percent by weight of ethylene oxide.
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    We are proposing the same ``in ethylene oxide service'' definitions
as used in MON. For process vents, we are proposing to define ``in
ethylene oxide service'' in the HON at 40 CFR 63.101 to mean each
process vent in a process that, when uncontrolled, contains a
concentration of greater than or equal to 1 ppmv undiluted EtO, and
when combined, the sum of all these process vents would emit
uncontrolled EtO emissions greater than or equal to 5 pounds per year
(2.27 kilograms per year). For storage vessels of any capacity and
vapor pressure, we are proposing to define ``in ethylene oxide
service'' in the HON at 40 CFR 63.101 to mean that the concentration of
EtO of the stored liquid is at least 0.1 percent by weight.
Additionally, we are proposing that unless specified by the
Administrator, owners and operators may calculate the concentration of
EtO of the fluid stored in a storage vessel if information specific to
the fluid stored is available such as concentration data from safety
data sheets. We are also proposing that the exemption for ``vessels
storing organic liquids that contain organic hazardous air pollutants
only as impurities'' listed in the definition of ``storage vessel'' at
40 CFR 63.101 does not apply for storage vessels in EtO service.
    We are proposing the same MON EtO-specific requirements \51\ in the
HON for HON process vents and storage vessels ``in ethylene oxide
service,'' except that we are proposing to add a requirement that if a
combustion device is used to comply with the concentration standard,
then the concentration must be corrected to 3 percent oxygen to
determine compliance.\52\ Accordingly, to help reduce risk from the
SOCMI source category to an acceptable level, we are proposing that HON
process vents in EtO service either reduce emissions of EtO by: (1)
Venting emissions through a closed vent system to a control device that
reduces EtO by greater than or equal to 99.9 percent by weight, or to a
concentration less than 1 ppmv for each process vent, or to less than 5
pounds per year for all combined process vents; or (2) venting
emissions through a closed vent system to a flare meeting the proposed
flare operating requirements discussed in section III.D.1 of this
preamble (see proposed 40 CFR 63.113(j)). To help reduce risks from the
SOCMI source category to an acceptable level, we are proposing that HON
storage vessels in EtO service either reduce emissions of EtO by: (1)
Venting emissions through a closed vent system to a control device that
reduces EtO by greater than or equal to 99.9 percent by weight or to a
concentration less than 1 ppmv for each storage tank vent; or (2)
venting emissions through a closed-vent system to a flare meeting the
proposed flare operating requirements discussed in section III.D.1 of
this preamble (see proposed 40 CFR 63.119(a)(5)). Additionally, we
propose removing the option to allow use of a design evaluation in lieu
of performance testing to demonstrate compliance for storage vessels in
EtO service to ensure that the required level of control is achieved
(see proposed 40 CFR 63.124(a)(1)(i) and (b)(3)). We are also proposing
that after promulgation of the rule, owners or operators that choose to
control emissions with a non-flare control device conduct an initial
performance test according to proposed 40 CFR 63.124 on each existing
control device in EtO service and on each newly installed control
device in EtO service to verify performance at the required level of
control. Additionally, we are proposing at 40 CFR 63.124(b) that owners
or operators conduct periodic performance testing on non-flare control
devices in EtO service every 5 years. Additional information on these
evaluated control options to reduce EtO risk from HON process vents and
storage vessels is found in the document titled Analysis of Control
Options for Process Vents and Storage Vessels to Reduce Residual Risk
of Ethylene Oxide in the SOCMI Source Category for Processes Subject to
HON, which is available in the docket for this action.
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    \51\ See 40 CFR 63.2493.
    \52\ We are proposing the concentration correction requirement
because, unlike MON sources with ethylene oxide which were using
scrubber controls, HON sources are generally using combustion
controls for ethylene oxide and a concentration correction for
combustion controls assures dilution with air is not an additional
strategy that facilities could use to bypass control requirements.
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ii. Equipment Leaks
    Emissions of EtO from equipment leaks occur in the form of gases or
liquids that escape to the atmosphere through connection points (e.g.,
threaded fittings) or through the moving parts of valves, pumps,
compressors, PRDs, and certain types of process equipment. The
applicable equipment is those components, including pumps, compressors,
agitators, PRDs, sampling collection systems, OEL, valves, and
connectors that contain or contact material that is 5 percent by weight
or more of organic HAP, operate 300 hours per year or more, and are not
in vacuum service. The equipment leak HON requirements vary by
equipment (component) type but require LDAR using monitoring with EPA
Method 21 of appendix A-7 to 40 CFR part 60 at certain frequencies
(e.g., monthly, quarterly, every 2 quarters, annually) and have varying
leak definitions (e.g., 500 ppm, 1,000 ppm, 10,000 ppm) depending on
the type of service (e.g., gas and vapor service or in light liquid
service). The LDAR requirements for components in heavy liquid service
include sensory monitoring and the use of EPA Method 21 monitoring if a
leak is identified. We provide more details about equipment leaks in
our technology review discussion (see section III.C.6 of this
preamble).
    Results from our risk assessment indicate that, for the source
category MIR of 2,000-in-1 million, approximately 20 percent is from
emissions of EtO related to HON equipment leaks. We also note that the
risk from EtO from HON equipment leaks at seven facilities (including
the facility driving the MIR) is >=100-in-1 million. To help reduce the
risk from the SOCMI source category to an acceptable level, for EtO
emissions from HON equipment leaks, we performed a review of available
measures for reducing EtO emissions from components that are most
likely to be in EtO service, which include connectors (in gas and vapor
service or light liquid service), pumps (in light liquid service), and
valves (in gas or light liquid service). Almost all equipment leak
emissions of EtO come from these three pieces of equipment. We
identified options to further strengthen LDAR practices for these three
pieces of equipment, including by lowering the leak definitions and/or
requiring more frequent monitoring with EPA Method 21 of 40 CFR part
60, appendix A-7, to find more equipment leaks faster and fix them.
    For gas/vapor and light liquid connectors in EtO service, we
identified three options: (1) Require connector monitoring at a leak
definition of 500 ppm with annual monitoring and no reduction in
monitoring frequency (i.e., no skip periods), (2) require connector
monitoring at a leak definition of 100 ppm with annual monitoring and
no reduction in monitoring frequency, and

(3) require connector monitoring at a leak definition of 100 ppm with
monthly monitoring and no reduction in monitoring frequency.
    For light liquid pumps in EtO service, we identified three options:
(1) Lower the leak definition from 1,000 ppm to 500 ppm with monthly
monitoring, (2) lower the leak definition from 1,000 ppm to 100 ppm
with monthly monitoring, or (3) require the use of leakless pumps
(i.e., canned pumps, magnetic drive pumps, diaphragm pumps, pumps with
tandem mechanical seals, pumps with double mechanical seals) with
annual monitoring with a leak definition of any reading above
background concentration levels.
    For gas/vapor and light liquid valves in EtO service, we identified
two options: (1) Require a leak definition of 500 ppm with monthly
monitoring and no reduction in monitoring frequency, or (2) lower the
leak definition from 500 ppm to 100 ppm with monthly monitoring and no
reduction in monitoring frequency.
    Due to the high residual risk for some of the facilities from
equipment leaks of EtO and the potential need for greater emission
reduction to meet an acceptable level of risk for the SOCMI source
category, we also evaluated a more stringent option that combines
several of the component options. We evaluated the combined option of
requiring monthly monitoring for valves (in gas/vapor and light liquid
service), connectors (in gas/vapor and light liquid service), and pumps
(light liquid service) in EtO service at a leak definition of 100 ppm
for valves and connectors and 500 ppm for pumps using EPA Method 21 of
40 CFR part 60, appendix A-7. This combined option also does not allow
equipment in EtO service to be monitored less frequently with skip
periods nor allow facilities to take advantage of the delay of repair
provisions. Increasing the monitoring frequency to monthly was analyzed
for connectors because they are the most numerous equipment components
at chemical facilities, and they contribute the most to the baseline
emissions from leaking equipment at the EtO emitting facilities.
    For the component specific control options, we calculated the EtO
baseline emissions and emissions after implementation of controls for
each facility using average VOC emission rates for each component, and
the component counts and the EtO weight percent of the process from the
responses to the EPA's CAA section 114 request. For the combined option
of monthly monitoring of gas and light liquid valves and connectors at
100 ppm and light liquid pumps at 500 ppm, we do not have emission
factors to estimate reductions for increased monitoring frequencies for
connectors. Where no simplified emission factor method exists to
determine potential reductions of applying the option, we estimated
emissions reductions based on the approach used in other rules,\53\
where detailed leak data was available or where a leak distribution
could be assumed. The equipment leaks model uses a Monte Carlo analysis
to estimate emissions from EtO facility equipment leaks. A detailed
discussion of the model is found in the memorandum Analysis of Control
Options for Equipment Leaks to Reduce Residual Risk of Ethylene Oxide
in the SOCMI Source Category for Processes Subject to HON, which is
available in the docket for this action.
---------------------------------------------------------------------------

    \53\ Gas Plant Equipment Leak Monte Carlo Model Code and
Instructions. October 21, 2021. EPA Docket No. EPA-HQ-OAR-2021-0317.
Control Options for Equipment Leaks at Gasoline Distribution
Facilities. October 20, 2021. EPA Docket No. EPA-HQ-OAR-2020-0371.
---------------------------------------------------------------------------

    We are proposing the same ``in ethylene oxide service'' definition
for equipment as used in MON.\54\ For equipment leaks, we are proposing
to define ``in ethylene oxide service'' in the HON at 40 CFR 63.101 to
mean any equipment that contains or contacts a fluid (liquid or gas)
that is at least 0.1 percent by weight of EtO. For HON equipment in EtO
service, in order to achieve greater emissions reductions to help meet
an acceptable level of risk for the SOCMI source category, we are
proposing the following combined requirements: monitoring of connectors
in gas/vapor and light liquid service at a leak definition of 100 ppm
on a monthly basis with no reduction in monitoring frequency or delay
of repair (see proposed 40 CFR 63.174(a)(3) and 40 CFR
63.174(b)(3)(vi)); light liquid pump monitoring at a leak definition of
500 ppm monthly (see proposed 40 CFR 63.163(b)(2)(iv)); and gas/vapor
and light liquid valve monitoring at a leak definition of 100 ppm
monthly with no reduction in monitoring frequency or delay of repair
(see proposed 40 CFR 63.168(b)(2)(iv) and 40 CFR 63.168(d)(5)).
Additional information on all evaluated control options to reduce EtO
risk from HON equipment leaks is found in the document titled Analysis
of Control Options for Equipment Leaks to Reduce Residual Risk of
Ethylene Oxide in the SOCMI Source Category for Processes Subject to
HON, which is available in the docket for this action.
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    \54\ See 40 CFR 63.2550.
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iii. Heat Exchange Systems
    Emissions of EtO from heat exchange systems occur when a heat
exchanger's internal tubing material corrodes or cracks, allowing some
process fluids to mix or become entrained with the cooling water.
Pollutants (e.g., EtO) in the process fluids may subsequently be
released from the cooling water into the atmosphere when the water is
exposed to air (e.g., in a cooling tower for closed-loop systems or
trenches/ponds in a once-through system). Heat exchange systems subject
to the HON are required to monitor for leaks of process fluids into
cooling water and take actions to repair leaks within 45 days if they
are detected (and facilities may delay the repair of leaks if they meet
certain criteria). The current HON MACT standard for heat exchange
systems allows the use of any method listed in 40 CFR part 136 to be
used to sample cooling water for leaks for the HAP listed in Table 4 to
subpart F (recirculating systems) and Table 9 to subpart G (once-
through systems) (and other representative substances such as TOC or
VOC that can indicate the presence of a leak can also be used). In
addition, the HON allows facilities to monitor for leaks using a
surrogate indicator of leaks (e.g., ion specific electrode monitoring,
pH, conductivity), provided that certain criteria in 40 CFR 63.104(c)
are met. We provide more details about heat exchange systems in our
technology review discussion (see section III.C.1 of this preamble).
    Results from our risk assessment indicate that EtO leaks from heat
exchange systems result in risks of 400-in-1 million at one facility
and 90-in-1 million at another. The HON heat exchange system technology
review (see section III.C.1 of this preamble) identified use of the
Modified El Paso Method as a development in practice for heat exchange
systems at HON-subject facilities. Specifically, we identified the
following control option for heat exchange systems: quarterly
monitoring with the Modified El Paso Method, using a leak action level
defined as a total strippable hydrocarbon concentration (as methane) in
the stripping gas of 6.2 ppmv (and not allowing delay of repair of
leaks for more than 30 days where a total strippable hydrocarbon
concentration (as methane) in the stripping gas of 62 ppmv or higher is
found). This option would also require follow-up monitoring at the same
monitoring location where the leak was identified to ensure that any
leaks found were fixed. For heat exchange systems, we are proposing to
define ``in ethylene oxide

service'' in the HON at 40 CFR 63.101 to mean each heat exchange system
in a process that cools process fluids (liquid or gas) that are 0.1
percent or greater by weight of EtO. To address the risk from EtO
emissions due to HON heat exchange system leaks, we evaluated the
following option for HON heat exchange systems ``in ethylene oxide
service'': (A) require use of the Modified El Paso Method (see section
III.C.1 of this preamble), (B) increase the Modified El Paso Method
monitoring frequency from quarterly to weekly, (C) reduce the allowed
amount of repair time from 45 days after finding a leak to 15 days from
the sampling date, and (D) prohibit delay of repair. We anticipate this
option would reduce EtO emissions from leaking heat exchange systems by
93 percent because leaks would be identified and repaired quicker, and
this is needed to help reduce risk from the SOCMI source category. For
this reason, we are proposing to require weekly monitoring for leaks
for heat exchange systems in EtO service using the Modified El Paso
Method (see proposed 40 CFR 63.104(g)(6)), and if a leak is found, we
are proposing owners and operators must repair the leak to reduce the
concentration or mass emissions rate to below the applicable leak
action level as soon as practicable, but no later than 15 days after
the sample was collected with no delay of repair allowed (see proposed
40 CFR 63.104(h)(6)). Additional information on this evaluated control
option to reduce EtO risk from HON heat exchange systems is found in
the document titled Analysis of Control Options for Heat Exchange
Systems to Reduce Residual Risk of Ethylene Oxide in the SOCMI Source
Category for Processes Subject to HON, which is available in the docket
for this action.
iv. Wastewater
    EtO is emitted into the air from wastewater collection, storage,
and treatment systems that are uncovered or open to the atmosphere
through volatilization of the compound at the liquid surface. Emissions
occur by diffusive or convective means, or both. Diffusion occurs when
organic pollutant concentrations at the water surface are much higher
than ambient concentrations. The organic pollutants volatilize, or
diffuse into the air, to reach equilibrium between the aqueous and
vapor phases. Convection occurs when air flows over the water surface,
sweeping organic vapors from the water surface into the air. The rate
of volatilization is related directly to the speed of the air flow over
the water surface.
    The current HON standards divide wastewater streams into Group 1
wastewater streams, which require controls, and Group 2 wastewater
streams, which generally do not require controls provided they do not
exceed Group 1 thresholds. The Group 1 and Group 2 designations for
wastewater streams are based on volumetric flow rate and total annual
average organic HAP concentration. The HON specifies performance
standards for treating Group 1 wastewater streams using open or closed
biological treatment systems or using a design steam stripper with vent
control. For APCDs (e.g., thermal oxidizers) used to control emissions
from collection system components, steam strippers, or closed
biological treatment, the HON provides owners or operators several
compliance options, including 95 percent destruction efficiency, a 20
ppmv outlet concentration, or design specifications for temperature and
residence time. We provide more details about wastewater streams in our
technology review discussion (see section III.C.5 of this preamble).
    Results from our risk assessment indicate that EtO emissions from
wastewater result in risks of 200-in-1 million at one facility and 70-
in-1 million at another. For wastewater, we are proposing to define
``in ethylene oxide service'' in the HON at 40 CFR 63.101 to mean each
wastewater stream that contains total annual average concentration of
EtO greater than or equal to 1 part per million by weight at any flow
rate. To help reduce the risk from EtO emissions to an acceptable
level, we are proposing that owners and operators of HON sources manage
and treat any wastewater streams that are ``in ethylene oxide service''
(see proposed 40 CFR 63.132(c)(1)(iii) and (d)(1)(ii)) as they would a
Group 1 wastewater stream. Additional information on this evaluated
control option to reduce EtO risk from HON wastewater streams is found
in the document titled Analysis of Control Options for Wastewater
Streams to Reduce Residual Risk of Ethylene Oxide in the SOCMI Source
Category for Processes Subject to HON, which is available in the docket
for this action.
    Finally, we are aware of at least two HON-subject facilities that
reported EtO emissions from heat exchange systems due to disposing EtO
entrained water (e.g., condensate water, quench and glycol bleeds) into
their cooling water. While these are not ``leaks'' from heat exchange
systems, this water is being combined with water in heat exchange
systems that should actually be considered a potential source of
wastewater, as it contains EtO. One of these facilities reported
approximately 2.5 tpy EtO were released to the atmosphere in 2017 from
this activity; the other facility reported about 0.5 tpy EtO emissions
(for 2017) from a similar activity. In order to help reduce risk from
the SOCMI source category to an acceptable level, and in an effort to
eliminate these types of EtO emissions from wastewater being injected
into heat exchange systems, we are also proposing to prohibit owners
and operators from injecting water into or disposing of water through
any heat exchange system in a CMPU meeting the conditions of 40 CFR
63.100(b)(1) through (3) if the water contains any amount of EtO, has
been in contact with any process stream containing EtO, or the water is
considered wastewater as defined in 40 CFR 63.101 (see proposed 40 CFR
63.104(k)).
v. Maintenance Vents
    We are proposing the new term ``maintenance vent'' for process
vents that are only used as a result of startup, shutdown, maintenance,
or inspection of equipment where equipment is emptied, depressurized,
degassed, or placed into service. We provide more details about
maintenance vents in section III.D.4 of this preamble. We identified
three HON-subject facilities that reported EtO emissions from
maintenance vents in their 2017 NEI from HON processes that use and
emit EtO. We determined that, in order to help reduce EtO risk from the
SOCMI source category to an acceptable level, facilities would need to
limit their amount of EtO being emitted through maintenance vents
(i.e., equipment openings). For this reason, we are proposing a
requirement that owners and operators cannot release more than 1.0 ton
of EtO from all maintenance vents combined in any consecutive 12-month
period (see proposed 40 CFR 63.113(k)(4)). We based this proposed limit
on the largest amount of EtO emissions reported in the 2017 NEI for all
maintenance vents combined at any single HON-subject facility (i.e.,
one facility reported about 1 ton of EtO from maintenance activities
which corresponded to 80-in-1 million risk). Facilities could use a
portable thermal oxidizer to control excess EtO emissions from their
maintenance vents in order to meet the proposed 1.0 tpy EtO maintenance
vent limit; \55\ however,

based on the 2017 NEI, we anticipate that all HON-subject facilities
with processes that use and emit EtO can already meet this proposed
emissions limit without additional control.
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    \55\ We surmised that a portable thermal oxidizer is a
reasonable control option for maintenance vents because it would
require a significant effort to identify and characterize each
potential release point to install permanent APCDs.
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vi. Flares
    We determined that to achieve an acceptable level of risk,
facilities need to limit the amount of ethylene oxide they are emitting
from flaring from all HON emission sources at their facility, even
after applying the control options for the other HON emission sources
that we evaluated to reduce risk to an acceptable level. This
determination is supported by the fact that there is one facility with
a risk of 500-in-1 million from flaring EtO and another facility with
risk of 90-in-1 million as a result of this same operation. Therefore,
we are proposing a requirement that owners and operators can send no
more than 20 tons of EtO to all of their flares combined in any
consecutive 12-month period from all HON emission sources at a facility
(see proposed 40 CFR 63.108(p)).
    We identified nine HON-subject facilities that reported the use of
flares in their 2017 NEI to control EtO emissions from HON processes
that use and emit EtO. Two of these facilities each reported about two
times more EtO emissions from their flares than the reported EtO
emissions from all the other seven HON-subject facilities combined.
Based on this reported emissions data, the highest risk source for
flaring emitted a combined total of 2.87 tpy of EtO from its flares. In
order to reduce the HON risk to an acceptable level, the EtO emissions
from all flares would need to be less than or equal to 0.40 tpy (in
addition to complying with other standards designed to reduce risk to
an acceptable level). Assuming 98 percent flare control efficiency and
back-calculating an EtO waste gas flare load, the maximum inlet load to
all flares combined would need to be 20 tpy. Using the reported EtO
emissions of 2.87 tpy from the highest emitting facility, we estimate
that the facility's current combined total EtO load to flares is about
143.5 tpy, and that the facility would need to reduce the combined
total EtO load to their flares by about 124 tpy to meet the EtO load
limit of 20 tpy. For these reasons, we are proposing a requirement that
owners and operators can send no more than 20 tons of EtO to all of
their flares combined in any consecutive 12-month period (see proposed
40 CFR 63.108(p)) to get to an acceptable level of risk from all HON
emission sources at a facility. A more thorough discussion of this
analysis is included in the document titled Analysis of Control Options
for Flares to Reduce Residual Risk of Ethylene Oxide in the SOCMI
Source Category for Processes Subject to HON, which is available in the
docket for this action.
vii. PRDs
    The HON currently regulates PRDs through equipment leak provisions
that are applied only after the pressure release event relief occurs
(i.e., conduct monitoring with EPA Method 21 of Appendix A-7 to 40 CFR
part 60 after each pressure release using a leak definition of 500 ppm)
to ensure they are properly reseated and not leaking after a PRD
release occurs; however, these provisions do not apply to an emissions
release from a PRD (see section III.D.2 of this preamble for more
detail). As previously discussed in section III.B.2.a.i of this
preamble, we are aware of some instances where PRD releases of EtO
emissions occurred for gas streams that would otherwise be treated as
process vents. These PRD releases contribute to a large portion of the
2000-in-1 million MIR (i.e., 75 percent) that we are proposing is
unacceptable. While the EPA is proposing to set work practice standards
for PRD releases (see section III.D.2 of the preamble), in order to
help reduce risk from the SOCMI source category to an acceptable level
we are also proposing at 40 CFR 63.165(e)(3)(v)(D) that any release
event from a PRD in EtO service is a violation of the standard to
ensure that these process vent emissions are controlled and do not
bypass controls.
viii. Summary
    For process vents, storage vessels, equipment leaks, heat exchange
systems, wastewater, maintenance vents, flares, and PRDs, we considered
the control options described above for reducing EtO risk from the
SOCMI source category that are associated with processes subject to the
HON. To reduce risk from the source category to an acceptable level, we
propose to require control of EtO emissions from: (1) Process vents,
(2) storage vessels, (3) equipment leaks, (4) heat exchange systems,
and (5) wastewater ``in ethylene oxide service'' (defined in this
proposal). We are also proposing requirements to reduce EtO emissions
from maintenance vents, flares, and PRDs. For process vents and storage
vessels in EtO service, we are proposing owners and operators reduce
emissions of EtO by either: (1) Venting emissions through a closed-vent
system to a control device that reduces EtO by greater than or equal to
99.9 percent by weight, to a concentration less than 1 ppmv for each
process vent and storage vessel, or to less than 5 lb/yr for all
combined process vents; or (2) venting emissions through a closed-vent
system to a flare meeting the proposed operating and monitoring
requirements for flares in NESHAP subpart F. For equipment leaks in EtO
service, we are proposing the following combined requirements:
monitoring of connectors in gas/vapor and light liquid service at a
leak definition of 100 ppm on a monthly basis with no reduction in
monitoring frequency and no delay of repair; light liquid pump
monitoring at a leak definition of 500 ppm monthly; and gas/vapor and
light liquid valve monitoring at a leak definition of 100 ppm monthly
with no reduction in monitoring frequency and no delay of repair. For
heat exchange systems in EtO service, we are proposing to require
owners or operators to conduct more frequent leak monitoring (weekly
instead of quarterly) and repair leaks within 15 days from the sampling
date (in lieu of the current 45-day repair requirement after receiving
results of monitoring indicating a leak), and delay of repair would not
be allowed. For wastewater in EtO service, we are proposing to revise
the Group 1 wastewater stream threshold for sources to include
wastewater streams in EtO service. For maintenance vents, we are
proposing a requirement that owners and operators cannot release more
than 1.0 ton of EtO from all maintenance vents combined in any
consecutive 12-month period. For flares, we are proposing a requirement
that owners and operators can send no more than 20 tons of EtO to all
of their flares combined from all HON emission sources at a facility in
any consecutive 12-month period. For PRDs in EtO service, we are
proposing that any atmospheric PRD release is a violation of the
standard.
    In all cases, we are proposing that if information exists that
suggests EtO could be present in these processes, then the emission
source is considered to be in EtO service unless sampling and analysis
is performed to demonstrate that the emission source does not meet the
definition of being in EtO service. We are proposing sampling and
analysis procedures at 40 CFR 63.109. Examples of information that
could suggest EtO is present in a process stream include calculations
based on safety data sheets, material balances, process stoichiometry,
or previous test results provided the results are still relevant to the
current operating conditions.
    Based on the proposed applicability thresholds, we expect that up
to 17 facilities will be affected by one or more

of the proposed EtO-specific standards; and we anticipate that all of
these facilities will be subject to the process vent, storage vessel,
equipment leak, wastewater, and PRD provisions. We do not expect any
facility to be impacted by the proposed 1.0 tpy maintenance vent EtO
emission limit, and only two facilities will be affected by the
proposed 20 tpy EtO flare load limit, although all facilities will be
required to comply with these standards.
b. Chloroprene Controls for P&R I Neoprene Production Processes
i. Process Vents and Storage Vessels
    Results from our risk assessment indicate that for the Neoprene
Production source category, 65 percent of the risk presented by
neoprene production processes (i.e., 300-in-1 million) and 12 of the
17.5 tpy of chloroprene in the reported emissions inventory are from
emissions associated with reaction processes and supporting equipment,
and storage vessels at the one neoprene production facility.
Specifically, 58 percent of the risk is associated with emissions from
the polymer building wall fans housing much of the operations for
creating neoprene, of which most of the emissions are from the opening
of the polymer reactors and straining of coagulate generated after the
batch polymerization occurs to make neoprene; 5 percent of the risk is
from emissions from unstripped emulsion storage vessels as they are
being opened and/or degassed; and 2 percent of the risk is from
emissions from the wash belt dryers. An additional 18 percent of the
risk is from wastewater sources, which are discussed in III.B.2.b.ii of
this preamble.
    For process vents, we are proposing to define ``in chloroprene
service'' in P&R I at 40 CFR 63.482 to mean each continuous front-end
process vent and each batch front-end process vent in a process at
affected sources producing neoprene that, when uncontrolled, contains a
concentration of greater than or equal to 1 ppmv undiluted chloroprene,
and when combined, the sum of all these process vents would emit
uncontrolled, chloroprene emissions greater than or equal to 5 lb/yr
(2.27 kg/yr). For storage vessels, we are proposing to define ``in
chloroprene service'' in P&R I at 40 CFR 63.482 to mean storage vessels
of any capacity and vapor pressure in a process at affected sources
producing neoprene storing a liquid that is at least 0.1 percent by
weight of chloroprene, which would require control of the unstripped
resin storage vessels and emissions from opening or degassing of these
sources. Additionally, we are proposing that unless specified by the
Administrator, owners and operators may calculate the concentration of
chloroprene of the fluid stored in a storage vessel if information
specific to the fluid stored is available such as concentration data
from safety data sheets. We are proposing to require emissions from
process vents and storage vessels in chloroprene service be routed to a
closed vent system to a non-flare control device that reduces
chloroprene by greater or equal to 99.9 percent by weight, or to a
concentration less than 1 ppmv for each process vent or storage vessel
vent, or less than 5 pounds per year for all combined process vents.
(see proposed 40 CFR 63.484(u)(1), 40 CFR 63.485(y)(1), and 40 CFR
63.487(j)(1)). Our proposed approach would require control of process
vent emissions from batch polymer reactors that the one neoprene
facility has already voluntarily controlled (but that are not currently
required to be controlled in P&R I) and that are considered in the
baseline emissions of our risk assessment. These proposed standards
would also capture emissions from the emulsion storage vessels,
strainers, and wash belt dryers. We determined that the only viable way
to meet these proposed standards is to enclose all of the polymer batch
reactors, emulsion storage vessels, strainers, and wash belt dryers and
route the vapors to a thermal oxidizer (and thereby reduce chloroprene
emissions from these sources, which are fugitive in nature). We costed
out permanent total enclosures, a thermal oxidizer, and ductwork and
associated support equipment using the procedures in EPA's Control Cost
Manual. Enclosing and routing vapors to a thermal oxidizer is expected
to achieve at least 99.9 percent reduction in chloroprene emissions
from the storage vessels and wash belt dryers. Due the openness of the
polymer building and other emission sources that could contribute to
emissions coming from the polymer building overall, we estimate that 90
percent of the chloroprene emissions will be collected in the
enclosures and be reduced by at least 99.9 percent in the thermal
oxidizer. The result of the control option is to reduce chloroprene
emissions and risk from the polymer building, unstripped resin emulsion
storage vessels, and the wash belt dryers from 12 tpy to 0.7 tpy.
Because of concerns that some of these emission sources may not
necessarily be considered process vents or emissions regulated for
storage vessels (e.g., since we are assuming permanent total enclosures
will be needed to collect these emissions since they could be
fugitive), we are also proposing a facility-wide chloroprene emissions
cap for all neoprene production emission sources as a backstop, the
result of which is based on our post-control emissions and risk for all
neoprene emission sources emitting chloroprene that are reported in the
emissions inventory and which is discussed in section III.B.2.b.v of
this preamble.
    Additional information on this evaluated control option to reduce
chloroprene risk from fugitives from polymer batch reactors, emulsion
storage vessels, strainers, and wash belt dryers with affected P&R I
sources producing neoprene is found in the document titled Analysis of
Control Options for Process Vents and Storage Vessels to Reduce
Residual Risk of Chloroprene Emissions at P&R I Affected Sources
Producing Neoprene, which is available in the docket for this action.
ii. Wastewater
    Chloroprene is emitted into the air from wastewater collection,
storage, and treatment systems that are uncovered or open to the
atmosphere through volatilization of the compound at the liquid
surface. Emissions occur by diffusive or convective means, or both.
Diffusion occurs when organic concentrations at the water surface are
much higher than ambient concentrations. The organics volatilize, or
diffuse into the air, to reach equilibrium between aqueous and vapor
phases. Convection occurs when air flows over the water surface,
sweeping organic vapors from the water surface into the air. The rate
of volatilization is related directly to the speed of the air flow over
the water surface.
    Similar to the HON, as discussed in section III.B.2.a.iv of this
preamble, the current P&R I standards divide wastewater streams into
Group 1 wastewater streams, which require controls, and Group 2
wastewater streams, which generally do not require controls provided
they remain below Group 1 thresholds. The Group 1 and Group 2
designations for wastewater streams are based on volumetric flow rate
and total annual average organic HAP concentration. P&R I specifies
performance standards for treating Group 1 wastewater streams using
open or closed biological treatment systems or using a design steam
stripper with vent control. For APCDs (e.g., thermal oxidizers) used to
control emissions from collection system components, steam strippers,
or closed biological treatment, P&R I provides owners or

operators several compliance options, including 95 percent destruction
efficiency, a 20 ppmv outlet concentration, or design specifications
for temperature and residence time. We provide more details about
wastewater streams in our technology review.
    Results from our risk assessment indicate that, for the Neoprene
Production source category, 18 percent of the risk (i.e., 80-in-1
million) and 2.6 of the 17.5 tpy of chloroprene in the reported
emissions inventory are from emissions associated with wastewater. For
wastewater, we are proposing to define ``in chloroprene service'' in
P&R I at 40 CFR 63.482 to mean each wastewater stream that contains
total annual average concentration of chloroprene greater than or equal
to 10.0 ppmw at any flow rate. To address the risk from chloroprene
emissions related to wastewater associated with affected P&R I sources
producing neoprene, we are proposing that owners and operators manage
and treat any existing wastewater streams that are ``in chloroprene
service'' (see proposed 40 CFR 63.501(a)(10)(iv)) as they would a Group
1 wastewater stream. Additional information on this evaluated control
option to reduce chloroprene risk from wastewater streams associated
with affected P&R I sources producing neoprene is found in the document
titled Analysis of Control Options for Wastewater Streams to Reduce
Residual Risk of Chloroprene From Neoprene Production Processes Subject
to P&R I, which is available in the docket for this action.
    Finally, for consistency with our proposal for the HON to eliminate
EtO emissions from wastewater being injected into heat exchange systems
(see section III.B.2.a.iv of this preamble), we are also proposing to
prohibit owners and operators from injecting water into or disposing of
water through any heat exchange system in an EPPU if the water contains
any amount of chloroprene, has been in contact with any process stream
containing chloroprene, or the water is considered wastewater as
defined in 40 CFR 63.482 (see proposed 40 CFR 63.502(n)(8)). The result
of all these wastewater controls will reduce chloroprene emissions from
wastewater from 2.6 tpy to 0.18 tpy in the reported emissions
inventory.
iii. Maintenance Vents
    We are proposing at 40 CFR 63.485(x) and 40 CFR 63.487(i) the new
term ``maintenance vent'' for process vents that are only used as a
result of startup, shutdown, maintenance, or inspection of equipment
where equipment is emptied, depressurized, degassed, or placed into
service. We provide more details about maintenance vents in section
III.D.4 of this preamble as well. We evaluated the option of limiting
the amount of chloroprene that a neoprene production facility can emit
annually through maintenance vents (i.e., equipment openings). Using
their reported emissions, we determined that in order to reduce the
neoprene source category risk to an acceptable level, the one neoprene
production facility would need to (in addition to complying with other
standards designed to reduce chloroprene risk) maintain its combined
total chloroprene maintenance vent emission releases at less than or
equal to 1.0 tpy. For this reason, we are proposing a requirement that
owners and operators cannot release more than 1.0 tons of chloroprene
from all maintenance vents combined in any consecutive 12-month period
(see proposed 40 CFR 63.485(z) and 40 CFR 63.487(i)(4)). We note that,
based on reported emissions, the neoprene production facility is
already meeting this proposed 1.0 tpy chloroprene maintenance vent
limit from its neoprene processes.\56\
---------------------------------------------------------------------------

    \56\ From reported Neoprene Unit Condition XVII permitted
emissions.
---------------------------------------------------------------------------

iv. PRDs
    P&R I currently regulates PRDs through equipment leak provisions
that are applied only after the pressure release event relief occurs
(i.e., conduct monitoring with EPA Method 21 of Appendix A-7 to 40 CFR
part 60 after each pressure release using a leak definition of 500 ppm)
to ensure they are properly reseated and not leaking after a PRD
release occurs; however, these provisions do not apply to an emissions
release from a PRD (see section III.D.2 of this preamble for more
detail). While we are not aware of PRD releases occurring from the
Neoprene Production source category, we are concerned that allowing
them could compound already unacceptable risk. Thus, while the EPA is
proposing to set work practice standards for PRD releases (see section
III.D.2 of the preamble), given the high potential risk posed by
chloroprene from PRD releases, we are also proposing at 40 CFR
63.165(e)(3)(v)(D) (by way of proposed 40 CFR 63.502(a)(2)) that any
release event from PRDs in chloroprene service in the Neoprene
Production source category facilities is a violation of the standard.
This is the same provision that we finalized in the MON for PRDs in EtO
service (see 40 CFR 63.2493(d)(4)(iv)), and that we are proposing for
HON PRDs in EtO service, to ensure that these emissions are controlled
and do not bypass controls.
v. Summary
    For process vents, storage vessels, wastewater, maintenance vents,
and PRDs, we considered the control options described above for
reducing chloroprene risk from the Neoprene Production source category.
To reduce risk from the source category to an acceptable level, we
propose to require control of chloroprene for: (1) Process vents, (2)
storage vessels, and (3) wastewater ``in chloroprene service'' (defined
in this proposal). We are also proposing requirements to reduce
chloroprene emissions from maintenance vents and PRDs. For process
vents and storage vessels in chloroprene service, we are proposing
owners and operators reduce emissions of chloroprene by venting
emissions through a closed-vent system to a control device that reduces
chloroprene by greater than or equal to 99.9 percent by weight, to a
concentration less than 1 ppmv for each process vent and storage
vessel, or to less than 5 lb/yr for all combined process vents. For
wastewater in chloroprene service, we are proposing to revise the Group
1 wastewater stream threshold for sources to include wastewater streams
in chloroprene service. For maintenance vents, we are proposing a
requirement that owners and operators cannot release more than 1.0 ton
of chloroprene from all maintenance vents combined in any consecutive
12-month period. For PRDs in chloroprene service, we are proposing that
any atmospheric PRD release is a violation of the standard. Lastly, in
order to ensure reductions in emissions and risk given that many
sources within the neoprene process are fugitive in nature, we are also
proposing a facility-wide chloroprene emissions cap for all neoprene
production emission sources as a backstop. After application of the
proposed controls to address unacceptable risk for process vents,
storage vessels, wastewater, maintenance vents, and PRDs, and including
remaining sources of emissions in the emissions inventory (e.g.,
equipment leaks), we are proposing at 40 CFR 63.483(a)(10) a facility-
wide chloroprene emissions cap of 3.8 tpy in any consecutive 12-month
period for all neoprene production emission sources.
    In all cases, we are proposing that if information exists that
suggests chloroprene could be present in these processes, then the
emission source is considered to be in chloroprene service unless
sampling and analysis is performed to demonstrate that the

emission source does not meet the definition of being in chloroprene
service. We are proposing sampling and analysis procedures at 40 CFR
63.509. Examples of information that could suggest chloroprene is
present in a process stream include calculations based on safety data
sheets, material balances, process stoichiometry, or previous test
results provided that the results are still relevant to the current
operating conditions.
    Based on the proposed applicability thresholds, we expect that only
one facility (i.e., the neoprene production facility) will be affected
by the proposed chloroprene-specific standards, and we anticipate that
this facility will be subject to the process vent, storage vessel,
wastewater, maintenance vent, and PRD provisions.
3. Determination of Risk Acceptability After Proposed Emission
Reductions
    As noted in sections II.A.1 and II.E of this preamble and in the
1989 Benzene NESHAP, the EPA sets standards under CAA section 112(f)(2)
using a two-step approach, with an analytical first step to determine
whether risks are acceptable. This determination ``considers all health
information, including risk estimation uncertainty, and includes a
presumptive limit on maximum individual lifetime [cancer] risk (MIR) of
approximately 1 in 10 thousand'' (54 FR 38044, 38045/col. 1, September
14, 1989). In the 1989 Benzene NESHAP, the EPA explained that ``[i]n
establishing a presumption for MIR, rather than a rigid line for
acceptability, the Agency intends to weigh it with a series of other
health measures and factors'' (id., at 38045/ col. 3). ``As risks
increase above this benchmark, they become presumptively less
acceptable under section 112, and would be weighed with the other
health risk measures and information in making an overall judgement on
acceptability'' (id.).
a. SOCMI
    Presented in the Table 4 of this preamble are the levels of
emissions control proposed to address unacceptable risks for the SOCMI
source category. This includes reducing emissions of EtO for HON
processes and requiring more stringent controls for process vents,
storage vessels, equipment leaks, heat exchange systems, wastewater,
maintenance vents, flares, and PRDs without considering costs.

Table 4--Nationwide EtO Risk Impact Control Options for the SOCMI Source
                                Category
------------------------------------------------------------------------
                                                             Percent
        Emission source             Description of      reduction of EtO
                                    proposed option         emissions
------------------------------------------------------------------------
Process Vent Controls \1\.....  Control emissions       99.9 percent.
                                 through a closed-vent
                                 system to a non-flare
                                 control device that
                                 reduces EtO by
                                 greater than or equal
                                 to 99.9 percent by
                                 weight, to a
                                 concentration less
                                 than 1 ppmv for each
                                 process vent, or to
                                 less than 5 lb/yr for
                                 all combined process
                                 vents.
Storage Vessel Controls \1\...  Control emissions       99.9 percent.
                                 through a closed-vent
                                 system to a non-flare
                                 control device that
                                 reduces EtO by
                                 greater than or equal
                                 to 99.9 percent by
                                 weight or to a
                                 concentration less
                                 than 1 ppmv.
Equipment Leak Controls.......  Monthly M21 monitoring  70-74 percent.
                                 of valves and
                                 connectors with a 100
                                 ppm leak definition
                                 and monthly
                                 monitoring of pumps
                                 at 500 ppm leak
                                 definition without
                                 skip periods or delay
                                 of repair for these
                                 pieces of equipment
                                 that are in EtO
                                 service.
Heat Exchange Systems Controls  Weekly monitoring for   93 percent.
                                 leaks using the
                                 Modified El Paso
                                 Method and repair of
                                 leaks required no
                                 later than 15 days
                                 after date of weekly
                                 sampling occurs.
Wastewater Controls...........  Control all wastewater  98 percent.
                                 with a total annual
                                 average concentration
                                 of EtO greater than
                                 or equal to 1 ppmw at
                                 any flow rate as if
                                 it were Group 1
                                 wastewater.
Maintenance Vent Emission Cap.  1.0 tpy limit.........  Proposing to
                                                         limit to
                                                         existing level
                                                         in emissions
                                                         inventory.
Flare Load Limit..............  20 tpy limit on amount  Site specific
                                 of EtO that could be    and would
                                 sent to a flare.        likely require
                                                         two facilities
                                                         to use a 99.9
                                                         percent control
                                                         rather than a
                                                         flare achieving
                                                         98 percent.
PRD releases..................  Work practice           Assumed 99.9
                                 standards make          percent
                                 atmospheric releases    control, as it
                                 from PRDs in EtO        would be
                                 service a violation     controlled as a
                                 from the standard.      process vent.
------------------------------------------------------------------------
\1\ Flares may also be used up to the flare load limit, though we do not
  expect this to occur given facilities would need to meet these more
  stringent control requirements after reaching the 20 tpy load limit.

    For the SOCMI source category, after implementation of the proposed
controls to address unacceptable risks, the MIR is reduced to 100-in-1
million (down from 2,000-in-1 million) with no facilities or
populations exposed to risk levels greater than 100-in-1 million. The
total population exposed to risk levels greater than or equal to 1-in-1
million living within 50 km (~31 miles) of a facility would be reduced
from 7.2 million people to 5.7 million people. The total estimated
cancer incidence of 2 drops to 0.4 excess cancer cases per year. The
maximum modeled chronic noncancer TOSHI for the source category remains
unchanged. It is estimated to be 2 (for respiratory effects) at two
different facilities (from maleic anhydride emissions at one facility
and chlorine emissions at another facility) with approximately 83
people estimated to be exposed to a TOSHI greater than 1. The estimated
worst-case off-site acute exposures to emissions from the SOCMI source
category also remain
unchanged, with a maximum modeled acute HQ of 3 based on the RELs for
chlorine and acrolein. Table 5 of this preamble summarizes the
reduction in cancer risks based on the proposed controls.

          Table 5--Cancer Risks After Implementation of Proposed Control for the SOCMI Source Category
----------------------------------------------------------------------------------------------------------------
                                        MIR (x-in-1      Population (>=1-   Population (>100-
          Control scenario                million)        in-1 million)       in-1 million)     Cancer incidence
----------------------------------------------------------------------------------------------------------------
Pre-Control Baseline...............              2,000          7,200,000              87,000                  2
Post-Control.......................                100          5,700,000                   0                0.4
----------------------------------------------------------------------------------------------------------------

    As noted earlier in this section, the EPA considers an MIR of
``approximately 1-in-10 thousand'' (i.e., 100-in-1 million) to be the
presumptive limit of acceptability (54 FR 38045, September 14, 1989)
and the proposed controls lower the MIR to 100-in-1 million. This is a
significant reduction from the pre-control MIR of 2,000-in-1 million.
For noncancer effects, the EPA has not established under section 112 of
the CAA a numerical range for risk acceptability as it has with
carcinogens, nor has it determined that there is a bright line above
which acceptability is denied. However, the Agency has established
that, as exposure increases above a reference level (as indicated by a
HQ or TOSHI greater than 1), confidence that the public will not
experience adverse health effects decreases and the likelihood that an
effect will occur increases.
    In considering the potential implications of HIs above 1 (and equal
to 2) for chlorine and maleic anhydride emissions, we note the basis
and development of the underlying noncancer health benchmarks. Both
chlorine and maleic anhydride are portal of entry irritants that, with
sufficient exposure, act as potent irritants of the eyes and
respiratory tract. Chronic exposure in human workers has been
associated with airflow obstruction and asthma-like attacks, indicating
a potential for people with asthma to have greater sensitivity to
effects of these pollutants. The health benchmarks for chlorine and
maleic anhydride represent exposure levels at (and below) which there
is not likely to be appreciable risk of deleterious effects over a
lifetime exposure, including for sensitive groups; however, the EPA has
not estimated an exposure level at and above which an appreciable risk
of deleterious effects would be expected.
    In the case of chlorine, the sensitive effect on which the
benchmark is based is an increased risk of nasal lesions. The chronic
exposure level at which this effect, which was observed in an
experimental animal study, is estimated is 0.004 mg/m\3\.\57\ \58\ In
the case of maleic anhydride, the sensitive effect is the occurrence of
mild hyperplasia in the nasal epithelium.59 60 The chronic
exposure level at which this effect, which was observed in several
experimental animal studies, is estimated is 0.021 mg/m\3\. To derive
the chronic health benchmarks, both of these human equivalent exposure
values were divided by 30 to account for the potential for people to be
more sensitive than animals and for some population groups, such as
people with asthma, to be more sensitive than the general population.
---------------------------------------------------------------------------

    \57\ Agency for Toxic Substances and Disease Registry (ATSDR).
2010. Toxicological profile for Chlorine. Atlanta, GA: U.S.
Department of Health and Human Services, Public Health Service.
    \58\ Klonne DR, Ulrich CE, Riley MG, et al. 1987. One-year
inhalation toxicity study of chlorine in Rhesus monkeys (Macaca
mulatta). Fundam Appl Toxicol 9:557-572.
    \59\ Office of Environmental Health Hazard Assessment (OEHHA).
2008. Technical Supporting Document for Noncancer RELs, Appendix D3.
    \60\ Short RD, Minor JL, Winston JM, Seifter J, and Lee C. 1978.
Inhalation of ethylene dibromide during gestation by rats and mice.
Toxicol. Appl. Pharmacol. 46:173-182.
---------------------------------------------------------------------------

    For both chlorine and maleic hydride, we note the small size of the
HI (2) in relation to the total uncertainty factor of 30 used in
derivation of both health benchmarks. In so doing, we also note a
somewhat reduced confidence in a conclusion that exposure at these
levels is without appreciable risk due to uncertainty, particularly for
sensitive populations. Finally, we note that the population exposed to
a TOSHI greater than 1 is relatively small (83 people).
    Therefore, considering all health information, including risk
estimation uncertainty, the EPA proposes that the resulting risks after
implementation of the proposed controls for the SOCMI source category
detailed in Section III.B.2.a. would be acceptable. We solicit comment
on all the proposed control requirements to reduce risk to an
acceptable level for the SOCMI source category.
b. Neoprene Production
    Presented in Table 6 of this preamble are the levels of emissions
control proposed to address unacceptable risks for the Neoprene
Production source category. This includes emission reductions of
chloroprene from process vents, storage vessels, wastewater,
maintenance vents, and PRDs without considering costs, as well as a
facility-wide emissions cap for chloroprene from all Neoprene
Production emission sources.

   Table 6--Nationwide Chloroprene Risk Impact Control Options for the
                   Neoprene Production Source Category
------------------------------------------------------------------------
                                                             Percent
                                    Description of        reduction of
        Emission source             proposed option        chloroprene
                                                            emissions
------------------------------------------------------------------------
Process Vent Controls.........  Control emissions       99.9 percent.
                                 through a closed-vent
                                 system to a non-flare
                                 control device that
                                 reduces chloroprene
                                 by greater than or
                                 equal to 99.9 percent
                                 by weight, to a
                                 concentration less
                                 than 1 ppmv for each
                                 process vent, or to
                                 less than 5 lb/yr for
                                 all combined process
                                 vents. This includes
                                 also capturing and
                                 controlling emissions
                                 from opening of the
                                 polymer reactors and
                                 strainers.
Storage Vessel Controls.......  Control emissions       99.9 percent.
                                 through a closed-vent
                                 system to a non-flare
                                 control device that
                                 reduces chloroprene
                                 by greater than or
                                 equal to 99.9 percent
                                 by weight or to a
                                 concentration less
                                 than 1 ppmv. This
                                 includes also
                                 capturing and
                                 controlling emissions
                                 from opening and/or
                                 degassing of the
                                 unstripped resin
                                 emulsion tanks.

Wastewater Controls...........  Control all wastewater  93 percent.
                                 with a total annual
                                 average concentration
                                 of chloroprene
                                 greater than or equal
                                 to 10 ppmw at any
                                 flow rate as if it
                                 were Group 1
                                 wastewater.
Maintenance Vent Emission Cap.  1.0 tpy limit.........  Proposing to
                                                         limit to
                                                         existing level
                                                         in emissions
                                                         inventory.
PRD releases..................  Work practice           None were
                                 standards make          reported in
                                 atmospheric releases    emissions
                                 from PRDs in            inventory,
                                 chloroprene service a   proposing
                                 violation from the      standard to
                                 standard.               ensure this
                                                         remains the
                                                         case.
Facility-wide emissions cap     3.8 tpy limit, which    79 percent.
 for chloroprene from all        is a backstop to
 Neoprene Production emission    ensure reductions in
 sources.                        emissions and risk
                                 given that many
                                 sources within the
                                 neoprene process are
                                 fugitive.
------------------------------------------------------------------------

    For the Neoprene Production source category, after implementation
of the proposed controls to address unacceptable risks, the MIR is
reduced to 100-in-1 million (down from 500-in-1 million) with zero
people exposed to risk levels greater than 100-in-1 million. The total
population exposed to risk levels greater than or equal to 1-in-1
million living within 50 km (~31 miles) of the facility would be
reduced from 690,000 people to 48,000 people. The total estimated
cancer incidence of 0.05 drops to 0.008 excess cancer cases per year.
Table 7 of this preamble summarizes the reduction in cancer risks based
on the proposed controls.

  Table 7--Nationwide Risk Impacts After Implementation of Proposed Controls for the Neoprene Production Source
                                                    Category
----------------------------------------------------------------------------------------------------------------
                                         MIR (x-in-1      Population (>=1-  Population (>100-
          Control scenario                 million)        in-1 million)      in-1 million)     Cancer incidence
----------------------------------------------------------------------------------------------------------------
Pre-Control Baseline................                500            690,000              2,100               0.05
Post-Control........................                100             48,000                  0              0.008
----------------------------------------------------------------------------------------------------------------

    Again, as noted earlier in this section, the EPA considers an MIR
of ``approximately 1-in-10 thousand'' (i.e., 100-in-1 million) to be
the presumptive limit of acceptability (54 FR 38045, September 14,
1989) and the proposed controls lower the MIR to 100-in-1 million, a
significant reduction in the pre-control MIR of 500-in-1 million.
Therefore, after implementation of the proposed controls for the
Neoprene Production source category detailed in Section III.B.2.a. and
considering all health information, including risk estimation
uncertainty, the EPA proposes that the resulting risks would be
acceptable for the Neoprene Production source category. We solicit
comment on all the proposed control requirements to reduce risk to an
acceptable level for the source category.
4. Ample Margin of Safety Analysis
    The second step in the residual risk decision framework is a
determination of whether the emission standards proposed to achieve an
acceptable risk level provide an ample margin of safety to protect
public health, or whether more stringent emission standards would be
required for this purpose. In making this determination, we considered
the health risk and other health information considered in our
acceptability determination, along with additional factors not
considered in the risk acceptability step, including costs and economic
impacts of controls, technological feasibility, uncertainties, and
other relevant factors, consistent with the approach of the 1989
Benzene NESHAP. Table 8 of this preamble presents the summary of costs
and EtO emission reductions we estimated for the proposed control
requirements to get the risks to an acceptable level for the SOCMI
source category. For details on the assumptions and methodologies used
in the costs and impacts analyses, see the technical documents titled,
Analysis of Control Options for Process Vents and Storage Vessels to
Reduce Residual Risk of Ethylene Oxide in the SOCMI Source Category for
Processes Subject to HON; Analysis of Control Options for Equipment
Leaks to Reduce Residual Risk of Ethylene Oxide in the SOCMI Source
Category for Processes Subject to HON; Analysis of Control Options for
Heat Exchange Systems to Reduce Residual Risk of Ethylene Oxide in the
SOCMI Source Category for Processes Subject to HON; Analysis of Control
Options for Wastewater Streams to Reduce Residual Risk of Ethylene
Oxide in the SOCMI Source Category for Processes Subject to HON; and
Analysis of Control Options for Flares to Reduce Residual Risk of
Ethylene Oxide in the SOCMI Source Category for Processes Subject to
HON, which are available in the docket for this rulemaking. We note
that for two fugitive EtO emission sources (i.e., equipment leaks and
wastewater), emission reductions (and subsequent cost-effectiveness
values for EtO) differ from reductions expected to occur from reported
emissions inventories due to use of model plants, engineering
assumptions made to estimate baseline emissions, and uncertainties in
how fugitive emissions may have been calculated for reported
inventories compared to our model plants analyses (and are documented
in the aforementioned technology review memorandum).

  Table 8--Nationwide EtO Emission Reductions and Cost Impacts for Control Options Considered for HON Processes
----------------------------------------------------------------------------------------------------------------
                                                   Total capital       Total       EtO emission        Cost
                 Control option                     investment      annualized      reductions     effectiveness
                                                       (MM$)      costs (MM$/yr)       (tpy)        ($/ton EtO)
----------------------------------------------------------------------------------------------------------------
A--Process Vent & Storage Vessel Controls.......            10.2            5.28            32.0         165,000
B--Equipment Leak Controls......................            0.18            3.53            42.3          83,500
C--Heat Exchange System Controls................           0.043            0.19            6.06          31,400
D--Wastewater Controls..........................            65.8            41.1             396         103,800
E--Maintenance Vent Emission Cap \1\............           0.017          0.0027               0             N/A
F--Flare Load Limit.............................            0.28            0.46            5.04          91,300
                                                 ---------------------------------------------------------------
    Total (A + B + C + D + E + F)...............            76.5            50.6             481         105,000
----------------------------------------------------------------------------------------------------------------
\1\ We anticipate that all facilities with HON processes that use and emit EtO can already meet the proposed
  maintenance vent emissions limit without additional control, thus only minimal costs are included.

    Table 9 of this preamble presents the summary of costs and
chloroprene emission reductions we estimated for the proposed control
options to get the risks to an acceptable level for the Neoprene
Production source category. For details on the assumptions and
methodologies used in the costs and impacts analyses, see the technical
documents titled Analysis of Control Options for Process Vents and
Storage Vessels to Reduce Residual Risk of Chloroprene Emissions at P&R
I Affected Sources Producing Neoprene; and Analysis of Control Options
for Wastewater Streams to Reduce Residual Risk of Chloroprene From
Neoprene Production Processes Subject to P&R I, which are available in
the docket for this rulemaking. We note that chloroprene emission
reductions from wastewater (and subsequent cost-effectiveness values
for chloroprene from wastewater) differ from reductions expected to
occur from reported emissions inventories due to use of model plants,
engineering assumptions made to estimate baseline emissions, and
uncertainties in how fugitive emissions may have been calculated for
reported inventories compared to our model plants analysis (and are
documented in the aforementioned memorandum).

  Table 9--Nationwide Chloroprene Emission Reductions and Cost Impacts for Control Options Considered for P&R I
                                          Processes Producing Neoprene
----------------------------------------------------------------------------------------------------------------
                                                                                Chloroprene        Cost
                                                   Total capital       Total         emission      effectiveness
                 Control option                     investment      annualized      reductions        ($/ton
                                                       (MM$)      costs (MM$/yr)       (tpy)       chloroprene)
----------------------------------------------------------------------------------------------------------------
A--Process Vent, Storage Vessel, & Maintenance              10.1            2.80            11.3         247,800
 Vent Controls..................................
B--Wastewater Controls..........................            5.84            7.56            17.7         427,000
                                                 ---------------------------------------------------------------
    Total (A + B)...............................            15.9            10.4            29.0         359,000
----------------------------------------------------------------------------------------------------------------

    For the ample margin of safety analyses, we evaluated the cost and
feasibility of available control technologies that could be applied to
HON processes and neoprene production processes to reduce risks
further, considering all of the health risks and other health
information considered in the risk acceptability determination
described above and the additional information that can be considered
only in the ample margin of safety analysis (i.e., costs and economic
impacts of controls, technological feasibility, uncertainties, and
other relevant factors). We note that the EPA previously made a
determination that the standards for the SOCMI source category and
Neoprene Production source category provide an ample margin of safety
to protect public health, and that the most significant changes since
that determination were the revised 2016 IRIS inhalation URE for EtO
and new 2010 IRIS inhalation URE for chloroprene. As such, we focused
our ample margin of safety analysis on cancer risk for these two
pollutants since EtO, even after application of controls needed to get
risks to an acceptable level, drives cancer risk and cancer incidence
(i.e., 60 percent of remaining cancer incidence is from EtO) for the
SOCMI source category and almost all the remaining cancer risk and
cancer incidence (i.e., 99.995 percent of remaining cancer incidence)
is from chloroprene for the Neoprene Production source category.
    For the SOCMI source category, no other control options for EtO
were identified beyond those proposed to reduce risks to an acceptable
level. Furthermore, the proposed EtO controls for process vents,
storage vessels, equipment leaks, heat exchange systems, wastewater,
and PRDs to reduce risks to an acceptable level are far more stringent
than other options we identified to control HAP generally (i.e., see
sections III.C and III.D of this preamble).
    For chloroprene emissions from HON-subject sources, we identified
control options for equipment leaks and maintenance activities in our
review of these standards (see sections III.C.6 and III.D.4 of this
preamble). These controls would likely reduce the cancer incidence and
number of people exposed to risks greater than or equal to 1. However,
the overall source category risk reductions would be relatively small.
Only approximately 3 percent of the SOCMI source category cancer
incidence after the proposed controls in section III.B.2 to reduce
risks to an acceptable level is due to chloroprene emissions. Also, of
the 5.7 million people with cancer risks greater than or equal to 1-in-
1 million after the proposed controls to reduce risks to an

acceptable level, approximately 48,000 people (or 0.8 percent of the
total) have risks greater than or equal to 1-in-1 million due to
chloroprene emissions from the SOCMI source category. However, as
described in sections III.C.6 and III.D.4, the options we evaluated for
equipment leaks and maintenance activities beyond the standards
currently in the HON (or that are being proposed for maintenance
activities) are not cost-effective.
    For the Neoprene Production source category, we did not identify
control options for chloroprene emissions from process vents, storage
vessels, wastewater, maintenance vents, and PRDs that reduced emissions
beyond those proposed in section III.B.2 to reduce risks to an
acceptable level. We also considered other potential sources of
chloroprene, in particular heat exchange systems and equipment leaks.
For heat exchange systems, no chloroprene emissions were reported in
the emissions inventory from this source and as such, no risk
reductions would be realized by requiring more stringent controls. For
equipment leaks, additional control options were identified that could
reduce risks further from this source and are discussed as part our
technology review (see section III.C.6 of this preamble). The options
would reduce chloroprene equipment leak emissions by 10-20 percent.
Approximately 14 percent of the Neoprene Production source category
cancer incidence after the proposed controls in section III.B.2 to
reduce risks to an acceptable level is due to chloroprene emissions
from equipment leaks. Also, of the 48,000 people with cancer risks
greater than or equal to 1-in-1 million after the proposed controls to
reduce risks to an acceptable level, approximately 16,000 people (or 34
percent of the total) have risks greater than or equal to 1-in-1
million due to chloroprene emissions from equipment leaks. Therefore, a
10-20 percent reduction in equipment leak emissions would reduce the
cancer incidence by approximately 1 to 4 percent and the number of
people with cancer risks greater than or equal to 1-in-1 million by
approximately 2,000 to 3,000 people (3 to 7 percent of the total).
However, as described in sections III.C and III.D, the options we
evaluated for equipment leaks are not cost-effective.
    In summary, based on our ample margin of safety analysis, we
propose that controls to reduce EtO emissions at HON processes and
chloroprene emissions at neoprene production processes to get risks to
an acceptable level would also provide an ample margin of safety to
protect public health. We also note the proposed changes to the flare
requirements, proposed standards for dioxins/furans, and proposed
standards to remove SSM exemptions (or provide alternative standards in
limited instances) that are in this proposed action and that we are
proposing under CAA sections 112(d)(2) and (3) will achieve additional
reductions in emissions and further strengthen our conclusions that the
standards continue to provide an ample margin of safety to protect
public health for the SOCMI and Neoprene Production source categories.
5. Adverse Environmental Effects
    Based on our screening assessment of environmental risk presented
in section III.A.4 of this preamble, we did not identify any areas of
concern with respect to environmental risk. Therefore, we have
determined that HAP emissions from the source categories do not result
in an adverse environmental effect, and we are proposing that it is not
necessary to set a more stringent standard to prevent, taking into
consideration costs, energy, safety, and other relevant factors, an
adverse environmental effect.

C. What are the results and proposed decisions based on our CAA section
112(d)(6) technology review and CAA section 111(b)(1)(B) NSPS reviews,
and what are the rationale for those decisions?

    In addition to the proposed EtO- and chloroprene-specific
requirements discussed in section III.B.2 of this preamble, under CAA
section 112(d)(6) we also evaluated developments in practices,
processes, and control technologies for heat exchange systems, storage
vessels, process vents, transfer racks, wastewater, and equipment leaks
for processes subject to the HON, P&R I, and P&R II (see sections
III.C.1 through III.C.6 of this preamble, respectively). Under CAA
section 111(b)(1)(B), for the review of NSPS subpart VVa, we evaluated
BSER for equipment leaks (see section III.C.6.b of this preamble); and
for the review of NSPS subparts III, NNN, and RRR we evaluated BSER for
process vents associated with air oxidation units, distillation
operations, and reactor processes, respectively (see section III.C.3.b
of this preamble). We analyzed costs and emissions reductions for each
emission source (e.g., process vents) by each rule. For NSPS, we
determined cost-effectiveness, cost per ton of emissions reduced, on a
VOC basis. For NESHAP, we determined cost-effectiveness on a HAP basis
from the VOC emissions. We also evaluated fenceline monitoring as a
development in practices considered under CAA section 112(d)(6) for the
purposes of managing fugitive emissions from sources subject to the HON
and P&R I (see section III.C.7 of this preamble).
1. Standards for Heat Exchange Systems
    Heat exchangers are devices or collections of devices used to
transfer heat from process fluids to another process fluid (typically
water) without intentional direct contact of the process fluid with the
cooling fluid (i.e., non-contact heat exchanger). There are two types
of heat exchange systems: Closed-loop recirculation systems and once-
through systems. Closed-loop recirculation systems use a cooling tower
to cool the heated water leaving the heat exchanger and then return the
newly cooled water to the heat exchanger for reuse. Once-through
systems typically use surface freshwater (e.g., from rivers) as the
influent cooling fluid to the heat exchangers, and the heated water
leaving the heat exchangers is then discharged from the facility. At
times, the internal tubing material of a heat exchanger can corrode or
crack, allowing some process fluids to mix or become entrained with the
cooling water. Pollutants in the process fluids may subsequently be
released from the cooling water into the atmosphere when the water is
exposed to air (e.g., in a cooling tower for closed-loop systems or
trenches/ponds in a once-through system). The term ``heat exchange
system'' is defined in HON and P&R I at 40 CFR 63.101 and 40 CFR 63.482
(which references 40 CFR 63.101) as any cooling tower system or once-
through cooling water system (e.g., river or pond water). A heat
exchange system can include more than one heat exchanger and can
include an entire recirculating or once-through cooling system.
However, the HON and P&R I do not describe a heat exchanger, closed-
loop recirculation system, or once-through cooling system as part of
its definition of ``heat exchange system''. Therefore, we are proposing
to revise the definition of ``heat exchange system'' at 40 CFR 63.101
and 40 CFR 63.482 (which references 40 CFR 63.101) to mean a device or
collection of devices used to transfer heat from process fluids to
water without intentional direct contact of the process fluid with the
water (i.e., non-contact heat exchanger) and to transport and/or cool
the water in a closed-loop recirculation system (cooling tower system)
or a once-through system (e.g., river or pond water). This is
consistent with the definition of ``heat exchange system'' used in the
MON. We are also

proposing (as is done in the MON) to make clear in this definition
that: (1) For closed-loop recirculation systems, the heat exchange
system consists of a cooling tower, all CMPU heat exchangers that are
in organic HAP service (for HON) or all EPPU heat exchangers that are
in organic HAP service (for P&R I), serviced by that cooling tower, and
all water lines to and from these process unit heat exchangers.; (2)
for once-through systems, the heat exchange system consists of all heat
exchangers that are in organic HAP service, servicing an individual
CMPU (for HON) or EPPU (for P&R I) and all water lines to and from
these heat exchangers; (3) sample coolers or pump seal coolers are not
considered heat exchangers for the purpose of this proposed definition
and are not part of the heat exchange system; and (4) intentional
direct contact with process fluids results in the formation of a
wastewater. This proposed definition would also apply to heat exchange
systems in ethylene oxide service as described in section III.B.2.iii
of this preamble.
    The HON and P&R I include an LDAR program for owners or operators
of certain heat exchange systems which meets the requirements of 40 CFR
63.104 (National Emission Standards for Organic Hazardous Air
Pollutants from the Synthetic Organic Chemical Manufacturing Industry).
The LDAR program specifies that heat exchange systems be monitored for
leaks of process fluids into cooling water and that owners or operators
take actions to repair detected leaks within 45 days. Owners or
operators may delay the repair of leaks if they meet the applicable
criteria in 40 CFR 63.104. The current HON and P&R I MACT standards for
heat exchange systems allow the use of any method listed in 40 CFR part
136 to be used to sample cooling water for leaks for the HAP listed in
Table 4 to subpart F (for HON) or Table 5 to 40 CFR 63, subpart U (for
P&R I) (recirculating systems) and Table 9 to subpart G (for HON) or
Table 5 to 40 CFR 63, subpart U (for P&R I) (once-through systems) (and
other representative substances such as TOC or VOC that can indicate
the presence of a leak can also be used). A leak in the heat exchange
system is detected if the exit mean concentration of HAP (or other
representative substance) in the cooling water is at least 1 ppmw or 10
percent greater than (using a one-sided statistical procedure at the
0.05 level of significance) the entrance mean concentration of HAP (or
other representative substance) in the cooling water. Furthermore, the
HON and P&R I allow owners or operators to monitor for leaks using a
surrogate indicator of leaks (e.g., ion-specific electrode monitoring,
pH, conductivity), provided that certain criteria in 40 CFR 63.104(c)
are met. The HON and P&R I initially require 6 months of monthly
monitoring for existing heat exchange systems. Thereafter, the
frequency can be reduced to quarterly. The leak monitoring frequencies
are the same whether water sampling and analysis or surrogate
monitoring is used to identify leaks.
    Our technology review identified one development in LDAR practices
and processes for heat exchange systems, the use of the Modified El
Paso Method \61\ to monitor for leaks. The Modified El Paso Method,
which is included in the MON, EMACT standards, and the Petroleum
Refinery Sector rule, was identified in our review of the RACT/BACT/
LAER clearinghouse database. It is also required by the Texas
Commission on Environmental Quality (TCEQ) for facilities complying
with their highly reactive volatile organic compound (HRVOC) rule
(i.e., 30 Texas Administrative Code (TAC) Chapter 115, Subchapter H,
Division 3). The Modified El Paso Method measures a larger number of
compounds than the current methods required in the HON and P&R I and is
more effective in identifying leaks. For heat exchange system LDAR
programs, the compliance monitoring option, leak definition, and
frequency of monitoring for leaks are all important considerations
affecting emission reductions by identifying when there is a leak and
when to take corrective actions to repair the leak. Therefore, we
evaluated the Modified El Paso Method for use at HON and P&R I
facilities, including an assessment of appropriate leak definitions and
monitoring frequencies.
---------------------------------------------------------------------------

    \61\ 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 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.
---------------------------------------------------------------------------

    In order to identify an appropriate Modified El Paso Method leak
definition for HON-subject facilities, we identified four rules, TCEQ's
HRVOC rule, the MON, the EMACT standards, and the Petroleum Refinery
Sector rule, all of which incorporate this monitoring method and have
leak definitions corresponding to the use of this methodology. We also
reviewed data submitted in response to a CAA section 114 request for
the Ethylene Production RTR where facilities performed sampling using
the Modified El Paso Method.
    The TCEQ's HRVOC rule, the MON, the EMACT standards, and the
Petroleum Refinery Sector rule have leak definitions of total
strippable hydrocarbon concentration (as methane) in the stripping gas
ranging from 3.1 ppmv to 6.2 ppmv. In addition, sources subject to the
MON, the EMACT standards, or the Petroleum Refinery Sector rule may not
delay the repair of leaks for more than 30 days where, during
subsequent monitoring, a total strippable hydrocarbon concentration (as
methane) in the stripping gas of 62 ppmv or higher is found. In
reviewing the Ethylene Production RTR CAA section 114 data, a clear
delineation in the hydrocarbon mass emissions data was noticed at 6.1
ppmv of total strippable hydrocarbon (as methane) in the stripping gas.
In addition, given that both the leak concentration and water
recirculation rate of the heat exchange system are key variables
affecting the hydrocarbon mass emissions from heat exchange systems,
the overall Ethylene Production RTR CAA section 114 data for all heat
exchange systems sampled generally showed lower hydrocarbon mass
emissions for leaks at or below 6.1 ppmv of total strippable
hydrocarbon (as methane) in the stripping gas compared to leaks found
above 6.1 ppmv of total strippable hydrocarbon (as methane) in the
stripping gas. Taking into account the range of actionable leak
definitions in use by other rules that require use of the Modified El
Paso Method currently (i.e., 3.1 ppmv-6.2 ppmv of total strippable
hydrocarbon (as methane) in the stripping gas), and the magnitude of
emissions for leaks as a result of total strippable hydrocarbon (as
methane) in the stripping gas above 6.1 ppmv compared to leaks
identified in the CAA section 114 sampling data as a result of other
actionable leak definitions, we chose to evaluate a leak definition at
the upper end of identified actionable leak definitions in our
analysis. Thus, the Modified El Paso Method leak definition we
evaluated was 6.2 ppmv of total strippable hydrocarbon concentration
(as methane) in the stripping gas for both new and existing heat
exchange systems, along with not allowing delay of repair of leaks for
more than 30 days where, during subsequent monitoring, a total
strippable hydrocarbon concentration (as methane) in the stripping gas
of 62 ppmv or higher is found.
    We determined an appropriate leak monitoring frequency by reviewing
the

current monitoring frequencies that HON and P&R I facilities are
subject to, along with frequencies for the TCEQ's HRVOC rule, the MON,
the EMACT standards, and the Petroleum Refinery Sector rule, and
information gathered in the Ethylene Production RTR CAA section 114
survey. As a first step, we reviewed whether it was still reasonable to
specify more frequent monitoring for a 6-month period after repair of
leaks. Our review of the Ethylene Production RTR CAA section 114 data
showed that no leaks were identified during the 6-month period post
repair for any of the facilities that reported leak emissions in their
heat exchange system compliance data. Thus, we find that re-monitoring
once after repair of a leak, at the monitoring location where the leak
was identified, is sufficient from a continuous compliance perspective
to demonstrate a successful repair. The monitoring frequencies
currently required by the HON and P&R I when no leaks are found were,
thus, considered the base frequencies (i.e., quarterly monitoring for
existing and new heat exchange systems). Once we determined the base
frequencies, we next considered more stringent monitoring frequencies.
Both the Petroleum Refinery Sector rule, which includes monthly
monitoring for existing sources, under certain circumstances, and the
TCEQ HRVOC rule, which includes continuous monitoring provisions for
existing and new sources, have more stringent monitoring frequencies.
However, the incremental HAP cost effectiveness to change from
quarterly to monthly monitoring and monthly to continuous monitoring
was found to be $40,000/ton and $500,000/ton, respectively. We conclude
that these costs are not reasonable for HON and P&R I facilities. Thus,
we chose to evaluate quarterly monitoring for existing and new heat
exchange systems (i.e., the base monitoring frequency currently in the
rule).
    Based on this technology review, we identified the following
control option for heat exchanger systems as a development in practice
that can be implemented at a reasonable cost: Quarterly monitoring for
existing and new heat exchange systems (after an initial 6 months of
monthly monitoring) with the Modified El Paso Method and a leak
definition of 6.2 ppmv of total strippable hydrocarbon concentration
(as methane) in the stripping gas.
    We then estimated the impacts of this control option assuming that
all 207 HON facilities and 19 P&R I facilities (10 of which are
collocated with HON facilities) would be affected by requiring the use
of the Modified El Paso Method. As part of our analysis, we assumed
owners or operators conducting quarterly monitoring for three or more
of these heat exchange systems would elect to purchase a stripping
column and FID analyzer and perform in-house Modified El Paso
monitoring (because the total annualized costs for in-house Modified El
Paso monitoring are less than the costs for contracted services). In
addition, we assumed repairs could be performed by plugging a specific
heat exchanger tube, and if a heat exchanger is leaking to the extent
that it needs to be replaced, then it is effectively at the end of its
useful life. Therefore, we determined that the cost of replacing a heat
exchanger is an operational cost that would be incurred by the facility
as a result of routine maintenance and equipment replacement, and it is
not attributable to the control option.
    Table 10 of this preamble presents the nationwide impacts for
requiring owners or operators at HON facilities (including 10 P&R I
facilities collocated with HON facilities) to use the Modified El Paso
Method and repair leaks of total strippable hydrocarbon concentration
(as methane) in the stripping gas of 6.2 ppmv or greater. Table 11 of
this preamble presents the nationwide impacts for requiring owners or
operators at P&R I facilities (not collocated with HON facilities) to
use the Modified El Paso Method and repair leaks of total strippable
hydrocarbon concentration (as methane) in the stripping gas of 6.2 ppmv
or greater. See the document titled Clean Air Act Section 112(d)(6)
Technology Review for Heat Exchange Systems Located in the SOCMI Source
Category that are Associated with Processes Subject to HON and for Heat
Exchange Systems that are Associated with Processes Subject to Group I
Polymers and Resins NESHAP; and Control Option Impacts for Heat
Exchange Systems that are Associated with Processes Subject to Group II
Polymers and Resins NESHAP, which is available in the docket for this
rulemaking, for details on the assumptions and methodologies used in
this analysis.
    Based on the costs and emission reductions for the identified
control option, we are proposing to revise the HON and P&R I for heat
exchange systems pursuant to CAA section 112(d)(6). We are proposing at
40 CFR 63.104(g)(4) \62\ to specify quarterly monitoring for existing
and new heat exchange systems (after an initial 6 months of monthly
monitoring) using the Modified El Paso Method and a leak definition of
6.2 ppmv of total strippable hydrocarbon concentration (as methane) in
the stripping gas. Owners and operators would be required to repair the
leak to reduce the concentration or mass emissions rate to below the
leak action level as soon as practicable, but no later than 45 days
after identifying the leak. We are also proposing at 40 CFR
63.104(j)(3) a delay of repair action level of total strippable
hydrocarbon concentration (as methane) in the stripping gas of 62 ppmv,
that if exceeded during leak monitoring, would require immediate repair
(i.e., the leak found cannot be put on delay of repair and would be
required to be repaired within 30 days of the monitoring event). This
would apply to both monitoring heat exchange systems and individual
heat exchangers by replacing the use of any 40 CFR part 136 water
sampling method with the Modified El Paso Method and removing the
option that allows for use of a surrogate indicator of leaks. We are
also proposing at 40 CFR 63.104(h) and (i) that repair include re-
monitoring at the monitoring location where a leak is identified to
ensure that any leaks found are fixed. We are proposing that none of
these proposed requirements would apply to heat exchange systems that
have a maximum cooling water flow rate of 10 gallons per minute or less
because owners and operators of smaller heat exchange systems would be
disproportionally affected and forced to repair leaks with a much lower
potential HAP emissions rate than owners and operators of heat exchange
systems with larger recirculation rate systems. Finally, we are
proposing at 40 CFR 63.104(l) that the leak monitoring requirements for
heat exchange systems at 40 CFR 63.104(b) may be used in limited
instances, instead of using the Modified El Paso Method to monitor for
leaks. We still maintain that the Modified El Paso Method is the
preferred method to monitor for leaks in heat exchange systems and are
proposing that the requirements of 40 CFR 63.104(b) may only be used if
99 percent by weight or more of all the organic compounds that could
potentially leak into the cooling water have a Henry's Law Constant
less than 5.0E-6 atmospheres per mole per cubic meter (atm-m\3\/mol) at
25[deg] Celsius. We selected this threshold based on a review of
Henry's Law Constants for the HAP listed in Table 4 to subpart F of 40

CFR part 63, as well as the water-soluble organic compounds listed in a
recent alternative monitoring request from a MON facility.\63\ Henry's
Law Constants are available from the EPA at https://comptox.epa.gov/dashboard/. Examples of HAP that have a Henry's Law Constant of less
than 5.0E-6 atm-m\3\/mol at 25[deg] Celsius are aniline, 2-
chloroacetophenone, diethylene glycol diethyl ether, diethylene glycol
dimethyl ether, dimethyl sulfate, 2,4-dinitrotoluene, 1,4-dioxane,
ethylene glycol monoethyl ether acetate, ethylene glycol monomethyl
ether acetate, methanol, and toluidine. Many of these HAP also have
very high boiling points, with most above 300 Fahrenheit, which means
they will generally stay in the cooling water and not be emitted to the
atmosphere. We solicit comment on all of the proposed requirements
related to heat exchange systems.
---------------------------------------------------------------------------

    \62\ We note that each of the HON citations mentioned in this
paragraph of this preamble are also applicable to P&R I facilities
pursuant to 40 CFR 63.502(n). In order for these proposed HON
citations to properly apply to P&R I facilities, we are proposing
substitution rule text at 40 CFR 63.502(n)(7).
    \63\ In May 2021, EPA Region 4 received a request from Eastman
Chemical Company to perform alternative monitoring instead of the
Modified El Paso Method to monitor for leaks in Eastman's Tennessee
Operations heat exchange systems, which primarily have cooling water
containing soluble HAP with a high boiling point. Eastman
specifically identified two HAP, 1,4-dioxane and methanol, which do
not readily strip out of water using the Modified El Paso Method.
Eastman's application for alternative monitoring included
experimental data showing that the Modified El Paso Method would
likely not identify a leak of these HAP in heat exchange system
cooling water. Eastman conducted Modified El Paso Method monitoring
under controlled scenarios to determine how much methanol and 1,4-
dioxane would be detected. The scenarios included solutions of water
and either methanol or 1,4-dioxane at concentrations of 1 part per
million by weight (ppmw), 20 ppmw, and 100 ppmw (as measured using
water sampling methods allowed previously in the MON). The Modified
El Paso Method did not detect any methanol or 1,4-dioxane from the 1
ppmw and 20 ppmw solutions (i.e., methanol and 1,4-dioxane did not
strip out of the water in detectable amounts). The Modified El Paso
Method detected very little HAP from the 100 ppmw solutions, with a
maximum of only 0.17 percent of the 1,4-dioxane stripping out and
being detected.

     Table 10--Nationwide Emissions Reductions and Cost Impact for Requiring the Modified El Paso Method for Heat Exchange Systems at HON Facilities
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Total
                                                         Total         VOC emission     HAP emission       HAP cost        annualized        HAP cost
          Control option            Total capital      annualized         table          reductions     effectiveness      costs with     effectiveness
                                    investment ($)     costs w/o        reductions         (tpy)         w/o recovery       recovery      with recovery
                                                     credits ($/yr)       (tpy)                        credits ($/ton)   credits ($/yr)  credits ($/ton)
--------------------------------------------------------------------------------------------------------------------------------------------------------
1................................         770,000          228,000              934               93            2,440        (612,700)          (6,560)
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Table 11--Nationwide Emissions Reductions and Cost Impact for Requiring the Modified El Paso Method for Heat Exchange Systems at P&R I Facilities
                                                          [Not collocated with HON facilities]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Total
                                                         Total         VOC emission     HAP emission       HAP cost        annualized        HAP cost
          Control option            Total capital      annualized       reductions       reductions    effectiveness w/    costs with     effectiveness
                                    investment ($)     costs w/o          (tpy)            (tpy)          o recovery        recovery      with recovery
                                                     credits ($/yr)                                    credits ($/ton)   credits ($/yr)  credits ($/ton)
--------------------------------------------------------------------------------------------------------------------------------------------------------
1................................          48,300            9,900               33                3            3,050         (19,320)          (5,940)
--------------------------------------------------------------------------------------------------------------------------------------------------------

2. Standards for Storage Vessels
    Storage vessels are used to store liquid and gaseous feedstocks for
use in a process, as well as to store liquid and gaseous products from
a process. Most HON, P&R I, and P&R II storage vessels are designed for
operation at atmospheric or near atmospheric pressures; pressure
vessels are used to store compressed gases and liquefied gases.
Atmospheric storage vessels are typically cylindrical with a vertical
orientation, and they are constructed with either a fixed roof or a
floating roof. Some, generally small, atmospheric storage vessels are
oriented horizontally. Pressure vessels are either spherical or
horizontal cylinders.
    The HON requires owners and operators control emissions from
storage vessels with capacities between 75 m\3\ and 151 m\3\ and a MTVP
greater than or equal to 13.1 kPa, and storage vessels with capacities
greater than or equal to 151 m\3\ and a MTVP greater than or equal to
5.2 kPa. Storage vessels meeting this criteria are considered Group 1
storage vessels. Owners and operators of HON Group 1 storage vessels
storing a liquid with a MTVP of total organic HAP less than 76.6 kPa
are required to reduce emissions of organic HAP by 95 percent (or 90
percent if the storage vessel was installed on or before December 31,
1992) utilizing a closed vent system and control device, or reduce
organic HAP emissions either by utilizing an IFR, an EFR, or by routing
the emissions to a process or a fuel gas system, or vapor balancing.
Owners and operators of HON Group 1 storage vessels storing a liquid
with a MTVP of total organic HAP greater than or equal to 76.6 kPa are
required to reduce emissions of organic HAP by 95 percent (or 90
percent if the storage vessel was installed on or before December 31,
1992) utilizing a closed vent system and control device, or reduce
organic HAP emissions by routing the emissions to a process or a fuel
gas system, or vapor balancing. In general, HON storage vessels that do
not meet the MTVP and capacity thresholds described above are
considered Group 2 storage vessels and are not required to apply any
additional emission controls provided they remain under Group 1
thresholds; however, they are subject to certain monitoring, reporting,
and recordkeeping requirements to ensure that they were correctly
determined to be Group 2 and that they remain Group 2. Generally, the
P&R I standards for storage vessels refer to the provisions in the HON.
As such, owners and operators of Group 1 storage vessels subject to P&R
I are required to control these vessels as prescribed in the HON.
    The P&R II standards for storage tanks (P&R II uses the term
``storage tank'' in lieu of ``storage vessel'' like the HON and P&R I)
do not specify any sort of stratification into groups. P&R II defines
``storage tank'' to mean tank or other vessel that is used to store
liquids that contain one or more HAP compounds.

As previously mentioned, process vents, storage tanks, and wastewater
systems combined are regulated according to a production-based emission
rate (e.g., pounds HAP per million pounds BLR or WSR produced) standard
for existing sources in both BLR (130 pounds) and WSR (10 pounds). For
new sources, BLR requires 98 percent reduction or an overall limit of
5,000 pounds of HAP per year. New WSR sources are limited to 7 pounds
of HAP per million pounds WSR produced.
    As part of our technology review for HON and P&R I storage vessels,
we identified the following emission reduction options: (1) Revising
the capacity and MTVP thresholds of the HON and P&R I to reflect the
MON existing source threshold which requires existing storage vessels
between 38 m\3\ and 151 m\3\ with a vapor pressure greater than or
equal to 6.9 kPa to reduce emissions of organic HAP by 95 percent
utilizing a closed vent system and control device, or reduce organic
HAP emissions either by utilizing an IFR, an EFR, or by routing the
emissions to a process or a fuel gas system, or vapor balancing; (2) in
addition to requirements specified in option 1, requiring upgraded deck
fittings \64\ and controls for guidepoles for all storage vessels
equipped with an IFR as already required in 40 CR 63, subpart WW; and
(3) in addition to requirements specified in options 1 and 2, requiring
the conversion of EFRs to IFRs through use of geodesic domes. We did
not identify any control options for storage tanks subject to P&R II.
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    \64\ Require all openings in an IFR (except those for automatic
bleeder vents (vacuum breaker vents), rim space vents, leg sleeves,
and deck drains) be equipped with a deck cover; and the deck cover
would be required to be equipped with a gasket between the cover and
the deck.
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    We identified option 1 as a technologically feasible development in
practices, processes, and control technologies for storage vessels used
at HON and P&R I facilities because it reflects requirements for
similar storage vessels that are located at chemical manufacturing
facilities subject to the MON. Option 2 is an improvement in practices
because these upgraded deck fittings and guidepole controls have been
required by other regulatory agencies and other EPA regulatory action
(e.g., Petroleum Refinery Sector rulemaking) since promulgation of the
HON and P&R I and are being used by some of the sources covered by the
SOCMI source category. Finally, we consider option 3 to be a
development in control technology because we found that some storage
vessels with EFRs have installed geodesic domes since promulgation of
the HON and P&R I.
    We used information about storage vessel capacity, design, and
stored materials that industry provided to the EPA in response to our
CAA section 114 request (see section II.C of this preamble) to evaluate
the impacts of all three of the options presented. We identified eight
HON storage vessels and two P&R I storage vessels from our CAA section
114 request that would be impacted by option 1; extrapolating this data
to all 207 HON facilities and 19 P&R I facilities (10 of which are
collocated with HON facilities), we estimated costs and emissions
reductions for 63 HON storage vessels and 4 P&R I storage vessels that
would be impacted by option 1. This same distribution would apply to
option 2. For option 3, we identified five HON EFR storage vessels and
zero P&R I EFR storage vessels from our CAA section 114 request that
would be impacted; extrapolating this data to all 207 HON facilities
and 19 P&R I facilities (10 of which are collocated with HON
facilities) we estimated costs and emissions reductions for 159 HON EFR
storage vessels and 5 P&R I EFR storage vessels \65\ that would be
impacted by option 3.
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    \65\ Although no EFR tanks were reported for P&R I as part of
our CAA section 114 request, we assumed five P&R I EFR storage
vessels based on the number of HON average EFR storage vessels per
HON CMPU that were reported.
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    Table 12 of this preamble presents the nationwide impacts for the
three options considered for HON facilities (including 10 P&R I
facilities collocated with HON facilities). Table 13 of this preamble
presents the nationwide impacts for the three options considered for
P&R I facilities (not collocated with HON facilities). See the document
titled Clean Air Act Section 112(d)(6) Technology Review for Storage
Vessels Located in the SOCMI Source Category that are Associated with
Processes Subject to HON, Storage Vessels Associated with Processes
Subject to Group I Polymers and Resins NESHAP, and Storage Vessels
Associated with Processes Subject to Group II Polymers and Resins
NESHAP, which is available in the docket for this rulemaking, for
details on the assumptions and methodologies used in this analysis,
including the calculations we used to account for additional HON and
P&R I facilities that did not receive a CAA section 114 request.
    We determined that option 2 (which includes option 1) is cost
effective and we are proposing, pursuant to CAA section 112(d)(6), to
revise the Group 1 storage capacity criterion (for HON and P&R I
storage vessels at existing sources) from between 75 m\3\ and 151 m\3\
to between 38 m\3\ and 151 m\3\ (see proposed Table 5 to subpart G),
and require upgraded deck fittings and controls for guidepoles for all
storage vessels equipped with an IFR as already required in 40 CR 63,
subpart WW (see proposed 40 CFR 63.119(b)(5)(ix), (x), (xi), and
(xii)). Considering the emissions reductions and high incremental cost
effectiveness, we determined that storage vessel option 3 is not cost
effective and are not proposing to revise the HON and P&R I to reflect
the requirements of this option pursuant to CAA section 112(d)(6). We
solicit comment on the proposed revisions for storage vessels.

             Table 12--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for Storage Vessels at HON Facilities
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                HAP incremental
                                                                            Total       VOC emission    HAP emission      HAP cost            cost
                    Control option                      Total capital    annualized      reductions      reductions     effectiveness    effectiveness
                                                       investment ($)   costs ($/yr)        (tpy)           (tpy)          ($/ton)      (from Option 1)
                                                                                ($/ton)
--------------------------------------------------------------------------------------------------------------------------------------------------------
1....................................................       1,727,000         327,400            58.0            40.6           8,070  .................
2....................................................       2,191,500         415,500            68.2            47.7           8,710             12,400
3....................................................      28,916,200       4,065,700            84.3            59.0          68,880                N/A
--------------------------------------------------------------------------------------------------------------------------------------------------------

            Table 13--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for Storage Vessels at P&R I Facilities
                                                          [Not collocated with HON facilities]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                HAP  incremental
                                                                            Total       VOC emission    HAP emission      HAP cost            cost
                    Control option                      Total capital    annualized      reductions      reductions     effectiveness    effectiveness
                                                       investment ($)   costs ($/yr)        (tpy)           (tpy)          ($/ton)      (from Option 1)
                                                                                ($/ton)
--------------------------------------------------------------------------------------------------------------------------------------------------------
1....................................................         109,000          20,700             3.7             2.6           7,960  .................
2....................................................         131,000          24,800             4.1             2.9           8,550             13,700
3....................................................         912,200         128,300             2.7             1.9          67,500                N/A
--------------------------------------------------------------------------------------------------------------------------------------------------------

3. Standards for Process Vents
    A process vent is a gas stream that is discharged during the
operation of a particular unit operation (e.g., separation processes,
purification processes, mixing processes, reaction processes). The gas
stream(s) may be routed to other unit operations for additional
processing (e.g., a gas stream from a reactor that is routed to a
distillation column for separation of products), sent to one or more
recovery devices, sent to a process vent header collection system
(e.g., blowdown system) and APCD (e.g., flare, thermal oxidizer, carbon
adsorber), and/or vented to the atmosphere. Process vents may be
generated from continuous and/or batch operations,\66\ as well as from
other intermittent types of operations (e.g., maintenance operations).
If process vents are required to be controlled prior to discharge to
the atmosphere to meet an applicable emissions standard, then they are
typically collected and routed to an APCD through a closed vent system.
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    \66\ P&R I and P&R II regulate process vents from both
continuous and batch operations. The HON and NSPS subparts III, NNN,
and RRR only regulate process vents if some, or all, of the gas
stream originates as a continuous flow.
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    NSPS subparts III, NNN, and RRR regulate gas streams from air
oxidation reactors, distillation columns, and other reactor processes,
respectively. Importantly, the NSPS subparts III, NNN, and RRR formed
the basis for the HON process vent MACT standards in that to be
considered a HON process vent, some or all of the gas stream must
originate as a continuous flow from an air oxidation reactor,
distillation unit, or other reactor process during operation of a CMPU.
P&R I regulates batch front-end process vents, continuous front-end
process vents, and aggregate batch vent streams from condensers,
distillation units, reactors, or other unit operations within an EPPU.
Generally, process vents subject to NSPS subparts III, NNN, or RRR, or
the HON and/or P&R I are grouped based on the flow rate, HAP
concentration, and a TRE index value.\67\ P&R II defines a process vent
as a point of emission from a unit operation, such as condenser vents,
vacuum pumps, steam ejectors and atmospheric vents from reactors and
other process vessels; and no further stratification into groups for
applicability is specified.
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    \67\ TRE is discussed in more detail below in section III.C.3.a
of this preamble (for NESHAP) and section III.C.3.b of this preamble
(for NSPS).
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    The results of our CAA section 112(d)(6) technology review for
process vents associated with HON, P&R I, and P&R II processes are
discussed in section III.C.3.a of this preamble. The results of our CAA
111(b)(1)(B) review for process vents subject to NSPS subparts III,
NNN, or RRR are discussed in section III.C.3.b of this preamble.
a. HON, P&R I, and P&R II
    As previously mentioned, the HON standards divide process vents
into Group 1 process vents, which require controls, and Group 2 process
vents, which generally do not require controls provided they remain
below Group 1 thresholds. A Group 1 HON process vent is a process vent
for which the vent stream flow rate is greater than or equal to 0.005
scmm, the total organic HAP concentration is greater than or equal to
50 ppmv, and the TRE index value is less than or equal to 1.0
(according to the determination procedures at 40 CFR 63.115). The TRE
index value is a measure of the supplemental total resource requirement
per unit VOC (or HAP) reduction. It takes into account all the
resources which are expected to be used in VOC (or HAP) control by
thermal oxidation and provides a dimensionless measure of resource
burden based on cost effectiveness. Resources include supplemental
natural gas, labor, and electricity. Additionally, if the off-gas
contains halogenated compounds, resources will also include caustic and
scrubbing and quench makeup water. For the HON and P&R I, the TRE index
value is derived from the cost effectiveness associated with HAP
control by a flare or thermal oxidation, and is a function of vent
stream flowrate, vent stream net heating value, hourly emissions, and a
set of coefficients. The TRE index value was first introduced in an EPA
document titled: Guideline Series for Control of Volatile Organic
Compound (VOC) Emissions from Air Oxidation Processes in Synthetic
Organic Chemical Manufacturing Industry (SOCMI) (see EPA-450/3-84-015,
December 1984). The EPA incorporated the TRE concept into the original
HON (see 59 FR 19468, April 22, 1994) and the original P&R I rulemaking
(see 61 FR 46906, September 5, 1996). The TRE index value is used in 40
CFR 63 subpart G and 40 CFR 63 subpart U as an alternative mode of
compliance for process vent regulations. The TRE index value can also
trigger monitoring, recordkeeping, and reporting requirements. In
general, as previously mentioned for the HON and P&R I, continuous
process vents with a TRE index value equal to or less than 1.0 are
required to be controlled. For additional details regarding the TRE
index value (including the equation and coefficients used to calculate
the TRE index value for the HON and P&R I), see the document titled
Clean Air Act Section 112(d)(6) Technology Review for Continuous
Process Vents Located in the SOCMI Source Category that are Associated
with Processes Subject to HON, Continuous Front-end and Batch Front-end
Process Vents Associated with Processes Subject to Group I Polymers and
Resins NESHAP, and Process Vents Associated with Processes Subject to
Group II Polymers and Resins NESHAP, which is available in the docket
for this rulemaking.
    The HON standards require uncontrolled Group 1 process vents to
reduce total organic HAP \68\ emissions by 98 percent by weight by
venting emissions through a closed vent system to any combination of
control devices or by venting emissions through a closed

vent system to a flare.\69\ The P&R I standards for continuous front-
end process vents use the same Group 1 flow rate, HAP concentration,
and TRE index value threshold criterion as the HON; refer to the same
provisions in the HON for group determination (i.e., owners and
operators of continuous front-end process vents subject to P&R I
determine whether control is required based on the flow rate, HAP
concentration, and TRE index value using the same HON determination
procedures at 40 CFR 63.115); and require the same level as control as
the HON (i.e., reduce total organic HAP \70\ emissions by 98 percent by
weight by venting emissions through a closed vent system to any
combination of control devices or by venting emissions through a closed
vent system to a flare).\71\
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    \68\ For HON, organic HAP refers to chemicals listed in Table 2
to NESHAP subpart F.
    \69\ See also, footnote 16, for halogenated vent streams that
are Group 1.
    \70\ For P&R I, organic HAP refers to chemicals listed in Table
5 to NESHAP subpart U.
    \71\ See also, footnote 16, for halogenated vent streams that
are Group 1.
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    The P&R I standards do not refer to the HON for batch front-end
process vents. The P&R I group determination for batch front-end vents
is based on annual HAP emissions and annual average batch vent flow
rate. Group 1 batch front-end process vent means a batch front-end
process vent releasing annual organic HAP emissions greater than or
equal to 11,800 kg/yr (26,014 lb/yr) and with a cutoff flow rate
greater than or equal to the annual average batch vent flow rate.\72\
The cutoff flow rate is calculated in accordance with 40 CFR 63.488(f).
Annual organic HAP emissions and annual average batch vent flow rate
are determined at the exit of the batch unit operation, as described in
40 CFR 63.488(a)(2). Annual organic HAP emissions are determined as
specified in 40 CFR 63.488(b), and annual average batch vent flow rate
is determined as specified in 40 CFR 63.488(e).
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    \72\ P&R I also contains standards for halogenated batch process
vents.
---------------------------------------------------------------------------

    The P&R II standards for process vents do not specify any sort of
stratification into groups. However, the rule does have different
performance testing requirements depending on whether the process vent
is part of a continuous process \73\ or if flow of gaseous emissions is
intermittent. As previously mentioned, process vents, storage tanks,
and wastewater systems combined are regulated according to a
production-based emission rate (e.g., pounds HAP per million pounds BLR
or WSR produced) standard for existing sources in both BLR (130 pounds)
and WSR (10 pounds). For new sources, BLR requires 98 percent reduction
or an overall limit of 5,000 pounds of HAP per year. New WSR sources
are limited to 7 pounds of HAP per million pounds WSR produced.