National Emission Standards for Hazardous Air Pollutants: Halogenated Solvent Cleaning, 47670-47690 [06-6927]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 71, Number 159 (Thursday, August 17, 2006)]
[Proposed Rules]
[Pages 47670-47690]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 06-6927]



[[Page 47669]]

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Part V





Environmental Protection Agency





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40 CFR Part 63



 National Emission Standards for Hazardous Air Pollutants: Halogenated 
Solvent Cleaning; Proposed Rule

Federal Register / Vol. 71, No. 159 / Thursday, August 17, 2006 / 
Proposed Rules

[[Page 47670]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2002-0009, FRL-8210-3]
RIN 2060-AK22


National Emission Standards for Hazardous Air Pollutants: 
Halogenated Solvent Cleaning

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The EPA is proposing revised standards to limit emissions of 
methylene chloride (MC), perchloroethylene (PCE), and trichloroethylene 
(TCE) from existing and new halogenated solvent cleaning machines. In 
1994, EPA promulgated technology-based emission standards to control 
emissions of methylene chloride (MC), perchloroethylene (PCE), 
trichloroethylene (TCE), 1,1,1,-trichloroethane (TCA), carbon 
tetrachloride (CT), and chloroform from halogenated solvent cleaning 
machines. Pursuant to the Clean Air Act (CAA) section 112(f), EPA has 
evaluated the remaining risk to public health and the environment 
following implementation of the technology-based rule and is proposing 
more stringent standards in order to protect public health with an 
ample margin of safety. The proposed standards are expected to provide 
further reductions of MC, PCE, and TCE beyond the 1994 national 
emission standards for hazardous air pollutants (NESHAP), through 
application of a facility-wide total MC, PCE, and TCE emission 
standard. In addition, EPA has reviewed the standards as required by 
section 112(d)(6) of the CAA and has determined that, taking into 
account developments in practices, processes, and control technologies, 
no further action is necessary at this time to revise the national 
emission standards. The term ``facility-wide'' applies to facilities 
with emissions associated with halogenated solvent cleaning activities 
only.

DATES: Comments. Comments must be received on or before October 2, 
2006.
    Public Hearing. If anyone contacts EPA requesting to speak at a 
public hearing by August 28, 2006, a public hearing will be held 
approximately 15 days following publication of this notice in the 
Federal Register.

ADDRESSES: Comments. Submit your comments, identified by Docket ID No. 
EPA-HQ-OAR-2002-0009, by one of the following methods:
     https://www.regulations.gov. Follow the on-line 
instructions for submitting comments.
     E-mail: a-and-r-docket@epa.gov.
     Fax: (202) 566-1741.
     Mail: Air and Radiation Docket, EPA, Mailcode: 6102T, 1200 
Pennsylvania Ave., NW., Washington, DC 20460. Please include a 
duplicate copy, if possible. We request that a separate copy of each 
public comment also be sent to the contact person listed below (see FOR 
FURTHER INFORMATION CONTACT).
    Hand Delivery: Air and Radiation Docket, EPA, Room B-102, 1301 
Constitution Ave., NW., Washington, DC 20004. Such deliveries are only 
accepted during the Docket's normal hours of operation and special 
arrangements should be made for deliveries of boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-
2002-0009. The EPA's policy is that all comments received will be 
included in the public docket without change and may be made available 
online at https://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 https://
www.regulations.gov, or e-mail. The https://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 https://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 and with any 
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 https://
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 https://www.regulations.gov or in hard copy at the Air and Radiation 
Docket, EPA/DC, EPA West, Room B-102, 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 (202) 566-1744, and the telephone 
number for the Air and Radiation Docket is (202) 566-1742.
    Public Hearing: If a public hearing is held, it will be held at 10 
a.m. at EPA's Environmental Research Center Auditorium, Research 
Triangle Park, NC, or at an alternate site nearby.

FOR FURTHER INFORMATION CONTACT: Mr. H. Lynn Dail, Natural Resources 
and Commerce Group (E143-03), Sector Policies and Programs Division, 
EPA, Research Triangle Park, NC 27711; telephone number (919) 541-2363; 
fax number (919) 541-3470, e-mail address: dail.lynn@epa.gov. For 
questions on the residual risk analysis, contact Mr. Dennis Pagano, 
Sector Based Assessment Group (C539-02), Health and Environmental 
Impacts Division, EPA, Research Triangle Park, NC 27711; telephone 
(919) 541-0502; fax number (919) 541-0840, e-mail address: 
pagano.dennis@epa.gov.

SUPPLEMENTARY INFORMATION:
    Regulated Entities. The categories and entities potentially 
regulated by the proposed rule include:

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                                                         Examples of
          Category               NAICS \1\ code          potentially
                                                     regulated entities
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Industry....................  Any of numerous       Operations at
                               industries using      sources that are
                               halogenated solvent   engaged in solvent
                               cleaning, primary     cleaning using MC,
                               affected industries   PCE, or TCE.
                               include those in
                               NAICS Codes
                               beginning with: 331
                               (primary metal
                               man.), 332
                               (fabricated metal
                               man.), 333
                               (machinery man.),
                               334 (computer and
                               electronic product
                               man.), 335
                               (electrical
                               equipment,
                               appliance, and
                               component man.);
                               336 (transportation
                               equipment man.);
                               337 (furniture and
                               related products
                               man.); and 339
                               (misc. man.).
Federal, State, local, and    ....................  Operations at
 tribal government.                                  sources that are
                                                     engaged in solvent
                                                     cleaning using MC,
                                                     PCE, or TCE.
------------------------------------------------------------------------
\1\ North American Industry Classification System.

    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be affected by the 
proposed rule. This proposal directs an owner or operator of 
halogenated solvent cleaning facilities to determine if whether the 
applicability criteria in 40 CFR 63.460 of subpart T (1994 national 
emission standards for Halogenated Solvent Cleaning) remains or whether 
these proposed standards require the facility to operate under the 
emission caps set forth. If you have any questions regarding the 
applicability of the proposed standards to a particular entity, consult 
the person listed in the preceding FOR FURTHER INFORMATION CONTACT 
section.
    Submitting CBI. Do not submit this information to EPA through 
https://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 public hearing is to be held should contact 
Ms. Dorothy Apple, Natural Resources and Commerce Group (E143-03), 
Sector Policies and Programs Division, EPA, Research Triangle Park, NC 
27711, telephone number: (919) 541-4487, e-mail address: 
apple.dorothy@epa.gov , at least 2 days in advance of the potential 
date of the public hearing. Persons interested in attending the public 
hearing also must call Ms. Apple 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 standards.
    Worldwide 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 (TTN). 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 https://
www.epa.gov/ttn/oarpg. The TTN provides information and technology 
exchange in various areas of air pollution control.
    Outline. The information presented in this preamble is organized as 
follows:

I. Background
    A. What is the statutory authority for regulating hazardous air 
pollutants (HAP)?
    B. What is halogenated solvent cleaning?
    C. What are the health effects of halogenated solvents?
    D. What does the 1994 halogenated solvent cleaning NESHAP 
require?
II. Summary of Proposed Requirements for New and Existing Major and 
Area Sources
III. Rationale for the Proposed Rule
    A. What is our approach for developing residual risk standards?
    B. How did we estimate residual risk?
    1. How did we estimate the emission and stack parameters for 
these sources?
    2. How did we estimate the atmospheric dispersion of the emitted 
pollutants?
    3. How were cancer and non-cancer risks estimated?
    4. What factors are considered in the risk assessment?
    C. What are the results of the baseline risk assessment?
    D. What is our proposed decision on acceptable risk?
    E. What is our proposed decision on ample margin of safety?
    1. What risk reduction alternatives did EPA evaluate?
    2. What are the costs of the proposed alternatives?
    3. What regulatory options is EPA proposing?
    4. Rationale for Option 1
    5. Rationale for Option 2
    6. Comparison of Option 1 and 2
    F. What is EPA proposing pursuant to CAA Section 112(d)(6)?
    G. What is the rationale for the proposed compliance schedule?
IV. Solicitation of Public Comments
    A. Introduction and General Solicitation
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 and Advancement Act

I. Background

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

    Section 112 of the CAA establishes a two-stage regulatory process 
to address emissions of hazardous air pollutants (HAP) from stationary 
sources. In the first stage, CAA section 112(d) calls for us to 
promulgate national technology-based emission standards for categories 
of 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 (known as ``major sources''), as well as for 
certain ``area sources'' emitting less than those amounts. For major 
sources, 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 maximum achievable control technology (MACT) 
standards.
    For area sources, CAA section 112(d)(5) provides that the standards

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may reflect generally available control technology or management 
practices in lieu of MACT, and are commonly referred to as generally 
available control technology (GACT) standards.
    CAA section 112(d)(6) then requires EPA 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 8 years.
    The second stage in standard-setting is described in section 112(f) 
of the CAA. EPA prepared 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.
    CAA section 112(f)(2) requires us to determine for each CAA section 
112(d) source category whether the MACT standards 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-a-million,'' EPA must promulgate residual risk standards for the 
source category (or subcategory) as necessary to provide an ample 
margin of safety. The EPA must also adopt more stringent standards to 
prevent an adverse environmental effect (defined in CAA 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 is halogenated solvent cleaning?

    Halogenated solvent cleaning machines use halogenated solvents 
(methylene chloride, perchloroethylene, trichloroethylene, 1,1,1,-
trichloroethane, carbon tetrachloride, and chloroform), halogenated 
solvent blends, or their vapors to remove soils such as grease, oils, 
waxes, carbon deposits, fluxes, and tars from metal, plastic, 
fiberglass, printed circuit boards, and other surfaces. Halogenated 
solvent cleaning is typically performed prior to processes such as 
painting, plating, inspection, repair, assembly, heat treatment, and 
machining. Types of solvent cleaning machines include, but are not 
limited to, batch vapor, in-line vapor, in-line cold, and batch cold 
solvent cleaning machines. Buckets, pails, and beakers with capacities 
of 7.6 liters (2 gallons) or less are not considered solvent cleaning 
machines.
    Halogenated solvent cleaning does not constitute a distinct 
industrial category, but is an integral part of many major industries. 
The five 3-digit NAICS Code that use the largest quantities of 
halogenated solvents for cleaning are NAICS 337 (furniture and related 
products manufacturing), NAICS 332 (fabricated metal manufacturing), 
NAICS 335 (electrical equipment, appliance, and component 
manufacturing), NAICS 336 (transportation equipment manufacturing), and 
NAICS 339 (miscellaneous manufacturing). Additional industries that use 
halogenated solvents for cleaning include NAICS 331 (primary metals), 
NAICS 333 (machinery), and NAICS 334 (electronic equipment 
manufacturing). Non-manufacturing industries such as railroad (NAICS 
482), bus (NAICS 485), aircraft (NAICS 481), and truck (NAICS 484) 
maintenance facilities; automotive and electric tool repair shops 
(NAICS 811); and automobile dealers (NAICS 411) also use halogenated 
solvent cleaning machines. We estimated that there were approximately 
16,400 batch vapor, 8,100 in-line, and perhaps as many as 100,000 batch 
cold cleaning machines in the U.S. prior to promulgation of the MACT 
standards. More recent information shows that the current number of 
cleaning machines is much lower than these pre-MACT estimates. We 
currently estimate the number of sources in this source category to be 
about 3,800 cleaning machines located at 1,900 facilities in the U.S. 
This estimate is based on information we collected in 1998, a year 
after compliance with the MACT occurred, and should reflect the 
decreases in HAP emissions and demand that were expected due to 
implementation of MACT control technologies and work practice 
standards. Recent evidence on solvent usage suggests that the number of 
sources in the source category may have declined further in the post-
MACT implementation years. An analysis of market data for halogenated 
solvents showed that the demand for degreasing solvents declined 
substantially in the 5 years following the implementation of MACT. From 
1998 to 2003, the demand for PCE, TCE, MC, and TCA for degreasing 
decreased by 39 percent, 35 percent, 23 percent, and 15 percent, 
respectively. The halogenated solvents carbon tetrachloride and 
chloroform are no longer used in this source category. The Montreal 
Protocol, a treaty signed on September 16, 1987, phased-out the 
production and consumption of these chlorofluorocarbons by January 1, 
1996. The Protocol also phased out TCA. TCA has not been manufactured 
for domestic use in the United States since January 1, 2002. Facilities 
with essential products or activities are allowed to continue their use 
of TCA, but for facilities with non-essential activities or products, 
they were allowed to use remaining TCA stockpiles until depleted.
    There are two basic types of solvent cleaning machines: Batch 
cleaners and in-line cleaners. Both cleaner types can be designed to 
use either solvent at room temperature (cold cleaners) or solvent vapor 
(vapor cleaners). The vast majority of halogenated solvent use is in 
vapor cleaning, both batch and in-line. The most common type of batch 
cleaner that uses halogenated solvent is the open-top vapor cleaner 
(OTVC).
    Batch cleaning machines, which are the most common type, are 
defined as a solvent cleaning machine in which individual parts or sets 
of parts move through the entire cleaning cycle before new parts are 
introduced. Batch cleaning machines include cold and vapor machines. In 
batch cold cleaning machines, the material being cleaned (i.e., the 
workload) is immersed, flushed, or sprayed with liquid solvent at room 
temperature. Most batch cold cleaners are small maintenance cleaners 
(e.g., carburetor cleaners) or parts washers that often use non-HAP 
solvent mixtures for cleaning. Batch cold cleaning equipment sometimes 
includes agitation to improve cleaning efficiency.
    In batch vapor cleaning machines, parts are lowered into an area of 
dense vapor solvent for cleaning. The most common type of batch vapor 
cleaner is the open-top vapor cleaner. Heating elements at the bottom 
of the cleaner heat the liquid solvent to above its boiling point. 
Solvent vapor rises in the machine to the height of chilled condensing 
coils on the inside walls of the cleaner. The condensing coils cool the 
vapor causing it to condense and return to the bottom of the cleaner. 
Cleaning occurs in the vapor zone above the liquid solvent and below 
the condensing coils, as the hot vapor solvent condenses on the cooler

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workload surface. The workload or a parts basket is lowered into the 
heated vapor zone with a mechanical hoist.
    Batch vapor cleaning machines vary greatly in size and design to 
suit applications in many industries. Batch vapor cleaner sizes are 
defined by the area of the solvent/air interface.
    Emissions from batch cold cleaning machines result from evaporation 
of solvent from the solvent/air interface ``carry out'' of excess 
solvent on cleaned parts, and other evaporative losses such as those 
that occur during filling and draining. Evaporative emissions from the 
solvent/air interface are continual whether or not the machine is in 
use. These evaporative losses can be reduced by limiting air movement 
over the solvent/air interface (e.g., with a machine cover or by 
reducing external drafts) or by limiting the area of solvent air 
interface (e.g., with a floating water layer). Emissions related to 
solvent carry out occur only when the cleaning machine is in use. Carry 
out emissions may be substantial, especially if excess solvent is not 
allowed to drain back into the machine. Carry out includes solvent film 
remaining on flat workload surfaces and liquid pooled in cavities. 
Factors affecting the amount of carry out loss include the speed of 
parts movement, workload shapes and materials, and work practices 
(e.g., turning over parts to drain cavities).
    The closed-loop cleaning system is a type of batch cleaner with a 
closed system capable of reusing solvent. Parts are placed inside a 
vacuum chamber. Vapor or liquid solvent is pumped in the chamber to 
clean the parts. Once cleaned, the parts are dried under vacuum and 
removed; the solvent is removed and recycled. Because these systems are 
constructed to maintain a vacuum, they have the potential to reduce 
emissions up to 97 percent.
    Cold and vapor in-line (i.e., conveyorized) cleaning machines, 
which include continuous web cleaners, employ automated parts loading 
and are used in applications where there is a constant stream of parts 
to be cleaned. In-line cleaners usually are used in large-scale 
industrial operations (e.g., auto manufacturing) and are custom-
designed for specific workload and production characteristics (e.g., 
workload size, shape, and production rate). In-line cleaners clean 
parts using the same general techniques used in batch cleaners: cold 
in-line cleaners spray or immerse parts in solvent, and vapor in-line 
cleaners clean parts in a zone of dense vapor solvent.
    Emissions from cold and vapor in-line cleaning machines result from 
the same mechanisms (e.g., evaporation, diffusion, carryout) that cause 
emissions from cold and vapor batch cleaning machines. However, the 
emission points for in-line cleaners are different from those for batch 
cleaners because of differences in machine configurations. In-line 
cleaning machines are semi-enclosed above the solvent/air interface to 
control solvent losses. In most cases, the only openings are the parts 
entry and exit ports. These openings are the only emissions points for 
downtime and idling modes. Carryout emissions add to emissions during 
the working mode. Idling and working mode emissions from the in-line 
cleaner are significantly less than emissions from an equally-sized 
batch vapor cleaner. However, in-line cleaners tend to be much larger 
than batch vapor cleaners. Some in-line cleaners have exhaust systems 
that pump air from inside the cleaning machine to an outside vent. 
Exhaust systems for in-line cleaners reduce indoor emissions from the 
cleaning machine but increase solvent consumption.
    Continuous cleaners are a subset of in-line cleaners and are used 
to clean products such as films, sheet metal, and wire in rolls or 
coils. The workload is uncoiled and conveyorized throughout the 
cleaning machine at speeds in excess of 11 feet per minute and recoiled 
or cut as it exits the machine. Emission points from continuous 
cleaners are similar to emission points from other inline cleaners. 
Continuous cleaners are semi-enclosed, with emission points where the 
workload enters and exits the machine. Squeegee rollers reduce carry 
out emissions by removing excess solvent from the exiting workload. 
Some continuous machines have exhaust systems similar to those used 
with some other in-line cleaners.

C. What are the health effects of halogenated solvents?

    Methylene chloride, perchloroethylene, 1,1,1,-trichloroethylene 
(TCA), and trichloroethylene are the primary halogenated solvents used 
for solvent cleaning. Carbon tetrachloride and chloroform are no longer 
used as degreasing solvents. Therefore, their health effects are not 
discussed in this section. The four solvents still in use are described 
below. All four produce acute and/or chronic non-cancer health effects 
at sufficient concentrations; three of the four have been classified as 
probable or possible human carcinogens by either EPA or other 
governmental or international agencies.
    Methylene chloride is predominantly used as a solvent. The acute 
effects of methylene chloride inhalation in humans consist mainly of 
central nervous system effects including decreased visual, auditory, 
and motor functions that may occur at or above 1-hour exposures of 690 
mg/m\3\, but these effects are reversible once exposure ceases. The 
effects of chronic exposure to methylene chloride suggest that the 
central nervous system is a potential target in humans and animals. 
ATSDR estimates that no adverse noncancer effects are likely in human 
populations chronically exposed at or below 1 mg/m3. Human 
studies are inadequate regarding methylene chloride and cancer. 
However, animal studies have shown significant increases in liver and 
lung cancer and benign mammary gland tumors following the inhalation of 
methylene chloride. On this basis, EPA classified methylene chloride as 
a Group B2, probable human carcinogen, with a cancer unit risk estimate 
(URE) of 4.7 x 10-7 ([mu]g/m\3\)-1, when assessed 
under the previous 1986 Cancer Guidelines. EPA is currently reassessing 
its potential toxicity and carcinogenicity. All activities related to 
this chemical reassessment are expected to be complete in late 2007.
    Perchloroethylene (PCE or tetrachloroethylene) is widely used for 
dry-cleaning fabrics and metal degreasing operations. The main effects 
of PCE in humans are neurological, liver, and kidney damage following 
acute (short-term) and chronic (long-term) inhalation exposure. The 
results of epidemiological studies evaluating the relative risk of 
cancer associated with PCE exposure have been mixed; some studies 
reported an increased incidence of a variety of tumors, while other 
studies did not report any carcinogenic effects. Animal studies have 
reported an increased incidence of liver cancer in mice, via inhalation 
and gavage (experimentally placing the chemical in the stomach), and 
kidney and mononuclear cell leukemia in rats.
    Although PCE has not yet been reassessed under the Agency's 
recently revised Guidelines for Cancer Risk assessment, it was 
considered in one review by the EPA's Science Advisory Board to be 
intermediate between a ``probable'' and ``possible'' human carcinogen 
(Group B/C) when assessed under the previous 1986 Guidelines. Since 
that time, the U.S. Department of Health and Human Services has 
concluded that PCE is ``reasonably anticipated to be a human 
carcinogen,'' and the International Agency for Research on Cancer has 
concluded that PCE is ``probably carcinogenic to humans.''

[[Page 47674]]

    Effects other than cancer associated with long-term inhalation of 
PCE in worker or animal studies include neurotoxicity, liver and kidney 
damage, and, at higher levels, developmental effects. To characterize 
noncancer hazard in lieu of the completed Integrated Risk Information 
System (IRIS) assessment, which is being revised, we used the Agency 
for Toxic Substances and Disease Registry's (ATSDR) Minimum Risk Level 
(MRL). This value is based on a study of neurological effects in 
workers in dry cleaning shops, and is derived in a manner similar to 
EPA's method for derivation of reference concentrations, including 
scientific and public review. Based on these effects, EPA estimates 
that no adverse noncancer effects are likely in human populations 
chronically exposed at or below 0.27 mg/m\3\.
    The Agency's IRIS chemical assessment for PCE is currently being 
revised. The current schedule indicates that a final IRIS determination 
on PCE is not expected until 2008 at the earliest. Because EPA has not 
yet issued a final IRIS document for PCE, to estimate cancer risk, we 
used the California EPA (CalEPA) unit risk estimate (URE) of 5.9 x 
10-6 (ug/m\3\)-1, as well as a URE value 
developed by the EPA's Office of Prevention, Pesticides and Toxic 
Substances (OPPTS) of 7.1 x 10-7 (ug/m\3\)-1. The 
final IRIS reassessment may result in a URE that is different from 
these two values. Among the available Acute Reference Levels (ARL), the 
one-hour California Reference Exposure Level (a REL value of 240 mg/
m\3\) was considered the most appropriate to use in the assessment 
because it may be used to characterize acute risk for exposure with an 
exposure duration of one hour.
    Most of the trichloroethylene (TCE) used in the United States is 
released into the atmosphere from industrial degreasing operations. 
Acute and chronic inhalation exposure to trichloroethylene can affect 
the human central nervous system, with symptoms such as dizziness, 
headaches, confusion, euphoria, facial numbness, and weakness. Liver, 
kidney, immunological, endocrine, and developmental effects have also 
been reported in humans. Acute effects may occur at or above 1-hour 
exposures of 700 mg/m\3\. CalEPA estimates that no adverse noncancer 
effects are likely in human populations chronically exposed at or below 
0.6 mg/m\3\. Animal studies have reported statistically significant 
increases in kidney, lung, liver, and testicular tumors. EPA classified 
trichloroethylene in Group B2/C, an intermediate between a probable and 
possible human carcinogen, when assessed under the previous 1986 Cancer 
Guidelines, but this classification has been withdrawn. CalEPA has 
derived a cancer URE of 2.0 x 10-6 (ug/m\3\)-1 
for TCE, which we used for our cancer risk assessment. EPA is currently 
reassessing the cancer classification of trichloroethylene.
    In 1999, TCA was used as a solvent for degreasing up until it was 
phased out in 2002. CalEPA estimates that no adverse noncancer effects 
are likely in human populations chronically exposed to TCA at or below 
1 mg/m\3\. EPA classified TCA in Group D, not classifiable as to human 
carcinogenicity, when assessed under the previous 1986 Cancer 
Guidelines. EPA is currently reassessing its potential toxicity 
(related to chronic and less-than-lifetime exposures). All activities 
related to chemical reassessment are expected to be complete in 2007. 
Although production and use of TCA has been phased-out since 1998, a 
declining quantity of TCA continued to be used until 2002, when all 
production of TCA ceased, and eventually, facilities used TCA stock-
piles until depleted. However, an exemption to the phase-out allows a 
few specialized facilities with essential activities or products to 
continue its use of TCA. TCA was profiled in the noncancer chronic risk 
assessment.
    The OPPTS toxicity profile for perchloroethylene (PCE) is published 
in an EPA publication entitled, Cleaner technologies substitutes 
assessment: professional fabricare processes. U.S. EPA Office of 
Pollution Prevention and Toxics, Washington DC. EPA 744-B-98-001; June 
1998. Complete toxicity profiles for the four HAPs may be obtained from 
the following Web sites: EPA's OPPTS Web site for perchloroethylene at 
https://www.epa.gov/dfe/pubs/garment/ctsa/fabricare.pdf; California 
EPA's Web site at https://www.oehha.ca.gov/air/hot_spots/; 
and the Agency for Toxic Substances and Disease Registry's Web site at 
https://www.atsdr.cdc.gov/toxpro2.html. Status reports for IRIS chemical 
reassessments are available at https://cfpub.epa.gov/iristrac/index.cfm.

D. What does the 1994 halogenated solvent cleaning NESHAP require?

    We promulgated national emission standards for halogenated solvent 
cleaning (59 FR 61805, December 2, 1994) and required existing sources 
to comply with the national emission standards by December 2, 1996. The 
halogenated solvent cleaner NESHAP requires batch vapor solvent 
cleaning machines and in-line solvent cleaning machines to meet 
emission standards reflecting the application of the maximum achievable 
control technology for major and area sources; area source batch cold 
cleaning machines are required to achieve generally available control 
technology. The rule regulates the emissions of the following 
halogenated HAP solvents: MC, PCE, TCE, TCA, CT, and chloroform. In 
1999, MC, PCE, TCE and TCA were the primary halogenated solvents used 
for solvent cleaning. Although production and use of TCA has been 
phased-out since 1998, a declining quantity of TCA continued to be used 
until 2002, with either facilities depleting existing stockpiles past 
2002 or facilities with essential products or activities continuing use 
of TCA. CT and chloroform are no longer used as degreasing solvents.
    The promulgated standard includes multiple alternatives to allow 
owners or operators maximum compliance flexibility. These alternatives 
include:
     Control equipment standards--As many as 10 combinations of 
emission control equipment, such as freeboard refrigeration devices and 
working-mode covers may be installed.
     Idling-mode emissions standards--Compliance may be 
demonstrated by maintaining monthly emission rates during the idling 
mode below specified standards.
     Overall emission standards--Solvent use and disposal 
records may be used to calculate average monthly emissions, which must 
remain below specified numerical limits.
    If an owner or operator of a batch vapor or in-line cleaning 
machine elects to comply with the equipment standard, they must install 
one of the control combinations listed in the regulation, use an 
automated parts handling system to process all parts, and follow 
multiple work practices. As an alternative to selecting one of the 
equipment control combinations listed in the regulation, an owner or 
operator may demonstrate that the batch vapor or in-line cleaning 
machine can meet the idling mode emission limit specified in the 
standards. In addition to maintaining this idling mode emission limit, 
the owner or operator of a batch vapor or in-line solvent cleaning 
machine must use an automated parts handling system to process all 
parts and comply with the work practice standards. A third alternative 
for complying with these standards is to comply with the overall 
solvent emissions limit. An owner or operator complying with the 
overall solvent emissions limit is required to ensure that the 
emissions from each

[[Page 47675]]

solvent cleaning machine are less than or equal to the solvent emission 
levels specified in the standard. Under this alternative standard, an 
owner or operator is not required to use an automated parts handling 
system or to comply with the work practice standards.
    The batch cold cleaning machine standard is an equipment standard. 
However, those owners or operators choosing the equipment options 
without the water layer must also comply with work practice 
requirements. There is no idling standard or overall solvent emissions 
standard for batch cold cleaning machines. Batch cold cleaning machines 
located at non-major sources are exempt from Title V permit 
requirements.
    The halogenated solvent cleaning NESHAP was estimated to reduce 
nationwide emissions of hazardous air pollutants (HAP) from halogenated 
solvent cleaning machines by 77,400 Mg/yr (85,300 tons per year) or 63 
percent by 1997 compared to the emissions that would result in the 
absence of the standards.

II. Summary of the Proposed Requirements for New and Existing Major and 
Area Sources

    Under the proposed standards, the requirements for all new and 
existing, major and area sources are the same. In addition to the MACT 
standard, the proposed revisions would require each facility to comply 
with a facility-wide solvent emission limit. As defined by this 
proposed rule, ``facility-wide solvent emissions'' are the combined 
emissions of PCE, TCE, and MC from all of a facility's solvent cleaning 
machines that are subject to the 1994 MACT standards (40 CFR Part 63, 
subpart T). Under CAA section 112(f), EPA has the discretion to impose 
residual risk standards on area sources regulated under generally 
available control technologies (GACT). The area sources subject to GACT 
in the halogenated solvent cleaning source category would not be 
subject to today's proposed standards. These sources are cold batch 
cleaners.
    The proposed rule would require the owner or operator of each 
facility to ensure that their facility-wide solvent emissions from all 
halogenated solvent cleaning activities are less than or equal to the 
solvent emission limits specified in the proposed options and 
summarized in Table 1 of this preamble. This approach gives the owner 
or operator of the facility the flexibility to choose any means of 
reducing the facility-wide emissions of PCE, TCE, and MC to comply with 
facility-wide emission limit. The proposed options are in addition to 
the existing NESHAP requirements and, therefore, all requirements of 
the existing NESHAP remain in place.
    Table 1 shows two sets of facility-wide emission limits--option 1 
and option 2. We are co-proposing both of these options and are 
soliciting comment on which of these two options is most appropriate. 
As can be seen in Table 1 of this preamble, each halogenated solvent 
has an associated facility-wide emission limit. These limits are for 
facilities that emit only a single halogenated solvent. If more than 
one halogenated solvent is used, the owner or operator of the facility 
must calculate the facility's weighted halogenated solvent cleaning 
emissions using equation 1 and comply with the limit in the last row of 
Table 1 of this preamble. Note that, depending on whether the CalEPA 
URE or the OPPTS URE for PCE is used to derive the PCE limit, that 
limit may be lower or higher. We request comment on the use of the 
CalEPA URE, the OPPTS URE, or some other value in deriving the PCE 
emission limit for the final rule.

 Table 1.--Summary of the Proposed Facility-Wide Annual Emission Limits
------------------------------------------------------------------------
                                  Proposed facility-  Proposed facility-
                                      wide annual         wide annual
        Solvents emitted          emission limits in  emission limits in
                                     kg--option 1        kg--option 2
------------------------------------------------------------------------
PCE only........................       \a\ 3,200 \b\       \a\ 2,000 \b\
                                            (26,700)            (16,700)
TCE only........................              10,000               6,250
MC only.........................              40,000              25,000
Multiple solvents--Calculate the              40,000             25,000
 MC-weighted emissions using
 equation 1.....................
------------------------------------------------------------------------
\a\ PCE emission limit calculated using CalEPA URE.
\b\ PCE emission limit calculated using OPPTS URE.

Equation 1:

    (kgs of PCE emissions x A) + (kgs of TCE emissions x B) + (kgs of 
MC emissions) = Weighted Emissions in kgs

    We developed a method for facilities using multiple HAP solvents to 
determine their emission limit by calculating their MC-equivalent 
emissions using the toxicity-weighted equation above. In the equation, 
the facility emissions of PCE and TCE are weighted according to their 
carcinogenic potency relative to that of MC. Thus, ``A'' in the 
equation is the ratio of the URE for PCE to the URE for MC, and the 
``B'' in the equation is the ratio of the URE for TCE to the URE for 
MC. The value of ``A'' is either 1.5 or 12.5, depending on whether we 
use the OPPTS URE or the CalEPA URE for PCE. The value for ``B'' is 
4.25. We believe there may be other approaches to arriving at emissions 
alternatives for multiple HAP use and we request comment on the use of 
the MC-equivalency method, or other possible calculation methods that 
we should consider, when establishing emission limits for facilities 
using more than one of the listed HAP solvents. We also request comment 
on whether the OPPTS URE, the CalEPA URE or some other value should be 
used in the implementation of the emission cap chosen for the final 
rule.
    Compliance with the emission limit is demonstrated by determining 
the annual PCE, TCE, and MC emissions for all cleaning machines at the 
facility. There is no additional equipment monitoring or work practice 
requirements associated with the facility-wide annual emissions limit. 
Annual emissions of these HAP are determined based on records of the 
amounts and dates of the solvents added to cleaning machines during the 
year, the amounts and dates of solvents removed from cleaning machines 
during the year, and the amounts and dates of the solvents removed from 
cleaning machines in solid waste. Records of the calculation sheets 
showing how the annual emissions were determined must be maintained. A 
facility will determine compliance with the standards by

[[Page 47676]]

comparing their annual MC-equivalent emissions versus the level in the 
final rule.
    We believe owners and operators currently have information 
available to immediately determine if they would be in compliance with 
today's proposed emissions limits. Current recordkeeping requirements 
in 40 CFR subpart T section 63.467 require each owner and operator of 
solvent cleaning machines to maintain, for 5 years, estimates of 
solvent content and annual solvent consumption for each solvent 
cleaning machine and any calculations showing how monthly emissions or 
3-month rolling average emissions were calculated. Moreover, current 
reporting requirements in 40 CFR subpart T Section 63.468 include an 
initial notification report, an initial statement of compliance report, 
annual compliance reports, and an exceedance report (required only when 
an exceedance occurs). In the initial notification report, owners and 
operators disclose an estimate of the annual halogenated HAP solvent 
consumption for each solvent cleaning machine. Furthermore, owners and 
operator submit annual reports that contain estimates of their solvent 
consumption for each solvent cleaning machine used during the period.
    We believe that there are multiple ways in which facilities could 
comply with the proposed rule. Our analysis also shows that some 
affected facilities can easily reduce emissions and risks through 
solvent switching. Solvent switching, in this case, is switching from a 
high risk solvent to one with lower health risks. Facilities can also 
reduce emissions by reducing solvent use, and by using careful work 
practices and traditionally available control options to further reduce 
emissions. Increased diligence in controlling lids, installing 
freeboard chillers, increased drying times, installing closed loop 
systems, and increasing the freeboard ratio would allow the higher 
emitting higher risk facilities to achieve compliance with this 
proposed standard. The available information indicates that solvent 
switching, vapor capture, maintenance, reduced solvent use and limiting 
cleaning runs would be the primary components of any small decrease in 
costs.
    In summary, we are proposing two options that cap facility-wide 
emissions at 40,000 and 25,000 kg/yr calculated as MC-equivalents.

III. Rationale for the Proposed Rule

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

    Section 112(f)(2)(A) of the CAA states that if the MACT standards 
for a source 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-
a-million, the Administrator shall promulgate [residual risk] 
standards * * * for such source category.''

    Halogenated solvent cleaning facilities subject to the proposed 
amendments emit known, probable, and possible human carcinogens. The 
docket for today's proposed rule contains documentation of the EPA's 
determination that the risk to the individual most exposed to emissions 
from halogenated solvent cleaning is expected to exceed 1-in-a-million. 
Even if we were to quantitatively consider the uncertainty and 
variability in the exposure and modeling assumptions used to derive our 
estimate of the risk to the individual most exposed, such an analysis 
is unlikely to change any decisions that would be made based on that 
level of risk.
    Following our initial determination that the individual most 
exposed to emissions from the source category considered exceeds a 1-
in-a-million individual cancer risk, our approach to developing 
residual risk standards is based on a two-step determination of 
acceptable risk and ample margin of safety. We followed the Benzene 
NESHAP approach in making CAA section 112(f) residual risk 
determinations.\1\ Our approach for this source category is the same 
approach outlined in the National Emission Standards for the Benzene 
NESHP Final Rule, (54 FR 38044, September 14, 1989.
---------------------------------------------------------------------------

    \1\ This is confirmed by the Legislative History to CAA Section 
112(f); see, e.g., ``A Legislative History of the Clean Air Act 
Amendments of 1990,'' vol. 1, page 877 (Senate Debate on Conference 
Report) ``stating that: * * * the managers intend that the 
Administrator shall interpret this requirement [to establish 
standards reflecting an ample margin of safety] in a manner no less 
protective of the most exposed individual than the policy set forth 
in the ``Residual Risk Report to Congress, March 1999. EPA-453/R-99-
001, p. ES-11)''.
---------------------------------------------------------------------------

B. How did we estimate residual risk?

    The EPA's ``Residual Risk Report to Congress'' (EPA-453/R-99-011) 
provides the general framework for conducting risk assessments to 
support decisions made under the residual risk program. The approach 
used to assess the risks associated with our halogenated solvent 
cleaning facilities is consistent with the technical approach and 
policies described in the Residual Risk Report to Congress. Details of 
the risk assessment performed in support of this proposal are presented 
below and provided in the risk document in the rulemaking docket.
1. How did we estimate the emission and stack parameters for these 
sources?
    Three sources of data were used to characterize the source category 
for the residual risk assessment: EPA's 1999 National Emissions 
Inventory (NEI) database; a sample of MACT compliance reports obtained 
from states and EPA regions; and information compiled from Clean Air 
Act Title V permits. Together, these sources provided data for 2,672 
unique cleaning machines at 1,167 unique facilities. The 1,167 
facilities represent approximately 61 percent of the 1,900 total 
facilities estimated to be in the source category.
    The majority of the data, approximately 90 percent, were obtained 
from the 1999 NEI database, (i.e., the NEI provided data on 1,093 
facilities). The types of data obtained from the NEI database include 
machine type (from SCC codes and unit descriptions), HAP emissions 
data, and stack characteristics. The compliance reports collected for 
the residual risk assessment provided information for 195 cleaning 
machines at 96 facilities. The types of data obtained from the 
compliance report include machine types, machines sizes, solvent 
consumption rates, HAP emissions data, compliance options, and control 
equipment choices. We gathered machine-specific data for continuous web 
cleaning machines from Title V permits and other sources. These data, 
which included 74 cleaning machines at seven facilities, were added to 
the cleaning machine data obtained from compliance reports.
    Halogenated solvent cleaning machines are co-located with many and 
diverse types of industries. An analysis of MACT source category codes 
in the 1999 NEI data found that approximately 74 percent of the 1,093 
halogenated solvent cleaning sources in our database are co-located 
with at least one other source category. Approximately 80 percent of 
the halogenated solvent emissions from solvent cleaning machines 
occurred at facilities where other source categories appeared to be co-
located. However, because of the diversity of co-located source 
categories, this risk assessment evaluated the emissions coming from 
the degreasing operations only and did not consider emissions of HAPs 
that were identified

[[Page 47677]]

for co-located, non-degreasing operations.
    The residual risk assessment used HAP emissions data from the 
assessment database described above, (i.e., the 1,167 facilities). 
These data were used to estimate the baseline residual risks for the 
facilities in the category and to evaluate regulatory options developed 
to look at further HAP emission reductions. Nearly all of the data 
reflects actual emissions (details of how EPA estimated emissions are 
discussed in the Risk Assessment for Halogenated Solvent Cleaning 
Source Category {Risk Assessment Support Document{time}  located in the 
docket for this proposed rulemaking). In the few instances where we had 
the data to estimate the MACT allowable emissions and to compare those 
estimates with the emissions reported in NEI, the allowable emissions 
were, on average, a factor of 2 higher.
    Compliance with the 1994 MACT is accomplished using one of three 
compliance options. Only two of the compliance options are based on a 
numerical limit and would allow estimates of MACT allowable emissions 
to be calculated if information on machine size were available. For 
these compliance options, allowable emission rates may exceed actual 
emissions. For the control equipment compliance option which does not 
include a numerical emission limit, allowable emissions cannot be 
estimated but could be considered equivalent to actual emissions. 
Approximately 58 percent of the facilities in our assessment (i.e., 
those using the control equipment compliance option) would fall into 
this category.
    Data obtained from MACT compliance reports required processing to 
prepare emissions rates for use in the residual risk assessment. The 
types of data and level of detail in the compliance reports varied 
depending upon which of the three MACT compliance options were chosen, 
the specific report type available (e.g., initial notification report, 
annual compliance reports) available, and the report format. To use as 
much of the available information as possible, emission rate estimation 
methods were developed for various combinations of available data (see 
Appendix A in the Risk Assessment Support Document for details). These 
methods were used to estimate actual emissions rates for each cleaning 
machine. If more than one machine existed at a facility, the machine-
level emission estimates were added together to yield facility-level 
totals.
    NEI provides emission data for each HAP and emission point at a 
source and are reported in kilograms per year. For the residual risk 
assessment, NEI emission rates were used as obtained from NEI. No 
further processing of the data (e.g., to standardized units) was 
needed. However, total facility-level emissions were calculated for 
each HAP when sources had multiple degreasing emission points (i.e., 
multiple degreasing machines).
    To fully represent the national coverage of these sources, we 
scaled results from the 1,167 facilities identified in our assessment 
database to the 1,900 facilities currently estimated to be in the 
source category. When this was done, the total estimated HAP emissions 
from the source category were approximately 16,000 tons per year. These 
emissions consist of 38 percent TCA, 35 percent TCE, 15 percent PCE, 
and 12 percent MC. The total estimated carcinogenic HAP emissions (MC, 
TCE and PCE) from the source category are approximately 9,700 tons/
year.
    MC emissions in 1999 were just over 1,300 tons from about 218 
facilities, while in 2002, about 400 tons were emitted from 194 
facilities, representing about a 70 percent decrease in emissions. 
About 11 percent of facilities using MC in 1999 ceased using MC or 
ceased degreasing operations altogether.
    In 1999, TCE emissions were 3,000 tons from about 320 facilities. 
In 2002, TCE emissions had decreased 24 percent to 2,300 tons; however, 
the number of facilities using TCE increased 10 percent to 357.
    In 1999, PCE emissions were estimated at about 1,300 tons from 
about 200 facilities, however by 2002, PCE emissions had increased 
approximately 73 percent to about 2,200 tons. There was a 10 percent 
drop in the number of facilities using PCE in 2002.
    In 1999, about 3,700 tons of TCA were emitted from about 565 
facilities. In 2002, TCA emissions were about 2,300 tons from 473 
facilities, representing a 38 percent decrease in emissions and a 16 
percent decrease in facilities using TCA.
    In 1991, TCA dominated use with 62 percent of the halogenated 
solvent degreasing demand. By 1998, the demand for TCA had decreased by 
87 percent. In a critical period between 1991 and 2002, TCA was being 
phased out while remaining stock-piles at facilities with non-essential 
activities were being used until depleted. In the 2002 NEI, there were 
decreases in emissions of TCA, MC and TCE (by about 1,400 tons, 900 
tons, and 700 tons, respectively) compared to 1999 NEI). From 1999 to 
2002, emissions of PCE increased 73 percent (by about 900 tons). 
Overall emissions data for the total of all four HAP from 1999 to 2002 
indicated a 23 percent reduction in total emissions and an 8 percent 
decrease in the number of facilities.
    Therefore, although it appears that between 1999 and 2002, 
decreases in use of TCA, MC and TCE were partially offset by increases 
in PCE use. This was due to switching HAP solvents, switching to other 
non-HAP cleaning technologies, and elimination of solvent cleaning 
altogether.
2. How did we estimate the atmospheric dispersion of emitted 
pollutants?
    A nationwide, multi-facility version of EPA's Human Exposure Model, 
HEM-Screen, was used to assess chronic exposure and risk. HEM-Screen 
contains an atmospheric dispersion model with meteorological data and 
year 2000 population data at the census block level from the U.S. 
Bureau of Census. HEM-Screen includes meteorological data for 348 
stations across the U.S. The model selects the meteorological data for 
the station closest to each facility and uses this to estimate long-
term (i.e., annual average or greater) ambient concentrations of 
pollutant air emissions for nodes on a radial grid surrounding each 
facility. HEM-Screen then estimates concentrations at individual census 
block centroid locations within this grid from the modeled 
concentration results for grid nodes.
    For assessment of risk and hazard from chronic exposures, it was 
assumed that the total annual emissions derived for each facility were 
evenly distributed over the course of a year (i.e., a constant emission 
rate).
    Although the HEM-Screen model can accommodate source-specific 
release parameters, the same values were used for stack height, stack 
diameter, exit gas velocity, and exit gas temperature for all sources. 
The release parameters used for the risk assessment were derived from 
data obtained from the 1999 NEI. All emissions in the analysis were 
modeled as point source releases emitted from vertical stacks. The 1999 
NEI includes release parameters for approximately 611 (out of the 
1,093) facilities. The arithmetic mean values for each parameter were 
used in this analysis as representative values for stack height, stack 
diameter, exit gas velocity, and exit gas temperature. A maximum 
modeling radius of 20 km around each facility was used, and flat 
terrain was assumed for all facilities (e.g., no complex terrain was 
included in the modeling).

[[Page 47678]]

    No adjustments were made to the estimated ambient concentrations 
for reactivity of the HAPs being assessed. The exposures of most 
interest for this chronic assessment (i.e., exposures that occur at the 
point of maximum impact and other exposures that result in appreciable 
cancer risks) occur in the immediate vicinity of the source and within 
a short time period of release (i.e., minutes). Therefore, the impact 
of reactivity of the HAPs is relatively insignificant in the context of 
this exposure scenario.
3. How were cancer and noncancer risks estimated?
    The residual risk analysis addresses halogenated solvent cleaning 
machines subject to the 1994 MACT standards (40 CFR Part 63, subpart T) 
and estimates potential risks due to HAP emissions from sources that 
emit one or more of the regulated HAPs that are still used (i.e., MC, 
PCE, TCE and TCA). The risk assessment did not include the HAPs carbon 
tetrachloride and chloroform because their use was phased out in 1996.
    The assessment only considered the inhalation pathway as the 
primary route of exposure for humans because all of the four remaining 
HAPs are highly volatile compounds. In addition, multimedia fugacity 
modeling results indicate that the majority (over 99 percent) of each 
of these four source category HAP partitions preferentially to air 
rather than water, soil, or sediment (Risk Assessment Support 
Document). Some persistent and bioaccumulative (PB) substances can also 
pose human health risks via exposure pathways other than inhalation. 
EPA has developed a list of PB HAPs based on information developed 
under the Pollution Prevention Program, the Great Waters program, and 
the Toxics Release Inventory and additional analysis conducted by 
OAQPS. None of the four HAPs found in halogenated solvent cleaning 
machine vapors are included on this list. Consequently, exposures to 
these four HAPs via non-inhalation pathways were assumed to be minimal 
for this source category, and a quantitative risk characterization for 
multi-pathway exposures to humans was not carried out as a part of the 
residual risk assessment.
    We evaluated the potential for these HAPs to pose risks to the 
environment by conducting a screening-level ecological risk assessment 
for the baseline scenario. This assessment was intended to determine if 
HAPs emitted from these facilities pose a risk to ecological receptors 
including threatened and endangered species. The scope of the 
ecological screen was based on the fact that the HAPs emitted are all 
volatile and were shown to preferentially partition to air rather than 
soil or water, (i.e., the majority of the HAPs emitted (over 99 
percent) will remain in the atmosphere rather than deposit onto soil, 
plants, or aqueous environments. A more detailed explanation of this 
screening assessment may be found in the Residual Risk support 
document.
    The analysis estimated the potential for emissions from this source 
category to result in increased cancer risk and chronic and acute 
(i.e., one-hour) non-cancer hazard. Table 2 of this preamble outlines 
the cancer and chronic non-cancer dose-response values we used on the 
analysis.

                          Table 2.--Cancer and Chronic Non-Cancer Dose-Response Values
----------------------------------------------------------------------------------------------------------------
                                                                  Chronic reference      Cancer Unit Risk  (URE)
                                                               concentration or (RfC)    Estimate ([mu]g/m\3\)-1
                             HAP                               similar value (mg/m\3\) -------------------------
                                                             --------------------------
                                                                 Value        Source       Value        Source
----------------------------------------------------------------------------------------------------------------
Methylene Chloride..........................................          1.0        ATSDR      4.7E-07         IRIS
Perchloroethylene...........................................         0.27        ATSDR      5.9E-06      CAL and
                                                                                            7.1E-07        OPPTS
Trichloroethylene...........................................          0.6          CAL      2.0E-06          CAL
1,1,1,-Trichloroethane......................................          1.0          CAL            -           -
----------------------------------------------------------------------------------------------------------------
Notes:
Source: EPA's air toxics Web site at https://www.epa.gov/ttn/atw/toxsource/summary.html, table 1 (values for
  assessing long-term inhalation risks) dated February 28, 2005. Specific source abbreviations: IRIS = EPA's
  Integrated Risk Information System; ATSDR = Agency for Toxic Substances and Disease Registry: CAL = California
  Environmental Protec