[Federal Register Volume 75, Number 81 (Wednesday, April 28, 2010)]
[Proposed Rules]
[Pages 22470-22496]
[FR Doc No: 2010-9363]

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Part III

Environmental Protection Agency

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40 CFR Parts 9 and 63

National Emission Standards for Hazardous Air Pollutants: Gold Mine Ore
Processing and Production Area Source Category and Addition to Source
Category List for Standards; Proposed Rule

Federal Register / Vol. 75, No. 81 / Wednesday, April 28, 2010 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 9 and 63

[EPA-HQ-OAR-2010-0239; FRL-9140-7]
RIN 2060-AP48

National Emission Standards for Hazardous Air Pollutants: Gold
Mine Ore Processing and Production Area Source Category and Addition to
Source Category List for Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: EPA is proposing to add the gold mine ore processing and
production area source category to the list of source categories
subject to regulation under the hazardous air pollutant section of the
Clean Air Act (CAA) due to their mercury emissions. EPA is also
proposing national mercury emission standards for this category based
on the emissions level of the best performing facilities which are well
controlled for mercury. EPA is soliciting comments on all aspects of
this proposed rule.

DATES: Comments must be received on or before May 28, 2010 unless a
public hearing is requested by May 10, 2010. If a hearing is requested
on this proposed rule, written comments must be received by June 14,
2010. Under the Paperwork Reduction Act, comments on the information
collection provisions must be received by the Office of Management and
Budget (OMB) on or before May 28, 2010.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-
OAR-2010-0239, by one of the following methods:
     Follow the on-line instructions for submitting comments at
the following Web address: http://www.regulations.gov.
     E-mail: Comments may be sent by electronic mail (e-mail)
to<EMAIL_ADDRESS>Attention Docket ID No. EPA-HQ-OAR-2010-
0239.
     Fax: Fax your comments to:<PHONE_NUMBER>, Attention
Docket ID No. EPA-HQ-OAR-2010-0239.
     Mail: Send your comments to: Air and Radiation Docket and
Information Center, Environmental Protection Agency, Mailcode: 2822T,
1200 Pennsylvania Ave., NW., Washington, DC 20460, Attention: Docket ID
No. EPA-HQ-OAR-2010-0239. Please include a total of two copies. In
addition, please mail a copy of your comments on the information
collection provisions to the Office of Information and Regulatory
Affairs, Office of Management and Budget (OMB), Attn: Desk Officer for
EPA, 725 17th St., NW., Washington, DC 20503.
     Hand Delivery or Courier: Deliver your comments to EPA
Docket Center, Room 3334, 1301 Constitution Ave., NW., Washington, DC
20460. Such deliveries are only accepted during the Docket Center'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-
2010-0239. EPA's policy is that all comments received will be included
in the public docket without change and may be made available online at
http://www.regulations.gov, including any personal information
provided, unless the comment includes information claimed to be
confidential business information (CBI) or other information whose
disclosure is restricted by statute. Do not submit information that you
consider to be CBI or otherwise protected through http://www.regulations.gov or e-mail. The http://www.regulations.gov Web site
is an ``anonymous access'' system, which means that EPA will not know
your identity or contact information unless you provide it in the body
of your comment. If you send an e-mail comment directly to EPA without
going through http://www.regulations.gov, your e-mail address will be
automatically captured and included as part of the comment that is
placed in the public docket and will be 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 http://www.regulations.gov index. Although listed in the index, some
information is not publicly available (e.g., CBI or other information
whose disclosure is restricted by statute). Certain other material,
such as copyrighted material, will be publicly available only in hard
copy form. Publicly available docket materials are available either
electronically in http://www.regulations.gov or in hard copy at the EPA
Docket Center, Public Reading Room, 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: For questions about these proposed
standards for gold mine ore processing and production, contact Mr.
Chuck French, Sector Policies and Program Division, Office of Air
Quality Planning and Standards (D243-02), Environmental Protection
Agency, Research Triangle Park, North Carolina 27711, telephone number
(919) 541-7912; fax number<PHONE_NUMBER>, e-mail address:
<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: The information presented 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?
II. Addition to Section 112(c)(6) Source Category List
III. Background Information
    A. What is the statutory authority and regulatory approach for
the proposed standards?
    B. What source category is affected by the proposed NESHAP?
    C. What are the production operations, emission sources, and
available controls?
IV. Summary of the Proposed Standards
    A. Do these proposed standards apply to my facility?
    B. When must I comply with the proposed standards?
    C. What are the proposed standards?
    D. What are the testing and monitoring requirements?
    E. What are the notification, recordkeeping, and reporting
requirements?
    F. What are the title V permit requirements?
    G. Emissions of Non-Mercury HAPs
    H. Request for Comments
V. Rationale for the Proposed Standards
    A. How did we select the affected source?
    B. How did we determine MACT?
    C. How did we select the testing, monitoring, and electronic
reporting requirements?
VI. Impacts of the Proposed Standards
    A. What are the emissions, cost, economic, and non-air
environmental impacts?
    B. What are the health benefits of reducing mercury emissions?
VII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act

    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations

I. General Information

A. Does this action apply to me?

    The regulated categories and entities potentially affected by the
proposed standards include:

------------------------------------------------------------------------
                                                         Examples of
             Category               NAICS Code \1\   regulated entities
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Industry:
    Gold Ore Mining...............          212221  Establishments
                                                     primarily engaged
                                                     in developing the
                                                     mine site, mining,
                                                     and/or
                                                     beneficiating
                                                     (i.e., preparing)
                                                     ores valued chiefly
                                                     for their gold
                                                     content.
                                                     Establishments
                                                     primarily engaged
                                                     in transformation
                                                     of the gold into
                                                     bullion or dore bar
                                                     in combination with
                                                     mining activities
                                                     are included in
                                                     this industry.
------------------------------------------------------------------------
\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
63.11640 of subpart EEEEEEE (National Emission Standards for Hazardous
Air Pollutants: Gold Mine Ore Processing and Production Area Source
Category). If you have any questions regarding the applicability of
this action to a particular entity, consult either the air permit
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 CBI to EPA through http://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), Office of Air Quality Planning and Standards, Environmental
Protection Agency, Research Triangle Park, NC 27711, Attention: Docket
ID No. EPA-HQ-OAR-2010-0239. Clearly mark the part or all of the
information that you claim to be CBI. For CBI contained 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 the 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 this proposed rule by May 10, 2010, a public hearing will be
held on May 13, 2010. If you are interested in attending the public
hearing, contact Ms. Pamela Garrett, Metals and Minerals Group (D243-
02), Sector Policies and Programs Division, U.S. EPA, Research Triangle
Park, NC 27711, telephone<PHONE_NUMBER> e-mail address:
<EMAIL_ADDRESS>to verify that a hearing will be held. If a
public hearing is held, it will be held at EPA's campus located at 109
T.W. Alexander Drive in Research Triangle Park, NC, or an alternate
site. If a hearing is requested by May 10, 2010, any persons interested
in presenting oral testimony at that hearing should contact Ms. Pamela
Garrett at least 2 days in advance of the date of the public hearing.

II. Addition to Section 112(c)(6) Source Category List

    Section 112(c)(6) of the CAA requires that EPA list categories and
subcategories of sources assuring that sources accounting for not less
than 90 percent of the aggregate emissions of each of the seven
specified Hazardous Air Pollutants (HAP) are subject to standards under
section 112(d)(2) or (d)(4). The seven HAP specified in section
112(c)(6) are as follows: alkylated lead compounds, polycyclic organic
matter, hexachlorobenzene, mercury, polychlorinated biphenyls, 2,3,7,9-
tetrachlorodibenzofurans, and 2,3,7,8-tetrachloridibenzo-p-dioxin.
    In 1998, EPA published a list of section 112(c)(6) categories (63
FR 17838, April 10, 1998). At that time, there was very little
available information on mercury emissions from gold mine ore
production and processing. Since the 1998 notice, a substantial amount
of data and information have become available on mercury emissions from
this source category. For example, in 2000, the first estimates of
mercury emissions from this source category were published in the
Toxics Release Inventory (TRI), largely because of the lower TRI
reporting threshold for mercury that went into effect about that time.
Following this, from 2001 to 2005, additional data and information were
collected through the Voluntary Mercury Reduction Program (VMRP), which
was a collaborative agreement between the State of Nevada Division of
Environmental Protection (NDEP), EPA's Region 9 Office, and four gold
mining companies. Then, in 2005-2006 the EPA's Office of Air Quality
Planning and Standards (OAQPS) and the NDEP sent questionnaires to a
number of companies seeking additional information and data on mercury
emissions. Moreover, starting in 2007 the NDEP has been requiring all
facilities in Nevada to conduct annual mercury emissions tests. Based
on these data collected over the past several years, along with
information about the industry processing and production levels and
activities in the early 1990s, EPA has estimated that the gold mine ore
processing and production emitted about 4.4 tons of mercury during the

baseline year (i.e., in 1990). These estimated mercury emissions in the
1990 inventory for gold mine ore processing and production are based on
emissions from the following thermal processes at gold mine ore
processing and production facilities: roasters, autoclaves, carbon
kilns, pregnant storage solution tanks (``preg tanks''),
electrowinning, melt furnaces, and retorts. We have updated our 1990
baseline emission inventory for section 112(c)(6) to reflect this
contribution of mercury from gold mine ore processing and production
and determined that this area source category contributed to the 90
percent of the aggregate emissions of mercury in 1990. Consequently, we
are adding the gold mine ore processing and production area source
category to the list of source categories under section 112(c)(6) on
the basis of mercury emissions.

III. Background Information

A. What is the statutory authority and regulatory approach for the
proposed standards?

    As mentioned above, CAA section 112(c)(6) requires that EPA set
standards under section 112(d)(2) or (d)(4). The mercury standards for
the gold mine ore processing and production area source category are
being established under CAA section 112(d)(2), which requires MACT
level of control. Under CAA section 112(d), the MACT standards for
existing sources must be at least as stringent as the average emissions
limitation achieved by the best performing 12 percent of existing
sources (for which the administrator has emissions information) for
source categories and subcategories with 30 or more sources, or the
best performing 5 sources for categories and subcategories with fewer
than 30 sources (CAA section 112(d)(3)(A) and (B)). This level of
minimum stringency is called the MACT floor. For new sources, MACT
standards must be at least as stringent as the emission control that is
achieved in practice by the best controlled similar source (CAA section
112(d)(3)). EPA also must consider more stringent ``beyond-the-floor''
control options. When considering beyond-the-floor options, EPA must
consider not only the maximum degree of reduction in emissions of HAP,
but must take into account costs, energy, and nonair quality health and
environmental impacts when doing so.

B. What source category is affected by the proposed NESHAP?

    The gold mine ore processing and production area source category
consists of facilities engaged in processing gold ore to recover gold
using one or more of the following process units: roasters, autoclaves,
carbon kilns, melt furnaces, mercury retorts, electrowinning, and/or
pregnant solution tanks. There were approximately 21 gold mine ore
processing and production facilities operating these processes in the
United States (U.S.) in 2008. The majority and the largest of these
facilities are located in Nevada. The other facilities currently
operating are in Alaska, California, Colorado, Montana, and Washington.
In 2007, the U.S. gold mine industry produced about 240 metric tons of
gold, and the value of gold mine production was about $5.1 billion.

C. What are the production operations, mercury emission sources, and
available controls?

    All gold mine operations in the U.S. begin by mining ores,
generally using large earth moving equipment. The ore is then subject
to crushing operations. After crushing, some ore may be pre-treated by
roasting or autoclaving. Subsequent to these operations the ore
undergoes some type of leaching process using a dilute cyanide
solution. The cyanide binds with the gold (and various impurities
including mercury) to produce a ``pregnant'' solution. The pregnant
solutions are further processed using various thermal processes (e.g.,
electrowinning, retorts and furnaces) to recover gold. The gold mine
ore processing and production area source category covers the thermal
processes that occur after the crushing, including roasting operations
(i.e., ore dry grinding, ore preheating, roasting, and quenching),
autoclaves, carbon kilns, electrowinning, preg tanks, retorts and
furnaces. Further details of the gold production processes are
described in section C.2 below.
1. Historical Background on Mercury Emissions
    Mercury, which is naturally present in the ores in various
concentrations, enters the gold recovery processes with the gold mine
ore. Most of this mercury is recovered as a by-product in the form of
liquid elemental mercury, or as a mercury precipitate, placed in closed
containers, and stored or sold to commercial metal companies. In
addition, a notable amount of mercury is currently captured by mercury
emission control devices (e.g., in carbon media) and is not recovered
for sale. Nevertheless, some portion of the mercury in the ore is
liberated to the air during the thermal processes resulting in mercury
emissions to the atmosphere. Without emissions controls the potential
for mercury emissions from these facilities would be quite high.
    In May 2000, EPA published the first estimates of mercury emissions
for gold mine ore processing and production facilities as part of the
EPA's TRI for year 1998. Total mercury air emissions reported to the
TRI in the 1998-2001 timeframe for this source category were about
14,000 pounds per year. However, EPA estimated (in the 1999 National
Emissions Inventory) that total mercury emissions from this category
were higher (about 23,000 pounds in 1999), and the mining industry
reported emissions to be 21,000 pounds in 2001. Even at that time, some
facilities had controls on processes to limit mercury emissions. Early
efforts to reduce or limit mercury emissions were due in part to
concerns about worker exposure to mercury. For example, for years
facilities that were processing ores with higher levels of mercury have
been using retorts to condense and capture the mercury in liquid
elemental form. Moreover, two of the largest facilities have been using
mercury specific emissions controls on their roasters since the mid-
1990s. Also, a number of facilities had carbon adsorption beds to
control mercury emissions on various thermal process units prior to
2001. We estimate that without these early controls the potential
emissions would have been much higher than 23,000 pounds (at least
37,000 pounds).
    Since 2001, mercury emissions from gold mine ore processing and
production have been further reduced. The reductions achieved since
2001 were obtained through programs implemented by the NDEP, EPA, and
industry. The first program for reducing mercury emissions from these
facilities was the Voluntary Mercury Reduction Program (VMRP). The VMRP
was a voluntary partnership between the NDEP, EPA Region 9, and four
large gold mining companies. The main goal of the VMRP, which was
officially adopted in June 2002, was to achieve significant, permanent
and rapid reductions in mercury air emissions from precious metal
processing operations. The VMRP focused on 5 large facilities in Nevada
that accounted for most of the reported emissions in 2001. Some mercury
emission reductions were quickly achieved by adding emission controls
to some of the thermal units that emit mercury at these facilities.
    To achieve further reductions in mercury emissions, the NDEP
converted the VMRP into a regulatory program, called the Nevada Mercury
Control Program (NMCP). As described on the NDEP Web site, the NMCP is
a State

regulatory program that supersedes and replaces the VMRP and requires
best available mercury emissions control technology on all thermal
units located at all precious metal mines in Nevada. The NMCP was
adopted March 8, 2006 and made effective May 4, 2006. The NMCP is a
case-by-case permit program in 2 phases. The NMCP also had an early
reduction program, which provided incentives for facilities to add
controls within the first 2 years of the program (by mid-2008). A few
facilities in Nevada took advantage of the early reduction program and
added mercury specific controls (sulfur impregnated carbon filters) in
2007 on various thermal units.
    In Phase 1 of the NMCP, which has recently been completed, permits
were issued that require comprehensive work practice standards for the
proper operation of existing mercury controls and the operations of the
thermal units to minimize mercury emissions until specific controls are
identified later under Phase 2 of the program. Phase 1 also required
annual stack testing, site inspections and emissions reporting to
collect data to assist in mercury emissions controls determinations in
Phase 2. Emissions data collected in Phase 1 of the NMCP were used in
the development of this proposed rule. Phase 2 has begun issuing
permits and all permits are scheduled for issuance by the end of
calendar year 2010. Implementation of controls will begin shortly after
permit issuance. The Phase 2 permit process is a technology review and
engineering analysis to determine the best available control technology
and mercury emission limits. Controls and mercury emissions limits will
be determined on a case-by-case analysis and will be unique to the
individual unit (not universal for the unit type). The NMCP is a
control-based program that will require thermal units in Nevada to have
a best available mercury control technology installed. The NDEP and EPA
have coordinated on the review and analyses of data on emissions,
controls, and monitoring approaches for mercury emissions from this
category, and collaborated to assure that the State program could co-
exist and provide an additional level of control for facilities in
Nevada while working in concert with the proposed National standards.
    As described further below, several facilities already have
effective mercury emissions controls in place on various thermal units.
We expect that a number of other facilities will need to add mercury
controls to comply with emissions limits set forth in this NESHAP,
resulting in further emissions reductions from this category.
2. Description of Gold Mine Ore Processing and Production
    The gold mine ore processing and production source category
consists of the following processes: roasting operations, autoclaves,
carbon regeneration kilns, electrowinning cells, pregnant solution
tanks, mercury retorts, and melt furnaces. Each facility may not have
every one of these processes because there are different production
paths that can be taken to recover gold from mine ore. Mercury can be
emitted from each of these thermal processes. Some of these processes
are already well controlled for mercury emissions; however, there are
some process units at several plants that are only partly controlled or
uncontrolled for mercury.
    The first step in gold mining is extracting the gold-containing
ores from surface or undergrounds mines, generally by using large-scale
earthmoving equipment. Samples of ore are examined to determine grade
and metallurgical characteristics. Broken rock is marked by type for
efficient processing. Based on its metallurgical makeup, the ore is
delivered to the proper processing location. Low grade ore is roughly
broken into small chunks, and high grade ore is delivered to a grinding
mill, where the ore is pulverized to a powder (milled ore).
    Depending on its metallurgical and other characteristics, the ore
may be pretreated in a roaster or autoclave prior to leaching, or it
may be sent directly to a leaching circuit without pretreatment. The
two main types of ore are oxide ore and refractory ore. If the process
of cyanide leaching can extract most of the gold contained in an ore
with no pretreatment, the ore is referred to as oxide ore; otherwise,
the ore is described as refractory ore. Oxide ore is sent directly to
the leaching circuit where cyanide is used to liberate the gold.
However, refractory ores contain organic carbon and/or sulfide mineral
grains which inhibit the efficient recovery of gold during cyanide
leaching. Roasters and autoclaves are used to oxidize the ore and
remove these components. Refractory ore containing carbon and sulfur is
roasted to over 1000 [deg]F, burning off the sulfide and carbon. The
product of this process, which is now basically an oxide ore, is routed
to a leaching circuit. Sulfide refractory ore without carbon is
oxidized in an autoclave to liberate the gold from sulfide minerals;
then it is sent to a leaching circuit. At all facilities, the ores are
eventually sent to some type of cyanide leaching process.
    Lower grade oxide ores generally undergo a heap leaching process,
whereby the ore is spread over large areas and dilute cyanide solution
is slowly dripped through and collected on liners and channels. During
the leaching process, cyanide binds with gold and other elements
(including mercury) producing a ``pregnant'' cyanide solution. At most
facilities that use this process, the next step involves pumping the
pregnant cyanide-gold solution to tanks with activated carbon where the
gold is adsorbed (collected) out of solution onto the activated carbon,
and the remaining cyanide solution is largely recycled. This carbon
adsorption step that follows the cyanide leaching is generally referred
to as the ``carbon-in-column'' process.
    Higher grade ores are generally milled. If the ore is a higher
grade ``oxide ore,'' it is milled and then generally sent directly to
carbon-in-leach processes where activated carbon is added along with
the milled ore and cyanide solution in tanks where the cyanide-gold
complexes adsorb onto activated carbon. In these units the leaching and
carbon adsorption occur together. If the higher grade ore is a
refractory ore, it is roasted or autoclaved first, then it is sent to
carbon-in-leach processes.
    However, a few facilities do not use carbon. Instead, these
facilities use a different, zinc precipitate process, which is
described later in this preamble.
    At all the facilities that use a carbon adsorption process, the
gold loaded carbon (which also contains mercury and other constituents)
is moved into a vessel where the gold is chemically stripped from the
carbon typically by using a concentrated caustic cyanide solution,
producing a concentrated cyanide-gold solution. Gold (along with other
metals and minerals) is drawn from this concentrated solution
electrolytically (in electrowinning cells). The concentrate from the
electrowinning cells is usually sent to a filter press to remove excess
moisture and then to a retort followed by a melt furnace. However, some
facilities do not have retorts. These facilities dry the concentrate
and then feed it directly to the melt furnace. Either way, the gold is
melted in furnaces into dore (pronounced ``doh-rey'') bars containing
up to 90 percent gold. Dore bars are subsequently sent to an external
refinery to be refined to bars of 99.9 percent or more pure gold. The
processing steps are discussed in more detail below. For processing
steps that emit mercury, the

discussion below also describes the points of mercury emissions and
available controls for such emissions.
3. Pretreatment of Refractory Ore
    As mentioned above, refractory ores have to be pretreated by
furnace oxidation (ore roasting) and/or pressure oxidation
(autoclaving) before they can be ready for cyanide leaching.
    Roasting Operations. The roasting operations that are sources of
mercury emissions include ore dry grinding where the ore is ground and
dried, preheating prior to roasting, roasting, and quenching. The
roaster is by far the process unit with the greatest potential for
mercury emissions because of the large quantity of ore processed and
the high roasting temperatures, which readily volatilize available
mercury from the ore. The mercury concentrations in the roasted ores
are high enough that elemental mercury can be recovered from the
roaster exhaust gas by condensation. The emission potential of the
ancillary roasting operations (dry grinding, pre-heating and quenching)
are much less than those from the roaster because they are operated at
much lower temperatures. Dry grinding of the ore prior to roasting is
primarily a source of particulate matter (PM) emissions; consequently,
baghouses are used for PM emission control. Ore preheaters used to
raise the ore temperature to facilitate roasting are typically equipped
with baghouses or wet scrubbers, which control particulate and some
oxidized mercury. Emissions from quenching (when the roasted ore is
cooled) are controlled by wet scrubbers, which remove particulate and
some oxidized mercury.
    Ore roasting is a combustion process where the milled ore is
oxidized in a fluidized bed roaster. During the combustion process, ore
components that interfere with the cyanide leaching of gold are
oxidized and therefore removed. As the ore exits the combustion
chamber, it typically enters a quench process, where the temperature is
reduced by contact with cooling water and the generation of steam. The
steam from the quench process is used as a heat source in other
processes at the mill, or may be sent directly to a cooling tower.
    There are three gold mine ore processing and production facilities
that have a total of six roasters. The mercury emissions generated
during roasting are mainly in gaseous elemental or oxidized forms of
mercury. A very small portion of the mercury emitted is in particulate
or particulate-bound form. Each of these roasters has complex gas
treatment systems to control not only these forms of mercury, but also
to control PM, sulfur dioxide (SO2), nitrogen oxides
(NOX), and carbon monoxide (CO). The PM control devices
remove particulate mercury and some oxidized mercury. A significant
amount of the elemental mercury is removed and recovered by
condensation (either in a condenser or gas cooling device), and the
three facilities with roasters use mercuric chloride scrubbers. These
scrubbers use a mercuric chloride scrubber liquor to complex with
mercury in the exhaust gas to precipitate a mercurous chloride
byproduct (calomel). These scrubbers are also referred to as ``calomel
scrubbers.'' The calomel precipitate is subsequently removed and is
either sent to electrowinning to recover the mercury, disposed of
offsite as a waste material, or a portion may be chlorinated to create
fresh mercuric chloride for the calomel scrubber liquor. An example of
the emissions controls and gas treatment train for a roaster includes a
hot gas electrostatic precipitator (ESP), wash tower, gas coolers,
fluorine tower, wet ESP, calomel scrubber, acid plant (for removal of
SO2 and conversion to sulfuric acid product), peroxide
scrubber (to control NOX), and regenerative thermal oxidizer
(for CO).
    Autoclaves. Autoclaves are pressure oxidation vessels that are used
to pretreat ores to increase gold recovery by cyanide leaching. The
milled ore is mixed with water to form a slurry, and is then acidified
with sulfuric acid. The acidified slurry is then pumped into the
autoclave vessel, where oxygen is used to increase the vessel pressure
to over 300 pounds per square inch, and the slurry is heated to 350
[deg]F to 430 [deg]F. The slurry is agitated in the reaction vessel and
is then discharged to a pressure relief chamber. There the liquid
content is flashed to steam, recovered, and returned to the pressurized
segment of the vessel.
    Most mercury is present in the gold ore as mercury sulfide, and
during autoclaving, the mercury sulfide combines with oxygen to form
mercury sulfate, which dissociates to some degree in the slurry.
Consequently, the mercury present in gaseous emissions from the
autoclave is mainly in the oxidized form.
    Three facilities have a total of eight autoclaves. All of the
autoclaves are equipped with wet venturi scrubbers, which remove most
of the particulate mercury and a significant portion of the oxidized
mercury present in the emissions. Venturi scrubbers have a specially
designed ``throat'' that increases the gas speed through the throat and
shears spray droplets to smaller sizes, which enhances mixing of the
droplets and particles and increases coagulation and collection.
4. Leaching
    As mentioned above, leaching generally takes place either directly
after crushing or milling, or after roasting or autoclaving. In heap
leaching, a dilute alkaline cyanide solution is distributed onto
crushed ore. The solution percolates through the ore, and the gold
reacts with free cyanide to form soluble gold-cyanide complexes. The
complexes migrate with the solution to an impermeable liner and flow to
a collection pond.
    The solution containing the precious metals is called the
``pregnant'' cyanide solution. During this process, mercury, also
present in the ore, may be leached into the gold-cyanide solution.
    Refractory ores, which have been roasted or autoclaved, are
generally leached in reaction vessels, referred to as vat leaching.
Activated carbon adsorbent is usually added to the leach vessels to
improve gold recovery. All five facilities in the U.S. that employ
roasters and/or autoclaves add activated carbon to these leach vessels,
where the leaching and carbon adsorption occur simultaneously in the
tank. This is called the ``carbon-in-leach'' process.
5. Carbon Adsorption Process
    As mentioned above, after leaching, the most common path for
recovering gold from the cyanide solution is carbon adsorption, where
the gold complexes in the pregnant solution are concentrated through
adsorption onto activated carbon. If mercury is present in the gold-
cyanide solution, it is also adsorbed onto the carbon. The gold-bearing
solution may be extracted from the leaching process and subsequently
introduced into a carbon adsorption column for concentration of the
gold content (i.e., the carbon-in-column process), or carbon may be
added into the leach process concurrent with leaching from the ore
(i.e., the carbon-in-leach process). All of these carbon adsorption
processes produce a ``loaded'' carbon, which contains gold and mercury
(and some other metals such as copper) as adsorbed cyanide complexes.
6. Carbon Desorption Processes
    The loaded carbon is then separated from the rest of the solution
or slurry by physical separation processes (such as with a screen). The
remaining cyanide solution is now considered ``barren'' and can either
be recycled back to the barren pond for use in the heap leaching
process, sent directly to the tailings impoundment (if the cyanide

concentrations are low), or sent to a cyanide destruction process and
then to a tailings impoundment once the cyanide levels are sufficiently
low.
    The loaded carbon, which contains gold-cyanide complexes, mercury,
and other metals, is stripped in a carbon strip tank to recover gold
(and other metals) typically using a heated caustic cyanide solution.
Adsorbed gold, as well as adsorbed silver, mercury, and other metals
are stripped from the carbon through desorption under pressurized or
atmospheric conditions, resulting in a more concentrated gold-
containing solution.
7. Description of Thermal Units Used After Carbon Desorption
    Carbon kilns. After gold has been removed from the activated carbon
through the stripping process, the carbon is usually regenerated and
then recycled back to the adsorption process. Regeneration is performed
to regain the adsorption capacity of the carbon. Rotary kilns known as
carbon kilns are used to regenerate the spent carbon. Because the
carbon can be oxidized in the kiln if air is present in the heating
chamber, steam is introduced to the kiln to prevent the infiltration of
air. As the carbon moves through the carbon kiln, it is heated, and
mercury and other remaining components are desorbed into the gas stream
in the kiln. Regenerated carbon exits the kiln and is captured and
quenched, and the gas stream is vented from the process, along with
combustion gas from heating the kiln chamber. The off-gas, containing
steam and mercury, is discharged to a pollution control device, such as
a carbon adsorber. The potential for mercury emissions from carbon
kilns is directly dependent on the mercury content of the stripped
carbon and whether there is a carbon adsorber or other device to
control mercury emissions.
    There are approximately 16 facilities with 18 carbon kilns. Most of
these carbon kilns have installed carbon adsorption units to control
mercury emissions, and some other facilities in Nevada have proposed in
their State permit applications under the NMCP to install carbon
adsorbers on their carbon kilns. One facility uses a hypochlorite
scrubber on its carbon kiln which oxidizes the elemental mercury to a
more soluble form and removes it as mercuric chloride.
    Pregnant storage solution tanks (``preg tanks''). The concentrated
gold-containing solution that was stripped from the carbon is
transferred to a preg tank, which serves as a storage and feed tank to
the electrowinning process (discussed below). The concentrated solution
also contains mercury, and mercury vapor can be emitted from the preg
tank vent. Two facilities have installed carbon adsorbers on their preg
tanks. In addition, five facilities in Nevada have proposed in their
State permit applications under the NMCP to install carbon adsorbers on
their preg tanks.
    Electrowinning cells. Recovery of gold, along with co-precipitated
metals such as silver and mercury, from concentrated carbon strip
solutions is performed in one of two ways: Electrowinning (the most
common process) or precipitation with zinc powder (discussed below).
Separation of gold through electrowinning is achieved by using an
electric potential to plate the gold (and other metals present) in
solution onto a cathode; steel wool is typically used as the plating
surface because of the large surface area it provides for gold
deposition. The plated cathode, or sponge, is then either removed from
the electrowinning cell, so that the gold-bearing sludge-like material
can be removed from the plated cathode, or the plated cathode can be
left in the electrowinning (EW) cell, but the current is turned off and
the remaining solution is drained out, then the material is removed
from the plated cathode. Either way, once the current has stopped, the
gold-bearing sludge-like material (known as ``EW concentrate'') is
separated from the cathode by physical means (such as shaking). The
gold-bearing EW concentrate is then ready for further processing.
During electrowinning, elemental mercury can vaporize and escape from
the cell with the other gases produced in the process; carbon
adsorption filters are effective in controlling these mercury
emissions.
    There are approximately 17 electrowinning units located at 14
plants. Five facilities have installed carbon adsorbers to control
mercury emissions from electrowinning. In addition, four facilities in
Nevada have proposed in their State permit applications under the NMCP
to install carbon adsorbers on their electrowinning units.
    Retorts. The EW concentrate may contain up to sixty weight percent
gold, depending on the mercury content of the cyanide solution, the
presence of other metals and minerals in the material, and the
configuration of the gold recovery process. EW concentrate with
significant mercury content is treated in a retort to remove mercury
moisture and other impurities. In this process, the EW concentrate is
placed in a pot or tray that is loaded into a heated oven under vacuum
pressure, usually for 12 to 24 hours at 600 [deg]C to 700 [deg]C to
remove up to 99 percent of the mercury. The EW concentrate is heated,
mercury is vaporized and then pulled through a condenser where it
condenses forming liquid mercury. The liquid mercury is recovered and
sent through a tube into a collection vessel. The remaining gold and
silver at the end of the retorting process typically contains less than
1 percent mercury (e.g., 1,000 to 8,000 mg/kg). The condenser allows
some mercury to discharge in the off gas, and a loss of 0.4 to 0.7
percent of the mercury from the condenser has been reported. There are
approximately 12 facilities that operate retorts, and all operate the
retort with a condenser and a carbon adsorption filter. A properly
designed and maintained carbon adsorption filter located downstream of
the condenser is expected to capture about 95 percent of the mercury in
the cooled gas.
    Melt furnaces. Smelting is the last step in gold mine ore
processing and production before the gold is sent to an off-site
commercial gold refinery. Even after retorting, the retorted gold
mixture still contains some impurities, including small concentrations
of base and ferrous metals, and some residual mercury. During this last
step, the retorted gold mixture (or EW concentrate for facilities that
do not have retorts) is melted in a refinery melt furnace, along with a
flux material that preferentially absorbs impurities, to produce a
purified commercial mixture of gold known as dore. The furnace is
heated to approximately 1500 [deg]C. Most of the remaining mercury is
volatilized in the melt furnace as elemental mercury or oxidized
mercury. The dore melt is poured into bars, and any flux slag that
hardens on the bars is removed with a mechanical chipper. The bars are
then shipped to a commercial gold refinery, where they are further
processed to produce gold bullion (99.9 percent pure gold).
    There are approximately 24 melt furnaces at 17 gold mine ore
processing and production facilities. All of the melt furnaces are
equipped with either fabric filters, ESPs, wet scrubbers, or a
combination thereof to control emissions of PM. The wet scrubbers also
remove most of the oxidized mercury, but do not remove elemental
mercury. Six facilities have installed carbon adsorbers to control both
oxidized and elemental mercury emissions from their melt furnaces. In
addition, three facilities in Nevada have proposed in their State
permit applications under NMCP to install carbon adsorbers on their
melt furnaces.

8. Non-Carbon Concentrate Process
    After leaching, approximately four facilities recover the gold from
the cyanide solution without using carbon by a process commonly known
as the Merrill-Crowe (MC) method. The cyanide solution containing gold
is separated from the ore by methods such as filtration and counter
current decantation and clarified in special filters, usually coated
with diatomaceous earth to produce a clarified solution. Zinc dust is
then added to the clarified solution. Because zinc has a higher
affinity for cyanide ions than does gold or other metals, zinc is
dissolved and gold, silver, and mercury precipitate as a solid. The
fine particulate metals are recovered by filtration processes. This
process is performed in deoxygenated, enclosed reaction cells.
    The precipitate (also known as MC concentrate) is processed in
retorts and melt furnaces, which are described above. The retorts and
melt furnaces are the sources of mercury emissions at facilities that
use non-carbon concentrate processes, and these processes are equipped
with carbon adsorbers or venturi scrubbers to control mercury
emissions. These facilities do not have carbon kilns since they do not
use carbon.

IV. Summary of the Proposed Standards

A. Do these proposed standards apply to my facility?

    These proposed mercury standards would apply to gold mine ore
processing and production facilities that are area sources that use any
of the following thermal processes: Roasting operations, autoclaves,
carbon kilns, preg tanks, electrowinning, retorts, and melt furnaces.
Separate mercury standards are proposed for each of the following three
affected sources: (1) Ore pretreatment processes (roasting operations
and autoclaves), (2) carbon processes (carbon kilns, preg tanks,
electrowinning, retorts, and melt furnaces at facilities that use
carbon to recover the gold from the cyanide solution), and (3) non-
carbon concentrate processes (retorts and melt furnaces at facilities
that do not use carbon to recover gold).
    We are proposing standards for both new and existing affected
sources. An affected source is an existing source if construction or
reconstruction commenced on or before April 28, 2010. An affected
source is a new source if construction or reconstruction commenced
after April 28, 2010.

B. When must I comply with the proposed standards?

    We are proposing that the owner or operator of an existing affected
source comply with the final rule no later than 2 years after
publication of that rule in the Federal Register. The owner or operator
of a new affected source is required to comply by the date of
publication of the final rule in the Federal Register or upon startup
of the affected source, whichever occurs later.

C. What are the proposed standards?

    We are soliciting comments on all aspects of this proposed rule
including, but not limited to, the data and calculations used to
establish the emissions limits, the proposed testing and monitoring for
emissions, and the parametric monitoring of control devices.
    The proposed standards are summarized in Table 1 of this preamble
and discussed in more detail below. These proposed standards establish
mercury MACT emission limits for three affected sources. The proposed
MACT standard for new and existing ore pretreatment processes is 149
pounds of mercury per million tons of ore processed (149 lb/million
tons). The proposed MACT standard for existing carbon processes is 2.6
pounds of mercury per ton of concentrate processed (2.6 lb/ton of
concentrate), and for new carbon processes is 0.14 pounds of mercury
per ton of concentrate (0.14 lb/ton of concentrate). Concentrate is the
gold-bearing sludge material that is processed in retorts. For
facilities without retorts, concentrate is the quantity processed in
melt furnaces before any drying. For new carbon processes, we are
proposing a compliance alternative of 97 percent control efficiency.
This alternative provides at least equivalent HAP reductions as the
MACT floor.

          Table 1--Summary of Proposed Mercury Emission Limits
------------------------------------------------------------------------
                                        Mercury emission limit
       Affected source       -------------------------------------------
                                 Existing source         New source
------------------------------------------------------------------------
Ore pretreatment processes..  149 lb/ton of ore...  149 lb/ton of ore.
Carbon processes............  2.6 lb/ton of         0.14 lb/ton of
                               concentrate.          concentrate or 97
                                                     percent reduction
                                                     in uncontrolled
                                                     emissions.
Non-carbon concentrate        0.25 lb/ton of        0.20 lb/ton of
 processes.                    concentrate.          concentrate.
------------------------------------------------------------------------

    The proposed MACT standard for existing non-carbon concentrate
processes is 0.25 pounds of mercury per ton of concentrate processed
(0.25 lb/ton of concentrate processed), and for new non-carbon
concentrate processes is 0.20 lb/ton of concentrate processed.

D. What are the testing and monitoring requirements?

1. Testing for Compliance With Emission Limits
    Any stack that is a discharge point for any thermal process at a
gold mine ore processing and production facility would be tested for
mercury emissions based on the average of a minimum of three runs per
stack at least once annually (i.e., once every four successive calendar
quarters) using EPA Method 29 in Appendix A-8 to part 60, the Ontario
Hydro Method (ASTM D6784-02, ``Standard Test Method for Elemental,
Oxidized, Particle-Bound and Total Mercury in Flue Gas Generated from
Coal-Fired Stationary Sources''), EPA Method 30A, or EPA Method 30B,
both in Appendix A-8 to part 60.
    We are proposing that the initial compliance test for new sources
be conducted within 180 days of the compliance date. The emissions for
each process stack (in lb/hr) would be multiplied by the number of
hours the process operated in the 6-month period following the
compliance date to determine the total mercury emissions for the
initial 6-month period. The process inputs used in the denominator of
the emission limit, including ore and concentrate, would be measured
and summed for each month to provide the total input (in tons) for the
initial 6-

month period following the compliance date. The sum of the emissions
(in lbs) for the 6-month period for all process units included in the
affected source would be divided by the total input for the 6-month
period to determine compliance with the emission limit. After the
initial 6-month period, all the stacks for the thermal process units
would be tested for mercury emissions annually.
    We are proposing that existing sources also conduct their initial
compliance test within 180 days of their compliance date. The emissions
for each process stack (in lb/hr) would be multiplied by the number of
hours the process operated in the 6-month period following the initial
compliance date to determine the emissions for the 6-month period. The
emissions for each process stack would be recorded in total pounds of
mercury for the 6-month period. The total mercury emissions for the
affected source for the 6 months would be determined by summing the
emissions for each process stack included in the affected source. The
total emissions for the 6-month period for the affected source would be
divided by the process input (concentrate or ore) for the 6-month
period to determine compliance with the emission limit.
    After the initial 6-month period, all of the stacks for the thermal
process units at new and existing sources would be tested for mercury
emissions annually. The total mercury emissions and process inputs for
each 12-month period would be calculated as described below to
determine compliance with the emissions limit.
    The process inputs used in the denominator of the emission limit,
including ore and concentrate, would be measured and summed to provide
the total input (in tons) for each month. For facilities with ore
pretreatment processes, the daily quantity of ore (in tons) would be
determined either by calibrated weigh scales or by measuring volumetric
flow rate and density and multiplying the two measurements. The daily
totals would be summed for each calendar month to provide a monthly
total for ore input. For facilities with carbon and/or non-carbon
processes affected sources, each batch of concentrate would be weighed
by scales, and the total of all batches would be summed for each
calendar month to produce monthly weights of concentrate.
    Emissions in lb/million tons of ore for each affected source of ore
pretreatment processes would be determined by summing the emissions for
all units in the pre-treatment processes affected source for the
appropriate time period (e.g., a 6-month period initially for new and
existing sources and the 12-month periods thereafter) and dividing this
sum of the emissions by the sum of the total ore processed (expressed
in millions tons) in all processes at the affected source for the
appropriate time period (i.e., 6 months or 12 months). Emissions in lb/
ton of concentrate for each affected source of carbon processes would
be determined by dividing the sum of the emissions from all carbon
processes at the affected source for the appropriate time period by the
sum of the tons of concentrate processed at the affected source for
each time period. Emissions in lb/ton of concentrate for each non-
carbon concentrate process affected source would be determined by
dividing the sum of the emissions from all non-carbon concentrate
process units at the affected source for each appropriate time period
by the sum of the concentrate (expressed in tons) processed in all
process units at the affected source for each time period.
    Mercury testing at both the inlet and outlet of all mercury
emissions control devices is proposed for new affected sources with
carbon processes that choose to demonstrate a 97 percent reduction in
emissions. The inlet and outlet of every process unit's control device
would be sampled, and the mercury emissions before and after control
(in lb/hr) would be multiplied by each process unit's operating hours
for the appropriate time period to determine the mercury emissions for
the time period. The initial tests would be done within 180 days of the
compliance date. For the first 6 months of operation, the inlet
emissions for all process units would be calculated and summed and
compared to the sum of the calculated outlet emissions for the 6-month
period. After the initial 6 months, annual tests would be conducted and
the calculations would be based on each 12 month period to determine
the percent reduction in mercury emissions.
    We have also considered other procedures for calculating the
mercury emission rate in pounds per ton of input to determine
compliance for the ore pretreatment group and possibly for the carbon
and non-carbon affected sources as well. For example, one approach for
the ore pre-treatment processes would be to divide the measured
emission rate (in pounds per hour) from the compliance test for each
autoclave and roasting operation by the ore throughput (in tons per
hour) for each autoclave and roasting operation as measured during the
performance tests. The result would be emissions in pounds per ton of
ore for each autoclave and roasting operation. Then the fraction of the
total ore processed in the previous 12 months would be calculated for
each roasting operation and autoclave, and the emissions from all
autoclaves and roasting operations in the group would be calculated as
the weighted average pounds per ton of ore to determine compliance
(i.e., the sum of fraction of total ore throughput times the pounds per
ton for each roasting operation and autoclave). With this approach, it
would not be necessary to monitor, record, and use the annual operating
hours for each unit to calculate emissions. A similar approach could
possibly also be used for the carbon and non-carbon groups. We are
requesting comment and supporting information on the advantages and
disadvantages of this possible alternative procedure and the proposed
procedure for determining compliance from the ore pretreatment
processes and the other process groups.
2. Monitoring Requirements
    Roasters. We are proposing two options for monitoring roaster
emissions: (1) Integrated sorbent trap mercury monitoring coupled with
parametric monitoring of scrubbers and (2) monitoring using a
continuous emission monitoring system (CEMS) for mercury. Both proposed
monitoring options would require establishment of operating limits to
detect and correct problems as soon as possible. An exceedance of an
operating limit would trigger immediate corrective action and would
require that the problem be corrected within 48 hours or that the feed
of ore to the roaster be stopped.
    The first option for monitoring emissions from roasters would be to
use the EPA Performance Specification (PS) 12B for integrated sorbent
trap mercury monitoring on a periodic basis coupled with parametric
monitoring of mercury scrubbers. We propose that under this option the
facility will sample and analyze weekly for mercury concentration
according to PS 12B. To determine appropriate sampling duration, we
propose that the owner or operator review the available data from
previous stack tests to determine the upper 99th percentile of the
range of mercury concentrations in the exit stack gas. Based on this
upper end of expected concentrations, the facility would select an
appropriate sampling duration that is likely to provide a valid sample
and not result in breakthrough of the sampling tubes. If breakthrough
of the sampling tubes occurs, the facility would re-sample using a
shorter sampling duration.
    We are proposing that the owner or operator of an affected source
would establish an operating limit for mercury

concentration for PS 12B monitoring during the initial compliance test
and maintain the mercury emissions below the established operating
limit. The specific method and equation to be used to establish the
operating limit are described in the proposed rule. If the operating
limit is exceeded, the facility would report the exceedance as a
deviation and take corrective actions within 48 hours to return the
emissions control system back to proper operation.
    In addition, we are proposing as part of this first monitoring
option (i.e., sorbent trap monitoring) that facilities with roasters
and calomel-based mercury control systems (also referred to as
``mercury scrubbers'') also establish operating limits for various
control parameters described below during their annual mercury
compliance stack test. We are proposing that each mercury scrubber be
equipped with devices to monitor the scrubber liquor flow rate,
scrubber pressure drop, and inlet gas temperature. Minimum operating
limits for the scrubber liquor flow rate and pressure drop would be
established based on the lowest average value measured during any of
the three runs of a compliant performance test. A maximum inlet
temperature would be established based on the highest temperature
measured during any of the three runs of the compliance test. In
addition to the parameters described above, we are proposing that the
facility must also monitor the mercuric ion concentration and the
chloride ion concentration four times per day or continuously monitor
the oxidation reduction potential and pH. These monitored parameters
would be maintained within the range specified by the scrubber's
manufacturer or within an alternative range approved by the permitting
authority. If any of the parameters are outside the specified range or
limit, corrective action would be taken to bring the parameters back to
the operating range or limit or else the facility would commence
shutdown of the roaster.
    As mentioned above, we are including an alternative option for
monitoring emissions from roasters, which is to install and operate a
continuous emission monitoring system (CEMS) for mercury. Under this
alternative option, facilities would not be required to do the
parametric monitoring of the mercury scrubbers described above under
the first option. A facility choosing the CEMS option would operate the
mercury CEMS according to EPA Performance Specification (PS) 12A
(except that calibration standards traceable to the National Institute
of Standards and Technology (NIST) are not required). This exception is
necessary because the mercury concentrations in the exhaust gases from
roasters can be higher than the range of concentrations that are
covered with the existing calibration standards traceable to NIST. The
current calibration standards traceable to NIST do not apply to the
full range of mercury concentrations that can be present in the exhaust
gases from roasters. However, calibration standards are available from
the manufacturers of mercury CEMS which can be used to calibrate these
CEMS for monitoring of roasters.
    In addition to following PS 12A, the facility would perform a data
accuracy assessment of the CEMS according to section 5 of Appendix F in
part 60. We are proposing that the owner or operator would establish an
operating limit for mercury concentration for the CEMS during a
compliance test for the roaster stack and monitor the daily average
mercury concentration in the roaster stack exhaust gas with the CEMS.
The specific method and equation to be used to establish the operating
limit are described in the proposed rule. If any daily average
concentration as measured with the CEMS exceeds the operating limit,
the facility would report the exceedance as a deviation and take
corrective actions within 48 hours to return the emission control
system back to proper operation. Regardless of whether deviations
occur, the owner or operator of any facility with a roaster would
submit a monitoring plan that includes quality assurance and quality
control (QA/QC) procedures sufficient to demonstrate the accuracy of
the CEMS. At a minimum, the QA/QC procedures would include daily
calibrations and an annual accuracy test for the CEMS.
    For facilities that control roaster mercury emissions with mercury
scrubbers, we are proposing not to require sorbent traps or mercury
CEMs monitoring if a facility demonstrates that the mercury emissions
from its roasters are consistently low and well controlled.
Specifically, if a facility can demonstrate that mercury emissions from
the roaster are less than 10 pounds of mercury per million tons of ore,
then the facility would be allowed to discontinue the use of the
sorbent trap or CEMS as described above. To demonstrate this, the
facility would conduct three or more consecutive independent
performance tests for mercury at least one month apart on the roaster
exhaust stacks and show that emissions are less than 10 pounds per
million tons of ore during normal operations for all tests. However,
such a facility would be required to perform the parametric monitoring
for mercury scrubbers and maintain parameters within the operating
ranges established in accordance with the proposed rule. Also, the
facility would continue to perform annual compliance tests of the
roaster stack. Moreover, if there is an increase in the mercury
concentration in the ore processed by the roaster that is higher than
any concentration measured during the previous 12 months, then the
facility would need to perform a compliance test within 30 days of the
first day that the new ore is processed to determine whether the
mercury emissions are still below 10 lbs per million tons of ore. If
any subsequent performance compliance test indicates that the roaster
is emitting more than 10 pounds of mercury per million tons of ore
input, then the facility would be required to monitor the roaster
emissions using the sorbent trap method or CEMS.
    Carbon Adsorbers. For process units (such as furnaces, kilns,
retorts, electrowinning, and autoclaves) that control mercury emissions
with a carbon adsorber, we are proposing three emissions monitoring
options. One proposed option involves monitoring the mercury
concentration at the exit of the carbon bed. A second option is based
on sampling the carbon bed for mercury. The third option is based on
changing out the carbon bed after a fixed period of time determined
based on historical operating experience.
    For the first option (i.e., the exit concentration monitoring
option), the mercury concentration would be measured periodically using
a sorbent trap according to EPA Method 30B. An operating limit would be
established through sorbent trap measurements obtained during the
initial compliance test. The mercury concentration would be measured
during each annual performance compliance test of each of the stacks
for the carbon processes using Method 30B. An operating limit would be
calculated from the average mercury concentration measured during the
compliance test multiplied by a factor. The factor is the MACT emission
limit for carbon processes divided by the sum of results of the
compliance test for all units within the carbon processes affected
source. Thereafter, if the established operating limit is exceeded, the
exceedance would be reported as a deviation and corrective action would
be triggered (e.g., replace the carbon in the bed). The specific
equations to calculate the operating limit are described in the
proposed rule. Initially, the facility would measure mercury
concentration in the exit gas monthly using Method 30B. Once mercury

concentrations reach 50 percent of the operating limit, the facility
would then need to perform weekly sampling and analysis using Method
30B. When the concentration reaches 90 percent of the operating limit,
to prevent an exceedance, the owner or operator would be expected to
replace the carbon in the control device within 30 days (or before the
operating limit is actually exceeded).
    The second proposed monitoring option, which is based on sampling
the carbon bed for mercury, would require conducting an initial
sampling of the carbon in the carbon bed 90 days after the replacement
of the carbon to determine mercury loading. A representative sample
would be collected from the carbon bed and analyzed using EPA Method
7471A, and the depth to which the sampler is inserted would be
recorded. Based upon sample results, a carbon loading would be
calculated for the system, and sampling would be performed quarterly
thereafter. When the carbon loading reaches 50 percent of the design
capacity of the carbon, monthly sampling would be performed until 90
percent of the carbon loading capacity is reached. The carbon would be
removed and replaced with fresh carbon no later than 30 days after
reaching 90 percent of capacity to ensure that the maximum mercury
loading as recommended by the manufacturer is not exceeded.
    The third proposed option would start with one of the two previous
options. After collecting at least two years of data under one of the
options described above, a facility would establish a change out time
for the carbon based on the two years of monitoring and could implement
this periodic change out instead of sampling and analysis after
approval by the permitting authority. However, if there is any
significant change in the process, input materials, or mercury control
system (e.g., an increase in operating rates or processing different
ores with higher mercury levels) then sampling and analysis (according
to the procedures in option 1 or option 2 described above) would be
required within 30 days to re-establish the carbon change out time.
    We are also proposing that the inlet stream to carbon adsorbers
applied to autoclaves, carbon kilns, melt furnaces, and retorts be
monitored for temperature and that the inlet temperature be maintained
below the maximum temperature established during the compliance tests.
If the maximum temperature is exceeded, the owner or operator would
analyze the outlet concentration using Method 30B within 30 days as
described above. If the concentration is below 90 percent of the
operating limit, the owner or operator could set a new temperature
operating limit 10 [deg]F above the previous operating limit. On the
other hand, if the concentration is more than 90 percent of the
operating limit, the facility would take corrective action to reduce
the temperature back down to below the maximum temperature recorded
during compliance tests and then retest emissions using Method 30B. If
the concentration is more than 90 percent of the operating limit based
on this subsequent test, then the facility must replace the carbon.
    Wet scrubbers. For each wet scrubber, we are proposing that
pressure drop and water flow rate be maintained at a minimum level
based on measurements during the initial or subsequent compliance
test(s).

E. What are the notification, recordkeeping, and reporting
requirements?

    The owner or operator of an existing or new affected source would
be required to comply with certain notification, recordkeeping, and
reporting requirements of the NESHAP General Provisions (40 CFR part
63, subpart A), which are identified in Table 1 of this proposed rule.
Each owner or operator of an affected source would submit an Initial
Notification according to the requirements in 40 CFR 63.9(a) through
(d) and a Notification of Compliance Status according to the
requirements in 40 CFR 63.9(h).
    Each owner or operator of an existing or new affected source would
be required to keep records to document compliance with the mercury
emission limits. Owners or operators of new and existing affected
sources would maintain records of all monitoring data. Other records
include monthly totals of ore quantity for ore pretreatment affected
sources, monthly quantities of concentrate for all other affected
sources, and monthly hours of operation for each process unit at each
affected source.
    If a deviation from this rule's requirements occurs, an affected
source would be required to submit a compliance report for that
reporting period. The proposed rule specifies the information
requirements for such compliance reports.
    We are also proposing to require electronic reporting of
performance evaluation data collected using methods compatible with
EPA's Electronic Reporting Tool (ERT). After December 31, 2011, within
60 days after the date of completing each performance evaluation
conducted to demonstrate compliance, the owner or operator would submit
the test data to EPA by entering the data electronically into EPA's
WebFIRE database through EPA's Central Data Exchange. The owner or
operator of an affected facility would enter the test data into EPA's
database using the ERT or other compatible electronic spreadsheet. Only
performance evaluation data collected using methods compatible with ERT
would be subject to this requirement to be submitted electronically
into EPA's WebFIRE database.

F. What are the title V permit requirements?

    Under section 502(a) of the CAA, all major sources and certain
other sources, including sources subject to section 112 standards, are
required to operate in compliance with a title V permit. Today's
proposal requires that gold mine ore processing and production area
sources comply with the title V permitting requirements. However,
section 502(a) of the CAA provides that the Administrator may exempt an
area source category (in whole or in part) from title V if she/he
determines that compliance with title V requirements is
``impracticable, infeasible, or unnecessarily burdensome'' on such
category. We are therefore soliciting comment on whether such an
exemption is appropriate under section 502(a) for any particular
sources in this category. Commenters should provide supporting data and
rationale to explain the bases for their comments.\1\
---------------------------------------------------------------------------

    \1\ For the factors that EPA considers in evaluating whether to
exercise the Agency's discretion to exempt area sources from title
V, please see National Emission Standards for Hazardous Air
Pollutants for Area Sources: Clay Ceramic Manufacturing, Glass
Manufacturing, and Secondary Nonferrous Metal Processing; Proposed
rule, 72 FR 53838, 53849-53853 (September 20, 2007).
---------------------------------------------------------------------------

G. Emissions of Non-Mercury HAPs

    EPA recently gathered data and evaluated emissions of other HAP,
including cyanide and non-mercury metals. The data indicate that the
gold mining processing and production category consists of only area
sources (i.e., facilities that emit less than ten tons per year of any
one HAP and less than 25 tons per year of any combination of HAP).
However, a few facilities are close to the major source threshold due
to hydrogen cyanide (HCN). For example, the largest facility emits an
estimated 5 to 9 tons of HCN per year. Emissions of all other HAPs,
including mercury, are individually significantly lower than the 10 ton
per year threshold for a single HAP and the 25 ton per year threshold
for a

combination of HAP. However, depending on how facilities manage their
cyanide processes, EPA believes that cyanide emissions could
potentially change a facility's status from area source to major
source. Although EPA would develop MACT standards if it ever identified
any major sources of gold mine ore processing and production, the MACT
standards in today's proposal apply only to area sources because those
are the only gold mine ore processing and production sources EPA has
identified.
    In light of the above, we are considering including in today's
NESHAP a provision under which sources may certify and demonstrate that
they are area sources of gold mine ore processing and production. We
would include in this area source NESHAP management practices for
cyanide processes that we believe would effectively limit cyanide
emissions and thus assure that sources maintain their area source
status. To the extent sources were concerned about their HCN emissions,
they could implement the management practices for cyanide processes
specified in this rule and certify to the Agency that they had done so.
Some management practices we are considering include: maintaining pH of
cyanide leach solutions greater than nine; burying leach lines whenever
practical and feasible; monitoring cyanide concentrations at the
perimeter and in a downwind direction of main emission sources; not
allowing puddles to form that are greater than 1 square meter on leach
pads; and in locations that have the highest potential for concentrated
emissions (e.g., mixing tanks, CIL tanks, loading stations) maintain
HCN air concentrations below a prescribed level (e.g., 5 ppm).
    We request comment on whether we should include the proposal
described above or some modification of it. We also request comment on
effective management practices to limit cyanide emissions, including
the practices described above as well as other approaches to manage
cyanide emissions.

H. Request for Comments

    As mentioned previously, we are soliciting comments on all aspects
of this proposed rule, including, but not limited to, the data and
calculations used to establish the emissions limits for mercury, the
proposed requirements and options for emissions testing and monitoring,
the parametric monitoring options for control devices, title V permit
requirements, and emissions of non-mercury HAPs.

V. Rationale for the Proposed Standards

A. How did we select the affected source?

    We are proposing individual MACT standards for each of the
following three affected sources in the gold mine ore processing and
production source category: ore pretreatment processes, carbon
processes, and non-carbon concentrate processes. These three affected
sources reflect the three primary different types of processes used in
this source category to produce gold. Moreover, many gold mine ore
processing and production facilities combine the emissions from
multiple process units within a single affected source and route them
to a single mercury emission control system and stack. Because we
cannot determine the mercury emissions from individual process units
that share a stack, it is difficult to establish emission standards for
each process unit within an affected source. Setting MACT standards for
each of the three affected sources accommodates the various stack and
control configurations for the process units within an affected source.
Emissions from all process units in the affected source would be summed
to determine compliance with the proposed MACT standard for that
affected source.
    As described above, the three affected sources differ in process
operations, the sources of mercury entering the processes, and the
nature of the emissions. Ore pretreatment processes include roasting
operations (roasters, ore dryers, ore pre-heaters, and quenchers) and
autoclaves that are used to pretreat refractory ore, which contains
organic carbon and/or sulfide mineral grains that prevent the initial
use of cyanide leaching to extract the gold effectively from the ore.
Mercury enters these processes with the ore. The potential for mercury
emissions from this affected source is directly related to the amount
of ore processed in the autoclaves and roasters; the proposed standard
for this affected source is therefore expressed in pounds of mercury
emissions per million tons of ore processed (lb/million tons of ore).
    Carbon processes include carbon kilns, electrowinning cells, melt
furnaces, retorts, and preg tanks at facilities that use carbon to
recover gold from pregnant cyanide solution. In developing a proposed
format for the emission limit for carbon processes, we examined the use
of loaded carbon, concentrate, and gold production in the denominator
of a pound per ton format. In other NESHAPs, we have typically used the
amount of feed throughput or the amount of product produced in the
denominator of the emission limit. For example, in the proposed
revisions to the Portland cement NESHAP (74 FR 21136, May 6, 2009), we
analyzed the data and developed the MACT floor in terms of pounds per
million tons of feed to the kiln and subsequently converted the
emission limit to a format of pounds per million tons of clinker (i.e.,
the product from the kiln). Although loaded carbon can be considered
the ``primary feed,'' we discovered there were potential issues with
its measurements (e.g., default values were used for density), we were
unsure that the data from different facilities were comparable, and it
was not a quantity that has been required to be reported under existing
State regulatory programs. We rejected the use of gold produced because
some facilities do not produce gold (they send the intermediate product
to offsite refineries), some facilities produce more silver than gold,
and the quantity of gold varies depending on the percent of gold in the
product. The primary intermediate product that is common to all of the
facilities with these carbon processes is the gold-bearing EW
concentrate, which is the input to retorts or melt furnaces. Further,
concentrate is closely related to the final product because it contains
about 60 percent gold, and because of its value, it is carefully and
accurately weighed and records of the quantities are kept. Concentrate
is also required to be reported under the NDEP program, so we had
comparable and reliable data from the different gold mine ore
processing and production facilities. Consequently, we decided that the
most appropriate format of the emission limit for the carbon processes
is lb/ton of concentrate.
    For the reasons discussed above, we are proposing the concentrate
format. However, we also considered using the amount of loaded carbon
for the denominator of the emission limit format for carbon processes
instead of concentrate, and we believe there may be merit in using
loaded carbon as the denominator. Therefore, we are soliciting comments
on the merits of both formats. In particular, we seek comments on
whether loaded carbon or concentrate would be the better format for
compliance determinations (e.g., accuracy and reliability of the
measurements, availability of records) or for other reasons or factors,
such as the processes present at a given plant, operating layout, or
offsite shipments for processing. We are also requesting

comment on whether the quantity of concentrate should be determined on
an ``as fed'' or dry basis, and if a dry basis, what methods could be
used to determine dry weight accurately and reproducibly.
    Non-carbon concentrate processes include retorts and melt furnaces
at facilities that use the Merrill Crowe process to produce gold. These
affected sources do not use carbon to recover gold and the only thermal
process units used to recover gold ore are retorts and furnaces. As
described above, during the non-carbon processes, zinc dust is added to
the cyanide solution after leaching to precipitate gold and other
metals (including mercury). The precipitate (or ``MC concentrate'') is
then processed in retorts and metal furnaces, liberating mercury from
the concentrate. The potential mercury emissions are therefore directly
related to the amount of concentrate processed; consequently for this
reason and the merits of using concentrate as discussed above, the
proposed standard for this affected source is expressed in lb/ton of
concentrate.

B. How did we determine MACT?

1. Selection of MACT Floors for Existing Sources for the Three Affected
Sources
    CAA section 112(d)(3)(B) requires that the MACT standards for
existing sources be at least as stringent as the average emission
limitation achieved by the best performing five sources (for which the
Administrator has or could reasonably obtain emissions information) in
a category with fewer than 30 sources. The gold mine ore processing and
production source category consists of fewer than 30 sources. As
mentioned above, we are proposing MACT standards for each of the
following three affected sources: ore pretreatment processes, carbon
processes, and non-carbon concentrate processes. We have mercury
emissions data on ore pretreatment processes for all five facilities in
the United States with ore pretreatment processes. We have mercury
emissions data on carbon processes for 11 facilities and mercury
emissions data on non-carbon concentrate processes for two facilities.
Pursuant to section 112(d)(3), the MACT floor limits for existing ore
pretreatment processes and carbon processes are based on the average
emission limitation achieved by the best performing five facilities for
each of these two affected sources, and the MACT floor limit for
existing non-carbon concentrate processes are based on the average
emission limitation achieved by the two facilities with such processes.
    To calculate the MACT floor limit for each of the affected sources,
we established and ranked sources' emissions from lowest to highest.
The data on which we based the limits are expressed in terms of pounds
of mercury emitted per ton of input, where the gold mine ore is the
input for the ore pretreatment processes and concentrate is the input
for the carbon processes and the non-carbon concentrate processes.
    We used the emissions data for those best performing affected
sources to determine the emission limits to be proposed, with an
accounting for variability. EPA must exercise its judgment, based on an
evaluation of the relevant factors and available data, to determine the
level of emissions control that has been achieved by the best
performing sources under variable conditions. The Court has recognized
that EPA may consider variability in estimating the degree of emission
reduction achieved by best-performing sources and in setting MACT
floors. See Mossville Envt'l Action Now v. EPA, 370 F.3d 1232, 1241-42
(DC Cir 2004) (holding EPA may consider emission variability in
estimating performance achieved by best-performing sources and may set
the floor at a level that a best-performing source can expect to meet
``every day and under all operating conditions'').
    To calculate the achieved emission limit, including variability, we
used the equation: \2\
---------------------------------------------------------------------------

    \2\ More details on the calculation of the MACT floor limits are
given in the technical memo in the docket.
---------------------------------------------------------------------------

UPL = xp + t * (vT) \0.5\

Where:

UPL = upper prediction limit (99 percent),
xp = average of the best performing MACT pool sources,
t = Student's t-factor evaluated at 99 percent confidence, and
vT = total variance determined as the sum of the within-
source variance and the between-source variance.

    The between-source variance is the variance of the average of the
best performing source averages. The within-source variance is the
variance of the MACT source average considering ``m'' number of future
individual test runs used to make up the average to determine
compliance. We are proposing that a compliance test would be based on
the average of three runs; consequently, the value of ``m'' used in the
statistical analysis is 3. This value of ``m'' is used to reduce the
variability to account for the lower variability when averaging of
individual runs is used to determine compliance in the future. For
example, if the average of three test runs is used to determine
compliance (m=3), the variability based on 3-run averages is lower than
the variability of the single run measurements in the data base, which
results in a lower UPL for the 3-run average.
    Our MACT floor limit calculations are based primarily on mercury
emissions data from annual testing that was required by NDEP for 2007
and 2008. However, we used data from 2006 for an autoclave at a Nevada
facility that was not tested in 2007 and did not operate in 2008. We
also used data from 2009 to replace 2008 test data at one Nevada
facility that was invalidated due to not following the procedures in
the State's testing protocol. In addition, we used 2010 test data for a
Nevada facility that installed new mercury emission controls on its
roasters and resumed operation in late 2009. The tests that generated
the data described above generally consisted of three runs per test per
process at each facility. There were cases where 2007 results represent
emissions before a control device was installed, and 2008 test results
were after a mercury emission control device had been installed. In
those cases, we used only the 2008 (controlled) test results to
determine the top performing facilities. Emissions from the tests (in
lb/hr) were multiplied by the number of hours the process operated in
the calendar year and then divided by the process input rate for the
year (in tons) to calculate the facility's performance for an affected
source (expressed as lbs of mercury emissions per ton of input
material).
    Source performance and the resulting MACT floor limits are
summarized in Tables 2, 3, and 4, for ore pretreatment, carbon, and
non-carbon concentrate processes, respectively.

            Table 2--MACT Floor Results for Ore Pretreatment
------------------------------------------------------------------------
                                                              Average
                                                            performance
                        Facility                            (lb/million
                                                             tons ore)
------------------------------------------------------------------------
A.......................................................              62
B.......................................................              64
C.......................................................              69
E.......................................................              90
D.......................................................             211
Average of top 5........................................              99
99% UPL existing (MACT Floor)...........................             175
99% UPL new (MACT Floor)................................             163
------------------------------------------------------------------------

            Table 3--MACT Floor Results for Carbon Processes
------------------------------------------------------------------------
                                                              Average
                                                            performance
                        Facility                              (lb/ton
                                                           concentrate)
------------------------------------------------------------------------
M.......................................................            0.06
N.......................................................            0.60
A.......................................................            1.5
H.......................................................            1.8
D.......................................................            2.9
F.......................................................            3.1
C.......................................................            3.7
I.......................................................            6.9
G.......................................................            9.7
B.......................................................           21
J.......................................................           39
Average of top 5........................................            1.4
99% UPL existing (MACT Floor)...........................            2.6
99% UPL new (MACT Floor)................................            0.14
------------------------------------------------------------------------

    Table 4--MACT Floor Results for Non-Carbon Concentrate Processes
------------------------------------------------------------------------
                                                              Average
                                                            performance
                        Facility                              (lb/ton
                                                           concentrate)
------------------------------------------------------------------------
K.......................................................            0.07
L.......................................................            0.11
Average of top 2........................................            0.09
99% UPL existing........................................            0.25
99% UPL new.............................................            0.20
------------------------------------------------------------------------

    The average emission rates for ore pretreatment and carbon
processes from the top five facilities performing these processes are
99 lbs/million tons ore and 1.4 lb/ton of concentrate, respectively.
The average emission rate for non-carbon concentrate processes from the
top two facilities performing these processes is 0.09 lb/ton of
concentrate. As previously discussed above, we account for variability
in setting floors, not only because variability is an element of
performance, but also because it is reasonable to assess best
performance over time. Here, for example, we know that the 2 to 5
lowest emitting affected sources' emission estimates are averages and
we expect that the actual emissions will vary over time. If we do not
account for this variability, we would expect that even the sources
that perform better than the floor on average would potentially exceed
the floor emission levels part of the time.
    For the lowest emitting sources (2 to 5 sources, depending on the
affected source), we calculated an average emission rate using the data
from multiple test runs for multiple processes. The results are shown
in Tables 2, 3, and 4 and represent the average performance of each
source from the sum of the average emissions from all process units
within the affected source. We then calculated the average performance
of the lowest emitting sources and the variances of the emission rates
for each process unit, which is a direct measure of the variability of
the data set. This variability includes the run-to-run and year-to-year
variability in the total mercury input to each process unit and
variability of the sampling and analysis methods over the testing
period, and it includes the variability resulting from site-to-site
differences for the lowest emitters. We calculated the MACT floor based
on the UPL (upper 99th percent) as described earlier from the average
performance of the lowest emitting sources, Students t-factor, and the
total variability, which was adjusted to account for the lower
variability when using 3-run averages to determine compliance. Our
calculations yield the following MACT floor limits for existing
sources: 175 lbs/million tons of ore for ore pretreatment processes,
2.6 lb/ton of concentrate for carbon processes, and 0.25 lbs/ton of
concentrate for non-carbon concentrate processes.
    The technologies for achieving the MACT floor for existing ore
pretreatment processes include mercury scrubbers on roasters and
venturi scrubbers on autoclaves and ancillary roaster operations. The
roasters and autoclaves at Facilities A, B, C, and E shown in Table 2
above are already equipped with these controls. Our MACT floor analysis
indicates that these facilities are achieving the MACT floor average of
99 lb/million tons of ore. The analysis also indicates that an emission
reduction will be needed for Facility D to achieve the MACT floor.
Currently Facility D also has venturi scrubbers on its autoclaves;
however, the emission control performance of these scrubbers will need
to be improved to achieve the MACT floor.
    To achieve the MACT floor for existing carbon processes, we expect
that facilities would need to install carbon adsorbers on all process
units that do not already have them (i.e., carbon adsorbers for carbon
kilns, electrowinning, preg tanks, retorts, and melt furnaces). Our
MACT floor analysis indicates that only Facilities M and N in Table 3
are achieving the MACT floor level of control; consequently, the other
nine facilities in Table 3 are expected to have to install carbon
adsorbers on all process units that do not already have them. The two
top performing facilities (M and N) are fully equipped with carbon
adsorbers (i.e., all of their process units are controlled by carbon
adsorbers). Facility M also processes ore which has significantly lower
mercury concentrations compared to the ore processed at most other
facilities. We believe the combination of processing ore with low
mercury content and the use of state-of-the-art mercury emission
controls result in emissions at Facility M that are considerably lower
than the other facilities.
    For the non-carbon concentrate processes, the MACT floor technology
is the use of carbon adsorbers on retorts and melt furnaces. We expect
that Facility L would probably need to install a carbon adsorber on
their melt furnace to achieve the MACT floor.
2. Selection of New Source Floors for the Three Affected Sources
    CAA section 112(d)(3) requires that the MACT floor limit for new
sources not be less stringent than the emission control that is
achieved in practice by the best controlled similar source. Table 2
above shows that Facility A has the lowest emission rate for ore
pretreatment processes and is therefore considered the ``best
controlled similar source'' for such processes. As previously
mentioned, this facility is equipped with calomel scrubbers on roasters
and venturi scrubbers on autoclaves. The emission rate for ore-
pretreatment processes at Facility A is 62 lbs/million tons ore, not
accounting for variability. Applying the UPL formula discussed earlier
to account for variability based on the emission test runs for all
affected process units at the best performing ore pretreatment affected
source (Facility A), we calculated the 99th percentile of performance,
which results in a new source MACT level of 163 lb/million tons of ore
for ore pre-treatment processes.
    Table 3 shows that Facility M has the lowest emission rate for
carbon processes and is therefore considered the ``best controlled
similar source'' for such processes. As previously mentioned, all
carbon process units at Facility M are well controlled with carbon
absorbers. The emission rate for carbon processes at Facility M is 0.06
lb/ton of concentrate. After applying the UPL formula as described
above to account for variability, the new source floor for carbon
processes based on the 99th percentile of performance is 0.14 lb/ton of
concentrate.
    For carbon processes at new sources, we are proposing a compliance
alternative to provide flexibility in determining compliance because of
the wide variety of process combinations and variations in input
material that

may be present at future new carbon process sources. A well-established
and conventional metric for expressing the degree of emission control
is the percent control of the target pollutant. As mentioned above,
Facility M is considered the ``best controlled similar source'' for
carbon processes. Test data were available for 2007 for Facility M when
the processes were uncontrolled, for 2008 when the controls were newly
installed, and from 2009 after over one year of operation. The test
results showed a 99.6 percent mercury emission reduction in 2008 and
93.5 percent reduction in 2009. Based on these results and considering
variability over time, we are proposing a compliance alternative of 97
percent reduction in mercury emissions for new carbon processes. This
compliance alternative was calculated based on the average reduction
achieved by the best performing source in 2008 and 2009.
    Table 4 shows that Facility K has the lowest emission rate for non-
carbon concentrate processes and is therefore considered the ``best
controlled similar source'' for such processes. The emission rate for
non-carbon concentrate processes at Facility K is 0.07 lb/ton of
concentrate (not accounting for variability). Again applying the UPL
formula as described above to account for variability, the new source
floor for non-carbon concentrate processes based on the 99th percentile
of performance is 0.20 lb/ton of concentrate.
3. Beyond the Floor Determination
    To evaluate opportunities for emission reductions beyond those
provided by the MACT floor, we typically identify control techniques
that have the ability to achieve an emissions limit more stringent than
the MACT floor. As mentioned above, the facilities with ore
pretreatment processes would have installed mercury scrubbers and
venturi scrubbers on their roasters and autoclaves, respectively, to
achieve the MACT floor for ore pretreatment processes. To achieve
further reductions in mercury beyond what can be achieved using mercury
scrubbers and venturi scrubbers, we identified as a beyond-the-floor
option the installation of both a refrigeration unit (or condenser) and
a carbon adsorber on autoclaves. This additional control system would
follow the existing venturi scrubbers to further reduce mercury
emission from autoclaves. Because the exhaust is saturated with water,
a refrigeration unit or condenser would be needed to remove water that
would otherwise adversely affect the adsorptive capacity of the carbon
adsorber. With this additional control system, all facilities with ore
pretreatment processes could achieve an average performance of 90 lb/
million tons of ore or less. This is lower than the average emission
rate of 99 lbs/million tons ore for ore pretreatment processes from the
top five facilities performing these processes.
    In determining whether to control emissions ``beyond-the-floor,''
we must consider the costs, non-air quality health and environmental
impacts, and energy requirements of such more stringent control. See
CAA Section 112(d)(2). We estimate that the capital cost for the
additional controls on the autoclaves would be $890,000 with a total
annualized cost of $720,000/yr. Mercury emissions would be reduced by
543 lbs, resulting in an estimated cost effectiveness of $1,300/lb.
Energy consumption would increase by about 730 megawatt-hours per year,
primarily due to the refrigeration unit. Solid waste generation and
disposal (spent carbon loaded with mercury) would increase by about 3
tons per year. (See Section VI.A for additional discussion of our
consideration of emissions, cost, and non-air impacts in developing
MACT standards for this source category.) After considering the costs
and the above-mentioned impacts associated with the use of a
refrigeration unit (or condenser) and a carbon adsorber on autoclaves,
we believe that the emission reduction that can be achieved with this
additional control system is justified under section 112(d) of the CAA.
Applying the UPL formula discussed earlier to account for variability,
the 99th percent UPL would be 149 lb/million tons of ore. We therefore
propose that the beyond-the-floor performance level of 149 lb/million
tons of ore is MACT for new and existing ore pretreatment processes.
    For the carbon processes, we estimate that 9 of the 11 facilities
for which we have data will need to improve control to meet the floor
limits because these 9 plants have an average emission control
performance that is above the MACT floor average performance. There are
a few facilities in the middle of the rankings that will probably only
need marginal improvements, but several facilities (especially those at
the bottom of the ranking that average several times the floor average)
will need significant improvements in mercury emission control. We
estimate that the MACT floor limit for the carbon processes will reduce
emissions by about 1,100 lbs per year, a reduction of 89 percent from
current levels. Our estimates of impacts for the MACT floor indicate
that most of the carbon processes currently have or will have carbon
adsorbers installed to effectively control mercury emissions at the
MACT floor level. Considering the very low mercury concentrations when
the carbon processes are performing at the MACT level of control, it is
difficult to identify a technology that can obtain efficient additional
percent reductions from low concentration streams. For a beyond-the-
floor analysis, we assumed that theoretically a second carbon
adsorption system could be installed in series with the first one and
would get an additional 90 percent reduction from the very low mercury
concentrations that result from the MACT floor level of control. We
acknowledge that there is uncertainty as to the additional percent
reduction the second control system might achieve. Nevertheless, we
estimate that the emission reduction would only be 12 lbs per year. The
capital cost was estimated as $3.2 million with a total annualized cost
of about $1.2 million/yr and a cost effectiveness of $100,000/lb.
Considering the significant cost and the small additional reduction in
emissions associated with a second carbon adsorption system and the
uncertainty that even that small reduction might be achieved, we
believe that the additional emission reduction from this beyond-the-
floor control option is not warranted under section 112(d).
    For the non-carbon concentrate processes, we expect that Facility L
would probably need to add a carbon adsorber to its melt furnace to
achieve the MACT floor level of control. For beyond the floor, we again
assumed that the existing carbon adsorbers would be supplemented by
adding a second control system of carbon adsorbers in series for all of
the melt furnaces. We estimated the capital cost for the second set of
control systems as $0.7 million and a total annualized cost of
$306,000/year. Emissions would be reduced by 7 lb/year, which results
in a cost effectiveness of $44,000/lb. Considering the very small
emission reduction from a second carbon adsorber system, and its high
capital and operating costs, we believe that the emission reduction
associated with this additional control system is not warranted under
section 112(d) of the CAA.

C. How did we select the testing, monitoring and electronic reporting
requirements?

    We are proposing testing and monitoring requirements to assure
compliance with the emission standards set forth in this proposed rule.
These compliance assurance provisions are based, in part, on
requirements that have been applied to this source category in State
operating permits, EPA

requirements applied to other industries that emit mercury, and an
understanding of how control devices and processes perform and can be
effectively monitored.
    We are proposing initial compliance stack tests for mercury (using
Method 29) within the first 180 days of the compliance date and annual
compliance tests thereafter for all thermal process units to determine
compliance with the proposed emission limits. The testing frequency and
procedures would be essentially the same as the NDEP requirements for
the facilities that are located in Nevada partly because the stack test
data that we used to develop the proposed emission limits were based on
the test methods applied in Nevada. To provide additional flexibility,
we propose to allow the use of the Ontario Hydro Method, Method 30A, or
Method 30B as alternatives to EPA Method 29.
    We also propose the following monitoring requirements to assure
compliance with the proposed MACT standards.
    Roasters. In addition to the annual stack test, we are proposing
two options for monitoring roaster emissions: (1) Integrated sorbent
trap mercury monitoring coupled with parametric monitoring of scrubbers
and (2) monitoring using a continuous emission monitoring system (CEMS)
for mercury. Both proposed monitoring options would require
establishment of operating limits to detect and correct problems as
soon as possible. An exceedance of an operating limit for the sorbent
trap or CEMS monitoring would trigger immediate corrective action and
would require that the problem be corrected within 48 hours or that the
feed of ore to the roaster be stopped.
    As part of this first monitoring option (i.e., sorbent trap
monitoring), we are also proposing that facilities with roasters and
mercury scrubbers establish operating limits for various parameters
during their compliance test (i.e., the annual stack test for mercury
emissions). The proposed parametric monitoring provides additional
compliance assurance by ensuring that the process and control devices
are operating properly. The proposed parameters for monitoring mercury
scrubbers are similar to those currently required to be monitored in
the title V operating permits issued by NDEP for roasters. We are
proposing that each mercury scrubber be equipped with devices to
monitor the scrubber liquor flow rate, scrubber pressure drop, and
inlet gas temperature. Minimum operating limits for the scrubber liquor
flow rate and pressure drop would be established based on the lowest
average value measured during any of the three runs of a compliant
performance test. A maximum inlet temperature would be established
based on the highest temperature measured during any of the three runs
of the compliance test. In addition to the parameters described above,
we are proposing that the facility would also monitor the mercuric ion
concentration and the chloride ion concentration four times per day or
continuously monitor the oxidation reduction potential and pH. These
monitored parameters would be maintained within the range specified by
the scrubber's manufacturer or within an alternative range approved by
the permitting authority. If any of the parameters are outside the
specified range or limit, corrective action would be taken to bring the
parameters back within the operating range or the facility would
commence shutdown of the roaster.
    As mentioned above, we are including a mercury CEMS as an
alternative for monitoring of mercury emissions from roasters. This
monitoring option would not require parametric monitoring of the
mercury scrubbers. Mercury CEMS have been applied at other industrial
sources that emit mercury, such as coal-fired power plants and cement
production plants, and these devices yield valuable information
regarding continuous emissions performance. We realize that mercury
CEMs have not yet been demonstrated on roasters at gold production
facilities and that there are currently no calibration standards
traceable to NIST within the range of mercury concentrations from
roasters. However, calibration standards are available from the
manufacturers of mercury CEMS. Based on the Agency's understanding and
experience relative to continuous mercury monitoring at other
industrial facilities, such as coal-fired power plants and cement
plants, as well as research experience, EPA believes that the CEMS can
be adequately calibrated with manufacturers' standards and be used as a
valuable tool to monitor roasting operations to detect deviations in
performance. We therefore believe that it is appropriate to propose the
use of mercury CEMS as a monitoring option for roasters. However, we
believe that it is appropriate to also propose an alternative
monitoring approach based on frequent (weekly) monitoring using a
sorbent trap method.
    We request comments on the viability of using mercury CEMs,
specifically for monitoring mercury emissions from roasters at gold ore
processing and production facilities. We request comments on
calibration methods, costs, reliability and other aspects of the CEMs.
We also request similar comments on the sorbent trap method.
    For facilities that control roaster mercury emissions with mercury
scrubbers, we are proposing that if a facility demonstrates, in
accordance with the demonstration requirements in the proposed rule,
that mercury emissions from the roaster are less than 10 pounds of
mercury per million tons of input ore, they can cease monitoring via
either the sorbent trap or the mercury CEMS. Such a facility would be
required to conduct the parametric monitoring for mercury scrubbers as
described above (under option one) and maintain parameters within the
operating ranges established in accordance with the proposed rule.
Also, the facility would continue to perform annual compliance tests of
the roaster stack to demonstrate emissions continue to be less than 10
pounds of mercury per million tons of input ore. We believe that for
roasters that are effectively controlled with mercury scrubbers (i.e.,
emitting less than 10 pounds per million tons of ore during normal
operations), parametric monitoring of the scrubbers would be
sufficient. This monitoring option provides additional incentive for
facilities to reduce emissions from roasters. However, if any
subsequent compliance tests indicate that the roaster is emitting more
than 10 pounds of mercury per million tons of ore input, then the
facility would be required to monitor the roaster emissions using a
sorbent trap method or CEMS.
    We are specifically requesting comments on the advantages and
disadvantages of the two options for monitoring emissions from roasters
along with any supporting data and documentation to support one or both
of the options. We are also requesting comment on the proposed daily
averaging time when using the mercury CEMS option and the frequency of
sampling when using the sorbent trap option. In addition, we are
requesting comments on the proposed monitoring approach for low-
emitting roasters with mercury scrubbers, as described in the paragraph
above, and possible alternatives to this approach. Moreover, we are
requesting comments on the parametric monitoring methods.
    Carbon Adsorbers. For process units (such as furnaces, kilns,
retorts, electrowinning, and autoclaves) that control mercury emissions
with a carbon adsorber, we are proposing three options. One option
involves monitoring the mercury concentration at the exit of the carbon
bed. A second

option, adopted from requirements in some NDEP permits, is based on
sampling the carbon bed for mercury. The third option is based on
changing out the carbon bed after a fixed period of time determined
based on historical operating experience.
    We believe that all three options could provide reasonable
assurance that the carbon adsorber is operating properly on a
continuing basis and that the carbon is replaced before breakthrough
occurs. Our current preference among the three proposed monitoring
options for carbon beds described above is the option of sampling the
exit gas from the carbon bed using EPA Method 30B along with continuous
temperature monitoring because this option provides a direct
measurement of the amount of mercury exiting the control device. We are
specifically requesting comments on the advantages and disadvantages of
the three options along with any supporting data and documentation.
Based on public comments, we intend to promulgate one or more of these
options or a modified version as necessary.
    We are also proposing that the inlet stream to carbon adsorbers
applied to autoclaves, carbon kilns, melt furnaces, and retorts be
monitored for temperature and that the inlet temperature be maintained
below the maximum temperature established during the compliance tests.
We believe the temperature monitoring is needed to detect any
excursions in mercury emissions caused by excessively high
temperatures. We are also considering a reduction in frequency of the
sampling and analysis based on historical data on the life of a new
carbon bed (e.g., quarterly sampling when the carbon bed is fresh and
monthly sampling after a specified period of time) and for processes
that are very small sources of mercury emissions. We are requesting
comments and supporting data on these options and others that may be
appropriate for monitoring carbon beds.
    Wet scrubbers. For each wet scrubber, we are proposing that
pressure drop and water flow rate be maintained at a minimum level
based on measurements during the initial or subsequent compliance
test(s). These parameters are the typical monitoring parameters
required by other MACT standards and by State operating permits for wet
scrubbers at gold mine ore processing and production facilities.
Monitoring these parameters ensures that wet scrubbers are operating
properly.
    Electronic reporting. The EPA must have performance test data to
conduct effective reviews of CAA Section 112 and 129 standards, as well
as for many other purposes including compliance determinations,
emissions factor development, and annual emissions rate determinations.
In conducting these required reviews, we have found it ineffective and
time consuming not only for us but also for other regulatory agencies
and source owners and operators to locate, collect, and submit
emissions test data because of varied locations for data storage and
varied data storage methods. One improvement that has occurred in
recent years is the availability of stack test reports in electronic
format as a replacement for cumbersome paper copies.
    In this action, we are taking a step to improve data accessibility.
Owners and operators of affected facilities would be required to submit
to an EPA electronic database an electronic copy of reports of certain
performance tests required under this rule. Data entry would be through
an electronic emissions test report structure called the Electronic
Reporting Tool (ERT) that will be used by the staff as part of the
emissions testing project. The ERT was developed with input from stack
testing companies who generally collect and compile performance test
data electronically and offices within State and local agencies which
perform field test assessments. The ERT is currently available, and
access to direct data submittal to EPA's electronic emissions database
(WebFIRE) will become available by December 31, 2011.
    The requirement to submit source test data electronically to EPA
would not require any additional performance testing and would apply to
those performance tests conducted using test methods that are supported
by ERT. The ERT contains a specific electronic data entry form for most
of the commonly used EPA reference methods. The Web site listed below
contains a listing of the pollutants and test methods supported by ERT.
In addition, when a facility submits performance test data to WebFIRE,
there would be no additional requirements for emissions test data
compilation. Moreover, we believe industry would benefit from
development of improved emissions factors, fewer follow-up information
requests, and better regulation development as discussed below. The
information to be reported is already required for the existing test
methods and is necessary to evaluate the conformance to the test
method.
    One major advantage of submitting source test data through the ERT
is that it provides a standardized method to compile and store much of
the documentation required to be reported by this rule while clearly
stating what testing information we require. Another important benefit
of submitting these data to EPA at the time the source test is
conducted is that it will substantially reduce the effort involved in
data collection activities in the future. Specifically, because EPA
would already have adequate source category data to conduct residual
risk assessments or technology reviews, there would likely be fewer or
less substantial data collection requests (e.g., CAA Section 114
letters). This results in a reduced burden on both affected facilities
(in terms of reduced manpower to respond to data collection requests)
and EPA (in terms of preparing and distributing data collection
requests).
    State/local/Tribal agencies may also benefit in that their review
may be more streamlined and accurate as the States will not have to re-
enter the data to assess the calculations and verify the data entry.
Finally, another benefit of submitting these data to WebFIRE
electronically is that these data will improve greatly the overall
quality of the existing and new emissions factors by supplementing the
pool of emissions test data upon which the emissions factor is based
and by ensuring that data are more representative of current industry
operational procedures. A common complaint we hear from industry and
regulators is that emissions factors are outdated or not representative
of a particular source category. Receiving and incorporating data for
most performance tests will ensure that emissions factors, when
updated, represent accurately the most current operational practices.
In summary, receiving test data already collected for other purposes
and using them in the emissions factors development program will save
industry, State/local/Tribal agencies, and EPA time and money and work
to improve the quality of emissions inventories and related regulatory
decisions.
    As mentioned earlier, the electronic data base that will be used is
EPA's WebFIRE, which is a Web site accessible through EPA's Technology
Transfer Network (TTN). The WebFIRE Web site was constructed to store
emissions test data for use in developing emissions factors. A
description of the WebFIRE data base can be found at http://cfpub.epa.gov/oarweb/index.cfm?action=fire.main.
    The ERT will be able to transmit the electronic report through
EPA's Central Data Exchange (CDX) network for storage in the WebFIRE
data base. Although ERT is not the only electronic interface that can
be used to submit source test data to the CDX for entry

into WebFIRE, it makes submittal of data very straightforward and easy.
A description of the ERT can be found at http://www.epa.gov/ttn/chief/ert/ert_tool.html.

VI. Impacts of the Proposed Standards

A. What are the emissions, cost, economic, and non-air environmental
impacts?

    We estimate the proposed MACT standard will reduce mercury
emissions from gold mine ore processing and production by 1,650 lb/year
from current emissions levels down to a level of 1,390 lb/year post-
MACT. The annual emissions expected after MACT (of 1,390 lbs) represent
a 73 percent reduction from 2007 emissions (5,000 pounds), more than 90
percent reduction from the emissions level in 2001 (about 23,000
pounds), and more than 96 percent reduction from uncontrolled emissions
levels (more than 37,000 pounds). The capital cost of emission controls
is estimated as $5 million with a total annualized cost of $2.3 million
per year. The capital costs for monitoring, reporting, and
recordkeeping are estimated as $1.0 to $1.3 million with a total
annualized cost of $0.8 to $1.5 million per year, depending on the
monitoring option that is chosen. The cost of compliance is estimated
to be less than 0.3 percent of sales. We therefore believe that the
economic impact on an affected company would be insignificant.
Electricity consumption is expected to increase by about 2,100
megawatt-hours per year due to increased fan capacity for carbon
adsorbers and the installation of refrigeration units or condensers on
a few process units. Non-hazardous solid waste (spent carbon containing
mercury that must be regenerated or disposed of) would increase by
about 7 tons per year.

B. What are the health benefits of reducing mercury emissions?

    Mercury is emitted to the air from various man-made and natural
sources. These emissions transport through the atmosphere and
eventually deposit to land or water bodies. This deposition can occur
locally, regionally, or globally, depending on the form of mercury
emitted and other factors such as the weather. The form of mercury
emitted varies depending on source type and other factors. Available
data indicate that the majority of air emissions from gold mine ore
processing and production facilities are in the form of gaseous
elemental mercury. This form of mercury can be transported very long
distances, even globally, to regions far from the emissions source
(becoming part of the global ``pool'') before deposition occurs.
However, this source category also emits some gaseous inorganic ionic
mercury forms (such as mercuric chloride), and smaller amounts of
particulate bound mercury. These forms have a shorter atmospheric
lifetime and can deposit to land or water bodies closer to the
emissions source. Furthermore, elemental mercury in the atmosphere can
undergo transformation into ionic mercury, providing a significant
pathway for deposition of emitted elemental mercury.
    As mentioned previously, the gold mine ore processing and
production source category emitted about 2.5 tons of mercury to the air
in 2007 in the U.S. Based on the EPA's National Emission Inventory,
about 103 tons of mercury were emitted from all anthropogenic sources
in the U.S. in 2005. Moreover, the United Nations has estimated that
about 2100 tons were emitted worldwide by anthropogenic sources in
2005.\3\ We believe that total mercury emissions in the U.S. and
globally in 2007 were about the same magnitude as in 2005. Therefore,
we estimate that in 2007 the gold mine ore processing and production
source category emitted about 2.5 percent of the total anthropogenic
mercury emissions in the U.S. and about 0.12 percent of the global
emissions.
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    \3\ United Nations Environment Programme/Arctic Monitoring and
Assessment Program (UNEP/AMAP). Study on mercury-emitting sources,
including emissions trends and cost and effectiveness of alternative
control measures: ``UNEP Paragraph 29 study.'' 2008. Available at:
http://www.chem.unep.ch/mercury/Paragraph29/Zero%20Draft%20Report%20March%208.doc.
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    Potential exposure routes to mercury emissions include both direct
inhalation, and consumption of fish containing methylmercury. The
primary route of human exposure to mercury emissions from industrial
sources is generally indirectly through the consumption of fish
containing methylmercury. As described above, mercury that has been
emitted to the air eventually settles into water bodies or onto land
where it can either move directly or be leached into water bodies. Once
deposited, certain microorganisms can change it into methylmercury, a
highly toxic form that builds up in fish, shellfish and animals that
eat fish. Consumption of fish and shellfish are the main sources of