[Federal Register: June 14, 2006 (Volume 71, Number 114)]
[Proposed Rules]
[Page 34421-34446]
[DOCID:fr14jn06-29]

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Part II

Environmental Protection Agency

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40 CFR Part 63

National Emission Standards for Hazardous Air Pollutants for Organic
Hazardous Air Pollutants From the Synthetic Organic Chemical
Manufacturing Industry; Proposed Rule

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2005-0475; FRL-8181-3]
RIN 2060-AK14

National Emission Standards for Hazardous Air Pollutants for
Organic Hazardous Air Pollutants From the Synthetic Organic Chemical
Manufacturing Industry

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule; amendments.

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SUMMARY: In 1994, EPA promulgated National Emission Standards for
Hazardous Air Pollutants (NESHAP) for the synthetic organic chemical
manufacturing industry (SOCMI). This rule is commonly known as the
hazardous organic NESHAP (HON) and established maximum achievable
control technology (MACT) standards to regulate the emissions of
organic hazardous air pollutants (HAP) from production processes that
are located at major sources.
    The Clean Air Act (CAA) directs EPA to assess the risk remaining
(residual risk) after the application of the MACT standards and to
promulgate additional standards if required to provide an ample margin
of safety to protect public health or prevent adverse environmental
effect. The CAA also requires us to review and revise MACT standards,
as necessary, every eight years, taking into account developments in
practices, processes, and control technologies that have occurred
during that time.
    Based on our findings from the residual risk and technology review,
we are proposing two options (to be considered with equal weight) for
emissions standards for new and existing SOCMI process units. The first
proposed option would impose no further controls, proposing to find
that the existing standards protect public health with an ample margin
of safety and prevent adverse environmental impacts, as required by
section 112(f)(2) of the CAA and would satisfy the requirements of
section 112(d)(6). The second proposed option would provide further
reductions of organic HAP at certain process units by applying
additional controls for equipment leaks and by controlling some storage
vessels and process vents that are uncontrolled under the current rule.
This option would also protect public health with an ample margin of
safety and prevent adverse environmental impacts, as required by
section 112(f)(2) of the CAA and would satisfy the requirements of
section 112(d)(6). Under this option, we are proposing that the
compliance deadlines for additional promulgated requirements would be
one to three years from the date of promulgation.

DATES: Comments. Written comments must be received on or before August
14, 2006.
    Public Hearing. If anyone contacts EPA by July 5, 2006 requesting
to speak at a public hearing, a public hearing will be held on July 14,
2006.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-
OAR-2005-0475, by one of the following methods:
     Federal eRulemaking Portal: http://www.regulations.gov.

Follow the on-line instructions for submitting comments.
     E-mail<EMAIL_ADDRESS>     Fax:<PHONE_NUMBER>.
     Hand Delivery: Air and Radiation Docket, Environmental
Protection Agency, 1301 Constitution Avenue, NW., Room B-108,
Washington, DC 20014. Such deliveries are accepted only during the
Docket's normal hours of operation and special arrangements should be
made for deliveries of boxed information.
     Mail: EPA Docket Center (EPA/DC), Environmental Protection
Agency, Mailcode 6102T, 1200 Pennsylvania Avenue, NW., Washington, DC
20460.
    Please include a total of two copies. We request that a separate
copy also be sent to the contact person identified below (see FOR
FURTHER INFORMATION CONTACT).
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-
2005-0475. EPA's policy is that all comments received will be included
in the public docket without change and may be made available online at
http://www.regulations.gov including any personal information provided,

unless the comment includes information claimed to be Confidential
Business Information (CBI) or other information whose disclosure is
restricted by statute. Do not submit information that you consider to
be CBI or otherwise protected through http://www.regulations.gov or e-mail. The http://www.regulations.gov Web site is an ``anonymous

access'' system, which means EPA will not know your identity or contact
information unless you provide it in the body of your comment. If you
send an e-mail comment directly to EPA without going through http://www.regulations.gov
, your e-mail address will be automatically captured

and included as part of the comment that is placed in the public docket
and made available on the Internet. If you submit an electronic
comment, EPA recommends that you include your name and other contact
information in the body of your comment with a disk or CD-ROM you
submit. If EPA cannot read your comment due to technical difficulties
and cannot contact you for clarification, EPA may not be able to
consider your comment. Electronic files should avoid the use of special
characters, any form of encryption, and be free of any defects or
viruses.
    Docket: All documents in the docket are listed in the http://www.regulations.gov
 index. Although listed in the index, some

information is not publicly available, e.g., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, will be publicly available only in hard copy.
Publicly available docket materials are available either electronically
in http://www.regulations.gov or in hard copy at the Air and Radiation

Docket, EPA/DC, EPA West, Room B102, 1301 Constitution Ave., NW.,
Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30
p.m., Monday through Friday, excluding legal holidays. The telephone
number for the Public Reading Room is<PHONE_NUMBER>, and the telephone
number for the Air and Radiation Docket is<PHONE_NUMBER>.
    Public Hearing: If a public hearing is held, it will be held at 10
a.m. at the Environmental Research Center Auditorium, Research Triangle
Park, NC, or at an alternate site nearby.

FOR FURTHER INFORMATION CONTACT: For questions about the proposed rule,
contact Mr. Randy McDonald, EPA, Office of Air Quality Planning and
Standards, Sector Policies and Programs Division, Coatings and
Chemicals Group (E143-01), Research Triangle Park, NC 27711; telephone
number<PHONE_NUMBER>; fax number<PHONE_NUMBER>; e-mail address:
<EMAIL_ADDRESS>For questions on the residual risk analysis,

contact Mr. Mark Morris, EPA, Office of Air Quality Planning and
Standards, Health and Environmental Impacts Division, Sector Based
Assessment Group (C404-01), Research Triangle Park, NC 27711; telephone
number<PHONE_NUMBER>; fax number<PHONE_NUMBER>; e-mail address:
<EMAIL_ADDRESS>

SUPPLEMENTARY INFORMATION: Regulated Entities. Categories and entities
potentially regulated by the proposed rule are SOCMI facilities that
are major sources of HAP emissions. The proposed rule would affect the
following categories of sources:

------------------------------------------------------------------------
                                      NAICS \1\   Example of potentially
              Category                   code       regulated entities
------------------------------------------------------------------------
Industry............................        325  Chemical manufacturing
                                                  facilities.
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\1\ North American Industrial Classification Code.

    This table is not intended to be exhaustive, but rather provides a
guide for readers regarding entities likely to be regulated by the
proposed rule. To determine whether your facility would be regulated by
the proposed rule, you should carefully examine the applicability
criteria in 40 CFR 63.100 of the rule. If you have any questions
regarding the applicability of the proposed rule to a particular
entity, contact the person listed in the preceding FOR FURTHER
INFORMATION CONTACT section.
    Submitting CBI. Do not submit this information to EPA through
http://www.regulations.gov or e-mail. Clearly mark the part or all of

the information that you claim to be CBI. For CBI information on a disk
or CD-ROM that you mail to EPA, mark the outside of the disk or CD-ROM
as CBI and then identify electronically within the disk or CD-ROM the
specific information that is claimed as CBI. In addition to one
complete version of the comment that includes information claimed as
CBI, a copy of the comment that does not contain the information
claimed as CBI must be submitted for inclusion in the public docket.
Information so marked will not be disclosed except in accordance with
procedures set forth in 40 CFR part 2.
    Public Hearing. Persons interested in presenting oral testimony or
inquiring as to whether a hearing is to be held should contact Randy
McDonald, Coatings and Chemicals Group, Sector Policies and Programs
Division (Mail Code C504-04), U.S. EPA, Research Triangle Park, North
Carolina, 27711, telephone number<PHONE_NUMBER>, electronic mail
address<EMAIL_ADDRESS>at least two days in advance of the
potential date of the public hearing. Persons interested in attending
the public hearing also must call Mr. Randy McDonald to verify the
time, date, and location of the hearing. A public hearing will provide
interested parties the opportunity to present data, views, or arguments
concerning the proposed amendments.
    World Wide Web (WWW). In addition to being available in the docket,
an electronic copy of the proposed rule is also available on the WWW
through the Technology Transfer Network Web site (TTN Web). Following
signature, a copy of the proposed rule will be posted on the TTN's
policy and guidance page for newly proposed or promulgated rules at
http://www.epa.gov/ttn/oarpg. The TTN provides information and

technology exchange in various areas of air pollution control.
    Organization of this Document. The information presented in this
preamble is organized as follows:

I. Background
    A. What is the statutory authority for regulating hazardous air
pollutants?
    B. What are SOCMI facilities?
    C. What are the health effects of HAP emitted from SOCMI
facilities?
    D. What does the HON require?
II. Summary of Proposed Revised Standards
III. Rationale for the Proposed Rule
    A. What is our approach for developing residual risk standards?
    B. How did we estimate residual risk?
    C. What are the residual risks from HON CMPUs?
    D. What is our proposed decision on acceptable risk?
    E. What is our proposed decision on ample margin of safety?
    F. What is EPA proposing pursuant to CAA section 112(d)(6)?
IV. Solicitation of Public Comments
    A. Introduction and General Solicitation
    B. Specific Comment and Data Solicitations
V. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination with
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
    I. National Technology Transfer Advancement Act
    J. Executive Order 12898: Federal Actions to Address
Environmental Justice in Minority Populations and Low-Income
Populations

I. Background

A. What is the statutory authority for regulating hazardous air
pollutants?

    Section 112 of the CAA establishes a two-stage regulatory process
to address emissions of HAP from stationary sources. In the first
stage, after EPA has identified categories of sources emitting one or
more of the HAP listed in section 112(b) of the CAA, section 112(d)
calls for us to promulgate national performance or technology-based
emission standards for those sources. For ``major sources'' that emit
or have the potential to emit any single HAP at a rate of 10 tons or
more per year or any combination of HAP at a rate of 25 tons or more
per year, these technology-based standards must reflect the maximum
reductions of HAP achievable (after considering cost, energy
requirements, and non-air health and environmental impacts) and are
commonly referred to as MACT standards. We published the MACT standards
for SOCMI on April 22, 1994 at 59 FR 19402 (codified at 40 CFR part 63,
subparts F, G, and H). The EPA is then required to review these
technology-based standards and to revise them ``as necessary (taking
into account developments in practices, processes and control
technologies)'' no less frequently than every eight years, under CAA
section 112(d)(6).
    The second stage in standard-setting is described in CAA section
112(f). This provision requires, first, that EPA prepare a Report to
Congress discussing (among other things) methods of calculating risk
posed (or potentially posed) by sources after implementation of the
MACT standards, the public health significance of those risks, the
means and costs of controlling them, actual health effects to persons
in proximity to emitting sources, and recommendations as to legislation
regarding such remaining risk. The EPA prepared and submitted this
report (Residual Risk Report to Congress, EPA-453/R-99-001) in March
1999. The Congress did not act on any of the recommendations in the
report, thereby triggering the second stage of the standard-setting
process, the residual risk phase.
    Section 112(f)(2) requires us to determine for source categories
subject to certain section 112(d) standards whether the emissions
limitations protect public health with an ample margin of safety. If
the MACT standards for HAP ``classified as a known, probable, or
possible human carcinogen do not reduce lifetime excess cancer risks to
the individual most exposed to emissions from a source in the category
or subcategory to less than 1-in-1 million,'' EPA must promulgate
residual risk standards for the source category (or subcategory) as
necessary to provide an ample margin of safety to protect public
health. The EPA must also adopt more stringent standards if necessary
to prevent adverse environmental effect (defined in section 112(a)(7)
as ``any significant and widespread adverse effect * * * to wildlife,
aquatic life, or natural resources * * *.''), but must consider cost,
energy, safety, and other relevant factors in doing so.

B. What are SOCMI facilities?

    The SOCMI is a segment of the chemical manufacturing industry that
includes the production of many high-volume organic chemicals. The
products of SOCMI are derived from approximately 10 petrochemical
feedstocks. Of the hundreds of organic chemicals that are produced by
the SOCMI, some are final products and some are the feedstocks for
production of other non-SOCMI chemicals or synthetic products such as
plastics, fibers, surfactants, pharmaceuticals, synthetic rubber, dyes,
and pesticides. Production of such non-SOCMI end products is not
considered to be part of SOCMI production and, as a result, the current
MACT standards do not (and the proposed standards would not) apply to
downstream synthetic products industries, such as rubber production or
polymers production, that use chemicals produced by SOCMI processes.
    The HON currently applies to chemical manufacturing process units
(CMPUs) that: (1) Are part of a major source as defined in CAA section
112; (2) produce as a primary product a SOCMI chemical listed in table
1 of 40 CFR part 63, subpart F; and (3) use as a reactant or
manufacture as a product, by-product, or co-product one or more of the
organic HAP listed in table 2 of 40 CFR part 63, subpart F.
    The HON defines a CMPU as the equipment assembled and connected by
pipes or ducts to process raw materials and to manufacture an intended
product. For purposes of the HON, a CMPU includes air oxidation
reactors and their associated product separators and recovery devices;
reactors and their associated product separators and recovery devices;
distillation units and their associated distillate receivers and
recovery devices; associated unit operations; and any feed,
intermediate and product storage vessels, product transfer racks, and
connected ducts and piping. A CMPU includes pumps, compressors,
agitators, pressure relief devices, sampling connection systems, open-
ended valves or lines, valves, connectors, instrumentation systems, and
control devices or systems.
    A SOCMI plant site can have several CMPUs, which could produce
totally separate and non-related products. In the background
information document for the HON, it was estimated that there were 729
CMPUs nationwide. Two hundred thirty-eight facilities have been
identified as subject to the HON. These HON facilities were identified
after extensive review of facility lists compiled by the EPA's Office
of Enforcement and Compliance Assurance, EPA Regional Offices, and the
American Chemistry Council (ACC).
    The five kinds of HAP emission points that are currently regulated
by the HON are storage vessels, process vents, wastewater collection
and treatment operations, transfer operations, and equipment leaks.
Each emission source type is briefly described below.
1. Storage Vessels
    Storage vessels contain chemical raw materials, products, and co-
products. Different types of vessels are used to store various types of
chemicals. Gases (chemicals with vapor pressures greater than 14.7
pounds per square inch absolute (psia)) are stored in pressurized
vessels that are not vented to the atmosphere during normal operations.
Liquids (chemicals with vapor pressures of 14.7 psia or less) are
stored in horizontal, fixed roof, or floating roof tanks, depending on
chemical properties and volumes to be stored. Liquids with vapor
pressures greater than 11 psia are typically stored in fixed roof tanks
that are vented to a control device. Volatile chemicals with vapor
pressures up to 11 psia are usually stored in floating roof tanks
because such vessels have lower emission rates than fixed roof tanks
within this vapor pressure range.
    Emissions from storage vessels typically occur as working losses.
As a storage vessel is filled with chemicals, HAP-laden vapors inside
the tank become displaced and can be emitted to the atmosphere. Also,
diurnal temperature changes result in breathing losses of organic HAP-
laden vapors from storage vessels.
2. Process Vents
    Many unit operations at SOCMI facilities generate gaseous streams
that contain HAP. These streams may be routed to other unit operations
for additional processing (i.e., a gas stream from a reactor that is
routed to a distillation unit for separation) or may be vented to the
atmosphere. Process vents emit gasses to the atmosphere, either
directly or after passing through recovery and/or control devices. The
primary unit operations in a SOCMI unit from which process vents
originate are reactor and air oxidation process units, and from the
associated product recovery and product purification devices. Product
recovery devices include condensers, absorbers, and adsorbers used to
recover products or co-products for use in a subsequent process, for
use as recycle feed, or for sale. Product purification devices include
distillation operations. The HON applies only to process vents that are
associated with continuous (non-batch) air oxidation, other reactor
processes, or distillation unit operations within a SOCMI process unit.
3. Process Wastewater
    For some synthetic organic chemicals, the manufacturing process
generates wastewater streams that contain HAP. Sources of wastewater
include: Water formed during the chemical reaction or used as a
reactant in a process; water used to wash impurities from organic
products or reactants; water used to cool organic vapor streams; and
condensed steam from vacuum vessels containing organics. Organic
compounds in the wastewater can volatilize and be emitted to the
atmosphere from wastewater collection and treatment units if these
units are open or vented to the atmosphere. Potential sources of HAP
emissions associated with wastewater collection and treatment systems
include drains, manholes, trenches, surface impoundments, oil/water
separators, storage and treatment tanks, junction boxes, sumps, basins,
and biological treatment systems.
4. Transfer Operations
    Synthetic organic chemical products are often transported by
railcars or tank trucks. Chemicals are transferred to these vehicles
through a loading rack, which can have multiple loading arms for
connection to several transport vehicles. Emissions can occur during
loading operations when residual vapors in transport vehicles and
transfer piping are displaced by chemicals being loaded.
5. Equipment Leaks
    Equipment leaks are fugitive releases of process fluid or vapor
from process equipment. These releases occur primarily at the interface
between connected components of equipment. The basic equipment
components that are prone to develop leaks include pumps, compressors,
process valves, pressure relief devices, open-ended lines, sampling
connections, flanges and other connectors, agitators, product
accumulator vessels, and instrumentation systems.

C. What are the health effects of HAP emitted from SOCMI facilities?

    Of the 131 organic HAP regulated by the HON (table 2 to subpart F
of part 63), EPA lists four as known carcinogens, 33 as probable
carcinogens, and 15 as possible carcinogens. The EPA classified agents
as carcinogens based on the weight of evidence in long-

term human studies of the association between cancer incidence and
exposure to the agent and in animal studies conducted under controlled
laboratory conditions. After evaluating the evidence, the agents were
placed into one of the following five categories: A--human carcinogen,
B--probable human carcinogen, C--possible human carcinogen, D--not
classifiable as to human carcinogenicity, and E--evidence of
noncarcinogenicity for humans. Category B is divided into two
subcategories: B1--indicates limited human evidence and B2--indicates
sufficient evidence in animals and inadequate or no evidence in humans.
    With the March 2005 publication of revised Guidelines for
Carcinogen Risk Assessment, EPA no longer uses the ``known, possible,
probable'' nomenclature for classifying the weight of evidence for
carcinogenicity of chemical compounds. Instead, EPA provides narrative
descriptions of the weight of evidence for carcinogenicity, as well as
the classifications ``carcinogenic to humans,'' ``likely to be
carcinogenic,'' ``suggestive evidence of carcinogenic potential,''
``inadequate information,'' and ``not likely.'' In time, the older
classification scheme described above will be replaced.
    The International Agency for Research on Cancer (IARC) also
classifies carcinogens based on the ``strength of the evidence for
carcinogenicity arising from human and experimental animal data.''
There are four groups under the IARC classification system: Group 1--
the agent is carcinogenic to humans, Group 2A--the agent is probably
carcinogenic to humans, Group 2B--the agent is possibly carcinogenic to
humans, Group 3--the agent is not classifiable as to its
carcinogenicity to humans, and Group 4--the agent is probably not
carcinogenic to humans. Of the 51 HON HAP classified by IARC, four are
Group 1, 33 are Group 2, and 14 are Group 3.
    Additionally, many of the HAP regulated by the HON may result in
noncarcinogenic effects at sufficient exposures. There is a wide range
of effects due to chronic exposures to HON HAP, such as the
degeneration of olfactory epithelium, peripheral nervous system
dysfunction, and developmental toxicity. Effects from acute exposures
range from mild to severe, and include skin, eye, and respiratory
system irritation. More detail on the health effects of individual HON
HAP may be found in numerous sources, including http://www.epa.gov/iris.html, http://www.atsdr.cdc.gov/mrls.html, and http://

http://www.oehha.ca.gov/air/acute_rels/index.html.

D. What does the HON require?

    The HON was proposed December 31, 1992 (57 FR 62608), and the final
rule was published April 22, 1994 (59 FR 19402). Subsequently, several
revisions to the rule have been issued: the first dated September 20,
1994 (59 FR 48175) and the last dated December 23, 2004 (69 FR 76859).
    The HON regulates organic HAP emissions from five types of emission
points: Storage vessels, process vents, wastewater collection and
treatment systems, transfer operations, and equipment leaks. For
storage vessels, process vents, process wastewater streams, and
transfer operations, the HON establishes applicability criteria to
distinguish between Group 1 emission points and Group 2 emission
points. Controls are required only for emission points meeting the
Group 1 criteria. Group 2 emission points are subject to recordkeeping
requirements only. Before implementation of the HON, total HAP
emissions were estimated to be 570,000 tons per year (tpy). We
estimated that after implementation of the HON, total HAP emissions
would be 66,000 tpy.
    The HON provides many different control options, but the primary
control requirements are summarized below.
1. Storage Vessels
    The HON requires that Group 1 vessels be equipped and operated with
an internal or an external floating roof, or reduce organic HAP
emissions by at least 95 percent. A Group 1 vessel has a capacity
greater than or equal to 40,000 gallons and contains a HAP with a vapor
pressure greater than or equal to 0.75 psia. A vessel is also Group 1
if it has a capacity greater than or equal to 20,000 gallons and less
than 40,000 gallons and contains a HAP with a vapor pressure greater
than or equal to 1.9 psia.
2. Process Vents
    The HON requires that the organic HAP emissions from Group 1
process vent streams be reduced by at least 98 percent by weight or
achieve an outlet concentration of 20 parts per million by volume
(ppmv) or less. A Group 1 process vent stream has a total organic HAP
concentration of greater than or equal to 50 ppmv and a total resource
effectiveness (TRE) of less than or equal to 1.0. Facilities also have
the option of sending the process vent to a flare or maintaining a TRE
index greater than 1.0. The TRE index is a measure of how costly a
particular process vent is to control (the higher the TRE index, the
more costly the control).
3. Process Wastewater
    The HON requires that Group 1 wastewater streams be treated to
reduce the HAP mass in the streams. Group 1 wastewater streams are
streams that meet one of several minimum flow and HAP concentration
criteria in the rule. The required mass removals are HAP-specific and
range from 31 percent (e.g., for methanol) to 99 percent (e.g., for
benzene). Emissions from collection and management units must be
suppressed from the point of generation to the treatment device. Air
emissions from treatment systems (except for open biological treatment
systems which have different requirements) must be collected in a
closed vent system and conveyed to a control device that reduces HAP
emissions by 95 percent (or achieves an outlet concentration of 20 ppmv
or less for combustion devices).
4. Transfer Operations
    The HON requires control of Group 1 transfer racks to achieve a 98
percent reduction of organic HAP or an outlet concentration of 20 ppmv.
Alternatively, facilities can use vapor balancing systems. A Group 1
transfer rack is a transfer rack that annually loads greater than or
equal to 0.17 million gallons of liquid products that contain organic
HAP with a rack weighted average vapor pressure greater than or equal
to 1.5 psia.
5. Equipment Leaks
    The HON requires equipment and work practice standards (in the form
of a leak detection and repair program) to reduce equipment leak
emissions. The equipment leak provisions apply to all equipment
components that are associated with a process subject to the HON and
that are in organic HAP service for 300 hours per year or more. The HON
requires valves to be monitored once per month (or implementation of a
quality improvement program) at each process unit with two percent or
greater leaking valves. The monitoring frequency may be decreased as
the percentage of leakers decreases or if the equipment leaks standards
are met over consecutive periods.

II. Summary of Proposed Revised Standards

    This proposal provides two options that we expect to choose between
for revising the HON rule. The first option is to retain the current
HON rule. The second option is to revise subparts F, G, and H to
require more stringent standards for process vents, storage vessels,
and equipment leaks that emit

or store certain HAP. As explained below, we propose that either option
would meet the requirements of both section 112(f)(2) and 112(d)(6).
Their difference results from how we weigh certain risk factors
(specifically, maximum individual lifetime cancer risk versus cancer
incidence, and their relative relationship to costs) within our
determination of what is necessary to protect public health with an
ample margin of safety under section 112(f)(2), and of what changes are
necessary under section 112(d)(6).

A. Summary of Option 1

    Under this option, the control requirements of 40 CFR subpart F, G,
and H would remain the same as under the current rule, and we would not
revise applicability criteria to require currently uncontrolled storage
vessels and process vents to control emissions, nor would we reduce the
percentage of leaking valves.

B. Summary of Option 2

    Under this option, the control requirements of 40 CFR subpart G
would remain the same as under the current rule, but the applicability
criteria for Group 1 storage vessels and process vents would be revised
so that additional emission points would be required to control
emissions. For equipment leaks, the first option would reduce, in
subpart H, the percentage of leaking valves.
    The existing applicability criteria for equipment leaks and Group 1
criteria for storage vessels and process vents would continue to apply.
After the rule becomes effective, an additional criterion would be
added. The additional criterion would apply only to emission points
that emit maleic anhydride, methyl bromide, acrolein, and any HAP for
which inhalation cancer unit risk estimates (UREs) have been
developed.\1\ A list of these HAP is given in proposed table 38 of 40
CFR, part 63, subpart G. This list may be amended over time as more
information indicates that some HAP should be added or removed.
---------------------------------------------------------------------------

    \1\ The URE is the upper-bound excess lifetime cancer risk
estimated to result from continuous exposure to an agent at a
concentration of 1 microgram per cubic meter ([mu]g/m3)
in air. For example, if a URE of 1.5 x 10-6 per [mu]g/
m3 is reported, then 1.5 excess cancer cases are expected
to develop per 1,000,000 people if exposed daily for a lifetime to 1
ug of the chemical in 1 cubic meter of air.
---------------------------------------------------------------------------

    The proposed changes to the standards, based on the second control
option, are summarized below:

------------------------------------------------------------------------
       Emission source          Proposed changes to standards (Option 2)
------------------------------------------------------------------------
Storage vessels..............  A group 1 storage vessel means a Group 1
                                storage vessel as currently defined in
                                Sec.   63.111 to subpart G of part 63.
                                On or after [DATE THE FINAL RULE IS
                                PUBLISHED IN THE FEDERAL REGISTER], a
                                group 1 storage vessel also includes
                                storage vessels that store one or more
                                HAP listed in table 38 to subpart G of
                                part 63, and have a combined HAP
                                emission rate greater than 4.54
                                megagrams per year (5.0 tons HAP per
                                year) on a rolling 12-month average.
Process vents................  A group 1 process vent means a Group 1
                                process vent as currently defined in
                                Sec.   63.111 to subpart G of part 63.
                                On or after [DATE THE FINAL RULE IS
                                PUBLISHED IN THE FEDERAL REGISTER], a
                                group 1 process vent also includes
                                process vents for which the vent stream
                                emits one or more HAP listed in table 38
                                to subpart G of part 63, and the TRE
                                index value is less than or equal to
                                4.0.
Equipment leaks..............  For CMPUs containing at least one HAP
                                listed in table 38 to subpart G of part
                                63, on or after [DATE THE FINAL RULE IS
                                PUBLISHED IN THE FEDERAL REGISTER],
                                monthly monitoring of equipment
                                components is required until the process
                                unit has fewer than 0.5 percent leaking
                                valves in gas/vapor service and in light
                                liquid service.
------------------------------------------------------------------------

    For storage vessels, emissions would be computed using the
procedures in Sec.  63.150. Group 2 storage vessels that contain table
38 HAP would be required to maintain records of rolling 12-month
average HAP emissions. For equipment leaks, the frequency of monitoring
could be reduced to quarterly, semi-annually, and annually if
successive monitoring periods show that facilities are able to maintain
less than 0.5 percent leakers. Monthly monitoring would be required if
the percent leakers exceeds 0.5 percent.
    Under Option 2, we are also proposing compliance dates for sources
subject to the proposed revised standards pursuant to section 112(i) of
the CAA. When Congress amended the CAA in 1990, it established a new,
comprehensive set of provisions regarding compliance deadlines for
sources subject to emissions standards and work practice requirements
that EPA promulgates under section 112. However, as discussed later in
this section of this preamble, Congress also left in place other
provisions in section 112(f)(4) that in certain respects are redundant
or conflict with the new compliance deadline provisions. These
provisions also fail to accommodate the new State-administered air
operating permit program added in title V of the amended CAA.
    For new sources, section 112(i)(1) requires that after the
effective date of ``any emission standard, limitation, or regulation
under subsection (d), (f) or (h), no person may construct any new major
source or reconstruct any existing major source subject to such
emission standard, regulation or limitation unless the Administrator
(or State with a permit program approved under title V) determines that
such source, if properly constructed, reconstructed and operated, will
comply with the standard, regulation or limitation.'' Section 112(a)(4)
defines a ``new source'' as ``a stationary source the construction or
reconstruction of which is commenced after the Administrator first
proposes regulations under this section establishing an emission
standard applicable to such sources.'' Under sections 112(e)(10) and
112(f)(3), any section 112(d)(6) emission standards and any residual
risk emission standards shall become effective upon promulgation. This
means generally that a new source that is constructed or reconstructed
after this proposed rule is published must comply with the final
standard, when promulgated, immediately upon the rule's effective date
or upon the source's start-up date, whichever is later.
    There are some exceptions to this general rule. First, section
112(i)(7) provides that a source for which construction or
reconstruction is commenced after the date an emission standard is
proposed pursuant to subsection (d) but before the date a revised
emission standard is proposed under subsection (f) shall not be
required to comply with the revised standard until 10 years after the
date construction or reconstruction commenced. This provision ensures
that new sources that are built in compliance with MACT will not be
forced to

undergo modifications to comply with a residual risk rule unreasonably
early.
    In addition, sections 112(i)(2)(A) and (B) provide that a new
source which commences construction or reconstruction after a standard
is proposed, and before the standard is promulgated, shall not be
required to comply with the promulgated standard until three years
after the rule's effective date, if the promulgated standard is more
stringent than the proposed standard and the source complies with the
proposed standard during the three-year period immediately after
promulgation. This provision essentially treats such new sources as if
they are existing sources in giving them a consistent amount of time to
convert their operations to comply with the more stringent final rule
after having already been designed and built according to the proposed
rule.
    For existing sources, section 112(i)(3)(A) provides that after the
effective date of ``any emission standard, limitation or regulation
promulgated under this section and applicable to a source, no person
may operate such source in violation of such standard, limitation or
regulation except, in the case of an existing source, the Administrator
shall establish a compliance date or dates * * * which shall provide
for compliance as expeditiously as practicable, but in no event later
than 3 years after the effective date of such standard[.]'' This
potential 3-year compliance period for existing sources under section
112(i)(3) matches the 3-year compliance period provided for new sources
subject to section 112(d), (f), or (h) standards that are promulgated
to be more stringent than they were proposed, as provided in sections
112(i)(1) and (2).
    As for new sources, there are exceptions to the general rule for
existing sources under section 112(i)(3), the most relevant being
section 112(i)(3)(B) allowance that EPA or a State title V permitting
authority may issue a permit granting a source an additional one year
to comply with standards ``under subsection (d)'' if such additional
period is necessary for the installation of controls. As explained
below, EPA now believes that this reference to only subsection 112(d),
rather than to section 112 in general, was accidental on Congress' part
and presents a conflict with the rest of the statutory scheme Congress
enacted in 1990 to govern compliance deadlines under the amended
section 112.
    Even though, in 1990, Congress amended section 112 to include the
comprehensive provisions in subsection 112(i) regarding compliance
deadlines, the enacted CAA also included provisions in section 112(f),
leftover from the previous version of the Act, that apply compliance
deadlines for sources subject to residual risk rules. These deadlines
differ in some ways from the provisions of section 112(i). First,
section 112(f)(4) provides that no air pollutant to which a standard
``under this subsection applies may be emitted from any stationary
source in violation of such standard * * *'' For new sources, this is a
redundant provision, since the new provisions added by Congress in
sections 112(i)(1), (2), (3), and (7)--which explicitly reach standards
established under section 112(f)--already impose this prohibition with
respect to new sources and provide for the allowable exceptions to it.
In contrast, for new sources, the prohibition in section 112(f)(4)
provides for no exception for a new source built shortly before a
residual risk standard is proposed, makes no reference to the new title
V program as an implementation mechanism, and, where promulgated
standards are more stringent than their proposed versions, makes no
effort to align compliance deadlines for new sources with those that
apply for existing sources. From the plain language of section 112(i),
it is clear that Congress intended in the 1990 amendments to
comprehensively address the compliance deadlines for new sources
subject to any standard under either subsections 112(d), (f), or (h),
and to do so in a way that accommodates both the new title V program
added in 1990 and the fact that where circumstances justify treating a
new source as if it were an existing source, a substantially longer
compliance period than would otherwise apply is necessary and
appropriate. It is equally clear that the language in section 112(f)(4)
fails on all these fronts for new sources.
    In addition, for existing sources, section 112(f)(4)(A) provides
that a residual risk standard and the prohibition against emitting HAP
in violation thereof ``shall not apply until 90 days after its
effective date[.]'' However, section 112(f)(4)(B) states that EPA ``may
grant a waiver permitting such source a period up to two years after
the effective date of a standard to comply with the standard if the
Administrator finds that such period is necessary for the installation
of controls and that steps will be taken during the period of the
waiver to assure that the health of persons will be protected from
imminent endangerment.'' These provisions are at odds with the rest of
the statutory scheme governing compliance deadlines for section 112
rules in several respects. First, the 90-day compliance deadline for
existing sources in section 112(f)(4)(A) directly conflicts with the
up-to-3-year deadline in section 112(i)(3)(A) allowed for existing
sources subject to ``any'' rule under section 112. Second, the section
112(f)(4)(A) deadline results in providing a shorter deadline for
ordinary existing sources to comply with residual risk standards than
would apply under section 112(i)(2) to new sources that are built after
a residual risk standard is proposed but a more stringent version is
promulgated. Third, while both section 112(i)(1), for new sources
subject to any section 112(d), (f), or (h) standard, and section
112(i)(3), for existing sources subject to any section 112(d) standard,
refer to and rely upon the new title V permit program added in 1990 and
explicitly provide for State permitting authorities to make relevant
decisions regarding compliance and the need for any compliance
extensions, section 112(f)(4)(B) still reflects the pre-1990 statutory
scheme in which only the Administrator is referred to as a decision-
making entity, notwithstanding the fact that even residual risk
standards under section 112(f) are likely to be delegated to States for
their implementation, and will be reflected in sources' title V permits
and need to rely upon the title V permit process for memorializing any
compliance extensions for those standards.
    While we appreciate the fact that section 112(i)(3)(B) refers
specifically only to standards under subsection 112(d), which some
might argue means that subsection 112(i)(3), in general, applies only
to existing sources subject to section 112(d) standards, we believe
that Congress inadvertently limited its scope and created a statutory
conflict in need of our resolution. Notwithstanding the language of
subparagraph (B), section 112(i)(3)(A) by its terms applies to ``any''
standard promulgated under ``section'' 112, which includes those under
subsection 112(f), in allowing up to a three year compliance period for
existing sources. Moreover, Congress clearly intended the section
112(i) provisions applicable to new sources to govern compliance
deadlines under section 112(f) rules, notwithstanding the language of
section 112(f)(4). This is because sections 112(i)(1) and (2)
explicitly reach standards under section 112(f). To read section
112(i)(3)(B) literally as reaching only section 112(d) standards, with
section 112(f)(4)(B) reaching section 112(f) standards, leaves the
question as to whether there can be compliance extensions for section

112(h) standards completely unaddressed by the statute, even though it
may in fact be necessary in complying with a section 112(h) work
practice standard to install equipment or controls. A narrow reading of
the scope of section 112(i)(3) also ignores the fact that in many
cases, including that of this proposed rule, the governing statutory
authority will be both section 112(f)(2) and section 112(d)(6)--the
only reasonable way to avoid a conflict in provisions controlling
compliance deadlines for existing sources in these situations is to
read the more specific and comprehensive set of provisions, those of
section 112(i), as governing both aspects of the regulation.
    Nothing in the legislative history suggests that Congress knowingly
intended to enact separate schemes for compliance deadlines for
residual risk standards and all other standards adopted under section
112. Rather, comparing the competing Senate and House Bills shows that
each bill contained its own general and/or specific versions of
compliance deadline provisions, and that when the bills were reconciled
in conference the two schemes were both accidentally enacted, without
fully modifying the various compliance deadline provisions in accord
with the modifications otherwise made to the section 112 amendments in
conference.
    We recognize that our existing regulations in the part 63 General
Provisions currently reflect the dual scheme presented by sections
112(f)(4) and 112(i) (See 40 CFR 63.6(c)(2), 63.6(i)(4)(ii)). In the
near future, we intend to revise those regulations to comport with our
interpretation, as explained above, to avoid confusion and situations
where a rule incorporates those provisions by reference such that
compliance deadlines are inconsistent with our interpretation. In the
meantime, notwithstanding the part 63 General Provisions, we are
proposing a compliance deadline for existing sources, under Option 2,
of three years for process vents and storage vessels and one year for
equipment leaks. The proposed compliance deadline for existing sources
of three years for process vents and storage vessels is realistic for
any affected facility that has to plan their control strategy, purchase
and install the control device(s), and bring the control device online.
Less time is required for compliance with the new equipment leak
requirements, but plants will have to identify affected equipment and
modify their existing leak detection and repair program to meet the new
requirements for monitoring frequency.

III. Rationale for the Proposed Rule

A. What is our approach for developing residual risk standards?

    Following our initial determination that the individual most
exposed to emissions from the category considered exceeds a 1-in-1
million individual lifetime cancer risk, our approach to developing
residual risk standards is based on a two-step determination of
acceptable risk and ample margin of safety. The first step is the
consideration of acceptable risk. The second step determines an ample
margin of safety to protect public health, which is the level at which
the standards are set (unless a more stringent standard is required to
prevent adverse environmental effect after the consideration of costs,
energy, safety, and other relevant factors).
    The terms ``individual most exposed,'' ``acceptable level,'' and
``ample margin of safety'' are not specifically defined in the CAA.
However, CAA section 112(f)(2)(B) refers positively to the
interpretation of these terms in our 1989 rulemaking (54 FR 38044,
September 14, 1989), ``National Emission Standards for Hazardous Air
Pollutants: Benzene Emissions from Maleic Anhydride Plants,
Ethylbenzene/Styrene Plants, Benzene Storage Vessels, Benzene Equipment
Leaks, and Coke By-Product Recovery Plants (Benzene NESHAP),''
essentially directing us to use the interpretation set out in that
notice. See also ``A Legislative History of the Clean Air Act
Amendments of 1990,'' volume 1, p. 877 (Senate debate on Conference
Report). We notified Congress in a report on residual risk that we
intended to utilize the Benzene NESHAP approach in making CAA section
112(f) residual risk determinations (see Residual Risk Report to
Congress, March 1999, EPA-453/R-99-001, p. ES-11).
    In the Benzene NESHAP (54 FR 38044, September 14, 1989), we stated
as an overall objective: * * * in protecting public health with an
ample margin of safety, we strive to provide maximum feasible
protection against risks to health from hazardous air pollutants by (1)
protecting the greatest number of persons possible to an individual
lifetime risk level no higher than approximately 1-in-1 million; and
(2) limiting to no higher than approximately 1-in-10 thousand [i.e.,
100-in-1 million] the estimated risk that a person living near a
facility would have if he or she were exposed to the maximum pollutant
concentrations for 70 years.''
    The Agency also stated that, ``The EPA also considers incidence
(the number of persons estimated to suffer cancer or other serious
health effects as a result of exposure to a pollutant) to be an
important measure of the health risk to the exposed population.
Incidence measures the extent of health risk to the exposed population
as a whole, by providing an estimate of the occurrence of cancer or
other serious health effects in the exposed population.'' The Agency
went on to conclude that ``estimated incidence would be weighed along
with other health risk information in judging acceptability.\2\'' As
explained more fully in our Residual Risk Report to Congress, EPA does
not define ``rigid line[s] of acceptability,'' but considers rather
broad objectives to be weighed with a series of other health measures
and factors (EPA-453/R-99-001, p. ES-11).
---------------------------------------------------------------------------

    \2\ In the benzene decision, the Agency considered the same risk
measures in the ``acceptability'' analysis as in the ``margin of
safety'' analysis, stating: ``In the ample margin decision, the
Agency again considers all of the health risk and other health
information considered in the first step. Beyond that information,
additional factors relating to the appropriate level of control will
also be considered, including costs and economic impacts of
controls, technological feasibility, uncertainties, and any other
relevant factors. Considering all of these factors, the Agency will
establish the standard a level that provides an ample margin of
safety to protect the public health, as required by section 112.''
---------------------------------------------------------------------------

B. How did we estimate residual risk?

    The Residual Risk Report to Congress provides the general framework
for conducting risk assessments to support decisions made under the
residual risk program. As acknowledged by the report, the design of
each risk assessment would have some common elements, including a
problem formulation phase, an analysis phase, and the risk
characterization phase.
    The primary risk assessment for the SOCMI source category focused
on inhalation exposures, both chronic and acute, to HAP emissions from
CMPUs that are subject to the HON. The primary risk assessment was
reviewed by Agency scientists before being used for this proposed
rulemaking. The emissions estimates used in the primary risk assessment
represented actual emissions that remain after the application of MACT,
not emissions at the rate allowed by the HON requirements
(``allowable'' emissions) that may be higher than actual emissions.
Some of the emission points subject to the HON may be controlled to a
higher level than required by the rules and some Group 2 points may be
controlled even though the rule does not require them to be. This may
be due to some State or local rules that are more stringent than the
HON, or because some facilities may reduce emissions for reasons other
than regulatory requirements. This means that the

estimated risks based on allowable emissions would be higher than the
risks estimated using actual emissions.
    For some HON emission points, we could estimate allowable
emissions; for others, it is nearly impossible. For equipment leaks,
because the standards are work practice standards the actual emissions
and allowable emissions are likely the same for equipment in the leak
detection and repair program required by the HON. More frequent
monitoring of equipment components (for example, monthly instead of
quarterly) could result in actual emissions being lower than allowable
emissions, but few, if any, sources monitor more frequently than
required by the HON. For wastewater and process vents, if a facility
chooses to control an emission point (to the level required in the
HON), there is no requirement to determine whether the point is
actually required to be controlled. A requirement to determine the
applicability of controls for such emission points was intentionally
not included in the HON because it was seen as an unnecessary burden
for points that would be controlled anyway. Consequently, there are
some emission points for which there is no readily available data that
can be used to determine the applicability of control requirements.
Without such data, there is no accurate way to determine allowable
emissions under the current rule. In addition, HAP emissions from
wastewater sources are likely controlled to a greater extent than the
rules require, but this overcontrol is impossible to estimate.
Emissions from transfer operations are small relative to the emissions
from other points, with emissions from controlled points nationally
accounting for less than one percent of total HON HAP emissions. Given
the small contribution to total emissions from transfer operations, any
differences between actual and allowable emissions would not be
significant relative to the total emissions from all HON emission
points.
    While we acknowledge that there is some uncertainty regarding the
differences between actual and allowable emissions, we believe that
there is neither a substantial amount of overcontrol of Group 1 sources
nor control of Group 2 sources so that actual emissions are a
reasonable approximation of allowable emissions. Basing this analysis
on actual emissions provides an acceptable approach to determining the
remaining risks to public health and the environment after application
of the MACT standards. Indeed, in this case, given the impossibility of
definitively estimating allowable emissions, we have no choice but to
rely upon the best available alternative information for assessing
remaining risks after application of MACT, industry supplied actual
emissions data. Uncertainty in the use of this data can be considered
in the selection of the standards as appropriate.
    Screening level assessments were also conducted to examine human
health and ecological risk due to multipathway exposure and to examine
the risks from entire plant sites (i.e., HON CMPUs and other HAP-
emitting processes). A full discussion of the primary and screening
level assessments is provided in the risk characterization document in
the public docket.
1. How did we estimate the atmospheric dispersion of HAP emitted from
HON CMPU sources?
    To estimate the dispersion of HAP emitted from HON CMPUs for the
inhalation and multipathway assessments, we used the Human Exposure
Model, version 3 (HEM-3), which incorporated the Industrial Source
Complex Short-term model, version 3 (ISCST-3). The ISCST3 dispersion
model is one of EPA's recommended models for assessing pollutant
concentrations from industrial facilities. The ISCST3 model handles a
wide range of different source types that may be associated with an
industrial source complex, including stack sources, area sources,
volume sources, and open pit sources.
    Inputs to the HEM-3 include source data to characterize the
emissions from the facility, the emission sources at the facility, and
the location of the facility. For the inhalation and multipathway
assessments, we used site-specific information for the base year 1999
for 104 of the 238 existing HON facilities. These data were collected
by the ACC through a voluntary survey and provided to EPA. These data
consisted of organic HAP emissions from five types of emission points
subject to the HON and included stack parameters, emission rates, and
location coordinates. Data were provided for 271 HON CMPUs in the 1999
data collection. When scaled to 238 HON facilities, 732 HON CMPUs would
be estimated for the industry. In the background information for the
HON, it was estimated that there were 729 HON CMPUs nationwide. The
similarities in the structure of the industry indicate that the 1999
collected data provide a reasonable picture of post-compliance
emissions of organic HAP, and that the process unit information used in
the residual risk analysis is representative of the CMPUs for the
entire industry.
    We recognize that the 1999 survey data have some uncertainties
regarding the sources responding to a voluntary data request and the
emissions reported. It is unclear the amount of bias that may exist in
the data and the extent to which the 104 facilities in the survey are
representative of the risks posed by the remaining facilities (see
section III.C.1. of this preamble for additional discussion). However,
the 1999 survey data are still the most detailed and comprehensive data
available, and we conclude that the data are appropriate for use in
conducting this residual risk assessment. Uncertainty in the use of
this data can be considered in the selection of the standards as
appropriate.
    Some inorganic HAP, such as hydrochloric acid and chlorine, may be
emitted from HON sources. However, these compounds were not considered
in this risk assessment because data were not available to characterize
emissions of those HAP. The HON regulates emissions of organic HAP only
and the 1999 ACC data provided information on organic HAP emissions
only. As discussed below in III.B.4, an additional analysis was
conducted using information in the National Emissions Inventory (NEI)
to estimate the risk from the entire plant site at which the HON CMPU
are located. The NEI information contained information on both organic
and inorganic HAP emitted from each facility. A comparison between the
analyses using the two different data sets showed that there were no
cases where the concentration of an inorganic HAP emitted from a HON
CMPU exceeded its reference value. Therefore, we concluded that not
including inorganic HAP in the primary risk assessment does not affect
the results of the analysis and that no further assessment of inorganic
HAP emissions is necessary.
2. How did we assess public health risk associated with HAP emitted
from HON CMPUs?
    The primary tool used to estimate individual and population
exposures in the inhalation and multipathway assessments was the Human
Exposure Model, Version 3 (HEM-3). The HEM-3 incorporates the ISCST3
air dispersion model and 2000 Census data, along with HAP dose response
and reference values, to estimate chronic and acute human health risks
and population exposure. This model is considerably more sophisticated,
and less conservative, than tools traditionally associated with
scoping-type analyses

(such as use of the Human Exposure Model, version 1.5). More
information on HEM-3 is available from the HEM-3 User's Guide.
    The HEM-3 performs detailed analyses of acute and chronic air
pollution risks for populations located near industrial emission
sources. The HEM-3 performs three main operations: dispersion modeling,
estimation of human health risks, and estimation of population
exposure. In order to perform these calculations, HEM-3 draws on three
data libraries provided with the model: A library of meteorological
data for over 60 stations, a library of census block internal point
locations, populations, and elevations to provide the basis for human
exposure calculations, and a library of pollutant unit risk factors and
reference concentrations used to calculate risks.
    In our assessment of public health risk associated with HAP emitted
from HON CMPUs, we considered risks of cancer and other health effects.
Cancer risks associated with inhalation exposure were assessed using
lifetime cancer risk estimates (i.e., assuming 70 years of exposure 24
hours a day for all individuals in a given location). The noncancer
risks were characterized through the use of hazard quotient (HQ) and
hazard index (HI) estimates. The HQ and HI also assume continuous
lifetime exposures. An HQ compares an estimated chemical intake (dose)
with a reference level below which adverse health effects are unlikely
to occur. Within the context of inhalation risk, EPA uses a ``Reference
Concentration (RfC)''. An RfC is an estimate (with uncertainty spanning
perhaps an order of magnitude) of a continuous inhalation exposure to
the human population (including sensitive subgroups) that is likely to
be without an appreciable risk of deleterious effects during a
lifetime. It can be derived from a NOAEL, LOAEL, or benchmark
concentration, with uncertainty factors generally applied to reflect
limitations of the data used. An HQ is calculated as the ratio of the
exposure concentration of a pollutant to its health-based reference
concentration. If the HQ is calculated to be less than 1, then no
adverse health effects are expected as a result of the exposure.
However, an HQ exceeding 1 does not translate to a probability that
adverse effects will occur. Rather, it suggests the possibility that
adverse health effects may occur. An HI is the sum of HQ for pollutants
that target the same organ or system. As with the HQ, values that are
below 1.0 are considered to represent exposure levels with no
significant risk of adverse health effects.
3. How did we assess multipathway impacts of HAP emissions from HON
CMPUs?
    The HON CMPUs at six of the 238 facilities emit HAP that are of
concern for potential adverse health impacts from pathways other than
inhalation (e.g., soil or fish ingestion). These HAP are often termed
persistent bioaccumulative toxics (PBTs). When deposited into soil and
water, PBT may be taken up by organisms and passed along the food
chain. The concentration of PBT in tissues can increase beyond the
concentration of the surrounding environment from one link in a food
chain to another (i.e., bioaccumulation and biomagnification). The
multipathway assessments estimated both human health and ecological
adverse impacts. Ecological impacts increase with PBTs because plants
and wildlife are exposed to pollutants in soil, water, and the food
chain, in addition to the air.
    Modeling the fate and transport of the PBTs through air, soil and
the food chain, and watersheds is a more complex and uncertain task
than estimating air transport for the inhalation pathway. Because of
the complexity and increased level of effort in both time and resources
and because gas phase compounds emitted from HON CMPUs are not
transferred to other media to any appreciable degree, we conducted a
simplified screening level approach to estimating media concentrations
of the PBTs. Due to the wide variety of species of plants and animals
potentially exposed, we needed to simplify fate and transport inputs
and methods through a health-protective, screening level approach and
screening level dose-response values.
    Adverse impacts on individuals of the most sensitive species
potentially exposed for each exposure pathway and HAP were first
estimated to indicate whether there is a potential problem to the
ecosystem. If no adverse impacts to the most sensitive species are
predicted, no adverse ecosystem impacts would be expected. If risks are
estimated to exceed a level of concern in the screening assessment,
more refined inputs and modeling techniques would be employed in
further assessments.
4. How did we assess risks for the entire plant site?
    Due to the substantial co-location of HON CMPUs with other HAP-
emitting processes, we also characterized how the risks resulting from
emissions from HON CMPUs relate to the risks resulting from emissions
from all processes (HON and non-HON processes) at the entire plant
site. In addition, we were interested in learning how well the HON CMPU
data, available for approximately half of the industry, represented the
entire industry. Therefore, an additional analysis was conducted to
estimate the risk from all HAP emitting processes at the entire plant
site.
    This analysis was conducted for 226 facilities where CMPUs subject
to the HON are located. The 1999 data submitted by the ACC that were
used in the CMPU analysis described in section B.1 could not be used
for this plant-level analysis because data were provided only on HON
CMPUs. However, the 1999 NEI contained information on HAP emissions
from the entire facility and was used for the analysis (hereafter
referred to as the NEI Assessment). On the other hand, the NEI data
were not used for the primary risk assessment because of the difficulty
in apportioning emissions to only HON CMPUs.
    The NEI Assessment considered only chronic cancer and noncancer
risk (not acute risk) because focusing only on chronic risk is adequate
to compare the risk posed by the HON CMPUs to the risk posed by the
entire plant site. Also, without additional information, it would be
difficult to characterize short-term emissions of sources that are not
affected by the HON. Whereas the HON CMPUs at a facility are typically
continuous and assumptions can be made about the temporal variability
of emissions, other processes may not be continuous and characterizing
the short-term emissions would be difficult.
    The HEM-3 model was used to estimate the maximum individual
lifetime cancer risks and lifetime noncancer HI values estimated to
result from emissions at each of these facilities. In addition, a brief
analysis was conducted to compare how the HON CMPUs contributed to the
situations where there is substantial co-location of SOCMI process
units with other HAP-emitting processes

C. What are the residual risks from HON CMPUs?

1. Health Risks From Chronic Inhalation Exposure
    Table 1 of this preamble shows the estimated maximum individual
lifetime cancer risk, maximum HI resulting from lifetime exposure,
population risk, and cancer incidence associated with HON CMPUs at 104
of the 238 existing facilities for which emissions data were available.
The size of the population at risk and cancer incidence estimated to be
associated with HON CMPUs were

extrapolated to the entire source category of 238 existing facilities
with HON CMPUs using the ratio of 2.3 (238/104). An inherent assumption
in using the simple 238/104 ratio is that the population densities
around the plants not assessed are similar to those of the 104 plants
that were assessed.
    The maximum individual lifetime cancer risk associated with any
source in the category is estimated to be approximately 100-in-1
million. This estimate characterizes the lifetime risk of developing
cancer for the individual facing the highest estimated exposure over a
70-year lifetime. With respect to chronic noncancer effects, HON CMPUs
at two facilities have a maximum respiratory HI that barely exceeds 1,
with only 20 people estimated to be exposed to HI levels greater than
1. As noted earlier, even an HI of 1 does not necessarily suggest a
likelihood of adverse effects.

 Table 1.--Risk Estimates Due to HAP Exposure Based on 70-Year Exposure
                                Duration
------------------------------------------------------------------------
                                                            Results
                                    Results for 104     extrapolated to
            Parameter                  surveyed            all  238
                                      facilities          facilities
------------------------------------------------------------------------
Maximum individual lifetime                   100                  100
 cancer risk (in a million).....
* Maximum hazard index (chronic                 1                    1
 respiratory effects)...........
Estimated size of population at
 risk from all HON CMPUs:
    >1-in-1 million.............          850,000            2,000,000
    >10-in-1 million............            4,000                9,000
    >100-in-1 million...........                0                    0
Annual cancer incidence (No. of                 0.06                 0.1
 cases).........................
------------------------------------------------------------------------
* An HQ exceeding 1 does not translate to a probability that adverse
  effects will occur. Rather, it suggests the possibility that adverse
  effects may occur.

    We compared the highest risks (maximum individual lifetime cancer
risk and maximum chronic HI) estimated for HON CMPUs at facilities in
the source category to the highest estimated risks from the NEI
Assessment. In the HON CMPU assessment conducted on the 104 facilities,
HON CMPUs at one facility were estimated to have a maximum individual
lifetime cancer risk of 100-in-1 million. Extrapolating this result to
the rest of the industry (i.e., 238 facilities) suggests that HON CMPUs
at two facilities are likely to be associated with a cancer risk of
100-in-1 million. In the NEI Assessment, three facilities were
estimated to have a maximum individual lifetime cancer risk greater
than 100-in-1 million where the risk was driven by HAP emissions from a
HON CMPU. The maximum individual lifetime cancer risk estimated for the
NEI Assessment was 300-in-1 million.
    For noncancer effects, the HON CMPUs at one of the 104 facilities
were estimated to have an HI of 1 in the HON CMPU assessment.
Extrapolating these results to the rest of the industry suggests HON
CMPUs at two facilities are estimated to have an HI of 1 for chronic
respiratory effects. In the NEI Assessment, five facilities were
estimated to have a maximum HI greater than 1 where risk was driven by
HAP emissions from HON CMPUs. The maximum estimated HI from the NEI
Assessment was 6.
    In comparing the two risk assessments, the extrapolated results
from the HON CMPU assessment are relatively consistent with the NEI
Assessment in terms of the number of facilities where HON CMPUs pose
risks in the range of 100-in-1 million. In addition, the magnitude of
the risks from the two studies is relatively close, considering the
health-protective nature of the NEI Assessment. Therefore, we
determined it was appropriate to use the estimated risks from the HON
CMPU assessment, which represents about half of the facilities in the
industry, to represent the risks from the entire industry.
Nevertheless, we acknowledge that the risks associated with HON
facilities not specifically included in this assessment may be higher
or lower than those assessed. Uncertainty in the use of this data can
be considered in the selection of the standards as appropriate.
    EPA toxicological assessments are currently underway for several
HAP emitted from HON CMPUs. For example, the cancer inhalation URE for
ethylene oxide is under review. Ethylene oxide is one of the HAP that
contributes significantly to the cancer risks for several HON CMPUs.
EPA has not yet completed a full evaluation of the data on which it
will determine a cancer URE for ethylene oxide. The schedule for the
ethylene oxide review and the reviews of other HAP can be found at:
http://cfpub.epa.gov/iristrac.

    Under section 112(o)(7) of the CAA, we are required to issue
revised cancer guidelines prior to the promulgation of the first
residual risk rule under section 112(f) (an implication being that we
should consider these revisions in the various residual risk rules). We
have issued revised cancer guidelines and also supplemental guidance
that specifically address the potential added susceptibility from
early-life exposure to carcinogens. The supplemental guidance provides
guidance for adjusting the slope of the dose response curve by applying
``age-dependent adjustment factors'' (which translates into a factor of
1.6 for lifetime exposures) to incorporate the potential for increased
risk due to early-life exposures to chemicals that are thought to be
carcinogenic by a mutagenic mode of action.
    Some evidence indicates that several HAP that are emitted from HON
CMPUs and that dominate the risks in our assessment may be carcinogenic
by a mutagenic mode of action, although for most carcinogenic HAP the
formal determination of mode of action has not yet been made. Thus, we
did not apply age-dependent adjustment factors to the cancer risk
estimates in our residual risk assessment for HON CMPUs.
2. Health Risks From Acute Inhalation Exposure
    In addition to chronic cancer and noncancer effects, acute effects
were also assessed. We used the ratio analogous to the HQ in which we
compared the maximum 1-hour average air concentration for each HAP
emitted from HON CMPUs at each facility with the lowest (i.e., most
health protective) of the available acute reference values for that
HAP. In this analysis, exposure estimates for 10 HAP exceeded at least
one acute reference value for HON CMPUs in at least one facility.
However, for eight of those HAP (acrylonitrile, benzene, chloroform,
ethylene glycol, formaldehyde, methyl bromide, methyl chloride, and
toluene) the estimated exceedances were only for no-effect reference
values. All estimated exposures were lower than available

mild-effect reference values. Given the protective nature of these no-
effect reference values, and the fact that the estimated exposures to
which they were compared are the highest expected for any 1-hour period
in five years, we concluded that the eight HAP do not pose a
significant health threat by acute inhalation.
    Estimated exposures to the other two HAP, acrolein and ethyl
acrylate, exceeded a mild-effect reference value at a single facility
with a HON CMPU. The estimated acrolein exposure of 100 micrograms per
cubic meter ([mu]g/m\3\) exceeded the acute exposure guideline level of
69 [mu]g/m\3\, and the estimated ethyl acrylate exposure of 50 [mu]g/
m\3\ exceeded the emergency response planning guideline value of 41
[mu]g/m\3\. Both exposure estimates were well below corresponding
reference values for more severe effects. Because these estimated 1-
hour exposures reflect the highest 1-hour concentrations near the
facility in a 5-year period and would at worst cause only mild,
reversible effects, EPA does not consider them to pose a significant
health threat.
    For 15 HAP, no mild-effects reference values were available, and
the lowest acute reference values for emergency planning uses are
associated with severe health effects. For these HAP, the 1-hour
exposure estimates were compared to these severe effects reference
values. The highest acute HQ is 0.02, suggesting that these HAP also
are very unlikely to pose health threats by acute inhalation exposure.
3. Multipathway Risks
    The lifetime cancer risk and noncancer adverse health impacts
estimated to result from multipathway exposure are well below levels
generally held to be of concern. Only two HAP emitted by HON CMPUs,
hexachlorobenzene and anthracene, were estimated to pose any potential
for exposures via routes beyond direct inhalation. The maximum cancer
risk estimated for exposures to these HAP is 0.2-in-1 million. For
noncancer impacts, the maximum HQ is 0.0004. From these low risk
estimates, we concluded that multipathway risks do not pose a higher
risk than inhalation exposure.
    As with human health impacts, all the ecological HQ values are well
below levels of concern, with the highest HQ being 0.05 from benthic/
sediment exposure by aquatic life to anthracene. The highest HQ is 0.02
from surface water exposure by aquatic life to hexachlorobenzene. We do
not believe these levels are high enough to pose adverse environmental
effects as defined in CAA section 112(a)(7).

D. What is our proposed decision on acceptable risk?

    Section 112(f)(2)(A) of the CAA states that if the MACT standards
applicable to a category of sources emitting a: ``* * * known,
probable, or possible human carcinogen do not reduce lifetime excess
cancer risks to the individual most exposed to emissions from a source
in the category * * * to less than 1-in-1 million, the Administrator
shall promulgate [residual risk] standards * * * for such source
category.'' Processes that would be subject to the proposed amendments
under our first proposed option emit known, probable, and possible
human carcinogens, and, as shown in table 1 of this preamble, we
estimate that the maximum individual lifetime cancer risk (discussed
below) associated with the standards of the 1994 HON is 100-in-1
million. Since the maximum individual lifetime cancer risk is greater
than 1 in a million, we are required to consider (residual risk)
standards.
    As discussed in section IV.A of this preamble, we used a two-step
process in establishing residual risk standards. The first step is the
determination of acceptability (i.e., are the estimated risks due to
emissions from these facilities ``acceptable''). This determination is
based on health considerations only. The determination of what
represents an ``acceptable'' risk is based on a judgment of ``what
risks are acceptable in the world in which we live'' (54 FR 38045,
quoting the Vinyl Chloride decision at 824 F.2d 1165) recognizing that
our world is not risk-free.
    In the 1989 Benzene NESHAP, we stated that a maximum individual
lifetime cancer risk of approximately 100-in-1 million should
ordinarily be the upper end of the range of acceptable risks associated
with an individual lifetime cancer source of pollution. We discussed
the maximum individual lifetime cancer risk as being ``the estimated
risk that a person living near a plant would have if he or she were
exposed to the maximum pollutant concentrations for 70 years.'' We
explained that this measure of risk ``is an estimate of the upper bound
of risk based on conservative assumptions, such as continuous exposure
for 24 hours per day for 70 years.'' We acknowledge that maximum
individual lifetime cancer risk ``does not necessarily reflect the true
risk, but displays a conservative risk level which is an upper bound
that is unlikely to be exceeded.''
    Understanding that there are both benefits and limitations to using
maximum individual lifetime cancer risk as a metric for determining
acceptability, we acknowledged in the 1989 Benzene NESHAP that
``consideration of maximum individual risk * * * must take into account
the strengths and weaknesses of this measure of risk.'' Consequently,
the presumptive risk level of 100-in-1 million provides a benchmark for
judging the acceptability of maximum individual lifetime cancer risk,
but does not constitute a rigid line for making that determination. In
establishing a presumption for the acceptability of maximum risk,
rather than a rigid line for acceptability, we explained in the 1989
Benzene NESHAP that risk levels should also be weighed with a series of
other health measures and factors, including the following:
     The numbers of persons exposed within each individual
lifetime risk range and associated incidence within, typically, a 50
kilometer (km) (about 30 miles) exposure radius around facilities;
     The science policy assumptions and estimation
uncertainties associated with the risk measures;
     Weight of the scientific evidence for human health
effects;
     Other quantified or unquantified health effects;
     Effects due to co-location of facilities and co-emission
of pollutants; and
     The overall incidence of cancer or other serious health
effects within the exposed population.
    In some cases, these health measures and factors taken together may
provide a more realistic description of the magnitude of risk in the
exposed population than that provided by maximum individual lifetime
cancer risk alone.
    Based upon the criteria identified above, for purposes of both of
our proposed options discussed below, we judge the level of risk of the
current HON rule to be acceptable for this source category. The
calculated maximum individual lifetime cancer risk associated with HON
CMPUs is 100-in-1 million. There are no people with estimated risks
greater than 100-in-1 million, which is the presumptively acceptable
level of maximum individual lifetime cancer risk under the 1989 Benzene
NESHAP criteria. The HON CMPUs at 32 facilities are estimated to pose
risks of between 10 and 100-in-1 million, with 9,000 people estimated
to be exposed in this risk range. The HON CMPUs at the remaining 206
facilities are estimated to pose risks of 10-in-1 million or less. For
the exposed population, total annual cancer incidence is estimated at
0.1 cases per

year. In addition, significant non-cancer health effects are not
expected. The HON CMPUs at only two of the 238 facilities are
associated with an HI greater than 1, with less than 20 people
estimated to be exposed at levels associated with an HI greater than 1.

E. What is our proposed decision on ample margin of safety?

    The second step in the residual risk decision framework is the
determination of standards with corresponding risk levels that are
equal to or lower than the acceptable risk level and that protect
public health with an ample margin of safety. In making this
determination, we considered the estimate of health risk and other
health information along with additional factors relating to the
appropriate level of control, including costs and economic impacts of
controls, technological feasibility, uncertainties, and other relevant
factors, consistent with the approach of the 1989 Benzene NESHAP.
    Many HON sites are located near other HON sites or other industrial
sites, and people who live in these areas may be exposed to HAP emitted
from multiple sources. We analyzed the effects of facility clusters on
cancer risk levels by modeling all facilities with HON CMPUs that are
located within 50 km of one another. The maximum individual lifetime
cancer risk of clustered emissions was similar to the highest maximum
individual lifetime cancer risk of a facility with a HON CMPU in that
cluster. We concluded, therefore, that cluster effects have little or
no significant effect on the risks to the individuals most exposed. The
individuals potentially exposed to the highest risks would typically
reside very near one of the facilities, and the resulting risk would be
almost entirely caused by that closest facility. While these
individuals may also be exposed to emissions from neighboring
facilities, we found that the risks are sufficiently lower than the
maximum risk posed by the nearby facility.
    Before developing our two general proposed options under sections
112(f)(2) and 112(d)(6), we considered three regulatory alternatives
for providing an ample margin of safety, assuming some degree of
additional control is warranted. In developing the regulatory
alternatives that assumed additional control is warranted, we wanted to
target further emission reductions to the extent possible to reduce
public health risks. Therefore, the alternatives were crafted to apply
only at CMPUs that emit either carcinogenic HAP, or HAP that are not
carcinogens but for which estimated exposure concentrations after
application of MACT exceed chronic noncancer thresholds. Acrolein,
methyl bromide, and maleic anhydride are the only three which exceed
chronic noncancer thresholds. These 47 carcinogenic and three
noncarcinogenic HAP are listed in proposed table 38 of 40 CFR, part 63,
subpart G.
    We did not have sufficiently detailed information to analyze the
possibility of controls on the various specific sources within a
facility but outside the HON source category. Because the facilities in
this source category also frequently have other non-HON processes we
could not always associate the reported emissions from the NEI
Assessment to a particular source category. As a result, we could not
evaluate the existing levels of control or the potential for applying
additional controls at the facilities where HAP emissions from non-HON
processes contributed to the risk. Our position on the potential
consideration of both source category-only emissions and facilitywide
emissions is fully discussed in the final coke oven batteries NESHAP
(70 FR 19996-19998, April 15, 2005).
    To develop possible regulatory alternatives, we first identified
the additional control measures that could be applied at a specified
cost to each of the five kinds of emission points regulated by the HON.
The feasible control measures then were combined to develop the
regulatory alternatives for assessing ample margin of safety. Control
measures were defined in terms of both an emission control technology
and the number of emission points controlled.
    The current HON standards for storage vessels, process vents,
equipment leaks, wastewater collection and treatment operations, and
transfer loading operations require the use of technologies such as
thermal oxidizers, carbon adsorbers, and steam strippers to reduce HAP
emissions by 95 to 98 percent. We did not identify any other
technically feasible control technologies that would reduce HAP
emissions beyond these levels.
    Consequently, to select control measures that would further reduce
HAP emissions from HON CMPUs, we considered changing the applicability
criteria to require control of uncontrolled emission points (i.e.,
certain Group 2 emission points under the original rule would become
Group 1 emission points under the revised rule). For equipment leaks,
we focused on reducing emissions from leaking valves in gas/vapor
service and in light liquid service since these equipment components
tend to have the highest emissions and, therefore, the greatest
influence on risks from equipment leaks. Our evaluation of the feasible
control measures for each of the five kinds of emission points is
contained in memoranda in the public docket, and our proposed
conclusions are summarized below.
1. Process Vent Control Measures
    To develop possible additional control measures for process vents,
we applied the current level of control (i.e., reduce HAP emissions by
98 percent) to the uncontrolled process vents reported in the ACC
survey. For CMPUs that emit at least one HAP listed in table 38, each
uncontrolled process vent emitting one or more of the HAP listed in the
proposed table 38 of subpart G of part 63, we calculated a TRE index
value, arrayed the TRE index values in ascending order (a higher TRE
index value means higher control costs), and evaluated the emission
reductions achieved by controlling each process vent. The TRE index
value is a measure of the cost of applying a thermal oxidizer on a vent
stream, based on vent HAP emissions, stream flow rate, net heating
value, and corrosion properties (i.e., presence of halogenated
compounds).
    The current HON rule requires 98 percent control of process vents
with a TRE of 1.0 or less at existing process units (corresponding to a
cost of approximately $3,000 per ton). The miscellaneous organic NESHAP
(40 CFR part 63, subpart FFFF) also affects the chemical manufacturing
industry and requires control of process vents with a TRE of 1.9 at
existing sources and a TRE of 5.0 at new sources. A TRE of 5.0
corresponds to a cost of approximately $15,000 per ton. In constructing
a risk-based alternative for process vents containing table 38 HAP and
considering control technology and cost, we analyzed impacts of further
reducing table 38 HAP without exceeding the control level for the
miscellaneous organic NESHAP (MON) for new sources (TRE of 5). We
considered control of new and existing HON process vents with a TRE
index value of 4.0 to be most reasonable.
    A TRE cut-off of 4.0 will reduce emissions of total HAP by 640 tpy
at HON CMPUs at 14 out of 238 total facilities that emit table 38 HAP.
The total capital cost would be $13 million with a total annualized
cost of $3.7 million. A TRE cut-off of 4.0 will also reduce emissions
of total volatile organic compounds (VOC) by 1,100 tpy at HON CMPUs at
14 facilities that emit table 38 HAP. This control measure is included
in our second proposed option

discussed below, but not in our first proposed option.
2. Storage Vessel Control Measures
    To develop possible additional control measures for storage
vessels, we applied the current HON MACT level of control (95 percent
reduction) to the uncontrolled tanks reported in the ACC survey. We
calculated the HAP emission reduction and cost for installing an
internal floating roof on existing fixed-roof vessels that contain any
HAP listed in the proposed table 38 of subpart G of part 63. We sorted
the storage vessels by decreasing emission reductions and determined
the cost per ton of HAP removed of controlling each tank. To achieve
emission reductions at the least cost, we selected a control measure
with the same cost as the process vent control measure. We evaluated
internal floating roofs on storage vessels with cost of approximately
$12,000 per ton of total HAP reduced or less for any individual vessel.
Since it is impracticable to develop a TRE for storage vessels, another
parameter was needed to characterize storage vessels with a cost of
$12,000 per ton removed. After analyzing the data, we expect that an
emission cutoff of five tons of HAP per year will ensure that no
individual storage vessel that contains a HAP from proposed table 38 of
40 CFR, part 63, subpart G would incur a control cost that exceeds
$12,000 per ton of HAP reduced. This emission cutoff would affect 7 out
of 238 facilities and would reduce total HAP emissions by 120 tpy, at a
total capital cost of $950,000 and a total annualized cost of $120,000.
The average cost of controlling storage vessels at the 7 facilities
would be $1,000 per ton of total HAP. The emission cut-off would also
reduce emissions of VOC by 210 tpy.
3. Process Wastewater Control Measures
    To develop possible additional control measures for process
wastewater streams, we applied the current HON MACT level of control
(i.e., steam stripper with control of overhead gases) to the emissions
from uncontrolled wastewater streams reported in the ACC survey. To
estimate HAP emission reductions, the removal performance of the steam
strippers was determined using the compound-specific fraction removed
values specified in tables 8 and 9 of subpart G of the HON. The
destruction of the overhead gases from the steam strippers was assumed
to be 95 percent (the same performance that is required in the current
HON standards). The estimated total HAP emission reduction for the ACC
facilities for which wastewater data were available was 495 tons/year.
    While the ACC data contained sufficient information to estimate HAP
emission reductions, flow rate data for individual streams, which is
necessary to estimate control costs, were not available. To determine
whether control of Group 2 wastewater streams would be feasible and
whether additional data gathering would be warranted, we estimated cost
per ton of HAP removed for each facility using the calculated HAP
emission reductions and steam stripper cost estimates developed for
model streams. The model streams were based upon comparable chemical
manufacturing processes and wastewater HAP emissions data from
rulemaking docket for the NESHAP for miscellaneous organic chemical
manufacturing (40 CFR part 63, subpart FFFF). These data were grouped
into HAP loading (kg/liter) ranges and default flow rates were
estimated for each range. The default flow rates were assigned to
wastewater streams for the facilities in the ACC survey data based upon
the HAP loading for each stream.
    Based on this analysis, 96 percent of the facilities had cost per
ton of HAP removed exceeding $12,000 per ton of total HAP reduced. The
average cost per ton of HAP removed for controlling Group 2 wastewater
streams was approximately $410,000 per ton of HAP reduced. Considering
these high costs, we concluded that it is not reasonable to require
additional controls for Group 2 wastewater streams, in light of the
minimal risk reduction obtained if additional controls were to be
imposed. As a result, additional controls for Group 2 wastewater
streams are not included in either of our two proposed options
discussed below.
4. Equipment Component Control Measures
    For leaking valves in gas/vapor service and in light liquid
service, the possible additional control measures available to reduce
HAP emissions are to either lower the leak definition, replace valves
with leakless valves, or conduct more frequent monitoring by reducing
the allowable percentage of leaking valves. We evaluated requiring
replacement of existing valves in gas/vapor service and in light liquid
service with leakless valves. However, we concluded that this method of
control is not appropriate because it is extremely expensive. To
implement this alternative, total industry capital costs would exceed
$5.7 billion, and total annualized costs were calculated to be $780
million. The alternative would reduce total HAP emissions by 1,800 tpy
and total VOC emissions by 3,200 tpy. The average cost of total HAP
removed of this control alternative would be $430,000 per ton of HAP.
    We also evaluated lowering the leak definition. Under Phase III of
the current HON equipment leak standards, facilities are required to
use a leak definition of 500 ppmv. However, we do not consider it
appropriate to reduce the leak definition below the 500 ppmv level. We
do not have any data that would indicate the emissions reduction or
effectiveness in reducing risks associated with lowering the
definition. Additionally, we do not have field data that validates that
lower concentrations can be identified using Method 21.
    The final method we evaluated to reduce HAP emissions from leaking
valves was to reduce the allowable percent of valve population that can
leak. Under the current HON standards, facilities are allowed to
conduct less frequent monitoring (quarterly, semiannually, annually) if
the percentage of leaking valves is less than two percent, but must
monitor more frequently (monthly) if the percentage of leaking valves
is more than two percent.
    We evaluated requiring facilities to reduce the number of leaking
valves in gas/vapor service and in light liquid service. Data supplied
by the industry indicated that the average percent leaking valves at
HON CMPUs is 0.5 percent. Requiring no more than 0.5 percent leakers
would reduce total HAP emissions by 910 tpy, and total VOC emissions by
1,600 tpy, from HON CMPUs at 174 facilities. The annual cost of
requiring 0.5 percent leakers was calculated to be $9.7 million per
year. This regulatory alternative would require no capital expenditures
but would impose additional labor costs. The average cost per ton of
total HAP removed of requiring 0.5 percent leakers is $11,000 per ton
of HAP.
    We also evaluated requiring no more than 1.0 percent leakers. The
total HAP emission reduction was estimated to be 420 tpy at an annual
cost of $10 million per year. For less than five percent increase in
annual cost, the 0.5-percent leak limit more than doubles the HAP
reduction achieved by a 1.0-percent limit.
    Under this control measure, facilities would conduct monthly
monitoring until the 0.5-percent limit is achieved. The monitoring
frequency would be reduced to quarterly, semi-annually, or annually if
successive monitoring periods show that facilities are able to maintain
0.5 percent leakers or less. However, monthly monitoring would be
required if the percent leakers exceeds 0.5 percent. While neither
requiring

leakless equipment nor lowering the leak definition are included in
either of our two proposed options discussed below, requiring 0.5
percent leaking valves (or less) is included in our second proposed
option, but not in our first proposed option.
5. Transfer Operation Control Measures
    We did not further evaluate controls for transfer operations
because the HAP emissions remaining after compliance with the HON are
very low. A total of 400 tpy of total HAP are emitted from controlled
and uncontrolled transfer operations at HON sources, but only 200 tpy
are from uncontrolled transfer operations. An additional 100 tpy are
from transfer operations that did not specify whether they are
controlled or uncontrolled. These emissions comprise less than three
percent of total HAP emissions from all HON CMPUs, and less than one
percent of the total risk from all HON CMPUs. Therefore, further
control of transfer operations would provide no significant reduction
of risk. The cost of controlling emissions from transfer operations
ranges from approximately $10,000 per ton of HAP to over $100,000 per
ton of HAP if there are already existing control devices that may be
used to reduce emissions. If a new combustion device or vapor recovery
device is also needed, the cost increases significantly. As a result,
further controls for transfer operations are not included in either of
our two proposed options discussed below.
6. Regulatory Alternatives
    The three regulatory alternatives are presented in table 2 of this
preamble along with the associated costs and emission reductions.
Alternative I would require control of storage vessels that store a HAP
listed in the proposed table 38 of 40 CFR part 63 of subpart G and emit
more than five tpy of HAP. Alternative II would require the same
controls as Alternative I plus control of process vents that have a TRE
index value less than or equal to 4.0 and emit one or more HAP listed
in the proposed table 38 of 40 CFR part 63, subpart G. Alternative III
would require the same controls as Alternative II plus the requirement
to reduce the number of leaking valves in gas/vapor service and in
light liquid service to less than 0.5 percent for valves that contain
at least one HAP listed in proposed table 38 of 40 CFR part 63, subpart
G. Table 3 of this preamble summarizes the risk reduction associated
with each regulatory alternative.

                                  Table 2.--Impacts of Regulatory Alternatives
----------------------------------------------------------------------------------------------------------------
                                                    Total
                                                  installed      Total      Total HAP     Average    Incremental
       Alt.           Control  requirement\*\      capital     annualized    emission     cost per     cost per
                                                  costs  ($     cost  ($    reduction    ton of HAP   ton of HAP
                                                   million)     million)      (tpy)       ($/ton)      ($/ton)
----------------------------------------------------------------------------------------------------------------
I.................  Reduce HAP emissions by 95             1         0.12          120        1,000
                     percent from storage
                     vessels that emit greater
                     than 5 tons per year of
                     HAP.
II................  Same as Alternative I plus            14            4          800        5,000        5,700
                     reduce HAP emissions by 98
                     percent from process vents
                     with a TRE value less than
                     or equal to 4.0.
III...............  Same as Alternative II plus           14           13        1,700        7,600      10,000
                     conduct monthly monitoring
                     of process unit valves
                     until the process unit has
                     fewer than 0.5 percent
                     leaking valves in gas/
                     vapor and in light liquid
                     service.
----------------------------------------------------------------------------------------------------------------
\*\ Applies to units that emit HAP listed in proposed table 38 of 40 CFR 63, subpart G.

                                Table 3.--Risk Impacts of Regulatory Alternatives
----------------------------------------------------------------------------------------------------------------
                                                                     Regulatory alternative
                  Parameter                   ------------------------------------------------------------------
                                                     Base              I                II              III
----------------------------------------------------------------------------------------------------------------
Risk to most exposed individual:
     Cancer (in a million)...................            100              100              100             60
    \*\ Noncancer (H1).......................              1                1                0.9            0.9
Size of population at cancer risk:
    >100-in-1 million........................              0                0                0              0
    >10-in-1 million.........................          9,000            9,000            9,000          7,000
    >1-in-1 million..........................      1,950,000        1,900,000        1,900,000      1,500,000
Number of plants at cancer risk level:
    >100-in-1 million........................              0                0                0              0
    >10-in-1 million.........................             32               32               32             32
    >1-in-1 million..........................            117              117              117            112
\*\ Population with HI >1....................             20               20                0              0
\*\ No. of Plants with HI >1.................              2                2                0              0
Cancer incidence.............................              0.1              0.1              0.1            0.09
Cancer incidence reduction (percent).........  ...............              2                2             10
HAP emission reduction (percent).............  ...............              1                6            13
----------------------------------------------------------------------------------------------------------------
\*\ If the HI is calculated to be less than 1, then no adverse health effects are expected as a result of the
  exposure. However, an HI exceeding 1 does not translate to a probability that adverse effects occur. Rather,
  it suggests the possibility that adverse health effects may occur.

7. Regulatory Decision for Residual Risk
    Based on the information analyzed for the regulatory alternatives,
we are proposing two options for our rulemaking on whether to establish
additional emissions standards to protect public health with an ample
margin of safety. The first proposed option is to maintain the current
level of control in the HON (i.e., the baseline option in table 2 of
this preamble) with no further modifications. The second proposed
option corresponds to Regulatory Alternative III. In the final rule, we
expect to select one of these

options, with appropriate modifications in response to public comments.
a. Rationale for Option 1
    For the first option of the proposed rulemaking, we are proposing
to make no changes to the current HON rule, instead proposing to find
that the current level of control called for by the existing MACT
standard represents both an acceptable level of risk (the cancer risk
to the most exposed individual is approximately 100-in-1 million) and
provides public health protection with an ample margin of safety. This
proposed finding is based on considering the additional costs of
further control (as represented by Option 2 [Regulatory Alternative
III]) against the relatively small reductions in health risks that are
achieved by that alternative.
    The Agency would conclude under this proposal that the $13 million
per year cost of Regulatory Option III would be unreasonable given the
minor associated improvements in health risks. Baseline cancer
incidence under the current HON rule is estimated at 0.1 cases per
year. Proposed Option 2 would reduce incidence by about 0.01 cases per
year. Statistically, this level of risk reduction means that Option 2
would prevent 1 cancer case every 100 years. Accordingly, the cost of
this option could be considered to be disproportionate to the level of
incidence reduction achieved. In addition, the Agency proposes to
conclude that the changes in the distribution of risks reflected in
table 3 of this preamble (i.e., the maximum individual cancer risk is
reduced by 40 percent to 60 in a million, 450,000 people's cancer risks
are shifted to levels below 1 in a million, and 20 people's noncancer
Hazard Index values would be reduced from above to below 1) are do not
warrant the costs. This change in the distribution of risk, that is,
the aggregate change in risk across an affected population of more than
one in a million reduces cancer risk by 0.01 cancers per year (i.e.,
one cancer across this population every on hundred years).
Consequently, under Option 1 we are proposing that it is not necessary
to impose any additional controls on the industry to provide an ample
margin of safety to protect public health. Compared to Option 2, the
rationale for Option 1 reflects a relatively greater emphasis on
considering changes in cancer incidence in determining what is
necessary to protect public health with an ample margin of safety and
correspondingly less emphasis on maximizing the total number of people
exposed to lifetime cancer risks below 1-in a million.
b. Rationale for Option 2
    For the second option, we are proposing that Regulatory Alternative
III provides an ample margin of safety to protect public health. This
option reduces HAP emissions and risks beyond the current MACT standard
using controls that are technically and economically feasible and that
pose no adverse environmental impacts. The controls will reduce cancer
risks to the most exposed individual by about 40 percent to 60 in a
million. Exposures for approximately 450,000 people will be reduced
from above the 1 in a million cancer risk level to below 1 in a million
cancer risk level, and no individual will be exposed to a noncancer HI
greater than 1. Note that these changes would reduce cancer incidence
by 0.01 cases per year (i.e., prevent one cancer case every hundred
years). The rationale for this option reflects a relatively greater
emphasis on maximizing the total number of people exposed to lifetime
cancer risks below 1 in a million, compared to that in Option 1, while
reflecting correspondingly less emphasis on various other public health
metrics such as incidence reduction.
    The annualized cost of Option 2 is $13 million. Our economic
analysis (summarized later in this preamble) indicates that this cost
will have little impact on the price and output of chemical and
petroleum feedstocks. However, the Agency is considering the adoption
of an approach, described elsewhere in this preamble, to allow sources
to avoid additional controls if they can demonstrate that the risks
posed by their HAP emissions already fall below certain low-risk
thresholds. Depending on the public comments received, we may include
this approach in the final rule, and this could result in some cost
saving at individual facilities. We did not include this potential cost
savings in our control cost calculations. It should be noted that the
avoidance of controls would also result in fewer incidence and VOC
reductions than those estimated above.

Discussion of Other Factors

    Besides HAP emission reductions, the second option (Regulatory
Alternative III) would reduce emissions of VOC by 2,900 tpy. Reducing
VOC provides the added benefit of reducing ambient concentrations of
ozone and may reduce fine particulate matter. We have not estimated the
benefits of these reductions but previous work suggests that the ozone
benefits per ton of VOC removed would span a large range, rarely
exceeding $1000 to $2000 per ton. The cost of this option translates
into about $4,300 per ton of VOC removed.
    While we believe that the risk assessment for this proposal is
appropriate for rulemaking purposes, we recognize that there are a
variety of uncertainties in the underlying models and data. These
include the uncertainties associated with the cancer potency values (of
the 52 HAP identified as ``carcinogens'', EPA classifies only four as
``known carcinogens,'' while the remaining carcinogens are classified
as either ``probable'' or ``possible'' carcinogens (using the 1986
nomenclature)), reference concentrations, uncertainties underlying
emissions data, emissions dispersion modeling in the ISCST3 model, and
the human behavior modeling (including assumptions of exposure for 24
hours a day for 70 years). One source of uncertainty is the reliance on
industry-supplied data that represent only a segment of the industry.
These data were not collected under the information collection
authority of section 114 of the CAA, but were the result of a voluntary
survey conducted by the industry trade association. It is unclear what
bias may exist in the data or the extent to which the 104 facilities in
the survey are representative of the maximum risks posed by the
remaining 134 facilities. Another source of potential uncertainty is
the use of data based on actual HAP emissions, rather than the maximum
allowable emissions under the current HON rule (which, as explained
above, are unknown and impossible to determine). An additional source
of uncertainty comes from our use of 1999 year emissions inventories.
Some HON facilities may have reduced their emissions since then to
comply with other CAA and state requirements; others may have increased
their emissions as a result of growth.

F. What is EPA proposing pursuant to CAA section 112(d)(6)?

    Section 112(d)(6) of the CAA requires us to review and revise MACT
standards, as necessary, every 8 years, taking into account
developments in practices, processes, and control technologies that
have occurred during that time. This authority provides us with broad
discretion to revise the MACT standards as we determine necessary, and
to account for a wide range of relevant factors.
    We do not interpret CAA section 112(d)6) as requiring another
analysis of MACT floors for existing and new sources. Rather, we
interpret the provision as essentially requiring us to

consider developments in pollution control in the industry (``taking
into account developments in practices, processes, and control
technologies''), and assessing the costs of potentially stricter
standards reflecting those developments (69 FR 48351). As the U.S.
Court of Appeals for the DC Circuit has found regarding similar
statutory provisions directing EPA to reach conclusions after
considering various enumerated factors, we read this provision as
providing EPA with substantial latitude in weighing these factors and
arriving at an appropriate balance in revising our standards. This
discretion also provides us with substantial flexibility in choosing
how to apply modified standards, if necessary, to the affected
industry.
    We took comment in two recently proposed residual risk rules on
whether, when we make a low-risk finding under section 112(f) (as would
occur under the first option proposed today), and ``barring any
unforeseeable circumstances which might substantially change this
source category or its emissions,'' we would need to conduct future
technology reviews under CAA section 112(d)(6). See Proposed Rule:
Magnetic Tape Manufacturing Operations, 70 FR 61417 (October 24, 2005);
Proposed Rule: Industrial Process Cooling Towers, 70 FR 61411 (October
24, 2005). Earlier, in the final residual risk rule for Coke Ovens, we
discussed the relationship between the findings underlying a section
112(f) determination and section 112(d)(6) revisions. National Emission
Standards for Coke Oven Batteries, 70 FR 19992, 20009 (April 15, 2005).
Today we further elaborate on how we expect we would address the need
for future reviews under certain circumstances, and we refine our
position regarding when revisions may be likely under section
112(d)(6). First, the Agency now interprets the language of section
112(d)(6) as being clear in requiring a periodic review no less
frequently than every 8 years. We also believe that the periodic review
should be of whatever section 112 standard applies to the relevant
source category, regardless of whether the original section 112(d) and/
or 112(h) NESHAP has, or has not, been revised pursuant to section
112(f)(2). We recognize that one could read the section 112(f)(2)
language to authorize EPA's setting a standard under subsection (f)(2)
separate from the NESHAP standard set under subsections (d) and/or (h).
Following this reading, one might argue that any review under (d)(6)
should be only of the (d)(2), (d)(4), or (d)(5) NESHAP standard, as
applicable. It is our position, however, that the better reading of
(f)(2) allows EPA to revise the relevant subsection (d) standard if the
agency determines residual risk so justifies under (f)(2); indeed, our
practice has been to follow this approach. See Coke Ovens, 70 FR 19993;
40 CFR 63.300-.311. This approach results in clearer and more effective
implementation because only one part 63 NESHAP would apply to the
source category, and is supported by the fact that section 112(d)(6)
refers to ``emission standards promulgated under this section''
(emphasis added), as opposed to ``subsection,'' in defining the scope
of EPA's authority to review and revise standards.
    Although the language of section 112(d)(6) is nondiscretionary
regarding periodic review, it grants EPA much discretion to revise the
standards ``as necessary.'' Thus, although the specifically enumerated
factors that EPA should consider all relate to technology (e.g.,
developments in practices, processes and control technologies), the
instruction to revise ``as necessary'' indicates that EPA is to
exercise its judgment in this regulatory decision, and is not precluded
from considering additional relevant factors, such as costs and risk.
EPA has substantial discretion in weighing all of the relevant factors
in arriving at the best balance of costs and emissions reduction and
determining what further controls, if any, are necessary. This
interpretation is consistent with numerous rulings by the U.S. Court of
Appeals for the DC Circuit regarding EPA's approach to weighing similar
enumerated factors under statutory provisions directing the agency to
issue technology-based standards. See, e.g. Husqvarna AB, v. EPA, 254
F.3d 195 (DC Cir. 2001).
    For example, when a section 112(d)(2) MACT standard alone obtains
protection of public health with an ample margin of safety and prevents
adverse environmental effects, it is unlikely that it would be
``necessary'' to revise the standard further, regardless of possible
developments in control options.\3\ Thus, the section 112(d)(6) review
would not need to entail a robust technology assessment.
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    \3\ Although, as discussed below, EPA might still consider
developments that could be substantially reduce or eliminate risk in
a cost-effective manner.
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    Two additional possible circumstances involving step 2 of the
benzene analysis also could lead to a similar result. First, if, under
step 2 of the benzene analysis, the ample margin of safety
determination that resulted in lifetime cancer risks above 1-in-1
million based on emissions after implementation of the (d)(2) MACT
standard was not founded at all on the availability or cost of
particular control technologies and there was no issue regarding
adverse environmental effect or health effects, and the facts
supporting those analyses (e.g., the public health and environmental
risk) remain the same, it is unlikely that advances in air pollution
control technology alone would cause us to revise the NESHAP because
the existing regulations would continue to assure an adequate level of
safety and protection of public health and prevention of adverse
environmental effects.
    Second, if, under step 2, we determined that additional controls
were appropriate for ensuring an ample margin of safety and/or to
prevent adverse environmental effects, and the revised standards
resulted in remaining lifetime cancer risk for non-threshold pollutants
falling below 1-in-1 million and for threshold pollutants falling below
a similar threshold of safety and prevented adverse environmental
effect, and the facts supporting those analyses (e.g., the
environmental and public health risks) remain the same, then it is
unlikely that further revision would be needed. As stated above, under
these circumstances we would probably not require additional emission
reductions for a source category despite the existence of new or
cheaper technology or control strategies, the exception possibly being
the development of cost-effective technology that would greatly reduce
or essentially eliminate the use or emission of a HAP. Therefore, in
these situations, a robust technology assessment as part of a review
under section 112(d)(6) may not be warranted.
    Note that the circumstances discussed above presume that the facts
surrounding the ample margin of safety and environmental analyses have
not significantly changed. If there have been significant changes to
fundamental aspects of the risk assessment then subsequent section
112(d)(6) reviews with robust technology assessments (and relevant risk
considerations) may be appropriate.
    Finally, if the availability and/or costs of technology were part
of either the rationale for an ample margin of safety determination
that resulted in lifetime cancer risk for non-threshold pollutants
above 1-in-1 million (or for threshold pollutants falling below a
similar threshold of safety) or affected the decision of whether to
prevent adverse environmental effect, it is reasonable to conclude that
changes in those costs or in the availability of technology could alter
our conclusions, even if risk factors (e.g., emissions profiles, RfC,
impacts on

listed species) remained the same. Under these circumstances,
subsequent section 112(d)(6) reviews with robust technology assessments
(and relevant risk considerations) would be appropriate.
    For HON process vents, storage vessels, process wastewater, and
transfer operations, we are not aware of advances in control techniques
that would achieve greater HAP emission reductions than the control
technologies that are used to comply with the current HON rule. These
technologies reduce HAP emissions by 95 to 98 percent for the various
regulated emission points. The only feasible options for additional
control would be to apply the existing HON reference technologies to
some Group 2 emission points that are not required to be controlled by
the current rule.
    For equipment leaks, leakless components could be installed to
reduce emissions from process equipment. Leakless components were
considered during the development of the current rule and were
determined not to represent MACT because of the high cost of replacing
thousands of equipment components and concern that equipment was not
available for all applications. The cost of leakless components has not
substantially declined since the promulgation of the current rule.
Therefore, we still consider the cost of leakless components to be
infeasible for broad application throughout the industry.
    Accordingly, for the section 112(d)(6) review, we considered the
same regulatory alternatives described above for residual risk (table 2
of this preamble). Based on the information analyzed for the regulatory
alternatives, we are proposing two options for emissions standards to
satisfy the requirements of section 112(d)(6) review. The first
proposed option is to maintain the current level of control in the HON
(i.e., the baseline option in table 3 of this preamble) with no further
modifications, tracking the first proposed option for residual risk.
The second proposed option corresponds to our second proposed option
under our residual risk analysis and proposes the additional control
requirements of Regulatory Alternative III. In the final rule, we
expect to select one of these options, with appropriate modifications
in response to public comments.
1. Rationale for Option 1
    Under the first option we are proposing to make no changes to the
current HON rule under our section 112(d)(6) authority. Section
112(d)(6)requires us to revise the NESHAP ``* * * as necessary (taking
into account developments in practices, processes, and control
technologies) * * *'' Our review found no new or improved control
technologies or practices for reducing HAP emissions beyond the
controls that are required by the current rule. Control costs have not
declined significantly. We found no changes in industry production
processes or practices that would lead to increased HAP emissions from
HON processes.
    Whether or not it is necessary to revise the current rule,
therefore, depends on the benefits of imposing additional emission
reductions and the associated cost. Option 2 would extend the
applicability of the current HON control requirements to some emission
points that currently are not subject to control requirements and would
require more frequent monitoring of equipment leaks. These emission
reductions would reduce cancer incidence by about 0.01 cases per year
and reduce the HI below 1 for about 20 individuals. Because these
controls would not reduce these particular factors significantly,
Option 1 proposes that the additional control costs are not necessary
under section 112(d)(6).
2. Rationale for Option 2
    By requiring additional control of storage vessels, process vents,
and equipment leaks, Option 2 (i.e., Regulatory Alternative III) would
reduce total HAP emissions by 1,700 tons/year. The capital costs are
estimated at $14 million with annualized costs of $13 million. The
second option has an average cost per ton of HAP of about $8,000 per
ton HAP removed and an incremental cost per ton of HAP of $10,000 per
ton HAP removed. Option 2 would satisfy the requirements of section
112(d)(6) because the controls have been demonstrated in practice and
can be implemented at an annual cost of $13 million with no adverse
energy or non-air environmental impacts. In addition, this second
option would reduce the total number of people exposed to maximum
lifetime cancer risks of at least 1-in-1 million by 450,000 and reduce
cancer incidence by 0.01 cases per year (an average of one case every
one hundred years). This option would apply controls only to CMPUs that
emit HAP listed in table 38 of the proposed rule. We estimate that
CMPUs that emit HAP not on table 38 of the proposed rule pose such low
risk (i.e., the current HON rule already protects public health with an
ample margin of safety for these pollutants) that imposing any
additional cost beyond the original MACT controls would not be
necessary. These units pose no cancer risk, no significant noncancer
risk, and no adverse ecological risks.

IV. Solicitation of Public Comments

A. Introduction and General Solicitation

    We request comments on all aspects of the proposed rulemaking. All
significant comments received during the public comment period will be
considered in the development and selection of the final rulemaking.

B. Specific Comment and Data Solicitations

    In addition to general comments on the proposed options (and, for
Option 2, the proposed revised standards), we particularly request
comments and data on the following issues:
1. Format of Control Alternatives
    We request comment on the format of the proposed standards under
Option 2 (i.e., Regulatory Alternative III). We structured regulatory
alternatives to build on the emission and risk reductions obtained by
controlling storage vessels, process vents, and equipment leaks. The
regulatory alternatives could have been structured differently (e.g.,
as singular alternatives considering risk). We are requesting comments
on other possible combinations of the proposed standards.
2. ``Low-risk'' Alternative Compliance Approach
    We request comment on whether the final rule should incorporate a
``Low-risk'' approach that would allow a facility to demonstrate that
the risks posed by HAP emissions from the HON affected sources (storage
vessels, process vents, process wastewater, transfer operations, and