National Emission Standards for Hazardous Air Pollutants: Mercury Emissions from Mercury Cell Chlor-Alkali Plants, 33258-33282 [E8-12618]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 73, Number 113 (Wednesday, June 11, 2008)]
[Proposed Rules]
[Pages 33258-33282]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-12618]



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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: https://www.regulations.gov: 
Follow the instructions for submitting comments.
     Agency Web Site: https://www.epa.gov/oar/docket.html. 
Follow the instructions for submitting comments on the EPA Air and 
Radiation Docket Web site.
     E-mail: a-and-r-docket@epa.gov. 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 
https://www.regulations.gov, including any personal information 
provided, unless the comment includes information claimed to be 
confidential business information (CBI) or other information whose 
disclosure is restricted by statute. Do not submit information that you 
consider to be CBI or otherwise protected through 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: jones.donnalee@epa.gov.

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: https://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

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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