data provided during the comment period by Huntsman Performance in
Conroe, Texas, the second highest risk-driving facility that was
identified at proposal. We agree with the information provided that two
emission units were incorrectly modeled as being subject to MON, when
in fact, they are subject to other standards. As such, in the final
rule these units are modeled at the whole facility-level only. We have
also updated Huntsman Performance's ethylene oxide equipment leak
emissions using the updated emissions data provided by the facility,
consistent with the EPA's standard practice of using the best available
data. The EPA believes that the updated data represents the best
available data because it is more recent (i.e., 2019), is based on
actual emissions measurements, reflects recent physical and operating
changes made to the process since the 2014 NEI emissions were reported,
and conservatively considers results below the detection limit as being
present at the detection limit. After considering all updates made to
the emissions data for Huntsman Performance, the ethylene oxide
emissions before controls are applied are estimated to be approximately
0.03 tpy based on actual and allowable emissions, compared to roughly
0.26 tpy estimated at proposal. The pre-control cancer risks are
estimated to be 20-in-1 million. After ethylene oxide-specific controls
are applied, the estimated post-control cancer risks are also 20-in-1
million. Risks are not reduced with the amendments because (1) storage
tank and process vent controls have no effect since these are not
sources of ethylene oxide emissions at this facility, and (2) equipment
leak Control Option 1 has no effect because this facility already meets
the LDAR requirements this option requires.
    We note that, after the comment period closed, the EPA met with
representatives from Huntsman Performance on March 12, 2020, to

discuss their comments posted to the docket on February 20, 2020, (see
Docket Item No. EPA-HQ-OAR-2018-0746-0073) and ask clarifying
questions. Subsequently, Huntsman Performance provided written
responses to these questions on April 27, 2020. The information
received in their April response further supports their prior assertion
from their February 2020 comments that the two units modeled as being
subject to MON at proposal should instead be modeled only at the whole
facility level and provides additional information related to
wastewater operations at the facility. No changes to facility emissions
or the risk assessment were made as a result of the April 2020
responses, beyond the changes already made based on their comments
submitted in February 2020. Meeting minutes for the referenced
discussion between the EPA and Huntsman Performance, as well as the
written responses Huntsman Performance provided in April 2020 to the
questions asked at this meeting, can be found in the memorandum,
Meeting Record for March 12, 2020, Meeting Between the U.S. EPA and
Representatives of Huntsman Performance, in the docket for this
rulemaking.
    Several commenters provided comments on the EPA's risk
acceptability and ample margin of safety determinations. Those comments
are as follows:
    Comment: Several commenters agreed with the EPA's determination
that the proposed emission standards for this source category would
achieve an acceptable risk level and protect public health with an
ample margin of safety. One commenter in support of the finding stated
that the Benzene NESHAP rulemaking expressly notes that ``[t]he
presumptive level provides a benchmark for judging the acceptability of
maximum individual risk (``MIR''), but does not constitute a rigid line
for making that determination.'' \15\ The commenter stated that, in the
Benzene NESHAP itself, the EPA found MIRs for two categories that
exceeded the standard 1-in-10,000 (100-in-1 million) presumptive
benchmark acceptable (200-in-1 million for Coke By-Product Recovery
Plants and 600-in-1 million for Equipment Leaks) based on uncertainties
in the data that suggested risks were overstated. The commenter
expressed that this precedent means that the EPA has authority to
accept a MIR that is above a 1-in-10 thousand (100-in-1 million)
benchmark, and that scientific uncertainty and the likely overstatement
of risks is a reasonable basis for doing so. The commenter stated that,
therefore, the EPA should make a similar acceptability determination
for the MON RTR rulemaking, given that comparable uncertainties exist
with the information and emissions estimates informing the risk
modeling.
---------------------------------------------------------------------------

    \15\ Commenter provided the following reference: 54 FR 38045,
September 14, 1989.
---------------------------------------------------------------------------

    However, other commenters questioned the justification for
proposing a regulation that would still allow a cancer risk of 200- to
300-in-1 million. One commenter stated that failing to set a health-
protective emission standard that eliminates unacceptable risk because
a risk factor ``could be'' lower is arbitrary and unlawful under CAA
section 112(f)(2). Other commenters said they believed that the 100-in-
1 million lifetime cancer risk cannot be considered safe or
``acceptable,'' and multiple commenters recommended that the EPA ensure
risks from ethylene oxide exposure are below 100-in-1 million. Two
commenters insisted that no level of health risks from HAP can be
presumed safe or ``acceptable'' and that the EPA must reduce risks to
the lowest possible level.
    Other commenters stated that the EPA must require companies to take
steps necessary to prevent all unacceptable health threats and to
provide an ``ample margin of safety to protect public health.''
Commenters further argued that the EPA did not establish an ``ample
margin of safety'' between what the EPA considers to be an acceptable
level of risk and the current emission limits, taking into account the
nature of the chemicals being emitted and the uncertainties in the
EPA's risk assessments, as required under CAA section 112(f)(2). The
commenter argued that the EPA has not shown that it has considered
whether the uncertainties regarding its health risk assessment require
a stronger standard.\16\
---------------------------------------------------------------------------

    \16\ Commenter provided the following reference: NRDC, 824 F.2d
at 1165 (``Congress . . . recognized in section 112 that the
determination of what is `safe' will always be marked by scientific
uncertainty and thus exhorted the Administrator to set emission
standards that will provide an `ample margin' of safety.'').
---------------------------------------------------------------------------

    Response: We agree with commenters that baseline risks for the
Miscellaneous Organic Chemical Manufacturing source category were
unacceptable. However, we disagree with commenters who objected to our
determinations of risk acceptability and ample margin of safety after
implementation of proposed controls. As explained in the preamble to
the proposed rule (84 FR 69182, December 17, 2019), section 112(f)(2)
of the CAA expressly preserves the EPA's use of the two-step process
for developing standards to address residual risk and interpret
``acceptable risk'' and ``ample margin of safety'' as developed in the
Benzene NESHAP (54 FR 38044, September 14, 1989). As explained in the
Benzene NESHAP, ``the first step judgment on acceptability cannot be
reduced to any single factor'' and, thus, ``[t]he Administrator
believes that the acceptability of risk under section 112 is best
judged on the basis of a broad set of health risk measures and
information.'' 54 FR 38046, September 14, 1989. Similarly, with regard
to the ample margin of safety determination, ``the Agency again
considers all of the health risk and other health information
considered in the first step. Beyond that information, additional
factors relating to the appropriate level of control will also be
considered, including cost and economic impacts of controls,
technological feasibility, uncertainties, and any other relevant
factors.'' Id. As also explained in the preamble to the proposed rule
(84 FR 69182, December 17, 2019), the EPA has adopted this approach in
its residual risk determinations, and the Court has upheld the EPA's
interpretation that CAA section 112(f)(2) incorporates the approach
established in the Benzene NESHAP into the statute. See NRDC v. EPA,
529 F.3d 1077, 1083 (D.C. Cir. 2008).
    As discussed previously, we have revised the residual risk
assessment for the final rule to incorporate additional data received
from a CAA section 114 request, as well as updated emissions data for
ethylene oxide received during the public comment period, for the two
facilities with cancer risks greater than 100-in-1 million at the time
of proposal. Revisions to the risk assessment incorporate the best
available data and result in an improved assessment of the risks from
these sources. The revised risk assessment (documented in the Residual
Risk Assessment for the Miscellaneous Organic Chemical Manufacturing
Source Category in Support of the 2020 Risk and Technology Review Final
Rule, which is available in the docket for this rulemaking) shows that,
both before and after application of Control Option 1, seven of the
eight facilities with equipment in ethylene oxide service have
estimated cancer risks below the 100-in-1 million benchmark. After
application of controls for process vents, storage tanks, and equipment
leak Control Option 1 as required by this final rule, the remaining
facility,

Lanxess, has estimated cancer risks of 200-in-1 million.
    Regarding the post-control cancer risks of 200-in-1-million, based
on the revised risk assessment, we note that 100-in-1 million cancer
risk is not a bright line indicating that risk is ``acceptable.'' As
noted by commenters, the EPA has previously accepted MIRs that exceeded
100-in-1 million (i.e., 200-in-1 million in the Benzene NESHAP, 54 FR
38047; 200-in-1 million in the National Emission Standards for Coke
Oven Batteries, 70 FR 19993; and 200-in-1 million in the National
Perchloroethylene Air Emissions Standards for Dry Cleaning Facilities,
71 FR 42731). We note that one commenter claimed that the EPA found a
cancer risk as high as 600-in-1 million acceptable for equipment leaks
in the Benzene NESHAP. This is inaccurate. A 600-in-1 million risk
estimate was discussed in the proposed Benzene NESHAP. However, this
estimate was found to be based on outdated emissions and, in the final
Benzene NESHAP, the EPA noted that while it did not have enough time to
do so, if it had estimated risks based on updated emissions
information, risks were expected to be approximately 100-in-1 million;
this was the basis for the risk acceptability determination (54 FR
38048).
    When considering risk acceptability, the EPA considers all of the
health risk information and the associated uncertainties (e.g.,
uncertainties in emissions, relevant health effects information), as
well as the inherent health protective nature of our risk assessment
methods. For example, many of the dose-response values we use for HAP
are considered plausible upper-bound estimates. For the revised risk
assessment for this source category, the risk driver was ethylene
oxide, and we used the 2016 EPA IRIS URE for ethylene oxide to
calculate increased cancer risk. As noted in the preamble to the
proposed rule, the modeled cancer risks due to emissions of ethylene
oxide are sensitive to the URE applied. For EPA's 2016 ethylene oxide
URE, the memorandum, Sensitivity of Ethylene Oxide Risk Estimates to
Dose-Response Model Selection, which is available in the docket for
this rulemaking (see Docket Item No. EPA-HQ-OAR-2018-0746-0027) and
discussed at length in the proposal preamble, highlighted two key
aspects (i.e., upper-bound estimate and dose-response model)
potentially contributing to the conservative (i.e., health protective)
nature of the final 2016 URE. When taken into account, these two
aspects provide important context for interpreting risks remaining
post-control and indicate that the risks are acceptable.
    Furthermore, we note that few people are exposed to cancer risks
greater than 100-in-1 million, one of the components of health risk
information considered when estimated cancer risks exceed the
presumptive benchmark of 100-in-1 million. We estimate that, of the
89,000,000 people living within 50 km of a source category facility,
107 (0.0001 percent) would be exposed to levels greater than 100-in-1
million due to emissions from the source category. We also note that
the number of people exposed to risks above 100-in-1 million is similar
to other rules where risks above 100-in-1 million were found to be
acceptable (100 people in the Benzene NESHAP, 54 FR 38047; 70 people in
the National Emission Standards for Coke Oven Batteries, 70 FR 19993;
and two people in the National Perchloroethylene Air Emissions
Standards for Dry Cleaning Facilities, 71 FR 42731). We also note that
the cancer incidence (0.09), while higher than the estimated incidence
for Dry Cleaning Facilities (0.002), is comparable to cancer incidence
used in acceptability determinations for the Benzene NESHAP (0.05) and
for Coke Oven Batteries (0.06), despite considerably more facilities in
this source category (194) compared to the others (12, 36, and four
facilities, respectively). Also, the percentage of people exposed to
cancer risks greater than or equal to 1-in-1 million (2 percent of the
population living near a facility) is within the range of other rules
such as the Benzene NESHAP (0.4 percent) and Coke Oven Batteries (12
percent).
    Finally, no other safe controls were identified to further reduce
risks. While equipment leak Control Option 2 for equipment in ethylene
oxide service was considered, based on comments and information
received on the proposed rule, it would not be appropriate to apply to
equipment in ethylene oxide service due to concerns of explosions.
Additional details on comments received and our response for equipment
leak Control Option 2 are provided in section IV.A.3.c of this
preamble.
    Therefore, we disagree with commenters that maintain that the EPA
should ensure that the MIR is substantially below the presumptive
benchmark of 100-in-1 million, or that the EPA must prevent all
unacceptable health risks. Considering all of the relevant health risk
information and factors discussed in the Benzene NESHAP and presented
in the proposal preamble, including the uncertainties discussed in
section III of the proposal preamble (i.e., the emissions dataset,
dispersion modeling, exposure estimates, and dose-response
relationships), the EPA's use of the 2016 IRIS URE for ethylene oxide
(which is developed to be health protective), and concerns raised by
commenters, we conclude that the risks from HAP emissions for the
Miscellaneous Organic Chemical Manufacturing source category, after
application of the requirements that we are adopting, including
application of the ethylene oxide-specific controls, will achieve
acceptable risks for this source category and provide an ample margin
of safety to protect human health (consistent with the Benzene NESHAP
framework).
c. Rule Changes
    Comment: Commenters requested that the EPA reconsider the ethylene
oxide thresholds for storage tanks and process vents identified in the
proposed definition of ``in ethylene oxide service'' because the
thresholds the EPA has proposed for defining process vents and storage
tanks in ethylene oxide service would encompass far more storage tanks
and process vents than the EPA has accounted for in the rulemaking
record. The commenters explained that ethylene oxide is used as a
reactant/intermediate in the production of a wide variety of chemicals.
The commenters added that because these chemicals are made with
ethylene oxide, they may contain small residual amounts of unreacted
ethylene oxide at concentrations much less than 0.1 percent. The
commenters said that even such low amounts of ethylene oxide would
represent ``knowledge that ethylene oxide could be present'' in a
number of process vents and storage tanks far beyond the number of
facilities identified in the rulemaking record. The commenters stated
that if finalized the requirement would likely result in a significant
number of storage tanks being subject to the ethylene oxide
requirements for which the EPA did not estimate the costs of control or
other compliance burden in their impacts analysis. Instead, the
commenters recommended revising the threshold to 0.1 percent by weight
for storage tanks; and noted that setting the concentration threshold
to 0.1 percent by weight as an annual average is consistent with the
``de minimis'' concentration threshold applicable to toxic chemical
release reporting under 40 CFR part 372 and the hazardous chemical
inventory reporting requirements under the Emergency Planning and
Community Right-To-Know Act (EPCRA). The commenters stated that
suppliers are not required to inform receiving companies of the

potential presence of ethylene oxide at levels in the 1 ppmw to 1,000
ppmw (0.1 percent) range; and facilities routinely report under these
programs and that standardizing the definition of ``in ethylene oxide
service'' will allow facilities to continue to use their current
chemical inventory tracking systems to determine whether ethylene oxide
could potentially be present.
    Some commenters also supported revising the threshold to 0.1
percent by weight for process vents. Other commenters supported
regulating process vents where the concentration of ethylene oxide
exceeds 20 ppmv on an annual average basis at the point of discharge to
the atmosphere or the point of entry into a control device. The
commenters noted that setting a 20 ppmv threshold for a vent to be
considered as being in ethylene oxide service would still be
sufficiently protective and would require what are now Group 2
continuous or batch process vents to be controlled. Some commenters
also suggested raising the 5 lb/yr mass threshold and clarifying where
process vent characteristics should be determined (after the last
recovery device but prior to the inlet of any control device that is
present and prior to release to the atmosphere). Several commenters
objected to the phrase in the proposed rule definition of ``in ethylene
oxide service'' as it relates to process vents that, when uncontrolled,
contains a concentration of greater than or equal to 1 ppmv undiluted
ethylene oxide ``anywhere in the process,'' and when combined, the sum
of all these process vents would emit uncontrolled, ``undiluted''
ethylene oxide emissions greater than or equal to 5 lb/yr (2.27 kg/yr).
Commenters questioned the use of the term ``undiluted'' as part of the
mass emission criteria. One commenter also asked for clarification that
some process vents may remain uncontrolled as long as the ethylene
oxide from all process vents (controlled and uncontrolled) is less than
5 lb/yr and also asked the EPA to clarify that the 5 lb/yr is on an
MCPU-by-MCPU basis.
    Response: After consideration of these comments, we agree that
storage tanks containing less than 1,000 ppmw of ethylene oxide (less
than 0.1 percent by weight) should not be considered in ethylene oxide
service. We agree that a 1,000 ppmw threshold that also corresponds to
the chemical inventory reporting requirements under EPCRA and other
supplier notification requirements does reduce the uncertainty for the
regulated community and eliminates the burden of performing analyses to
demonstrate compliance with the rule, while preserving the emissions
reductions associated with continuing to regulate those storage tanks
containing significant amounts of ethylene oxide. The 1,000 ppmw
threshold is also identical to the ``in ethylene oxide service''
criterion for applicability to the ethylene oxide-specific requirements
for equipment leaks, which should also streamline applicability
determinations for process equipment, piping, and storage tanks.
Because of its reactivity, ethylene oxide is stored either as a pure
component or in solution with other material in very low concentrations
(e.g., at impurity levels). We agree with commenters that emissions
from tanks storing impurity levels of ethylene oxide are very low and
do not result in additional risk. We agree that raising this threshold
will reduce the cost of compliance for those facilities that may store
and use a chemical that contains ethylene oxide at very low levels but
for which emissions are negligible. We are also not providing
additional constraints or clarifications on the determination of the
threshold (e.g., providing averaging times) for this revised threshold
as we believe it is no longer needed and note that the EPCRA and
supplier notifications will generally be the basis for applicability
determinations.
    We are not revising the threshold for process vents. First, we do
not support the same threshold for process vents as tanks (1,000 ppmw),
as some commenters suggest, because this value would essentially exempt
all ethylene oxide-containing process vents that we have information on
in the source category and would, therefore, not result in any
reductions in emissions or risks. Other commenters have suggested a
lower threshold of 20 ppmv ethylene oxide. We note that the process
vent ethylene oxide concentrations measured in response to the CAA
section 114 request ranged from 4 ppmv to 120 ppmv, and the
quantifiable detection limit was below 0.5 ppmv. Therefore, we consider
the proposed 1 ppmv threshold reasonable in terms of being measurable
and quantifiable and also appropriate for the vent stream
characteristics we intended to regulate that resulted in risk
reductions. We also are not revising the 5 lb/yr mass threshold for the
process vents, as the commenters did not suggest an alternative value
to the mass-based threshold, although we agree that it was our intent
that it be applied on an MCPU-by-MCPU basis. We also are not finalizing
suggested provisions for sampling sites to remain consistent with the
current MON requirements regarding the determination of uncontrolled
emissions as they apply to both batch and continuous process vents. The
location for determining the concentration and mass threshold is
already provided in the MON, which includes ``the point of discharge to
the atmosphere or the point of entry into a control device'' as the
location of the process vent. For this reason, we are also revising the
definition of ``in ethylene oxide service'' to remove the phrase
``anywhere in the process'' to clarify, as we have adequately specified
the point at which the process vent characteristics should be
evaluated. Finally, we have also removed the phrase ``undiluted'' from
the mass-based criteria in the definition of in ethylene oxide service
as we agree it does not apply to a mass-based threshold.
    Comment: One commenter contended that the preamble discussion and
proposed language in the rule is unclear as to whether the existing
0.005 weight percent total organic HAP cut-off in 40 CFR 63.107(d) of
the continuous process vent definition (as referenced by the MON's
continuous process vent definition in 40 CFR 63.2550) and the 50 ppmv
HAP and 200 lb/yr uncontrolled HAP emission cut-offs in the batch
process vent definition in 40 CFR 63.2550 still apply relative to the
definition of ``in ethylene oxide service'' for process vents. The
commenter requested the EPA confirm that since there is not specific
language in the rule eliminating these exemptions for continuous and
batch process vents in ethylene oxide service, we assume that the
exemptions could still potentially apply. The commenter explained their
interpretation of the proposed rule is that before the ethylene oxide
requirements for process vents apply, the gas stream or emission stream
must first meet the ``continuous process vent'' or ``batch process
vent'' definition in 40 CFR 63.2550.
    Response: The commenter is incorrect in their interpretation. In
the proposed and final rule, process vents in ethylene oxide service
are defined separately, and the existing 0.005 weight percent total
organic HAP cut-off in 40 CFR 63.107(d) of the continuous process vent
definition (as referenced by the MON's continuous process vent
definition in 40 CFR 63.2550) and the 50 ppmv HAP and 200 lb/yr
uncontrolled HAP emission cut-offs in the batch process vent definition
in 40 CFR 63.2550 do not apply to the definition of ``in ethylene oxide
service'' for process vents. Nevertheless, we are clarifying the
definitions of ``batch process vent'' and ``continuous process vent''
in the final rule to make clearer that these cut-offs

do not apply to process vents in ethylene oxide service. We note that
process vents could contain HAP other than ethylene oxide, and,
therefore, it is possible that a process vent could be both in ethylene
oxide service and also considered a Group 1 or Group 2 process vent.
Owners or operators should consider all definitions that may apply as
well as all control requirements when evaluating applicability and
compliance obligations.
    Comment: In response to our request for comment on the co-proposed
Control Options for equipment leaks in ethylene oxide service, some
commenters supported requiring equipment leak Control Option 2 for
equipment in ethylene oxide service because health risks are
unacceptable. One commenter contended that the EPA allowing the
residual risks from these two highest risk facilities to be above the
EPA's acceptable cancer risk level of 100-in-a-million, after leak
controls, would set an unsatisfactory precedent for future RTRs. The
commenter suggested that the EPA consider this an iterative process
with regards to leak controls and pursue the goal of further reducing
risks below the 100-in-a-million cancer risk level. Other commenters
requested that the EPA apply Control Option 2 to all facilities in
ethylene oxide service.
    Some commenters did not support either equipment leak Control
Option 1 or 2 for equipment in ethylene oxide service, but if the EPA
were to finalize one of the options, they would prefer Control Option 1
with modifications. One commenter contended that the risks from the two
facilities are substantially overstated so neither option is necessary,
but Control Option 1 would be sufficient to reduce risks. Some
commenters opposed the use of leakless valves in Control Option 2 for
ethylene oxide service because of safety concerns. The commenters
contended that leakless valves are more likely to trap ethylene oxide
in valve cavities, and stagnant ethylene oxide polymerizes, creating
heat that can cause explosions. The commenters added that the EPA
inadequately addressed these safety issues and cited no actual
experience with such designs in ethylene oxide service.
    Commenters contended that the EPA's cost analysis for leakless
valves significantly underestimates costs. One commenter added that the
EPA's estimate does not include costs for engineering analysis or
installation of valves, which are typically 2 to 3 times the equipment
cost. One commenter added that engineering costs could be significant
as bellows valves are heavier than existing equipment and evaluation
for additional piping supports would be required, and the larger size
of these valves would likely require reconfiguration and refabricating
process piping for required clearance. The commenter continued that
replacing existing valves with leakless valves will require an extended
process shutdown to clear and purge the process and then replace the
valves and that the EPA provides no information on the time to do this
or the cost to affected companies of lost production.
    Response: We agree that Control Option 1 for equipment in ethylene
oxide service would sufficiently reduce risks, and we are finalizing
Control Option 1 in the final rule, except as discussed later in this
section of the preamble, in lieu of prohibiting PRDs in ethylene oxide
service from releasing directly to the atmosphere, we are clarifying in
the final rule that these PRDs must comply with the pressure release
management work practice standards proposed at 40 CFR 63.2480(e) and
(f), and any release event from PRDs in ethylene oxide service is a
deviation of the standard. During the comment period, commenters
provided updated information on their facilities, including specific
information regarding sources in their facility that are subject to the
MON, emissions from each source, controls in use, and operating
information. We updated the risk assessment for the two facilities
that, at proposal, had a MIR greater than 100-in-1 million. As
discussed previously in this section of the preamble, after application
of the ethylene oxide-specific controls for process vents, storage
tanks, and equipment leaks from co-proposed Control Option 1, we find
that the revised risks are acceptable and that the final standards will
achieve an ample margin of safety to protect human health.
    We reviewed whether Control Option 2 would provide additional
emission reductions but determined that Control Option 2 was not
appropriate to apply to equipment in ethylene oxide service based on
comments and information received on the proposed rule. First, we
reviewed the comments and information provided by the commenters and
agree that there are potential safety concerns with the use of leakless
valves for ethylene oxide service. We agree that many leakless valve
designs, such as bellows seal valves, have extended packing cylinders,
which have more volume and areas where ethylene oxide can be trapped
and polymerize, resulting in the valve stem to stop working and the
potential for explosions. No information was provided by commenters or
identified from our review of available data for other sources that
indicated that leakless valves are being or have been used for ethylene
oxide service. Because of the safety concerns and no evidence that
leakless valves are successfully being used for ethylene oxide service
at this time, the final rule does not require their use. The current
MON rule already requires gas and light liquid valves to be monitored
at a leak definition of 500 ppm, and we did not propose different leak
definitions for valves as part of Control Option 1. Secondly, although
leakless pumps have been used instead of light liquid pumps for
processes in ethylene oxide service, new data obtained during the
comment period from Lanxess indicated that this facility does not have
pumps in light liquid service that would be subject to the leakless
pump requirement. Therefore, a requirement to install leakless pumps
for light liquid pumps would not result in any changes to the estimated
risks. As a result of the comments and information received and the
results of the revised Risk Assessment, we are finalizing Control
Option 1 for equipment leaks.
    Comment: Several commenters disagreed with the operating parameters
we proposed to require be continuously monitored for scrubbers used to
control emissions from process vents and storage tanks in ethylene
oxide service. Several commenters noted that column pressure drop is a
reliable measurement for scrubbers that can identify flooding
conditions, but may not identify channeling conditions, when scrubber
efficiency is depleted as gas flow ``channels'' around the liquid
blowdown. One commenter contended that background documents in the
rulemaking docket do not have any justification for requiring a maximum
pressure drop as an operating parameter limit, but speculated that the
EPA had proposed a maximum to address a decrease in removal efficiency
due to plugging or fouling of the packed bed. Commenters stated that
engineering design should be allowed for establishing the critical
process parameters for monitoring. One commenter stated that setting
the maximum operating limit as the average measured during the
performance test is impracticable because the pressure drop during the
performance test will be measured when the packing material is
cleanest. The commenter added that over time the packing material may
foul and pressure drop may increase, but not to an extent which causes
decreased performance. The commenter continued that the pressure drop
will increase as

either gas flow or liquid flow through the scrubber increases. The
commenter added that the requirement to operate below a maximum
pressure drop conflicts with the requirement to operate above a minimum
liquid to gas ratio. The commenter concluded that if the EPA retains
the requirement to operate below a maximum pressure drop in the final
rule, facilities should be allowed to set the maximum pressure drop
based on manufacturer's recommendations or an engineering evaluation,
not the average pressure drop measured during the most recent
performance test.
    Additionally, several commenters contended that monitoring liquid
feed pressure is redundant with monitoring liquid-to-gas ratio and
should not be included in the final rule. Commenters contend that
monitoring feed pressure is an indirect method to assess scrubber
liquid supply, while monitoring the scrubber liquid-to-gas ratio
requires direct measurement of the liquid inlet flow rate.
    Response: The EPA is maintaining the requirement to monitor
pressure drop across the scrubber and liquid feed pressure to the
scrubber in the final rule. As commenters note, pressure drop across a
scrubber is a valuable piece of information on the operation of the
scrubber. It can indicate issues with flooding, plugging, channeling,
and fouling of the control device. However, we do agree with commenters
that it may be challenging to establish the maximum pressure drop at
the same time as the minimum liquid-to-gas ratio is established. The
liquid-to-gas ratio is the primary parameter of concern in a typical
wet scrubber system because it ensures that there is enough liquid
available to clean the gas flowing through the system. Therefore, while
we are maintaining the requirement to monitor pressure drop across the
scrubber, in the final rule, we are allowing a pressure drop range to
be established based on the manufacturer's recommendation or
engineering analysis.
    We disagree with commenters that the liquid feed pressure is
redundant to the liquid flow rate. While the liquid feed pressure
should indicate that liquid is flowing in the system, liquid feed
pressure is also important for determining that the liquid is being
appropriately dispersed within the scrubbing system, which is not
something that the liquid flow rate alone can indicate. We think that
ensuring the dispersion of the liquid stream is especially critical in
ethylene oxide control, in order to ensure that the ethylene oxide
adsorbs into the liquid stream so that it can undergo the conversion
reaction. However, we are also aware that increases in liquid feed
pressure can also be caused by blockages in the nozzle, and as such,
the minimum pressure could be met without the nozzle properly atomizing
the liquid stream. While we continue to believe that this is an
important operating parameter for ethylene oxide scrubbers, we believe
that this parameter does not necessarily need to be based on the
performance test, and that the manufacturer should be able to provide
information on what pressure in the nozzle will ensure proper operation
of the nozzle. Therefore, while we are maintaining the requirement to
monitor liquid feed pressure, in the final rule, we are allowing a
liquid feed pressure range to be established based on the
manufacturer's recommendation or engineering analysis.
    Comment: Commenters requested the EPA revise the requirement to
demonstrate compliance with the operating parameter limits for
scrubbers used to control emissions from process vents and storage
tanks in ethylene oxide service from an instantaneous basis to a daily
average basis. Commenters explained that a daily average is consistent
with the currently applicable requirements of 40 CFR part 63, subpart
SS. One commenter stated that an instantaneous compliance demonstration
with a measured value will likely lead to operators unnecessarily
adjusting operating parameters in response to brief excursions due to
changing process conditions. Another commenter explained that automated
controls which maintain flow rate, temperature, pH, and other variables
are typically ``feedback'' based or ``closed loop control,'' and even
the best tuned controllers have some amount of response time. The
commenter added that instantaneous compliance demonstrations will
invariably lead to operators manually attempting to adjust control
system variables which will likely lead to overshoot and potentially
decreased control efficiency and concluded that the EPA must allow some
amount of averaging to account for the inherent response time of
control systems and deadtime of process response.
    One commenter added that a daily average aligns better with the
process of establishing the parameter operating limits during a
performance test, which typically consists of three 1-hour runs.
Another commenter contended that the rule should at least allow for 3-
hour averages and stated this would be more consistent with other 40
CFR part 63 MACT rules (such as the Hazardous Organic NESHAP (HON)) and
with the process of establishing the parameter operating limits during
a performance test (i.e., testing typically consists of three 1-hour
runs).
    Response: The EPA is changing the continuous compliance
requirements for the operating parameters, such that compliance with
the operating parameter limits is determined on an hourly average basis
instead of an instantaneous basis. We agree that instantaneous limits
on operating parameters may cause some unintended consequences with
control loops and that some degree of averaging is warranted.
    While we acknowledge that compliance with other operating
parameters for MON sources is based on a daily average, per the
requirements in 40 CFR part 63, subpart SS, we do not agree that this
averaging basis is appropriate for operating parameters on control
devices used for ethylene oxide process vents and storage tanks.
Control devices used for ethylene oxide emissions operate differently
than other control devices and are required to achieve better control
than other control devices. In order to achieve 99.9-percent control
from these devices, it is important to ensure that the ethylene oxide
control is continuously occurring. These control devices tend to be
used on batch processes, where the ethylene oxide emissions may
fluctuate greatly with different steps in the process. Longer averaging
times could mask issues with achieving the required control efficiency
during brief periods of higher ethylene oxide loading to the control
device (e.g., during tank loading events). In order to ensure
continuous compliance with the control efficiency requirement, we are
requiring compliance with the operating parameters be based on a 1-hour
average in the final rule.
    Comment: Commenters interpreted the proposed language at 40 CFR
63.2493(d)(4) to mean that (1) the discharge piping on PRDs in ethylene
oxide service cannot be routed to the atmosphere and (2) any release
event is an automatic violation of the MON rule. Commenters contended
that the proposed rule seems to require that the PRD be directed to
some form of emission control equipment, such as a flare. Commenters
opposed requiring all PRDs in ethylene oxide service vent to a control
device. Commenters contended the requirement would create safety
concerns including the hydraulic limitations of the flare or other
control device, backpressure limitations on the PRDs, and the
incompatibility of

chemicals in vent streams in downstream controls. Commenters noted that
ethylene oxide is a compound which contains oxygen and is highly
reactive, extremely flammable, and can violently decompose with a
significant release of heat in the absence of air, and ethylene oxide
also tends to polymerize, which could result in plugging of the closed
vent system or control device. The commenter concluded that existing
closed vent systems and control devices require careful evaluation to
determine if emissions from such events can be safely controlled.
    A commenter stated that because they are of limited duration and
number, such events would not lower cancer risks, which are based on
long term exposures. The commenter pointed out that the EPA makes no
mention of PRDs when discussing ethylene oxide risk drivers.
    The commenter stated that the same technical limitations that apply
to PRDs in general also apply to those in ethylene oxide service.
Commenters supported requiring PRDs in ethylene oxide service to comply
with the proposed PRD work practice at 40 CFR 63.2480(e). A commenter
stated that other existing EPA regulations already require the owner/
operator to minimize or eliminate the potential for such releases, such
as the EPA regulations at 40 CFR part 302 and 40 CFR part 355 have a
10-pound reportable quantity for ethylene oxide if a release from any
equipment occurs. The commenter added that if a release greater than 10
pounds occurs, then the owner/operator must report it to the National
Response Center, the State Emergency Response Commission (typically a
state environmental agency), and the Local Emergency Planning Committee
when the owner/operator has knowledge of such a release.
    A commenter added that a MON MCPU may not have a flare or may be
located in an area of a larger site where there is not adequate land
space for a flare.
    A commenter added that if a new flare or other emission control
equipment is required, design and installation of a flare system or
other emission control equipment within 2 years of the final date of
this rule is not practical. Commenters stated that typically, it takes
3 years to properly engineer the project, obtain capital authorization
and funding, procure the equipment, and construct and start-up the
equipment. Commenters noted that the EPA has not provided any
background information in the preamble or in the rule docket that
addresses costs or the feasibility of installing large flares or other
air emission control equipment within the 2-year compliance period.
    Response: We are revising the proposed requirement that PRDs in
ethylene oxide service must not vent directly to the atmosphere. In
lieu of prohibiting PRDs in ethylene oxide service from releasing
directly to the atmosphere, we are clarifying in the final rule that
these PRDs must comply with the pressure release management work
practice standards proposed at 40 CFR 63.2480(e) and (f). We are also
clarifying that any release event from PRDs in ethylene oxide service
is a deviation of the standard. We are finalizing these requirements
pursuant to CAA section 112(f)(2), on the basis for risks being
unacceptable. Where we find risks are unacceptable, the EPA must
determine the emissions standards necessary to reduce risk to an
acceptable level. Because emissions of ethylene oxide from this source
category result in unacceptable risks, we proposed and are finalizing
requirements that would reduce risks to an acceptable level, including
provisions that would make all PRD releases of ethylene oxide directly
to the atmosphere a violation of the standard. We believe that there
are very few PRDs in ethylene oxide service that vent to the
atmosphere. Note that the proposed rule does not specify that PRDs must
be controlled with flares; in fact, the detailed information we have
indicate that most of these emission sources are controlled using
scrubbers. Further, we reviewed emission release reports from the
National Response Center for the 5-year period beginning in 2015
through 2019 and identified only one reported release of ethylene oxide
from an ethylene oxide production facility which is not part of the
Miscellaneous Organic Chemical Manufacturing source category. Also,
during the public comment period, commenters did not submit any
specific information on the existence of, or lack of, ethylene oxide
releases from PRDs in the Miscellaneous Organic Chemical Manufacturing
source category. Therefore, we maintain that controlling PRDs in
ethylene oxide service is possible, and in fact represents the majority
of industry's practice in this source category.
4. What is the rationale for our final approach and final decisions for
the risk review?
    As noted in our proposal, the EPA sets standards under CAA section
112(f)(2) using ``a two-step standard-setting approach, with an
analytical first step to determine an `acceptable risk' that considers
all health information, including risk estimation uncertainty, and
includes a presumptive benchmark on MIR of approximately 1-in-10
thousand'' (84 FR 54278, October 9, 2019; see also 54 FR 38045,
September 9, 1989). We weigh all health risk factors in our risk
acceptability determination, including the cancer MIR, cancer
incidence, the maximum cancer TOSHI, the maximum acute noncancer HQ,
the extent of noncancer risks, the distribution of cancer and noncancer
risks in the exposed population, multipathway risks, and the risk
estimation uncertainties.
    Since proposal, our determinations regarding risk acceptability,
ample margin of safety, or adverse environmental effects have not
changed. However, after proposal, commenters provided updated
information on their facilities, including specific information
regarding sources in their facility that are subject to the MON,
emissions from each emissions source, controls in use, and operating
information. We updated the risk assessment for the two facilities
that, at proposal, had a MIR greater than 100-in-1 million. The revised
risk assessment (see document, Residual Risk Assessment for the
Miscellaneous Organic Chemical Manufacturing Source Category in Support
of the 2020 Risk and Technology Review Final Rule, which is available
in the docket for this rulemaking) shows that, after application of
controls finalized in this rulemaking, the MIR for the source category
is 200-in-1 million.
    As discussed in section IV.A.3.b of this preamble, the 100-in-1
million cancer risk is not a bright line indicating that risk is
``acceptable''; rather, we consider this health metric in conjunction
with a variety of health factors and their associated uncertainties to
determine whether the risk is acceptable. We considered the number of
people exposed to risks greater than 100-in-1 million (107 people, or
0.0001 percent of the population living near a facility in the source
category), the cancer incidence (0.09), and the number of people
exposed to cancer risk levels greater than 1-in-1 million (1,400,000
people, or 2 percent of the population living near a facility in the
source category), which are consistent with other rules where risks
above 100-in-1 million were found to be acceptable (see section
IV.A.3.b of this preamble for more details). We also considered that no
safe controls were identified to further reduce risks. Therefore,
considering the uncertainties inherent in all risk assessments as
discussed in the preamble to the proposed rule (i.e., the emissions
dataset, dispersion modeling, exposure

estimates, and dose-response relationships) (see 84 FR 69219) and the
EPA's use of the 2016 IRIS URE for ethylene oxide (which is developed
to be health protective), and additional considerations discussed here
and in more detail in section IV.A.3.b of this preamble, after
application of the ethylene oxide-specific controls for process vents,
storage tanks, and equipment leaks from co-proposed Control Option 1,
we find that the risks are acceptable and that the final standards will
achieve an ample margin of safety to protect human health.

B. Technology Review for the Miscellaneous Organic Chemical
Manufacturing Source Category

1. What did we propose pursuant to CAA section 112(d)(6) for the
Miscellaneous Organic Chemical Manufacturing source category?
    Based on our technology review for the Miscellaneous Organic
Chemical Manufacturing source category, we proposed under CAA section
112(d)(6) changes to the standards for equipment leaks and heat
exchange systems, and we proposed no changed under CAA section
112(d)(6) for process vents, storage tanks, transfer racks, and
wastewater streams. We provide a summary of our findings, as proposed,
in this section.
a. Equipment Leaks
    In our technology review for the Miscellaneous Organic Chemical
Manufacturing source category, we identified developments in LDAR
practices and processes for equipment leaks (excluding equipment in
ethylene service). We identified four options for lowering the leak
definition for certain process and component types and requiring
periodic monitoring, and the options varied by leak definition level,
process type (i.e., batch process v. continuous process), component
type, and monitoring frequency. Refer to section IV.D.1 of the proposal
preamble (84 FR 69182, December 17, 2019) for a summary of the four
options. Based on our evaluation of the costs and emission reductions
of each of the four options, we determined that the most cost-effective
strategy was to lower the leak definition for pumps in light liquid
service (in an MCPU that has no continuous process vents and is part of
an existing source) from 10,000 ppmv to 1,000 ppmv with monthly
monitoring and initial monitoring within 30 days after initial startup
of the equipment, which we proposed pursuant to CAA section 112(d)(6)
to further reduce HAP emissions from equipment leaks for MON equipment
not in ethylene service.
    For a detailed discussion of the EPA's findings, refer to the
memorandum, Clean Air Act Section 112(d)(6) Technology Review for
Equipment Leaks Located in the Miscellaneous Organic Chemical
Manufacturing Source Category, which is available in the docket for
this rulemaking (see Docket Item No. EPA-HQ-OAR-2018-0746-0003).
b. Heat Exchange Systems
    In our technology review for the Miscellaneous Organic Chemical
Manufacturing source category, we identified one development in
practices and processes for heat exchange systems, the use of the
Modified El Paso Method \17\ for monitoring for leaks from heat
exchange systems. We determined that this method is more effective in
identifying leaks and measures a larger number of compounds than the
methods previously required in the MON. After evaluating state and
Federal regulations requiring the Modified El Paso Method, as well as
emission data collected for the Ethylene Production RTR (refer to
section II.D of the proposal preamble (84 FR 69182, December 17, 2019)
and the Ethylene Production RTR rulemaking docket, Docket ID No. EPA-
HQ-OAR-2017-0357), we proposed pursuant to CAA section 112(d)(6) to
require use of the Modified El Paso Method with a leak definition of
6.2 ppmv of total strippable hydrocarbon concentration (as methane) in
the stripping gas to further reduce HAP emissions from both new and
existing heat exchange systems, as well as to disallow delay of repair
of leaks if the measured concentration meets or exceeds 62 ppmv. Based
on an evaluation of incremental HAP cost effectiveness to increase the
monitoring frequency, we proposed no changes to the monitoring
frequency previously required under the MON for monitoring for leaks
from heat exchange systems, which continues to be monthly monitoring in
the first 6 months following startup of a source and quarterly
monitoring thereafter. We also proposed to require re-monitoring at the
monitoring location where a leak is identified to ensure that any leaks
found are fixed. Further, we proposed that none of these proposed
requirements for heat exchange systems apply to heat exchange systems
that have a maximum cooling water flow rate of 10 gpm or less. Refer to
section IV.D.2 of the proposal preamble (84 FR 69182, December 17,
2019) for a summary of our rationale for selecting the proposed leak
method, leak definition, and limitation on delay of repairs, as well as
our rationale for retaining the previous monitoring schedule.
---------------------------------------------------------------------------

    \17\ The Modified El Paso Method uses a dynamic or flow-through
system for air stripping a sample of the water and analyzing the
resultant off-gases for volatile organic compounds (VOC) using a
common flame ionization detector (FID) analyzer. The method is
described in detail in Appendix P of the TCEQ's Sampling Procedures
Manual: The Air Stripping Method (Modified El Paso Method) for
Determination of Volatile Organic Compound (VOC) Emissions from
Water Sources. Appendix P is included in the docket for this
rulemaking (see Docket Item No. EPA-HQ-OAR-2018-0746-0024).
---------------------------------------------------------------------------

    For a detailed discussion of the EPA's findings, refer to the
memorandum, Clean Air Act Section 112(d)(6) Technology Review for Heat
Exchange Systems Located in the Miscellaneous Organic Chemical
Manufacturing Source Category, which is available in the docket for
this rulemaking (see Docket Item No. EPA-HQ-OAR-2018-0746-0007).
c. Process Vents, Storage Tanks, Transfer Racks, and Wastewater Streams
    In our technology review of process vents, storage tanks, transfer
racks, and wastewater streams for the Miscellaneous Organic Chemical
Manufacturing source category, we identified no cost-effective
developments in practices, processes, or control technologies for these
emissions sources that would achieve a greater HAP emission reduction
beyond the emission reduction already required by MON. Therefore, we
proposed no revisions to the MON pursuant to CAA section 112(d)(6) for
process vents, storage tanks, transfer racks, and wastewater streams.
For a detailed discussion of the EPA's findings, refer to the
memorandum, Clean Air Act Section 112(d)(6) Technology Review for
Process Vents, Wastewater, Transfer Racks, and Storage Tanks Located in
the Miscellaneous Organic Chemical Manufacturing Source Category, which
is available in the docket for this rulemaking (see Docket Item No.
EPA-HQ-OAR-2018-0746-0008). This analysis is also described in detail
in section IV.B of the preamble to the proposal preamble (84 FR 69182,
December 17, 2019).
2. How did the technology review change for the Miscellaneous Organic
Chemical Manufacturing source category?
    We are finalizing the results of the technology review for the
Miscellaneous Organic Chemical Manufacturing source category as
proposed (84 FR 69182, December 17, 2019), with the following
exceptions.

    For equipment leaks not in ethylene oxide service, based on
comments received on the proposal, we are clarifying in the final rule
that the initial monitoring of equipment is only required if the new or
replaced equipment is subject to Table 6 to 40 CFR part 63, subpart
FFFF, and is also subject to periodic monitoring with EPA Method 21 of
appendix A-7 to 40 CFR part 60 and that the initial monitoring does not
apply to equipment classified as unsafe-to-monitor or difficult-to-
monitor equipment.
    For heat exchange systems, we are taking final action on the
proposed requirement to monitor leaks from heat exchange systems using
the Modified El Paso Method consistent with the December 17, 2019, RTR
proposal. However, based on comments received on the proposed
rulemaking, we are also making some technical clarifications to allow
compliance with the Modified El Paso Method using an alternative mass-
based leak action level of total strippable hydrocarbon equal to or
greater than 0.18 kilograms per hour (instead of the proposed
concentration-based leak action level) for small heat exchange systems
with a recirculation rate of 10,000 gpm or less.
3. What key comments did we receive on the technology review, and what
are our responses?
    This section provides comment and responses for the key comments
received regarding our proposed revisions for equipment leaks; heat
exchange systems; and process vents, transfer racks, storage tanks, and
wastewater streams. Other comment summaries and the EPA's responses for
additional issues raised regarding these activities, as well as issues
raised regarding our proposed revisions, can be found in the document
Summary of Public Comments and Responses for the Risk and Technology
Review for Miscellaneous Organic Chemical Manufacturing, available in
the docket for this rulemaking.
    For equipment leaks not in ethylene oxide service, we received
comments on potential issues and problems associated with the proposed
requirements for pumps in light liquid service (in an MCPU that has no
continuous process vents and is part of an existing source) to meet a
leak definition of 1,000 ppmv and requiring facilities to initially
monitor for equipment leaks within 30 days after initial startup of the
equipment. See section IV.B.3.a of this preamble for further details.
    For heat exchange systems, the EPA received additional information
from commenters on costs necessary for control of these sources as well
as comments on a number of technical clarifications and allowance of
compliance with an alternative mass-based leak action level should the
EPA finalize the requirements for heat exchange systems. See section
IV.B.3.b of this preamble for further details.
    For process vents, transfer racks, equipment leaks, and wastewater
streams, the comments were supportive of the determination that no
cost-effective developments from the technology review were found. See
section IV.B.3.c of this preamble for further details.
a. Equipment Leaks
    Comment: A commenter requested the EPA not finalize the lowering of
the leak definition for batch light liquid pumps from 10,000 ppm to
1,000 ppm because it inadvertently removes existing exemptions for all
pumps. The commenter contended that instead of simply nullifying 40 CFR
63.2480(b)(5), which sets the leak definition to 10,000 ppm for batch
pumps, the language in 40 CFR 63.2480(b)(6) appears to apply to all
pumps, not just those for batch processes. The commenter added that as
a result, the leak definitions for pumps in specific service (i.e.,
polymerizing polymers and food/medical service) and the 2,000 ppm
repair threshold in subparts H and UU will be overwritten. The
commenter contended that the EPA has provided no analysis or
justification for such a change. The commenter added that if the
revision is intended to apply only to batch pumps, this results in
continuation of different standards for batch and continuous pumps. The
commenter suggested that to clarify the requirements and streamline
compliance the EPA should apply the same standards to all pumps in
light liquid service.
    Response: We agree with the commenter that the proposed requirement
of a leak definition of 1,000 ppm for light liquid pumps at both batch
and continuous processes directly in the MON rule inadvertently
overrode facilities complying with the equipment leak requirements in
subparts H and UU as the MON references both rules for leak
definitions. The intention of the proposed requirement was to make the
light liquid pump requirements for batch processes the same as the
existing requirements for continuous processes and streamline the
requirements by codifying them in the MON rule. The intention was not
to remove the existing exemptions or repair requirements. We have
revised the final rule to require light liquid pumps in batch and
continuous processes that are not in ethylene oxide service to comply
with the requirements in 40 CFR part 63, subpart H or UU, or 40 CFR
part 65, subpart F, which is a leak definition of 1,000 ppmv, by
removing the exemption for light liquid pump monitoring in 40 CFR
63.2480(b)(5) and 40 CFR 63.2480(c)(5) and removing the proposed leak
definition in the MON.
    Comment: Some commenters requested the EPA not finalize the
proposed requirements at 40 CFR 63.2480(b)(7) and (c)(11) that specify
initially monitoring leaks 30 days after initial startup of the
equipment. The commenters contended this requirement adds a significant
burden that the EPA did not consider, nor has the EPA provided any
justification as to whether this requirement would provide any
emissions reductions.
    One commenter contended that 40 CFR 63.2480(b)(7) and (c)(11)
specify that ``each piece of equipment'' must be monitored initially
for leaks within 30 days after initial startup of the equipment and
that the term ``Equipment'' is already defined in the MON at 40 CFR
63.2550. The commenter contended that this could be interpreted to
require this 30-day monitoring requirement to apply to every single
piece of equipment within the scope of the ``Equipment'' definition
regardless of monitoring exemptions or the fact that some component
types do not require routine monitoring. The commenter stated that
equipment excluded from monitoring under the MON (e.g., equipment
routed to control, fuel gas or a process; equipment in heavy liquid
service; instrumentation systems; open-ended lines and valves; and
connectors) should be excluded from this new requirement. The commenter
also contended that pumps and agitators are already checked weekly and
monthly and thus should be excluded from this new requirement and that,
for clarity and simplicity, it would be simplest to limit these new
requirements to gas and light liquid valves. The commenter also
requested that the EPA clarify that ``replacement'' does not include
reinstalling an item of equipment that has been removed for inspection
or repair. The commenter provided an example of PRDs that are typically
removed for bench testing and then replaced. The commenter continued
that since the bench test confirms the PRD does not open until the set
pressure is reached, there is no need to test it outside of the normal
periodic schedule. The commenter also identified repaired equipment as
already being required to re-monitor within 15 days and thus should
also be

excluded from the 30-day requirement. Another commenter recommended
that this initial monitoring requirement should also apply only to
equipment that is subject to periodic monitoring with EPA Method 21 of
appendix A-7 to 40 CFR part 60.
    Some commenters stated that the proposed requirement would require
significant training of maintenance and operations staff and
development and implementation of tracking systems to ensure no
equipment component is replaced or added without conducting the 30-day
monitoring. Commenters stated that this will place a significant burden
and cost to an MCPU and that the EPA did not consider the burden
associated with tagging, updating the LDAR program, and managing the
component-by-component leak schedule this proposed requirement will
impose, especially for equipment that is added or replaced frequently
within an MCPU.
    Commenters contended some MON processes restrict additional
personnel, such as LDAR personnel, in their operating areas for safety
reasons; and some equipment is never safe to monitor while in service.
The commenters added that safety restrictions may be in place for a
period of time, which then reduces the number of days in the 30-day
period for the initial monitoring. One commenter concluded that a 30-
day period is not long enough to organize the initial monitoring for
these components or even components in less restricted areas.
    One commenter stated that the compliance date section in 40 CFR
63.2445(g)(3) does not mention when the 30-day requirement in 40 CFR
63.2480(b)(7) and (c)(11) becomes effective, so it appears that the
language might be effective the date the final rule is published. The
commenter recommended that the requirement in 40 CFR 63.2480(b)(7) and
(c)(11) to initially monitor each piece of equipment for leaks within
30 days after initial startup of equipment should be amended to
reference the language in 40 CFR 63.162(g) of HON subpart H and 40 CFR
65.3(d) of the Consolidated Federal Air Rule to determine the first
monitoring period depending on how many days are left in the week,
weeks remaining in the month, months remaining in the quarter, and
quarters remaining in the year. Two commenters stated that if the EPA
promulgates these requirements, the proposed applicability date should
be changed from December 17, 2019, to 3 years after the date of
publication of the final rule. One commenter stated that if the EPA
promulgates these requirements, more time is needed, such as 3 months
from the time components initially are in organic HAP service. The
commenter contended that the EPA cannot impose requirements
retroactively and that time is needed to develop the infrastructure to
address this requirement.
    One commenter contended that this change is presented as a
``clarification'' in the preamble discussion, but no such requirement
was part of the negotiated rulemaking \18\ that established the part 63
LDAR program, nor is such a requirement suggested in the existing
language as shown by the EPA's need to propose new language to this
rule to impose this requirement. The commenter claimed that this is a
new requirement, not a clarification. The commenter added that as such,
it must be justified under CAA section 112(d)(6). Commenters contended
that nothing is presented in the MON record to show there is a problem
with current (generally quarterly) periodic monitoring as specified in
the existing 40 CFR part 63, subpart H or UU, or 40 CFR part 65,
subpart F. One commenter said that the EPA appears to have recognized
the challenges to implementing initial monitoring requirements 30 days
after initial startup of equipment and cited the HON as it requires
only new sources to initially monitor only valves in gas/vapor service
and light liquid service quarterly. The commenter presumed that this
provision was added to the HON for new sources because of the results
of the MACT determination under the HON. The commenter concluded that
the EPA had not conducted a MACT determination for this proposed
provision under the MON, nor has it completed a cost-benefit or risk
analysis necessary to add this requirement under this technology or
risk review.
---------------------------------------------------------------------------

    \18\ Commenter provided the following reference: 57 FR 62617-
62619 (December 31, 1992).
---------------------------------------------------------------------------

    One commenter contended that by claiming this new requirement is a
``clarification'' it could mistakenly be construed as applying to all
part 63 and 65 LDAR programs. The commenter stated that proposing this
change in the MON RTR rulemaking does not provide adequate notice and
an opportunity for comment to most of the sources potentially impacted.
The commenter recommended that the EPA should clarify that this is a
new requirement and is only applicable to sources subject to the MON
and that it is not a clarification of existing requirements in 40 CFR
part 63, subpart H or UU, or in 40 CFR part 65, subpart F.
    Response: The EPA did not intend for the requirement to initially
monitor components 30 days after initial startup of the equipment to
apply as broadly as the commenters have interpreted. We intended for
the requirement to only apply to new or replaced equipment regulated
under the MON that must be periodically monitored with EPA Method 21.
Similar requirements were promulgated in 40 CFR part 60, subparts VV
and VVa. We agree with the commenters that the requirement to monitor
equipment within 30 days of startup is not appropriate for equipment
that are classified as unsafe-to-monitor or difficult-to-monitor due to
their locations and safety concerns.
    In the final rule, we are clarifying at 40 CFR 63.2480(b)(7) and
(c)(11) that monitoring leaks within 30 days after initial startup
applies only to new or replaced equipment that is subject to Table 6 to
40 CFR part 63, subpart FFFF, and is also subject to periodic
monitoring with the EPA Method 21 of appendix A-7 to 40 CFR part 60. We
are also clarifying that the requirement does not apply to equipment
classified as unsafe-to-monitor or difficult-to-monitor equipment.
Following the initial monitoring, the equipment may follow the periodic
monitoring program applicable to each affected process unit. We are not
changing the compliance date for this requirement in the final rule,
and the requirement will be effective the date the final rule is
published in the Federal Register. This requirement only applies to new
and replaced components, and as such, we expect facilities are able to
appropriately plan ahead for installation of new components.
    We disagree with commenters that a 112(d)(6) review is needed for
this requirement. The requirement to conduct initial monitoring of
equipment for leaks within 30 days of startup is a clarification to the
compliance provisions of an existing work practice, not a new work
practice. As discussed earlier, a similar change was made for 40 CFR
part 60, subpart VV. As we stated in that rulemaking (72 FR 64862), the
change is a clarification of the initial monitoring requirements. The
clarification is intended to provide certainty to owners or operators
on the timeframe in which this compliance activity must be conducted.
b. Heat Exchange Systems
    Comment: We received comments in support of and against the
proposal to require use of the Modified El Paso Method for detecting
and repairing leaks in heat exchange systems.
    One commenter supported the use of the Modified El Paso Method, and
stated that in the Ethylene Production

rulemaking, the EPA found that at least 20 heat exchange systems (at
eight facilities) are already required by TCEQ's highly reactive
volatile organic compounds (HRVOC) rule to conduct continuous Modified
El Paso Method monitoring.
    Some commenters opposed the proposed control requirements for heat
exchange systems, stating the requirements were not cost effective when
considering the actual costs to repair leaks. Some commenters said that
the costs provided in Table 3 of the memorandum, Clean Air Act Section
112(d)(6) Technology Review for Heat Exchange Systems Located in the
Miscellaneous Organic Chemical Manufacturing Source Category for the
Final Rule, significantly underestimate the true cost associated with
leak repair at MON facilities. The commenters contended that the EPA
has not taken into account that after identifying a leak, maintenance
and operations personnel must develop a strategy and schedule to remove
the leaking exchanger from service to conduct the repair. The commenter
explained that this activity involves identifying and selecting options
for bypassing the process stream from the leaking system, determining
the amount of production turndown necessary while the exchanger is out
of service, identifying and selecting the appropriate contract
personnel, and scheduling the work so that it does not conflict with
any other planned maintenance. The commenters said these steps alone
require approximately 128 personnel hours. In addition to these costs,
the commenters said that the EPA did not include costs for bypassing
the leaking system to avoid a total shutdown, which may include renting
and plumbing temporary heat exchangers. The commenters also said that
the EPA did not include costs for the rental and installation of cranes
and scaffolding for accessing the heat exchanger for repairs or costs
for specialized contracted maintenance support to de-head the exchanger
and perform the repair. The commenters contended that repair costs
range from $200,000 to $400,000 per event, not considering lost profit
due to turndown or shutdown of the production unit. Factoring in these
additional costs and using the EPA's calculated HAP emissions
reductions of 31 tons per year, the commenters said the revised cost
effectiveness becomes $161,930 per ton of HAP. The commenters cited the
NESHAP final RTR for Friction Materials Manufacturing Facilities (83 FR
19511) where the EPA found a $3,700 per ton cost for a permanent total
enclosure not cost effective, and the NESHAP proposed RTR for the
Petroleum Refinery Sector (79 FR 36916) where the EPA found a $14,100
per ton cost for lowering leak definitions not cost effective. The
commenters stated that the EPA acknowledges in the preamble that
emissions from heat exchange systems have no discernable impact on
cancer risk for the modeled facilities and that additional controls for
heat exchange systems are not necessary to provide an ample margin of
safety.
    One commenter requested that the EPA reconsider the cost
information submitted on heat exchanger leak repairs in the context of
MON, independent of the prior decision made for the Ethylene Production
RTR. The commenter said that the EPA's response to their similar
comment for the Ethylene Production RTR, that heat exchange systems for
ethylene production facilities were not cost effective, was not
persuasive. The commenter said that the EPA must consider the entire
cost of a heat exchanger repair for the additional/incremental repairs
that will be required as a result of lower effective leak definitions
and restrictions to the delay of repair provisions; for example, if the
current rule requires 4 leaks to be repaired, and the revised rule
requires 5 leaks to be repaired, the incremental cost is the entire
repair cost for the 5th repair, not a subset of the repair costs,
because the current rule would not require the 5th repair at all. In
addition, the commenter said they provided a detailed account of
several components of repair costs and the range of typical repair
costs, yet the EPA did not consider this information in the final rule
for the Ethylene Production RTR (signed on March 12, 2020). The
commenter also objected to the EPA's response, to similar comments in
the pre-publication of the final rule for the Ethylene Production RTR,
that the ACC did not provide additional information for the agency to
determine the amount of time additional leaks would have to be fixed
under the revised heat exchange system standards. The commenter
contended that EPA already had sufficient data. The commenter said the
EPA based the leak distribution analysis in the technology review
memorandum for heat exchange systems at ethylene production facilities
on continuous monitoring data from 13 heat exchange systems at six
facilities, and the EPA indicated that no leaks in the data were above
the current rule threshold; thus, all leaks at the average leak
distribution chosen for analysis that were above the new leak detection
threshold would be considered ``incremental repairs.''
    One commenter contended that requiring the Modified El Paso method
is not cost effective in all cases. The commenter stated that in
certain cases, where soluble type HAP or VOC are the dominant organic
species on the process side of the heat exchanger, the current leak
detection method (i.e., cooling water sampling to detect leaks) is
``adequate,'' and, therefore, the costs to change to using the El Paso
method are ``not justified.'' The commenter explained that mandated
conversion of their 56 heat exchanger systems (HES) to the Modified El
Paso method would require installation of tubing and taps to set up
sampling stations for the El Paso apparatus. The commenter added that
where there is not room or access close by the HES, remote stations
would have to be established. In order to take the measurements, the
commenter stated that an LDAR Method 21 technician must accompany
operators to the sampling locations and move the El Paso apparatus from
location to location; otherwise, multiple El Paso sampling devices
would have to be installed. The commenter contended that the costs
associated with the proposed change are not justified when the current
method is adequate to detect leaks.
    Response: The EPA is finalizing the proposed technology review
revision under CAA section 112(d)(6) for heat exchange systems to use
the Modified El Paso Method, with some minor technical clarifications
that are discussed elsewhere in this section of this preamble and in
the Summary of Public Comments and Responses for the Risk and
Technology Review for the Miscellaneous Organic Chemical Manufacturing
Source Category, available in the docket for this rulemaking. However,
we disagree with commenters who said these proposed revisions are not
cost effective. We believe that the developments we identified for heat
exchange systems at MON sources are cost effective. We note that the
existing MACT standards that were finalized in 2003 contain LDAR
provisions; therefore, many of the costs mentioned by commenters (i.e.,
planning, bypassing, various equipment rental/purchase costs, and costs
for scaffolding) are associated with repair costs that would have
already been incurred under the existing MACT standards. Also, many of
the items associated with cost that are listed by the commenters are
not required by the rule, and the commenters did not provide sufficient
information

demonstrating why these costs represent an average heat exchange system
at a MCPU. For example, facilities may have additional heat exchange
system capacity available to them at their facility and may opt to use
this capacity to repair the leak, at no additional expense, yet this
was not considered by commenters.
    Furthermore, because commenters did not provide information
sufficient for us to evaluate the percentage of time additional leaks
would have to be fixed under the proposed heat exchange system
standards compared to the original MACT standards, we continue to
believe that the majority, if not all, of the repair costs cited by
commenters would have been accounted for and incurred as a result of
the original MACT standards and that simply plugging a leaking heat
exchanger would more likely represent the average cost additionally
incurred by MON sources as a result of this technology review
development. In addition, we stated in the proposed rule that we
considered a heat exchanger that was leaking to the extent that it
needed to be replaced to be effectively at the end of its useful life,
so the cost of replacing the heat exchanger would be an operational
cost that would be incurred by the facility as a result of routine
maintenance and equipment replacement and not attributable to the work
practice standard.
    Thus, given all of this information, we continue to believe that
the only costs that would be additionally incurred by the proposed heat
exchange system standards would be costs associated with the difference
between doing leak sampling using water sampling methods and leak
sampling using the Modified El Paso Method as well as with costs
associated with combined operator and maintenance labor to find and
repair a leak by plugging it. We also maintain that for almost all MON
facilities,\19\ the use of the Modified El Paso method is much more
sensitive in terms of being able to identify leaks of organic HAP
compared to water sampling methods, and monitoring for a single
surrogate parameter of organic HAP such as total strippable hydrocarbon
can be easily accomplished with a single measurement using a common
flame ionization detector (FID).
---------------------------------------------------------------------------

    \19\ We are aware of only one MON facility where it is possible
that the only HAP that has potential to be present in a heat
exchange system is methanol and/or ethylene glycol. In this specific
case, the Modified El Paso method may not be as sensitive as water
sampling methods; and the owners or operators of this facility could
submit more detailed information regarding their specific situation
to the EPA and request an alternative test method or an alternative
monitoring method pursuant to 40 CFR 63.7(f) and 40 CFR 63.8(f),
respectively. Under 40 CFR 63.7(f) and 40 CFR 63.8(f) (in subpart
A--General Provisions), a source may apply to the EPA for permission
to use alternative test methods or alternative monitoring
requirements in place of any required testing methods, performance
specifications, or procedures in the final rule or any amendments.
---------------------------------------------------------------------------

    We note that, based on data collected for ethylene sources, we
anticipate that the subsequent leak distribution would reasonably
represent implementation of the Modified El Paso Method because it is
the average leak distribution of 13 heat exchange systems at 6 ethylene
facilities using this method. However, given that the initial leak
distribution is based on a heat exchange system employing continuous
Modified El Paso monitoring, it is likely that emission reduction
estimates are understated given that the average MON facility does not
have such readily available information on leaks and would only acquire
such information on a quarterly basis using considerably higher leak
sensitive test methods. In other words, and as described in more detail
in our technology review memorandum for heat exchange systems (see
Clean Air Act Section 112(d)(6) Technology Review for Heat Exchange
Systems Located in the Miscellaneous Organic Chemical Manufacturing
Source Category For the Final Rule, which is available in the docket
for this rulemaking), the initial leak frequency distribution would
likely show considerably higher percentages of larger leaks due to the
sensitivity of the current water sampling method requirements in the
rule and due to the fact that the dataset was developed from facilities
employing continuous monitoring as opposed to less frequent (e.g.,
quarterly or monthly) monitoring. However, this was the best available
data available to the agency, and so we used these conservative
estimates. Based on our analysis, we find that the revised standards we
proposed for heat exchange systems are cost effective at $8,530/ton of
HAP without consideration of product recovery and the requirement has
the potential to lead to a cost savings with product recovery.
Therefore, we are finalizing the revisions for heat exchange systems
that we proposed under the technology review with some minor technical
clarifications that are discussed elsewhere in this document.
    We also note, with respect to other rules where we have determined
control options to not be cost effective at varying levels of cost
effectiveness, that other compelling factors in those rulemaking
records likely led the EPA to those determinations and that each
rulemaking record is unique and should be judged based on its own
merits. With respect to the two proposed rules commenters cite (i.e.,
friction materials RTR and petroleum refinery RTR) where the EPA
determined certain controls to not be cost effective, the EPA considers
a number of rule-specific factors when determining what is, and what is
not, cost effective. Regardless, and as stated above, we believe that
the developments we identified for heat exchange systems at MON sources
are cost effective, and we are finalizing these revisions under our CAA
section 112(d)(6) authority.
    Comment: Two commenters recommended the EPA revise the heat
exchange system requirements to include an alternative mass-based leak
definition because it would reduce the overall costs of the final rule.
The commenters argued that by only defining a leak on a concentration
basis, smaller facilities with lower heat exchange system recirculation
rates would be forced to identify and fix leaks with a much lower
potential HAP emissions rate than facilities with larger recirculation
systems. The commenters provided the EPA with survey results showing
that 69 heat exchange systems subject to the MON rule have
recirculation flowrates between 200 gpm and 80,000 gpm, except for four
systems that have a flowrate greater than 80,000 gpm and that the
average cooling water flow rate is 43,500 gpm. Based on this
information, the commenters suggested the EPA establish an alternative
leak action level of 1.6 pounds per hour of total strippable
hydrocarbon and a delay of repair action level of 16 pounds per hour of
total strippable hydrocarbon for systems with a recirculation flowrate
less than or equal to 40,000 gpm. Another commenter said that the EPA
must reduce the leak definition and aim to achieve zero leaks. The
commenter also supported the use of the Modified El Paso Method,
pointing out that in the Ethylene Production RTR, the EPA found that at
least 20 heat exchange systems (at eight facilities) are already
required by TCEQ's HRVOC rule to conduct continuous Modified El Paso
Method monitoring.
    Response: We agree with commenters that an alternative mass-based
leak action level is warranted (in lieu of a concentration-based leak
action level) and that, by not finalizing such an alternative, smaller
heat exchange systems with low recirculation rates would be
disproportionally affected and forced to repair leaks with a much lower
potential HAP emissions rate than facilities with larger recirculation
rate systems. As commenters allude to, the goal of this alternative is
to avoid

disproportionally impacting small heat exchange systems with low
emissions potential. To that end and given that this is a technology
review under CAA section 112(d)(6), consideration of where it is cost
effective to repair a leaking heat exchange system is a consideration
for this alternative mass-based leak action level. In the technology
review memorandum, Clean Air Act Section 112(d)(6) Technology Review
for Heat Exchange Systems Located in the Miscellaneous Organic Chemical
Manufacturing Source Category For the Final Rule, available in the
docket for this rulemaking, we determined that the nationwide impacts
for HAP cost effectiveness (without consideration of product recovery)
at $8,530/ton of HAP would be the HAP cost effectiveness for an average
heat exchange system in the source category that has a recirculation
rate of approximately 14,000 gpm. We also generally consider technology
review developments to be near the upper end of acceptable cost
effectiveness for organic HAP if the cost effectiveness is
approximately $10,000/ton (or approximately 1.2 times higher than the
cost effectiveness estimated for the average heat exchange system at
MON sources). Since the recirculation rate directly correlates to mass
emissions potential at the same leak concentration, the mass emissions
for a heat exchange system with recirculation rate of 10,000 gpm or
less (rounded to one significant figure) would be at least 1.2 times
smaller compared to a 14,000 gpm recirculation rate system, and the
annual costs to find and repair leaks would not change. As such, we
determined that heat exchange systems with a recirculation rate of
10,000 gpm or less would be less cost effective to monitor and repair
because the HAP cost effectiveness would be approximately $10,000/ton
of HAP or more. Therefore, to alleviate the concern about
disproportionally impacting small heat exchange systems with low HAP
emissions potential, and to ensure our technology review developments
are cost effective for all heat exchange systems in the source
category, we are finalizing an alternative total hydrocarbon mass-based
emissions rate leak action level (as methane) of 0.18 kilograms per
hour (0.4 pounds per hour) for heat exchange systems in the
Miscellaneous Organic Chemical Manufacturing source category that have
a recirculation rate of 10,000 gpm or less. We also agree that for
consistency, and to not disproportionately impact small heat exchange
systems, an alternative mass-based leak action level of 1.8 kilograms
per hour (4.0 pounds per hour) for delay of repair for heat exchange
systems with a recirculation rate of 10,000 gpm or less is warranted.
c. Process Vents, Storage Tanks, Transfer Racks, and Wastewater Streams
    Comment: Commenters supported the EPA's conclusion under the
technology review that there are no cost-effective technology
developments for process vents, storage tanks, transfer racks, and
wastewater streams.
    Response: We acknowledge the commenters' support for the EPA's
technology review conclusions.
4. What is the rationale for our final approach for the technology
review?
    Our technology review focused on the identification and evaluation
of developments in practices, processes, and control technologies that
have occurred since the MON standards were originally promulgated on
November 10, 2003 (68 FR 63852), and further amended on July 1, 2005
(70 FR 38562), and July 14, 2006 (71 FR 40316). Specifically, we
focused our technology review on all existing MACT standards for the
various emission sources in the Miscellaneous Organic Chemical
Manufacturing source category, including, storage vessels, process
vents, transfer racks, equipment leaks, wastewater streams, and heat
exchange systems. In the proposal, we identified cost-effective
developments only for equipment leaks and heat exchange systems, and we
proposed to revise the standards for these two emissions sources under
the technology review. We did not identify developments in practices,
processes, or control technologies for process vents, transfer racks,
storage tanks, and wastewater streams. Further information regarding
the technology review can be found in the proposed rule (84 FR 69182,
December 17, 2019) and in the supporting materials in the rulemaking
docket at Docket ID No. EPA-HQ-OAR-2017-0357.
    During the public comment period, we received several comments on
our proposed determinations for the technology review. The comments and
our specific responses and rationale for our final decisions can be
found in section IV.B.3 of this preamble and in the document, Summary
of Public Comments and Responses for the Risk and Technology Review for
Miscellaneous Organic Chemical Manufacturing, available in the docket
for this rulemaking. No information presented by commenters has led us
to change our proposed determination under CAA section 112(d)(6) for
process vents, transfer racks, storage tanks, and wastewater streams,
and we are finalizing our determination that no changes to these
standards are warranted. However, substantive information was submitted
by commenters on proposed revisions for equipment leaks. Based on these
comments, we are finalizing revisions for equipment leaks and making
some technical clarifications to clarify that the initial monitoring of
equipment is only required if the new or replaced equipment is subject
to Table 6 to 40 CFR part 63, subpart FFFF, and is also subject to
periodic monitoring with Method 21 of appendix A-7 to 40 CFR part 60
and that the initial monitoring does not apply to equipment classified
as unsafe-to-monitor or difficult-to-monitor equipment. In addition,
substantive information was also submitted by commenters on proposed
revisions for heat exchange systems, and based on this information, we
are finalizing revisions to require the Modified El Paso Method for
heat exchange systems. We are also making some technical clarifications
to allow compliance with the Modified El Paso Method using an
alternative mass-based leak action level instead of a concentration-
based leak action level for small heat exchange systems with a
recirculation rate of 10,000 gpm or less.

C. Amendments Pursuant to CAA Section 112(d)(2) and (3) and 112(h) for
the Miscellaneous Organic Chemical Manufacturing Source Category

1. What did we propose pursuant to CAA section 112(d)(2) and (3) and
112(h) for The Miscellaneous Organic Chemical Manufacturing source
category?
    Under CAA sections 112(d)(2) and (3) we proposed to amend the
operating and monitoring requirements for a subset of flares in the
Miscellaneous Organic Chemical Manufacturing source category. We
proposed that the subset of flares include flares in the Miscellaneous
Organic Chemical Manufacturing source category that either (1) control
ethylene oxide emissions, (2) control emissions from processes that
produce olefins, or (3) control emissions from processes that produce
polyolefins. In our proposal, we also proposed that flares controlling
propane dehydrogenation (PDH) processes be included in the specified
subset since the PDH process produces olefins such as propylene. We
also proposed at 40 CFR 63.2535(m) to clarify that owners or operators
of flares that are not considered to be in the specified subset but are
subject to the

flare provisions of 40 CFR 60.18 or 63.11 may elect to comply with the
new proposed flare standards in lieu of the provisions of 40 CFR 60.18
or 63.11.
    We proposed at 40 CFR 63.2450(e)(5) to directly apply the petroleum
refinery flare rule requirements in 40 CFR part 63, subpart CC, to the
flares in the specified subset with clarifications, including, but not
limited to, specifying that several definitions in 40 CFR part 63,
subpart CC, that apply to petroleum refinery flares also apply to the
flares in the specified subset, adding a definition and requirements
for pressure-assisted multi-point flares, and specifying additional
requirements when a gas chromatograph or mass spectrometer is used for
compositional analysis. Specifically, we proposed to retain the General
Provisions requirements of 40 CFR 63.11(b) and 40 CFR 60.18(b) such
that flares in the specified subset operate pilot flame systems
continuously and that these flares operate with no visible emissions
(except for periods not to exceed a total of 5 minutes during any 2
consecutive hours) when the flare vent gas flow rate is below the
smokeless capacity of the flare. We also proposed to consolidate
measures related to flare tip velocity and new operational and
monitoring requirements related to the combustion zone gas for flares
in the specific subset. Further, in keeping with the elimination of the
SSM exemption, we proposed a work practice standard related to the
visible emissions and velocity limits during periods when a flare in
the specified subset is operated above its smokeless capacity (e.g.,
periods of emergency flaring). We proposed eliminating the cross-
references to the General Provisions and instead specifying all
operational and monitoring requirements that are intended to apply to
the flares in the specified subset in the MACT standards.
    In addition, we proposed provisions and clarifications for periods
of SSM and bypasses, including PRD releases, bypass lines on closed
vent systems, maintenance activities, and certain gaseous streams
routed to a fuel gas system to ensure that CAA section 112 standards
apply continuously, consistent with Sierra Club v. EPA 551 F. 3d 1019
(D.C. Cir. 2008). For PRD releases, we proposed definitions at 40 CFR
63.2550 of ``pressure release,'' ``pressure relief device,'' and
``relief valve'' and under CAA section 112(h) we proposed a work
practice standard for PRDs at 40 CFR 63.2480(e)(3), (6), and (7) that
consists of using at least three prevention measures and performing
root cause analysis and corrective action in the event that a PRD does
release emissions directly to the atmosphere. (Examples of prevention
measures include flow indicators, level indicators, temperature
indicators, pressure indicators, routine inspection and maintenance
programs or operator training, inherently safer designs or safety
instrumentation systems, deluge systems, and staged relief systems
where the initial PRD discharges to a control system.) We proposed that
PRDs in ethylene oxide service may not vent directly to atmosphere. We
also proposed to require that sources monitor PRDs that vent to
atmosphere using a system that is capable of identifying and recording
the time and duration of each pressure release and of notifying
operators that a pressure release has occurred. We proposed at 40 CFR
63.2480(e)(4) that PRDs that vent through a closed vent system to a
control device or to a process, fuel gas system, or drain system must
meet minimum requirements for the applicable control system. In
addition, we proposed at 40 CFR 63.2480(e)(5) that the following types
of PRDs would not be subject to the work practice standard for PRDs
that vent to the atmosphere: (1) PRDs with a design release pressure of
less than 2.5 pounds per square inch gauge (psig); (2) PRDs in heavy
liquid service; (3) PRDs that are designed solely to release due to
liquid thermal expansion; and (4) pilot-operated and balanced bellows
PRDs if the primary release valve associated with the PRD is vented
through a control system. Finally, we proposed at 40 CFR 63.2480(e)(8)
to require future installation and operation of non-flowing pilot-
operated PRDs at all affected sources.
    For bypass lines on closed vent systems, we proposed at 40 CFR
63.2450(e)(6) that an owner or operator may not bypass the air
pollution control device (APCD) at any time, and if a bypass is used,
then the owner or operator must estimate and report the quantity of
organic HAP released. We proposed and are taking final action on this
revision because bypassing an APCD could result in a large release of
regulated organic HAP to the atmosphere (the removal efficiency
required by the MON ranges from 95 to 99.9 percent, depending on the
type of emission source). The MON requirements we are finalizing thus
provide the Agency with the information necessary to evaluate these
incidents and determine whether enforcement action is necessary to
address such releases to ensure they do not recur. We are also taking
final action to allow the use of a cap, blind flange, plug, or second
valve on an open-ended valve or line to prevent a bypass. For these
reasons, we maintain that the MON as revised is consistent with Sierra
Club v. EPA, 551 F.3d 1019 (D.C. Cir. 2008), because the rule requires
compliance with emission standards at all times as required by CAA
section 112(d) and because the rule includes sufficient monitoring,
recordkeeping and reporting requirements to allow the EPA to evaluate
and address any unauthorized releases of HAP emissions.
    For maintenance activities, we proposed a work practice standard at
40 CFR 63.2455(d)(1) requiring that, prior to opening process equipment
to the atmosphere, the equipment must either (1) Be drained and purged
to a closed system so that the hydrocarbon content is less than or
equal to 10 percent of the LEL; (2) be opened and vented to the
atmosphere only if the 10-percent LEL cannot be demonstrated and the
pressure is less than or equal to 5 psig, provided there is no active
purging of the equipment to the atmosphere until the LEL criterion is
met; (3) be opened when there is less than 50 lbs of VOC that may be
emitted to the atmosphere; or (4) for installing or removing an
equipment blind, depressurize the equipment to 2 psig or less and
maintain pressure of the equipment where purge gas enters the equipment
at or below 2 psig during the blind flange installation, provided none
of the other proposed work practice standards can be met. For cases
where an emission source is required to be controlled in the MACT
standards but is routed to a fuel gas system, we proposed that any
flare receiving gases from that fuel gas system derived from an MCPU
that has processes and/or equipment in ethylene oxide service or that
produces olefins or polyolefins, and utilizing fuel gas whereby the
majority (i.e., 50 percent or more) of the fuel gas in the fuel gas
system is derived from an MCPU, comply with the proposed flare
operating and monitoring requirements.
    More information concerning our proposed requirements under CAA
section 112(d)(2) and (3) and 112(h) can be found in section IV.A of
the proposal preamble (84 FR 69182, December 17, 2019).
2. How did the revisions pursuant to CAA section 112(d)(2) and (3) and
112(h) change since proposal?
    The EPA is finalizing the revisions to the monitoring and
operational requirements for flares, as proposed, except that we are
not finalizing the work practice standard for velocity exceedances for
flares operating above

their smokeless capacity. We are also clarifying in the final rule that
a ``flare that controls ethylene oxide emissions'' is a flare that
controls ethylene oxide emissions from affected sources in ethylene
oxide service as defined in 40 CFR 63.2550. In addition, we are
clarifying in the final rule that ``an MCPU that produces olefins or
polyolefins'' include only those MCPUs that manufacture ethylene,
propylene, polyethylene, and/or polypropylene as a product; by-products
and impurities as defined in 40 CFR 63.101, as well as wastes and trace
contaminants, are not considered products.
    Also, we are adding a separate degassing standard in the final rule
at 40 CFR 63.2470(f) for storage vessels subject to control
requirements based on comments that owners or operators have
historically considered degassing emissions from shutdown of storage
vessels to be covered by their SSM plans per 40 CFR 63.63.2525(j) and
relied on the language in 40 CFR 63.6(e)(1) and 40 CFR 63.2450(a)(1)
that back-up control devices are not required. The standard requires
owners or operators to control degassing emissions for floating roof
and fixed roof storage vessels until the vapor space concentration is
less than 10 percent of the LEL. Storage vessels may be vented to the
atmosphere once the storage vessel degassing concentration threshold is
met (i.e., 10-percent LEL) and all standing liquid has been removed
from the vessel to the extent practical.
3. What key comments did we receive on the proposal revisions pursuant
to CAA section 112(d)(2) and (3) and 112(h), and what are our
responses?
    This section provides comment and responses for the key comments
received regarding our proposed revisions for flares and clarifications
for periods of SSM, including PRD releases and storage vessel emptying
and degassing. Other comment summaries and the EPA's responses for
additional issues raised regarding these activities, as well as issues
raised regarding our proposed revisions for bypass lines on closed vent
systems, maintenance activities, and certain gaseous streams routed to
a fuel gas system, can be found in the document, Summary of Public
Comments and Responses for the Risk and Technology Review for
Miscellaneous Organic Chemical Manufacturing, available in the docket
for this rulemaking.
a. Flares
    Comment: We received comments in support of our proposal to
establish similar requirements for flares (controlling ethylene oxide
or emissions from processes that produce olefins and/or polyolefins)
used in the Miscellaneous Organic Chemical Manufacturing source
category as the flare requirements established in the 2015 Petroleum
Refinery NESHAP, including the incorporation of the net heating value
of the combustion zone gas (NHVcz) calculation and limits. One
commenter said they supported the proposed strengthened operational and
monitoring requirements because of the toxic nature of ethylene oxide
and the photochemical reactivity of the olefins and polyolefins
emissions.
    Another commenter cited various enforcement cases where the EPA
found flare efficiency problems and applied flare operational and
monitoring improvements to chemical plants. The commenter said that
because MON sources do not currently have separate flare management
plan requirements (as refineries do under CAA section 111 NSPS
standards), it is particularly important and necessary for the EPA to
update the flare requirements in this rule to assure that flares are
working correctly to reduce HAP emissions. Also, the commenter
reiterated the EPA's determination that measuring the net heating value
of the flare gas, as it enters the flares, is insufficient to determine
combustibility because facilities add steam and other gases not
accounted for and that flare performance data shows that the net
heating value of vent gas in the combustion zone must reach at least
270 British thermal units per standard cubic foot (Btu/scf). Some
commenters also supported the EPA's proposal ``that owners or operators
may use a corrected heat content of 1,212 Btu/scf for hydrogen, instead
of 274 Btu/scf, to demonstrate compliance with the NHVcz operating
limit,'' because the data show that the control efficiency of a flare
drops off significantly below this level. However, the commenters also
suggested other improvements to the proposed flared revisions. The
commenters recommended that the EPA also consider the following
measures to help assure compliance with 98-percent destruction
efficiency and said that these measures should be evaluated under CAA
section 112(d)(6).
     Revise the standards to account for ``developments'' that
improve emissions controls by eliminating or drastically reducing
routine flaring, such as augmented flare capacity;
     The HAP emission rates from flares during malfunctions
when process gases are routed to flares from process equipment should
not be less stringent than the emission limits that apply to such units
during normal operations.
     Set further limits on routine flaring that comply with CAA
section 112(d)(2) and (3), and 112(f).
     Require continuous video monitoring and recording for
flares equipped with video monitoring and flares that vent more than 1
million scf per day.\20\
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    \20\ Commenter provided the following reference: See 84 FR
54296; BAAQMD sec. 12-11-507: Requiring continuous video monitoring
and recording for flares equipped with video monitoring and flares
with vent gas more than 1 million scf/day; SCAQMD Rule 1118(g)(7):
Requiring continuous video monitoring and recording; Consent Decree,
United States of America v. Marathon Petroleum Company LP et al.,
No. 12-cv-11544 (E.D. Mich.) (April 5, 2012); Consent Decree, United
States of America et al. v. BP Products North America Inc., No. 12-
cv-0207 (N.D. Ind.) (May 23, 2012); Consent Decree, United States of
America v. Shell Oil Company et al., No. 13-cv-2009 (S.D. Tex.)
(July 10, 2013); Consent Decree, United States of America v. Flint
Hills Resources Port Arthur, LLC, No. 14-cv-0169, at 12 (E.D. Tex.)
(March 20, 2014).
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     Set limits on flaring that require flare gas recovery and
other steps to reduce regular and routine flaring.
    Response: Except for minor clarifications discussed in the response
to comment document for this rulemaking, the EPA is finalizing the
flare operational and monitoring requirements at 40 CFR 63.2450(e)(5),
as proposed, as supported by several commenters. We disagree with one
commenter's request that we mandate additional measures to ensure 98-
percent flare destruction efficiency on top of those being finalized in
this action under our CAA section 112(d)(2) and (3) authority. Flares
are one of many APCDs that owners or operators of MCPUs can use to
control HAP emissions from the Miscellaneous Organic Chemical
Manufacturing source category and are not specific affected emission
sources in the Miscellaneous Organic Chemical Manufacturing source
category; thus, the flare requirements we are finalizing are already
designed to ensure flares meet a minimum destruction efficiency of 98
percent, consistent with the MACT control requirements.
    We disagree with commenters that we should impose the additional
measures for flares under our CAA section 112(d)(6) authority because
the revisions to the flare requirements are associated with compliance
with the MACT standards established pursuant to CAA sections 112(d)(2)
and (3). The rulemaking record contains the analyses on options we
analyzed for our technology review, and owners or operators of MCPUs
can chose from a variety of APCDs to demonstrate

compliance with the underlying MACT standards. Notably the commenter
does not recommend similar actions to minimize or eliminate the use of
thermal oxidizers, carbon absorbers, or other control devices that may
be employed to control HAP emissions from the affected emission sources
at an MCPU. Eliminating the routine use of flares as an acceptable APCD
would only increase the use of these other types of APCD (at
potentially significant cost) without any net emissions reductions from
the MCPU (provided that the flare is meeting the required control
efficiency). In addition, flare gas recovery has not been demonstrated
at MCPU in the Miscellaneous Organic Chemical Manufacturing source
category, and commenters did not provide sufficient information about
requiring use of such systems specific to this source category.
    We disagree with the commenter's specific request to require
continuous video monitoring and recording for flares equipped with
video monitoring and flares that vent more than 1 MMscf/day. We are not
removing the requirement to conduct EPA Method 22 monitoring because it
has always been required for flares; however, because EPA Method 22
does not allow the use of a video camera, we have provided for the use
of video camera surveillance monitoring in the final rule as an
alternative to EPA Method 22 monitoring. Observation via the video
camera feed can be conducted readily throughout the day and will allow
the operators of the flare to watch for visible emissions at the same
time they are adjusting the flare operations. We note that in order for
an owner or operator to be able to use the video camera surveillance
monitoring option, the owner or operator must continuously record (at
least one frame every 15 seconds with time and date stamps) images of
the flare flame at a reasonable distance above the flare flame and at
an angle suitable for visual emissions observations. The owner or
operator must also provide real-time video surveillance camera output
to the control room or other continuously manned location where the
camera images may be viewed at any time.
    Lastly, with respect to consent decrees cited by the commenter, we
note that the requirements in consent decrees are negotiated
settlements and are not based on any analysis required in CAA section
112 and do not factor in nationwide impacts specific to a source
category of concern, which in this case is the Miscellaneous Organic
Chemical Manufacturing source category.
    Comment: Commenters requested the EPA clarify in 40 CFR
63.2450(e)(5) that the requirements only apply to (1) flares
controlling emissions from sources in ethylene oxide service as defined
in 40 CFR 63.2550 and (2) flares used as an APCD to comply with the
emission limits and work practice standards in Tables 1, 2, 4, and 5 to
40 CFR part 63, subpart FFFF, for emission sources located at MCPUs
that produce olefins and/or polyolefins. A commenter said that the
introductory language in 40 CFR 63.2450(e)(5) is ambiguous and appears
to indicate that a flare that controls any amount of ethylene oxide or
any amount of other HAP from olefins or polyolefins production
processes would be subject to the proposed requirements. In addition,
the commenter requested that the EPA limit the applicability of the
revised provisions to those MCPUs producing lighter olefins and
polyolefins and that heavy olefin (e.g., hexene) and heavy polyolefin
(e.g., polybutene) production should be excluded because heavier
materials used in such processes have much less potential to be flared.
The commenter requested that the EPA define the phrase ``MCPUs that
produce olefins or polyolefins'' and said that MCPUs may generate
olefins or polyolefins as a by-product or impurity and these small
amounts of materials do not justify the compliance costs associated
with meeting the new flare requirements. The commenter recommended the
EPA adopt definitions similar to those for ``Product, By-product,'' and
``Impurity'' found in the HON (i.e., 40 CFR 63.101).
    Other commenters said the EPA must apply the proposed flare
improvements to all MON flares, not just the subset that controls
ethylene oxide and emissions from olefin/polyolefin processes. One
commenter said that the refinery flare requirements, as proposed, will
only apply to 16 of 145 flares in the source category and reiterated
that this is less than 10 percent of the flares in the Miscellaneous
Organic Chemical Manufacturing source category. The commenter said the
EPA did not sufficiently explain why the flare improvements should not
be applied to all MON flares.
    Response: First, as a general matter, the Miscellaneous Organic
Chemical Manufacturing source category broadly encompasses a wide
variety of chemical production processes not covered elsewhere under
other 40 CFR part 63 NESHAP and, as such, is a ``catch all'' for a wide
variety of processes producing various types of chemical products. The
primary goal of applying the new suite of flare requirements to a
certain flare subset is two-fold: (1) To ensure continuous compliance
with the MON MACT standards at all times for the largest flare systems
in the source category where the Agency has compelling data that show
that the flare types and vent gases being controlled (e.g., olefinic
vent gases that contain ethylene and/or propylene) could have
deteriorated flare performance issues, and (2) to ensure continuous
compliance with the MON MACT standards at all times for flare systems
controlling ethylene oxide, the cancer risk driving HAP for the source
category. In particular, when the EPA reviewed available data about
flare APCDs being used in the Miscellaneous Organic Chemical
Manufacturing source category and the potential for deteriorated
combustion efficiencies to occur during certain modes of operation
(e.g., over-assisting steam-assisted flares), we determined that vent
gases consisting of olefinic material can be over-assisted and that
flare performance for these types of MCPUs could be diminished (i.e.,
consistent with the passive fourier transfer infrared spectrometry
(PFTIR) test data reviewed and that formed the basis of the Petroleum
Refinery requirements at 40 CFR part 63, subpart CC, we cross-reference
in this final rule for the MON). In addition, the EPA has recently
reviewed and approved a number of AMEL requests from MON facilities
that produce olefins/polyolefins, and this subset of facilities in the
Miscellaneous Organic Chemical Manufacturing source category comprises
the largest flare systems in the source category, making issues of
deteriorated flare performance of particular concern. With respect to
flares controlling emissions of ethylene oxide, the EPA also wanted to
ensure that these flare systems would be subject to more stringent
compliance assurance requirements to ensure over-assisting does not
occur for these flare types given risks associated with ethylene oxide
in the source category. Thus, these two criteria were chosen to
constitute the basis of our flare subset given both the data before us
and the concern for potential risk issues if deteriorated flare
performance were to occur for flares controlling emissions of ethylene
oxide from the source category. Given that we do not have sufficient
data about the types of flares and flare vent gases that the other
various MCPUs outside the flare subset would be controlling, we are
unable to determine whether the new suite of flare requirements would
be necessary or warranted as the existing suite of flare requirements
may be sufficient for these

other flares. Commenters did not provide the Agency with any
information about this, including test data, flare vent gas
characteristics, and specific instances of deteriorated flare
performance for flares outside the flare subset, thus we disagree that
we should broadly apply these new flare requirements to all flares in
the source category without this information. We note, however, that we
proposed and are finalizing as an alternative that owners or operators
of flares outside the flare subset may opt to comply with the new suite
of flare requirements should they choose.
    With respect to comments requesting the EPA to clarify what was
meant when referring to production of olefins and/or polyolefins, we
are adding a definition for ``MCPUs that produce olefins or
polyolefins'' for purposes of the new suite of flare requirements only
and clarifying that these MCPUs include production of ethylene,
propylene, polyethylene, and polypropylene given that these are the
largest flare systems in the Miscellaneous Organic Chemical
Manufacturing source category and because they are controlling olefinic
vent gases that contain ethylene and propylene, which have been shown
in our data to exhibit certain operating scenarios where over-assisting
and deteriorated flare performance could occur.
    Lastly, we agree with commenters that the language at 40 CFR
63.2450(e)(5) could be construed as ambiguous for purposes of
controlling ethylene oxide emissions. As such, we are clarifying in the
rule text that our intent was to control all emissions generated from
affected sources ``in ethylene oxide service,'' as that term is defined
in the final rule.
    Comment: We received comments in support of and against the
proposed work practice requirements for visible emissions and flare tip
velocity. One commenter said that MON flares operate similarly to
refinery flares in that MON flares are typically designed with a
``smokeless capacity'' for normal operations and a ``hydraulic load
capacity'' to handle large volumes of flare gas in an emergency. The
commenter said that it was reasonable for the EPA to use smoking and
tip velocity events reported for ethylene production and refineries to
develop emergency flaring provisions for the Miscellaneous Organic
Chemical Manufacturing source category because the data on the number
of visible emissions events and velocity exceedances for MON flares are
not comprehensive of all MON facilities in the subset identified by the
EPA. However, the commenter said that because ethylene flares are twice
as likely to have visible emissions events as refinery flares, and
because it is reasonable to use smoking event data for ethylene flares
to represent MON flares, the EPA should set the backstop for the work
practice standard to 6 smoking events in 3 years for MON flares in the
identified subset.
    Another commenter objected to the EPA's proposed emergency flaring
provisions for smoking flares and said that the provisions are
arbitrary and capricious because they do not meet the requirement from
CAA section 112(h) that work practice standards be consistent with CAA
section 112(d)(2) and (d)(3). The commenter argued that the EPA's
assumption regarding the frequency of emergency flaring events using
events at refineries and ethylene production facilities does not
satisfy the requirement in CAA section 112(d)(2) that the Administrator
``determine'' what is achievable regarding the frequency of emergency
flaring events. The commenter said the EPA's reliance on data from
refineries and ethylene production facilities, and lack of analysis of
the frequency of emergency flaring events at MON facilities, means that
the exemption provision violates the CAA section 112(d) requirement
that the EPA determine what is achievable for sources ``in the category
or subcategory to which such emission standard applies.'' The commenter
requested that the EPA remove the emergency flaring provisions because
the EPA needs to collect data from MON sources to set a standard that
could satisfy CAA section 112(d)(2) and (d)(3).
    In addition, the commenter said that even though the visible
emission exemption at issue is for smoking flare events when flares are
operating above their smokeless capacity, the EPA (in the present
proposed rule, as well as in its analyses regarding refinery and
ethylene production flares) only reached conclusions and analyzed data
regarding what is achievable for smoking flare events regardless of
whether the flares were operating above or below their smokeless
capacity. The commenter argued that the EPA has not determined what is
achievable for flares when operating above their smokeless capacity.
The commenter also said the EPA has not performed any analysis of how
often the best performers would exceed flare tip velocity limits when
operating above smokeless capacity, and the EPA has only purported to
analyze smoking flare events (without regard to whether the events
occurred above smokeless capacity). The commenter stated that the EPA
also ignored data that contradict its conclusion regarding the
exemption allowing flare tip velocity events because the ACC data that
the EPA relied upon to establish the emergency flaring exemption in the
ethylene production proposal reported no tip velocity events among any
of the 45 flares from the ACC survey. The commenter contended that the
ACC data suggest that the best performing flares (at least at ethylene
production facilities) would have zero tip velocity exceedances over
three years, meaning that the EPA's conclusion that the best performers
would have one or two exceedances over that same period is arbitrary
and capricious and contrary to CAA section 112(d). The commenter stated
that, unlike the MON proposed rule, the EPA finalized in the Ethylene
Production RTR rulemaking the requirement that the maximum flare tip
velocity operating limit applies at all times.
    Response: We are taking final action on the proposed work practice
requirements for visible emissions and flare tip velocity as several
commenters suggested. We disagree that we should set the backstop for
the work practice standard to 6 smoking events in 3 years for MON
flares in the identified subset. The commenter did not provide enough
data (i.e., information on visible emissions from MON flares in the
identified subset) for the EPA to justify revising the proposed
requirements. We also disagree with another commenter that we did not
analyze the frequency of emergency flaring events at MON facilities and
that reliance on data from refineries and ethylene production
facilities means that the exemption provision violates the CAA section
112(d) requirement that the EPA determine what is achievable for
sources ``in the category or subcategory to which such emission
standard applies.'' We contend that the data used in our analysis
represents the best available data available to the agency for the
Miscellaneous Organic Chemical Manufacturing Source Category. As stated
in our technical memorandum, Control Option Impacts for Flares Located
in the Miscellaneous Organic Chemical Manufacturing Source Category,
available in the docket for this rulemaking (see Docket Item No. EPA-
HQ-OAR-2018-0746-0006), although ACC provided some information about
visible emissions events and velocity exceedances for MON flares, the
data are not comprehensive of all MON flares in the identified subset.
Therefore, we did not use the ACC data to determine the number of
smoking and tip velocity events that we used in our analysis for

the Miscellaneous Organic Chemical Manufacturing source category, but
rather this information is based on smoking and tip velocity events
reported for two different source categories (refineries and ethylene
production). Best performing flares at refineries have events once
every 6 years, and ethylene flare best performers have events once
every 7 years. We noted that some flares control process gases from
both the Miscellaneous Organic Chemical Manufacturing source category
and from the Ethylene Production source category at the same facility.
Therefore, we surmised that it is likely that MON flares in the
identified subset would have a visible emissions event between every 6
and 7 years. As a conservative approach, we then concluded the best
performing MON flares in the identified subset have a visible emissions
event once every 7 years. Even if the best-performing flare
``typically'' only has one event every 7 years, the fact that visible
emissions events are random by nature (unpredictable, not under the
direct control of the owner or operator) makes it difficult to use a
short term time span to evaluate a backstop to ensure an effective work
practice standard. Thus, when one considers a longer time span of 20
years, our analysis shows that 3 smoking events in 3 years would appear
to be ``achievable'' for the average of the best performing flares.
That said, we do acknowledge that the data we received from ACC's
survey from the Ethylene Production source category identifies zero
exceedances of the flare tip velocity during a smoking event. Also, the
MON-specific data that ACC provided is limited to only one MON
facility, of which 44 of these events were associated with pressure-
assisted flares, and no velocity events were reported by any other MON
site. Thus, we agree with the commenter that our proposed determination
of the frequency of these velocity events at the best performing
sources is not supported, and we are not finalizing the proposed work
practice standard for when the flare vent gas flow rate exceeds the
smokeless capacity of the flare and the tip velocity exceeds the
maximum flare tip velocity operating limit. Instead, we are finalizing
provisions that require compliance with the maximum flare tip velocity
operating limit at all times, regardless of whether the flare is
operating above its smokeless capacity.
b. PRDs
    Comment: Several commenters supported the PRD work practice
requirements, agreeing it is technically and economically infeasible to
establish emission limitations for PRDs that are not designed to vent
through a control system. The commenters added that the EPA's approach
meets their obligations under CAA section 112. One commenter noted that
even states that have stringently regulated PRDs, such as California,
have not established numerical emissions limits. The commenter added
that because these events are triggered by a variety of non-routine
process conditions across a variety of different processes, there is no