---------------------------------------------------------------------------

    \73\ P&R II defines ``continuous process'' to mean a process
where the inputs and outputs flow continuously throughout the
duration of the process. Continuous processes are typically steady-
state.
---------------------------------------------------------------------------

    As part of our technology review for HON and P&R I continuous
process vents, we identified the following emission reduction options:
(1) Remove the TRE concept in its entirety, remove the 50 ppmv and
0.005 scmm Group 1 process vent thresholds, and redefine a HON Group 1
process vent and P&R I Group 1 continuous front-end process vent
(require control) as any process vent that emits greater than or equal
to 1.0 lb/hr of total organic HAP; (2) the same requirements specified
in option 1, but redefine a HON Group 1 process vent and P&R I Group 1
continuous front-end process vent (require control) as any process vent
that emits greater than or equal to 0.10 lb/hr of total organic HAP;
and (3) keep the TRE concept and keep the 50 ppmv and 0.005 scmm Group
1 process vent thresholds, but change the TRE index value threshold
from 1.0 to 5.0. We did not identify any control options for P&R II
process vents.
    We identified options 1 and 2 as developments in practices,
processes, and control technologies for multiple reasons. First, we
identified at least one chemical manufacturing NESHAP (i.e., ethylene
production) that does not use the TRE index value as criteria for
determining whether a process vent should be controlled. Second, based
on the responses to our CAA section 114 request, we observed that some
facilities are voluntarily controlling continuous process vents that
are not required by the HON and P&R I to be controlled per the results
of the TRE index value calculation. Of the 13 HON facilities that
received the CAA section 114 request, at least three facilities
confirmed they were voluntarily controlling some of their Group 2
process vents. We expect other HON and P&R I facilities will do this
too because some facilities stated in their response to the CAA section
114 request that, pursuant to 40 CFR 63.113(h), many of their process
vents are voluntarily designated as Group 1 process vents ``so that TRE
calculations are not required.'' In other words, some facilities are
likely electing to control certain process vents that have TRE index
values greater than 1.0. Third, based on the responses to our CAA
section 114 request, we observed that facilities are routing multiple
continuous process vents to a single APCD. This is significant because
the current use of the TRE index value is only based on controlling a
single process vent with a single APCD, an unrealistic scenario when
compared to how chemical manufacturing facilities actually control
their process vents. It is much more likely that a facility routes
numerous process vents to the same APCD. Finally, also based on
responses to our CAA section 114 request, one facility provided over
300 pages of modeled runs that were used to help the facility determine
certain characteristics of their continuous HON and P&R I process vents
for inputs to TRE index value calculations. The facility had originally
included these modeled runs with their Notification of Compliance
Status report; we reviewed this information and concluded that
determining a TRE index value for certain process vent streams is often
theoretical, can be extremely complicated, and is uncertain. In
addition, because the TRE index value is largely a theoretical
characterization tool, it can be very difficult to enforce. In order to
calculate a TRE index value, owners and operators must determine
numerous input values; and without the correct amount of process
knowledge, verifying inputs can be problematic.
    We identified option 3 as a development in practices, processes,
and control technologies because we determined that another chemical
manufacturing NESHAP (i.e., the MON) contains a TRE index value
threshold criteria (i.e., less than or equal to 1.9) that is more
stringent than the HON and P&R I TRE index value threshold criteria
(i.e., less than or equal to 1.0). Additionally, we identified one
particular state rule that uses a more stringent TRE index value
threshold than the HON and P&R I TRE index value threshold
criteria.\74\ This state rule requires owners and operators of air
oxidation processes to control any process vent stream or combination
of process vent streams with a TRE index value less than or equal to
6.0.\75\
---------------------------------------------------------------------------

    \74\ See Illinois Title 35: Subtitle B: Chapter I: Subchapter C:
Parts 218 and 219 (i.e., Organic Material Emission Standards And
Limitations For The Chicago Area Subpart V: Batch Operations And Air
Oxidation Processes; and Organic Material Emission Standards And
Limitations For The Metro East Area Subpart V: Batch Operations And
Air Oxidation Processes).
    \75\ Although the TRE equation for Illinois Title 35: Subtitle
B: Chapter I: Subchapter C: Parts 218 and 219 has a different set of
TRE coefficients than that of the HON and P&R I, we examined
multiple scenarios and determined that a process vent not required
to be controlled by the HON or P&R I could still be required to be
controlled by this Illinois rule. For example, a halogenated process
vent with a net heating value of 100 MJ/scm, a flowrate of 0.82 scm/
min, a TOC mass flow rate of 9 kg/hr, and a HAP mass flow rate of 1
kg/hr would yield a TRE of 3.87 using the HON and/or the P&R I TRE
equation (and 3.87 is above the HON and P&R I index value thresholds
of 1.0 so no control would be required); however, this same stream
would yield a TRE of 5.28 using the Illinois rule TRE equation (and
5.28 is below the Illinois rule TRE index value threshold of 6.0, so
control is required).

---------------------------------------------------------------------------

    To evaluate impacts of all three of the options presented, we used
information from about 50 Group 2 continuous process vents that was
provided by 9 of the 13 HON facilities (including 1 P&R I facility
collocated with a HON facility) that received the CAA section 114
request. Using vent stream flowrates, vent stream net heating values,
and VOC and HAP emission rates (which we obtained from TRE index value
calculations that facilities provided in their response to the CAA
section 114 request) and the methodology from the sixth edition of the
EPA Air Pollution Control Cost Manual,\76\ we first calculated a cost
effectiveness for installing ductwork and a blower on each vent,
assuming each of these vents could be routed to an existing control
device achieving 98 percent by weight emission reduction. Given that
many of the Group 2 continuous process vents have a very low flow rate
and/or emission rate, we found that even installing simple ductwork and
a blower would not be cost effective for the majority of these vents.
However, we did identify 23 of these Group 2 continuous process vents
(a subset of the 50 Group 2 process vents from responses to our CAA
section 114 request) for which we found this scenario to be cost
effective (i.e., $1,100 per ton of VOC/HAP or less). Using this subset
of Group 2 continuous process vents, we extrapolated a set of
distributions and parameters that we could apply to all 207 HON
facilities and 19 P&R I facilities in order to evaluate impacts of all
three of the options presented for continuous HON and P&R I process
vents, noting that six of the 23 Group 2 continuous process vents are
already voluntarily controlled even though the HON and P&R I do not
require them to be. For Group 2 continuous process vents already
voluntarily being controlled, we assumed owners and operators use
existing APCDs. For Group 2 process vents not already being voluntarily
controlled, we assumed owners and operators would need to install an
APCD; therefore, we estimated costs to install a thermal oxidizer using
the EPA's control cost template.\77\ We estimated that 16 HON
facilities operating 48 HON Group 2 process vents (32 of which are
already voluntarily controlled and 16 that are not currently
controlled) and 3 P&R I facilities operating 9 P&R I Group 2 continuous
front-end process vents (in which all nine are not currently
controlled) would be impacted by option 1 (i.e., control process vents
with a total organic HAP emission rate greater than 1.0 lb/hr). For
option 2 (i.e., control process vents with a total organic HAP emission
rate greater than 0.10 lb/hr), we estimated that 48 HON facilities
operating 287 HON Group 2 process vents (96 of which are already
voluntarily controlled and 191 that are not currently controlled) and 3
P&R I facilities operating 30 P&R II Group 2 continuous front-end
process vents (in which all 30 are not currently controlled) would be
impacted. For option 3 (i.e., control process vents with a TRE index
value less than or equal to 5.0), we estimated that 16 HON facilities
operating 64 HON Group 2 process vents (32 of which are already
voluntarily controlled and 32 that are not currently controlled) and 3
P&R I facilities operating nine P&R II Group 2 continuous front-end
process vents (in which all 9 are not currently controlled) would be
impacted.
---------------------------------------------------------------------------

    \76\ EPA, 2002. EPA Control Cost Manual, Sixth Edition. January
2002. Publication Number EPA/452/B-02-001.
    \77\ Refer to the file ``Incinerators and Oxidizers Calculation
Spreadsheet (note: updated on 1/16/2018) (xlsm)'' which follows the
methodology from the sixth edition of the EPA Air Pollution Control
Cost Manual and can be found at the following website: https://www.epa.gov/economic-and-cost-analysis-air-pollution-regulations/cost-reports-and-guidance-air-pollution.
---------------------------------------------------------------------------

    Table 14 of this preamble presents the nationwide impacts for the
three options considered for continuous process vents at HON
facilities. Table 15 of this preamble presents the nationwide impacts
for the three options considered for continuous process vents at P&R I
facilities. We determined that option 1 is cost effective and we are
proposing, pursuant to CAA section 112(d)(6), to remove the TRE concept
in its entirety from the HON and P&R I. We are also proposing, pursuant
to CAA section 112(d)(6), to remove the 50 ppmv and 0.005 scmm Group 1
process vent thresholds from the HON Group 1 process vent definition
and P&R I Group 1 continuous front-end process vent definition, and
instead require owners and operators of HON or P&R I process vents that
emit greater than or equal to 1.0 lb/hr of total organic HAP to reduce
emissions of organic HAP using a flare meeting the proposed operating
and monitoring requirements for flares (see section III.D.1 of this
preamble); or reduce emissions of total organic HAP or TOC by 98
percent by weight or to an exit concentration of 20 ppmv, whichever is
less stringent. We are not proposing to revise the HON and P&R I to
reflect the requirements of process vent options 2 and 3 pursuant to
CAA section 112(d)(6). We determined that process vent option 2 is not
cost effective, and while we believe option 3 is cost effective, it
would require keeping the TRE concept in the rule which for reasons
explained above is not desired. We solicit comment on the proposed
revisions for process vents for the HON and P&R I.

 Table 14--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for Continuous Process
                                             Vents at HON Facilities
----------------------------------------------------------------------------------------------------------------
                                                       Total       VOC emission    HAP emission      HAP cost
         Control option            Total capital    annualized      reductions      reductions     effectiveness
                                  investment ($)   costs ($/yr)        (tpy)           (tpy)          ($/ton)
----------------------------------------------------------------------------------------------------------------
1...............................       1,218,000       3,150,000             436             436           7,200
2...............................       5,732,000      10,329,000             809             533          19,400
3...............................       1,493,000       3,208,000             441             441           7,300
----------------------------------------------------------------------------------------------------------------

 Table 15--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for Continuous Process
                                            Vents at P&R I Facilities
----------------------------------------------------------------------------------------------------------------
                                                       Total       VOC emission    HAP emission      HAP cost
         Control option            Total capital    annualized      reductions      reductions     effectiveness
                                  investment ($)   costs ($/yr)        (tpy)           (tpy)          ($/ton)
----------------------------------------------------------------------------------------------------------------
1...............................         198,000         586,000            51.0            51.0          11,500
2...............................         557,000       1,242,000            80.1            72.4          17,200
3...............................         215,000         590,000            54.8            54.8          10,800
----------------------------------------------------------------------------------------------------------------

    As part of our technology review for P&R I batch front-end process
vents, we identified the following emission reduction option: revise
the P&R I control threshold for batch front-end process vents from
26,014 lb/yr on an individual vent basis to 10,000 lb/yr on an
aggregate vent basis. We identified this option as a development in
practices, processes, and control technologies based on our comparison
of the batch process vent requirements in the NESHAP for Chemical
Manufacturing Area Sources (CMAS) compared to those in P&R I. We note
that CMAS regulates batch process vents from nine area source
categories in the chemical manufacturing sector. Owners and operators
of a CMAS CMPU with collective uncontrolled organic HAP emissions
greater than or equal to 10,000 lb/yr from all batch process vents
associated with an affected CMPU must meet emission limits for organic
HAP emissions. GACT for batch process vents is defined in the CMAS
NESHAP as 85 percent control for existing batch process units (and 90
percent for new units) that have uncontrolled organic HAP emissions
equal to or greater than 10,000 lb/yr. As mentioned in the CMAS NESHAP
rulemaking,\78\ this applicability threshold of 10,000 lb/yr per batch
process was also used in the MON and provides indicia of the size of a
CMPU because the MON applies to major sources of HAP. The EPA used
information from the baseline facility MON database and determined that
costs to meet an 85 percent control requirement for existing CMAS CMPUs
with uncontrolled organic HAP emissions equal to or greater than 10,000
lb/yr were reasonable ($8,700/ton). We also note that, based on a
response to our CAA section 114 request, a facility (the only facility
that received the CAA section 114 request and is subject to P&R I)
reported to the EPA that it is controlling its five batch front-end
process vents even though P&R I does not require these vents to be
controlled.\79\
---------------------------------------------------------------------------

    \78\ See 74 FR 56008, October 29, 2009.
    \79\ As previously mentioned, the P&R I control threshold for
batch front-end process vents is on an individual vent basis; and
each of the batch front-end process vents at this facility releases
annual organic HAP emissions less than 11,800 kg/yr (26,014 lb/yr)
which is below the control threshold of P&R I.
---------------------------------------------------------------------------

    To evaluate impacts of the option presented for P&R I batch front-
end process vents, we used information from the batch process vent
impacts analysis for the CMAS final rule.\80\ We selected the 90
percent control option model plant shown in Table 3 of this impacts
analysis for sources subject to P&R I (instead of the 85 percent
control option model plant shown in Table 2 of the impacts analysis) to
prevent backsliding of the current P&R I requirements which reflect
MACT instead of the GACT standards of CMAS. We assumed that all
facilities subject to P&R I have batch process vents that would require
control under the option evaluated (i.e., under the option to change
the Group 1 batch front-end process vent threshold to 10,000 lb/yr on
an aggregate vent basis), but as previously mentioned, one facility is
already voluntarily controlling their batch front-end process vents. As
a result, we estimated impacts to the remaining 18 facilities subject
to P&R I.
---------------------------------------------------------------------------

    \80\ RTI, 2009. Revised Impacts Analysis for Batch Process Vents
Chemical Manufacturing Area Source NESHAP. October 14, 2009. EPA
Docket No. EPA-HQ-OAR-2008-0334-0075.
---------------------------------------------------------------------------

    Table 16 of this preamble presents the nationwide impacts for the
option considered for batch front-end process vents at P&R I
facilities. We determined that this option is cost effective and we are
proposing, pursuant to CAA section 112(d)(6), to remove the annual
organic HAP emissions mass flow rate, cutoff flow rate, and annual
average batch vent flow rate Group 1 process vent thresholds from the
Group 1 batch front-end process vent definition in P&R I at 40 CFR
63.482 (these thresholds are currently determined on an individual
batch process vent basis). Instead, owners and operators of batch
front-end process vents that release a total of annual organic HAP
emissions greater than or equal to 4,536 kg/yr (10,000 lb/yr) from all
batch front-end process vents combined would be required to reduce
emissions of organic HAP from these process vents using a flare meeting
the proposed operating and monitoring requirements for flares (see
section III.D.1 of this preamble); or reduce emissions of organic HAP
or TOC by 90 percent by weight (or to an exit concentration of 20 ppmv
if considered an ``aggregate batch vent stream'' as defined by the
rule). We solicit comment on the proposed revisions for batch process
vents for P&R I.

     Table 16--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for Batch Front-End Process Vents at P&R I Facilities
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Total         VOC emission     HAP emission       HAP cost
                           Control option                             Total capital      annualized       reductions       reductions     effectiveness
                                                                      investment ($)    costs ($/yr)        (tpy)            (tpy)           ($/ton)
--------------------------------------------------------------------------------------------------------------------------------------------------------
1..................................................................         811,000          650,700              105              105            6,200
--------------------------------------------------------------------------------------------------------------------------------------------------------

    We did not identify any developments in practices, processes, or
control technologies for P&R II process vents that would achieve a
greater HAP emission reduction beyond the emission reduction already
required by P&R II. Therefore, we are not proposing any changes to P&R
II for this emission

process group based on our technology review.
    For further details on all of our assumptions and methodologies we
used in these analyses, 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.
b. NSPS Subparts III, NNN, and RRR
    As previously mentioned, this action presents the EPA's review of
the requirements of 40 CFR part 60, subparts III, NNN, and RRR pursuant
to CAA section 111(b)(1)(B). As described in section II.G.2 of this
preamble, the statutory review of these NSPS focused on whether there
are any emission reduction techniques that are used in practice that
achieve greater emission reductions than those currently required by
these NSPS and whether any of these developments in practices have
become the BSER. Based on this review, we have determined that the BSER
for reducing VOC emissions from these SOCMI processes remain
combustion, and the current standards of 98 percent reduction of TOC
(minus methane and ethane) or reduction of TOC (minus methane and
ethane) to an outlet concentration of 20 ppmv on a dry basis corrected
to 3 percent oxygen, or use of a flare as an APCD continue to reflect
the BSER. However, we are proposing to remove the alternative of
maintaining a TRE index value greater than 1 without the use of control
device. In addition, we are proposing additional requirements to
provide greater assurance of compliance with the standards. We are also
proposing standards that would apply during startup, shutdown,
maintenance, or inspection of any of the air oxidation units,
distillation operations, and reactor processes affected facilities
under the applicable NSPS where the affected facility is emptied,
depressurized, degassed, or placed into service. The rationales for
each of these proposed actions are presented in more detail below.
Pursuant to CAA section 111(a), the proposed NSPS included in this
action would apply to facilities that begin construction,
reconstruction, or modification after April 25, 2023 (see section
III.F.2 of this preamble).
    NSPS subparts III, NNN, and RRR regulate vent streams \81\ from:
SOCMI air oxidation units for which construction, reconstruction, or
modification commenced after October 21, 1983 that use air (or a
combination of air and oxygen) as an oxidizing agent to produce one or
more of the chemicals listed in 40 CFR 60.617; SOCMI distillation
operations for which construction, reconstruction, or modification
commenced after December 30, 1983 which produce any of the chemicals
listed in 40 CFR 60.667 as a product; and SOCMI reactor processes for
which construction, reconstruction, or modification commenced after
June 29, 1990 which operate as part of a process unit which produces
any of the chemicals listed in 40 CFR 60.707 as a product. The SOCMI
NSPS subparts III, NNN, and RRR regulate VOC emissions in the form of
TOC. In promulgating these rules, the EPA determined that, for sources
with a TRE index value equal to or less than 1.0, the BSER is the use
of thermal incineration or flare achieving 98 percent by weight control
efficiency or a concentration of 20 ppmv on a dry basis corrected to 3
percent oxygen. At the time of promulgation, the EPA stated that any
control technology can be used to meet BSER as long as it can be
demonstrated that the selected control technology is at least as
effective as BSER at reducing VOC emissions. For affected facilities
with a TRE index value greater than 1.0, BSER is no control and sources
are required to maintain a TRE index value greater than 1.0. As
previously mentioned, the TRE index value is a measure of the
supplemental total resource requirement per unit VOC (or HAP for
NESHAP) reduction (see section III.C.3.a of this preamble). 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 SOCMI NSPS
subparts III, NNN, and RRR, the TRE index value is derived from the
cost effectiveness associated with VOC control 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). In general, similar to the HON
and P&R I, process vents with a TRE index value equal to or less than
1.0 are required to be controlled under SOCMI NSPS III, NNN and RRR.
For additional details regarding the TRE index value (including the
equation and coefficients used to calculate the TRE index value for the
SOCMI NSPS subparts III, NNN, and RRR), see the document titled CAA
111(b)(1)(B) review for the SOCMI air oxidation unit processes,
distillation operations, and reactor processes NSPS subparts III, NNN,
and RRR, which is available in the docket for this rulemaking.
---------------------------------------------------------------------------

    \81\ Vent stream means: any gas stream, containing nitrogen
which was introduced as air to the air oxidation reactor, released
to the atmosphere directly from any air oxidation reactor recovery
train or indirectly, after diversion through other process equipment
(for NSPS subpart III); any gas stream discharged directly from a
distillation facility to the atmosphere or indirectly to the
atmosphere after diversion through other process equipment (for NSPS
subpart NNN); and any gas stream discharged directly from a reactor
process to the atmosphere or indirectly to the atmosphere after
diversion through other process equipment (for NSPS subpart RRR). In
all cases, the vent stream excludes relief valve discharges and
equipment leaks.
---------------------------------------------------------------------------

    We reviewed the RACT/BACT/LAER clearinghouse database, other
subsequent EPA, state, and local regulatory development efforts related
to process vents, and responses to our CAA section 114 request for
advances in process operations, design or efficiency improvements, or
other systems of emission reduction.
    While we find no change in the BSER for reducing VOC emissions from
air oxidation units, distillation operations, and reactor processes, we
are proposing certain revisions to the current standards. First, we are
proposing to remove the option of maintaining a TRE index value greater
than 1 as an alternative to controlling emissions. We are proposing
this change based on the following observations we made with respect to
the NSPS TRE index. We observed that some facilities subject to NSPS
subpart III, NNN, and/or RRR are voluntarily controlling process vents
even though such control is not required under the applicable NSPS
because their calculated NSPS TRE index value is greater than 1. At
least three HON facilities that are also subject to at least one of the
three process vent NSPS confirmed in response to our CAA section 114
request, that they were voluntarily controlling some of their Group 2
process vents even though control is not required under either the HON
or the applicable NSPS. We expect

other facilities that are subject to the HON and at least one of the
NSPS subparts III, NNN, and RRR will do this too because some
facilities stated in their response to the CAA section 114 request
that, pursuant to 40 CFR 63.113(h), many of their process vents are
voluntarily designated as HON Group 1 process vents ``so that TRE
calculations are not required.'' In other words, some facilities are
likely electing to control certain process vents that have TRE index
values greater than 1.0. In addition, based on the responses to our CAA
section 114 request, we observed that facilities are routing multiple
process vents to a single APCD. This is significant because the current
use of the TRE index value is only based on controlling a single
process vent with a single APCD, an unrealistic scenario when compared
to how chemical manufacturing facilities actually control their process
vents. It is much more likely that a facility routes numerous process
vents to the same APCD. For the reason stated above, we no longer
believe that TRE index value accurately represents the BSER, and
because a single APCD can control emissions from multiple process
vents, control could be cost-effective even at a TRE index value of
greater than 1. Finally, also based on responses to our CAA section 114
request, one HON and P&R I facility (that is also subject to all three
process vent NSPS) provided over 300 pages of modeled runs that were
used to help the facility determine certain characteristics of their
process vents for inputs to HON and P&R I TRE index value calculations.
We reviewed this information and concluded that determining a TRE index
value for certain process vent streams is often theoretical, can be
extremely complicated, and is uncertain. In addition, because the TRE
index value is largely a theoretical characterization tool, it can be
very difficult to enforce. In order to calculate a TRE index value,
owners and operators must determine numerous input values; and without
the correct amount of process knowledge, verifying inputs can be
problematic. We evaluated the cost of requiring that a facility control
all process vents irrespective of its TRE index value and the average
cost per facility is provided in Table 17 of this preamble. In
addition, given the complexity of chemical manufacturing facilities and
their use of APCDs (e.g., integrated with numerous emission sources
subject to various chemical manufacturing related NSPS and NESHAP), we
found the cost to be cost effective based on the cost-effectiveness we
evaluated for four different NSPS triggering scenarios described
further below (see Table 18 of this preamble). For the reasons stated
above, we believe that proposing to remove the option to maintain a
greater than 1 TRE index value as an alternative to emission reduction
under NSPS subparts IIIa, NNNa, and RRRa make practical and enforceable
sense. In other words, for NSPS subparts IIIa, NNNa, and RRRa, we are
proposing owners and operators reduce emissions of total organic carbon
(TOC) (minus methane and ethane) from all vent streams of an affected
facility (i.e., SOCMI air oxidation unit processes, distillation
operations, reactor processes for which construction, reconstruction,
or modification after April 25, 2023 by 98 percent by weight or to a
concentration of 20 ppmv on a dry basis corrected to 3 percent oxygen,
whichever is less stringent, or combust the emissions in a flare
meeting more stringent operating and monitoring requirements for flares
(we discuss these flare requirements further below in this section)
(see proposed 40 CFR 612a(a), 40 CFR 60.662a(a), and 40 CFR
60.702a(a)).
    We are also proposing to tighten up the requirements for flares.
All three NSPS subparts allow the use of a flare in accordance with the
flare general provisions at 40 CFR 60.18 as an alternative to meeting
the numeric standards. The EPA had previously believed flares could
achieve 98 percent emission reduction if it were operated in accordance
with 40 CFR 60.18. See, e.g., 55 FR 26913. Because the NSPS reflect the
BSER under conditions of proper operation and maintenance, in doing its
review, we also evaluate and determine the proper testing, monitoring,
recordkeeping and reporting requirements needed to ensure compliance
with the emission standards. In doing so, in our review of several
chemical and petrochemical sector related NESHAP, such as MON, the
EMACT standards, and Petroleum Refineries NESHAP, we identified new
operating and monitoring requirements for flares that are different
than those specified in 40 CFR 60.18.\82\ The EPA included these flare
requirements in recent RTR rulemakings in order to ensure flares used
as APCDs achieve 98 percent HAP destruction efficiencies and these
flare requirements are also being proposed for HON and P&R I (this is
discussed in detail in section III.D.1 of this preamble). We evaluated
the costs of these improved flared requirements and the average cost
per facility is provided in Table 17 of this preamble. In addition,
given the complexity of chemical manufacturing facilities and their use
of APCDs (e.g., integrated with numerous emission sources subject to
various chemical manufacturing related NSPS and NESHAP), we found the
cost to be cost effective based on the cost-effectiveness we evaluated
for four different NSPS triggering scenarios described further below
(see Table 18 of this preamble). In light of the above, we are
proposing to include in the new NSPS subparts the same operating and
monitoring requirements for flares that we are proposing for flares
subject to the HON and P&R I (see proposed 40 CFR 619a, 40 CFR 60.669a,
and 40 CFR 60.709a).
---------------------------------------------------------------------------

    \82\ In general the differences include: new requirements to
operate pilot flame systems continuously and that flares operate
with no visible emissions (except for periods not to exceed a total
of 5 minutes during any 2 consecutive hours) when the flare vent gas
flow rate is below the smokeless capacity of the flare; new
requirements related to flare tip velocity and the combustion zone
gas; and new work practice standards related to the visible
emissions and velocity limits during periods when the flare is
operated above its smokeless capacity (e.g., periods of emergency
flaring). For the specific flare requirements, refer to: 40 CFR
63.1103(e)(4) (EMACT standards), 40 CFR 63.2450(e)(5) (MON), and 40
CFR 63.670 and 40 CFR 63.671 (Petroleum Refinery Sector rule).
---------------------------------------------------------------------------

    Third, we are proposing to amend the definition of vent streams
such that the emission standards would also apply to PRD emissions.
Currently, the NSPS subparts III, NNN, and RRR exclude ``relief valve
discharges'' from the definition of vent stream (see 40 CFR 60.611, 40
CFR 60.661, and 40 CFR 60.701) and therefore, emissions from PRDs \83\
are currently excluded from emissions standards in these NSPS. However,
the preambles to the proposed and final subparts were silent on the
reason for this exclusion in the definition of a ``vent stream.''
Further, in reviewing the RACT/BACT/LAER clearinghouse database, we
identified at least one SOCMI facility that has requirements for
reactor process vents such that no PRD may emit directly to the
atmosphere under any circumstance, and the capture system must be
inspected regularly to verify integrity. In light of the above, we are
proposing to the ``vent stream'' definition to remove the exclusion of
``relief valve discharge.''
---------------------------------------------------------------------------

    \83\ The acronym ``PRD'' means pressure relief device and is
common vernacular to describe a variety of devices regulated as
relief valve discharges.
---------------------------------------------------------------------------

    Fourth, we are proposing to expressly prohibit emissions from
affected facilities bypassing an APCD at any time. In our review of
several chemical and petrochemical sector related NESHAP, none of the
rules allow regulated emissions from a process vent to bypass an APCD
at any time, and if a bypass is used, it is considered a

violation and the owner or operator is required to estimate and report
the quantity of regulated emissions released.\84\ The EPA included
these requirements for bypasses in recent RTR rulemakings because
bypassing an APCD could result in a release of regulated emissions from
a process vent into the atmosphere.\85\ Currently, the NSPS subparts
III and NNN do not contain any requirements for bypass lines, and NSPS
subpart RRR only requires owners and operators to document when a vent
stream being routed to an APCD is diverted through a bypass line
resulting in emissions to the atmosphere; therefore, it is unclear
whether the current standards prohibit bypassing an APCD, which could
result in a release of otherwise regulated emissions from a process
vent into the atmosphere. We are therefore proposing in NSPS subparts
IIIa, NNNa, and RRRa that an owner or operator may not bypass the APCD
at any time, that a bypass is a violation (see proposed 40 CFR
60.612a(b)(2), 40 CFR 60.662a(b)(2), and 40 CFR 60.702a(b)(2)), and
that owners and operators must estimate and report the quantity of TOC
released should any such violation occur (see proposed 40 CFR
60.615a(d)(1) and (2), 40 CFR 60.665a(d)(1) and (2), and 40 CFR
60.705a(d)(1) and (2)).
---------------------------------------------------------------------------

    \84\ See 40 CFR 63.1103(e)(6), 40 CFR 63.1109(g), and 40 CFR
63.1110(e)(6) (EMACT standards); 40 CFR 63.2450(e)(6), 40 CFR
63.2520(e)(12), and 40 CFR 63.2525(n) (MON); and 40 CFR 63.644(c),
40 CFR 63.660(i)(2), and 40 CFR 63.655(g)(6)(iii) and (i)(4)
(Petroleum Refinery Sector rule).
    \85\ See 85 FR 40386, July 6, 2020 (EMACT standards), 85 FR
49084, August 12, 2020 (MON), and 80 FR 75178, December 1, 2015
(Petroleum Refinery Sector rule).
---------------------------------------------------------------------------

    Also, we are proposing in the new NSPS subparts additional control
device requirements for adsorbers when such APCD is used to meet the
emission standards in the applicable NSPS. In our review of the MON, we
identified requirements for adsorbers that cannot be regenerated and
regenerative adsorbers that are regenerated offsite (see 40 CFR
63.2450(e)(7)). The MON requires owners and operators of this type of
APCD to use dual adsorbent beds in series and conduct daily monitoring
because the use of a single bed does not ensure continuous compliance
unless the bed is replaced well before breakthrough.\86\ The EPA
included these requirements in their recent RTR rulemaking for MON in
order to ensure owners and operators monitor for performance
deterioration for these specific types of APCDs and these requirements
are also being proposed for HON and P&R I (see section III.E.5.b of
this section for additional information about this). Currently, the
NSPS subparts III, NNN, and RRR do not contain any requirements for
adsorbers that cannot be regenerated and regenerative adsorbers that
are regenerated offsite. We evaluated the cost of these requirements
for adsorbers and the average cost per facility is provided in Table 17
of this preamble. In addition, given the complexity of chemical
manufacturing facilities and their use of APCDs (e.g., integrated with
numerous emission sources subject to various chemical manufacturing
related NSPS and NESHAP), we found the cost to be cost effective based
on the cost-effectiveness we evaluated for four different NSPS
triggering scenarios described further below (see Table 18 of this
preamble); therefore, in order to ensure that continuous compliance is
achieved for NSPS subpart IIIa, NNNa, and RRRa facilities at all times
when controlling VOC emissions (i.e., for those facilities that choose
to use adsorbers that cannot be regenerated and regenerative adsorbers
that are regenerated offsite as BSER to meet the 98-percent control or
a 20 ppmv TOC outlet concentration emission standard), we are proposing
to include at 40 CFR 60.613a(a)(6), 40 CFR 60.663a(a)(6), and 40 CFR
60.703a(a)(6) the same monitoring requirements for adsorbers that
cannot be regenerated and regenerative adsorbers that are regenerated
offsite that we are proposing for the HON and P&R I.
---------------------------------------------------------------------------

    \86\ According to the MON, ``breakthrough'' means the time when
the level of HAP or TOC, measured at the outlet of the first bed,
has been detected is at the highest concentration allowed to be
discharged from the adsorber system and indicates that the adsorber
bed should be replaced.
---------------------------------------------------------------------------

    Lastly, consistent with Sierra Club v. EPA, 551 F.3d 1019 (D.C.
Cir. 2008),\87\ we are proposing standards for periods of startup and
shutdown, which are currently not subject to the emission standards in
NSPS subparts III, NNN and RRR. For this effort, we identified, as part
of our review of the RACT/BACT/LAER clearinghouse database, some SOCMI
facilities in Texas that have specific requirements related to
maintenance, startup, and shutdown for equipment and vessel openings
related to process vents (i.e., opening air oxidation unit processes,
distillation operations, and reactor processes) and we found that these
requirements are included in several SOCMI related NESHAP (i.e., EMACT
standards, the MON, and/or the petroleum refineries NESHAP) (we discuss
these requirements further below in this section of the preamble).
Given that many SOCMI processes that are subject to the SOCMI NSPS are
also located at chemical plants subject to these related NESHAP and
these facilities use the same APCDs to comply with all of these rules
(to reduce both VOC and HAP emissions), we also examined the process
vent provisions from each of these rules. Review of the NESHAP
standards mentioned above revealed several related requirements that
did not exist at the time the EPA promogulated NSPS subparts III, NNN,
and RRR.
---------------------------------------------------------------------------

    \87\ In Sierra Club, the court vacated the SSM exemption
contained in 40 CFR 63.6(f)(1) and 40 CFR 63.6(h)(1). The court
explained that under section 302(k) of the CAA, emissions standards
or limitations must be continuous in nature and that an SSM
exemption violates this requirement. The EPA believes the reasoning
in Sierra Club applies equally to section 111 standards.
---------------------------------------------------------------------------

    As previously mentioned in our review of the RACT/BACT/LAER
clearinghouse database and as found in our review of in several
chemical and petrochemical sector related NESHAP,\88\ the EPA has
included a work practice standard for maintenance vents requiring
owners and operators to meet certain conditions before they open
equipment to the atmosphere, including opening equipment to the
atmosphere that are related to NSPS process vents (e.g., air oxidation
units, distillation operations, and reactor processes). This work
practice standard requires that, prior to opening process equipment to
the atmosphere, the equipment must either: (1) Be drained and purged to
a closed system so that the hydrocarbon content is less than or equal
to 10 percent of the LEL; (2) be opened and vented to the atmosphere
only if the 10-percent LEL cannot be demonstrated and the pressure is
less than or equal to 5 psig, provided there is no active purging of
the equipment to the atmosphere until the LEL criterion is met; (3) be
opened when there is less than 50 pounds of VOC that may be emitted to
the atmosphere; or (4) for installing or removing an equipment blind,
depressurize the equipment to 2 psig or less and maintain pressure of
the equipment where purge gas enters the equipment at or below 2 psig
during the blind flange installation, provided none of the other
proposed work practice standards can be met.\89\ We evaluated the cost
associated with this work practice standard and the average cost per
facility is provided in Table 17 of this preamble. In addition, given
the complexity of chemical manufacturing facilities and their use of
APCDs (e.g., integrated with numerous emission

sources subject to various chemical manufacturing related NSPS and
NESHAP), we found the cost to be cost effective based on the cost-
effectiveness we evaluated for four different NSPS triggering scenarios
described further below (see Table 18 of this preamble). We determined
that these work practice standards for maintenance vents (i.e.,
equipment openings related to process vents) is a technique used in
practice that achieves emission reductions during startup, shutdown,
maintenance, or inspection of any of the air oxidation units,
distillation operations, and reactor processes affected facilities
under the applicable NSPS where the affected facility is emptied,
depressurized, degassed, or placed into service. CAA section 111(h)(1)
authorizes the Administrator to promulgate ``a design, equipment, work
practice, or operational standard, or combination thereof'' if in his
or her judgment, ``it is not feasible to prescribe or enforce a
standard of performance.'' Equipment openings related to process vents
are not ``emitted through a conveyance designed and constructed to emit
or capture such pollutant'' (see CAA section 111(h)(2)) and it is not
possible to characterize each of these potential release points. For
these reasons (which are the same reasons we discuss in section
III.D.4.a of this preamble for including a work practice standard for
maintenance activities in the HON and P&R I), we are proposing these
work practice standards for maintenance vents in NSPS subparts IIIa,
NNNa, and RRRa as the standards reflecting the BSER during periods of
startup and shutdown (see proposed 40 CFR 612a(c), 40 CFR 60.662a(c),
and 40 CFR 60.702a(c)).
---------------------------------------------------------------------------

    \88\ See 40 CFR 63.1103(e)(5) (EMACT standards), 40 CFR
63.2450(v) (MON), and 40 CFR 63.642(c) (Petroleum Refinery Sector
rule).
    \89\ The EPA added these equipment opening requirements in the
recent RTR to be consistent with Sierra Club.
---------------------------------------------------------------------------

    As mentioned above, we analyzed cost and emission reductions as
part of our evaluation of each of the options considered above. We used
the average cost and emission reductions that we determined for process
vents subject to the HON to evaluate the costs, emission reductions,
and cost-effectiveness of each of the options considered above for NSPS
subparts IIIa, NNNa, and RRRa. Table 17 of this preamble summarizes
these average HON cost and emission reductions.

    Table 17--Average Cost and Emission Reductions for Process Vents Subject to the HON Used for the Suite of
             Proposed Process Vent Requirements Evaluated for the NSPS Subparts IIIa, NNNa, and RRRa
----------------------------------------------------------------------------------------------------------------
                                                                                Total annual     VOC emission
                  Description                    Total capital   Total annual    cost w/recovery    reductions
                                                investment ($)    cost ($/yr)    credits ($/yr)        (tpy)
----------------------------------------------------------------------------------------------------------------
Flare monitoring requirements \1\.............       3,752,200         789,200           789,200              93
Maintenance vent requirements \2\.............  ..............             460               460  ..............
Revising the standard from a TRE calculation            39,300          98,400            98,400             9.1
 to control of all vent streams \3\...........
Adsorber monitoring (carbon cannisters) \4\...          26,500           2,500             2,500            0.21
----------------------------------------------------------------------------------------------------------------
\1\ For additional details, see the document titled Control Option Impacts for Flares Located in the SOCMI
  Source Category that Control Emissions from Processes Subject to HON and for Flares that Control Emissions
  from Processes Subject to Group I and Group II Polymers and Resins NESHAPs, which is available in the docket
  for this rulemaking.
\2\ For additional details, see the document titled Review of Regulatory Alternatives for Certain Vent Streams
  in the SOCMI Source Category that are Associated with Processes Subject to HON and Processes Subject to Group
  I and Group II Polymers and Resins NESHAPs, which is available in the docket for this rulemaking.
\3\ For additional details, 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.
\4\ For additional details, see the document titled Analysis of Monitoring Costs and Dual Bed Costs for Non-
  Regenerative Carbon Adsorbers Used in the SOCMI Source Category that are Associated with Processes Subject to
  HON and for Non-Regenerative Carbon Adsorbers that are Associated with Processes Subject to Group I Polymers
  and Resins NESHAP, which is available in the docket for this rulemaking.

    We also evaluated the costs of requiring the suite of proposed
requirements described above to SOCMI nationwide. We conducted an
analysis to estimate how many non-HON NSPS affected facilities are
expected/projected to be subject to the suite of proposed process vent
requirements presented above. Given that we are proposing these same
suite of process vent requirements for HON facilities, we only
considered non-HON NSPS affected facilities here under CAA section 111
so as to not double count cost and emission reductions from affected
facilities that are subject to both these SOCMI NSPS and the HON. An
affected facility can become subject to SOCMI NSPS subpart IIIa, NNNa,
or RRRa under one of the following scenarios: (1) The affected facility
is at a new greenfield facility; (2) the affected facility is a new
affected facility at an existing plant site; (3) an existing affected
facility is modified; or (4) an existing affected facility triggers the
reconstruction requirements. For scenario 1 (i.e., affected facility is
at a new greenfield facility), we assumed only one non-HON greenfield
facility will trigger NSPS subpart IIIa, NNNa, or RRRa over the next 5
years (we do not expect any non-HON greenfield facilities, but to be
comprehensive in our analysis, we assumed one). For comprehensiveness,
we also assumed this greenfield facility would not be subject to the
EMACT standards, MON, and Petroleum Refinery Sector rule; and the
facility will use one flare and one non-flare APCD to control all their
process vents from SOCMI NSPS unit operations. We used facility
responses to our CAA section 114 request to help us determine the
number of facilities that could potentially trigger scenarios 2, 3, and
4.
    For scenario 2 (i.e., new affected facilities constructed at
existing plant sites), we estimate six new affected facilities will be
built and be subject to new requirements in a new NSPS subpart IIIa,
NNNa, or RRRa over the next 5 years. Facilities responding to our CAA
section 114 request had 500 unit operations subject to either NSPS
subpart III, NNN, or RRR; and only one of these unit operations was new
construction in the last 5 years and not subject to the HON. We
determined that there are currently 284 SOCMI facilities subject to
either NSPS subpart III, NNN, or RRR; and 196 of these are non-HON-
subject facilities.\90\ Based on responses

to our CAA section 114 request, HON facilities have on average 45 unit
operations per facility. Assuming non-HON facilities are smaller, we
estimate that non-HON facilities subject to either NSPS subpart III,
NNN, or RRR have 15 unit operations per facility. Assuming the same
distribution of new construction for non-HON facilities, we estimate
that six new affected facilities (one new unit operation per non-HON
facility subject to either NSPS subpart III, NNN, or RRR), would have
been constructed in the last 5 years (1/500*15*196). This analysis
assumes that the same number of unit operations that were constructed
in the last 5 years would be constructed in the next 5 years. We then
assumed two of the six new affected facilities (or about 33 percent)
are collocated at a petroleum refinery, MON, and/or EMACT facility.
Therefore, two of the six unit operations would already be complying
with requirements in the NSPS (because of the NESHAP); and we also
assumed that of the remaining four new unit operations, two will not
use a flare to comply with the NSPS.
---------------------------------------------------------------------------

    \90\ As of March 2022, according to the OECA's ECHO tool, there
were 284 facilities located in the United States that are
potentially subject to at least one of the process vent NSPS
subparts III, NNN, and/or RRR. The list of facilities is available
in the document titled Lists of Facilities Subject to the HON, Group
I and Group II Polymers and Resins NESHAPs, and NSPS subparts VV,
VVa, III, NNN, and RRR, which is available in the docket for this
rulemaking.
---------------------------------------------------------------------------

    For Scenarios 3 and 4 (i.e., existing facility is modified or
reconstructed), we estimate 12 existing affected facilities will
trigger new requirements in a new NSPS subpart IIIa, NNNa, or RRRa over
the next 5 years due to modification or reconstruction. As mentioned
previously, facilities responding to our CAA section 114 request had
500 unit operations subject to either III, NNN, or RRR; however, only
two of these unit operations were modified or reconstructed in the last
5 years and not subject to the HON. Using similar procedure as
described above for scenario 2, we estimate that 12 modified or
reconstructed affected facilities (one modified or reconstructed unit
operation per non-HON facility subject to the NSPS), would have been
modified or reconstructed in the last 5 years (2/500*15*196). This
analysis assumes that the same number of unit operations that were
modified or reconstructed in the last 5 years would be modified or
reconstructed in the next 5 years. We then assumed four of the 12 (or
about 33 percent) modified or reconstructed affected facilities are
collocated at a refinery, MON, and/or EMACT facility. Therefore, four
of the 12 unit operations are already complying with requirements in
the NSPS (because of the NESHAP); and we also, assumed that of the
remaining eight modified or reconstructed unit operations, four will
not use a flare to comply with the NSPS.
    Table 18 of this preamble below presents the nationwide impacts for
the suite of proposed process vent requirements presented above that we
considered for vent streams subject to new NSPS subparts IIIa, NNNa,
and RRRa. The cost-effectiveness for the suite of process vent
requirements evaluated under this NSPS review is $4,570 per ton VOC
(cost-effectiveness w/recovery credits), which we consider to be cost
effective. See the document titled CAA 111(b)(1)(B) review for the
SOCMI air oxidation unit processes, distillation operations, and
reactor processes NSPS subparts III, NNN, and RRR, which is available
in the docket for this rulemaking, for details on the assumptions and
methodologies used in this analysis.
    For the reasons stated above, pursuant to CAA section 111(b)(1)(B),
we are proposing new SOCMI NSPS to: (1) Remove the TRE index value
concept in its entirety and require all process vents from an affected
facility be controlled; (2) eliminate the relief valve discharge
exemption from the definition of ``vent stream'' such that any relief
valve discharge to the atmosphere of a vent stream is a violation of
the emissions standard; (3) prohibit an owner or operator from
bypassing the APCD at any time, and to report any such violation
(including the quantity of TOC released to the atmosphere); (4) require
that flares used to reduce emissions comply with the same flare
operating and monitoring requirements as those we have promulgated for
flares used in SOCMI-related NESHAP; (5) require work practice
standards for maintenance vents during startup, shutdown, maintenance,
or inspection of any of the air oxidation units, distillation
operations, and reactor processes affected facilities under the
applicable NSPS where the affected facility is emptied, depressurized,
degassed, or placed into service; and (6) add control device
operational and monitoring requirements for adsorbers that cannot be
regenerated and regenerative adsorbers that are regenerated offsite
(see section III.E.5.b of this preamble). We are proposing that
affected facilities that are constructed, reconstructed, or modified
after April 25, 2023 would be subject to these proposed requirements in
NSPS subparts IIIa, NNNa, and/or RRRa.

    Table 18--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for Non-HON Vent
                            Streams Triggering NSPS Subparts IIIa, NNNa, and/or RRRa
----------------------------------------------------------------------------------------------------------------
                                                                                Cost-
                                                                   Total annual    VOC emission    effectiveness
            Scenario               Total capital   Total annual      cost  w/       reductions      w/recovery
                                  investment ($)    cost ($/yr)      recovery          (tpy)      credits ($/ton
                                                                  credits ($/yr)                       VOC)
----------------------------------------------------------------------------------------------------------------
Scenario 1 (i.e., one affected         1,665,300         461,000         461,000              93           4,960
 facility at a new greenfield
 facility)......................
Scenario 2 (i.e., new affected         7,609,500       1,780,000       1,780,000             392           4,540
 facility at six existing
 facilities)....................
Scenarios 3 and 4 (i.e., 12           15,192,500       3,558,000       3,558,000             783           4,540
 existing affected facilities
 modified or triggers the
 reconstruction requirements)...
                                 -------------------------------------------------------------------------------
    Total.......................      24,467,300       5,799,800       5,799,800           1,269           4,570
----------------------------------------------------------------------------------------------------------------

4. Standards for Transfer Racks
    We did not identify any developments in practices, processes, or
control technologies for HON transfer racks that would achieve a
greater HAP emission reduction beyond the emission reduction already
required by the HON. Therefore, under CAA section 112(d)(6) we are not
proposing any changes to the

HON for this emission process group based on our technology review.\91\
We note, however, that under CAA section 112(d)(2) and (3) we are
proposing changes to the applicability threshold for HON transfer racks
to fill a regulatory gap in the current HON (see section III.D.8 of
this preamble).
---------------------------------------------------------------------------

    \91\ P&R I and P&R II sources do not have transfer racks as
emission sources.
---------------------------------------------------------------------------

5. Standards for Wastewater
    As previously mentioned, HAP are emitted into the air from
wastewater collection, storage, and treatment systems that are
uncovered or open to the atmosphere through volatilization of organic
compounds 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.
    The HON defines wastewater to mean water that: (1) Contains either:
(i) an annual average concentration of Table 9 (to NESHAP subpart G)
compounds of at least 5 ppmw and has an annual average flow rate of
0.02 liter per minute (lpm) or greater or (ii) an annual average
concentration of Table 9 (to NESHAP subpart G) compounds of at least
10,000 ppmw at any flow rate, and that (2) is discarded from a CMPU
that meets all of the criteria specified in 40 CFR 63.100 (b)(1)
through (3). Wastewater is process wastewater or maintenance
wastewater. For process and maintenance wastewaters and certain liquid
streams in open systems within a CMPU, the HON defines Group 1
wastewater streams at existing sources as having: either a total annual
average concentration of Table 9 (to NESHAP subpart G) compounds
greater than or equal to 10,000 ppmw at any flow rate; or a total
annual average concentration of compounds in Table 9 to NESHAP subpart
G greater than or equal to 1,000 ppmw, and the annual average flow rate
is greater than or equal to 10 liter per minute. NESHAP subpart G
provides owners and operators several control options for wastewater
tanks, surface impoundments, containers, individual drain systems, and
oil-water separators. NESHAP subpart G also specifies performance
standards for treating 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, NESHAP subpart G 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.
    P&R I defines wastewater similarly to how the term is defined in
the HON, except instead of referring to Table 9 (to NESHAP subpart G)
compounds, P&R I refers to Table 5 (to NESHAP subpart U) compounds. The
standards for wastewater in NESHAP subpart U refer to the provisions in
NESHAP subpart G. Generally, the P&R I Group 1 wastewater threshold is
the same as in the HON, except P&R I refers to compounds that meet the
definition of organic HAP in 40 CFR 63.482 in addition to those listed
in table 9 of NESHAP subpart G, and P&R I exempts wastewater that
pertain solely and exclusively to organic HAP listed on table 8 of
NESHAP subpart G).
    P&R II defines wastewater as aqueous liquid waste streams exiting
equipment at an affected source. No further stratification into groups
for applicability is specified. As previously mentioned, process vents,
storage tanks, and wastewater systems \92\ 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 sources
require 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.
---------------------------------------------------------------------------

    \92\ P&R II defines a wastewater system as a system made up of a
drain system and one or more waste management units; and a
wastewater management unit means any component, piece of equipment,
structure, or transport mechanism used in storing, treating, or
disposing of wastewater streams, or conveying wastewater between
storage, treatment, or disposal operations.
---------------------------------------------------------------------------

    As part of our CAA section 112(d)(6) technology review for HON and
P&R I wastewater streams, we evaluated tightening the HON and P&R I
wastewater Group 1 applicability thresholds. Specifically, we evaluated
the option (option 1) to require owners and operators to manage and
treat existing wastewater streams with total annual average
concentration of Table 9 (to NESHAP subpart G) compounds (for HON) and
Table 5 (to NESHAP subpart U) compounds (for P&R I) greater than or
equal to 1,000 ppmw at any flow rate; or greater than or equal to 10
ppmw at a flow rate of 10 lpm or greater. We did not identify any
control options for P&R II wastewater streams.
    Table 19 of this preamble presents the nationwide costs and impacts
for the wastewater stream control option considered for HON facilities.
Table 20 of this preamble presents the nationwide costs and impacts for
the wastewater stream control option considered for P&R I facilities.
For details on the assumptions and methodologies used in this analysis,
see the document titled Clean Air Act Section 112(d)(6) Technology
Review for Wastewater Streams Located in the SOCMI Source Category that
are Associated with Processes Subject to HON and for Wastewater Streams
that are Associated with Processes Subject to Group I and II Polymers
and Resins NESHAP, which is available in the docket for this
rulemaking.
    We determined that the option to revise wastewater stream Group 1
threshold applicability (i.e., to require control of existing
wastewater streams with total annual average concentration of Table 9
to subpart G compounds (for HON) or Table 5 to 40 CFR 63, subpart U
compounds (for P&R I) greater than or equal to 1,000 ppmw at any flow
rate; or greater than or equal to 10 ppmw at a flow rate of 10 lpm or
greater) is not cost effective based on the costs and emission
reductions presented. Therefore, we 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). Also, we did not identify any developments in
practices, processes, or control technologies for P&R II wastewater
that would achieve a greater HAP emission reduction beyond the emission
reduction already required by P&R II. Therefore, we are not proposing
any changes to P&R II for this emission process group based on our
technology review.

            Table 19--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for Wastewater Streams at HON Facilities
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Total         VOC emission     HAP emission       HAP cost
                           Control option                             Total capital      annualized       reductions       reductions     effectiveness
                                                                      investment ($)    costs ($/yr)        (tpy)            (tpy)           ($/ton)
--------------------------------------------------------------------------------------------------------------------------------------------------------
1..................................................................     504,766,000      210,739,500            2,755            2,755           76,500
--------------------------------------------------------------------------------------------------------------------------------------------------------

           Table 20--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for Wastewater Streams at P&R I Facilities
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Total         VOC emission     HAP emission       HAP cost
                           Control option                             Total capital      annualized       reductions       reductions     effectiveness
                                                                      investment ($)    costs ($/yr)        (tpy)            (tpy)           ($/ton)
--------------------------------------------------------------------------------------------------------------------------------------------------------
1..................................................................      46,847,800       22,548,200              220              220          102,500
--------------------------------------------------------------------------------------------------------------------------------------------------------

6. Standards for Equipment Leaks
    As previously mentioned, emissions of VOC and HAP from equipment
leaks occur in the form of gases or liquids that escape to the
atmosphere through many types of connection points (e.g., threaded
fittings) or through the moving parts of certain types of process
equipment during normal operation. Equipment regulated by the HON, P&R
I, and P&R II includes agitators, compressors, connectors,
instrumentation systems, OEL, PRDs, pumps, sampling collection systems,
and valves \93\ 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 results of our CAA section 112(d)(6)
technology review for equipment leaks associated with HON, P&R I, and
P&R II processes are discussed in section III.C.6.a of this preamble.
Equipment regulated by NSPS subpart VVa includes connectors,
compressors, PRDs, pumps, sampling collection systems, OEL, and valves
that contain or contact material that are 10 percent by weight or more
of VOC, operate 300 hours per year or more, and are not in vacuum
service. The results of our CAA 111(b)(1)(B) review for equipment leaks
subject to NSPS subpart VVa are discussed in section III.C.6.b of this
preamble.
---------------------------------------------------------------------------

    \93\ We believe P&R II contains a typographical error in that
valves are currently excluded from the definition of equipment leaks
at 40 CFR 63.522; see section III.D.10 of this preamble for our
rationale for this conclusion and our proposal to address this
issue.
---------------------------------------------------------------------------

a. HON, P&R I, and P&R II
    The HON, P&R I, and P&R II standards for BLR, require owners or
operators to meet the control requirements of NESHAP subpart H which
contains the MACT standard for equipment leaks, including LDAR
provisions and other control requirements. Subpart H was also
identified in P&R II as the appropriate level of control for facilities
producing WSR, but additional compliance options were allowed in the
P&R II rule for WSR sources. We are proposing to no longer allow the
additional compliance options for WSR sources, and to require that all
sources comply with the HON equipment leaks regulations (see section
III.D.10 of this preamble for further details about this proposed
amendment). Depending on the type of equipment, the standards require
either periodic monitoring for and repair of leaks, the use of
specified equipment to minimize leaks, or specified work practices.
Monitoring for leaks generally must be conducted using EPA Method 21 in
appendix A-7 to 40 CFR part 60 or other approved equivalent monitoring
techniques. The equipment leak HON, P&R I, and P&R II 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 (e.g., visual, audible, olfactory).
    The practices, processes, and control technologies considered
during MACT development for equipment leaks at HON, P&R I, and P&R II
facilities included LDAR. To identify developments for the technology
review, we reviewed responses to our CAA section 114 request, the BACT/
LAER database, and evaluated other federal regulations (i.e., the
Petroleum Refinery Sector rule, MON, and NSPS subpart VVa) and state
regulations (i.e., the Texas fugitive emissions rules \94\ applicable
to petrochemical processes). Also, the EPA conducted a general analysis
in a 2011 equipment leaks study \95\ to identify the latest
developments in practices, processes, and control technologies for
equipment leaks at chemical manufacturing facilities and petroleum
refineries and estimated the impacts of applying those practices,
processes, and control technologies to model facilities. We used this
2011 equipment leaks analysis as a reference for conducting the
technology review for equipment leaks at HON, P&R I, and P&R II
facilities.
---------------------------------------------------------------------------

    \94\ 30 TAC 115, subchapters D and H, Division 3.
    \95\ Hancy. 2011. Memorandum from Hancy, C., RTI International
to Howard, J., EPA/OAQPS. Analysis of Emissions Reduction Techniques
for Equipment Leaks. December 21, 2011. EPA Docket ID No. EPA-HQ-
OAR-2010-0869.
---------------------------------------------------------------------------

    Our technology review for equipment leaks of HAP (e.g., broader
than the EtO discussed in section II.B.2.a.ii of this preamble)
identified several developments in LDAR practices and processes: (1)
Lowering the leak definition for valves in light liquid service from
500 ppm to 100 ppm with monthly monitoring and skip periods; (2) in
addition to requirements specified in option 1, lowering the leak
definition for valves in gas and vapor service from 500 ppm to 100 ppm
with monthly monitoring and skip periods; and (3) in addition to
requirements specified in option 2, lowering the leak definition for
pumps in light liquid service from 1,000 ppm to 500 ppm with monthly
monitoring. For all other component types, we did not identify
developments in LDAR practices and processes in the chemical
sector.\96\
---------------------------------------------------------------------------

    \96\ We note that while other technologies such as optical gas
imaging and sensor networks may be considered developments in
monitoring for equipment leaks, the EPA did not evaluate these
options further as we have insufficient information on how use of
such monitoring technology compares to current EPA Method 21
practices for chemical sector sources and we are soliciting comment
on these technologies. See section V of this preamble for more
details.

---------------------------------------------------------------------------

    Emissions reductions were estimated for the new developments that
we identified using component counts and emission factors. The
component counts were derived using data provided to the EPA in
response to our CAA section 114 request (see section II.C of this
preamble). We developed model component counts for 207 HON facilities,
19 P&R I facilities (and 10 of the P&R I facilities are collocated with
HON processes), and 5 P&R II facilities (and 3 of the P&R II facilities
are collocated with HON processes). We then multiplied the number of
nationwide HON, P&R I, and P&R II processes \97\ by the model component
counts to estimate the nationwide component counts. Subsequently,
baseline emissions and emissions after implementation of the controls
for each component were calculated using these nationwide component
counts and emission factors and leak frequencies for the chemical
manufacturing industry from the 2011 equipment leaks study.
---------------------------------------------------------------------------

    \97\ We used information from the 2006 RTR HON proposal preamble
(see pg. 34434: https://www.govinfo.gov/content/pkg/FR-2006-06-14/pdf/06-5219.pdf) to estimate the number of HON CMPUs nationwide. In
2006, the EPA estimated 729 CMPUs nationwide from 238 HON facilities
based off information from the American Chemistry Council. We scaled
this data to 207 HON facilities [(207 x 729)/238 = 634]. For P&R I
facilities we assumed 1 EPPU per facility resulting in 19 EPPU's.
For P&R II facilities we assumed each facility had 1 process unit
associated with either WSR or BLR processes resulting in 5 process
units total.
---------------------------------------------------------------------------

    Costs were then calculated for the baseline and control options,
which reflect the cost to implement an LDAR program for each component.
Note that the difference between the costs for the baseline and control
options is the incremental cost to comply with the controls.
Furthermore, because the control options result in chemicals in process
lines not leaking and therefore, not being lost, we present costs both
with and without this consideration. To estimate savings in chemicals
not being emitted (i.e., lost) due to the equipment leak control
options, we applied a recovery credit of $900 per ton of VOC to the
emission reductions in the analyses.
    We calculated the VOC and HAP cost effectiveness by dividing the
incremental annual costs by the emissions reductions. Table 21 of this
preamble presents the nationwide costs and impacts for the suite of
equipment leak control options considered for HON facilities (including
10 P&R I facilities and 3 P&R II facilities collocated with HON
facilities). Table 22 of this preamble presents the nationwide costs
and impacts for the suite of equipment leak control options considered
for P&R I facilities (not collocated with HON facilities). Table 23 of
this preamble presents the nationwide costs and impacts for the suite
of equipment leak control options considered for P&R II facilities (not
collocated with HON facilities). For details on the assumptions and
methodologies used in this analysis, see the document titled Clean Air
Act Section 112(d)(6) Technology Review for Equipment Leaks Located in
the SOCMI Source Category that are Associated with Processes Subject to
HON and for Equipment Leaks that are Associated with Processes Subject
to Group I and II Polymers and Resins NESHAP, which is available in the
docket for this rulemaking.
    Based on the costs and emission reductions for each of the options,
we determined that none of them are cost effective. Therefore, we are
not proposing to revise the HON, P&R I, and P&R II to reflect the
requirements of these options pursuant to CAA section 112(d)(6).

              Table 21--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for HON Equipment Not in EtO Service
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Average
                                                               Total           Total                       Average  HAP    Average  HAP     incremental
                                           Total capital    annualized      annualized     HAP emission        cost            cost          HAP cost
             Control option               investment ($)     costs w/o      costs with      reductions     effectiveness   effectiveness   effectiveness
                                                          credits ($/yr)  credits ($/yr)       (tpy)       with credits   w/o credits ($/  with credits
                                                                                ($/ton)          ton)           ($/ton)
--------------------------------------------------------------------------------------------------------------------------------------------------------
1.......................................       2,079,000         538,400         393,000              16          25,000          34,000  ..............
2.......................................       3,637,000         872,000         672,000              22          31,000          40,000          47,000
3.......................................        4,926,00       1,325,000       1,105,000              24          46,000          55,000         217,000
--------------------------------------------------------------------------------------------------------------------------------------------------------

                      Table 22--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for P&R I Equipment
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Average
                                                               Total           Total                         HAP cost        HAP cost       incremental
                                           Total capital    annualized      annualized     HAP emission    effectiveness   effectiveness     HAP cost
             Control option               investment ($)     costs w/o      costs with      reductions     with credits   w/o credits ($/  effectiveness
                                                          credits ($/yr)  credits ($/yr)       (tpy)          ($/ton)          ton)        with credits
                                                                                ($/ton)
--------------------------------------------------------------------------------------------------------------------------------------------------------
1.......................................          62,300          16,100          11,700            0.48          24,000          34,000  ..............
2.......................................         109,000          26,200          20,200            0.67          30,000          39,000          45,000
3.......................................         148,000          40,500          33,900            0.73          46,000          55,000         228,000
--------------------------------------------------------------------------------------------------------------------------------------------------------

                      Table 23--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for P&R II Equipment
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Average
                                                               Total           Total                         HAP cost        HAP cost       incremental
                                           Total capital    annualized      annualized     HAP emission    effectiveness   effectiveness     HAP cost
             Control option               investment ($)     costs w/o      costs with      reductions     with credits   w/o credits ($/  effectiveness
                                                          credits ($/yr)  credits ($/yr)       (tpy)          ($/ton)          ton)        with credits
                                                                                ($/ton)
--------------------------------------------------------------------------------------------------------------------------------------------------------
1.......................................          16,400           4,300           3,200            0.13          25,000          33,000  ..............
2.......................................          28,700           7,000           5,400            0.18          30,000          39,000          44,000
3.......................................          39,400          10,700           8,900            0.19          47,000          56,000         350,000
--------------------------------------------------------------------------------------------------------------------------------------------------------

b. NSPS Subpart VVa
    This action presents the EPA's review of the requirements of 40 CFR
part 60, subpart VVa pursuant to CAA section 111(b)(1)(B). As described
in section II.G.2 of this preamble, the statutory review of these NSPS
focused on whether there are any emission reduction techniques that are
used in practice that achieve greater emission reductions than those
currently required by these NSPS and whether any of these developments
in practices have become the BSER. Based on this review, we have
determined that the BSER for reducing VOC emissions from equipment
leaks from SOCMI processes remain work practice standards based on
LDAR. However, we have determined that there are techniques used in
practice related to LDAR of certain equipment that achieve greater
emission reductions than those currently required by NSPS subpart VVa.
We are proposing that BSER for gas and light liquid valves is the same
monitoring in an LDAR program as NSPS subpart VVa, but now at a leak
definition of 100 ppm, and BSER for connectors is monitoring in the
LDAR program at a leak definition of 500 ppm and monitored annually,
with reduced frequency for good performance. The rationale for this
proposed action is presented in more detail below. Pursuant to CAA
section 111(a), the proposed NSPS included in this action would apply
to facilities that begin construction, reconstruction, or modification
after April 25, 2023 (see section III.F.2 of this preamble).
    NSPS subpart VVa regulates equipment leaks from SOCMI affected
facilities whose construction, reconstruction, or modification
commenced after November 7, 2006. NSPS subpart VVa addresses fugitive
emissions of VOC from SOCMI affected facilities. Fugitive emissions are
emissions caused by leaks in processing equipment. NSPS subpart VVa
defines the affected facility as the ``group of all equipment within a
process unit,'' with equipment meaning ``each pump, compressor,
pressure relief device, sampling connection system, open-ended valve or
line, valve, and flange or other connector in VOC service and any
devices or systems required by this subpart.'' In other words, the
affected facility is the collection of all the valves, pumps, etc.,
within a process unit. For the purpose of NSPS subpart VVa, the process
units are those components assembled to produce any of the chemicals
listed in 40 CFR 60.489a of subpart VVa. In promulgating NSPS subpart
VVa, the EPA determined that BSER is work practice standards for
equipment leaks based on LDAR and other control requirements. The
standards apply to connectors, compressors, PRDs, pumps, sampling
collection systems, OEL, and valves in VOC service. A piece of
equipment is in VOC service if it contains or contacts a fluid that is
at least 10 percent by weight or more of VOC. Depending on the type of
equipment, the standards require either periodic monitoring for and
repair of leaks, the use of specified equipment to minimize leaks, or
specified work practices. Monitoring for leaks must be conducted using
EPA Method 21 in appendix A-7 to 40 CFR part 60 or other approved
equivalent monitoring techniques. These standards are generally the
same as those for HON equipment leaks, except the standards apply to
VOC instead of HAP, and the connector monitoring requirements in VVa
were stayed.\98\
---------------------------------------------------------------------------

    \98\ See 73 FR 31372, June 2, 2008.
---------------------------------------------------------------------------

    For our review of NSPS subpart VVa, we reviewed the RACT/BACT/LAER
clearinghouse database, and other EPA, state, and local regulatory
development efforts related to equipment leaks to determine advances in
process operations, design or efficiency improvements, or other systems
of emission reduction. The 2011 equipment leaks study (see section
III.C.6.a of the preamble) considered a 100 ppm leak definition, and we
identified at least one regulation, in the Bay Area Air Quality
Management District (BAAQMD), that requires gas and light liquid valves
to meet a 100 ppm leak definition. Additionally, in recent consent
decrees, the EPA has required low-emitting gas and light liquid valves
be used.\99\ Low-emitting valves use low emission packing in the valve
stem to reduce emissions below 100 ppm, but even these low-emitting
valves can eventually leak over time, as valve packing can deteriorate
as valves get used more and more. Discussions with valve manufacturers
have also shown that low-emitting valves are comparable in cost to
normal valves and are considered by at least one manufacturer to be the
valve standard commonly used by their customers. Because low-emitting
valves do not continually keep leaks below 100 ppm, the EPA did not
consider these valves as best system of emission reduction. Instead,
the EPA evaluated BSER based on LDAR at different leak definitions.
---------------------------------------------------------------------------

    \99\ https://www.epa.gov/sites/default/files/2013-09/documents/dowchemical-cd.pdf.
---------------------------------------------------------------------------

    We also evaluated the HON equipment leak requirements as many NSPS
process units are already complying with such requirements. The HON
equipment leak standards require monitoring connectors at a leak
definition of 500 ppm annually, with reduced monitoring frequency with
good performance. These are the same requirements as the stayed VVa
connector monitoring requirements.
    Based on the information gathered from our review of NSPS subpart
VVa, we evaluated the following two control options. Option 1 was
lowering the leak definition for gas and light liquid valves from 500
ppm to 100 ppm. Option 2 was Option 1 plus adding connector monitoring
requirements from the stayed 2006 subpart VVa final rule, which is also
consistent with the current HON requirements.
    For both options considered, we calculated the average costs and
cost effectiveness on an affected facility basis. Table 24 of this
preamble summarizes these average costs, cost-effectiveness, and
emissions reductions on an affected facility basis. For

additional details, see the document titled CAA 111(b)(1)(B) review for
the SOCMI Equipment Leaks NSPS Subpart VVa which is available in the
docket for this rulemaking.

                            Table 24--Average Cost and Environmental Impacts for Equipment Leak Options per Affected Facility
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Total annual                    Cost-effectiveness w/recovery
                                                           Total capital   Total annual       cost w/      VOC emission         credits ($/ton VOC)
                     Control option                       investment ($)    cost ($/yr)      recovery       reductions   -------------------------------
                                                                                credits ($/yr)       (tpy)          Average       Incremental
--------------------------------------------------------------------------------------------------------------------------------------------------------
Option 1: Gas and LL valve monitoring monthly at a leak           10,100           2,360           1,780            0.64           2,780             N/A
 definition of 100 ppm, with skip periods \1\...........
Option 2: Option 1 plus connector monitoring annually at         208,300          38,800          30,500               9           3,390           3,400
 a leak definition of 500 ppm, with skip periods........
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Skip periods refers to reduced monitoring frequency, i.e., skipping monitoring during some periods due to good performance.

    We are proposing to determine Option 2 to be cost-effective for
new, modified, and reconstructed sources. Many SOCMI facilities are
already complying with these requirements. Based on the results of our
analysis, we are proposing BSER for NSPS subpart VVb to be NSPS subpart
VVa plus revising the equipment leak standards in a new subpart VVb to
lower the leak definition for gas and light liquid valves from 500 ppm
to 100 ppm and include requirements for connectors consistent with the
HON requirements.
    We conducted an analysis to estimate how many affected facilities
are expected/projected to be subject to the proposed equipment leak
requirements presented above. An affected facility can become subject
to NSPS subpart VVb under one of the following scenarios: (1) The
affected facility is at a new greenfield facility; (2) the affected
facility is a new affected facility at an existing plant site; (3) an
existing affected facility is modified; or (4) an existing affected
facility triggers the reconstruction requirements. For scenario 1
(i.e., affected facility is at a new greenfield facility), we assumed
only one greenfield facility, with two process units, will trigger NSPS
subpart VVb over the next 5 years. We used facility responses to our
CAA section 114 request to help us determine the number of facilities
that could potentially trigger scenarios 2, 3, and 4.
    For scenario 2 (i.e., new affected facilities constructed at
existing plant sites), we assessed information from facilities
responding to the EPA's CAA section 114 request. The responses to the
CAA section 114 request showed 34 affected facilities subject to NSPS
subparts VV or VVa. One of the affected facilities was a new
construction in the last 5 years. The OECA's ECHO tool (https://echo.epa.gov) indicates there are currently 592 SOCMI facilities
subject to subpart VV or VVa. We assumed an average of two affected
facilities per plant site. Assuming the same distribution of new
construction, 34 new affected facilities would have been constructed in
the last 5 years for all SOCMI facilities. The analysis assumes that
the same number of affected facilities that were constructed in the
last 5 years would be constructed in the next 5 years.
    For scenario 3 (i.e., existing facility is modified) and scenario 4
(i.e., existing facility triggers reconstruction requirements),
facilities responding to the EPA's CAA section 114 request did not
report any modified or reconstructed facilities in the last 5 years or
in the last 10 years. Eight of the 34 affected facilities discussed in
scenario 2 indicated either modification or reconstruction since their
construction, ranging back to the 1940's. We assumed the eight affected
facilities were modifications because the reconstruction requirements
are less likely to be triggered. For scenario 3 we assumed that at
least one affected facility would be modified in the next 5 years,
likely by addition of new unit operations that would increase the
number of components. We also assumed that no affected facilities will
trigger the reconstruction requirements in scenario 4.
    Table 25 of this preamble presents the nationwide impacts for the
Option 2. See the document titled CAA 111(b)(1)(B) review for the SOCMI
Equipment Leaks NSPS Subpart VVa, which is available in the docket for
this rulemaking, for details on the assumptions and methodologies used
in this analysis. We are proposing that affected facilities that are
constructed, reconstructed, or modified after April 25, 2023 would be
subject to these proposed requirements in NSPS subpart VVb. We solicit
comment on all of the proposed requirements related to standards for
equipment leaks in new NSPS subpart VVb.

Table 25--Nationwide Emissions Reductions and Cost Impacts of Control Options Considered for Affected Facilities
                                           Triggering NSPS Subpart VVb
----------------------------------------------------------------------------------------------------------------
                                                                                Cost-
                                                                   Total annual    VOC emission    effectiveness
            Scenario               Total capital   Total annual       cost w/       reductions      w/recovery
                                  investment ($)    cost ($/yr)      recovery          (tpy)      credits ($/ton
                                                                  credits ($/yr)                       VOC)
----------------------------------------------------------------------------------------------------------------
Scenario 1 (i.e., two affected           416,600          77,500          60,900              18           3,380
 facilities at a new greenfield
 facility)......................
Scenario 2 (i.e., 34 new               7,081,700       1,317,900       1,035,800             313           3,310
 affected facilities)...........
Scenarios 3 and (i.e., one               208,300          38,800          30,500               9           3,390
 modified existing affected
 facility)......................
                                 -------------------------------------------------------------------------------

    Total.......................       7,706,600       1,434,200       1,127,200             340           3,320
----------------------------------------------------------------------------------------------------------------

7. Standards for Fenceline Monitoring
    Fenceline monitoring refers to the placement of monitors along the
perimeter of a facility to measure pollutant concentrations. Coupled
with requirements for root cause analysis and corrective action upon
triggering an actionable level, this work practice standard is a
development in practices considered under CAA section 112(d)(6) for the
purposes of managing fugitive emissions. The measurement of these
pollutant concentrations and comparison to concentrations estimated
from mass emissions via dispersion modeling is used to ground-truth
emission estimates from a facility's emissions inventory. If
concentrations at the fenceline are greater than expected, the likely
cause is that there are underreported or unknown emission sources
affecting the monitors. In addition to the direct indication that
emissions may be higher than inventories would suggest, fenceline
monitoring provides information on the location of potential emissions
sources because it provides complete spatial coverage of a facility.
Further, when used with a mitigation strategy, such as root cause
analysis and corrective action upon exceedance of an action level,
fenceline monitoring can be effective in reducing emissions and
reducing the uncertainty associated with emissions estimation and
characterization. Finally, public reporting of fenceline monitoring
data provides public transparency and greater visibility, leading to
more focus and effort in reducing emissions. Fenceline monitoring has
not yet been required or considered in prior rulemaking actions or
regulations governing SOCMI, P&R I or P&R II HAP emissions, but has
been required for Petroleum Refineries in 40 CFR part 63, subpart CC
(see 40 CFR 63.658). As such we evaluated the application of fenceline
monitoring as a development in practices, processes, and control
technologies pursuant to CAA section 112(d)(6). As further explained
below, our evaluation only focuses on HON and P&R I facilities that
use, produce, store, or emit benzene, 1,3-butadiene, chloroprene,
ethylene dichloride, EtO, or vinyl chloride.
    Fenceline monitoring has been successfully applied to the petroleum
refineries source category as a technique to manage and reduce benzene
emissions from fugitive emissions sources such as storage vessels,
wastewater treatment systems, and leaking equipment. In 2015, the EPA
promulgated the RTR for the petroleum refineries source category and
required that refineries install and operate fenceline monitors
following EPA Reference Method 325 A/B to monitor benzene emissions.
The 2015 rule (80 FR 75178) required that refineries install and begin
operating passive diffusive tube monitors by 2018 and report benzene
emissions monitoring data to the EPA beginning in 2019.\100\
Additionally, the 2015 rule required that refineries conduct a root
cause analysis to identify sources of high fenceline monitoring
readings (i.e., above an annual action level) and then develop a
corrective action plan to address the sources and reduce emissions to a
level that will bring fenceline monitoring concentrations below the
action level.\101\ To date, the EPA has received fenceline monitoring
data for more than four years.\102\ These data show that petroleum
refinery fenceline concentrations have dropped by an average of 30
percent since the inception of the monitoring program requirements.
These results illustrate that fenceline monitoring is an effective tool
in reducing emissions and preserving emission reductions on an ongoing
basis for these sources.
---------------------------------------------------------------------------

    \100\ See 40 CFR 63.658(a) and 40 CFR 63.655(h)(8).
    \101\ 40 CFR 63.658(f)-(h).
    \102\ Quarterly fenceline monitoring reports are available
through the EPA's WebFIRE database at https://cfpub.epa.gov/webfire/. The EPA has also developed a dashboard to improve public
access to this data. The dashboard is available at https://awsedap.epa.gov/public/extensions/Fenceline_Monitoring/Fenceline_Monitoring.html?sheet=MonitoringDashboard.
---------------------------------------------------------------------------

    The majority of emissions from sources covered by the HON and P&R I
are fugitive in nature and are often difficult to characterize and
quantify. In order to assess the effect of emissions for purposes of
risk characterization, we rely on the assumption that reported
emissions are accurate. Thus, if the reported inventories are accurate,
all facilities should be able to meet the fenceline concentration
action levels considering the controls we are proposing. Further,
fenceline monitoring provides the facility and the EPA with an
understanding of where the concentrations of toxic HAP exceed expected
concentrations and provide a path for owners and operators to further
identify the root causes of such exceedances and to mitigate emissions
from these sources. For facilities regulated by the HON or P&R I, the
EPA identified six specific HAP that we determined were the most
appropriate, useful, and suitable for inclusion on the fenceline
monitoring program. These compounds were identified as cancer risk
drivers in the prior RTRs for the HON and P&R I conducted in 2006 (HON)
and 2008 and 2011 (P&R I) or identified as cancer risk drivers in the
residual risk reviews proposed in this action, and each is emitted
(largely as fugitive emissions) from processes at HON and P&R I
sources.\103\ As part of our CAA section 114 request, we also collected
fenceline monitoring data for these compounds at various facilities and
often found them to be present in concentrations that were higher than
our modeling of reported emissions inventories would predict.\104\
Although the model to monitor averages are not quantitatively
comparable because they are based on different time periods (i.e., an
annual average versus 7 sampling periods), the monitored concentrations
typically exceeded concentrations established by the modeling; in some
cases, by multiple orders of magnitude. This is an indicator that
reported emissions may be underestimated. Therefore, in this action,
the EPA is proposing at 40 CFR 63.184 to implement a fenceline
monitoring

program under CAA section 112(d)(6) to limit fugitive emissions. We are
proposing to require fenceline monitoring at facilities in the SOCMI
and P&R I source categories that use, produce, store, or emit benzene,
1,3-butadiene, chloroprene, EtO, ethylene dichloride, or vinyl
chloride. A brief summary of the proposed fenceline sampling
requirements and our rationale for selecting the corrective action
concentration levels are provided below. We solicit comment on the
proposed standards for fenceline monitoring.
---------------------------------------------------------------------------

    \103\ P&R II sources do not emit any of these six pollutants.
    \104\ See model to monitor comparison in the document entitled
Clean Air Act Section 112(d)(6) Technology Review for Fenceline
Monitoring located in the SOCMI Source Category that are Associated
with Processes Subject to HON and for Fenceline Monitoring that are
Associated with Processes Subject to Group I Polymers and Resins
NESHAP, which is available in the docket for this rulemaking.
---------------------------------------------------------------------------

    Developments in monitoring technology and practices. The EPA
reviewed the available literature and identified two different methods
for monitoring fugitive emissions of benzene, 1,3-butadiene,
chloroprene, ethylene dichloride, EtO, and vinyl chloride around a
chemical facility. These methods include: (1) Passive diffusive tube
monitoring networks for the measurement of benzene, 1,3-butadiene,
chloroprene, and ethylene dichloride; and (2) Canister monitoring
networks for the measurement of EtO and vinyl chloride. We considered
these monitoring methods as developments in practices under CAA section
112(d)(6) for purposes of managing fugitive emission sources at
chemical manufacturing facilities.
    Fenceline passive diffusive tube monitoring networks employ a
series of diffusive tube samplers at set intervals along the fenceline
to measure a time-integrated \105\ ambient air concentration at each
sampling location. A diffusive tube sampler consists of a small tube
filled with an adsorbent, selected based on the pollutant(s) of
interest, and capped with a specially designed cover with small holes
that allow ambient air to diffuse into the tube at a small, fixed rate.
Diffusive tube samplers have been demonstrated to be a cost-effective,
accurate technique for measuring concentrations of pollutants (e.g.,
benzene) resulting from fugitive emissions in a number of studies
106 107 as well as in the petroleum refining sector.\108\ In
addition, diffusive samplers are used in the European Union to monitor
and maintain air quality, as described in European Union directives
2008/50/EC and Measurement Standard EN 14662-4:2005 for benzene. The
International Organization for Standardization developed a standard
method for diffusive sampling (ISO/FDIS 16017-2). In recent years, the
EPA has expanded the use of diffusive sorbent tubes through our CAA
Section 114 authority to evaluate fenceline concentrations of HAP in
addition to benzene, such as chloroprene and 1,3-butadiene. To support
these efforts, the EPA used existing uptake rates included in EPA
Methods 325A/B at 40 CFR part 63, Appendix A, and when necessary,
developed new uptake rates.\109\ Therefore, the EPA is proposing to
require fenceline monitoring of benzene, chloroprene, 1,3-butadiene,
and ethylene dichloride measured with 14-day sampling periods using
diffusive tube samplers in accordance with EPA Methods 325A/B at 40 CFR
part 63, Appendix A. The EPA notes that based on recent studies, we
will be incorporating new sorbents and revised uptake rates for certain
pollutants in an upcoming revision to EPA Method 325B.\110\
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    \105\ Time-integrated sampling refers to the collection of a
sample at a controlled rate. The sample provides an average
concentration over the sample period. For the diffusive tube
samplers, the controlled rate of sampling is dictated by the uptake
rate. The uptake rate is the amount of a compound that can be
absorbed by a particular sorbent over time during the sampling
period.
    \106\ McKay, J., M. Molyneux, G. Pizzella, V. Radojcic.
Environmental Levels of Benzene at the Boundaries of Three European
Refineries, prepared by the CONCAWE Air Quality Management Group's
Special Task Force on Benzene Monitoring at Refinery Fenceline (AQ/
STF-45), Brussels, June 1999.
    \107\ Thoma, E.D., M.C. Miller, K.C. Chung, N.L. Parsons, B.C.
Shine. 2011. Facility Fenceline Monitoring using Passive Samplers,
J. Air & Waste Manage Assoc. 61: 834-842.
    \108\ See EPA-HQ-OAR-2010-0682; fenceline concentration data
collected for the petroleum refining sector rulemaking can be
accessed via the Benzene Fenceline Monitoring Dashboard at https://awsedap.epa.gov/public/extensions/Fenceline_Monitoring/Fenceline_Monitoring.html?sheet=MonitoringDashboard.
    \109\ Docket Reference to ``Method 325B Addendum A, Evaluation
of Chloroprene Uptake Rate Report.''
    \110\ Markes International Ltd. Uptake Rate Tests: Tests for a
range of compounds onto four sorbent types over periods of 1 and 2
weeks. September 27, 2022.
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    In this action, the EPA is proposing a new EPA reference method to
monitor the concentration of EtO and vinyl chloride from facility
fenceline locations, EPA Method 327 to 40 CFR part 63, Appendix A. EPA
Method 327 is a canister sampling and analysis method that provides
procedures for measuring trace levels of targeted VOC (including
organic HAP) in ambient air. It draws upon the guidance in Method TO-
15A \111\ for canister sampling and further develops this guidance into
a robust method specific for fenceline monitoring, defining required
data quality objectives, and incorporating existing best practices into
the method. In EPA Method 327, ambient air samples are collected using
specially prepared and pre-cleaned evacuated stainless-steel canisters.
For analysis, a known volume of air is directed from the canister to a
pre-concentrator, and the targeted VOC from the sample are measured
using a gas chromatograph-mass spectrometer (GC-MS). The EPA is
proposing to require fenceline monitoring of EtO and vinyl chloride
with 24-hour sampling periods once every 5 days using canister sampling
in accordance with EPA Method 327 at 40 CFR part 63, appendix A. This
monitoring frequency is necessary to ensure that all onsite processes
are monitored regularly and approaches the time-integrated sampling of
EPA Methods 325A/B, while still maintaining the cost effectiveness of
implementing a canister monitoring network. A sampling frequency of
every five days will also help to reduce the possibility of only
monitoring emission spikes such that the annual average concentration
is indicative of the actual average emissions from the site.
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    \111\ https://www.epa.gov/sites/default/files/2019-12/documents/to-15a_vocs.pdf.
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    The EPA considered requiring EPA Method 327 for monitoring ethylene
dichloride, because ethylene dichloride is almost always going to be
monitored alongside vinyl chloride. Because vinyl chloride is monitored
with EPA Method 327, monitoring ethylene dichloride with EPA Method 327
would simplify the monitoring and increase the cost effectiveness of
implementing the fenceline monitoring program. However, in this action
EPA has chosen to require EPA Methods 325A/B for monitoring ethylene
dichloride because based on the available data, at least one vinyl
chloride monomer facility reported emissions of chloroprene, which
would require that facility to monitor for chloroprene with EPA Methods
325A/B. Because monitoring with EPA Methods 325A/B is more continuous
than with EPA Method 327 and the results with EPA Methods 325A/B
generally have less variability, monitoring with EPA Methods 325A/B is
the preferred approach. We are however soliciting comment on whether we
should allow the use of EPA Method 327 for monitoring fenceline
concentration of ethylene dichloride for sites that have to monitor
fenceline concentrations of vinyl chloride but do not have to monitor
fenceline concentrations of chloroprene, benzene, or 1,3-butadiene.
    While EPA Method 327 is based on Method TO-15A, there are notable
differences between the two methods. EPA Method 327 addresses some of
the challenges encountered while performing sampling and analysis of
EtO with Method TO-15A by incorporating best practices into the method.
EPA Method 327 also is written

to mandate actions within the method as opposed to providing guidance
on how the method should be performed. The major differences between
Method TO-15A and Method 327 include the following, but are not limited
to:
     Updated sample cleanliness requirements and removal of the
option for glass bottles and non-rigid containers.
     invalidation of samples that do not meet initial and final
canister pressure requirements.
     requirement to examine chromatograms for potential
interferences, with a strong recommendation for the use of full scan
ion spectra MS mode during analysis.
     requirements for certification and recertification of
standards to ensure the quality and stability of the standards.
     requirements for one field blank and one field duplicate
for each sampling period.
     requirement for the field blank diluent gas to be
humidified zero air.
     maximum allowed sample holding time of 7 days.
     requirement to drift correct measured values based on
continuous calibration verification criteria according to the
procedures in EPA Method 325B.
    To achieve the lowest possible detection limits with canister
sampling, the EPA has determined that it is necessary to mandate these
best practices within EPA Method 327. Although facilities were asked to
follow these best practices in the CAA section 114 request, the data
submitted in response to the request indicated there are sampling and
analysis issues that still need to be addressed, especially in regard
to measuring EtO.
    While the EPA acknowledges that there are some drawbacks of time-
integrated sampling, including the lack of immediate feedback on the
acquired data and the loss of short-term temporal information, our
experience with the fenceline monitoring program in the petroleum
refining sector has proven that these systems are capable of achieving
meaningful emissions reductions by allowing earlier detection of
significant fugitive emissions than conventional source-specific
monitoring, such as through a periodic leak detection program with EPA
Method 21 of 40 CFR part 60, appendix A-7. Additionally, time-
integrated monitoring systems are generally lower-cost and require less
labor than time-resolved \112\ monitoring systems; they generally have
lower detection capabilities as well. Time-resolved monitoring stations
have been used for a variety of pollutants in a variety of settings and
the methods are well-established. However, compared to the passive
diffusive tube monitoring stations or canister sampling, time-resolved
monitoring stations are more expensive, more labor-intensive, and
generally require highly-trained staff to operate. The EPA acknowledges
the state of technology is advancing and that the capabilities of these
systems will continue to improve and that the costs will likely
decrease. Therefore, we are providing a pathway for an owner or
operator to request use of other types of monitoring networks to
demonstrate compliance with the fenceline standards through a request
for an alternative test method under the provisions of 40 CFR 63.7(f).
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    \112\ Time resolved monitoring involves sampling within short
timeframes (generally on the magnitude of minutes to hours) in order
to see the variation in concentration of a compound in near real
time.
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    Siting, design, and sampling requirements for fenceline monitors.
The EPA is proposing that fenceline monitors be deployed to measure
fenceline concentrations of benzene, 1,3-butadiene, chloroprene,
ethylene dichloride, EtO, and vinyl chloride at chemical manufacturing
facilities subject to the HON or P&R I. A primary requirement for a
fenceline monitoring system is that it provides adequate spatial
coverage for determination of representative pollutant concentrations
at the boundary of the facility. In an ideal scenario, fenceline
monitors would be placed so that any fugitive plume originating within
the facility would have a high probability of intersecting one or more
monitors, regardless of wind direction. Therefore, we are proposing
that for passive diffuse tube monitoring of benzene, 1,3-butadiene,
chloroprene, and ethylene dichloride, facilities determine the
appropriate number and location of fenceline sampling monitors using
the siting method requirements described in EPA Method 325A of 40 CFR
part 63, Appendix A. Sample collection and analysis of the passive
tubes would be performed according to EPA Methods 325A and 325B of 40
CFR part 63, appendix A.
    For canister monitoring of EtO and vinyl chloride, the EPA is
proposing that each facility would place 8 canisters evenly spaced on
the monitoring perimeter. The monitoring perimeter may be the facility
fenceline or may be inside the facility fenceline as long as all
sources of the monitored compound(s) are contained within the
perimeter. Because we recognize that the spatial coverage provided by
this arrangement is less than that provided under EPA Method 325A, the
EPA is also proposing that facilities would be required to move the
canister sampling locations with alternating sampling periods in order
to ensure complete spatial coverage of the facility. For facilities
with emission sources of monitored pollutants that are not contained
within one contiguous area, the EPA is proposing that these secondary
areas would be monitored as well, with the number of canisters on the
secondary area dictated by the size of the area. The proposed
requirements for siting the canisters are described in NESHAP subpart H
(see proposed 40 CFR 63.184). While we recognize that EPA Method 325A
contains an option for siting passive tubes by determining the
geographic center of the facility and spacing the tubes based on
measured angles from the center point, the EPA has chosen not to
provide a similar approach for the canisters in order to simplify the
siting of the canisters. We request comment on the proposed approach
for siting the canisters and whether we should provide an alternative
siting approach based on measured angles from the center point.
    For each sampling period (2-week period for passive tubes or 24-
hour period for canisters), the facility would determine a delta c,
calculated as the lowest sample value for the compound of interest
subtracted from the highest sample value for the compound of interest.
This approach is intended to subtract out the estimated contribution
from background emissions that do not originate from the facility. The
delta c for the most recent year of samples (26 sampling periods for
passive tubes and 73 sampling periods for canisters) would be averaged
to calculate an annual average delta c. The annual average delta c
would be determined on a rolling basis, meaning that it is updated with
every new sample (i.e., for passive tubes, every 2 weeks a new annual
average delta c is determined from the most recent 26 sampling periods
and for canisters, every 5 days a new annual average delta c is
determined from the most recent 73 sampling periods). This rolling
annual average delta c would be calculated for each compound of
interest and compared against a concentration action level for each
pollutant.
    Action levels and rationale. As mentioned above, the EPA is
proposing to require facilities subject to the HON and P&R I to take
corrective action to reduce fugitive emissions if monitored fenceline
concentrations exceed a specific concentration action level on a

rolling annual average basis.\113\ For benzene, 1,3-butadiene, ethylene
dichloride, and vinyl chloride, we selected the proposed fenceline
action levels by modeling fenceline HAP concentrations using the
emissions inventories used in the residual risk assessment of the
facility-wide review of the SOCMI source category and Neoprene
Production source category (e.g., 2017 NEI), assuming that those
reported emissions represented full compliance with all proposed HON or
P&R I requirements, adjusted for additional control requirements we are
proposing in this action.\114\ We estimated the long-term fenceline
post-control HAP concentrations at each facility using the post-control
facility-wide emissions inventory and the EPA's HEM. Concentrations
were estimated by the model at a set of polar grid receptors centered
on each facility, as well as surrounding census block centroid
receptors extending from the facility outward to 50 km (~31 miles). For
purposes of this modeling analysis, we assumed that the nearest off-
site polar grid receptor was the best representation of each facility's
fenceline concentration in the post-control case, unless there was a
census block centroid nearer to the fenceline than the nearest off-site
polar grid receptor or an actual receptor was identified from review of
the site map. In those instances, we estimated the fenceline
concentration as the concentration at the census block centroid. Only
receptors (either the polar or census block) that were estimated to be
outside the facility fenceline were considered in determining the
maximum HAP concentration level for each facility. After modeling each
facility, we then selected the maximum annual average benzene, 1,3-
butadiene, ethylene dichloride, and vinyl chloride fenceline
concentration modeled at any facility as the action level for that HAP.
Thus, if the reported inventories are accurate, all facilities should
be able to meet the fenceline concentration action levels. We note that
this analysis does not correlate to any particular metric related to
risk. The maximum annual average HAP concentrations modeled at the
fenceline for any facility, rounded to one significant figure, were 9
micrograms per cubic meter ([mu]g/m\3\, benzene),\115\ 3 [mu]g/m\3\
(1,3-butadiene), 4 [mu]g/m\3\ (ethylene dichloride), and 3 [mu]g/m\3\
(vinyl chloride). Therefore, the EPA is proposing these fenceline
concentrations as action levels for these four HAP.
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    \113\ Calculated every two weeks for benzene, 1,3-butadiene,
ethylene dichloride, and chloroprene. Calculated every five days for
ethylene oxide and vinyl chloride.
    \114\ We note that 10 of the 19 facilities with P&R I processes
also have HON processes.
    \115\ Since we are considering facility-wide emissions, an
action level of 9 [mu]g/m\3\ was chosen for benzene since the
refinery who set the action level in 2015 for that source category
is also a HON facility.
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    Due to current limitations in method detection limits for EtO and
chloroprene, and the concerns for cancer risk driven by these two
pollutants, we selected the proposed fenceline action levels to be
equal to three times the representative detection limit (RDL) for these
two pollutants, as this is the minimum concentration that can be
measured with reasonable certainty. The RDL is based on the results of
the best performing testing companies and laboratories using the most
sensitive analytical procedures. A multiplication factor of three is
used to reduce the imprecision of the method until the imprecision in
the sampling and analysis is similar to the precision of other EPA
methods. The RDL for chloroprene was determined to be 0.09 [mu]g/m\3\,
and the RDL for EtO was determined to be 0.07 [mu]g/m\3\. Therefore,
the EPA is proposing action levels of 0.3 [mu]g/m\3\ for chloroprene
and 0.2 [mu]g/m\3\ for EtO. We acknowledge that these proposed
concentrations are lower than the fenceline modeled concentrations for
EtO and chloroprene from facilities in the SOCMI and Neoprene
Production source categories after implementation of our proposed
standards; however, considering whole facility risks, and in light of
the configuration of the emission sources subject to these rules that
contribute to whole facility risk that remain for the impacted
communities after the imposition of controls, we set the action levels
of chloroprene and EtO at facility boundaries as low as possible
(considering method detection limitations) to ensure emission