[Federal Register Volume 73, Number 113 (Wednesday, June 11, 2008)]
[Proposed Rules]
[Pages 33257-33282]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E8-12618]



[[Page 33257]]

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Part V





Environmental Protection Agency





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40 CFR Part 63



National Emission Standards for Hazardous Air Pollutants: Mercury 
Emissions from Mercury Cell Chlor-Alkali Plants; Proposed Rule

Federal Register / Vol. 73, No. 113 / Wednesday, June 11, 2008 / 
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2002-0017; FRL-8576-3]
RIN 2060-AN99


National Emission Standards for Hazardous Air Pollutants: Mercury 
Emissions from Mercury Cell Chlor-Alkali Plants

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: This action proposes amendments to the national emission 
standards for hazardous air pollutants (NESHAP) for mercury emissions 
from mercury cell chlor-alkali plants. This NESHAP (hereafter called 
the ``2003 Mercury Cell MACT'') limited mercury air emissions from 
these plants. Following promulgation of the 2003 Mercury Cell Maximum 
Achievable Control Technology (MACT) NESHAP, EPA received a petition to 
reconsider several aspects of the rule from the Natural Resources 
Defense Council (NRDC). NRDC also filed a petition for judicial review 
of the rule in the U.S. Court of Appeals for the DC Circuit. By a 
letter dated April 8, 2004, EPA granted NRDC's petition for 
reconsideration, and on July 20, 2004, the Court placed the petition 
for judicial review in abeyance pending EPA's action on 
reconsideration. This action is EPA's proposed response to NRDC's 
petition for reconsideration.
    We are not proposing any amendments to the control and monitoring 
requirements for stack emissions of mercury established by the 2003 
Mercury Cell MACT. This proposed rule would amend the requirements for 
cell room fugitive mercury emissions to require work practice standards 
for the cell rooms and to require instrumental monitoring of cell room 
fugitive mercury emissions. This proposed rule would also amend aspects 
of these work practice standards and would correct errors and 
inconsistencies in the 2003 Mercury Cell MACT that have been brought to 
our attention.

DATES: Comments. Comments must be received on or before August 11, 
2008.
    Public Hearing. If anyone contacts EPA by June 23, 2008 requesting 
to speak at a public hearing, a hearing will be held on July 11, 2008.

ADDRESSES: You may submit comments, identified by Docket ID No. EPA-HQ-
OAR-2002-0017, by any of the following methods:
     Federal eRulemaking Portal: http://www.regulations.gov: 
Follow the instructions for submitting comments.
     Agency Web Site: http://www.epa.gov/oar/docket.html. 
Follow the instructions for submitting comments on the EPA Air and 
Radiation Docket Web site.
     E-mail: [email protected]. Include Docket ID No. EPA-
HQ-OAR-2002-0017 in the subject line of the message.
     Fax: (202) 566-9744.
     Mail: National Emission Standards for Hazardous Air 
Pollutants for Mercury Cell Chlor-alkali Plants Docket, Environmental 
Protection Agency, EPA Docket Center (EPA/DC), Air and Radiation 
Docket, Mail Code 2822T, 1200 Pennsylvania Ave., NW., Washington, DC 
20460. Please include a total of two copies.
     Hand Delivery: EPA Docket Center, Public Reading Room, EPA 
West, Room 3334, 1301 Constitution Ave., NW., Washington, DC 20460. 
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-
2002-0017. 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 www.regulations.gov 
or e-mail. The 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 
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 
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, is not placed on the Internet and will be 
publicly available only in hard copy form. Publicly available docket 
materials are available either electronically through 
www.regulations.gov or in hard copy at the National Emission Standards 
for Hazardous Air Pollutants for Mercury Cell Chlor-alkali Plants 
Docket, EPA/DC, EPA West, Room 3334, 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 Docket is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: Dr. Donna Lee Jones, Sector Policies 
and Programs Division, Office of Air Quality Planning and Standards 
(D243-02), Environmental Protection Agency, Research Triangle Park, 
North Carolina 27711, telephone number: (919) 541-5251; fax number: 
(919) 541-3207; e-mail address: [email protected].

SUPPLEMENTARY INFORMATION:

I. General Information

A. Does this action apply to me?

    The regulated categories and entities potentially affected by this 
proposed action include:

 
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             Category                   NAICS code \1\                 Examples of regulated entities
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Industry..........................  325181...............  Alkalis and Chlorine Manufacturing.
Federal government................  .....................  Not affected.

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State/local/tribal government.....  .....................  Not affected.
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\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 this 
action. To determine whether your facility would be regulated by this 
action, you should examine the applicability criteria in 40 CFR 63.7682 
of subpart IIIII, National Emission Standards for Hazardous Air 
Pollutants (NESHAP): Mercury Emissions from Mercury Cell Chlor-Alkali 
(hereafter called the ``2003 Mercury Cell MACT''). If you have any 
questions regarding the applicability of this action to a particular 
entity, consult either the air permitting authority for the entity or 
your EPA regional representative as listed in 40 CFR 63.13 of subpart A 
(General Provisions).

B. What should I consider as I prepare my comments to EPA?

    Do not submit information containing confidential business 
information (CBI) to EPA through www.regulations.gov or e-mail. Send or 
deliver information identified as CBI only to the following address: 
Roberto Morales, OAQPS Document Control Officer (C404-02), 
Environmental Protection Agency, Office of Air Quality Planning and 
Standards, Research Triangle Park, North Carolina 27711, Attention 
Docket ID EPA-HQ-OAR-2002-0017. Clearly mark the part or all of the 
information that you claim to be CBI. For CBI information in 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.

C. Where can I get a copy of this document?

    In addition to being available in the docket, an electronic copy of 
this proposed action will also be available on the Worldwide Web (WWW) 
through the Technology Transfer Network (TTN). Following signature, a 
copy of this proposed action will be posted on the TTN's policy and 
guidance page for newly proposed or promulgated rules at the following 
address: http://www.epa.gov/ttn/oarpg/. The TTN provides information 
and technology exchange in various areas of air pollution control.

D. When would a public hearing occur?

    If anyone contacts EPA requesting to speak at a public hearing 
concerning the proposed amendments by June 23, 2008, we will hold a 
public hearing on July 11, 2008. If you are interested in attending the 
public hearing, contact Ms. Pamela Garrett at (919) 541-7966 to verify 
that a hearing will be held. If a public hearing is held, it will be 
held at 10 a.m. at the EPA's Environmental Research Center Auditorium, 
Research Triangle Park, NC, or an alternate site nearby.

E. How is this document organized?

    The supplementary information in this preamble is organized as 
follows:

I. General Information
    A. Does this action apply to me?
    B. What should I consider as I prepare my comments to EPA?
    C. Where can I get a copy of this document?
    D. When would a public hearing occur?
    E. How is this document organized?
II. Background Information
    A. Reconsideration Overview
    B. Industry Description
    C. Regulatory Background
    D. Details of the Petition for Reconsideration
III. Summary of EPA's Reconsideration and Proposed Amendments
    A. What were the issues that EPA reconsidered, and what are 
EPA's proposed responses?
    B. What amendments are EPA proposing?
    C. What are the impacts of these proposed rule amendments?
IV. 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 (Energy Effects)
    I. National Technology Transfer Advancement Act
    J. Executive Order 12898: Federal Actions to Address 
Environmental Justice in Minority Populations and Low-Income 
Populations

II. Background Information

A. Reconsideration Overview

    On December 19, 2003, EPA promulgated the National Emission 
Standards for Hazardous Air Pollutants for Mercury Emissions from 
Mercury Chlor-alkali Plants (40 CFR part 63, subpart IIIII, 68 FR 
70904), hereafter called the ``2003 Mercury Cell MACT.'' This rule for 
mercury cell chlor-alkali plants implemented section 112(d) of the 
Clean Air Act (CAA), which required all categories and subcategories of 
major sources listed under section 112(c) to meet hazardous air 
pollutant emission standards reflecting the application of the maximum 
achievable control technology (MACT). Mercury cell chlor-alkali plants 
are a subcategory of the chlorine production source category listed 
under the authority of section 112(c)(1) of the CAA. In addition, 
mercury cell chlor-alkali plants were listed as an area source category 
under section 112(c)(3) and (k)(3)(B) of the CAA. The 2003 Mercury Cell 
MACT satisfied our requirement to issue 112(d) regulations under each 
of these listings (for mercury).
    The 2003 Mercury Cell MACT contained numerical emission limitations 
for the point sources of mercury emissions at mercury cell chlor-alkali 
plants. It also required that the plants either install mercury 
monitoring systems on the point source vents or that they test each 
vent manually at least once per week. The compliance date for the 2003 
Mercury Cell MACT was December 19, 2006.
    The 2003 Mercury Cell MACT also contained a set of work practice 
standards to address fugitive mercury emissions from the cell rooms. We 
determined that these procedures represented the MACT for the industry, 
and were considerably more stringent than the 40 CFR part 61 subpart E 
NESHAP requirements for control of mercury emissions (hereafter called 
the ``part 61 Mercury NESHAP'') that were applicable to this industry 
prior to the 2003 Mercury Cell MACT. An alternative compliance option 
was included in the 2003 Mercury Cell MACT that required mercury

[[Page 33260]]

monitoring systems to be installed in the cell rooms with mandatory 
problem correction when a site-specific mercury concentration action 
level is exceeded. As of December 19, 2006, the compliance date for the 
2003 Mercury Cell MACT, all facilities but one have chosen this 
alternative compliance option.
    On February 17, 2004, the Natural Resources Defense Council (NRDC) 
submitted to EPA an administrative petition asking us to reconsider 
several aspects of the 2003 Mercury Cell MACT under Clean Air Act 
section 307(d)(7)(B). On the same day, NRDC and the Sierra Club filed a 
petition for judicial review of the 2003 Mercury Cell MACT in the U.S. 
Court of Appeals for the DC Circuit (Civ. No. 04-1048). The focus of 
many of the issues raised in the petition for reconsideration was EPA's 
treatment of the fugitive cell room emissions in the 2003 Mercury Cell 
MACT. Specifically, NRDC asked EPA to reconsider (1) the decision to 
develop a set of work practice requirements under Clean Air Act section 
112(h) in lieu of a numeric emission limitation for cell rooms; (2) the 
decision to make the promulgated work practices optional for sources 
that choose to undertake continuous monitoring; (3) the decision to not 
require existing facilities to convert to a mercury-free chlorine 
manufacturing process; (4) the elimination of the previously applicable 
part 61 rule's 2,300 grams/day plant-wide emission limitation; and (5) 
the decision to create a subcategory of mercury cell chlor-alkali 
plants within the chlorine production category.
    By a letter dated April 8, 2004, Jeffrey Holmstead, then-EPA 
Assistant Administrator for Air and Radiation, notified the NRDC that 
EPA had granted NRDC's petition for reconsideration of the 2003 Mercury 
Cell MACT. On July 20, 2004, the Court granted EPA's motion to hold the 
case in abeyance pending EPA's action on reconsideration of the 2003 
Mercury Cell MACT. Today's notice is EPA's proposed response to NRDC's 
petition for reconsideration.

B. Industry Description

    There currently are five operating mercury cell chlor-alkali plants 
in the U.S., with one of these plants planning to convert to non-
mercury technology by 2012. These five plants are in Augusta, Georgia; 
Ashtabula, Ohio; Charleston, Tennessee; New Martinsville, West 
Virginia; and Port Edwards, Wisconsin. The Port Edwards, Wisconsin 
facility is the one that is expected to convert to non-mercury 
technology.
    Mercury cell chlor-alkali plants produce chlorine and caustic soda 
(sodium hydroxide) or caustic potash (potassium hydroxide) in an 
electrolytic reaction using mercury. A mercury cell plant typically has 
many individual cells housed in one or more cell buildings. Mercury 
cells are electrically connected together in series.
    At a mercury cell chlor-alkali plant, mercury is emitted from point 
sources (i.e., stacks) and fugitive sources. Mercury also leaves the 
plant in wastewater and solid wastes. There are three primary point 
sources of mercury emissions at mercury cell plants: The end-box 
ventilation system vent, the by-product hydrogen system vent, and the 
mercury thermal recovery unit vents. Every mercury cell plant has a 
hydrogen by-product stream, and most have an end-box ventilation 
system. However, not all of the plants have thermal mercury recovery 
units. Of the five plants currently operating, all five facilities have 
end-box ventilation systems and two have thermal mercury recovery 
units.
    In addition to the stack emissions, there are fugitive mercury 
emissions at these plants. The majority of fugitive mercury emissions 
occur from sources inside the cell room such as leaks from cells, 
decomposers, hydrogen piping, and other equipment. Fugitive mercury 
emissions also occur during maintenance activities such as cell or 
decomposer openings, mercury pump change-outs, and end-box seal 
replacements, etc. All of this equipment and activities are located in 
the cell room, so these fugitive mercury emissions would be emitted via 
the cell room ventilation system.
    There are potential fugitive air emission sources outside of the 
cell room. These potential outside sources include leaks of mercury-
contaminated brine in the brine treatment area, the wastewater system, 
and the handling and storage of mercury contaminated wastes.

C. Regulatory Background

    The part 61 Mercury NESHAP, which applied to all mercury cell 
chlor-alkali chlorine production plants prior to the 2003 Mercury Cell 
MACT, contained a numerical emission limit for mercury of 2,300 grams 
per day (g/day) for the entire plant. Point sources were limited to 
1,000 g/day of mercury. If plants conducted a series of detailed 
design, maintenance, and housekeeping procedures, they were permitted 
under the part 61 rule to assume that fugitive mercury emissions from 
the cell room were 1,300 g/day, without having to demonstrate as such. 
All the mercury cell plants complied with the part 61 Mercury NESHAP 
using these assumptions rather than testing and determining actual 
fugitive cell room mercury emissions. Therefore, the extent of actual 
plant-wide and cell room emissions that occurred under the part 61 rule 
could not be precisely determined.
    In the 2003 Mercury Cell MACT rulemaking, pursuant to Clean Air Act 
section 112(d)(2) and (3), the regulatory analyses for the stack 
control requirements were based on the practices and controls of the 
lowest emitting plants out of the eleven facilities operating at the 
time of the MACT analyses. Existing mercury cell chlor-alkali 
production facilities with end-box ventilation systems were required by 
the 2003 Mercury Cell MACT to limit the aggregate mercury emissions 
from all by-product hydrogen streams and end-box ventilation system 
vents to not exceed 0.076 grams (g) mercury (Hg) per megagram (Mg) 
chlorine (Cl2) for any consecutive 52-week period. Existing 
mercury cell chlor-alkali production facilities without end-box 
ventilation systems were required to limit the mercury emissions from 
all by-product hydrogen streams to not exceed 0.033 g Hg/Mg 
Cl2 for any consecutive 52-week period.
    The 2003 Mercury Cell MACT contained a set of work practice 
standards to address and mitigate fugitive mercury releases at mercury 
cell chlor-alkali plants. The MACT analysis for the requirements to 
reduce fugitive mercury emissions was based on the best practices of 
the eleven facilities operating at the time of the July 2002 proposal 
for the Mercury Cell MACT (see 67 FR 44672, July 3, 2002). These work 
practice provisions included specific equipment standards such as the 
requirement that end boxes either be closed (that is, equipped with 
fixed covers), or that end box headspaces be routed to a ventilation 
system (40 CFR 63.8192, ``What work practice standards must I meet?'', 
and Tables 1 through 4 to subpart IIIII of part 63). Other examples 
include requirements that piping in liquid mercury service have smooth 
interiors, that cell room floors be free of cracks and spalling (i.e., 
fragmentation by chipping) and coated with a material that resists 
mercury absorption, and that containers used to store liquid mercury 
have tight-fitting lids (Table 1 to subpart IIIII of part 63). The work 
practice standards also included operational requirements. Examples of 
these include requirements to allow electrolyzers and decomposers to 
cool before opening, to keep liquid mercury in end boxes and mercury

[[Page 33261]]

pumps covered by an aqueous liquid at a temperature below its boiling 
point at all times, to maintain end box access port stoppers in good 
sealing condition, and to rinse all parts removed from the decomposer 
for maintenance prior to transport to another work area (Table 1 to 
subpart IIIII of part 63).
    A cornerstone of the work practice standards was the inspection 
program for equipment problems, leaking equipment, liquid mercury 
accumulations and spills, and cracks or spalling in floors and pillars 
and beams. Specifically, the 2003 Mercury Cell MACT required that 
visual inspections be conducted twice each day to detect equipment 
problems, such as end box access port stoppers not securely in place, 
liquid mercury in open containers not covered by an aqueous liquid, or 
leaking vent hoses (Table 2 to subpart IIIII of part 63). If a problem 
was found during an inspection, the owner or operator was required to 
take immediate action to correct the problem. Monthly inspections for 
cracking or spalling in cell room floors were also required as well as 
semiannual inspections for cracks and spalling on pillars and beams. 
Any cracks or spalling found were required to be corrected within 1 
month. Visual inspections for liquid mercury spills or accumulations 
were also required twice per day. If a liquid mercury spill or 
accumulation was identified during an inspection, the owner or operator 
was required to initiate cleanup of the liquid mercury within 1 hour of 
its detection (Table 3 to subpart IIIII of part 63). In addition to 
cleanup, the 2003 Mercury Cell MACT required inspection of the 
equipment in the area of the spill or accumulation to identify the 
source of the liquid mercury. If the source was found, the owner or 
operator was required to repair the leaking equipment as discussed 
below. If the source was not found, the owner or operator was required 
to reinspect the area every 6 hours until the source was identified or 
until no additional liquid mercury was found at that location. 
Inspections of specific equipment for liquid mercury leaks were 
required once per day. If leaking equipment was identified, the 2003 
Mercury Cell MACT required that any dripping mercury be contained and 
covered by an aqueous liquid, and that a first attempt to repair 
leaking equipment be made within 1 hour of the time it is identified. 
Leaking equipment was required to be repaired within 4 hours of the 
time it is identified, although there are provisions for delaying 
repair of leaking equipment for up to 48 hours (Table 3 to subpart 
IIIII of part 63) under certain conditions.
    Inspections for hydrogen gas leaks were required twice per day. For 
a hydrogen leak at any location upstream of a hydrogen header, a first 
attempt at repair was required within 1 hour of detection of the 
leaking equipment, and the leaking equipment was required to be 
repaired within 4 hours (with provisions for delay of repair if the 
leaking equipment was isolated). For a hydrogen leak downstream of the 
hydrogen header but upstream of the final control device, a first 
attempt at repair was required within 4 hours, and complete repair 
required within 24 hours (with delay provisions if the header is 
isolated) (Table 3 to subpart IIIII of part 63).
    The work practice standards in the 2003 Mercury Cell MACT required 
that facilities institute a floor level mercury vapor measurement 
program (See Sec.  63.8192, ``What work practice standards must I 
meet?'', specifically paragraph (d)). Under this program, mercury vapor 
levels are periodically measured and compared to an action level of 
0.05 mg/m3. The 2003 Mercury Cell MACT specified the actions to be 
taken when the action level is exceeded. If the action level was 
exceeded during any floor-level mercury vapor measurement evaluation, 
facilities were required to take specific actions to identify and 
correct the problem (Sec.  63.8192(d)(1) through (4)).
    As an alternative to the full set of work practice standards 
(including the floor-level monitoring program), the 2003 Mercury Cell 
MACT included a compliance option to institute a cell room monitoring 
program (See Sec.  63.8192, ``What work practice standards must I 
meet?'', specifically paragraph (g)). In this program, owners and 
operators continuously monitor the mercury concentrations in the upper 
portion of each cell room and take corrective actions as soon as 
practicable when a site-specific mercury vapor level is detected. The 
cell room monitoring program was not designed to be a continuous 
emissions monitoring system inasmuch as the results would be used only 
to determine relative changes in mercury vapor levels rather than 
compliance with a cell room emission or operating limit (68 FR 70922).
    As part of the cell room monitoring program, the owner or operator 
was required to establish an action level for each cell room based on 
preliminary monitoring to determine normal baseline conditions (See 
Sec.  63.8192, ``What work practice standards must I meet?'', 
specifically paragraph (g)(2)). Once the action level(s) was 
established, continuous monitoring of the cell room was required during 
all periods of operation. If the action level was exceeded at anytime, 
actions to identify and correct the source of elevated mercury vapor 
were required to be initiated as soon as possible. If the elevated 
mercury vapor level was due to a maintenance activity, the owner or 
operator was required to ensure that all work practices related to that 
maintenance activity were followed. If a maintenance activity was not 
the cause, inspections and other actions were needed to identify and 
correct the cause of the elevated mercury vapor level. Owners and 
operators utilizing this cell room monitoring program option were 
required to develop site-specific cell room monitoring plans describing 
their monitoring system and quality assurance/quality control 
procedures that were to be used in their monitoring program (Table 5 to 
subpart IIIII of part 63).
    The 2003 Mercury Cell MACT established the requirement for owners 
and operators to routinely wash surfaces throughout the plant where 
liquid mercury could accumulate (See Sec.  63.8192, ``What work 
practice standards must I meet?'', specifically paragraph (e)). Owners 
and operators were required to prepare and follow a written washdown 
plan detailing how and how often certain areas specified in the 2003 
Mercury Cell MACT were to be washed down to remove any accumulations of 
liquid mercury (Table 7 to subpart IIIII of part 63).
    For new or reconstructed mercury cell chlor-alkali production 
facilities, the 2003 Mercury Cell MACT prohibited mercury emissions.
    Several mercury cell plants have closed or converted to membrane 
cells since the promulgation of the 2003 Mercury Cell MACT. When these 
situations have occurred at plants with on-site thermal mercury 
recovery units, it has been common for these units to continue to 
operate to assist in the treatment of wastes associated with the 
shutdown/conversion. Under the applicability of the 2003 Mercury Cell 
MACT, these units are no longer an affected source after the chlorine 
production facility ceased operating. Although these mercury recovery 
units were required to continue to use controls as per their state 
permits, these proposed amendments would require any mercury recovery 
unit to continue to comply with the requirements of the Mercury Cell 
MACT for such units even after closure or conversion of the chlorine 
production facility, as long as

[[Page 33262]]

the mercury recovery unit continues to operate to recover mercury.

D. Details of the Petition for Reconsideration

    On February 17, 2004, under section 307(d)(7)(B) of the Clean Air 
Act, the NRDC submitted to EPA an administrative petition asking us to 
reconsider the 2003 Mercury Cell MACT. NRDC and the Sierra Club also 
filed a petition for judicial review of the rule in the U.S. Court of 
Appeals for the DC Circuit (NRDC v. Sierra Club v. EPA, Civ. No. 04-
1048). Underlying many of the issues raised in the petition for 
reconsideration was the uncertainty associated with the fugitive 
emission estimates used by EPA in the rulemaking. In particular, the 
NRDC had concerns over the inability of mercury cell plants to account 
for all the mercury added to their processes to replace mercury that 
leaves in products or wastes or leaves via air emissions. NRDC, along 
with a number of other concerned parties who submitted comments on the 
July 2002 proposed rule, believed that the majority of this ``missing'' 
or unaccounted mercury must be lost through fugitive emissions. They 
also contended that recognition of this asserted fact would cause EPA 
to change many of the decisions that had been made in developing and 
promulgating the 2003 Mercury Cell MACT. Specifically, NRDC raised the 
following five issues in its petition:

    (1) EPA refused to establish a numeric emission standard for the 
cell room, choosing instead to develop a set of work practices 
designed to minimize emissions. NRDC argued that under Clean Air Act 
section 112(h) EPA is permitted to substitute work practices for 
emission limits only upon a finding that ``it is not feasible * * * 
to prescribe or enforce an emission standard.''
    (2) EPA's 2003 Mercury Cell MACT unreasonably backtracked from 
the work practices the Agency proposed. As part of the regulatory 
effort, EPA had surveyed the work practices used by facilities in 
the industry and concluded that the housekeeping activities that 
sources followed to comply with the part 61 Mercury NESHAP 
represented the MACT floor. The EPA then required these detailed 
housekeeping practices that were based upon the best levels of 
activity in the industry. But despite the results of its survey and 
findings, EPA made the work practices optional in the 2003 Mercury 
cell MACT, allowing facilities to choose not to do the housekeeping 
activities and to instead perform continuous monitoring. EPA then 
stated that ``a comprehensive continuous cell room monitoring 
program should be sufficient to reduce fugitive mercury emissions 
from the cell room without imposing the overlapping requirements of 
the detailed work practices.''
    (3) EPA failed to consider non-mercury technology as a beyond-
the-floor MACT control measure for existing sources even though 
eliminating the mercury cell process would totally eradicate mercury 
emissions and also would be cost-effective, based on NRDC's 
expectations of the amount of fugitive mercury emissions from 
subject sources.
    (4) EPA eliminated a 2,300 g/day limit on plant-wide mercury 
emissions that existed under the part 61 Mercury NESHAP. NRDC stated 
that doing so violated the CAA because the law generally prohibits 
the new emission standards under section 112 from weakening more 
stringent existing requirements.
    (5) EPA inappropriately decided to create a subcategory of 
mercury cell plants within the chlorine production category.

    In a letter dated April 8, 2004, EPA generally granted NRDC's 
petition for reconsideration, and indicated we would respond in detail 
in a subsequent rulemaking action. In addition, in meetings between EPA 
staff and NRDC representatives, EPA agreed to address the uncertainty 
of EPA's fugitive mercury emissions from this industry. The Court 
stayed the litigation while the Agency addressed the uncertainty 
issues, conducted additional testing, and reconsidered the rulemaking.

III. Summary of EPA's Reconsideration and Proposed Amendments

    In this section, we describe actions that we undertook in support 
of the proposed reconsideration of the rule, especially as related to 
the issues raised by NRDC in its petition for reconsideration. We 
present our proposed conclusions and decisions in response to NRDC's 
petition, and we summarize the rule amendments that we are proposing in 
today's action, along with our estimate of the impacts of these 
amendments.
    These proposed amendments would be applicable to affected 
facilities when the final rule amendments are published, with proposed 
compliance periods of 60 days for facilities that have complied with 
the 2003 Mercury Cell MACT by selecting the continuous cell room 
monitoring option of that rule, and 2 years for facilities that have 
complied with the 2003 Mercury Cell MACT by selecting the work practice 
option. Mercury recovery units at sites where mercury cells are closed 
or converted after the date that the final rule amendments are 
published would be required to comply with the requirements of the 
final amendments as long as they are in operation.

A. What were the issues that EPA reconsidered, and what are EPA's 
proposed responses?

    As discussed above in section (II)(D), NRDC's petition listed five 
specific issues. Our reconsideration of each of these issues is 
addressed below. First, however, we also present a discussion of 
another issue that we believe relates to much of NRDC's petition: The 
magnitude of the fugitive mercury emissions from mercury cell chlor-
alkali plants.
1. Magnitude of Fugitive Mercury Emissions from Mercury Cell Chlor-
alkali Plants
    It has been difficult to quantify fugitive mercury emissions from 
mercury cell chlor-alkali plants. During most of the time when the 2003 
Mercury Cell MACT was being developed, we were aware of fewer than five 
mercury emissions studies conducted over the last 30 or more years in 
the U.S. and Europe that measured fugitive emissions from mercury cell 
plants. Two of these studies were conducted by EPA in the early 1970's 
and formed the basis for the assumption of 1,300 g/day mercury cell 
room emissions of the part 61 Mercury NESHAP. During the development of 
the 2003 Mercury Cell MACT, EPA conducted a study at Olin Corporation's 
mercury cell plant in Augusta, Georgia (hereafter called ``Olin 
Georgia''), that provided an additional estimate of fugitive mercury 
emissions.
    In the time period since mercury cell chlor-alkali plants were 
required to comply with the part 61 Mercury NESHAP, which was 
promulgated in April of 1973, we are not aware of any facility that 
conducted testing to demonstrate compliance with the cell room emission 
limitation of the part 61 Mercury NESHAP. Instead, all facilities 
carried out the set of approved design, maintenance, and housekeeping 
practices and assumed fugitive mercury emissions of 1,300 g/day, as was 
permitted by the part 61 NESHAP.
    The sensitivity and concern over the actual levels of fugitive 
mercury emissions from the cell rooms was exacerbated by the inability 
of the industry to fully account for all the mercury that was added to 
the cells. In the preamble to the final 2003 Mercury Cell MACT (68 FR 
70920), we stated the following: ``Even with this decrease in 
consumption, significant mercury remains unaccounted for by the 
industry. The mercury releases reported to the air, water, and solid 
wastes in the 2000 Toxics Release Inventory (TRI) totaled around 14 
tons. This leaves approximately 65 tons of consumed mercury that is not 
accounted for in the year 2000.'' While industry representatives 
provided explanations for this discrepancy, they could not fully 
substantiate their theories.

[[Page 33263]]

    Although we acknowledged the uncertainty in the accounting of all 
the mercury, we stated in the 2003 Mercury Cell MACT that no evidence 
has ever been provided to indicate that the unaccounted mercury is 
emitted to the atmosphere via fugitive emissions from the cell room or 
otherwise. In its petition for reconsideration and in other 
correspondence, NRDC cites information that it believes supports a 
conclusion that the unaccounted mercury is emitted from the cell room. 
However, NRDC did not address studies that have been conducted to 
measure fugitive mercury emissions from mercury cell plants that rebut 
that conclusion.
    Historically, the highest daily emission rate reported for any cell 
room has been approximately 2,700 g/day for a plant operating in 1971, 
which was before the part 61 Mercury NESHAP was in effect. More recent 
studies show fugitive mercury emissions considerably lower than the 
1,300 g/day assumption in the part 61 Mercury NESHAP. For example, a 
study in 1998 at the Holtrachem facility in Orrington, Maine, estimated 
a fugitive mercury emission rate between 85 and 304 g/day. A study in 
Sweden in 2001 estimated a daily fugitive emission rate of 252 g/day. 
While NRDC cites various peripheral aspects of the EPA study in 2000 
study at Olin's Georgia mercury cell plant, NRDC does not discuss a 
primary conclusion of the test: That the facility was estimated to have 
an average fugitive mercury emission rate of 472 g/day.
    While we were confident that the fugitive emissions from cell rooms 
were not at the very high levels estimated by NRDC (at several tons per 
year (tpy) per plant), we recognized that the body of fugitive mercury 
emissions data could be improved. Therefore, as part of our 
reconsideration of the 2003 Mercury Cell MACT, we collected additional 
information on fugitive mercury emissions from mercury cell chlor-
alkali plants. The primary purpose of this effort was to address 
whether the fugitive emissions from a mercury cell chlor-alkali plant 
are on the order of magnitude of the historical assumption of 1,300 g/
day, corresponding to 0.5 tons per year (tpy) per plant, or on the 
order of magnitude of the unaccounted for mercury in 2000, which would 
correspond to 3 to 5 tpy per plant, or at some other level.
    In planning our information gathering efforts for this test 
program, we recognized that all of the previous studies were relatively 
short term. Fugitive mercury emissions from a mercury cell plant occur 
for numerous reasons, with significant emission sources likely being 
leaking or malfunctioning equipment and maintenance activities that 
expose mercury normally enclosed in process equipment to the 
atmosphere. One noteworthy NRDC criticism of the Olin Georgia study was 
that no major ``invasive'' maintenance activities were performed during 
the testing. Therefore, in designing our new study, we collected data 
over a number of months during a wide range of operating conditions and 
during times when all major types of maintenance activities were 
conducted.
    Consequently, as part of the reconsideration efforts for the 2003 
Mercury Cell MACT, EPA sponsored a test program to address the issue of 
the magnitude of the fugitive mercury emissions at mercury cell chlor-
alkali plants. We visited five mercury cell chlor-alkali plants to 
identify and evaluate the technical, logistical, and/or safety issues 
associated with the measurement of fugitive emissions from the mercury 
cell rooms as part of a test program. The result of these efforts was 
that we sponsored two emissions testing programs: One at the Olin 
mercury cell chlor-alkali plant in Charleston, Tennessee (hereafter 
called ``Olin Tennessee''), to estimate mercury emissions from one of 
its three cell rooms; and the other at the Occidental Chemical mercury 
cell chlor-alkali plant in Muscle Shoals, Alabama (hereafter called 
``Occidental Alabama''), to estimate their total site mercury 
emissions. These testing programs are discussed in detail later in this 
notice.
    In addition to these emissions measurements, we also collected 
mercury emissions data from the continuous mercury monitoring system 
installed at three mercury cell plants: The Occidental facility in 
Delaware City, Delaware (hereafter called ``Occidental Delaware''); 
Occidental Alabama; and Olin Tennessee, which was also a site for the 
EPA emissions measurement tests. We also performed validation studies 
of the air flow measurement systems and mercury monitors at these three 
facilities.
    In addition, we compared maintenance logs and mercury emissions 
data to establish the correlation, if any, between maintenance 
activities and mercury emissions using data from Occidental's 
facilities. And finally, we addressed the issue of significant sources 
of fugitive mercury emissions from outside the cell room from the data 
acquired at the EPA-sponsored total site emissions tests at Occidental 
Alabama.
    The descriptions of the emissions testing and data gathering 
efforts are summarized below along with our estimates of fugitive 
mercury emissions derived from these studies. The full emissions test 
reports, two memoranda that summarize the test reports, validation 
reports, and summaries of the mercury monitoring system emissions data 
analyses can be found in the docket to this proposed rule (EPA-HQ-OAR-
2004-0017), and were previously provided to NRDC and industry 
representatives.
a. Description of EPA-Sponsored Mercury Emissions Tests at Two 
Facilities
    Olin--Charleston, Tennessee. This test was performed over a six-
week period from August to October 2006 using a long-path ultraviolet 
differential optical absorption spectrometer (UV-DOAS) to continuously 
measure the mercury concentration in the ventilator and an optical 
scintillometer (anemometer) to measure the velocity. Emission estimates 
were reported for each 24-hour period. The test report can be found in 
the docket, item number EPA-HQ-OAR-2002-0017-0056.3.
    The Olin Tennessee facility has three cell rooms installed adjacent 
to one another. The E510 cellroom (startup in 1962) is a simple 
rectangular design with two rows of cells. The E812 cell room (startup 
in 1968) is also a simple rectangular design with two rows of cells. In 
1974, Olin added a third cell room with additional E812 cells just 
south of the existing E812 cell room. A central control area was 
installed between the E510 and E812 cell rooms. In addition, an 
elevator and computer equipment area was installed between the two 
original plants. The area between the original E812 cells and the E812 
10-cell Expansion is fully open. Each of the three cell rooms has a 
full length, natural draft ventilator mounted on the roof. Fans have 
been installed at the cell floor level around the perimeter of the E510 
and E812 cell rooms to enhance cool air flow in key work areas. In 
addition, high velocity fans were installed near the central control 
area to aid air movement in ``dead zones'' created by the control area 
walls. There are no exhaust fans in any of the cell rooms.
    Logistical and cost considerations resulted in the E510 cell room 
being selected for the EPA test. Continuously measuring the mercury 
emissions from more than one ventilator simultaneously was not 
practical, based on the limited availability of equipment and the 
complexities related to the operation of a number of highly 
sophisticated

[[Page 33264]]

measurement devices. The small size of the E812 Expansion cell room 
excluded it from consideration, and the complicated flow patterns 
between the E812 and E812 Expansion rooms would have made it very 
difficult to account for all the associated uncertainties using only 
one monitor. The configuration of the E510 cell room, the relatively 
straightforward air flow pattern, and the structure of the ventilator 
(which allowed easy access and a clear path for the beams) made it the 
obvious choice for the test program to optimize our ability to obtain 
the most reliable data.
    Occidental--Muscle Shoals, Alabama. This test was conducted over 53 
days, from September 21, 2006, through November 12, 2006, to measure 
total site mercury emissions. For this study, the ``total site'' 
included emissions via the cell room ventilation system, the stacks/
point sources (thermal mercury recovery unit vent, hydrogen byproduct 
vent, end-box ventilation vent), and any fugitives that occurred 
outside of the cell room in adjacent process areas. The measurement 
approach used a Vertical Radial Plume Mapping (VRPM) measurement 
configuration employing three open-path UV-DOAS instruments for 
elemental mercury concentration measurements, in conjunction with 
multipoint ground level mercury measurements with a Lumex mercury 
analyzer. The total site mercury emissions were estimated using these 
concentration measurements and meteorological data (e.g., wind speed, 
wind direction).
    The measurement systems operated on a 24 hour, 7 day per week basis 
for the 53-day campaign. The 3-beam VRPM configuration used to estimate 
elemental mercury emissions from the facility was located at a fixed 
position and fixed orientation on site for the duration of the project. 
Calculations of mercury flux through the VRPM plane were conducted only 
when specific data quality indicators involving wind speed, wind 
direction, path averaged concentration ratios and instrument operation 
were met. During the 53-day emissions test program, VRPM mercury flux 
values were able to be calculated for 23 days. Data were reported as 
daily (24 hour) emission values that were extrapolated from rolling 20-
minute averages calculated every four minutes. A total of 1,170 mercury 
emission flux estimates were produced during the 23 days. The test 
report can be found in the docket, item number EPA-HQ-OAR-2002-0017-
0056.5.
    The cell room at the now closed Occidental Alabama plant was a 
rectangular building measuring 260 feet by 357 feet. The cell room 
consisted of two rows of cells broken into four sections. The cell room 
took up half of a larger building, with a wall separating the cell room 
from the other half of the building that was used for equipment 
storage. The peak of the roof was over the wall separating the cell 
room from the other side of the building. The ventilation for the cell 
room consisted of both induced and forced draft fans. There were 43 
forced-draft fans positioned on the side wall of the building pushing 
air towards the center of the building. There were two rows of induced-
draft fans on the roof of the cell building. One row, containing 33 
fans, was directly over the center of the two rows of cells. The other 
row, which contained 32 fans, was at the peak of the roof. The result 
was that the building was constantly under a slightly negative 
pressure.
b. EPA Validations of Mercury Monitoring Systems in Cell Rooms of 
Mercury Chlor-Alkali Plants
    During the time we were planning the testing programs to estimate 
fugitive mercury emissions via an EPA-sponsored test program, the 
mercury cell chlor-alkali industry was undertaking its own long-term 
mercury emissions estimation efforts. Two Occidental mercury cell 
plants (Delaware and Alabama) installed mercury monitoring systems in 
their cell rooms in 2005, and the Olin Tennessee facility installed a 
mercury monitoring system in 2006. The plants used these systems to 
identify and correct mercury emission episodes in accordance with the 
alternative cell room monitoring program of the 2003 Mercury Cell MACT. 
Specifically, the facilities monitored physical and chemical parameters 
in the cell room, such as air flow and mercury concentration, that 
allowed the continuous estimation of the relative mass of mercury 
emissions leaving the cell room. Since these plants had already 
installed and were currently running their mercury monitoring systems, 
we included the collection and evaluation of data from these systems in 
our data gathering program. The overall goal of our validation program 
was to provide a qualitative assessment of the mercury monitoring 
systems at these three facilities.
    There were three specific objectives of the EPA validation studies. 
The first objective was to verify that facility data processing and 
archiving were being performed correctly. This was accomplished through 
comparison of facility data with independently calculated values for 
elemental mercury mass emission rates. These independent calculations 
utilized the same equations and raw input data as the company data 
systems. The second objective was to establish a confidence level for 
the accuracy of the measured elemental mercury concentrations. To 
accomplish this, a systems assessment was performed using calibration 
standards to challenge the mercury analyzer with a known concentration 
of mercury and to compare the analysis results with the certified 
concentration of the calibration standard. The goal of this assessment 
was an evaluation of short-term operation of the elemental mercury 
analyzer and effectiveness of routine maintenance and calibration 
activities that may impact long-term operation of the instrument. The 
third objective was to establish a confidence level associated with the 
flow determinations. Since each cell room has a unique ventilation 
system, this flow determination validation was done somewhat 
differently for each mercury monitoring system.
    The following are descriptions of the mercury monitoring system at 
each faculty and the results of the corresponding validation studies. 
The final reports for the validation program at the two Occidental 
facilities can be found in the docket to this rule (see docket items 
EPA-HQ-OAR-2002-0017-0057 and 0017-0058). The validation tests 
performed at Olin's Tennessee facility are included within the 
emissions test report described above (see docket item number EPA-HQ-
OAR-2002-0017-0056.3).
    Occidental--Delaware City, Delaware. Validation tests were 
performed by EPA at Occidental's now closed facility in Delaware the 
weeks of August 22, 2005, and September 9, 2005. The cell room at the 
Delaware City Plant was a rectangular building measuring 352 feet by 
140 feet. The cell room consisted of two independent circuits, and each 
circuit was broken into two sections, resulting in four quadrants. The 
air flow in the cell room was via natural convection; there were no 
fans to provide either induced or forced draft air flow. During the 
summer months, approximately 40 percent of the sides on the lengthwise 
span were removed to improve ventilation. There were two rows of roof 
ventilators. Each ventilator was in two discrete sections for a total 
of four sections (corresponding to the four quadrants of the cell 
room).
    The mercury monitoring system at the Occidental Delaware facility 
was a Mercury Monitoring System Model MMS-16 analyzer manufactured by 
Mercury Instruments GmbH Analytical Instruments in Germany. It collects 
samples from 16 points and analyzes

[[Page 33265]]

them for elemental mercury using a Model VM-3000 ultraviolet absorption 
analyzer. The mercury monitoring system takes one sample per minute, 
meaning that a sample is taken from each point once every 16 minutes. 
The sampling sequence is established so that a sample is taken from 
each quadrant once every four minutes. The flow rate for the building 
is estimated using a convective air flow model. The inputs to this 
model are atmospheric and ridge vent temperatures (which are 
continuously monitored), intake and discharge areas, and stack height.
    The validation of the Occidental Delaware mercury monitoring system 
confirmed the accuracy of the data collection, calculation, and 
archiving system. With regard to the data quality of the mercury 
analyzer, mercury calibration accuracy results for the Delaware City 
instrument were 20 percent and 10 percent for the mid- and high-range 
calibration standards, respectively. Specifically, the analyzer 
reported a concentration of 8 micrograms per cubic meter ([mu]g/
m3) for the 10 [mu]g/m3 standard and a 
concentration of 45 [mu]g/m3 for the 50 [mu]g/m3 
standard. These results, along with the line integrity test results, 
suggest that the high range calibration of this instrument was offset 
in a negative direction.
    A qualitative assessment of the accuracy of the Delaware City 
facility's approach to flow estimation was made with independent, on-
site, flow measurements using a vane anemometer at the roof vents. 
These measurements, covering multiple sampling points, were averaged 
and compared to the average air flow determined using the convective 
flow model equations used to estimate the flow. This evaluation showed 
that the difference between the anemometer and convective flow model 
methods was 29 percent, with the convective flow model reporting a 
higher value than the anemometer tests.
    Occidental--Muscle Shoals, Alabama. Validation tests were performed 
by EPA at Occidental Alabama the week of September 12, 2005. The 
mercury monitoring system at this facility was a Mercury Monitoring 
System Model MMS-16 analyzer manufactured by Mercury Instruments GmbH 
Analytical Instruments in Germany. The elemental mercury concentration 
is measured using a Model VM-3000 ultraviolet absorption analyzer. The 
mercury monitoring system collects samples from 65 points (at the inlet 
to each induced draft fan) and combines them in groups of three or four 
to provide a representative profile of the cell room in a 20 point 
sample array. The mercury monitoring system takes one sample per 
minute, meaning that a sample is taken from each point once every 20 
minutes. We previously described the cell room at Occidental Alabama, 
above.
    To estimate the flow rate from the cell room, Occidental tested 
each fan to determine the flow rate at standard conditions and to 
correct the actual flow rate based on continuous monitoring of 
temperature, pressure, and humidity. The assessment of the accuracy of 
the Muscle Shoals facility's flow estimation procedure was made with 
independent, on-site, flow measurements at each of the 65 fan outlets. 
The total flow through all 65 fans was measured at five points within 
the fan exhaust area using an anemometer. The exhaust flow from each 
fan was determined by averaging these five flow values. Total flow from 
the cell room was determined by subsequently summing the flow from each 
fan during the test period. The difference between the anemometer and 
fan flow model methods was slightly more than 7 percent, with the 
exhaust fan model reporting a higher value than the anemometer 
validation tests.
    The validation of the Occidental Alabama continuous mercury 
monitoring system confirmed the accuracy of the data collection, 
calculation, and archiving system of the facility. The mercury 
calibration accuracy results for the Muscle Shoals facility instruments 
were 4.0 percent and 0.2 percent, for the mid- and high-range 
calibration standards, respectively. These results indicate that the 
Muscle Shoals mercury analyzer was in good operating condition with no 
apparent calibration problems at the time of the validation test.
    Olin--Charleston, Tennessee. Validation tests were performed by EPA 
at the Olin Tennessee facility during the month of September 2006. We 
previously described the cell rooms at the Olin Tennessee plant, above. 
This facility has two separate mercury monitoring systems: One for the 
E510 cell room and one for the E812/E812 Expansion rooms. These mercury 
monitoring systems are Mercury Monitoring System Model MMS-16 analyzers 
manufactured by Mercury Instruments GmbH Analytical Instruments in 
Germany. The mercury monitoring system collect samples from individual 
points and analyze them for elemental mercury using a Model VM-3000 
ultraviolet absorption analyzer. In each of the cell rooms, there are 
five sampling points evenly spaced along the ventilators. In addition 
to the sample points in the ventilators (five for the E510 system and 
ten for the E812/812 Expansion system), each mercury monitoring system 
has one sample point dedicated to continuously measuring mercury for 
point sources subject to the 2003 Mercury Cell MACT, and one point used 
for calibration. Each point is sampled for one minute and the 
concentration is held and used in calculating the overall cell room 
average concentration until the point is sampled in the next cycle. 
Hourly and daily rolling averages are then calculated and stored. The 
flow rates for the cell rooms are estimated separately using a 
convective air flow model. The inputs to this model are atmospheric and 
ridge vent temperatures (which are continuously monitored), intake and 
discharge areas, discharge height, and fans on/off operation.
    The mercury calibration accuracy results for the instrument in the 
E510 cell room were approximately 8 percent and 19 percent for the mid 
and high range calibration standards, respectively. For the E812/812 
Expansion System, the results were approximately 5 percent and 20 
percent for the mid and high range calibration standards, respectively. 
Both analyzers indicated higher concentrations than the certified 
calibration standards provided by the manufacturer.
    Manual flow measurements were made in each of the cell room roof 
vents using a vane anemometer. These manual flow measurements were not 
compared directly with flow rates estimate by Olin's convective flow 
model. The accuracy of the facility's model was assessed in a two-step 
process. The manual measurements for the E510 cell room were first 
compared with the air flow measurements estimated using the optical 
anemometer in the EPA test, and then compared with the estimates from 
the Olin flow model. The accuracy determination between the optical 
flow monitor and the manual flow measurements was slightly lower than 
10 percent. The flow rate estimated using the Olin flow model was 
approximately 5 percent higher than the flow rate measured by the 
optical flow monitor over the entire testing period.
c. Analyses of Cell Room Maintenance Logs and Mercury Emissions Data
    Occidental also provided detailed maintenance records for the April 
through November 2005 (Delaware) and August 2005 through January 2006 
(Alabama) time periods in addition to their emissions data. They also 
provided production data and details of ``alarm events'' for this 
period, where an alarm event was a situation in which the monitoring 
system recorded a mercury concentration above established action 
levels. When such an alarm occurred,

[[Page 33266]]

Occidental personnel were dispatched to the area of the cell room where 
the elevated concentration was detected to identify the specific cause 
and to take corrective actions. We performed an analysis of the effect 
of maintenance activities, alarm events, production levels, and ambient 
conditions on daily fugitive mercury emission levels. While we 
recognize that maintenance activities and alarm events can result in 
short-term spikes in emissions, our analyses of the data did not show 
any correlation between daily fugitive mercury emissions and these 
events. The only factor that showed any correlation, albeit weak, to 
daily emissions was the ambient temperature. The report of these 
analyses can be found in the docket.
d. No Significant Fugitive Sources of Mercury From Outside the Cell 
Room
    In addition to obtaining total site emission estimates at 
Occidental Alabama, we attempted to ascertain whether fugitive sources 
outside of the cell room were contributors of measurable emissions by 
performing a material balance on the contributors to the total site 
emissions and solving for the outside fugitive component.
    The ``total site'' mercury emissions for this study included 
emissions via the cell room ventilation system, the stacks/point 
sources (thermal mercury recovery unit vent, hydrogen by-product vent, 
end-box ventilation vent), and any fugitives that occurred outside of 
the cell room in adjacent process areas. From a material balance 
analysis of these data, we concluded that fugitive sources outside the 
cell room do not contribute measurable mercury emissions when compared 
to fugitive emissions from the cell room (see docket items EPA-HQ-OAR-
2002-0017-0056.5 and 0017-0056.6).
e. New EPA Fugitive Mercury Emission Estimates for Cell Rooms
    We used eight separate fugitive mercury emission data sets from 
three different mercury cell chlor-alkali plants in 2005 and 2006 to 
produce a new estimate of fugitive mercury emissions from cell rooms. 
The time periods of data collection range from 6 weeks to over 30 
weeks, all of which provided an opportunity to include a complete range 
of maintenance activities and operating conditions. Two of the data 
sets were generated via EPA-sponsored test programs and the others were 
collected from cell room mercury monitoring systems that were validated 
by EPA. Summaries of the data sets can be found in the docket.
    The daily mercury emission rates extrapolated from these data sets 
ranged from around 20 to 1,300 g/day per facility. The average daily 
emission rates ranged from around 420 g/day to just under 500 g/day per 
facility, with the mean of these average values being slightly less 
than 450 g/day per facility.
    The purpose of this effort was to address whether the fugitive 
emissions from a mercury cell chlor-alkali plant are on the order of 
magnitude of the historical assumption of 1,300 g/day (or 0.5 tpy per 
plant) or on the order of magnitude of the unaccounted for mercury in 
2000 (3 to 5 tpy per plant, which equates to around 10,000 g/day). The 
information we obtained shows that fugitive emissions are on the order 
of magnitude of the historical assumption of 1,300 g/day. There was no 
evidence obtained during any of the studies that indicated that 
fugitive mercury emissions were at levels higher than 1,300 g/day. In 
addition, all of the studies that produced these data were of 
sufficient duration to encompass all types of maintenance activities, 
including the major ``invasive'' procedures that were not conducted 
during the earlier test at the Olin Georgia facility. The length of 
these studies was also sufficient to include emissions from a variety 
of process upsets, such as: Liquid mercury spills, leaking cells, and 
other process equipment, and other process upsets (see docket items 
EPA-HQ-OAR-2002-0017-0021 and 0017-0029).
    The results of the almost one million dollar study of fugitive 
emissions from mercury cell chlor-alkali plants sponsored by EPA 
enables us to conclude that the levels of fugitive emissions for 
mercury chlor-alkali plants are much closer to the assumed emissions in 
the part 61 Mercury NESHAP, of 1,300 g/day/plant (around 0.5 tons/yr/
plant) than the levels assumed by NRDC (3 to 5 tons/yr/plant). The 
results of this study suggest that the emissions are routinely less 
than half of the 1,300 g/day level, with overall fugitive emissions 
from the five operating facilities estimated at less than 1 ton per 
year of mercury.
f. Conclusions on the Use of Mercury Monitoring Systems as a Work 
Practice Tool
    In the data we obtained or examined, we saw discrepancies between 
the measured concentrations and the calibrated standards, and 
differences between the flow rates estimated by the cell room systems 
and those estimated by anemometers (manual or optical), as summarized 
above. The differences for the measurement of the mercury concentration 
were as high as 20 percent, and the differences in the measurements for 
the flow rates were as high as 29 percent. Such differences lead us to 
conclude that these systems would not be suitable to accurately 
demonstrate compliance with a numeric standard, because of the 
potential for errors in compliance determinations due to uncertainties 
in the measurement techniques. However, since the goal of this effort 
was to assess the order of magnitude of fugitive mercury emissions from 
the cell room, we concluded that data from these systems were 
appropriate for that purpose since the differences were well within an 
order of magnitude.
    Our observations at these three plants during the validation 
programs resulted in recognition of the ability of the mercury 
monitoring system to be used as a work practice tool to reduce fugitive 
emissions in the cell room. When the 2003 Mercury Cell MACT was 
promulgated, we thought that the mercury monitoring system could help 
identify problems before significant emission events occurred. However, 
at that time no mercury cell plant in the United States had installed 
such technology so there was no opportunity to assess their 
effectiveness. Now, with data from the three plants described above, we 
can conclusively say that the mercury monitoring systems aid in the 
identification and correction of fugitive emission problems and help 
plants refine their standard operating procedures and work practices to 
further reduce emissions. Therefore, we believe that the use of such 
systems as a tool to determine the effectiveness of work practices has 
been demonstrated. We estimate that the cost of installing a system in 
a cell room is about $120,000, which equates to a total annual cost 
(including annualized capital cost and operation and maintenance costs) 
of slightly over $25,000 per year. We believe that in the long term 
these systems will result in continued decreases in fugitive mercury 
emissions as plants will be able to identify emission-reducing 
improvements in their processes and practices. Therefore, we are 
proposing to require all mercury cell chlor-alkali plants to install 
cell room mercury monitoring systems and to develop a cell room 
monitoring plan.
g. Estimate of the Efficiency of the Cell Room Monitoring Program To 
Reduce Fugitive Emissions
    In the 2003 Mercury Cell MACT, we noted our inability at that time 
to quantify the emission effects of adopting the cell room work 
practices, a point also noted by NRDC in its petition for

[[Page 33267]]

reconsideration. However, we are now able to better estimate the 
emissions reductions achieved by the cell room monitoring program and 
work practices for these amendments using the results of the test 
programs and other information gathering efforts, as described above.
    We estimated that baseline mercury emissions prior to the 2003 
Mercury Cell MACT were 1,300 g/day per facility (68 FR 70923). This 
equated to nationwide pre-MACT baseline fugitive emissions of 4.7 tpy. 
The test program data suggest that on average, the fugitive mercury 
emissions from a single facility are approximately 450 g/day, which 
equates to nationwide emissions of 0.9 tpy. Therefore, we estimate that 
the combination of the work practices promulgated in the 2003 Mercury 
Cell MACT combined with cell room monitoring reduces fugitive mercury 
emissions from a single facility by over 65 percent from the pre-MACT 
levels. On a nationwide basis, we estimate that fugitive mercury 
emissions have been reduced by approximately 86 percent, including 
plant closures.
    The point source emissions (from hydrogen vents, end-box 
ventilation systems, and mercury recovery units) from the five mercury 
cell plants expected to be in operation after these amendments are 
finalized are around 0.4 tons/yr total. Therefore, our estimate of the 
nationwide total mercury emissions from all emission sources (point and 
fugitive) at these plants is around 1.3 tons/yr.
2. Elimination of Uncertainty Regarding the ``Missing'' Mercury
    Mercury is not consumed in the mercury cell chlor-alkali plant 
process. Therefore, in theory, the amount of mercury that is added to 
the process should be equal to the amount of mercury that leaves the 
process in either air, water, or waste pathways. In other words, the 
mercury going into the system should approximately equal the mercury 
leaving the system, where the ``system'' is the entire plant. 
Historically, the industry has had a difficult time closing this 
mercury balance, as the amount of mercury added has exceeded the amount 
measured in the wastes, wastewater, products, and air leaving the 
plant. This difference has been referred to as the ``missing'' or 
unaccounted mercury. The primary basis for NRDC's estimates of fugitive 
mercury emissions from mercury cell chlor-alkali plants was the 65 tons 
of mercury that could not be fully accounted for by the industry at 
that time in their plant-wide inventories (in 2000).
    The EPA emissions testing and data gathering efforts discussed 
above did not independently resolve the unaccounted mercury issue. 
However, since promulgation of the 2003 Mercury Cell MACT, the level of 
mercury that is unaccounted for by the industry has diminished 
drastically. The industry reported a total of 7 tons of unaccounted for 
mercury in 2004, and 3 tons in 2005,\a\ with the estimate for 2006 even 
lower.
---------------------------------------------------------------------------

    \a\ ``NINTH ANNUAL REPORT TO EPA for the Year 2005, May 15, 
2006.'' http://www.epa.gov/region5/air/mercury/9thcl2report.pdf.
---------------------------------------------------------------------------

    This reduction in the unaccounted mercury is likely due to 
increased efforts by the affected industry to inventory and track 
mercury in their plants, rather than to large reductions in mercury 
being released to the air, water, or in wastes. During our visits to 
mercury cell plants since promulgation of the 2003 Mercury Cell MACT, 
we have developed a fuller understanding of the components of a plant-
wide mercury balance.
    One of the most significant improvements in estimating this balance 
has been in the estimation of the amount of mercury in the cells. Most 
plants now utilize a radioactive tracer method to estimate the mercury 
inventory in the cells. Previously, some plants did not use scientific 
methods to conduct an inventory of the mercury in the cells. The 
radioactive tracer method is accurate to around 1 percent. So, for a 
mercury cell plant that has about 300 tons of mercury in the cells, 
this error could cause the mercury balance to be inaccurate by about 3 
tons. For plants that did not conduct a scientific inventory, their 
errors could result in significantly greater variability in the mercury 
inventory estimates for the mercury cells. If each of 10 plants had 
only factors of two errors in the accuracy of their mercury cell 
measurements, the effect could be 60 or more tons of unaccounted 
mercury for the cells alone.
    Another area where significant improvement in the mercury balances 
has occurred is in estimating the amount of liquid mercury present in 
pipes and other process equipment. As plants perform maintenance on 
process equipment, they have measured the amount of mercury recovered 
and have developed accumulation factors that are now incorporated into 
the mercury balances procedures.
    The 3 tons of unaccounted mercury reported in 2005 for the eight 
plants then in operation is, on average, approximately 750 pounds (lb) 
per plant. Significantly contributing to this number are the 
uncertainties in the various measurement techniques used to develop the 
inventory. While the affected industry must continue to strive to 
account for every pound of mercury that enters their processes, the 
degree of uncertainty regarding the unaccounted mercury has been 
substantially reduced since the time of promulgation of the 2003 
Mercury Cell MACT.
3. Emission Limitation for Cell Room
    Two of the issues raised by NRDC in its petition for 
reconsideration are related to their objection that the 2003 Mercury 
Cell MACT did not include a numeric emission standard for fugitive 
emissions from the cell room. First, NRDC states that EPA failed to 
adequately justify that a numeric emission limitation was not feasible 
per the criteria prescribed in section 112(h) of the Clean Air Act 
(CAA). These criteria govern EPA's decisions to require a work practice 
standard (or a design, equipment, or operational standard) in lieu of a 
numerical standard under section 112. The CAA section 112(h)(1) 
provides that the EPA can prescribe, consistent with sections 112(d) or 
(f), a work practice if in the judgment of the Administrator it is not 
feasible to prescribe or enforce an emission standard. The CAA section 
112(h)(2) then defines the phrase ``not feasible to prescribe or 
enforce an emission standard'' to mean either ``(A) a hazardous air 
pollutant or pollutants cannot be emitted through a conveyance designed 
and constructed to emit or capture such pollutant, or that any 
requirement for, or use of, such a conveyance would be inconsistent 
with any Federal, State or local law, or (B) the application of 
measurement methodology to a particular class of sources is not 
practicable due to technological and economic limitations.'' NRDC 
argued that EPA did not provide sufficient rationale that a numeric 
limit for the cell room is infeasible in order to support a work 
practice standard in lieu of a numeric standard. Rather, NRDC referred 
to the EPA test program at Olin's Georgia plant in 2000 as evidence 
that the technology is available to monitor the cell room. Second, NRDC 
states that EPA illegally eliminated the 2,300 g/day limit on plant-
wide mercury emissions that existed under the part 61 Mercury NESHAP.
    Both of NRDC's objections regard the 2003 Mercury Cell MACT's 
addressing of emissions from the cell rooms only through maintenance 
activities. NRDC noted in their petition that while EPA stated that we 
expected these maintenance activities would minimize

[[Page 33268]]

mercury emissions, we did not quantify the effect adopting these 
practices would have on the emissions.
    In setting the work practice standards in the form of maintenance 
activities in the 2003 Mercury Cell MACT, we referred to section 112(h) 
of the CAA to provide clarification on how EPA must determine the 
feasibility of prescribing or enforcing an emission standard. NRDC 
claims that EPA failed to provide adequate justification that any of 
the section 112(h)(2) conditions were met, and therefore that we did 
not validly conclude that the establishment or enforcement of a numeric 
emission limitation is infeasible.
    We continue to maintain that it is not feasible to prescribe or 
enforce an emission limitation for fugitive emissions from the cell 
room. We also maintain that fugitive emissions from mercury cells and 
associated equipment is a clear example of the type of situation to be 
addressed by the provisions of section 112(h). The various points 
leading to our opinion on the feasibility of establishing an emission 
standard, as well as our response to the claim that we inappropriately 
removed a previously existing standard, are discussed below.
a. Mercury Emissions From Mercury Cells and Associated Equipment Cannot 
Be Emitted Through a Conveyance Designed and Constructed To Emit or 
Capture Mercury
    In its petition, NRDC discusses the ``cell room'' as if the room 
itself is the source of mercury emissions. This perception 
oversimplifies the actual situation. There are numerous potential 
sources of fugitive mercury emissions associated with mercury cells, 
ranging from the cells and decomposers to the hydrogen processing 
system to hundreds of pumps, valves, and connectors in the process 
piping. On average, cell rooms contain around 60 mercury cells, each 
with a decomposer. Fugitive mercury emissions primarily occur when the 
cells and the other process equipment develop leaks.
    EPA has a long history of demonstrating that ``equipment leaks'' in 
the chemical industry are justifiably regulated by design, equipment, 
work practice, and operational standards in accordance with section 
112(h). One of the best examples of EPA's regulation of equipment leaks 
is the Hazardous Organic NESHAP, or HON (40 CFR part 63, subpart H), 
which regulates equipment leaks from the synthetic organic chemical 
manufacturing industry through only work practices 57 FR at 62666 
(December 31, 1992). A few examples of many other MACT standards that 
use similar work practice programs to address equipment leaks include 
the Gasoline Distribution MACT (40 CFR part 63, subpart R) 59 FR at 
5868 (February 8, 1994); the Generic MACT which covers numerous source 
categories (40 CFR part 63, subparts TT and UU) 63 FR at 55197 (October 
14, 1998); and the Miscellaneous Coatings MACT (40 CFR part 63, subpart 
HHHHH) 67 FR at 16168 (April 4, 2002).
    However, design, equipment, work practice, and operational 
standards are not unique to organic HAP emissions. Other examples 
include the MACT for Hydrogen Fluoride, which is covered under the 
Generic MACT cited above and the Coke Ovens Pushing, Quenching, and 
Battery Stacks MACT (40 CFR part 63, subpart CCCCC) 66 FR at 35338 
(July 3, 2001).
    We do not believe that the cell room building can be considered as 
a conveyance designed and constructed to emit or capture mercury. The 
primary purpose of the cell room building is not to capture mercury 
emissions, but rather, to protect the process equipment from the 
weather and other potentially damaging elements. Similarly, the primary 
purpose of the ventilation systems in the cell room is to remove the 
heat generated in the electrolytic process, and not to remove the 
mercury. As noted earlier, there are numerous sources of fugitive 
emission sources in the cell room, ranging from the large cells and 
decomposers to individual valves. In order to effectively emit and 
capture mercury emissions from these sources, separate enclosed 
conveyance systems would need to be designed and constructed for 
individual potential emission sources or for groups of potential 
emission sources. Even if construction of such enclosures was 
physically possible, it would severely limit access to process 
equipment, thus hindering plant personnel from performing maintenance. 
This could, in effect, result in increased fugitive emissions.
    Therefore, due to the nature of the sources of fugitive emissions 
from mercury cells and associated equipment, we conclude that these 
emissions cannot be emitted through a conveyance designed and 
constructed to emit or capture mercury.
b. The Application of Measurement Methodology to Fugitive Emission 
Sources From Mercury Cells and Associated Processes in Cell Rooms for 
Compliance Purposes is not Practicable due to Technological and 
Economic Limitations
    In the 2003 Mercury Cell MACT, we stated that our reason for 
establishing work practices instead of numeric emission limits was 
based on factors associated with the practicality and feasibility of 
setting a limit against which compliance realistically can be measured 
and enforced. EPA cited three reasons for our conclusion in the 2003 
Mercury Cell MACT:

    (1) Mercury emission monitors have not been used in the past to 
monitor fugitive emissions at mercury cell chlor-alkali facilities 
for compliance demonstrations;
    (2) Variability in the number and location of exhaust vents at 
these facilities affects the amount and potential variability of air 
moved through the cell rooms, thus affecting calculations of 
fugitive mass emission rates; and
    (3) Variability of the cell room roof configurations within the 
industry affects the feasibility of using continuous mercury 
monitoring systems at each facility.

    While NRDC did not directly refute these statements, it provided 
three specific points to support its view that emissions from cell 
rooms could be feasibly measured from a technological perspective: (1) 
Although EPA envisioned that chlor-alkali plants could install cell 
room mercury vapor monitoring to comply with the 2003 Mercury Cell 
MACT, EPA did not show why this monitoring could not also 
quantitatively measure mercury emissions from the cell room for a 
standard; (2) since all of the operating plants already conduct basic 
monitoring of the cell room in keeping with Occupational Safety and 
Health Administration (OSHA) standards for worker exposure to mercury, 
EPA should also be able to require testing for its own standards; and 
(3) EPA ignored and failed to take advantage of a substantial EPA 
monitoring initiative at the Olin Georgia mercury cell plant, launched 
in 2000, which demonstrated that a measurement program needed to 
support an emission limit can be feasibly applied to the cell room. 
According to NRDC, the mercury vapor monitoring program required by the 
2003 Mercury cell MACT and the monitoring programs conducted by mercury 
cell plants to comply with OSHA standards are proof that a numeric 
standard is technically feasible.
    We know that the two types of monitoring cited by NRDC can be used 
reliably to identify leaks and thereby reduce fugitive mercury 
emissions. The floor-level monitoring program of the 2003 Mercury Cell 
MACT, which is used to identify potential mercury leaks and other 
problems that could result in increased fugitive mercury emissions, is 
similar to the use of Method 21 to identify leaking equipment in 
volatile organic chemical service.

[[Page 33269]]

    Method 21 requires that a portable instrument be used to detect 
volatile organic compound (VOC) leaks from individual sources such as 
pumps, valves, etc. This instrument, often called a ``sniffer,'' 
measures the VOC concentration. Concentrations above specified levels 
that are defined to constitute a leak result in a requirement for 
corrective action to repair the leak. Though Method 21 is an extremely 
useful method for identifying leaking equipment, it could not and has 
not ever been required to demonstrate compliance with a numerical 
emission standard. In fact, section 2.1 of Method 21 specifically 
states ``This method is intended to locate and classify leaks only, and 
is not to be used as a direct measure of mass emission rate from 
individual sources.''
    The OSHA worker safety program requires plants to measure mercury 
concentrations in areas where workers could be exposed to mercury 
vapor. According to OSHA standards, employee exposure to airborne 
mercury compounds may not exceed an 8-hour time-weighted average limit 
of 1 mg/10 M3 (0.1 mg/M3). Mercury cell plants 
typically comply with this standard by periodically measuring the 
mercury concentration at selected points throughout the cell room at 
the floor level. If concentrations approach the exposure limit, workers 
are required to wear respirators to lessen their exposure in areas 
where the high concentrations were identified. However, these 
measurements of employee exposure to mercury vapor do not represent the 
mercury concentration from the entire cell room and cannot be linked to 
continuous compliance with a numeric standard.
    The EPA test at Olin's Georgia facility in 2000 not only provided 
insights into monitoring techniques that could be implemented at 
mercury cell plants to help reduce fugitive emissions, it also helped 
answer some of the questions regarding the magnitude of fugitive 
mercury emissions at mercury cell plants. This knowledge and experience 
were a key aspect of our conclusions that a cell room monitoring 
program could be an effective means of reducing fugitive emissions. The 
success of this test program also played a large role in moving the 
industry forward to develop and implement cell room monitoring programs 
that are proving to be valuable in minimizing potential mercury 
emission events in a manner not previously possible.
    However, the Olin Georgia test program was not used to demonstrate 
the ability of the Olin Georgia plant, or any other facility, to comply 
with a numeric emission standard. In the conclusions of the test report 
from the Olin Georgia tests, it was stated that ``roof vent 
instrumentation may be a useful tool for process monitoring in some 
facilities to identify problems in the operation of the cells that may 
require corrective action.'' In the report for the Olin Georgia study, 
it is further noted that cell room conditions changed rapidly, which 
affected their emissions measurements; therefore, mercury emission data 
collection worked best when it was taken over a short period of time. 
It was also stated in the Olin Georgia report that the mercury 
concentrations in the roof vent were not homogeneously stratified and 
the concentration of mercury was not consistent along the length of the 
ventilator.
    We do not agree with NRDC that the success of the Olin Georgia 
tests can be extrapolated to the mercury chlor-alkali industry's 
ability to quantitatively measure fugitive emissions from all mercury 
cell rooms for the purposes of an emission standard. We provide 
additional information on this subject, below.
    Olin Georgia Cell Room Configuration--The Olin Georgia cell 
building is a single structure that is approximately 200 feet long and 
100 feet wide. The peak of the building is around 50 feet tall, and 
there is a single ventilator that runs the entire length of the 
building at the peak. The building has two stories, with the bottom 
floor open to the atmosphere on three sides. The second floor, which 
contains the mercury cells and decomposers, has wall panels that can be 
opened or closed depending on ambient conditions. Ventilation occurs 
via natural convection. Therefore, in periods when ambient temperatures 
are higher and the sides are opened, the flow rate through the building 
increases significantly.
    In EPA's Olin Georgia study, the mercury concentration was measured 
by a UV-DOAS, and an optical scintillometer (anemometer) was used to 
measure the air flow rate from the cell room. A single beam from each 
of these instruments was shot along the path of the ventilator slightly 
above the ``throat'' of the ventilator. A preliminary hypothesis might 
be that concentration and flow measurements taken along this exit point 
could provide a ``reasonable representation'' of the emissions from the 
cell building. However, a ``reasonable representation'' to obtain an 
estimate of mercury emissions for monitoring purposes is not equivalent 
to an ``exact measurement'' for the purpose of demonstrating compliance 
with a numeric emission standard. There were several aspects of the 
Olin Georgia study that prevent us from considering the measurement 
methodologies used in this study as methods to determine compliance, 
not the least of which is the potential adverse effect of high 
electromagnetic field on air flow measurement made with the current 
state-of art instrument operation. These include the variability of air 
flow due to the bottom floor being open to the atmosphere on three 
sides, and the second floor, which contains the mercury cells and 
decomposers, having wall panels that are open or closed depending on 
ambient conditions, with the ventilation occurring via natural 
convection, hence the inherent variability.
    Cell Room Configurations of Three Other Facilities in the 
Industry--Prior to the Olin Georgia tests, EPA and the industry's trade 
organization, the Chlorine Institute, worked together to examine the 
facilities in the industry to be able to select a mercury cell chlor-
alkali plant that would provide the best opportunity for a testing 
program to be successful. Olin's Georgia, plant was a clear choice for 
this program, given the configuration of the cell room and the 
ventilation system. The cell rooms at many of the other operating 
mercury cell plants, however, were not nearly as conducive to accurate 
measurement of flow and concentration.
    As the first example, Olin Tennessee has three cell rooms adjacent 
to one another in one cell building. At this facility, the bottom floor 
is largely open on all sides. Two of the cell rooms are simple 
rectangular designs with an enclosed space for control equipment 
between them. One of these cell rooms has wall panels that can be 
removed on three sides. The second of these cell rooms has removable 
panels on the ends, but is fully open to the third cell room on the 
side opposite the control equipment. The third cell room has another 
industrial process sharing the building at one end, and has removable 
panels on two of the walls. Each of the three cell rooms has a full 
length, natural draft ventilator mounted on the roof. Although the room 
ventilation is designed to allow the hot air to naturally flow out to 
the cool outside environment (convective), fans have been installed at 
the cell floor level around the perimeter of the first two cell rooms 
to move the cool air to flow in and around key work areas. In addition, 
high velocity fans were installed near the central control equipment 
space to aid air movement. There is also cross-mixing of air flow 
between the three cell rooms. Although we used one of the cell rooms 
for our 2006 monitoring study,

[[Page 33270]]

described in detail above, we rejected the other two rooms based on the 
same analysis that we used to choose the E510 room. The inability to 
accurately estimate air flow in two of these three cell rooms would be 
a barrier to quantitatively estimating a flow rate and in turn an 
emission rate for compliance purposes.
    As another example, the cell room building at the Pioneer mercury 
cell chlor-alkali plant in St. Gabriel, Louisiana, has a rectangular 
shape, with the bottom floor basically open on all sides. The roof over 
the upper floor where the mercury cells are housed is double-pitched to 
produce two bays, with a full-length vent along each roof ridge that 
allows convective air flow out of the cell building. In addition, there 
are induced draft fans in each bay along the narrow (end) wall of the 
cell room to pull air out of the room. Therefore, the ventilation is a 
combination of convection and induced draft in a number of directions.
    A third example is the ventilation for the cell room at ERCO's 
mercury cell chlor-alkali plant in Port Edwards, Wisconsin, which 
consists of three different types of vents on the cell room roof. Two 
natural convection ridge ventilators are located at the two roof peaks 
of the building. Each ridge is equipped with dampers. Six exhaust fans 
are located on the cell room roof on either side of the roof gutter 
running down the center of the building. The round opening for these 
exhaust fans is approximately six feet in diameter. Eight rectangular 
natural convection ventilators are also located on the roof, on either 
side of the roof gutter running down the center of the building, 
between the ridge ventilators and the exhaust fans. The windows and 
doors to the cell room are opened or closed as needed to control the 
temperature in the cell room. In the summertime nearly all the doors 
and windows are open, and in the wintertime they are nearly all shut. 
In addition, there are two adjoining buildings with openings to the 
cell room.
    From the above descriptions of cell rooms at Olin Georgia and three 
other facilities in the industry, the single UV-DOAS and optical 
anemometer system employed in the roof vents at the Olin Georgia plant 
would not be sufficient to quantitatively measure mercury emissions 
from this facility or any other cell room for compliance with a 
standard. Specifically, with the natural drafts, numerous ridge 
ventilators and other discharge points from these cell rooms, it would 
not be feasible to configure a system using multiple instruments to 
accurately measure the concentration and flow rate of the exhaust 
streams over all operating time periods to comply with an emission 
standard. The detailed cell room design information and test results 
described above for facilities in this industry supports our conclusion 
in the 2003 Mercury Cell MACT that it is not technologically feasible 
to accurately measure the mercury emissions from mercury cell rooms 
throughout the industry in a manner sufficient for compliance with an 
emission standard.
    Estimating Building Replacement Costs--While this does not relate 
to identification of the MACT floor and, as discussed below, we do not 
believe it is practical to impose such a requirement as a beyond-floor 
requirement, for the purposes of this proposed rule we explored a 
scenario where all facilities would tear down their existing cell room 
structures and replace them with a design equivalent to Olin Georgia's. 
We chose this facility since it was used to provide short-term cell 
room mercury emission estimates that have been generally accepted as a 
good representation of the magnitude of facility cell room emissions 
during the tests, and was cited as an example by NRDC in its petition.
    We estimate that the cost for such construction efforts could be in 
the range of $10 to $20 million per facility. Documentation of this 
analysis can be found in the docket. We conclude that this is not an 
economically feasible option. We also do not believe that an industry-
wide construction effort of this type to be practical, given that we do 
not expect any difference in the emission reduction that would be 
achieved by a numeric standard as opposed to combination of a cell room 
monitoring program and work practices that would be required if we 
promulgated today's proposed amendments. Details of our cost estimate 
can be found in the docket.
c. Part 61 Mercury NESHAP Allowed Facilities to Assume Cell Room 
Emissions of 1,300 g/day and did not Require Compliance with an 
Emission Standard
    With regard to the second objection raised by NRDC relating to the 
lack of a numeric standard (i.e., that EPA illegally eliminated the 
numeric emission limit for the cellroom in the part 61 Mercury NESHAP), 
NRDC stated that this long-existing regulation included a numeric 
emission standard that applied plant wide, which included the cell 
room. NRDC also stated in its petition that one alternative for 
demonstrating compliance with a standard such as that in the part 61 
Mercury NESHAP is an EPA-approved emission test method, such as EPA 
Method 101 (part 61, Appendix B).
    The part 61 Mercury NESHAP contained a plant-wide mercury emission 
limitation of 2,300 g/day, which included a 1,000 g/day limit for stack 
sources of mercury (end-box ventilation system and hydrogen vents). 
However, there was no other limit specified as such in the rule. The 
stack limit at 1,000 g/day and the total facility limit of 2,300 g/day 
effectively resulted in a 1,300 g/day default limit for fugitive 
mercury sources from the cell room by subtraction, but no such separate 
limit for fugitive emissions existed in the rule.
    The part 61 Mercury NESHAP further required compliance tests using 
Methods 101 and 102 for the point sources. While the part 61 Mercury 
NESHAP did include testing provisions for cell room ventilation systems 
using Method 101, that rule also allowed sources to alternatively 
demonstrate compliance with the rule by using approved design, 
maintenance, and housekeeping practices. In this case, the part 61 
Mercury NESHAP allowed facilities to assume that their cell room 
emissions were 1,300 g/day, without actually requiring them to 
demonstrate achievement of this level of emissions.
    The part 61 Mercury NESHAP applied to mercury cell chlor-alkali 
plants for more than 30 years. During that time, we are not aware of a 
single facility that has demonstrated compliance with the rule by 
conducting a test of a cell room ventilation system and showing that 
fugitive emissions were in fact no higher than 1,300 g/day. This fact 
further supports our conclusions regarding the infeasibility of 
applying measurement methodology to fugitive emissions from the cell 
rooms for purposes of demonstrating compliance with a numeric limit.
    Prior to the 2003 Mercury Cell MACT, all of the mercury cell chlor-
alkali industry instituted the design, maintenance, and housekeeping 
practices in the part 61 Mercury NESHAP and used the default 1,300 g/
day emissions assumption for fugitive mercury emissions from the cell 
room. For all practical purposes, the establishment of more detailed 
and more stringent MACT-level work practices in the 2003 Mercury Cell 
MACT was an improvement of the requirements used to comply with the 
part 61 Mercury NESHAP. This is evident in the findings of our testing 
and information gathering efforts discussed earlier, which showed cell 
room emission levels consistently lower than 1,300 g/day. As also 
discussed

[[Page 33271]]

previously, the average fugitive emission rate measured during the 
testing and other information gathering efforts was around 450 g/day. 
In 2006, the average reported mercury emissions from point sources 
averaged around 200 g/day, meaning that the overall plant average 
emission rate is on the order of around 650 g/day. A 2,300 g/day 
emission limit would not be representative of the average fugitive 
emissions level achieved by the best performing sources. In fact, a 
2,300 g/day limit represents a level of emissions that is likely three 
or four times as high as the average emissions of the worst performing 
source. Accordingly, in our view the combination of the point source 
limits and work practice requirements in the 2003 Mercury Cell MACT is 
more stringent than the 2,300 g/day emission limitation in the part 61 
Mercury NESHAP. Further, we believe the amendments proposed today 
further strengthen the fugitive emissions reduction program beyond both 
the part 61 NESHAP and the 2003 Mercury Cell MACT.
d. Conclusion Regarding the Lack of Emission Limitation for Cell Room
    In conclusion, consistent with CAA section 112(h), we believe that 
we have established in the discussions above that it is not feasible to 
prescribe or enforce an emission standard in this case. There are two 
independent bases for this conclusion. First, consistent with CAA 
section 112(h)(2)(A), we have concluded that fugitive mercury emissions 
from a mercury cell chlor-alkali plant cannot be emitted through a 
conveyance designed and constructed to emit or capture such pollutant. 
Second, consistent with CAA section 112(h)(2)(B), we have established 
that the application of measurement technology to mercury cell rooms is 
not practicable due to technological and economic limitations. Finally, 
we believe that the plant-wide emission limit from the part 61 Mercury 
NESHAP was a standard to which no mercury cell facility had ever 
demonstrated compliance by way of emissions testing, is not an 
enforceable standard today, and, more importantly, does not reflect the 
MACT level of emissions control required under CAA section 
112(d)(3)(B). Therefore, we did not unlawfully remove any actual 
requirement of the part 61 Mercury NESHAP. Instead, the 2003 Mercury 
Cell MACT adopted a set of MACT-level work practice requirements under 
section 112(h) that are more stringent in terms of controlling fugitive 
mercury emissions than was allowed in the part 61 NESHAP.
    We believe that the enhanced work practices and operational 
standards of today's proposed rule would be a more reasonable and 
effective method in reducing fugitive mercury emissions than inaccurate 
attempts to meet a numeric emissions limit. The 60 percent reduction in 
mercury emissions obtained by comparing the assumed part 61 Mercury 
NESHAP emission levels for the cell rooms to the measured post-2003 
Mercury Cell MACT emissions levels, as noted above, have shown that 
work practices alone are effective. The work practices that would be 
required in today's proposed amendments would allow sources to spend 
their time and efforts identifying and correcting problems rather than 
attempting to perform testing to determine compliance with an emissions 
limit which would not provide representative data. The detailed 
documentation of the work practices during the setting of the action 
level we are proposing in today's rule would also ensure that the 
lowest emissions levels are maintained through the year. For these 
reasons, the effectiveness of today's proposed amendments is not 
compromised by the absence of a numeric emission limit for fugitive 
emissions from the cell room.
4. Combining the Monitoring Program with Work Practices
    Section 63.8192 of the 2003 Mercury Cell MACT, ``What work 
practices standards must I meet?'', allows facilities to institute a 
cell room monitoring program to continuously monitor the mercury vapor 
concentration in the upper portion of each cell room as an alternative 
to work practice standards. One of the objections raised by NRDC was 
that this provision backtracked from the Agency's proposed work 
practice standards. NRDC pointed out that in the 2003 Mercury Cell 
MACT, EPA concluded that the housekeeping activities that facilities in 
the industry follow to comply with the part 61 mercury NESHAP 
represented the MACT floor and that requiring practices based upon the 
most detailed activities in the industry (i.e., ``beyond-the-floor'' 
practices) was justified. But NRDC was concerned because the work 
practices in the 2003 Mercury Cell MACT were optional if facilities 
chose to do continuous monitoring and, therefore, this option would 
allow sources to avoid conducting activities that represent the MACT 
floor. NRDC argued that this was a violation of section 112(d)(3) of 
the CAA, which requires all facilities to meet the MACT floor.
    We believe that facilities should continue to perform housekeeping 
activities when the action level for the cell room monitoring program 
is established. The facilities that have chosen to implement the cell 
room monitoring program have continued to perform the housekeeping 
activities. Since we know that there is benefit to doing both the 
monitoring and the work practices, we are proposing to amend the 2003 
Mercury Cell MACT to require both a cell room monitoring program and 
work practice standards. This should remove the basis for NRDC's 
objection to the 2003 Mercury Cell MACT having made the work practice 
requirements optional. Because it is our intention that the primary 
focus of the facility should be towards finding and correcting leaks 
quickly, which directly results in emission reductions, and we believe 
the level of recordkeeping for the routine work practices in the 2003 
Mercury Cell MACT detracts from the work practice efforts, we are 
reducing the burden of paperwork for the work practices, except during 
the setting of the action level. Therefore, the amendments proposed 
today would reduce the day-to-day recordkeeping provisions associated 
with the work practices and would instead include a requirement for 
weekly ``checklists'' certifying that the work practices are being 
performed.
    The proposed amendments would add the requirements for detailed 
records of work practices during the semi-annual period of 14 to 30 
days when the action level is established. Because we are proposing to 
require both work practice measures and a cell room monitoring program, 
we believe that a reduction in day-to-day recordkeeping will not 
diminish the effectiveness of the cell room fugitive emission reduction 
program.
    As part of the proposed amendments, we would eliminate the floor-
level monitoring program required in the 2003 Mercury Cell MACT for 
facilities that chose the work practice option since it would be 
redundant and a less effective alternative to the cell room monitoring 
program. The cell room monitoring program accomplishes the same 
purpose, except that it requires continuous monitoring of the mercury 
concentration. In addition to its continuous nature, the monitoring is 
also required to be conducted in the upper portion of the cell room 
building. The floor-level program primarily identifies only leaking 
equipment at the floor level. By monitoring all the process equipment, 
the cell room monitoring program would detect elevated concentrations 
from any equipment in the cell room.

[[Page 33272]]

5. Other Monitoring Amendments
    In addition to proposing to require all facilities to develop and 
implement a cell room monitoring program, we are proposing to amend 
some of the requirements of the existing cell room monitoring program 
as well as correcting errors from the 2003 Mercury Cell MACT. These 
proposed monitoring amendments are described below.
a. Establishment of the cell-room monitoring action level
    The cell-room monitoring action level of the 2003 Mercury Cell MACT 
was a concentration that set in motion a series of required procedures 
to identify and correct problems that could result in increased 
fugitive mercury emissions. To establish the action level, the 2003 
Mercury Cell MACT required that the owner or operator collect cell room 
concentration data for the first 30 days following the compliance date 
and establish an action level at the 75th percentile of the data. As 
mercury cell chlor-alkali plants installed and began to operate these 
continuous mercury monitoring systems, we became aware of several 
aspects of these provisions that could be improved. First, we believe 
that the 75th percentile is not the appropriate level for the action 
level. When the action level is exceeded, the 2003 Mercury Cell MACT 
required that owners and operators take significant actions to identify 
and correct the situation causing the increased mercury concentration. 
Establishing the level at the 75th percentile resulted in the action 
level being exceeded approximately 25 percent of the time. We would 
prefer that plant resources be expended when there is a real problem 
that can impact mercury emissions (e.g., a leak in hydrogen piping, a 
seal failure on a decomposer, etc.), rather than to constantly 
investigate and document action level exceedences caused by normal 
process variations. Therefore, we are proposing that the action level 
be established at the 90th percentile of the data set. Since this level 
would be established during the performance and documentation of the 
work practices, we believe that an action level at 90 percent would be 
sufficient to ensure proper equipment operation.
    We also have come to realize that ambient conditions (temperature, 
humidity, etc.), and the seasonal reconfiguration of the cell rooms can 
have a significant impact on the cell room concentration. Therefore, we 
are proposing that the facilities re-establish their action level at 
least once every six months. Due to the increased frequency of action 
level determinations and the work practice documentation, we are 
reducing the minimum amount of time that plants must collect data to 14 
days, although time periods up to 30 days can be used.
b. Weekly Certification of Work Practice Inspections
    Sources that elected to comply with the work practice standards in 
the 2003 Mercury Cell MACT were required to keep detailed records of 
each inspection. Sources that elected to comply with the cell room 
monitoring program were required to keep detailed records of actions 
taken whenever an action level is exceeded. We believe that if sources 
are required to comply with both the work practice provisions and the 
cell room monitoring program provisions, these levels of recordkeeping 
are not necessary. Therefore, we are proposing to eliminate the 
requirements for detailed records associated with the work practice 
inspections and instead we are proposing to require a weekly 
certification that all the required work practices are being conducted. 
We believe that it is still important that the facilities keep records 
of instances where elevated mercury concentrations are measured, along 
with records of the associated causes and corrective actions. 
Therefore, we are proposing to maintain the detailed recordkeeping 
requirements during the 14 to 30 days of setting the action level of 
the cell room monitors.
c. Miscellaneous Measurement Amendments
    Detection limit for mercury emission monitor analyzers. Paragraph 
(a)(2) of Sec.  63.8242, ``What are the installation, operation, and 
maintenance requirements for my continuous monitoring systems?,'' 
requires that mercury continuous emission monitor analyzers have a 
detector with the capability to detect a mercury concentration at or 
below 0.5 times the mercury concentration level measured during the 
performance test. Since promulgation of the 2003 Mercury Cell MACT, we 
determined that setting the analyzer detection capability in reference 
to the concentration level during the performance test could be 
problematic. We realized that a concentration of 0.5 times the mercury 
concentration could, in cases of low mercury concentrations, be 
infeasible for the monitoring devices on the market. Information 
available to us at this time shows that 0.1 [mu]g/m3 is the detection 
limit of commonly commercially available analyzers. We believe that 
analyzers with detection limits at this level are more than sufficient 
to determine compliance with the emission limitations in the 2003 
Mercury Cell MACT. Therefore, we are proposing to revise this paragraph 
to require a detector with the capability to detect a mercury 
concentration at or below 0.5 times the mercury concentration measured 
during the test, or 0.1 [mu]g/m3, whichever is greater.
    Averaging period for mercury recovery unit compliance. The 2003 
Mercury Cell MACT is inconsistent as to whether the rule requires a 
daily average or an hourly average to determine continuous compliance 
with the emissions standard for mercury recovery units found at Sec.  
63.8190(a)(3) of Sec.  63.8190 ``What emission limitations must I 
meet?''. Paragraph (b) of Sec.  63.8243, ``What equations and 
procedures must I use to demonstrate continuous compliance?'', clearly 
indicates that this averaging period is daily: ``You must calculate the 
daily average mercury concentration using Equation 2 * * *'' However, 
paragraph (b) of Sec.  63.8246, ``How do I demonstrate continuous 
compliance with the emission limitations and work practice 
standards?'', states that for each mercury thermal recovery unit vent, 
``you must demonstrate continuous compliance with the applicable 
emission limit specified in Sec.  63.8190(a)(3) by maintaining the 
outlet mercury hourly-average concentration no higher than the 
applicable limit.''
    It was our intention for compliance to be based on a daily average, 
as detailed below, and the inclusion of ``hourly'' in paragraph (b) of 
Sec.  63.8246, ``How do I demonstrate continuous compliance with the 
emission limitations and work practice standards?'', was a drafting 
error. Therefore, we are proposing to correct this error by replacing 
``hourly'' in Sec.  63.8246(b) with ``daily.'' In the proposal Federal 
Register notice for the 2003 Mercury Cell MACT (67 FR 44678, July 3, 
2002), we clearly stated our intention when we summarized the 
requirements as follows:

    ``To continuously comply with the emission limit for each by-
product hydrogen stream, end-box ventilation system vent, and 
mercury thermal recovery unit, we are proposing that each owner and 
operator would continuously monitor outlet elemental mercury 
concentration and compare the daily average results with a mercury 
concentration operating limit for the vent * * * .''
    ``Continuous compliance would be demonstrated by collecting 
outlet elemental mercury concentration data using a continuous 
mercury vapor monitor, calculating daily averages, and documenting 
that the calculated daily average values are no higher than 
established operating limits. Each daily average vent elemental 
mercury concentration greater than the established

[[Page 33273]]

operating limit would be considered a deviation.

6. Creation of the Mercury Cell Chlor-Alkali Subcategory
    As stated in the preamble to the final 2003 Mercury Cell MACT (68 
FR 70905), we divided the chlorine production source category into two 
subcategories: (1) Mercury cell chlor-alkali plants and (2) chlorine 
production plants that do not rely upon mercury cells for chlorine 
production. In December 2003 (68 FR 70949), we issued our final 
decision to delete the subcategory of the chlorine production source 
category for chlorine production plants that do not utilize mercury 
cells to produce chlorine and caustic. This action was made under our 
authority in CAA section 112(c)(9)(B)(ii), and was not challenged in a 
petition for judicial review. Nor did anyone ask us to reconsider that 
action pursuant to CAA section 307(d)(7)(B). The objection raised by 
NRDC in its petition for reconsideration of the 2003 Mercury Cell MACT 
was that by subcategorizing mercury cell chlor-alkali plants, the worst 
industry performers are insulated from controls that could otherwise be 
driven by sources with no mercury emissions at all (i.e., the non-
mercury chlorine producers), resulting in standards inconsistent with 
what NRDC believes is the MACT floor. According to NRDC, if the MACT 
floor for mercury emissions was determined for the chlorine production 
source category as a whole, the best-performing 12 percent of sources 
in the category would be mercury-free. NRDC stated that well over half 
of the chlorine production industry as a whole uses either membrane or 
diaphragm cell technology. Therefore, NRDC asserted that EPA is 
compelled by section 112(d)(3)(A) of the CAA to require sources to 
convert to a non-mercury process as MACT.
    We have a long history of using subcategorization to appropriately 
differentiate between types of emissions and/or types of operations 
when analyzing whether air pollution control technology is feasible for 
groups of sources. As we stated in the preamble to the Initial List of 
Categories of Sources under section 112(c)(1) of the CAA Amendments of 
1990, we have the authority to distinguish among classes, types, and 
sizes of sources in establishing emission standards (57 FR 31576, July 
16, 1992). Subcategories, or subsets of similar emission sources within 
a source category, may be defined if technical differences in emissions 
characteristics, processes, control device applicability, or 
opportunities for pollution prevention exist within the source 
category. This policy is supported by section 112(d)(1), the 
legislative history, our prior rulemakings, and judicial precedent.
    EPA's broad authority to establish categories and subcategories of 
industry sources is firmly established, and has been recognized as 
entitled to substantial deference by the U.S. Court of Appeals for the 
D.C. Circuit and by the U.S. Supreme Court. See, e.g., Davis County 
Solid Waste Mgmt v. EPA, 101 F.3d 1395, 1405 (DC Cir. 1996) (EPA has 
``substantial discretion to create categories of sources for which 
standards must be promulgated''); see also Lignite Energy Council v. 
EPA, 198 F.3d 930, 933 (DC Cir. 1999) (upholding EPA's refusal to 
subdivide a category and noting that the Court was ``[m]indful of the 
high degree of deference we must show to EPA's scientific judgment'' on 
this question); Chemical Mfrs. Ass'n v. EPA, 470 U.S. 116, 131 (1985) 
(``the means used by EPA to define subcategories'' under the Clean 
Water Act ``are particularly persuasive cases for deference to the 
Agency's interpretation'').
    Under CAA section 112, that authority is subject only to the 
consideration that, ``to the greatest extent practicable,'' categories 
and subcategories be established ``consistent with'' the source 
categories that EPA had established under other CAA programs (i.e., CAA 
section 111's ``new source performance standards'' (NSPS) and the 
``prevention of significant deterioration'' (PSD) program). 42 U.S.C. 
7412(c)(1). Having identified these general touchstones, however, 
Congress stated that ``Nothing in the preceding sentence limits the 
Administrator's authority to establish subcategories under this 
section, as appropriate.'' 42 U.S.C. 7412(c)(1). Further, CAA section 
112(d)(1) provides that EPA ``may distinguish among classes, types, and 
sizes of sources within a category or subcategory.'' 42 U.S.C. 
7412(d)(1). The legislative history confirms Congress' intent to give 
EPA broad discretion, noting that the CAA ``provides discretionary 
authority to the Administrator to list categories or subcategories 
under section 112(c),'' and that ``it is vital to utilize 
subcategorization to prevent the cost-ineffective application of * * * 
MACT.'' Statement of Rep. Bliley, Oct. 26, 1990, 1 Legis. Hist. at 
1225-26.
    Traditionally, EPA has established CAA section 112 subcategories 
for regulation based upon ``factors such as process operations (type of 
process, raw materials, chemistry/formulation data, associated 
equipment, and final products); emission characteristics (amount and 
type of HAP); control device applicability; and opportunities for 
pollution prevention.'' 64 FR 56493, 56494 (Oct. 20, 1999). These 
factors relate to the appropriate application and achievement of 
emission standards.
    When EPA has declined to establish subcategories for CAA section 
112 standards, we have done so because subcategorization would not 
affect the achievability of the standards, due to a lack of 
differences, for example, between sources' sizes or designs. (See, for 
example, 64 FR 52828, 52859 in regard to declining to subcategorize 
hazardous waste incinerators because it would not result in standards 
that are more achievable.) On the other hand, where differences in 
design and operation between types of sources in a category clearly do 
affect the achievability of standards, EPA has reasonably 
subcategorized. As the DC Cir. has observed, ``one legitimate basis for 
creating additional subcategories must be the interest in keeping the 
relation between `achieved' and `achievable' in accord with common 
sense and the reasonable meaning of the statute.'' Sierra Club v. EPA, 
479 F.3d 875, 885 (DC Cir. 2007)(Williams, concurring)(remanding and 
vacating NESHAP for brick and ceramic kilns on other grounds).
    One example of EPA's reasonable subcategorization that presented 
issues very similar to those raised in the chlorine production industry 
was in the NESHAP for primary copper smelters, 67 FR 40478 (June 12, 
2002). There, the existing source MACT determination focused only on 
the emissions levels achieved by primary copper smelters using the 
relatively older batch copper converter process, while the more state 
of the art continuous flash converter process, due to its unique design 
and operation, achieved significantly more stringent levels, especially 
in terms of controlling process fugitive emissions. 67 FR at 40488. 
Commenters argued that EPA should have included the flash converter 
smelters in the existing source MACT analysis, but we concluded that 
batch converters and continuous flash converters were so distinct that 
it was necessary to place them in separate subcategories and to apply 
the rule's requirements only to the batch converter smelters. 67 FR at 
40489. However, we did identify the continuous flash converter smelter 
as the ``best controlled similar source,'' and thereby required that 
level of performance as new source MACT and prohibited construction of 
new batch converter smelters. 67 FR at 40489. While this issue was not

[[Page 33274]]

challenged in the subsequent litigation of the rule, it should be noted 
that the Court was fully aware of EPA's differentiation and remarked 
upon it without criticism. Sierra Club v. EPA, 353 F.3d 976, 981 (DC 
Cir. 2004) (``The rulemaking only concerned those primary copper 
smelters that use `batch copper converters'''). We maintain that the 
creation of the mercury cell chlor-alkali chlorine production 
subcategory was warranted, was consistent with our prior practice (and, 
in particular, with the differentiated approach we took for primary 
copper smelters), and add the following in support of our conclusion.
    With regard to differences in emission characteristics, the HAP 
emitted by mercury cell chlor-alkali processes and non-mercury cell 
chlor alkali processes are different, due to the fundamental 
differences in production processes and materials used at the two types 
of plants. While chlorine and hydrogen chloride are emitted by all 
chlor-alkali processes, mercury emissions are unique to the mercury 
cell subcategory. There are no mercury emissions from chlor-alkali 
plants that utilize electrolytic cells other than mercury cells, simply 
because those plants do not use or depend upon mercury as a material in 
their production processes. Therefore, it is not realistic to think of 
those plants as ``controlling'' mercury emissions levels, or of having 
any level of performance in ``limiting'' mercury emissions. It would 
likewise be unrealistic to base a MACT level of mercury emissions 
performance on such sources, where no mercury emissions at all are even 
possible and no actual control measures are, in fact, taken to limit 
mercury emissions. Rather, within the chlorine production source 
category, these plants represent a different process type, which does 
not provide information to assess the best levels of emissions control 
performance at source types where mercury emissions in fact occur.
    Second, while chlorine and caustic are produced in all chlor-alkali 
processes via an electrolytic reaction, the processes are significantly 
different, apart from the basic difference in one subcategory using 
mercury and the other not using it. In addition, there are differences 
in the products, particularly the caustic products. The basic reaction 
that occurs in any chlor-alkali process is the electrolysis of brine, 
which contains sodium (or potassium) chloride in water, to form 
chlorine, hydrogen, and sodium (or potassium) hydroxide. However, the 
manner in which this reaction occurs and associated equipment (i.e., 
the ``cells'') is vastly different.
    In diaphragm cells, a diaphragm separates the electrolytic cell 
into an anode compartment and a cathode compartment. Chlorine is formed 
in the anode compartment, and hydrogen and sodium (potassium) hydroxide 
are produced in the cathode compartment. Membrane cells have the same 
basic design, except that the compartments are separated by a membrane 
instead of a diaphragm. The primary difference is that the membrane 
only allows migration of sodium ions from the anode compartment to the 
cathode compartment, which results in a purer raw hydroxide product. 
While cell models differ, typical diaphragm cells are around 10 feet 
wide and 8 feet long. Membrane cells are of comparable size to 
diaphragm cells.
    Mercury cells are considerably different from diaphragm and 
membrane cells. First, the reaction occurs in two distinct operations 
in two separate vessels. The electrolytic cell, which is typically 
around 50 feet long and 5 feet wide, produces chlorine gas. A separate 
decomposer, which is typically a cylindrical vessel around 5 feet tall 
and 3 feet in diameter, produces hydrogen gas and sodium (or potassium) 
hydroxide. The cell and decomposer are linked at the two ends by an 
inlet endbox and an outlet endbox.
    While the basic products are the same between mercury cell and non-
mercury cell processes, there are distinct differences in the quality 
of the products produced. The products from mercury cell processes 
include a concentrated (50 percent) hydroxide and very pure hydrogen 
and chlorine. In contrast, diaphragm cells produce very low 
concentration and impure hydroxide solutions that require expensive 
multi-stage evaporators to strengthen the solution, and the chlorine 
produced in membrane cells typically has a high oxygen content.
    Therefore, we believe that there are significant differences in 
mercury cell and non-mercury cell processes. While there may be common 
aspects of auxiliary processes (e.g., chlorine liquefaction), the most 
basic aspect of chlor-alkali facilities (i.e., the electrolytic cells 
that produce the chlorine, hydrogen, and caustic) are dissimilar.
    Finally, a comparison of mercury controls or pollution prevention 
opportunities between mercury cell processes and non-mercury cell 
processes is not possible since the non-mercury cell processes do not 
emit any mercury. We do not believe that it would be reasonable to 
impose the multi-million dollar conversion of a mercury cell process to 
a non-mercury cell process as either a control device application or a 
pollution prevention procedure for this industry. In conclusion, we 
continue to maintain that non-mercury chlor-alkali chlorine production 
processes are separate processes from mercury cell chlor-alkali 
chlorine production and, specifically, are not methods of controlling 
mercury emissions.
7. Consideration of Non-Mercury Chlor-Alkali Technology as a Beyond-
The-Floor Control Requirement
    Section 112(d)(3) of the Clean Air Act establishes the minimum 
requirements (i.e., the ``floor'') for MACT rules. Section 112(d)(2) 
requires us to consider alternatives that are more stringent than the 
MACT floor (i.e., ``beyond-the-floor'' options). In beyond-the-floor 
controls, we are required to consider the impacts that might result 
from imposing such controls, including cost, non-air quality health and 
environmental impacts, and energy requirements. In developing the 2003 
Mercury Cell MACT, we considered beyond-the-floor alternatives for 
every emission source. In fact, each numerical emission limit for point 
sources, along with the work practices for fugitive sources, represents 
a beyond-the-floor level of control. In addition, mercury emissions 
from new mercury cell chlor-alkali production facilities were 
prohibited, as we identified as the ``best controlled similar source'' 
a non-mercury chlorine production facility, even though such a source 
is not in the same subcategory as existing mercury cell chlor-alkali 
facilities. This approach is similar to how we differentiated between 
batch converter primary copper smelters (which comprised the existing 
source subcategory) and continuous flash converter smelters (which were 
not in the regulated subcategory, but drove the new source floor) in 
the primary copper smelters MACT rulemaking, discussed above. See 67 FR 
40478, 40488-89 (June 12, 2002).
    In its petition NRDC argued that the 2003 Mercury Cell MACT does 
nothing to limit the use of mercury cell technology by existing chlor-
alkali plants, and that the Agency ignored a known technique for 
reducing mercury emissions from this industry, namely, conversion to 
non-mercury processes. According to NRDC, requiring the industry to 
convert to a non-mercury process is cost-justified and would provide 
significant non-air quality benefits. In support of its argument, NRDC 
pointed to EPA's determination at proposal that a cost effectiveness of 
$9,000 per pound was warranted for the beyond-the-floor control level 
for

[[Page 33275]]

control of mercury from by-product hydrogen streams without end-box 
ventilation systems. NRDC provided an analysis that indicated the cost 
effectiveness associated with conversion of existing mercury cell 
plants to non-mercury technology ranged from $6,700 to $13,400 per 
pound. NRDC noted that the $9,000 per pound cost effectiveness, 
determined by the Agency to be warranted for by-product hydrogen 
streams without end-box ventilation systems was within this range 
calculated for conversion to nonmercury technology.
    In response to NRDC's concerns that we did not evaluate the 
conversion of mercury cell chlor-alkali production plants to non-
mercury technology, we performed an analysis to determine the capital 
and annual costs of this action. In performing the analysis, we used 
information from all readily available sources of information. A 
memorandum outlining this analysis, along with copies of all materials 
used, can be found in the docket for this rulemaking.
    The EPA test program described above showed that the fugitive 
emissions from the mercury cell room averaged less than 450 g/day (or 
360 pounds per year, lb/yr) per facility. Using this average figure for 
fugitive emissions, and 2004 TRI emissions data for point (stack) 
source emissions, we estimate that the average cost effectiveness 
associated with conversion to non-mercury technology would be 
approximately $14,000 per pound, as opposed to the $9,000 per pound 
used by NRDC as a benchmark, which is an increase of almost 60 percent.
    Further, our analysis showed that the average capital cost of 
conversion for one mercury cell chlor-alkali facility in the U.S. was 
approximately $68 million per plant. Nationwide, the capital cost was 
estimated to be nearly $340 million. The average annualized facility 
costs for this conversion were estimated to be approximately $7.5 
million or $38 million nationwide. This cost impact would be 
approximately 11 percent of revenues. In contrast, during the original 
rulemaking the total per-facility capital costs associated with 
controlling mercury from by-product hydrogen streams, end box 
ventilation systems, and mercury recovery units were estimated to be 
$180,000, with the associated annual costs approximately $160,000 per 
year. These values were estimated to be less than 0.3 percent of 
revenues. Therefore, we are proposing to reject conversion to non-
mercury technology as a beyond-the-floor control requirement because of 
the high cost impact this forced conversion would impose on the 
facilities in the industry.
    While we are not proposing to require mercury cell chlor-alkali 
plants to convert to mercury-free technology, we encourage owners and 
operators of the remaining mercury chlor-alkali plants to continue to 
explore this option. We also applaud those companies that have decided 
to convert their mercury cell plants processes to membrane cells 
voluntarily.

B. What amendments are EPA proposing?

    The proposed rule amendments resulting from our reconsideration 
efforts, as per the rationale discussed in detail above in section 
III.A, are as follows:
    (1) Daily Work Practices--These would be required for all 
facilities with weekly certification of the performance of these work 
practices;
    (2) Mercury Monitoring--This would be required for all facilities, 
with the compliance periods for implementing this requirement, as 
described below, dependent upon whether the facility currently operates 
such a system for compliance with the 2003 Mercury Cell MACT;
    (3) Documenting Work Practices--Detailed recordkeeping of the work 
practices would be required for the time period during the semi-annual 
setting and resetting of the action level of the continuous cell room 
monitors;
    (4) Setting the Continuous Monitoring Action Level-- This would be 
done for a minimum of 14 days and up to 30 days, at least every six 
months;
    (5) Action Level--This would be set at 90th percentile of the data 
acquired during the re-setting time period(s).
    (6) Compliance Period for the Amendments--All sources would be 
required to continue to comply with the 2003 Mercury Cell MACT until 
these new compliance dates, below:
    (a) For sources that had previously elected to comply with the cell 
room monitoring program, we are proposing a compliance date 60 days 
from the date the final rule amendments appear in the Federal Register. 
This will allow facilities to plan and implement the work practice 
requirements and to gather data to establish a new action level in 
accordance with the revised requirements.
    (b) For sources that did not opt to comply with the cell room 
monitoring program in the 2003 Mercury Cell MACT, we are proposing that 
they will have two years from the effective date of the final rule 
amendments to comply. We believe that this amount of time is necessary 
for these facilities to design, purchase, and install the necessary 
monitoring equipment and to develop the various aspects of the program.
    (7) Correct Compliance Errors--We are also proposing two changes to 
correct errors and to improve the compliance provisions of the rule, as 
follows:
    (a) The detection limit for mercury continuous emission monitor 
analyzers would be changed to a capability to detect a mercury 
concentration at or below 0.5 times the mercury concentration measured 
during the test, or 0.1 [mu]g/m3, whichever is greater; and
    (b) The frequency of determining continuous compliance with the 
emissions standard for mercury recovery units would be changed to a 
daily average, as in paragraph (a)(3) of Sec.  63.8190, ``What emission 
limitations must I meet?'', from an incorrect hourly average as in 
found at paragraph (b) of Sec.  63.8246, ``How do I demonstrate 
continuous compliance with the emission limitations and work practice 
standards?'', in the 2003 Mercury Cell MACT.
    (8) Revise Work Plan Notification of Compliance Status--In 
conjunction with these new requirements, we are also proposing to 
require that all plants submit a Revised Work Plan Notification of 
Compliance Status report 60 days after their compliance date. This 
report would include certifications that the work practices and cell 
room monitoring program are being followed. The cell room monitoring 
plan, including the initial action level and supporting data, would 
also be required to be submitted in this report. In order that the 
Revised Work Plan Notification of Compliance Status would be complete 
with all information related to the work practice standards, we are 
also proposing that the wash down plan and the mass of virgin mercury 
added to the cells for 2001 through 2006 be re-submitted. This Revised 
Work Practices Notification of Compliance Status report would not 
require any information related to compliance with the emission 
limitations in paragraph (a)(3) of Sec.  63.8190, ``What emission 
limitations must I meet?''
    (9) Applicability of Requirements for Thermal Recovery Units at 
Closed or Converted Facilities--As several mercury cell chlor-alkali 
plants have closed or converted to membrane cells since the 
promulgation of the 2003 Mercury Cell MACT, the question has arisen 
whether the thermal recovery units that continue to operate in order to 
assist in the clean up of the site after the mercury cells have ceased 
to operate are subject to the emission limitations for thermal recovery 
units in Sec.  63.8190,

[[Page 33276]]

``What emission limitations must I meet?'' specifically paragraph 
(a)(3).
    In answering the question ``Am I subject to this subpart?'', 
paragraph Sec.  63.8182(a) states, ``You are subject to this subpart if 
you own or operate a mercury cell chlor-alkali plant.'' In addressing 
``What parts of my plant does this subpart cover?'', Sec.  63.8184(a) 
then states: ``This subpart applies to each affected source at a plant 
site where chlorine and caustic are produced in mercury cells. This 
subpart applies to two types of affected sources: The mercury cell 
chlor-alkali production facility, as defined in paragraph (a)(1) of 
this section; and the mercury recovery facility, as defined in 
paragraph (a)(2) of this section.'' \b\
---------------------------------------------------------------------------

    \b\ Sections 63.8184(a)(1) and (2) describe the affected source 
types and emissions points within a ``plant site'' subject to the 
rule.
---------------------------------------------------------------------------

    Therefore, if a mercury recovery unit is being operated at a plant 
site that contains both an mercury cell chlor-alkali plant and an 
mercury recovery unit, the subpart clearly applies to both types of 
affected sources at the plant site. However, Sec. Sec.  63.8182(a) and 
63.8184(a) suggest that for the subpart to apply, there must be mercury 
cell-based production of chlorine and caustic occurring at the overall 
plant site. This is reinforced by the subpart's later definitions of 
``mercury cell chlor-alkali plant'' and ``mercury recovery facility'' 
located at Sec.  63.8266, ``What definitions apply to this subpart?''. 
This section defines the ``mercury cell chlor-alkali plant'' as all 
contiguous or adjoining property that is under common control, where 
mercury cells are used to manufacture product chlorine, product 
caustic, and by-product hydrogen and where mercury may be recovered 
from wastes. It then defines ``mercury recovery facility'' as 
consisting of all processes and associated operations needed for 
mercury recovery from wastes at a mercury cell chlor-alkali plant. In 
other words, for a mercury recovery unit to be subject to the rule, the 
rule currently reads that it must be functioning in support of an 
operating mercury cell chlor-alkali plant.
    To be consistent with EPA's mandate and intent in the 2003 Mercury 
Cell MACT to control mercury emissions from mercury chlor-alkali 
facilities, we believe that the mercury recovery units in this 
situation should continue to comply with the requirements, and 
therefore are proposing to amend the applicability provisions in Sec.  
63.8182, ``Am I subject to this subpart?'', specifically paragraph (a) 
and in Sec.  63.8184, ``What parts of my plant does this subpart 
cover?'', specifically paragraph (a); and the definitions of ``mercury 
cell chlor-alkali plant'' and ``mercury recovery facility'' in Sec.  
63.8266, ``What definitions apply to this subpart?'', to make this 
clear. Mercury recovery units that are at plants where the mercury 
cells were shut down or converted prior to the date that the final rule 
is published would have one year to comply.

C. What are the impacts of these proposed rule amendments?

    The proposed amendments would make the cell room monitoring program 
mandatory for all mercury cell chlor-alkali plants and would 
potentially impact all currently operating plants. However, the level 
of these impacts will vary depending on whether a plant previously 
elected to purchase and install a continuous mercury monitoring system 
in its cell room to comply with the cell room monitoring program 
alternative of the 2003 Mercury Cell MACT.
    The only changes that plants that are currently complying via the 
cell room monitoring program alternative option would need to make 
would be associated with the implementation of the work practices. 
However, we believe that this will not result in any additional impacts 
to these plants since we believe that plants are already doing the work 
practices although they may not be keeping all the records associated 
with them. Therefore, we conclude that the net result is that there 
will be no appreciable impact on these plants. (At this time, all 
plants except one fit into this group.) We believe the burden of 
recordkeeping during setting the action level would be offset by the 
reduced recordkeeping associated with changing the action level from 
the 75 percentile to the proposed 90 percentile in these amendments.
    For the single plant that has elected not to purchase, install, and 
operate a cell room monitoring system to comply via the cell room 
monitoring program alternative, there would be measurable cost impacts 
to purchase and install equipment. We estimate that the capital cost of 
a monitoring system is about $120,000, and that the total annual cost 
(including annualized capital cost and operation and maintenance costs) 
is slightly more than $25,000 per year. We believe that this value is a 
low percentage of the annual revenues for this facility (considerably 
less than 1 percent) and is a reasonable cost considering the nature of 
the emissions. Lacking the financial information about this one 
facility, we invite comment on our assumption that this capital cost is 
a reasonable percent of revenues. Any labor costs associated with the 
additional recordkeeping requirements associated with the cell room 
monitoring program would be offset by the reduction in the 
recordkeeping and reporting that the plant is currently doing to comply 
with the work practice standards of the 2003 Mercury Cell MACT. This 
reduction in labor may have the additional benefit to offset the 
capital costs of the new equipment.
    We do not believe that there will initially be substantial emission 
reductions associated with today's amendments. However, we believe that 
as these plants continue to increase their knowledge of the causes of 
fugitive mercury emissions in the cell room through operation of the 
cell room monitoring program, mercury emissions will continue to 
steadily decrease.
    The lack of fugitive emissions information prior to the 2003 
Mercury Cell MACT promulgation did not allow us to estimate the mercury 
reductions associated with MACT work practices. As discussed above, we 
can now estimate that these practices reduce fugitive mercury emissions 
around 65 percent from the pre-MACT levels. On a nationwide basis, we 
estimate that fugitive mercury emissions have been reduced by 
approximately 86 percent from pre-MACT levels, including plant 
closures. Our estimate of the nationwide total mercury emissions from 
these plants is approximately 1 ton/yr. This represents a reduction of 
88 percent from the pre-MACT levels allowed by the part 61 NESHAP, 
including point source and fugitive emissions, and plant closures.

IV. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

    This action is not a ``significant regulatory action'' under the 
terms of Executive Order 12866 (58 FR 71735, October 3, 1993) and is 
therefore not subject to review under the Executive Order.

B. Paperwork Reduction Act

    The information collection requirements in this proposed rule have 
been submitted for approval to OMB under the Paperwork Reduction Act, 
44 U.S.C. 3501 et seq. The information collection request (ICR) 
document prepared by EPA has been assigned EPA ICR number 2046.04.
    These proposed amendments result in changes to the information 
collection requirements in the regulation. This information is being 
collected to assure compliance with the regulation. The

[[Page 33277]]

required notifications, reports, and records are essential in 
determining compliance, and are required of all affected facilities. 
The recordkeeping and reporting requirements in this proposed rule are 
based on the requirements in EPA's NESHAP General Provisions (40 CFR 
part 63, subpart A). The recordkeeping and reporting requirements in 
the General Provisions are mandatory pursuant to section 114 of the CAA 
(42 U.S.C. 7414). All information other than emissions data submitted 
to EPA pursuant to the information collection requirements for which a 
claim of confidentiality is made is safeguarded according to CAA 
section 114(c) and the Agency's implementing regulations at 40 CFR part 
2, subpart B.
    The annual burden for this information collection averaged over the 
three years following promulgation of these amendments is estimated to 
be a total of 3,800 labor hours per year. The average annual reporting 
burden is 16 hours per response, with approximately 3 responses per 
facility for 5 respondents. The only capital/startup costs are 
associated with the installation of a cell room monitoring system at 
one facility, since we know that these systems are already in place at 
the other four facilities. The total capital/startup cost annualized 
over its expected useful life is $13,000. The total operation and 
maintenance is $60,000 per year. There are no estimated costs 
associated with purchase of services. Burden is defined at 5 CFR 
1320.3(b).
    An agency may not conduct or sponsor, and a person is not required 
to respond to, a collection of information unless it displays a 
currently valid OMB control number. The OMB control numbers for EPA's 
regulations in 40 CFR are listed in 40 CFR part 9.
    To comment on the Agency's need for this information, the accuracy 
of the provided burden estimates, and any suggested methods for 
minimizing respondent burden, EPA has established a public docket for 
this action, which includes this ICR, under Docket ID number EPA-HQ-
OAR-2002-0017. Submit any comments related to the ICR for this proposed 
rule to EPA and OMB. See ADDRESSES section at the beginning of this 
notice for where to submit comments to EPA. Send comments to OMB at the 
Office of Information and Regulatory Affairs, Office of Management and 
Budget, 725 17th Street, NW., Washington, DC 20503, Attention: Desk 
Office for EPA. Since OMB is required to make a decision concerning the 
ICR between 30 and 60 days after June 11, 2008, a comment to OMB is 
best assured of having its full effect if OMB receives it by July 11, 
2008. The final rule will respond to any OMB or public comments on the 
information collection requirements contained in these proposed 
amendments.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act generally requires an agency to 
prepare a regulatory flexibility analysis of any rule subject to notice 
and comment rulemaking requirements under the Administrative Procedure 
Act or any other statute unless the agency certifies that the rule 
would not have a significant economic impact on a substantial number of 
small entities. Small entities include small businesses, small not-for-
profit enterprises, and small governmental jurisdictions.
    For the purposes of assessing the impacts of this proposed rule on 
small entities, small entity is defined as: (1) A small business that 
meets the Small Business Administration size standards for small 
businesses, as defined by the Small Business Administration's (SBA) 
regulations at 13 CFR 121.201; (2) a small governmental jurisdiction 
that is a government of a city, county, town, school district, or 
special district with a population of less than 50,000; and (3) a small 
organization that is any not-for-profit enterprise which is 
independently owned and operated and is not dominant in its field.
    After considering the economic impacts of this proposed rule on 
small entities, I certify that this action will not have a significant 
economic impact on a substantial number of small entities. This 
proposed rule is estimated to impact a total of five sources, with one 
of the five facilities estimated to be small entity. We have estimated 
that small entity compliance costs, as assessed by the facilities' 
cost-to-sales ratio, are expected to be less than 3 percent of 
revenues. New sources are already prohibited from using the technology 
of this proposed rule by virtue of the 2003 Mercury Cell MACT's 
provisions; consequently, we did not estimate any impacts for new 
sources since this rulemaking would not impose any new requirements on 
them.
    Although this proposed rule will not have a significant economic 
impact on a substantial number of small entities, EPA nonetheless has 
tried to reduce the impact of this rule on small entities.
    We continue to be interested in the potential impacts of this 
proposed action on small entities and welcome comments on issues 
related to such impacts.

D. Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public 
Law 104-4, establishes requirements for Federal agencies to assess the 
effects of their regulatory actions on State, local, and tribal 
governments and the private sector. Under section 202 of the UMRA, EPA 
generally must prepare a written statement, including a cost-benefit 
analysis, for proposed and final rules with ``Federal mandates'' that 
may result in expenditures by State, local, and tribal governments, in 
the aggregate, or by the private sector, of $100 million or more in any 
one year. Before promulgating an EPA rule for which a written statement 
is needed, section 205 of the UMRA generally requires EPA to identify 
and consider a reasonable number of regulatory alternatives and adopt 
the least costly, most cost-effective, or least burdensome alternative 
that achieves the objectives of the rule. The provisions of section 205 
do not apply when they are inconsistent with applicable law. Moreover, 
section 205 allows EPA to adopt an alternative other than the least 
costly, most cost-effective, or least burdensome alternative if the 
Administrator publishes with the final rule an explanation why that 
alternative was not adopted. Before EPA establishes any regulatory 
requirements that may significantly or uniquely affect small 
governments, including tribal governments, it must have developed under 
section 203 of the UMRA a small government agency plan. The plan must 
provide for notifying potentially affected small governments, enabling 
officials of affected small governments to have meaningful and timely 
input in the development of EPA regulatory proposals with significant 
Federal intergovernmental mandates, and informing, educating, and 
advising small governments on compliance with the regulatory 
requirements.
    This proposed rule contains no Federal mandates (under the 
regulatory provisions of Title II of the UMRA) for State, local, or 
tribal governments or the private sector. The rule imposes no 
enforceable duty on any State, local or tribal governments or the 
private sector. (Note: The term ``enforceable duty'' does not include 
duties and conditions in voluntary federal contracts for goods and 
services.) Thus, this proposed rule is not subject to the requirements 
of sections 202 and 205 of the UMRA. EPA has determined that this rule 
contains no regulatory requirements that might significantly or 
uniquely affect small governments.

[[Page 33278]]

E. Executive Order 13132: Federalism

    Executive Order 13132 (64 FR 43255, August 10, 1999) requires EPA 
to develop an accountable process to ensure ``meaningful and timely 
input by State and local officials in the development of regulatory 
policies that have federalism implications.'' ``Policies that have 
federalism implications'' is defined in the Executive Order to include 
regulations that have ``substantial direct effects on the States, on 
the relationship between the national government and the States, or on 
the distribution of power and responsibilities among the various levels 
of government.''
    This proposed rule does not have federalism implications. It will 
not have substantial direct effects on the States, on the relationship 
between the national government and the States, or on the distribution 
of power and responsibilities among the various levels of government, 
as specified in Executive Order 13132. This proposed rule does not 
impose any requirements on State and local governments. Thus, Executive 
Order 13132 does not apply to this proposed rule.
    In the spirit of Executive Order 13132, and consistent with EPA 
policy to promote communications between EPA and State and local 
governments, EPA specifically solicits comment on this proposed rule 
from State and local officials.

F. Executive Order 13175: Consultation and Coordination With Indian 
Tribal Governments

    Executive Order 13175 (65 FR 67249, November 6, 2000), requires EPA 
to develop an accountable process to ensure ``meaningful and timely 
input by tribal officials in the development of regulatory policies 
that have tribal implications.'' This proposed rule does not have 
tribal implications, as specified in Executive Order 13175. This 
proposed rule imposes no requirements on tribal governments. Thus, 
Executive Order 13175 does not apply to this rule. EPA specifically 
solicits additional comment on this proposed rule from tribal 
officials.

G. Executive Order 13045: Protection of Children From Environmental 
Health and Safety Risks

    EPA interprets Executive Order 13045 (62 FR 19885, April 23, 1997) 
as applying to those regulatory actions that concern health or safety 
risks, such that the analysis required under section 5-501 of the Order 
has the potential to influence the regulation. This action is not 
subject to Executive Order 13045 because it is based solely on 
technology performance.

H. Executive Order 13211 (Energy Effects)

    This rule is not subject to Executive Order 13211, ``Actions 
Concerning Regulations That Significantly Affect Energy Supply, 
Distribution, or Use'' (66 FR 28355 (May 22, 2001)) because it is not a 
significant regulatory action under Executive Order 12866.

I. National Technology Transfer Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement 
Act of 1995 (``NTTAA''), Public Law 104-113 (15 U.S.C. 272 note) 
directs EPA to use voluntary consensus standards in its regulatory 
activities unless to do so would be inconsistent with applicable law or 
otherwise impractical. Voluntary consensus standards are technical 
standards (e.g., materials specifications, test methods, sampling 
procedures, and business practices) that are developed or adopted by 
voluntary consensus standards bodies. NTTAA directs EPA to provide 
Congress, through OMB, explanations when the Agency decides not to use 
available and applicable voluntary consensus standards.
    This proposed rulemaking does not involve technical standards. 
Therefore, EPA is not considering the use of any voluntary consensus 
standards.

J. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations

    Executive Order 12898 (59 FR 7629, February 16, 1994) establishes 
Federal executive policy on environmental justice. Its main provision 
directs Federal agencies, to the greatest extent practicable and 
permitted by law, to make environmental justice part of their mission 
by identifying and addressing, as appropriate, disproportionately high 
and adverse human health or environmental effects of their programs, 
policies, and activities on minority populations and low-income 
populations in the United States.
    EPA has determined that this proposed rule will not have 
disproportionately high and adverse human health or environmental 
effects on minority or low-income populations because it increases the 
level of environmental protection for all affected populations without 
having any disproportionately high and adverse human health or 
environmental effects on any population, including any minority or low-
income population. The nationwide standards would reduce HAP emissions 
and thus decrease the amount of emissions to which all affected 
populations are exposed.

List of Subjects in 40 CFR Part 63

    Environmental protection, Air pollution control, Hazardous 
substances, Incorporation by reference, Reporting and recordkeeping 
requirements.

    Dated: May 30, 2008.
Stephen L. Johnson,
Administrator.
    For the reasons set forth in the preamble, title 40, chapter I, 
part 63 of the Code of Federal Regulations is proposed to be amended as 
follows:

PART 63--[AMENDED]

    1. The authority citation for part 63 continues to read as follows:

    Authority: 42 U.S.C. 7401 et seq.

Subpart IIIII--[AMENDED]

    2. Section 63.8182 is amended by revising paragraph (a) to read as 
follows:


Sec.  63.8182  Am I subject to this subpart?

    (a) You are subject to this subpart if you own or operate a mercury 
cell chlor-alkali production facility or a mercury recovery facility at 
a mercury cell chlor-alkali plant.
* * * * *
    3. Section 63.8184 is amended by revising paragraph (a) 
introductory text to read as follows:


Sec.  63.8184  What parts of my plant does this subpart cover?

    (a) This subpart applies to two types of affected sources at a 
mercury cell chlor-alkali plant: The mercury cell chlor-alkali 
production facility, as defined in Sec.  63.8266, ``What definitions 
apply to this subpart,'' and the mercury recovery facility, as also 
defined in Sec.  63.8266.
* * * * *
    4. Section 63.8186 is amended by revising paragraph (a) and adding 
paragraph (e) to read as follows:


Sec.  63.8186  When do I have to comply with this subpart?

    (a) If you have an existing affected source, you must comply with 
the applicable provisions no later than the dates specified in 
paragraph (a)(1) of this section and in either paragraph (a)(2) or (3) 
of this section.
    (1) You must comply with each emission limitation, work practice 
standard, and recordkeeping and reporting requirement in this subpart 
that applies to you no later than

[[Page 33279]]

December 19, 2006, with the exception of the requirements listed in 
paragraphs (a)(1)(i) through (4) of this section.
    (i) Section 63.8192(h) and (i);
    (ii) Section 63.8236(e) and (f);
    (iii) Section 63.8252(f); and
    (iv) Section 63.8254(e).
    (2) If you were complying with the cell room monitoring program 
provisions in Sec.  63.8192(g) on June 11, 2008 as an alternative to 
the work practice standards in Sec.  63.8192(a) through (d), you must 
comply with the provisions in Sec.  63.8192(h) and (i) no later than 6 
months after publication of the final rule in the Federal Register. At 
the time that you are in compliance with Sec.  63.8192(h) and (i), you 
will no longer be subject to the provisions of Sec.  63.8192(g).
    (3) If you were complying with the work practice standards in Sec.  
63.8192(a) through (d) on June 11, 2008, you must comply with the 
provisions in Sec.  63.8192(h) and (i) no later than 2 years after 
publication of the final rule in the Federal Register. At the time that 
you are in compliance with Sec.  63.8192(h) and (i), you will no longer 
be subject to the provisions of Sec.  63.8192(a) through (d).
* * * * *
    (e) If you have a mercury recovery facility at a mercury cell 
chlor-alkali plant where the mercury cell chlor-alkali production 
facility ceased production of product chlorine, product caustic, and 
by-product hydrogen prior to the publication of the final rule in the 
Federal Register, you must comply with each emission limitation, work 
practice standard, and recordkeeping and reporting requirement in this 
subpart that applies to your mercury recovery unit by 1 year after the 
publication of the final rule in the Federal Register.
    5. Section 63.8192 is amended by revising the introductory text; 
and adding paragraphs (h) and (i) to read as follows:


Sec.  63.8192  What work practice standards must I meet?

    Prior to the applicable compliance date specified in Sec.  
63.8186(a)(2) or (3), you must meet the work practice requirements 
specified in paragraphs (a) through (f) of this section. As an 
alternative to the requirements specified in paragraphs (a) through (d) 
of this section, you may choose to comply with paragraph (g) of this 
section. After the applicable compliance date specified in Sec.  
63.8186(a)(2) or (3), you must meet the work practice requirements 
specified in paragraphs (e), (f), (h), and (i) of this section.
* * * * *
    (h) You must meet the work practice standards in Tables 1 through 4 
to this subpart and the associated recordkeeping requirements in Table 
12 to this subpart. You must adhere to the response intervals specified 
in Tables 1 through 4 to this subpart at all times. Nonadherence to the 
intervals in Tables 1 through 4 to this subpart constitutes a deviation 
and must be documented and reported in the compliance report, as 
required by Sec.  63.8254(b), with the date and time of the deviation, 
cause of the deviation, a description of the conditions, and time 
actual compliance was achieved. As provided in Sec.  63.6(g), you may 
request to use an alternative to the work practice standards in Tables 
1 through 4 to this subpart.
    (i) In addition to the work practice standards in paragraph (h) of 
this section, you must institute a cell room monitoring program to 
continuously monitor the mercury vapor concentration in the upper 
portion of each cell room and to take corrective actions as quickly as 
possible when elevated mercury vapor levels are detected. You must 
prepare and submit to the Administrator a cell room monitoring plan 
containing the elements listed in Table 11 to this subpart and meet the 
requirements in paragraphs (i)(1) through (4) of this section.
    (1) You must utilize a mercury monitoring system that meets the 
requirements of Table 8 to this subpart.
    (2) You must establish action levels according to the requirements 
in paragraphs (i)(2)(i) through (iii) of this section. You must 
establish an initial action level after the compliance date specified 
in Sec.  63.8186(a)(2) or (3), and you must re-establish an action 
level at least once every six months thereafter.
    (i) You must measure and record the mercury concentration for at 
least 14 days and no more than 30 days using a system that meets the 
requirements of paragraph (i)(1) of this section. For the initial 
action level, this monitoring must begin on the applicable compliance 
date specified for your affected source in Sec.  63.8186(a)(2) or (3).
    (ii) Using the monitoring data collected according to paragraph 
(i)(2)(i) of this section, you must establish your action level at the 
90th percentile of the data set.
    (iii) You must submit your initial action level according to Sec.  
63.8252(f) and subsequent action levels according to Sec.  63.8252(g).
    (3) Beginning on the compliance date specified for your affected 
source in Sec.  63.8186(a)(2) or (3), you must continuously monitor the 
mercury concentration in the cell room. Failure to monitor and record 
the data according to Sec.  63.8256(e)(4)(iii) for 75 percent of the 
time in any 6-month period constitutes a deviation.
    (4) If the average mercury concentration for any 1-hour period 
exceeds the currently applicable action level established according to 
paragraph (i)(2) of this section, you must meet the requirements in 
either paragraph (i)(4)(i) or (ii) of this section.
    (i) If you determine that the cause of the elevated mercury 
concentration is an open electrolyzer, decomposer, or other maintenance 
activity, you must record the information specified in paragraphs 
(i)(4)(i)(A) through (C) of this section.
    (A) A description of the maintenance activity resulting in elevated 
mercury concentration;
    (B) The time the maintenance activity was initiated and completed; 
and
    (C) A detailed explanation of how all the applicable requirements 
of Table 1 to this subpart were met during the maintenance activity.
    (ii) If you determine that the cause of the elevated mercury 
concentration is not an open electrolyzer, decomposer, or other 
maintenance activity, you must follow the procedures specified in 
paragraphs (i)(4)(ii)(A) and (B) of this section until the mercury 
concentration falls below the action level. You must also keep all the 
associated records for these procedures as specified in Table 12 to 
this subpart. Nonadherence to the intervals in paragraphs (i)(4)(ii)(A) 
and (B) of this section constitutes a deviation and must be documented 
and reported in the compliance report, as required by Sec.  63.8254(b).
    (A) Within 1 hour of the time the action level was exceeded, you 
must conduct each inspection specified in Table 2 to this subpart, with 
the exception of the cell room floor and the pillars and beam 
inspections. You must correct any problem identified during these 
inspections in accordance with the requirements in Tables 2 and 3 to 
this subpart.
    (B) If the Table 2 inspections and subsequent corrective actions do 
not reduce the mercury concentration below the action level, you must 
inspect all decomposers, hydrogen system piping up to the hydrogen 
header, and other potential locations of mercury vapor leaks using a 
technique specified in Table 6 to this subpart. If a mercury vapor leak 
is identified, you must take the appropriate action specified in Table 
3 to this subpart.
    6. Section 63.8230 is amended by revising paragraph (b) and by 
adding paragraph (c) to read as follows:

[[Page 33280]]

Sec.  63.8230  By what date must I conduct performance tests or other 
initial compliance demonstrations?

* * * * *
    (b) For the applicable work practice standards in Sec.  63.8192(a) 
through (g), you must demonstrate initial compliance within 30 calendar 
days after the compliance date that is specified for your affected 
source in Sec.  63.8186(a)(1).
    (c) For the applicable work practice standards in Sec.  63.8192(e), 
(f), (h), and (i), you must demonstrate initial compliance within 60 
calendar days after the applicable compliance date that is specified 
for your affected source in Sec.  63.8186(a)(2) or (3).
    7. Section 63.8236 is amended by revising paragraph (c) 
introductory text and by adding paragraphs (e) and (f) to read as 
follows:


Sec.  63.8236  How do I demonstrate initial compliance with the 
emission limitations and work practice standards?

* * * * *
    (c) For each affected source, you have demonstrated initial 
compliance with the applicable work practice standards in Sec.  
63.8192(a) through (g) if you comply with paragraphs (c)(1) through (7) 
of this section:
* * * * *
    (e) After the [date of publication of the final rule in the Federal 
Register], for each affected source, you have demonstrated initial 
compliance with the applicable work practice standards in Sec.  
63.8192(e), (f), (h), and (i) if you comply with paragraphs (e)(1) 
through (4) of this section:
    (1) You certify in your Revised Work Practice Notification of 
Compliance Status that you are operating according to the work practice 
standards in Sec.  63.8192(h).
    (2) You have submitted your cell room monitoring plan as part of 
your Revised Work Practice Notification of Compliance Status and you 
certify in your Revised Work Practice Notification of Compliance Status 
that you are operating according to the continuous cell room monitoring 
program under Sec.  63.8192(i) and that you have established your 
initial action level according to Sec.  63.8192(i)(2).
    (3) You have re-submitted your washdown plan as part of your 
Revised Work Practice Notification of Compliance Status and you re-
certify in your Revised Work Practice Notification of Compliance Status 
that you are operating according to your washdown plan.
    (4) You have re-submitted records of the mass of virgin mercury 
added to cells for the 5 years preceding December 19, 2006, as part of 
your Revised Work Practice Notification of Compliance Status.
    (f) You must submit the Revised Work Practice Notification of 
Compliance Status containing the results of the initial compliance 
demonstration according to the requirements in Sec.  63.8252(f).
    8. Section 63.8242 is amended by revising paragraph (a)(2) to read 
as follows:


Sec.  63.8242  What are the installation, operation, and maintenance 
requirements for my continuous monitoring systems?

    (a) * * *
* * * * *
    (2) Each mercury continuous emissions monitor analyzer must have a 
detector with the capability to detect a mercury concentration at or 
below 0.5 times the mercury concentration level measured during the 
performance test conducted according to Sec.  63.8232, or 0.1 [mu]g/
m\3\, whichever is greater.
* * * * *
    9. Section 63.8246 is amended by revising the first sentence of 
paragraph (b)(1) introductory text to read as follows:


Sec.  63.8246   How do I demonstrate continuous compliance with the 
emission limitations and work practice standards?

* * * * *
    (b) * * * (1) For each mercury thermal recovery unit vent, you must 
demonstrate continuous compliance with the applicable emission limit 
specified in Sec.  63.8190(a)(3) by maintaining the outlet mercury 
daily-average concentration no higher than the applicable limit. * * *
* * * * *
    10. Section 63.8252 is amended by adding paragraphs (f) and (g) to 
read as follows:


Sec.  63.8252   What notifications must I submit and when?

* * * * *
    (f) You must submit a Revised Work Practice Notification of 
Compliance Status according to paragraphs (f)(1) and (2) of this 
section.
    (1) You must submit a Revised Work Practice Notification of 
Compliance Status before the close of business on the date 60 days 
after the applicable compliance date in date Sec.  63.8186(a)(2) or 
(3). The Revised Work Practice Notification of Compliance Status must 
contain the items in paragraphs (f)(1)(i) through (iii) of this 
section:
    (i) A certification that you are operating according to the work 
practice standards in Sec.  63.8192(h).
    (ii) Your cell room monitoring plan, including your initial action 
level determined in accordance with Sec.  63.8192(i)(2), and a 
certification that you are operating according to the continuous cell 
room monitoring program under Sec.  63.8192(i).
    (iii) Your washdown plan, and a certification that you are 
operating according to your washdown plan under Sec.  63.8192(e).
    (2) Records of the mass of virgin mercury added to cells for the 5 
years preceding December 19, 2006.
    (g) You must submit subsequent action levels determined in 
accordance with Sec.  63.8192(i)(2), along with the supporting data 
used to establish the action level, within 30 calendar days after 
completion of data collection.
    11. Section 63.8254 is amended by revising paragraph (b)(7) 
introductory text to read as follows:


Sec.  63.8254   What reports must I submit and when?

* * * * *
    (b) * * *
    (7) For each deviation from the requirements for work practice 
standards in Tables 1 through 4 to this subpart that occurs at an 
affected source (including deviations where the response intervals were 
not adhered to as described in Sec.  63.8192(b)), each deviation from 
the cell room monitoring program monitoring and data recording 
requirements in Sec.  63.8192(i)(3), and each deviation from the 
response intervals required by Sec.  63.8192(i)(4) when an action level 
is exceeded, the compliance report must contain the information in 
paragraphs (b)(1) through (4) of this section and the information in 
paragraphs (b)(7)(i) and (ii) of this section. This includes periods of 
startup, shutdown, and malfunction.
* * * * *
    12. Section 63.8256 is amended by revising paragraph (c) 
introductory text and adding paragraph (e) to read as follows:


Sec.  63.8256  What records must I keep?

* * * * *
    (c) Records associated with the work practice standards that must 
be kept prior to the applicable compliance date in Sec.  63.8186(a)(2) 
or (3).
* * * * *
    (e) Records associated with the work practice standards that must 
be kept after the applicable compliance date in Sec.  63.8186(a)(2) or 
(3).
    (1) You must keep the records specified in paragraphs (e)(1)(i) and 
(ii) of this section.
    (i) A weekly record certifying that you have complied with the work 
practice standards in Tables 1 through 4 to this subpart. This record 
must, at minimum,

[[Page 33281]]

list each general requirement specified in paragraphs (e)(1)(i)(A) 
through (D) of this section. Figure 1 to this subpart provides an 
example of this record.
    (A) The design, operation, and maintenance requirements in Table 1 
to this subpart;
    (B) The required inspections in Table 2 to this subpart;
    (C) The required actions for liquid mercury spills and 
accumulations and hydrogen and mercury vapor leaks in Table 3 to this 
subpart; and
    (D) The requirements for mercury liquid collection in Table 4 to 
this subpart.
    (ii) The records specified in Table 12 to this subpart related to 
mercury and hydrogen leaks.
    (2) You must maintain a copy of your current washdown plan and 
records of when each washdown occurs.
    (3) You must maintain records of the mass of virgin mercury added 
to cells for each reporting period.
    (4) You must keep your current cell room monitoring plan and the 
records specified in paragraphs (e)(4)(i) through (vi) of this section.
    (i) Records of the monitoring conducted in accordance with Sec.  
63.8192(i)(2)(i) to establish your action levels, and records 
demonstrating the development of these action levels.
    (ii) During each period that you are gathering cell room monitoring 
data in accordance with the requirements of Sec.  63.8192(i)(2)(i), 
records specified in Table 9 to this subpart.
    (iii) Records of the cell room mercury concentration monitoring 
data collected.
    (iv) Instances when the action level is exceeded.
    (v) Records specified in Sec.  63.8192(i)(4)(i) for maintenance 
activities that cause the mercury vapor concentration to exceed the 
action level.
    (vi) Records of all inspections and corrective actions taken in 
response to a non-maintenance related situation in which the mercury 
vapor concentration exceeds the action level as specified in Table 12 
of this subpart.
    13. Section 63.8266 is amended by revising the definitions of 
``Mercury cell chlor-alkali plant'' and ``Mercury recovery facility'' 
to read as follows:


Sec.  63.8266   What definitions apply to this subpart?

* * * * *
    Mercury cell chlor-alkali plant means all contiguous or adjoining 
property that is under common control, where a mercury cell chlor-
alkali production facility and/or a mercury recovery facility is 
located. A mercury cell chlor-alkali plant includes a mercury recovery 
facility at a plant where the mercury cell chlor-alkali production 
facility ceases production.
* * * * *
    Mercury recovery facility means an affected source consisting of 
all processes and associated operations needed for mercury recovery 
from wastes generated by a mercury cell chlor-alkali plant.
* * * * *
    14. Subpart IIIII of Part 63 is amended by revising the table 
heading for table 5 to read as follows:

Table 5 to Subpart IIIII--Required Elements of Floor-Level Mercury 
Vapor Measurement and Cell Room Monitoring Plans Prior to the 
Applicable Compliance Date Specified in Sec.  63.8186(a)(2) or (3)

    15. Subpart IIIII of Part 63 is amended by revising the 
introductory text of table 9 to read as follows:

Table 9 To Subpart IIIII of Part 63--Required Records for Work Practice 
Standards

    As stated in Sec.  63.8256(c), you must keep the records (related 
to the work practice standards) specified in the following table prior 
to the applicable compliance date specified in Sec.  63.8186(a)(2) or 
(3). After the applicable compliance date specified in Sec.  
63.8186(a)(2) or (3), you must keep the records (related to the work 
practice standards) specified in the following table during the period 
when you are collecting cell room monitoring data in accordance with 
Sec.  63.8192(i)(2)(i) to establish your action level:
    16. Subpart IIIII of Part 63 is amended by adding table 11 to read 
as follows:

Table 11 to Subpart IIIII.--Required Elements Cell Room Monitoring Plans
 After the Applicable Compliance Date Specified in Sec.   63.8186(a)(2)
                                 OR (3)
    Your Cell Room Monitoring Plan required by Sec.   63.8192(i) must
           contain the elements listed in the following table:
------------------------------------------------------------------------
   You must specify in your cell room
         monitoring plan * * *               Additional requirements
------------------------------------------------------------------------
1. Details of your mercury monitoring    ...............................
 system.
2. How representative sampling will be   Include some pre-plan
 conducted.                               measurements to demonstrate
                                          the profile of mercury
                                          concentration in the cell room
                                          and how the selected sampling
                                          locations ensure conducted
                                          representativeness.
3. Quality assurance/quality control     Include a description of how
 procedures for your mercury monitoring   you will keep records or other
 system.                                  means to demonstrate that the
                                          system is operating properly.
4. Your current action level...........  Include the background data
                                          used to establish your current
                                          level. Records of previous
                                          action levels must be kept for
                                          5 years in accordance with
                                          Sec.   63.8258, but are not
                                          required to be included as
                                          part of your cell room
                                          monitoring plan.
------------------------------------------------------------------------

    17. Subpart IIIII of Part 63 is amended by adding table 12 to read 
as follows:

    Table 12 to Subpart IIIII of Part 63.--Required Records for Work
  Practice Standards After the Applicable Compliance Date Specified in
                       Sec.   63.8186(a)(2) OR (3)
As stated in Sec.   63.8256(e)(1), you must keep the records (related to
     the work practice standards) specified in the following table:
------------------------------------------------------------------------
                                          You must record the following
             For each * * *                     information * * *
------------------------------------------------------------------------
1. Liquid mercury spill or accumulation  a. Location of the liquid
 identified during an inspection          mercury spill or accumulation.
 required by Table 2 to this subpart or  b. Method you use to clean up
 at any other time.                       the liquid mercury spill or
                                          accumulation.
                                         c. Date and time when you clean
                                          up the liquid mercury spill or
                                          accumulation.

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                                         d. Source of the liquid mercury
                                          spill or accumulation.
                                         e. If the source of the liquid
                                          mercury spill or accumulation
                                          is not identified, the time
                                          when you reinspect the area.
2. Liquid mercury leak or hydrogen leak  a. Location of the leak.
 identified during an inspection         b. Date and time you identify
 required by Table 2 to this subpart or   the leak.
 at any other time.                      c. If the leak is a liquid
                                          mercury leak, the date and
                                          time that you successfully
                                          contain the dripping liquid
                                          mercury.
                                         d. Date and time you
                                          successfully stop the leak and
                                          repair the leaking equipment.
------------------------------------------------------------------------

    18. Subpart IIIII of Part 63 is amended by adding figure 1 as 
follows:
[GRAPHIC] [TIFF OMITTED] TP11JN08.002

[FR Doc. E8-12618 Filed 6-10-08; 8:45 am]
BILLING CODE 6560-50-P