and Products, 67 FR 72276 and 72288 (December 4, 2002);
and

Proposed National Emissions Standards for Hazardous Air Pollutants for
Chemical Manufacturing, 73 FR 58352 and 58365 (Oct. 6, 2008).

Commenter 2845 stated that EPA should establish two subcategories for
mercury based on the concentration of mercury in the limestone, and
should set beyond-the floor standards for the high-mercury limestone
kilns requiring a 75 percent system removal efficiency. EPA’s Figure 1
and Table 3 of the proposal preamble clearly show two outliers with
mercury concentrations that far exceed those of any other sources in the
database.

Commenter 2845 stated that as EPA further notes in the preamble, [The
Ash Grove Durkee kiln] has voluntarily entered into an enforceable
agreement to install activated carbon (the best control technology
currently available so far as is known) to control its mercury
emissions…Closure of this kiln and possibly other high mercury
emitting kilns is a possible consequence of a single standard without
subcategories. The same would be true for other kilns not in EPA’s
database that are similarly situated. This would be a result that
Congress clearly did not intend. As the House Report for the 1990 CAA
Amendments states, MACT is not intended to require unsafe control
measures, or to drive sources to the brink of shutdown. House Rep. No.
101-490, at 328 (1990).

. Creating a ≥225 ppb subcategory also is consistent with the
legislative history of the CAA. When 112(d) standards were developed,
the possibility of requiring substitution of cleaner ore stocks was
considered. In the Conference Committee report, Congress stated that the
Administrator shall not consider the substitution of, or other changes
in, metal- or mineral-bearing raw materials that are being used as
feedstocks or material inputs… Conference Committee Explanatory
Statement.

Response: Because EPA is choosing not to exercise its discretion to
create a subcategory for high mercury emitters with high mercury
limestone quarries, it is unnecessary to respond to these comments.

Best performers

Comment: One commenter (2911) stated that the holding that best
performers are those with the lowest emission levels is binding
precedent on the plain meaning of the CAA, and it reflects repeated
holdings of the D.C. Circuit to the same effect. To attempt to rank
cement kilns by control efficiency would not only contravene the CAA but
set bad policy and dangerous agency precedent.

Response: EPA is choosing in this rule to rank best performers based on
emission levels (as normalized, for Hg and PM), and believes that this
is a reasonable and permissible approach for this rule.

2.5.2	Adequacy of Floor Determinations (Existing and New)

Overly lenient standards

Comment: Several commenters (2144, 2867, and 2879) stated that EPA’s
analysis of the floor resulted in overly lenient standards. They stated
that EPA should conduct simulations such as Monte Carlo and use other
statistical tools to handle truncated distributions. The commenter notes
that the proposed emission standard is greater than the 30-day
characteristics of any of the best performing 12 percent of the surveyed
kilns, resulting in a standard less stringent than the highest emitter
among the best performing kilns rather than equal to or more stringent
than the average emissions from the best performing 12 percent.
Commenter 2879 provided examples of alternative statistical analysis of
data that could be used to more rigorously determine the expected
average of the best performing 12 percent.

Commenter 2867 made the following recommendations:

Lower the proposed emission standard for existing kilns towards the
simple statistical average of 27.4 lb/MM tons of clinker consistent with
the plain reading of the law (average of best 12%) and leave the
proposed value for new kilns unchanged at 14 lb/MM tons feed (23.1
lb/ton clinker).

Resist attempts by industry advocates to introduce new variability
schemes in the determination of the final mercury standard.

Any subcategorization (if allowed at all) for the purposes of the
mercury limit should be in terms of time to achieve the standard and not
the magnitude of the standard.

Response: Monte Carlo simulation or bootstrap simulation has been used
to account for different types of uncertainties. The suggestion by the
commenters follows this recent tendency to use simulation techniques to
account for uncertainties in the data. However, for this rule, we
decided to use the Student’s t-test, which is called for when you have
only a relatively small, random sample of emissions data available for
analysis. EPA is not adopting any subcategories in this rule.

Analysis of variability

Comment: Many commenters (2830, 2836, 2841, 2845, 2858, 2859, 2863,
2864, 2874, and 2889) stated that the limited data used by EPA in
setting the proposed mercury limit does not adequately reflect the
significant variability in mercury emissions and EPA’s MACT floor
analysis resulted in overly stringent limits. They recommended that EPA
re-evaluate the data upon which the mercury standard for existing kilns
was derived, and use different statistical analyses.

Commenters 2830 and 2845 recommended using the statistical analysis used
to set other NESHAP standards and programs under the CWA and the
Resource Conservation and Recovery Act (RCRA), which gives more accurate
consideration of the variability in certain data sets.

Commenters 2859 and 2864 support commenter 2845’s discussion of an
alternative approach to analyzing the mercury data set used to determine
the MACT floor. This commenter recommended using the UTL method to
account for variability within the data set. The commenter’s UTL
analysis of the mercury data resulted in an alternative mercury floor no
less than 51.5 lbs/million tons of kiln feed for existing units and 14.2
lbs/million tons of kiln feed for new units. The commenter included
detailed statistical analysis in support of their recommended limits.
Commenter 2830 stated that the appropriate NESHAP standard for mercury
should be between 43 lbs/million tons of clinker and 50 lbs/million tons
of clinker for existing units.

Commenters 2844, 2845, 2859, 2863, 2874, and 2889 stated that by using
data collection over only 30 days, EPA has failed to capture the
variability of the performance of those units. The commenters recommend
collecting data over a wide range of operating conditions or developing
alternative operating scenarios and the effects of alternative operating
conditions can be determined via mass balance calculations (by changing
the mix of materials and the mercury contents of those materials).
Commenters 2858, 2859, and 2874 noted that causes of variability such as
variations in raw materials and fuels, wasting of varying amounts of
kiln dust, and the production of different products were not adequately
addressed in the data collection process. Commenter 2863 provided three
years of results of analysis to highlight the variability of the mercury
content of their feed limestone, which all comes from the same quarry
and mineral formation. Limestone mercury concentrations ranged from 424
ppb to 1740 ppb.

Commenters 2845, 2863, and 2864 noted that EPA considered only 30-day
samples of emissions data from various units in setting the mercury
standards, and in addition, EPA considered a kiln that was producing a
product during the 30-day data collection period that resulted in an
emission profile that was not representative of normal operations of the
kiln. If this kiln’s production of this product is weighted based on
the kiln’s actual production, its emissions increase and it is no
longer one of the best performing sources.

Commenter 2845 conducted a site-specific variability analysis that
included interviewing plant personnel of the 11 MACT floor kilns.
Independently from the 30-day emissions data collected by EPA, the
analysis focused on normal and foreseeable operations of the kilns used
by EPA to propose the mercury standard. Each of the kilns in EPA’s
proposed MACT floor was reviewed for variations in products, raw
materials, fuels, operating conditions, and the effectiveness of
pollution controls. The commenter also considered EPA data regarding
mercury content of fuels that are used or could reasonably be used by
the facilities in the MACT floor. The analysis demonstrated that
foreseeable circumstances at units in the MACT floor justify an existing
source mercury standard of 106 lbs/million tons of kiln feed and 36
lbs/million tons of kiln feed for new sources. The commenter provided
detailed supporting information in an appendix.

Commenter 2841 disagrees with EPA’s approach of mass balance tracking
the feed materials and assuming that all mercury entering the kiln
system would be emitted from the stack. Using a mass balance for such a
significant standard will result in significant costs with the real
possibility of little or no environmental benefit. It would be far more
appropriate to allow time for facilities collect more data and further
to allow each facility to determine the speciation of this naturally
occurring mercury in their limestone quarries and other sources of raw
materials. It may be appropriate to subcategorize by species of mercury
or other similar approaches, if enough data is collected.

Response: We carefully reviewed the comments on the analysis of
variability. (See the docket for the detailed review of these comments.)
It is clear that the commenters mistakenly believed that EPA intended to
set the MACT floor using the 99th percentile. The 99th percentile of a
data set, is the data value at which 99 percent of the data will be
found. They also state that because EPA was using a modified UPL, that
EPA was calculating a future probability rather than the 99th percentile
for the actual data, which they wrongly considered inconsistent with the
intention of the CAA. They stated that because of the small size of the
data sets for mercury, PM, and HCl that EPA’s choice of the 99th
percentile was faulty and they recommended that an upper tolerance limit
(UTL) for smaller data sets be used. They state that the UTL does
generate the 99th percentile. For larger data sets, such as the THC
data, the actual 99th percentile can be used. UTL is not for prediction
purposes, so it won’t say what the data will be in the future. The
prediction properties are a characteristic of the UPL. Both UPL and UTL
are based on the present data, but UPL take into account the future
observations variability. If the idea is to obtain an upper bound that
is greater than the 99 percentile, then the UTL works. The UTL will
generally be a larger number than the 99 percentile. This was not
EPA’s intention but we realize that our explanation at proposal was
not sufficiently clear. Based on comments and our reanalysis of our
methods, we realized that there was an error in the UPL equation at
proposal that has been corrected.

In response to comments, we re-evaluated the statistical analysis used
for the proposed rule and made changes to improve it. The changes we
made and why are discussed in the preamble to the final rule and in
supporting documentation in the docket and include why we continue to
believe the use of the UPL is the most appropriate statistical approach,
how we accounted for variability (including intra-quarry variability),
and other changes to the analysis since proposal. We disagree with the
commenters who said 30 days of data are insufficient, and we continue to
believe that the 30 data points provided from 30 days of sampling of all
kiln inputs for 89 kilns is a robust sample of the population of cement
kilns and adequate to characterize the variability encountered at each
individual kiln, especially as supplemented with the estimates of
intra-quarry variability. The top performing kilns used raw materials
and fuels from different sources, wasted varying amounts of cement kiln
dust, and included different types of kilns operating under various
operating conditions. Moreover, as discussed in the preamble, we
continued to refine our analysis and revised it to further refine
estimates of intra-quarry variability. We also corrected the case cited
by the commenter for the kiln that had an emissions profile that was not
representative of its normal product mix, and this kiln is no longer in
the top performing 12 percent.

We have also addressed in the preamble to the final rule the
commenter’s suggestion that, under “foreseeable circumstances,”
the MACT floor for mercury would be higher. In addition, we note here
that the 30-day rolling average form of the mercury standard allows an
owner or operator to detect trends in increasing mercury emissions over
days and to take corrective actions, whether by improving mercury
emission control devices or changing certain kiln inputs, before the
limit is necessarily exceeded. The 30-day rolling average provides much
more flexibility in dealing with foreseeable events than would a shorter
term averaging period (such as an hourly or daily average).

Our use of mass balance tracking of mercury to develop the mercury
emission limit is reasonable because it is based on the knowledge that,
in the absence of a mercury emission control device, the mercury in the
kiln’s inputs is emitted. We see no reason why the use of a mass
balance approach rather than collecting data on speciated mercury
emissions (as the commenter suggests) would result in significant costs
with little or no environmental benefit, nor did the commenter provide
information that would support such a claim. There is also no reasoning
or information presented that would indicate that it might have been
appropriate to subcategorize by species of mercury or other similar
approach, and we do not believe such approaches are warranted.

Use of subcategories

Comment: Many commenters (2842, 2893, 2928, 2984, 2987, 2989, 2994,
3001, 3005, 3023, 3030, 3034, 3038, 3045, 3052, 3056, 3057, 3059, 3061,
3062, 3063, 3065, 3073, 3074, 3077, 3098, 3101, 3104, 3105, 3107, 3110,
3125, 3128, 3130, 3132, 3226, and 3227) agreed with EPA’s decision to
not create subcategories in establishing mercury standards.

Commenter 2928 stated that because of the current effectiveness of
mercury controls available to cement plants, as well as a variety of new
control options available by the 2013 deadline these new proposed
emission standards set, it is not necessary to allow for subcategories
for cement plants that claim the mercury content of their limestone is
to blame for their emissions.

Commenter 2893 stated that subcategorization based on limestone
composition unfairly depreciates the value of cleaner limestone sources
and undermines the intent of the proposed rule.

Commenter 2999 disagreed with the proposed subcategorization of plants
based on their limestone mercury levels, but sees the value of a
temporary subcategory for existing cement plants to allow those plants
more time to comply with mercury emissions rules if they have recently
made substantial investments to lower mercury emissions using a
reasonably close to state of the art technology.

Commenter 2828 stated that there are multiple options for the ultra-high
mercury emitting kilns:

Use of limestone with lower mercury levels, including transport of
limestone from sources within a 5 to 10 mile radius.

Installation of serial pollution control systems.

The combination of fuel selection (more natural gas, less coal), coal
and limestone washing, and multiple mercury control systems. The mercury
control systems could include ACI injection, followed by a baghouse, and
then if needed, another ACI/baghouse system.

Several commenters (2144, 2840, and 2845) argued for the creation of
subcategories. Commenter 2144 stated that EPA should create an interim
hyper mercury limestone subcategory only for the two kilns that
exhibited estimated emissions greater than 1,000 lb/yr and require the
least stringent of 90 percent Mercury removal and the final mercury
standard. The kilns in the hyper Mercury limestone category would
ultimately meet the final emissions standard and phase out the
alternative 90 percent removal requirement.

Commenter 2840 suggested that for a subcategory of cement plants with
elevated mercury levels in their limestone, EPA could require employment
of maximum achievable control technology to reduce mercury emissions and
limit the use of offsite materials containing elevated levels of
mercury.

Commenter 2845 stated that EPA should subcategorize emission sources by
mercury concentration in the limestone to address variability and
ability to comply issues. Given that cement kilns must use limestone
from a nearby quarry to produce clinker, they should be seen as
essentially co-joined with that quarry for purposes of
subcategorization. Mercury emissions characteristics are based in large
part on available limestone and it is unreasonable and arbitrary not to
establish subcategories where technical differences between different
types or classes of cement kilns result in different emissions
characteristics.

Commenters 2844, 2845, 2863, 2900, and 2917 stated that EPA should
provide a new subcategory for kilns that have a high concentration of
mercury or other HAP in the limestone quarries servicing those kilns. As
recognized in EPA’s proposal, these kilns likely would be unable to
meet the proposed standards even after installing state-of-the-art
controls. While there are a limited number of facilities in EPA’s data
set with this issue, commenter 2845 stated that there may be other
similarly situated kilns throughout the United States, not reflected in
the data set. Commenters 2844, 2845, and 2900 proposed a subcategory
that results in a high MACT floor emission rate and then proposed that
EPA use beyond-the-floor consideration to apply state-of-the-art
controls on those facilities. For sources in the proposed subcategory
for units with high mercury concentrations in the limestone, Commenter
2845 proposed a 75 percent removal standard as the beyond-the-floor
limit, which reflects the best percent removal of mercury that may be
obtained through technology at those particular sources.

Commenters 2298, 2483, 2502, 2503, 2506, 2507, 2651, 2653, 2654, 2660,
2661, 2667, 2670, 2671, 2672, 2676, 2811, 2812, 2813, 2830, 2832, 2833,
2840, 2841, 2845, 2863, 2874, 2886, 2900, 2903, 2904, 2973, 2974, 2979,
2982, 2983, 2996, 2997, 3012, 3013, 3014, 3016, 3031, 3036, 3039, 3046,
3052, 3058, 3066, 3071, 3075, 3079, 3081, 3083, 3085, 3090, 3091, 3093,
3095, 3096, 3097, 3100, 3102, 3111, 3114, 3115, 3116, 3119, 3120, 3122,
3123, 3125, 3126, 3127, 3129, 3134, 3135, 3141, 3144, 3147, 3153, 3155,
3157, 3158, 3159, 3166, 3174, 3175, 3177, 3178, 3180, 3204, 3208, 3209,
3210, 3211, 3213, 3217, 3218, and 3219 stated that EPA should provide a
new subcategory for kilns that have a high concentration of mercury in
the limestone quarries servicing those kilns. As specifically recognized
in EPA’s proposal, these kilns likely would be unable to meet the
proposed standards even after installing state-of-the-art controls.

Commenter 2863 recommended the following actions on subcategorization
for purposes of the mercury standard:

No use of fly ash as an additive in the raw feed;

Implementation of dust shuttling to the maximum extent possible without
impacting product quality;

Implementation of a Mercury Minimization Plan to minimize mercury in the
raw materials imported from off-site; and

Implementation of a Control Enhancement Action Plan.

Response: The EPA reasons for declining to establish a subcategory for
high mercury emitting kilns with high mercury levels in their quarried
limestone are set out in the preamble to the final rule. We also
examined other actions on developing subcategories suggested by
Commenter 2863 and concluded that although these actions might help to
reduce mercury emissions at a given kiln, they do not provide a basis
for subcategorization, nor could they be used to represent MACT. We have
concluded that subcategorization for mercury emissions, which was the
subject of the comments provided above, is not necessary or warranted
because the mercury emission limits can be met with the application of
mercury emission controls and/or other practices, such as those that
reduce the amount of mercury in inputs to the kiln.

We also disagree with a commenter’s statement that a 75 percent
removal standard should be the beyond-the-floor limit because ACI
technology for mercury will achieve higher removal levels than 75
percent, and for some kilns with high mercury inputs, a removal of only
75 percent would not even represent the MACT floor. We also disagree
with the development of “interim” standards and note that the CAA
provides the allowable schedule for compliance for existing sources in
section 112(i)(3) (with some discretion by EPA and the permitting
authority when extra time is needed to install emission controls).

Pounds of mercury per million tons of feed includes fuel in denominator

Comment: One commenter (2849) stated that EPA incorrectly calculated the
conversion from pounds per million tons of feed to pounds per million
tons of clinker when it developed its mercury floor levels. When EPA
computed its mercury balance for each of the 89 kilns it used in the
mercury MACT floor calculation, it used total mercury inputs from raw
materials and fuels, then subtracted out the mercury output from kiln
dust not recirculated to the kiln, to arrive at a calculated mercury
emission (in pounds). It then divided these pounds of mercury emissions
by the total quantity of raw material plus fuels inputs to arrive at
emission units that were entitled pounds of mercury per million tons of
feed. In fact, a more correct title for these emission units should have
been pounds of mercury per million tons of feed plus fuel.

Response: The commenter’s characterization of EPA’s approach to
calculating mercury emissions per ton of clinker is partially correct
with the exception that we did not, as the commenter states, include the
quantity of fuel along with the quantity of feed materials in
calculating mercury emissions in pounds per million tons of clinker. In
response to the comment, we reviewed the approach used as well as the
data to confirm that fuel materials were correctly categorized and not
included in the sum of raw materials for each kiln.

To calculate mercury emissions per ton of clinker, all materials
reported in the responses to EPA’s May 8, 2007 information collection
requests (ICR) were entered into an Access database. All materials (feed
and fuel) were classified in a raw materials table and through database
queries into one of the following categories:

Limestone

Shale

Clay

Fly ash/bottom ash

Sand	Iron

Other raw materials

Coal/coke/fossil fuel

Tires/TDF

Wasted CKD

To be considered as a feed material, the reported raw materials for each
kiln could not also be in a fuel or CKD category. Mercury emissions per
million tons of feed were then converted to emissions per million tons
of clinker by multiplying by the conversion factor of 1.65 tons of feed
per ton of clinker. Although EPA’s approach for calculating mercury
emissions per ton of clinker was designed to exclude fuel in the
denominator, it is possible that a minor, uncommon fuel material used at
a kiln was incorrectly classified as a feed material. However, coal,
coke, other fossil fuels and tire derived fuel constituted nearly all of
the fuel for most kilns and a misclassification of a minor fuel material
as feed, or vice versa, would not have any significant effect on a
kiln’s final emission rate.

Data suggest a 12-month average standard

Comment: One commenter (2864) stated that although EPA collected 30 days
of mercury input data for 89 kilns, the Agency also collected annual
data on the mass inputs and the amount of material collected in the PM
control device (or alkali PM control device) that is wasted rather than
returned to the kiln. The annual average data were used to calculate the
mass-balance mercury emissions, which were then used to establish the
mercury floor. The commenter stated that this is an annual mercury
emission rate and EPA should establish a rolling 12-month average
mercury MACT standard.

Response: As stated previously, EPA’s legal obligation in establishing
MACT floors is to reasonably estimate the average performance achieved
by the best performing 12 percent of best performing sources, or for new
sources, the performance of the best controlled similar source. The
statute does not speak to the issue of permissible averaging times in
constructing standards, so it may be that in factually appropriate
cases, a choice of averaging time to account for best performing
sources’ variability could be legitimate. However, automatic (i.e., a
priori) determinations to adopt long-term averages for any type of data
set regardless of circumstances of sources’ performance and robustness
of the data set, would go too far. We chose a 30-day averaging period
for the mercury emission limit. The use of a 30 day average (as opposed
to hourly or daily averages) tends to reduce variability, and also best
reflects the nature of the data from which the floor was derived and
assures that several operating cycles of raw mill on and off are
included in each average. The mercury limit is based on a 30-day
averaging period to be consistent with the averaging periods for other
regulated kiln pollutants, and adequately allows additional operating
flexibility to meet the limit. Finally, EPA is setting the compliance
period using 30-day averaging periods for enforcement reasons in that
EPA can periodically determine compliance with the emission limits and
avoid long periods in which sources may be emitting at unacceptably high
levels.

Provide alternative removal efficiency standard

Comment: Several commenters (2845 and 2874) stated that EPA should set
an industry-wide MACT floor set on the basis of percent removal, or
system removal efficiency (SRE) to be used as an alternative to the
currently proposed mass-rate based emission limit.

Response: For the reasons stated in the preamble to the final rule (and
comment responses therein), EPA is not expressing standards, or
determining MACT floor, on a per cent reduction basis. No commenter
provided a convincing response to how such an approach, in this rule,
properly accounts for the role of HAP in kiln inputs. Nor did commenters
address how such a standard could even be constructed for mercury, where
there is essentially no system removal because kilns are uncontrolled
and mercury volatilizes.

2.5.3	Beyond the Floor Determinations

Comment: Several commenters (2845 and 2863) stated that EPA correctly
explains that if it did not subcategorize based on mercury concentration
in the limestone, it would not be appropriate to establish a
beyond-the-floor standard for mercury for either new or existing
sources. Doing so would not be cost-effective. As a result of the much
higher mercury emissions from kilns in a subcategory of sources with
high mercury concentration in the limestone; however, a beyond-the-floor
standard may be appropriate. The commenter states that such a
beyond-the-floor standard should be expressed in terms of system removal
efficiency (i.e., percentage reduction of mercury entering the kiln in
the raw materials and fuel). The commenter further states that a
75 percent system removal efficiency for mercury would represent a
stringent beyond the floor standard for both new and existing sources
that nevertheless could be achieved through the use of ACI, the best
mercury control available.

Commenter 2898 recommended that EPA address fuel-switching as a beyond
the floor option. EPA should explain what site-specific circumstances
might influence the substitution of low-mercury materials and fuels for
some facilities, and why the practice could not be applied uniformly on
a national basis. The commenter suggests that EPA fully explore
non-technology emission reduction options in the beyond the floor
discussion, including fuel-switching.

Response: EPA agrees that a beyond-the-floor standard is not appropriate
for mercury given the decision not to subcategorize. See preamble for
response to comment to consider fuel switching.

2.5.4	Compliance Assurance

Form of the Standard

Comment: Commenter 2879 stated that CEMS readings and clinker production
calculations can be unreliable. Rather than assuming that kiln operators
can accurately determine the mercury emissions per million tons of
clinker on a 30 day average basis, EPA should determine the mercury CEMS
concentration that corresponds to the proposed 43 lb/MM ton clinker, or
the appropriate value representing the average of the best performing
12%.

Commenter 2889 suggested that EPA conduct error analysis to evaluate the
ability of a source to comply with the mercury monthly block average
emission limit. To comply with the mercury limit in the proposed
amendments, a cement kiln operator will have to measure (1) the mercury
concentration in the gas stream, (2) the gas flow rate in the stack, and
(3) the clinker production rate. These three sources of data will be
combined to determine compliance with the monthly block average limit.
Considering the low emission rate in the proposed amendments, EPA should
evaluate the inherent measurement error associated with these quite
different measurements. Cement kilns could appear to be out of
compliance simply because of slight unavoidable variability of the
accuracy of the three measurements. This problem could be reduced
slightly by simply applying a mercury concentration limit in the gas
stream without any reference to the clinker production rate.

Response: Issues related to clinker measurement are addressed in the
preamble to the final rule.  Other facilities in the utility industry
and the cement industry are currently measuring mercury concentrations
at and below these levels using a CEMS.

Data supports mass balance approach

Comment: Several commenters (2844, 2845, 2855, 2859, and 2901) stated
that EPA has provided no support for its assumption that the
mass-balance data used to establish the mercury MACT floors can be
correlated to continuous emissions monitoring data to demonstrate
compliance. The commenters stated that there is no basis for the
Agency’s assumption that conservation of mass data calculations made
for the cement industry correlate with the emission measurements that
may be made in the future with mercury CEMS.

Response: The mercury emission standard is based on a MACT floor of
pounds of mercury emissions per ton of clinker, adjusted for
variability. We believe that the analysis described in the proposal
notice and in the docket does support a correlation between the MACT
floors and continuous monitoring data collected on a 30-day rolling
average.

Comment: Commenter 2844 stated that CEMS will create compliance issues
that are not related to emissions compliance; CEMS represent a very high
added cost beyond any value; and EPA should adopt mercury limits that
allow the use of mass balance calculations.

Commenters 2855 and 2874 stated that EPA should reconsider a sampling
and analysis program involving kiln inputs as an acceptable option to
CEMS for demonstrating compliance with a mercury standard. Commenter
2855 stated that this approach should be allowed because EPA relied on
this approach to establish the mercury standards, and for low level
mercury emitting facilities that can comply with the standards without
add-on controls, the solid material sampling programs could be focused
to optimize accuracy and minimize costs.

Commenter 2855 stated that facilities that control mercury emissions
from cement kilns or kiln/in-line raw mills should be allowed to use
solid or liquid material sampling and analysis to demonstrate mercury
removal as an optional monitoring approach. Facilities that waste cement
kiln dust (CKD) or implement dust management programs to minimize
mercury emissions should be allowed to implement solid material sampling
and analysis procedures to quantify the mass of mercury removed. The
optimal sampling location and approach must be determined on a
site-specific basis. Similarly, sources with add-on controls should be
allowed to implement material sampling and analysis procedures to
quantify the mass of mercury removed and subtract the documented mercury
removed to determine compliance with mercury standards.

Commenter 2888 recommended that since the orientation of monovent kilns
does not provide a means for a stack flow meter (there is no stack) or a
CEM, these kilns should perform a mass balance of the material flows
into and out of the process, for purposes of demonstrating compliance
with the NESHAP mercury standard.

Response: Mercury is a unique pollutant because the amount of mercury
input to the system equals the amount of mercury output. In the absence
of control devices, input equals output, and a material balance approach
is feasible. However, the cost of collecting such data on a daily basis
is comparable to the cost of a mercury monitoring system. In addition,
in order to meet the mercury standards, many sources will install
control devices. In order to conduct a material balance on this now more
complicated system, we would have to determine a reliable control device
efficiency value and require continuous monitoring of control device
parameters. Given these costs and uncertainties, we conclude that
continuous monitoring at the stack is the best method to determine
compliance. As always, however, sources are allowed to request
source-specific approval of alternative compliance methods under the
part 63.7 General Provisions.

CEMS not demonstrated in cement manufacturing

Comment: Many commenters (2830, 2845, 2846, 2855, 2858, 2859, 2879,
2887, and 2890) stated that CEMS are not a proven technology and should
not be required to determine compliance.

Commenters 2588, 2844, 2845, 2846, 2858, and 2890 stated that EPA has no
data showing that mercury CEMS are feasible on cement kilns and that
emissions from cement kilns will likely be outside of the range of the
current CEMS technology. The commenters stated that EPA must evaluate
mercury CEMS through long-term field trials at cement plants in
accordance with the proposed performance specifications and quality
assurance procedures before imposing this regulatory requirement. The
commenters proposed a mass-balance approach for monitoring, which is
accurate and was used by EPA in setting the mercury standard.

Commenter 2855 stated that mercury sorbent trap monitoring systems have
not been evaluated through long term field trials at cement plants in
the United States (U.S.) in accordance with the proposed performance
specifications and quality assurance procedures, so the reliability and
performance of these measurement systems and the adequacy of the
technical specifications cannot be determined.

Commenters 2855 and 2900 disagreed with EPA’s interpretation of the
operating experience with mercury CEMS in Germany. The commenters stated
that mercury CEMS are inaccurate and difficult to maintain. Further,
mercury CEMS operating in Germany are subject to monitoring regulations
that are different than the U.S. regulations and are used in a different
regulatory context than that proposed by EPA. The monitors used in
Germany, or those available from other European or Asian manufacturers
were not able to demonstrate acceptable performance in the Electric
Power Research Institute (EPRI) Trimble County Mercury CEMS study.

Commenter 2855 stated that there is no legitimate technical basis on
which to establish detailed performance specifications or quality
assurance (QA) requirements for these CEMS. There is no legitimate
technical basis to conclude that these CEMS could meet such requirements
over any extended period when installed and operated at a cement plant.
The commenter recommended that EPA evaluate the performance of mercury
CEMS at cement kiln systems and acquire the information necessary to
serve as the basis for technical specifications and requirements. After
such information is available and analyzed, EPA should re-propose
appropriate and demonstrated performance specifications and quality
assurance procedures for mercury CEMS to monitor kiln and kiln/in-line
raw mill mercury emissions.

Commenter 2855 disagreed with EPA’s interpretation that mercury CEMS
can be applied to the cement industry based on successful use on utility
boilers. The commenter evaluated the following issues:

Number of Installations in the Utility Industry – there are 35 – 40
continuous mercury monitors (CMMs) installed and certified to date (not
yet with a NIST traceable calibration source).

NIST Certification – In mercury CEM certification requirements
outlined in Performance Specification (PS)-12A, it states that all
calibration and span gases must be NIST certified. The draft protocols
were just released by NIST in July 2009. The major vendors of mercury
CEM are just now advertising NIST-certified calibration sources.
Therefore, none of the mercury CEMs that have been previously installed
are certified. NIST does not currently directly certify oxidized mercury
calibrations. The Interim EPA Traceability Protocols now in place
provide for certification of evaporative generators by certification of
the individual components of the calibrator. Therefore, the language
used in Section 7.0 that refers to a NIST trace oxidized mercury
calibrator needs to be clarified or changed.

Difficulties Encountered in the Utility Industry – The commenter gave
examples of power plants’ difficulties with mercury CEMS.

Installation on Wet Stacks – Installing a mercury CEMS on a wet stack
can result in problems: plugging, corrosion, and buildup of solids.
Although wet scrubbers are not currently common in the cement industry,
under the proposed rule, they may be required to a greater extent, and
many of these same problems with mercury CEMs potentially could occur
for the cement industry as well.

Data Output Requirements – There is no need for dry basis measurements
under the proposed rule and the language in either Subpart LLL should be
included to provide an exemption from this requirement for cement plants
or PS-12A should be revised. This language needs to be clarified by EPA.

Cost – The commenter provided information about CEMS costs, estimating
that if mercury CEMS were installed on all non-waste-burning U.S. cement
facilities, the total capital costs would be approximately $45 million,
with annual operating costs being about $25 million.

Commenter 2901 stated that CEMS should not be used as a compliance
method for cement plants for the following reasons:

EPA reported in 1997 on an experiment where CEMS were installed on a
cement kiln burning hazardous waste. The Agency found substantial
problems regarding mercury CEMS measurement accuracy and precision,
deciding not to require Mercury CEMS at cement plants. The commenter
stated that the primary issue is whether there is a NIST traceable
standard that can be used to calibrate the unit. Because compliance is
based on the production rate and using a 30-day average, it is difficult
to know what range to calibrate these units.

The reliability of CEMS on cement kiln stacks has not been demonstrated
in the U.S., where standards and requirements are different.
Demonstrations in the U.S. at coal-fired power plants have different
conditions than those at cement kilns.

There is no legal imperative for EPA to require CEMS. Under the CAA,
EPA’s monitoring requirements must provide a reasonable assurance of
compliance with emission standards Sierra Club v. EPA, 353 F.3d 976,
990-991 (DC Cir 2004) (Copper Smelters) citing Natural Res. Def.
Council, Inc. v. EPA, 194 F.3d 130, 136 (D.C. Cir 1999).

Response: See response in preamble.

Comment: Commenter 2890 stated that CEMS represent a requirement that is
beyond the floor.

Response: Assuming the argument that measuring methodology can be
considered to be part of a standard, the use of CEMs to measure the
mercury standard does not make the standard more stringent. The mercury
standard was developed on the basis of 30-day data samples, and is
measured over the same duration. The standard was also developed on a
mass balance basis whereby essentially all input mercury was considered
to be emitted (except for the few kilns equipped with wet scrubbers).
This is essentially a worst case assumption (attributing no removal to
baghouses, for example). Given that the standard is measured over the
identical duration as was the underlying data, and that actual emissions
are measured so that kilns are no longer presumed to emit all inputted
mercury, we repeat that use of a CEM does not make the standard more
stringent and thereby constitute a beyond-the-floor standard.

Comment: Several commenters (2155, 2867, 2891, 2894, and 2898) supported
EPA’s decision to require mercury compliance monitoring using CEMS.

Commenter 2867 reports that their own inquiry to the German Federal
Environment Agency, (Umweltbundesamt [UBA]) regarding the mercury-CEMS
features of the proposed cement MACT rule, which found the mercury CEMS
QA suitable to ensure quality measurements. According to the commenter,
UBA has the most experience in the world among environmental agencies in
the field of mercury-CEMS including the cement industry. The commenter
also cited the experience of the Ash Grove Durkee, Oregon facility. The
commenter noted that the results for this facility presented at the 2008
Air and Waste Management Association (AWMA) Conference in Oregon showed
that the mercury-CEMS registered the same average stack mercury
emissions reading (0.027 g/s) when the raw mill was on as the average
value of the Methods 324 and OH. The commenter stated that this
indicates that mercury-CEMS are feasible, precise and accurate compared
with the conventional in-stack sampling methods at low and at elevated
emission rates.

Commenter 2894 stated that as manufacturer of mercury monitoring
instrumentation, they are in the process of installing mercury CEMS on
U.S.-based cement kilns. There are no technical obstacles to the use of
mercury CEMS in this type of environment.

Response: We agree with these commenters that mercury CEMS should be
used for compliance monitoring.

Wet vs. Dry Concentration Format for CEMS

Comment: One commenter (2894) stated that in order to maximize accuracy
in mercury mass emission calculations, mercury CEMs should report
mercury concentrations as μg/m3 (at 20 ºC, 760 mm mercury pressure) on
a wet basis. No correction for O2, carbon dioxide (CO2) or any other gas
should be performed. Stack flow rate should also be measured on a wet
basis, in m3/min (at 20 ºC, 760 mm mercury) at the same point in the
process, with no correction for any diluent gas.

Commenter 2894 recommended calculating mercury emissions using a wet
concentration and wet flow rate in equation 5 (Ref Eq. 5, page 21187,
col 2) rather than the currently required dry concentration and dry flow
rate. A dry mercury concentration is not required to calculate mass
emissions and would actually reduce the accuracy. In the event that a
dry concentration is absolutely required, the rule should make it clear
that the same (BWS) factor must be used to correct both the mercury
concentration and the flow rate. This factor should be a calculated
value; a moisture analyzer is not required since the two occurrences of
the BWS factor cancel arithmetically.

Commenter 2855 said that there is no need for dry basis measurements
under the proposed rule, and the language in either Subpart LLL should
be included to provide an exemption from this requirement for cement
plants or PS-12A should be revised. This language needs to be clarified
by EPA.

Response: We agree with the commenters that dry concentrations and flow
measurements are not required to calculate mass emissions. It is
important that the measurements are on the same basis, wet or dry, for
the calculations. The equations have been modified and clarifying text
added. We have revised to standard to state that dry measurements are
not required.

Comment: One commenter (2837) recommended that the period for
calibration drift check should be defined by system operator, rather
than defining this period on the basis of any one of the available
technologies. The commenter also recommended that EPA define how the
operator is to demonstrate the validity of the operator-defined
calibration check period.

Response: Requirements for calibration checks, including the frequency
(once daily), are specified in Appendix F, Procedure 5. The procedures
to be used are based on manufacturers’ recommendations.

Establish standard as CEM concentration

Comment: One commenter (2879) recommended that EPA should measure
mercury emissions using a CEM, reconciling CO2 emissions with mass
balance emissions and establishing the standard as a CEM concentration.

Response: Under the final testing and monitoring requirements, CEMS or
sorbent trap monitors are required to continuously measure mercury
emissions. See the preamble discussion under final testing and
monitoring requirements for more information on EPA’s decision.

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.

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 the 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.

See the preamble discussion under format of the normalized standards in
the NESHAP and the NSPS, for more information on EPA’s decision.

All mercury phases should be monitored

Comment: One commenter (2638) stated that all phases of mercury should
be monitored and PS 12A and Procedure 5 should be rewritten to include
total mercury. The commenter stated it is contrary to the intent of the
CAA to set emission limits for only vapor phase mercury and requested
that the EPA change its emission limit from one based on vapor phase
mercury to one based on total mercury that includes both PM and vapor
phases.

One commenter (2638) stated that all physical phases of all HAP metals,
including mercury, need to be measured during SSM events. For example,
if mercury is captured on powdered activated carbon, which in turn is
captured on a fabric filter, the percentage of mercury in the PM
fraction downstream of the fabric filter during malfunctions could and
would be expected to be significant.

Commenter 2638 stated that total mercury monitoring can now be
undertaken with proven methods, and will be consistent with Congress’
desire for the EPA to require enhanced monitoring where it is
appropriate to assure continual compliance with emission limits. The
commenter provided several reports describing alternative measurement
methods.

Response: The mercury standard is based on total mercury data in the
form of mercury inputs to the source. As part of this reconsideration
tests were performed at five facilities with wet scrubbers. Testing was
performed at the scrubber inlet and outlets. We believe tests at a wet
scrubber outlet would represent a situation where particulate mercury
would most likely be present due to the lower temperatures involved
(below 200OF). On average the amounts of particulate mercury measured at
both locations was below 1 percent. Given this fact, we believe that
measurement of total mercury would add unnecessary expense and
complexity to mercury monitoring. However, sources are able to request
approval for source-specific monitoring requirements from EPA under
section 63.7 (f) of the General Provisions.

Measurement bias not considered in achievability of standard

Comment: One commenter (2855) stated that EPA did not consider the
allowed measurement bias for mercury CEMS or sorbent tube monitoring
programs on the achievability of the emission standards.

Response: We disagree that either the mercury CEMS or the mercury test
Method 30B include an inherent measurement bias. All measurement data
are subject to some degree of variability which would include
measurement error (e.g., interference) and imprecision (e.g.,
measurement repeatability). The procedures in Performance Specification
12A promulgated with this rule account for both measurement error and
imprecision in calculating the relative accuracy of the CEMS. Secondly,
we believe that any inherent variability of data due to measurement
imprecision is reasonably addressed in calculating the floor and
emissions limits. The data used to establish the limits represent
emissions tests from multiple facilities and we subjected the data to
statistical procedures to account for variance.

Contradiction in performance test duration

Comment: One commenter (2855) stated that §63.1349(b)(5)(i) specifies a
mercury performance test duration of a calendar month, which contradicts
the averaging period of the proposed emission standard of a 30-day
rolling average.

Response: We do not consider this a contradiction because both
monitoring periods have different purposes. The performance test for a
calendar month is to ensure that the control device and the CEMS are
both working correctly. The 30-day rolling average is the compliance
demonstration period. We are proposing additional clarifications such as
a definition of “kiln operating day” to further address questions
regarding the compliance demonstration period. In general, if the kiln
operates during a 24-hour period, the CEMS must operate too.

Initial performance demonstration recommendations

Comment: One commenter (2855) stated that the initial performance
demonstration should be based on a properly calibrated and compliant
CEMS or Sorbent Trap System (if such systems become available and are
demonstrated to perform acceptably), and the initial performance test
result must be based on the calculated average lb mercury/million ton
clinker produced for 30 kiln operating days. A definition for kiln
operating day must be established and must reflect a specified number of
hours of kiln or raw material dryer operation at normal production
conditions and a minimum number of hours of quality assured monitoring
data. Days with fewer operating hours or insufficient monitoring data
are not included in the 30 day average.

Response: We agree that a definition of “kiln operating day” is
needed, and have added it to the final rule. We have not specified a
minimum number of hours of kiln or raw material dryer operation; a kiln
operating day is any day the kiln is operating, and all valid data (for
hours when the process is operating) for all operating days are included
in the 30 day average.

Request daily instead of hourly mercury concentration data

Comment: One commenter (2855) stated §63.1349(b)(5)(i) requires
collection of hourly mercury concentration data which will not be
available for sorbent trap monitoring systems and is not required by
PS-12B. The commenter suggested that daily mercury emission rate
averages would be adequate.

Response: The final rule has been clarified to address this situation.
For example, if sorbent traps are collected every 7 days, each daily
average would be assumed to equal the 7-day average.

Testing with raw mill on and raw mill off

Comment: One commenter (2855) stated that EPA should clarify that
separate performance tests are not required for mill on and mill off
conditions in the discussion in §63.1349(b)(5)(i) about demonstrating
mercury compliance.

Response: We have clarified this language in the final rule to state
that the raw mill off testing provision for mercury does not apply to a
kiln equipped with and demonstrating compliance using a mercury CEMS.

Calculation of monthly mercury emissions

Comment: One commenter (2894) disagreed with the calculations to
determine monthly mercury mass emissions (Ref Eq. 5, page 21187, col 2).
The commenter stated that this calculation could result in large biases.
The commenter suggested an alternative calculation that multiplies the
hourly average mercury concentrations by the hourly average flow rates
and totals these values for the month to determine mercury mass
emissions.

Commenter 2894 stated that total monthly mercury mass emission must be
divided by the clinker production rate during the same calendar month in
order to determine compliance. Mercury monitoring systems of any type
are capable of determining only mercury concentrations. It appears that
even the most conscientious plant operators will thus not know until
well after the month has elapsed whether they were in compliance for
that month.

Commenter 2894 stated that in cases where plant operators go through the
effort to install systems capable of continuously measuring mercury
concentrations and stack flow rates, it seems only fair and reasonable
that the EPA devise a metric that allows plants to determine on an
ongoing basis whether they are complying with the regulation.

Response: The commenter misinterpreted compliance equation 5 (74 FR at
21187) to require a determination of monthly mercury mass emissions and
a monthly average flow rate. As recommended by the commenter, section
63.1349 (b)(5)(i) of the final rule requires the kiln owner or operator
to measure and record hourly mercury concentration data and stack gas
volumetric flow rates. These measurements are to be used to calculate
daily mercury emission rates. Owners or operators are also required to
operate a system to measure the hourly clinker production rates, either
directly or indirectly through measuring kiln feed rates and applying a
factor for converting feed rates to clinker production rates (section
63.1350(o)). They must record both the daily kiln feed rates and clinker
production rates. Using the daily mercury concentration data, daily
stack gas flow rates and daily production rates, the owner or operator
can track their performance on an ongoing daily basis rather than once a
month.

<IP_ADDRESS>	Performance Specification 12A, 12B, and Procedure 5

PS-12A

Comment: One commenter (2638) stated that PS-12A should not be
generalized to unspecified source categories other than portland cement.
Because emission standards and measurement methods are not written
independent of each other, defining the measurement method in effect
defines the emission limit/standard for other, unspecified sources. By
generalizing this measurement technology to vapor phase mercury, the EPA
appears to want to generalize the emission standards for other, as yet
to be specified sources to vapor phase mercury. By doing this, the EPA
greatly inhibits the development of new methods that might measure total
mercury.

Response: EPA will only apply PS-12A to other source categories through
specific notice and comment rulemaking, and only when it is appropriate
to do so. We are not opposed to the concept that PS-12A could also be
applied to monitoring systems that also incorporate non-gaseous mercury
in the mercury measurement for this or any other appropriate source
category (see §63.7 (f)). However, EPA does not have any evidence that
any appreciable non-gaseous mercury is present in the emissions from
this particular source category.

Comment: One commenter (2638) stated that PS-12A and ongoing quality
assurance should be re-written to replace contemporary
technology-specific requirements with generalized measurement-objective
driven requirements. The commenter provided comments about testing
linearity, calibration drift, accuracy, system integrity, reagents and
standards, and span value.

Response: We disagree that PS-12A is technology-specific. We recognize
that some performance procedures of PS-12A may be more difficult for
some instruments and that some modifications to performance procedures
may be necessary. EPA has a program in place to deal with this situation
through the alternative test method request and approval/disapproval
provisions of §63.7(f).

Comment: One commenter (2638) suggested specific changes to PS-12A and
Procedure 5:

Subsection 6.1.1 Data Recorder Scale: Should be replaced to simply
require the operator to include the range defined by the zero and span
values. The EPA proposed requirement seems to be based on old technology
and defining this range with a specific numeric requirement (two times
the standard) serves no functional purpose and unnecessarily restricts
development.

Subsection 6.1.2 CE determination: Change zero to low and upscale to
high.

Section 8.0 PS Tests: The EPA should re-write this section around
clearly defined analytical objectives of establishing the CEMS initial
accuracy, precision, linearity, stability and system integrity based on
some of the same principals used in EPA Method 301.

Subsection 8.1.3 Extraction point: This should be re-written to allow
for possible in situ monitoring systems that do not require sample
extraction.

Section 3.0 Definitions: A new subsection should be added defining zero
or the bottom of the range for valid results, and instructions as to
what value to use when a result falls below this defined concentration.
The commenter recommended that zero be replaced with detection limit as
defined by the EPA in Title 40, Appendix B Part 136 as the minimum
concentration of a substance that can be measured and reported with 99%
confidence that the analyte concentration is greater than zero. If the
concentration is less than this concentration, the reported value should
be replaced with a concentration equal to the detection limit.

Response: Subsection 6.1.1 of PS-12A has been revised in response to
comments received. Subsection 6.1.2 PS-12A has been revised to be
consistent with Section 7.1 of PS-12A on reference gases. The relative
accuracy test audit or RATA of PS-12A is designed to assess the overall
performance of the instrumental measurement system, including the
representativeness of the sampling (i.e., probe location). PS-12A is not
intended to address method detection limits.

Comment: One commenter (2837) provided analytical detail related to
initial and on-going quality assurance:

National Institute of Standards and Technology (NIST) certified
traceable sources of elemental and oxidized mercury vapors are not
generally needed to demonstrate CEMS compliance with performance based
quality parameters such as linearity, accuracy, precision, stability or
system integrity for either initial CEMS certification or on-going
quality assurance and should be removed from both PS-12A and Procedure
5.

The calibration check requirement currently in PS-12A and Procedure 5
allows the same mercury generator used to calibrate the CEMS to be used
to check the calibration. Thus, they are not independent and a drift in
the generator output would cause a drift in the CEMS calibration.
Spiking mercury into clean, conditioned, interference-free air does not
provide traceability to NIST standards for assurance of calibration
accuracy.

Spiking mercury into clean, conditioned, interference-free air does not
provide quality assurance of system integrity, analyte transportability,
sensor response, etc.

The current calibration drift check period is technology specific and
should be defined by the system operator with performance-based
protocols to demonstrate the applicability of the selected period.

Response: The NIST traceability and daily calibration requirements of
PS-12A are consistent with the Agency’s other compliance monitoring
requirements in 40 CFR Part 60 which require NIST traceable
“protocol” gases for CEMS quality assurance/quality control. This
approach has proven to be very effective for assessing overall system
performance (e.g., sample transport and analyzer accuracy) through
introduction of the reference gases at the CEMS probe. Dynamic spiking
with elemental and oxidized mercury gases through the probe would be
another way to accomplish this performance check and would certainly be
encouraged as a potential alternative test method procedural request
under §63.7(f). EPA believes that the requirements for NIST
traceability of calibration gas generators are sufficient to address
drift of the generators.

Comment: One commenter (2855) stated that PS-12A requires a system
integrity check using an oxidized mercury NIST calibration source, which
is designed to ensure the convertor portion of the mercury CEM is
converting all of the mercury to elemental mercury. The commenter stated
that there is a discrepancy between the oxidized and elemental mercury
calibrators of about 7% in both Tekran and ThermoScientific instruments
and that the cause of this discrepancy is still unknown.

Response: The commenter is correct regarding the discrepancy between the
oxidized and elemental mercury calibrators of about 7 percent for the
Tekran instrument; however, the Interim EPA Traceability Protocol for
Qualification and Certification of Elemental Mercury Gas Generators and
the Interim EPA Traceability Protocol for Qualification and
Certification of Oxidized Mercury Gas Generators (July 01, 2009)
recognizes this issue and provides a straightforward remedy. The
protocol specifies that until the time that NIST traceability of
evaporative oxidized mercury standards generators can be evaluated by
direct measurement, the generator manufacturers may use a model-specific
factor in their software to adjust the calibrated output of their HgCl2
generator to correspond with their NIST certified elemental generators,
thus negating the discrepancy. The generator manufacturer must then
provide the end user with the exact value of this correction factor and
instructions for its application, and have derivation data available to
the end user.

Comment: One commenter (2855) stated that EPA should not revert to 2004
CEMS performance specifications and should not require any
specifications that are more restrictive than the 40 CFR 75, Appendix A
and B requirements promulgated in January 2008.

Response: After consideration of the potential variability between the
learning curves of CEMS operators that new users of Hg CEMS may
experience, we have revised the relative accuracy specification in
PS-12A from 10 percent to 20 percent. We believe, however, that the
implication of this change is minor and short-lived because most
facilities that install mercury CEMS will find that they readily achieve
relative accuracies far better than 20 percent.

Comment: One commenter (2855) stated that after field validation, and
promulgation of instrumental CEMS and technical specifications and after
NIST traceable calibration standards at the necessary concentrations are
available, EPA should allow at least one year for purchase, installation
and start-up of CEMS and a one-year trial implementation period before
requiring the use of monitoring data to demonstrate compliance with
emission limits.

One commenter (2144) recommended that EPA consider alternative QA
procedures for mercury CEMS but without delaying final rule
promulgation.

Response: The amendment to the Portland Cement NESHAP will not become
effective until 60 days following promulgation for new sources and
existing sources will have up to 3 years to install controls and
monitoring systems (see Section 63.1350(i)). The National Institute of
Standards and Technology (NIST) has recently completed certification of
a ‘NIST Prime’ elemental mercury gas generator at concentrations of
41, 68, 85, 105, 140, 185, 230, 287, and 353 µg/m3 and mercury gas
generator vendors may now submit elemental mercury gas generators for
certification to serve as ‘Vendor Primes’. Therefore NIST traceable
mercury gas standards can now be made available in concentrations that
exceed the equivalent mass standards for both existing and new kilns by
between one and two orders of magnitude, thus providing the capability
to accurately report excursions well beyond either standard. The rule
effective date should provide ample time for facilities to meet mercury
monitoring system installation and certification requirements.

Comment: One commenter (2855) provided the following specific comments
on PS-12A:

Establishing the span value at twice the concentration corresponding to
the emission limitation is acceptable for cement plants provided that
reasonable provisions are included for certification and quality
assurance of the mercury CEMS when emissions exceeding the span value
are periodically encountered (such as for plants with in-line raw mills
during mill off operation). The commenter provided suggested amendments
to the Subpart LLL monitoring provisions.

The definition of span value should be changed, explicit procedures for
its calculation should be added, and the value should be rounded to
established ranges. The definition could be modified by the addition of
the phrase Span value means the upper limit of intended measurement
range during normal ‘mill on’ operation which may be exceeded during
‘mill off’ operation or other short-term conditions lasting less
than 24 consecutive kiln operating hours. Or the first sentence in the
EPA proposed definition could be eliminated. Alternatively the span
value could be specified in the applicable Subpart (Subpart LLL) where
the specific requirements are more appropriately addressed.

Response: We have modified the definition of span in PS-12A to provide
additional flexibility and have adopted the commenter’s suggestion to
include source category-specific provisions regarding the span in
paragraph 63.1350(n) of Subpart LLL. We agree that the quality of
measurements outside the calibration range should be assessed and could
be further documented by extending the calibration range or other
appropriate means. The commenter provided the following three approaches
that EPA would consider appropriate:

If emissions exceed the span value for more than 5 percent of the kiln
operating time, the CEMS operator could conduct “direct
calibrations” of the Hg analyzer bypassing the dilution module.
Because the Thermo and Tekran Hg CEMS operate on a dilution ratio of 30
or 50 to 1, the calibrated range of the Hg analyzer will be 30 or 40
times the upscale calibration value. Hence, for a system calibrated to
measure 0-10 µg/m3 through the entire measurement system, the analyzer
would be calibrated accurate to between 0 and 300 µg/m3.

The ability of the CEMS to quantitatively transport high concentration
levels of oxidized Hg through the probe, filter, filter cake, sample
lines, and the ability of the CEMS converter to reduce the oxidized Hg
to elemental Hg should be confirmed initially and quarterly by injecting
a high level HgC12 calibration gas standard at the sample probe,
upstream of the PM filter. This high level system integrity test should
be performed at a concentration approximating the maximum hourly
emission concentration during the preceding three months or other
representative high level concentration. The high level system integrity
check is acceptable if: the stable Hg CEMS response is within ± (some
percentage to be determined based on future field evaluations) of the
reference value, and the system returns to normal operating level within
30 minutes of ceasing the calibration gas injection, or the time
integrated Hg CEMS response is equivalent to the total mass of HgC12
injected within ± (some percentage to be determined based on future
field evaluations).

As an alternative to the high level system integrity checks, the CEMS
operator could elect to demonstrate the accuracy of Hg CEMS measurements
exceeding the span level by conducting a three-run relative accuracy
audit (RAA), preferably when mercury levels are outside the calibrated
range of the CEMS . The three-run RAA would be performed using Method
30B as the reference method following the procedures described in
Procedure 5.

Comment: One commenter (2855) said that specific procedures should be
provided in Subpart LLL for the calculation of the emission
concentration equivalent to the 43 lb/million ton clinker (existing
sources) or 14 lb/million ton clinker (new sources).

Response: Facilities can rearrange Equation 3 of Subpart LLL in order to
calculate these quantities using their production rates and volumetric
flow rates.

Comment: One commenter (2855) said that the calculated span value should
be rounded to the nearest 10 μg/m3 level as has been the practice for
mercury CEMS because of technical limitations associated with the
elemental Mercury gas generators and specific requirements to establish
NIST traceability.

Response: We have modified the definition of span in Section 3.5 PS-12A
to allow for additional flexibility in setting the span and have used
commenter’s recommendations and added a provision in paragraph
63.1350(n) of Subpart LLL to allow for rounding of the span value to the
nearest multiple of 10 µg/m3 of total mercury.

Comment: One commenter (2855) said that the PS-12A requirements at 6.1.1
Data Recorded Scale are misleading, ambiguous and obsolete and should be
replaced by a relevant specification for data recording and an
appropriate definition, (consistent with Span Value) for the high level
value.

Response: Subsection 6.1.1 of PS-12A regarding the data recorder scale
has been revised to respond to comments received. We have simplified the
specification to clarify that the scale must at a minimum include zero