Page 1 of 212

 December 16, 2010

 

SUMMARY OF COMMENTS AND RESPONSES FOR THE PROPOSED GOLD MINE ORE 

PROCESSING AND PRODUCITON NESHAP

CONTENTS

A. Statutory Requirements.................................. 11

1. Listing of the Gold Mine Ore Processing and Production 

Source Category Under Section 112(c)(6) ..................... 11

2. Calculation of Mercury Emissions for the 1990 Inventory . 15

3. Emission Standards for HAP Other Than Mercury ........... 19

4. Emission Standards for Fugitive Emissions ............... 24

5. Major Source Determination .............................. 28

6. GACT for Mercury Instead of MACT ........................ 35

7. Title V Permit Exemption ................................ 42

8. Early Reduction Provisions in Section 112(i)(5) ......... 55

9. Federalism Impacts ...................................... 56

10. Reconstruction ......................................... 57

B. Applicability........................................... 65

C. MACT Floors............................................. 69

1. Consideration of Variability in Determining Floors ...... 69

2. General Comments on MACT ................................ 92

3. MACT for the Ore Pretreatment Group ..................... 95

4. MACT for Carbon Processes .............................. 107

5. Compliance Alternative for New Carbon Process Sources .. 113

6. Beyond the Floor for the Carbon Group .................. 118

D. Compliance Determinations.............................. 118

1. Timing for Compliance Determinations ................... 118

2. Test Methods ........................................... 128

3. Emission Limits Based on the Quantity of Concentrate ... 135

4. Alternative Calculation for Determining Compliance ..... 136

5. Compliance Calculations and Procedures ................. 138

6. Multiple Emission Units ................................ 141

E. Monitoring............................................. 142

1. Continuous Compliance .................................. 142

2. Operating Limits ....................................... 150

3. Mercury Concentration Monitoring for Roasters .......... 157

4. Parametric Monitoring of Roasters ...................... 170

5. Exceeding the Operating Limits for Roasters ............ 178

6. Monitoring Wet Scrubbers ............................... 189

7. Carbon Adsorber Monitoring ............................. 195

8. Monitoring of Multiple Units Ducted to One Stack ....... 205

9. Monitoring Mercury Concentration in Roaster Ore ........ 206

F. Miscellaneous Comments................................. 207

1. Tracking the Fate of Mercury ........................... 207
Page 2 of 212

2. Costs, Economic, and Environmental Impacts ............. 209

3. Definitions ............................................ 210

4. Roasters Are Well Controlled ........................... 210

5. Record Keeping and Reporting........................... 210

6. Technical Clarifications ............................... 211
Page 3 of 212

TABLE 1. LIST OF COMMENTERS ON PROPOSED ACTION ON THE GOLD MINE ORE 

PROCESSING AND PRODUCTION NESHAP

Docket Item Commenter Affiliation 

EPA-HQ-OAR-2010-0239-0149 M. Brady Concerned citizen 

EPA-HQ-OAR-2010-0239-0150 M.G. Miller Concerned citizen

EPA-HQ-OAR-2010-0239-0177 J. Wise Concerned citizen

EPA-HQ-OAR-2010-0239-0178 E. E. Eigbokhan Concerned citizen

EPA-HQ-OAR-2010-0239-0180 C. Redstone Concerned citizen

EPA-HQ-OAR-2010-0239-0181 A. Zeigler Concerned citizen

EPA-HQ-OAR-2010-0239-0182 L. Johnson Concerned citizen

EPA-HQ-OAR-2010-0239-0183 J. Public Concerned citizen

EPA-HQ-OAR-2010-0239-0184 H. G. Ehrbar Concerned citizen

EPA-HQ-OAR-2010-0239-0194 C. Ralph ICMJ Mining Journal

EPA-HQ-OAR-2010-0239-0195 D. Ingraham Concerned citizen

EPA-HQ-OAR-2010-0239-0196 Anonymous Concerned citizen

EPA-HQ-OAR-2010-0239-0203 Anonymous Concerned citizen

EPA-HQ-OAR-2010-0239-0204 R. F. Carter Concerned citizen

EPA-HQ-OAR-2010-0239-0205 J. Cummings Concerned citizen

EPA-HQ-OAR-2010-0239-0206 M. Warner Concerned citizen

EPA-HQ-OAR-2010-0239-0207 Mass Comment Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0208 Chris Ralph ICMJ Mining Journal

EPA-HQ-OAR-2010-0239-0209 J. Saunders Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0210 L. Lamberth Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0211 M. Sage Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0212 M. Engelman Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0213 M. McLaughlin Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0214 M. Donian Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0215 M. Hauck Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0216 N. O. Rolon Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0217 P. Matejcek Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0218 P. Rizzo Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0219 A. Fulmer Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0220 P. Chaiken Concerned citizen; mass e-mail campaign
Page 4 of 212

Docket Item Commenter Affiliation 

EPA-HQ-OAR-2010-0239-0221 R. J. Goff Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0222 R. Tafanelli Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0223 R. Kofler Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0224 R. Bienek Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0225 S. Ecolano Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0226 S. Anderson Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0227 S. Roth Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0228 S. Bragg Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0229 S. Lacy Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0230 A. Sherwood Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0231 T. Palmer Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0232 T. Kelley Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0233 V. Brandt Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0234 C. Mead Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0235 J. Gintzler Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0236 M. A. McDonald Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0237 M. Reed Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0238 B. Deckard Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0239 B. Feiss Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0240 B. Johnson Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0241 C. Brady Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0242 C. Okstel Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0243 R. Grimmer Concerned citizen

EPA-HQ-OAR-2010-0239-0244 C. Ralph ICMJ Mining Journal
Page 5 of 212

Docket Item Commenter Affiliation 

EPA-HQ-OAR-2010-0239-0245 A. Dattner Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0246 C. Boehle Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0247 D. Splisbury Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0248 E. Rodgers Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0249 F. De Nicola Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0250 I. Cree Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0251 J. Klein Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0252 J. G. Garey Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0253 J. Netson Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0254 A. Berenzy Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0255 G. Stradtman Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0256 J. Archuleta Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0257 Anonymous Concerned citizen

EPA-HQ-OAR-2010-0239-0258 Sharon G. Cox

On behalf of Steven C. Borell, Executive 

Director, Alaska Miners Association (AMA)

EPA-HQ-OAR-2010-0239-0259 Kevin Pylka

Manager Environmental Permitting and 

Compliance, Polymet Mining

EPA-HQ-OAR-2010-0239-0260 Sharon G. Cox 

On behalf of Steven C. Borell, Executive 

Director, Alaska Miners Association, Inc.

EPA-HQ-OAR-2010-0239-0261 C. Lish Concerned citizen

EPA-HQ-OAR-2010-0239-0262 Rob Dubuc Staff Attorney, Western Resource Advocates

EPA-HQ-OAR-2010-0239-0263 G. Bloss Concerned citizen

EPA-HQ-OAR-2010-0239-0264 S. Ogata Concerned citizen

EPA-HQ-OAR-2010-0239-0265 Anonymous Concerned citizen

EPA-HQ-OAR-2010-0239-0266 Anonymous Concerned citizen

EPA-HQ-OAR-2010-0239-0267 J. Varner Concerned citizen
Page 6 of 212

Docket Item Commenter Affiliation 

EPA-HQ-OAR-2010-0239-0268 Michael J. Elges

Chief, Bureau of Air Pollution Control, 

Department of Conservation and Natural

Resources, Nevada Division of Environmental 

Protection

EPA-HQ-OAR-2010-0239-0269 Benjamin L. Brandes

Director, Air Quality, National Mining 

Association

EPA-HQ-OAR-2010-0239-0270 Bonnie Gestring Earthworks

EPA-HQ-OAR-2010-0239-0271 John R. Jacus

Attorney, Davis Graham and Stubbs LLP, on 

behalf of Great Basin Gold Inc. and Rodeo 

Creek Gold, Inc.

EPA-HQ-OAR-2010-0239-0272 Glenn C. Miller

Professor, Department of Natural Resources and 

Environmental Science, University of Nevada

EPA-HQ-OAR-2010-0239-0273 Frank Ongaro

Executive Director, Mining Minnesota

EPA-HQ-OAR-2010-0239-0274 Michael J. Tomko

Parsons Behle and Latimer on behalf of Barrick 

Goldstrike Mines, Inc. and Barrick Cortez, Inc.

EPA-HQ-OAR-2010-0239-0275 Alice Edwards

Acting Director, Division of Air Quality, Alaska 

Department of Environmental Conservation

EPA-HQ-OAR-2010-0239-0276 S. Sanderson President, Colorado Mining Association (CMA)

EPA-HQ-OAR-2010-0239-0277 Brook M. Brisson

Clean Water and Mining Program Director, 

Northern Alaska Environmental Center (NAEC)

EPA-HQ-OAR-2010-0239-0278 K. Zamzow Center for Science in Public Participation

EPA-HQ-OAR-2010-0239-0279 Luke Russell 

Vice President Environmental Services, Coeur 

d'Alene Mines

EPA-HQ-OAR-2010-0239-0280 Peter O'Connor 

Vice President Environmental Law & 

Government, AngloGold Ashanti North America 

Inc. (AGANA)

EPA-HQ-OAR-2010-0239-0281 D. Chambers 

Center for Science in Public Participation 

(CSP2)

EPA-HQ-OAR-2010-0239-0282 Justin Hayes Program Director, Idaho Conservation League

EPA-HQ-OAR-2010-0239-0283 James Pew Sierra Club and Earthjustice
Page 7 of 212

Docket Item Commenter Affiliation 

EPA-HQ-OAR-2010-0239-0284 Kendra Zamzow 

Center for Science in Public Participation 

(CSP2) on behalf of Joel Reynolds, Solutions 

Statistical Consulting (SSC)

EPA-HQ-OAR-2010-0239-0285 Michael J. Tomko 

Counsel, Parsons Behle & Latimer on behalf of 

Kinross Gold USA, Inc.

EPA-HQ-OAR-2010-0239-0286 C. Cullen Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0287 D. Inouye Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0288 J. Wheeler Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0289 M. Santarelli Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0290 M. Bresnan Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0291 B. Pelts Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0292 M. Rausch Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0293 M. Heaviland Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0294 D. Conrey Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0295 A. Nowak Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0296 E. McCabe Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0297 E. Kompanek Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0298 N. Bartol Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0299 R. DeWald Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0300 R. Krousoff Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0301 D. Hudson Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0302 E. Pearlman Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0303 R. Rutemoeller Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0304 G. Goffe Concerned citizen; mass e-mail campaign
Page 8 of 212

Docket Item Commenter Affiliation 

EPA-HQ-OAR-2010-0239-0305 G. Fairbanks Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0306 G. Wingard Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0307 H. Savage Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0308 R. Lauster Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0309 D. Diegoli Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0310 A. Rapalyea Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0311 A. Page Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0312 D. Deming Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0313 D. Mack Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0314 D. Schmitt Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0315 Dr. D. Kyte Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0316 E. Mosimann Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0317 H. Carr Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0318 H. Peach Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0319 J. Carter Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0320 J. Unruh Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0321 J. Allen Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0322 J. and V. Wagner Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0323 J. Eakins Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0324 K. Ramsey Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0325 AC 6.30 54 Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0326 M. Kelner Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0327 S. Buesing Concerned citizen; mass e-mail campaign
Page 9 of 212

Docket Item Commenter Affiliation 

EPA-HQ-OAR-2010-0239-0328 T. Robinson Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0329 T. Kane Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0330 B. Campbell Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0331 V. Phillips Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0332 Mark Compton 

Manager, Government Affairs on behalf of 

Laura Skaer, Executive Director, Northwest 

Mining Association (NWMA)

EPA-HQ-OAR-2010-0239-0333 V. Olson Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0334 W. Evans Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0335 W. Davis Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0336 B. Dickinson Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0337 C. Jackson Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0338 C. Harris Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0339 C. Lawrence Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0340 K. Nezelek Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0341 T. Crowley President, Nevada Mining Association

EPA-HQ-OAR-2010-0239-0342 Denise Kennedy

Holland & Hart LLP on behalf of the Newmont 

Mining Corporation

EPA-HQ-OAR-2010-0239-0343 Anonymous Concerned citizen

EPA-HQ-OAR-2010-0239-0344 Ryan Deshon President, A&B Prospecting Supplies, Inc.

EPA-HQ-OAR-2010-0239-0345 S. Justice Concerned citizen

EPA-HQ-OAR-2010-0239-0346 R. Maddox Concerned citizen

EPA-HQ-OAR-2010-0239-0347 A. Buster Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0348 L. Brown Concerned citizen

EPA-HQ-OAR-2010-0239-0349 A. Evenson Concerned citizen

EPA-HQ-OAR-2010-0239-0350 S. D. Barry Concerned citizen
Page 10 of 212

Docket Item Commenter Affiliation 

EPA-HQ-OAR-2010-0239-0351 J. R. Jacus

Attorney, Davis Graham and Stubbs LLP, on 

behalf of Great Basin Gold Inc. and Rodeo 

Creek Gold, Inc.

EPA-HQ-OAR-2010-0239-0352 N. Pastos Concerned citizen

EPA-HQ-OAR-2010-0239-0353 C. Wassilie Concerned citizen; mass e-mail campaign

EPA-HQ-OAR-2010-0239-0354 A. Jackson Concerned citizen 

EPA-HQ-OAR-2010-0239-0357 J. and K. Mitchell Concerned citizen

EPA-HQ-OAR-2010-0239-0358 B. Whittenberg Concerned citizen
Page 11 of 212

1. Listing of the Gold Mine Ore Processing and Production 

Source Category Under Section 112(c)(6)

A. Statutory Requirements 

Comment: Several commenters (0277, 0282, 0283) stated 

that adding the gold mine ore processing and production category 

to the list of categories required by Clean Air Act (CAA) 

section 112(c)(6) was correct and required because gold mines 

accounted for a significant portion of the aggregate emissions 

of mercury in the baseline year (1990) and because they still do 

so today. Other commenters 0269, 0271, 0274, 0280, 0332, 0341, 

0342, 0351) stated that EPA does not have the authority to list 

gold mining processing and production as a source category under 

section 112(c)(6) and noted that section 112(c)(6) requires EPA 

to list, by 1995, categories of sources that make up 90 percent 

of the 1990 emissions for a subset of hazardous air pollutants 

(HAP), including mercury. The commenters said that EPA 

concluded its statutory listing obligation for mercury in 1998 

with the publication of a list of source categories constituting 

90 percent of aggregate mercury emissions, and that gold mining 

was not included on that list in 1998. In addition, the 

commenters said that the CAA requires EPA to list all categories 

under section 112(c)(6) by 1995 and complete issuance of 

standards for all listed sources by 2000, a task that would be 
Page 12 of 212

impossible if EPA had the authority to add source categories ad 

infinitum. 

Response

The core requirement of section 112(c)(6) is that EPA 

“shall ... list categories and subcategories of sources assuring 

that sources accounting for not less than 90 per centum of the 

aggregate emissions of each such pollutant” are subject to 

standards under either 112 (d)(2) or (d)(4). EPA reasonably 

interprets section 112(c)(6) as allowing it to revise the list 

: We appreciate the commenter’s support in listing 

the gold mine processing and production area source category 

pursuant to section 112(c)(6). We disagree, however, with the 

commenters that assert that EPA is precluded from listing 

additional categories pursuant to section 112(c)(6). The 

commenters appear to be arguing that EPA is limited to a single 

listing opportunity under section 112 (c)(6) and, having not 

listed gold mine ore processing and production in the initial 

1998 listing effort, EPA is now foreclosed from doing so. There 

is nothing in the language of section 112(c)(6), however, that 

precludes EPA from listing additional source categories to the 

extent EPA determines that those categories are needed to meet 

the 90 percent requirement in section 112(c)(6). Indeed, the 

commenter’s reading is contrary to the fundamental purpose of 

section 112(c)(6).
Page 13 of 212

to add categories, where, as here, it determines that it needs 

the additional categories to meet the 90 percent requirement in 

section 112(c)(6). Indeed, EPA has previously revised the 

section 112(c)(6) list to add a source category, where EPA 

determined that category was needed to meet its 90 percent 

requirement for mercury. See

As explained in the proposed rule, we have a 1990 baseline 

emissions inventory, and it is against this baseline that we 

assess compliance with the 90 percent requirement for each of 

the pollutants specified in section 112(c)(6). EPA explained in 

the initial 1998 listing notice that it was using 1990 as the 

baseline year for assessing compliance with the 90 percent 

requirement. As EPA has developed emission standards for the 

sources included on the initial section 112(c)(6) list, it has 

acquired additional information on those sources and their 

emissions in 1990, which has resulted in some revisions to the 

1990 baseline emissions inventory estimates. These revisions 

resulted in the need to regulate an additional source category. 

72 FR 74087 (Dec. 28, 2007) 

(adding area source electric arc furnaces to the section 

112(c)(6) list). 

See 72 FR 74087 (setting standards for area source electric arc 

furnaces).
Page 14 of 212

In addition to obtaining additional information concerning 

the source categories on the initial list, EPA has obtained 

additional information concerning the 1990 emissions of other 

sources. As explained in the preamble to the proposed rule, at 

the time of the initial section 112(c)(6) listing, there was 

very little available information on mercury emissions from gold 

mine ore processing and production. See 75 FR 22471. Because 

EPA lacked emissions information on mercury emissions from this 

source category at the time of the listing decision, EPA was 

unable to estimate the 1990 baseline mercury emissions from the 

gold mine ore processing and production source category and 

include this category in the first listing effort. Based on 

information that became available after the initial listing, EPA 

now finds that regulation of the area source gold mine ore 

processing and production category is needed to meet the 90 

percent requirement for mercury. 75 FR 22471. Under the 

commenters’ view, EPA cannot add any additional categories to 

the section 112(c)(6) list following the initial listing. If 

true, EPA could not meet its section 112(c)(6) obligation – a 

result Congress could not have intended. EPA reasonably 

interprets section 112 (c)(6) in a manner that allows the Agency 

to achieve that provision’s core requirement. EPA repeats that 

it sees nothing in the language or purpose of section 112(c)(6) 
Page 15 of 212

that precludes it from listing additional source categories as 

needed. 

Finally, Congress left to EPA’s discretion which categories 

and subcategories of sources to include on the section 112(c)(6) 

list. We have determined that we need the gold mine ore 

processing and production source category to meet the 90 percent 

requirement in section 112(c)(6) for mercury and are therefore 

now setting standards for that category.

We also reject the comment that the task of completing 

standards by 2000 would be impossible if EPA had the authority 

to add source categories. Nevertheless, EPA is under a court 

ordered deadline to complete section 112(c)(6) standards by 

January 16, 2011. (Sierra Club v. EPA, Consolidated Case No. 

01-1537, D.D.C).

 

2. Calculation of Mercury Emissions for the 1990 Inventory

Comment: Some commenters (0341, 0342) claimed that EPA did 

not provide an adequate basis for its 1990 emissions estimate 

for gold mining processing and production. Specifically, they 

questioned EPA’s estimated emissions of 4.4 tons from this 

source category in the 1990 baseline year. 

Response: Although the commenters question EPA’s estimated 

emissions of 4.4 tons from this source category in the 1990 
Page 16 of 212

baseline year, they did not provide an alternative method for 

calculating such emissions or alternative data or assumptions 

that should be used. They also did not explain what they think 

the 1990 baseline emissions should have been. EPA continues to 

maintain that its baseline emissions estimate is reasonable. 

The methodology EPA used to derive that estimate is described in 

docket item EPA-HQ-OAR-2010-0239-0175.

Comment: Several commenters (0341, 0342) stated that Phase 

2 permits under the Nevada Mercury Control Program (NMCP), which 

are scheduled for issuance by the end of 2010, will result in 

MACT-level controls on all thermal units at Nevada gold mines. 

According to the commenters, these permits are the culmination 

of a seven-year collaborative effort between NDEP and the gold 

mining industry to substantially reduce mercury emissions from 

gold mine processes, and it is an effort EPA repeatedly 

recognized and agreed should be implemented in lieu of a federal 

MACT. The commenters said that prior to EPA’s decision in late 

2008 to list gold mining as a source category under section 

112(c)(6), the Agency repeatedly lauded the NDEP’s mercury 

emission control program and stated that EPA had no intention of 

issuing MACT standards to control mercury emissions from gold 

mines. The commenters stated that in 2002, EPA’s Director of 
Page 17 of 212

the Emission Standards Division sent a memorandum1

The commenters said that the proposal does not address how 

the NESHAP will result in reductions in mercury at gold mines in 

areas of the country other than Nevada, where the mercury 

content of the ore in gold mines is non-existent or only a 

fraction of the amount found in Nevada, and based on EPA’s TRI 

database, Nevada accounted for 99 percent of mercury emissions 

associated with gold mining operations in the United States. 

According to the commenters, this shows that if Nevada has an 

equivalent mercury control program for the gold mining industry, 

then there is nothing to be gained from imposing a federal 

to the 

Director of Region IX’s Air Division stating that EPA 

“endorse[d] the program’s goal of achieving significant, 

permanent, and rapid reductions in mercury air emissions” and 

indicated that EPA “currently ha[s] no intentions of listing 

gold mines for the development of MACT standards.” The 

commenters also said that EPA made a similar public statement in 

2005 as part of its Questions and Answers on the NMCP where EPA 

noted that Nevada’s voluntary mercury reduction program would 

achieve faster emission reductions than under a MACT standard 

rulemaking. 

 1 The commenter cited and attached a memo from Sally L. Shaver, Director, 

Emission Standards Division regarding EPA’s support of the Voluntary Mercury 

Air Emissions Reduction Program for the Gold Mining Industry. May 5, 2002.
Page 18 of 212

program, and if EPA acknowledges that the mines in Nevada are 

already well controlled, then the listing of gold mining and the 

promulgation of an additional layer of regulation at substantial 

cost to industry but with little environmental benefit, is both 

legally indefensible and practically unsupportable. The 

commenters said that EPA stated in the proposal that the 

proposed MACT is designed “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.” The commenters believe that as a policy 

matter, it is an inefficient and inappropriate use of Agency 

resources to list a new source category that is already wellcontrolled when EPA still has not met its obligation to issue 

standards for those sources listed more than 10 years ago.

Response: As explained above, we are regulating the gold 

mine ore processing and production source category to meet the 

90 percent requirement in section 112(c)(6) for mercury and are 

therefore setting standards for that category. Based on our 1990 

baseline inventory for section 112(c)(6) and other emissions 

information for subsequent years, we estimate that this industry 

was among the top ten highest emitting categories of mercury 

emissions in the U.S. in 1990 and has remained in the top 10 

since that time. Moreover, even though most emissions are from 
Page 19 of 212

facilities located in Nevada, several commenters expressed 

serious concerns about the potential for mercury emissions from 

new gold mines in other States (e.g., Alaska). We share these 

concerns about potential emissions from new gold mine 

facilities. Finally, Congress left to EPA’s discretion which 

categories and subcategories of sources to include on the 

section 112(c)(6) list. We are regulating the gold mine ore 

processing and production source category to meet the 90 percent 

requirement in section 112(c)(6) for mercury and are therefore 

now promulgating a federal NESHAP for existing and new gold mine 

ore processing and production facilities. 

3. Emission Standards for HAP Other than Mercury

Comment: Several commenters (0270, 0283)stated that CAA 

section 112(c)(6) provides that EPA must “list categories and 

subcategories of sources assuring that sources accounting for 

not less than 90 percent of each [enumerated] pollutant are 

subject to standards under subsection (d)(2) or (d)(4) of this 

section.” The commenters also stated that the D.C. Circuit has 

held repeatedly that when EPA sets standards for a category or 

subcategory of sources under section 112(d)(2), EPA has a 

statutory duty to set emission standards for each HAP that the 

sources in that category or subcategory emit (e.g., National 

Lime Ass’n v. EPA, 233 F.3d 625, 633-634 (D.C. Cir. 2000)). The 
Page 20 of 212

commenters concluded that when EPA sets standards for gold mines 

under section 112(d)(2), as section 112(c)(6) requires it to do, 

EPA must set section 112(d)(2) emission standards for all the 

HAP that gold mines emit. 

The commenters said that EPA appears to believe that 

because gold mines are needed only to reach the section 

112(c)(6) requirement of 90 percent for mercury and not for the 

other pollutants enumerated in section 112(c)(6), EPA’s only 

obligation under section 112(c)(6) is to set section 112(d)(2) 

standards for mercury. The commenters said that section 

112(c)(6) expressly requires EPA to issue section 112(d)(2) 

standards for the “sources” in the categories listed under 

section 112(c)(6), not some subset of the pollutants that those 

sources emit, and that section 112(d)(2) standards must include 

emission standards for each HAP that a source category emits. 

The commenters continued by stating that nothing in the CAA 

exempts EPA from this requirement. The commenters concluded 

that, had Congress wished to give EPA discretion to set 

standards for only some of the pollutants emitted by a category 

listed under section 112(c)(6), it would have done so expressly.

Response: EPA disagrees with the comment that, even though 

EPA lists a category under section 112(c)(6) due to the 

emissions of one or more HAP specified in that section, EPA must 
Page 21 of 212

issue emission standards for all HAP (including HAP not listed 

in section 112(c)(6)) that sources in that category emit. The 

commenter cited in support the opinion by the United States 

Court of Appeals for the D.C. Circuit in National Lime Ass’n v. 

EPA, 233 F.3d 625, 633-634 (D.C. Cir. 2000)). The part of the 

National Lime opinion referenced in the comment dealt with EPA’s 

failure to set emission standards for certain HAPs emitted by 

major sources of cement manufacturing because the Agency found 

no sources using control technologies for those HAP. In 

rejecting EPA’s argument, the court stated that EPA has “a 

statutory obligation to set emission standards for each listed 

HAP.” Id. at 634. The Court noted the list of HAP in section 

112(b) and stated that section 112(d)(1) requires that EPA 

“promulgate regulations establishing emission standards for each 

category or subcategory of major sources ... of hazardous air 

pollutants listed for regulation..” Id. (Emphasis added). For 

the reasons stated below, we do not believe that today’s final 

rule is controlled by or otherwise conflicts with the National 

Lime decision.

National Lime did not involve section 112(c)(6). That 

provision is ambiguous as to whether standards for listed source 

categories must address all HAP or only the section 112(c)(6) 

HAP for which the source category was listed. Section 112 
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(c)(6) requires that “sources accounting for not less than 90 

per centum of the aggregate emissions of each such [specific] 

pollutant are subject to standards under subsection (d)(2) or 

(d)(4).” This language can reasonably be read to mean standards 

for the section 112(c)(6) HAP or standards for all HAP emitted 

by the source. Under either reading, the source would be 

subject to a section 112(d)(2) or (d)(4) standard.

The commenter insists that once a section 112(d)(2) 

standard comes into play, all HAP must be controlled (per 

National Lime

The facts here support the reasonableness of EPA’s 

approach. Gold mine ore processing is an area source category 

listed under section 112(c)(6) for regulation under section 

112(d)(2) solely due to its mercury emissions. There is special 

statutory sensitivity to regulation of area source categories in 

section 112. For example, an area source category may be listed 

for regulation under section 112 if EPA makes an adverse effects 

). But this result is not compelled by the 

pertinent provision, section 112(c)(6). That provision is 

obviously intended to ensure controls for specific persistent, 

bioaccumulative HAP, and this purpose is served by a reading 

which compels regulation under section 112(d)(2) only of the HAP 

for which a source category is listed under section 112(c)(6), 

rather than for all HAP. 
Page 23 of 212

finding pursuant to Section 112(c)(3) or if EPA determines that 

the area source category is needed to meet its section 112(c)(3) 

obligations to regulate urban HAP or its section 112(c)(6) 

obligations to regulate certain persistent bioaccumulative HAP. 

Therefore, unless an area source category emits a section 

112(c)(3) urban HAP or a section 112(c)(6) HAP and EPA 

determines that such category is needed to meet the 90 percent 

requirement set forth in section 112(c)(3) and (c)(6), findings 

related to adverse human health or environmental effects are 

required before EPA can regulate that area source category --

findings EPA is unable to make for non-mercury HAP emitted from 

the gold mine ore processing and production source category at 

this time. Moreover, to the extent EPA lists an area source 

category pursuant to section 112(c)(3) (whether that finding is 

based on adverse effects to human health or the environment or a 

finding that the source is needed to meet the 90 percent 

requirement in section 112(c)(3), the statute gives EPA 

discretion to set generally available control technology 

(“GACT”) standards for such sources. 42 U.S.C. 7412(d)(5). 

EPA does not interpret section 112 (c)(6) to create a means 

of automatically compelling regulation of all HAP emitted by 

area sources unrelated to the core object of section 112(c)(6), 

which is control of the specific persistent, bioaccumulative 
Page 24 of 212

HAP, and thereby bypassing these otherwise applicable 

preconditions to setting section 112(d) standards for area 

sources. Nor does National Lime address the issue, since the 

case dealt exclusively with major sources.2 233 F. 3d at 633. 

Consequently, EPA disagrees with the comment that it is 

compelled to promulgate section 112(d)(2) MACT standards for all 

HAP emitted by gold mine ore processors.

4. Emission Standards for Fugitive Emissions

Comment

 2

 EPA acknowledges that major sources regulated under section 112 must be subject to MACT 

standards for all HAP emitted from the source category consistent with National Lime. 

: Several commenters (0270, 0283) stated that it is 

well known that gold mines have significant fugitive emissions 

of mercury and other HAP, but that EPA did not propose standards 

for these emissions or mention them in its proposal. The 

commenters said that EPA has a statutory obligation to set 

standards for gold mine mercury emissions under section 

112(d)(2) and (3), and under these provisions, EPA must set 

emission standards for all the mercury emissions from the listed 

category. The commenters also stated that EPA has a statutory 

obligation to set standards for all the other HAP that gold 

mines emit, including their fugitive emissions of such other 

HAP. According to the commenters, EPA may not choose to set 
Page 25 of 212

standards for the emissions from gold mines’ stacks while 

ignoring the significant fugitive emissions from their leach 

piles and tailing ponds. The commenters believe that EPA’s 

failure to set emission standards for these fugitive emission 

sources is unlawful, and its failure to address the issue in the 

proposal is arbitrary and capricious. 

The commenters said that EPA must determine the floor for 

fugitive emission sources based on the fugitive emission levels 

from the leach piles and tailing ponds with the lowest emission 

levels, and it must then determine the maximum achievable degree 

of reduction in fugitive emissions from leach piles and tailing 

ponds pursuant to section 112(d)(2). The commenters stated that 

means to control fugitive emissions are available, such as 

enclosing their leaching operations, as many mines around the 

world already do. By enclosing the leaching process, the 

commenter believes that mines could eliminate this source of 

fugitive emissions. Several commenters (0270, 0278, 0283) also 

stated that mines should not send tailings into open tailing 

ponds but into closed and carefully controlled treatment 

facilities that would remove mercury and other HAP from the 

tailings and prevent their release to the air. The commenters

recommended that EPA evaluate the use of sulfur-based complexing 

agents, such as dimethyldithiocarbamate or 
Page 26 of 212

diethyldithiocarbamate, for removing mercury during 

cyanidization of gold. According to the commenters, research 

indicates that these products appear useful for substantially 

reducing mercury in process solution during heap leaching, and 

thereby significantly reducing the amount of mercury released 

over time.

Several environmental group commenters (0263, 0270, 0277, 

0281, 0312, 0321, 0348) believe the proposed regulation should 

provide a standard set of calculations to estimate fugitive 

emissions, and mines should be required to incorporate this 

information into their monitoring reports. The commenters noted 

that a recent study found that mercury air emissions from mining 

disturbances are approximately 20 percent of the total mercury 

emitted. Commenters stated that mines should use instruments 

similar to those used in the Eckley and Gustin research to 

monitor fugitive sources.

Response: Due to the lack of information, we have not 

included fugitive mercury emissions at gold mine facilities in 

our 1990 baseline emission estimate (or in our more recent 

emissions estimates) for the gold mine ore processing and 

production area source category. Accordingly, these fugitive 

emissions are not part of the source category we are listing and 

regulating in this final rule. Other than the recent 
Page 27 of 212

preliminary research at two facilities, we have no data on 

fugitive mercury emissions at gold mine facilities. The recent 

preliminary research suggests that some fugitive emissions may 

be occurring at these facilities from large non-point sources 

such as tailings ponds, leach fields and waste rock piles. 

However, it is our understanding that this preliminary research 

has not yet been published or peer-reviewed. Thus, at this 

juncture, we do not have sufficient information on fugitive 

emissions.

Furthermore, we have very little information on how these 

fugitive mercury emissions might be controlled. A few 

commenters suggested that certain compounds were available that 

may be useful for limiting these emissions. However, as far as 

we know, there has been no demonstration that these compounds 

would work effectively to limit the emissions, and we do not 

know the costs or potential adverse impacts of applying these 

chemicals. Therefore, we question the feasibility and 

practicality of applying these chemicals to limit fugitive 

mercury emissions from these non-point sources. We also 

question the feasibility and practicality of enclosing the 

leaching operations or the tailings ponds, as suggested by some 

commenters. 
Page 28 of 212

As explained in the proposed rule, the gold mine ore processing 

and production area source category covers the thermal processes 

that occur after ore crushing, including roasting operations 

(i.e., ore dry grinding, ore preheating, roasting, and 

quenching), autoclaves, carbon kilns, electrowinning, preg 

tanks, mercury retorts, and furnaces. The data and calculations 

used to derive the estimated 4.4 tons of mercury emissions for 

this source category for the 1990 baseline inventory for section 

112(c)(6) reflect emissions from the thermal processes described 

above, and the final MACT standards address all of these 

processes. 

5. Major Source Determination

Comment: One commenter (0283) noted that the proposal 

states the following: “data indicate that the gold mining 

processing and production category consists of only area sources 

(i.e. facilities that emit less than 10 tons per year of any 

single HAP and less than 25 tons per year of any combination of 

HAP).” 75 Fed. Reg. at 22479. The commenter did not support the 

area source determination for gold mines processing and 

production facilities. The commenter also claimed that the 

proposal indicates that actual emissions of hydrogen cyanide 

(HCN) at a few facilities are near the major source threshold. 

The commenter continued by saying that “by basing its evaluation 
Page 29 of 212

of whether gold mines are major sources on their actual 

emissions instead of their potential emissions, EPA violates 

both the Clean Air Act and its own regulations.” 

The commenter also stated that EPA’s failure to apply the 

same variability analysis in calculating gold mines’ potential 

to emit that was used in setting floors was internally 

inconsistent, unexplained, and arbitrary and capricious. The 

commenter noted that the proposal requested comment on a 

certification process that would allow gold mines to avoid major 

source status whereby companies could certify that they are area 

sources by implementing certain “management practices” and then 

certifying to EPA that they had done so. The commenter stated 

that such a certification process would be unlawful in 

calculating a sources “potential to emit” because the management 

practices are not “control equipment,” “restrictions on hours of 

operation or on the type or amount of material combusted, 

stored, or processed,” and would not be “federally enforceable.”

Other commenters (0274, 0342)supported EPA’s conclusion and 

determination that the gold mines are area sources of HAP. 

According to the commenters, EPA’s methodology in making this 

determination was extremely conservative and resulted in higher 

calculated HCN emissions than may actually be present. For 

instance, EPA did not apply what the commenters believe to be a 
Page 30 of 212

key correction factor to account for the fact that much of the 

mass transfer of HCN for large surface areas is expected to be 

gas phase limited. Application of this correction factor would 

have reduced the estimates for HCN emissions from the mines 

tested by approximately 40-50%. The commenters also stated that 

fence line testing at selected gold mine operations demonstrated 

that there was no concern with fenceline levels of HCN 

emissions, and that these levels of HCN were below all 

applicable public health standards.

The commenters and others (0269, 0279, 0280, 0285, 0332)

believe that, because the gold mines are area sources of HCN, 

they should not be subject to section 112 work practice 

standards or newly developed certification requirements. The 

commenters noted that it is not technically practical to set 

systematic work practice standards to reduce HCN emissions for 

every gold mining operation to follow because each mine is 

unique in its mineralogy and cyanide leaching processes, and 

different process solution pH values are necessary to enhance 

gold recovery. 

The commenters explained that for economic, health, and 

safety reasons, they already implement work practice standards 

designed to minimize HCN. The commenter concluded that the 

combination of these work practice standards and the annual TRI 
Page 31 of 212

reporting more than adequately ensure that gold mining 

operations will remain area sources of HCN.

Response: Contrary to the assertions of one of the 

commenter’s, EPA did not state in the preamble to the proposed 

rule that the sources at issue had actual emissions ranging from 

5 to 9 tons. By contrast, EPA stated that “a few facilities are 

close to the major source threshold due to hydrogen cyanide 

(HCN).” 75 FR 22479. EPA failed to clarify in the preamble to 

the proposed rule that the range of 5 to 9 tons represented 

potential to emit calculations for the largest-emitting sources. 

Specifically, as explained in the document “Estimated Emissions 

of HCN from Gold Mine Facilities in the U.S.” (which is 

available in the docket for this rulemaking), EPA estimated the 

potential to emit for the five largest sources assuming that 

these sources would be operating every day of the year, 24 hours 

a day, at 100 percent of its current capacity. These 

assumptions and calculations resulted in a potential to emit 

estimate of 5 tons of HCN per year for the largest source. EPA 

then completed a second set of calculations, using the same 

assumptions (i.e., operating every day of the year, 24 hours a 

day, at full capacity), but without applying the surface area 

correction factor, and those calculations resulted in a 

conservative potential to emit estimate of 9 tons of HCN per 
Page 32 of 212

year for the largest source. The emission estimates for the 

remaining large facilities were all below 9 tons. 

The commenters correctly point out that in determining 

whether a source is a “major source” under CAA section 112, we 

must consider the source’s potential to emit, as well as its 

actual emissions. See CAA section 112(a)(1) and 40 CFR 63.2. 

As noted above, we specifically examined the sources’ potential 

to emit and concluded that all sources’ potential to emit were 

below the major source thresholds.

Some commenters allege that EPA significantly overestimated 

HCN emissions from the larger sources by not accounting for 

certain correction factors. They assert that if one were to 

account for the appropriate correction factors in developing the 

potential to emit values, HCN emissions would “range from 3.7-

4.5 tpy for the larger mines compared to the 5-9 tpy estimate” 

(See document titled “PTE Emission Estimates for HCN” by the 

Nevada Mining Association, which is available in the docket for 

this action). Other commenters make a blanket, unsupported 

assertion that the Agency has underestimated HCN emissions from 

the source category because they believe that without the 

management practices currently employed by sources in the 

category, HCN emissions would exceed the major source thresholds 

at the larger sources. These latter commenters, however, made 
Page 33 of 212

only conclusory statements and did not demonstrate that HCN 

emissions from the larger sources would exceed the major source 

thresholds if the management practices were not employed.

In sum, EPA has developed conservative estimates of the 

sources’ potential to emit HCN. At one end of the range EPA 

estimates potential emissions of 5 tons per year of HCN for the 

largest source, which is well below the major source threshold 

of 10 tons per year of a single HAP. At the other end of the 

range EPA estimates potential emissions of 9 tons per year for 

that same largest source, which is a conservative estimate and 

is still below the major source threshold. The emission 

estimates for the remaining large facilities were all below 9 

tons. We understand that the sources at issue implement various 

management practices as part of their operations to minimize the 

use and emissions of cyanide to protect workers, to comply with 

Mine Safety and Health Administration (MSHA) standards, to 

comply with their agreements to the International Cyanide Code, 

and for economic reasons (to reduce operational and supply 

costs). We currently do not have sufficient information to 

explicitly quantify emissions reductions achieved through these 

management practices, but nothing in the record suggests that 

the facilities would be major sources if they failed to employ 

the management practices. Accordingly, we are taking final 
Page 34 of 212

action today to list the gold mine ore processing and production 

area source category and regulate its mercury emissions pursuant 

to CAA section 112(c)(6).

Although not required, we intend to send letters to various 

Gold Mining Processing and Production companies pursuant to 

Section 114 of the Clean Air Act to confirm our conclusion that 

the sources’ potential to emit remain below major source 

thresholds.

Comment: A commenter stated that EPA’s failure to apply the 

same variability analysis in calculating gold mines’ potential 

to emit that was used in setting floors was internally 

inconsistent, unexplained, and arbitrary and capricious. 

Response: We do not believe that the variability analysis 

used in establishing the MACT limits is appropriate for 

estimating sources’ potential to emit (PTE) of these sources. 

In determining the MACT limits, we used the 99% UPL method to 

assess variability of the best performers, This approach is 

designed to estimate a MACT floor level that is equivalent to 

the average of the best performing sources based on future 

compliance tests. The 99 percent UPL represents the value 

below which the mean of future compliance tests would fall 99 

percent of the time. A 99 percent level of confidence means 

that a facility, whose emissions are consistent with the best 
Page 35 of 212

performing sources, has one chance in 100 of exceeding the 

emission standard. In contrast, the purpose of the PTE 

calculation is not estimating the emission level achieved in 

practice by the best performing sources. Rather, it is to 

determine whether any source has a potential to emit at or above 

a major source threshold. For the PTE calculation, we derive 

our best estimate, or estimates, of the average emissions that 

would occur over the course of the year (i.e., long-term 

average) assuming the source is operating at the maximum 

capacity under its physical and operational design.

 

6. GACT for Mercury Instead of MACT

Comment: Several industry commenters (0271, 0274, 0280, 

0332, 0341, 0342, 0351) noted that EPA acknowledged that all 

gold mining operations are area sources of mercury emissions and 

suggested that rather than subjecting these area sources to MACT 

requirements that are required for major sources, section 112 

allows EPA to adopt generally available control technology 

(“GACT”) for such smaller sources of HAP. The commenters 

believe that the language of section 112(d)(5) includes all area 

sources listed under section 112(c)(6) and that section 

112(d)(5) does not restrict from which paragraph in subsection 

(c) the source listing must originate. The commenters said 
Page 36 of 212

that absent such a limitation, section 112(d)(5) vests EPA with 

the authority to use a GACT standard for an area source listed 

under any of the paragraphs of subsection (c), including section 

112(c)(6). The commenters claim that while EPA has indicated 

that it interprets section 112(c)(6) as not allowing it to 

promulgate a GACT for area sources, EPA reads an exception into 

section 112(d)(5) that does not exist, and that instead, section 

112(d)(5) is itself an exception to the mandatory provisions of 

section 112(c)(6). The commenters believe that the proper 

reading of section 112(c)(6) requires EPA to develop MACT 

standards for major sources while giving the EPA the authority 

to use a GACT standard for area sources. According to the 

commenters, this reading is supported by both the legislative 

history and EPA’s early comments regarding the interpretation of 

the CAA. The commenters said that in the House Report on the 

1990 CAA Amendments, under which sections 112(c)(6) and (d)(5) 

arise, the Committee stated that:

Controls under subsection 112(d) for area source 

categories and subcategories may require the use of 

generally available control technologies or 

management practices by sources to reduce emissions, 

as elected by EPA, in lieu of MACT and residual risk 

provisions of subsection 112(f). The Committee, in 

establishing the area source provisions of this 

section, has given EPA discretion to use this 

standard in all appropriate cases.3

 3 The commenters cited: H. Rep. No.101-490, Part 1, at 329 (1990).
Page 37 of 212

The commenters stated that there is no language in the 

report indicating that Congress intended to prohibit the 

application of section 112(d)(5) to area sources listed under 

section 112(c)(6), and instead, the Committee indicated that all 

area source categories were subject to EPA’s discretion to use a 

GACT standard. The commenters said that as such, section 

112(d)(5) should be read to apply to all area sources listed 

under section 112(c), including area sources listed under 

section 112(c)(6). According to the commenters, EPA originally 

shared this understanding of section 112(d)(5) when promulgating 

MACT standards under section 112(c)(6) for control of several 

HAPs, including mercury, emitted from hazardous waste 

combustors. The commenters said that EPA has stated that “[f]or 

area sources, section 112(c)(6) requires the Agency to establish 

either MACT standards under section 112(d)(2), or generally 

available control technology (GACT) standards under section 

112(d)(5)” (citing 62 FR 24212, 24214, May 2, 1997). The 

commenters stated that in this instance, EPA recognized that the 

language of section 112(d)(5) permitted the Agency to establish 

GACT standards for all area sources listed under section 112(c). 

The commenters continued by saying that in later 

rulemakings, EPA shifted its position, and that in a 1999 

rulemaking under section 112(c)(6), EPA stated that a 
Page 38 of 212

“permissible” reading of the statute was to ignore the language 

in section 112(d)(5) providing EPA with discretion for all area 

sources listed under section 112(c) and instead read section 

112(c)(6) as imposing a mandatory MACT standard which was not 

subject to the exception contained in section 112(d)(5). The 

commenters said that EPA reasoned that because the language 

providing for the exception was not located in section 112(c)(6) 

and section 112(c)(6) contained specific standards, the 

exception contained in the section 112(d) should not be read to 

apply to subsection (c)(6). According to the commenters, EPA 

also cited the policy-based rationale that the purpose of 

section 112(c)(6) was to “assure that the maximum available 

control technology is applied to control the emission of the 

most dangerous HAPs” (citing 64 FR 31898, 31911, June 14, 1999). 

However, the commenters believe that EPA’s reasoning ignores the 

plain reading of the statute, and that while section 112(c)(6) 

creates a default position of subjecting all sources listed 

under it to a MACT standard, section 112(d)(5) explicitly 

creates an exception for the limited subset of area sources 

listed pursuant to section 112(c). In addition, the commenters 

believe that the congressional intent behind section 112(d)(5) 

and cited by EPA, namely, that area sources should be treated 

differently from major sources owing to their smaller size and 
Page 39 of 212

emission levels, supports this interpretation. The commenters 

conclude that EPA’s reading of section 112 is erroneous and that 

EPA should recognize that section 112(d)(5) allows EPA to use a 

GACT standard for area sources listed under section 112(c)(6).

The commenters also believe that from a policy perspective, 

EPA should use its discretion to apply GACT standards to the 

gold mine ore processing and production area source category 

because Congress, in allowing EPA to use a GACT standard for 

area sources, recognized that area sources are different from 

major sources in both the level of emissions and the level of 

scrutiny to which their emissions should be subject (citing 74 

FR 69194, 69199, December 30, 2009). The commenters stated that 

the costs of applying a MACT standard to area source gold mines 

are not justified where all but a few mines with mercury 

emissions are already well-controlled and the MACT standards 

required for major sources run a distinct risk of imposing 

excessive economic burdens on area sources. According to the 

commenters, Congress considered this burden when drafting 

section 112 and provided EPA with the discretion to issue a GACT 

standard and allowed EPA to consider costs in setting the GACT 

floor. 

The commenters said that the adequacy of State regulations 

also is an important factor in addressing the cost effectiveness 
Page 40 of 212

of technology standards because EPA often looks to the 

effectiveness of State programs when determining whether area 

sources should be subject to a GACT or a MACT standard. The 

commenters stated that in Nevada, where all but a few of the

gold mines are located, mercury is already substantially 

controlled through the NMCP, and the added costs of compliance 

with a MACT standard provide no additional environmental 

benefit. 

Response: We disagree with the comment that the CAA gives 

EPA discretion to promulgate GACT standards pursuant to section 

112(d)(5) for area source categories required to be regulated 

under section 112(c)(6). Section 112(c)(6) of the CAA 

explicitly requires that “sources accounting for not less than 

90 per centum of the aggregate emissions of each [pollutant 

specified in this provision] are subject to standards under 

subsection 112(d)(2) or (d)(4)....” (Emphasis added). The plain 

language of section 112(c)(6) requires that the Agency set 

standards under section 112(d)(2) or (d)(4). There is no 

ambiguity in this language and thus the legislative history 

cited by the commenter is irrelevant. As such, the Agency is 

appropriately setting standards for the sources at issue 

pursuant to section 112(d)(2).
Page 41 of 212

The commenter argues that section 112(d)(5) trumps the very 

specific language in section 112(c)(6). We disagree. Congress 

unambiguously required the Agency to set standards for these 

persistent, bioaccumulative HAP under section 112(d)(2) or 

(d)(4). Had Congress wanted us to permit EPA to issue GACT 

standards for the 112 (c)(6) HAP, it would have said that EPA 

could issue standards under section 112(d), as it did in section 

112(k)(3)(B) of the Act, noting that area sources shall be 

subject to standards issued pursuant to “subsection (d) of this 

section.” Congress could not have been more precise in section 

112(c)(6), and we reject the commenter’s interpretation. 

Finally, the commenter cites to a proposed rule that the 

Agency issued years ago, noting that the Agency solicited 

comment as to whether EPA could interpret section 112(c)(6) as

allowing EPA to set GACT standards for area sources under 112

(c)(6). The commenter fails to note that EPA rejected that 

position in the final rule. See NESHAP for Hazardous Waste 

Combusters, 64 FR 52827, 52837. Specifically, EPA stated that 

“the CAA provides independent authority to regulate [112(c)(6) 

HAP] under MACT standards, even if the emissions are from area 

sources.... Thus, all sources covered by today’s rule would have 

to control these hazardous air pollutants to MACT levels....” 
Page 42 of 212

EPA’s interpretation was not challenged. EPA maintains that 

interpretation in this final rule. EPA has consistently 

maintained that standards under section 112(d)(2) or (d)(4) are 

required for the pollutants listed in section 112(c)(6). In 

this case, we are setting a section 112(d)(2) MACT standard for 

mercury, which is the 112(c)(6) pollutant that forms the basis 

for the listing of the source category at issue here.

7. Title V Permit Exemption

Comment

• EPA did not properly determine whether some or all sources 

in the category are major sources by determining each 

source’s potential to emit, and instead estimated that 

sources’ actual emissions were below the major source 

threshold. If any source in the category is a major 

source, it must obtain a title V permit. 

: In the proposal preamble, EPA solicited comment 

on whether a title V exemption “is appropriate under section 

502(a) for any particular sources in this category.” One 

commenter (0283) offered the following reasons for not exempting 

gold mines from title V permitting requirements:

• The CAA allows EPA to exempt area sources from title V 

permitting only if it establishes that compliance with the 

title V permitting requirements would be “impracticable, 

infeasible or unnecessarily burdensome.” However, EPA does 

not claim that such requirements are “impracticable,” 

“infeasible,” or “unnecessarily burdensome” for gold mines 

and does not provide support for such a claim with record 

evidence. Accordingly, EPA has no basis for exempting gold 

mines from title V permitting requirements. 

• It is feasible and within the gold mining companies’ 

financial means to comply with title V permitting 

requirements, and a persuasive showing could not be made 
Page 43 of 212

that compliance with title V would be “unnecessarily 

burdensome.” 

The commenter believes that the text and legislative 

history of the CAA make plain that Congress intended ordinary 

citizens to be able to get emissions and compliance information 

about air toxics sources and to be able to use that information 

in enforcement actions and in public policy decisions on a State 

and local level. According to the commenter, Congress did not 

think that enforcement by States or other government entities 

was enough; if it had, Congress would not have enacted the 

citizen suit provisions, and the legislative history of the CAA 

would not show that Congress viewed citizens’ access to 

information and ability to enforce CAA requirements as highly 

important both as an individual right and as a crucial means to 

ensuring compliance. The commenter said that if a source does 

not have a title V permit, it is difficult or impossible, 

depending on the laws, regulations, and practices of the State 

in which the source operates, for a member of the public to 

obtain relevant information about its emissions and compliance 

status or to bring enforcement actions. The commenter believes 

that exempting a source category from title V permitting 

requirements deprives both the public generally and individual 

members of the public who would obtain and use permitting 
Page 44 of 212

information of citizen oversight and enforcement that Congress 

viewed as necessary. The commenter stated that to the extent 

the informational and enforcement benefits provided by title V 

permits can be considered a burden at all for gold mines, they 

far outweigh that burden and are by no means unnecessary.

The commenter also noted that title V provides important 

monitoring benefits and that title V permits must contain 

requirements, including monitoring, sufficient to assure 

compliance with emission standards. The commenter believes that 

EPA’s proposed standards would not provide such assurance and 

that title V permits are necessary to provide adequate 

monitoring. The commenter concluded by stating that the 

legislative history the CAA shows that Congress did not intend 

EPA to exempt source categories from compliance with title V 

unless doing so would not adversely affect public health, 

welfare, or the environment; however, exempting gold mines from 

title V would adversely affect public health, welfare and the 

environment by depriving the public of the important 

informational and enforcement benefits.

One commenter (0268) stated that additional title V 

permitting would subject both the source and the State agency to 

additional resource burdens. The commenter points out that 

major sources of criteria pollutant emissions are currently 
Page 45 of 212

subject to title V permit requirements in Nevada and that 

sources not subject to major source permitting requirements are 

subject to Nevada’s minor source permitting program. In 

addition, the NMCP requires all mining sources to obtain 

mercury-specific operating permits to construct. The commenter 

believes that these permit programs would provide a strong basis 

for implementing and enforcing any federal MACT requirements for 

the gold mining industry, and there would be nothing gained in 

terms of improved compliance by subjecting these sources to 

title V permitting. The commenter recommends that subpart 

EEEEEE not require that all gold mine ore processing and 

production facilities obtain title V permits.

Several industry commenters (0269, 0271, 0274, 0276, 0279, 

0280, 0285, 0332, 0341, 0342, 0351) stated that EPA should 

exercise its discretion and exempt the gold mine ore processing 

and production area source category from the title V 

requirements as impracticable, infeasible, and unnecessarily 

burdensome. The commenters said that EPA’s analyses to date 

have focused primarily on the “unnecessarily burdensome” 

criterion of this delegation of Agency discretion, and the 

commenters believe that when considered together and in light of 

EPA’s findings in other similar rulemakings for area sources, 

the four factors set forth in the Exemption Rule support a 
Page 46 of 212

finding that title V permitting is “unnecessarily burdensome” 

for the gold mine ore processing and production area source 

category. The following paragraphs provide their lengthy 

comments on their suggested title V permit exemption. 

In discussing the first factor of the Exemption Rule, 

whether title V would result in significant improvements to the 

compliance requirements, the commenters referred to an excerpt 

from the Exemption Rule:

This preamble refers to this evaluation as probing 

whether title V is ‘unnecessary’ to improve compliance 

for these NESHAP requirements at area sources. Thus, a 

finding that title V does not result in significant 

improvements to compliance, as compared to operating 

subject to the NESHAP without a title V permit, is 

described as supporting a conclusion that title V 

permitting is ‘unnecessary’ for area sources in that 

category, consistent with the ‘unnecessarily 

burdensome’ criterion of section 502(a) of the Act. 

(See 70 FR 75323.) 

The commenters also said that EPA clarified in the 

Exemption Rule that “it has been EPA’s consistent position that 

post-1990 NESHAP include all monitoring required under the Act” 

(citing 70 FR 75324.) According to the commenters, the proposed 

NESHAP for the gold mine ore processing and production area 

source category includes extensive monitoring, recordkeeping, 

and reporting requirements that are more comprehensive than 

title V requirements. The commenters stated that the proposed 

standards require comprehensive annual compliance testing, 
Page 47 of 212

submission of a monitoring plan, extensive monitoring, and 

specific recordkeeping and notification requirements in addition 

to those provided for in the General Provisions, and in 

addition, Nevada’s comprehensive mercury emissions control 

program imposes sampling and monitoring requirements and 

requires that permit holders retain monitoring and supporting 

information for 5 years after sample collection. The commenters 

believe that Nevada regulations and permits provide an

additional layer of compliance assurance on the federal NESHAP 

that obviates the need for title V permitting and that Nevada’s 

program provides a permit platform for implementing the MACT for 

the gold mine ore processing and production area source category 

in essentially the same manner as a title V permit, which in 

conjunction with the compliance requirements in EPA’s proposed 

rule, are sufficient to assure compliance. The commenters 

claimed that the additional layering of title V does not 

“significantly improve” upon the proposed and existing 

compliance requirements.

The commenters stated that the second factor in the 

Exemption Rule is whether title V permitting would impose 

significant burdens on the area source category and whether the 

burdens would be aggravated by any difficulty the sources may 

have in obtaining assistance from permitting agencies. The 
Page 48 of 212

commenters said that there are extensive administrative burdens 

and costs associated with the title V permitting process, 

including mandatory activities that have been previously 

identified by EPA (citing 75 FR 31912, June 4, 2010): reading 

and understanding permit program guidance and regulations; 

obtaining and understanding permit application forms; answering 

follow-up questions from permitting authorities after the 

application is submitted; reviewing and understanding the 

permit; collecting records; preparing and submitting monitoring 

reports on a 6-month or more frequent basis; preparing and 

submitting prompt deviation reports, as defined by the State, 

which may include a combination of written, verbal, and other 

communications methods; collecting information, preparing and 

submitting the annual compliance certification; preparing 

applications for permit revisions every 5 years; and, as needed, 

preparing and submitting applications for permit revisions. The 

commenters stated that if area source gold mines were also 

subject to title V permitting, they would have to comply with 

three layers of time- and cost-intensive permit requirements 

that would involve performance of duplicative source testing and 

monitoring and maintenance of duplicative records. The 

commenters claimed that many of the area source gold mines that 

would be subject to the proposed rule are owned and operated by 
Page 49 of 212

small entities that are already required to comply with

comprehensive State permitting requirements for mercury

emissions and that requiring title V permits for them would 

result in resources being redirected away from more useful and 

necessary efforts, including the Nevada mercury control program.

The commenters explained that the third factor in the 

Exemption Rule is closely related to the second factor and 

examines whether the costs of title V permitting for the area 

source category would be justified, taking into consideration 

any potential gains in compliance likely to occur for such 

sources. The commenters claim that there do not appear to be 

any gains in compliance to justify the additional costs that 

would be imposed on these area sources from title V permitting 

based on the lack of significant improvements in compliance

requirements discussed in the first and fourth factors and the 

substantial additional costs and burdens associated with title V 

compliance discussed in the second factor. The commenters 

concluded that imposing title V permit requirements on these 

area sources would only serve to increase costs burdens on these 

facilities without any environmental benefits that are not 

already conferred under existing programs and the proposed 

NESHAP.
Page 50 of 212

The commenters noted that the fourth factor in the 

Exemption Rule analysis is whether there are implementation and 

enforcement programs in place that are sufficient to assure 

compliance with the NESHAP for the area source category, without 

relying on title V permits. The commenters claimed that the 

proposed rule includes all necessary monitoring to effectively 

implement its requirements, and the area sources for the gold 

mine ore processing and production are already permitted under 

State permit programs. According to the commenters, all nontitle V sources in Nevada are required to hold “Class II” 

operating permits that must contain, among other things, all 

applicable emission limitations and standards, including those 

operational requirements and limitations that ensure compliance 

with the conditions of the operating permit and all requirements 

for monitoring, testing and reporting that apply to the 

stationary source. The commenters said that other States where 

gold mine ore processing and production area source are located 

either would be covered by a comparable delegated State air 

program or by EPA. The commenter believes that requiring area 

sources to obtain title V permits is not justified because of 

the burdens that would result from layering another set of 

procedural requirements on area source gold mines on top of 
Page 51 of 212

State and NESHAP requirements and the minimal gains in 

compliance that might result from title V permitting.

The commenters stated that EPA regularly provides title V 

exemptions for area sources similar to gold mine ore processing 

and production area sources and cited examples from the past 

year: prepared feeds manufacturing, paints and allied products 

manufacturing, asphalt processing and asphalt roofing 

manufacturing, and the chemical preparations industry. The 

commenters said that in the two cases in which EPA required area 

sources to obtain title V permits, EPA carved out certain area 

sources that are synthetic minor sources with high levels of 

previously uncontrolled HAPs, which installed air pollution 

control devices in order to reduce HAP emissions to below major 

source thresholds (citing as examples the proposed rule for 

industrial, commercial, and institutional boilers and the final 

rule for chemical manufacturing area sources). According to the 

commenters, the gold mine ore processing and production area 

sources are not synthetic minor sources that installed control 

technology solely to reduce emissions below major source 

thresholds and instead are far more similar to those area 

sources for which EPA has provided title V exemptions. The 

commenters claim that the existing and proposed compliance and 

monitoring requirements for the gold mines are generally more 
Page 52 of 212

stringent than those found in the other NESHAPs for which EPA 

has granted a title V permit exemption.

The commenters stated that exempting the gold mine ore 

processing and production area source category from title V 

permitting will not adversely affect public health, welfare, or 

the environment because title V permits are designed to ensure 

that procedural requirements are followed, but do not generally 

impose substantive air quality control requirements. The 

commenters believe the procedural requirements in the proposed 

rule are adequate to protect public health and the environment, 

and in Nevada where the most mines are located, the State is 

implementing a comprehensive regulatory program that EPA 

acknowledges would provide “an additional level of control” for 

these facilities. According to the commenters, requiring title

V permits for those gold mine ore processing and production 

facilities that presently have duly issued non-title V permits 

also carries the potential of adversely affecting public health, 

welfare, or the environment by shifting State agency resources 

away from ensuring compliance with a program that is reducing 

mercury emissions from gold mines.

The commenters stated that EPA should exempt the gold mine 

ore processing and production area source category from title V 

permitting requirements because they are unnecessarily 
Page 53 of 212

burdensome, and at a minimum, EPA should exempt area source gold 

mines that are subject to Nevada’s comprehensive mercury control 

program if EPA determines that the entire area source category 

should not be exempt from title V. The commenters said that 

Nevada has also implemented a regulatory program specifically 

designed for mercury emissions from gold mines, and it is 

focused exclusively on the precious metals mining industry and 

the regulation of mercury from that industry. The commenters 

observed that the Nevada program requires all gold mining 

sources, including area sources, to hold mercury operating 

permits to construct, which must contain all applicable 

requirements concerning controls for mercury emissions, emission 

limits and standards, and are particularly suited for addressing 

federal MACT standards. The commenters concluded that the 

Nevada mercury control program and the required operating 

permits to construct provide a solid foundation for implementing 

and enforcing any federal MACT requirements for the gold mining 

industry, and there would be nothing gained in terms of improved 

compliance with such a standard by subjecting these sources to 

title V permitting. 

Response: After reviewing the comments, we continue to 

believe that it is appropriate that all gold mine ore processing 

and production facilities be required to obtain title V permits. 
Page 54 of 212

Most of the other area source categories for which we have 

provided title V permit exemptions have hundreds or thousands of 

facilities that are mostly owned by small businesses. In 

contrast, there are an estimated 21 facilities that are subject 

to this final rule, and, based on our research and analyses, 

none of the facilities are owned by small businesses; most of 

these facilities are owned by large, and in some cases, multinational, corporations. Therefore, we conclude that the 

argument of financial burden, which has supported title V 

exemption for other source categories, does not apply to the 

gold mining industry (see Economic and Small Business Analysis, 

which is available in the docket). 

Currently, it is our understanding that 7 of the 21 

facilities that will be subject to the final rule already have 

title V permits (5 in Nevada and 2 in other states). Further, 

there are approximately 5 facilities in all other States (i.e., 

except Nevada) that do not currently have title V permits that 

will be subject to this final rule, so title V permitting will 

apply to no more than a few facilities in any one of these other 

States. Therefore, we do not believe the requirement for title 

V permitting will be overly burdensome to the permitting 

authorities in those States. Although there are more facilities 

in Nevada that will be subject to the final rule, as the 
Page 55 of 212

commenters point out, Nevada already has an effective permitting 

system in place. Five of the 14 gold mine facilities in Nevada 

already have title V permits. Because of Nevada’s existing 

permitting system and experience with title V permitting, we do 

not think that it is an undue burden on the State of Nevada to 

require title V permits from the other gold mine facilities 

located within the State. We also think it is important for the 

public in States where these facilities are located to have 

access to emissions and monitoring data and the opportunity for 

public involvement in the permitting of these facilities that is 

provided by title V permitting. 

8. Early Reduction Provisions in Section 112(i)(5)

Comment: One commenter (0342) stated that many Nevada gold 

mines have achieved 90 percent reductions in mercury emissions 

from the 2000 baseline year, due to Nevada voluntary programs, 

and should be eligible for the early reduction provisions of 

section 112(i)(5). The commenter explained that the regulatory 

requirements of 40 CFR part 63, subpart D outline a process at 

the State level for section 112 delegated programs for 

demonstration of a 90 percent reduction from a baseline 

emissions estimate. The commenter expects that Nevada will 

receive expedited delegation of this proposed NESHAP, and the 

commenter requests clarification that Nevada gold mining 
Page 56 of 212

facilities will have the option to demonstrate a 90 percent 

reduction in mercury emissions under Nevada’s delegated NESHAP 

program.

Response:

9. Federalism Impacts

 This comment is not relevant to the requirements 

of the final rule. We refer the commenter to the provisions of 

40 C.F.R. Subpart D, which implements the CAA section 112(i)(5) 

early reduction program. Subpart D details the precise 

requirements needed to qualify for the early reduction program.

Comment: Several commenters (0341, 0342) believe that 

EPA’s rule will have federalism issues concerning the trust 

between State air agencies and the EPA. The commenters stated 

that NDEP invested substantial time and effort into the 

development of the NMCP, and both NDEP and the gold mines moved 

forward with the regulatory program with assurances from EPA 

that it was fully supportive of the program and would not 

promulgate MACT standards if the NMCP was adopted and 

implemented. The commenters believe that if a State cannot rely 

on EPA’s representations, as an agent of the federal government, 

States like Nevada will be much less willing to step up and 

commit necessary resources to address a problem in a timely and 

efficient matter. The commenters concluded that not only is 

this detrimental to the cooperation required between federal and 
Page 57 of 212

State government for successful government operation and notions 

of federalism, but it is detrimental to the environment, because 

it creates a disincentive for States (and sources) to take early 

action to address a problem (despite EPA encouragement and, what 

turn out to be, false promises).

Response: In the process of developing this rule, we have 

communicated and coordinated with NDEP, including sharing data, 

discussing control technologies and options, and various other 

technical issues. We greatly appreciate NDEP’s assistance 

throughout this process, and we have confidence that the two 

agencies will continue their joint effort in addressing the 

emissions from this sourc category. 

10. Reconstruction

Comment: Several commenters (0274, 0285, 0341, 0342) 

supported the development of three separate affected source 

categories and said they consist of logical collections of 

process units that facilitate the establishment of not just 

emission standards and compliance demonstrations, but also 

reconstruction determinations. They believe it is appropriate 

to group under each of the umbrella “affected sources” all the 

equipment associated with the use of each particular process in 

order to ensure a reasonable application of the reconstruction 

provisions found in the General Provisions (citing 40 CFR Part 
Page 58 of 212

63, Sections 63.2 and 63.5(e)). The commenters asked that EPA 

reaffirm that the 50 percent fixed capital cost trigger for 

determining reconstruction would be measured against all 

equipment components needed for the defined processes, and that 

reconstruction at one affected source as defined in the standard 

will not affect or result in reconstruction at another affected 

source.

The commenters also noted that the definition of 

“reconstruction” authorizes EPA to establish special provisions 

in a particular standard for the application of the 

reconstruction criteria to the affected source and said that EPA 

has noted that such provisions could be “warranted by technical 

and economic considerations” arising from “the functional 

interrelationship of equipment encompassed by the affected 

source. . . .” (citing 66 FR 16324, March 23, 2001). The 

commenters said that the “carbon processes” affected source 

illustrates that the affected source can consist of several 

pieces of interconnected equipment that together constitute the 

process line, and for an existing source, it can be anticipated 

that production needs will give rise to the need to add more 

pieces of equipment to an existing carbon process line or even 

to install a whole new carbon process line. The commenters 

provided three examples and said that consideration of whether 
Page 59 of 212

or where new MACT requirements should apply in these examples 

(described below) warrants the development of special 

reconstruction provisions in this standard, or EPA should 

clarify that the three examples would not be considered 

reconstruction under the proposed rule.

The commenters’ first example was adding a new component to 

an existing carbon process, in which case they said the 

definition of “reconstruction” makes clear that replacement of a 

single component within an affected source, or the rebuilding 

and replacement of several components within an affected source, 

would trigger new source MACT requirements only if the 50 

percent cost trigger and the feasibility criteria were met. 

According to the commenters, it is likely that operational 

constraints inherent at each site would prevent an existing 

process line from being able to meet new MACT requirements where 

existing equipment is being replaced.

The second example provided by the commenters was the 

construction of a new carbon group due to expansion at a 

facility that has an existing carbon group, where the new carbon 

process will be separate from existing carbon processes and will 

have separate pollution control equipment, but the cost of 

construction of the new carbon process group will exceed the 50 

percent cost trigger for the reconstruction provisions. The 
Page 60 of 212

commenters suggest that the new carbon process will be subject 

to the MACT standard for new carbon processes; however, the 

existing carbon process will remain subject to the MACT standard 

for existing carbon processes (i.e., the construction of the new 

carbon process will not be deemed to constitute reconstruction 

of the existing carbon process group). The commenters said that 

the proposed rule states that “the affected sources are ... each 

collection of carbon processes at a gold mine ore processing and 

production facility ...” and note that the definition 

specifically makes reference to “each collection.” According to 

the commenters, the existing and new carbon process groups in 

the second example each constitute separate collections of 

process equipment, hence, the construction of the new carbon 

process group does not constitute reconstruction of the existing 

carbon group. The commenters stated that they believe the

reason for subjecting an existing affected source that undergoes 

reconstruction to a MACT standard for new affected sources is 

due to the fact that extensive changes are being undertaken such 

that it is reasonable and appropriate to require the source to 

upgrade controls as part of the reconstruction effort. The 

commenters said that EPA had previously explained that EPA 

“agree[s] that new source MACT should be applied to units for 

which new source MACT is reasonable” (citing 66 FR 16322, March 
Page 61 of 212

23, 2001), which is consistent with the definition of 

“reconstruction” (i.e., the definition specifies that before 

something will be deemed to constitute “reconstruction,” it must 

be “technologically and economically feasible for the 

reconstructed source to meet the relevant standards ...”). 

According to the commenters, the existing carbon process group 

in the example is not undergoing any changes, it is no different 

from any other existing carbon affected source, and the control 

systems for the existing and new carbon processes will be 

independent of one another. Consequently, they concluded that 

it would not be reasonable to impose the more stringent new 

source MACT standard on the existing carbon process group simply 

because of the construction of a separate carbon group. 

The third example provided by the commenters was the 

installation of new pollution control equipment. The commenters 

stated that EPA has recognized that it is not appropriate in the 

calculation of the cost criteria for the definition of 

reconstruction to include costs of control equipment that is 

installed for the purposes of emission control:

Costs associated with the purchase and installation of 

air pollution control equipment (e.g., baghouses, 

electrostatic precipitators, scrubbers, etc.) are not 

considered in estimating the fixed capital cost of a 

comparable entirely new facility unless that control 

equipment is required as part of the process (e.g., 

product recovery). (See 40 FR 58416, December 16, 

1975.) 
Page 62 of 212

The commenters believe that to allow such costs to be counted in 

the reconstruction determination would penalize existing sources 

for investing in the control equipment to meet the standard, and 

for the same reason, when an operator installs air pollution 

control equipment, there should be no requirement to undertake a 

reconstruction determination at all.

The commenters asked that EPA either clarify that the three 

examples would not be considered reconstruction, or 

alternatively, add the following provisions to the proposed 

rule: (1) an addition of a new piece of equipment to address 

production requirements is not considered a reconstruction, (2) 

the expansion of a facility by the construction of a completely 

new process line will not be considered a reconstruction of an 

existing process line, and (3) the installation of air pollution 

control equipment to comply with this standard is not considered 

a reconstruction.

Response

Reconstruction, unless otherwise defined in a relevant 

standard, means the replacement of components of an 

affected or a previously nonaffected source to such an 

extent that:

: The determination of what constitutes a 

reconstruction is directly tied to the definition of the 

affected source and the definition of reconstruction in the part 

63 General Provisions:
Page 63 of 212

(1) The fixed capital cost of the new components 

exceeds 50 percent of the fixed capital cost that 

would be required to construct a comparable new 

[affected] source; and

(2) It is technologically and economically feasible 

for the reconstructed source to meet the relevant 

standard(s) established by the Administrator (or a 

State) pursuant to section 112 of the Act. Upon 

reconstruction, an affected source, or a stationary 

source that becomes an affected source, is subject to 

relevant standards for new sources, including 

compliance dates, irrespective of any change in 

emissions of hazardous air pollutants from that 

source.

For each of the four affected sources in the final rule, we 

have defined the affected source as the collection of processes 

associated within each affected source. Consequently, if one 

process within the affected source is upgraded or replaced with 

a new process, the 50 percent fixed capital cost criterion would 

be based on the fixed capital cost of replacing all processes in 

the affected source, not just the capital cost of the process 

being upgraded or replaced. For example, if a new carbon kiln 

is added to an existing group of carbon processes with mercury 

retorts, the capital cost of the new carbon kiln would be 

divided by the fixed capital cost of constructing a comparable 

new affected source containing all of the processes within the 

existing affected source of carbon processes with mercury 

retorts to calculate the percent for comparison to the 50 

percent criterion. 
Page 64 of 212

With regard to the scenario where a new carbon process with 

a mercury retort is installed, the affected source is defined as 

the collection of all applicable processes within the affected 

source, and because of this, a facility could not have two 

carbon processes with mercury retorts affected sources, such as 

the commenter suggested, where one group is new and the other is 

existing. For example, if a new group of carbon processes with 

mercury retorts is installed at a facility in addition to an 

existing group of carbon processes with mercury retorts, the two 

groups (all carbon processes with mercury retorts at the 

facility) collectively would be a single affected source. In 

this case, the fixed capital cost criterion would be based on 

the fixed capital cost of replacing the existing affected source 

with a comparable new affected source, and if the new processes 

exceed 50 percent of that cost, all of the carbon processes with 

mercury retorts would be subject to the new source limit for 

carbon processes. There would not be separate and different 

emission standards for the two sets of carbon sources with 

mercury retorts (the older group and newer group) because the 

collection of all of these processes is the affected source. 

We do not see a necessity to provide criteria for this 

final rule that are different from the requirements in the 

General Provisions for determining what constitutes a 
Page 65 of 212

reconstruction. We also think it is appropriate to exclude the 

cost of emission control equipment from the cost calculation for 

reconstruction determinations. 

B. Applicability

Comment:

• Gold mining operations that produce less than 100 

pounds of concentrate per year. (This would exempt 

analytical labs that perform small bench scale 

processing tests on gold ores.)

 Several commenters (0258, 0260) stated the rule 

should exempt individuals (prospectors), laboratories, small 

mining operations, and non-leaching operations. The commenters 

urged EPA to include in the final rule all of the following 

exemptions to avoid the problem of unintended regulation of 

sources that were not meant to be included in the source 

category:

• Gold mining operations that do not leach or dissolve 

gold. (This exempts placer and other non-leaching 

operators, including both small commercial efforts as 

well as individual recreation-type prospectors.)

• Gold mining operations that process less than 1,000 

tons per year of gold ore. (This would exempt certain 

small scale pilot plants and related testing 

operations.)
Page 66 of 212

The commenters said that the exemptions suggested above will not 

reduce in any way the effectiveness of the proposed rule in 

controlling mercury emissions from the targeted larger mines, 

nor will they lead to increased mercury emissions, but they will 

exclude regulation of a large number of small operators who do 

not emit any significant mercury.

Response

Further, as mentioned above in section IV, we are 

clarifying in this final rule that this area source category 

does not include individual prospectors and very small pilot 

scale mining operations. Prospectors and other very small 

pilot-scale operations (e.g., operations that produce or process 

less than 100 pounds of concentrate per year) are very small and 

were not included in the section 112(c)(6) inventory that was 

the basis for the listing of gold mine ore processing and 

production source category. We believe that emissions from the 

very small scale operations described above to be very minimal. 

: Section 63.11640(c) of the proposed rule 

provides that the emissions standards for this area source 

category do not apply to research and development facilities, as 

that term is defined under CAA section 112(c)(7). We did not 

receive any adverse comments concerning this provision, and are 

finalizing the provision in this rule. 
Page 67 of 212

By contrast, the commenter’s suggested 1,000 tons/yr ore 

threshold may include operations beyond the very small scale 

pilot operations discussed above. We believe that the 100 

pounds of concentrate per year more appropriately reflect these 

very small scale operations. 

We are not making the suggested change of excluding 

operations that do not leach or dissolve gold because certain 

gold mine facilities in the source category use flotation or 

gravity flotation processes and perform thermal processing of 

concentrate in melt furnaces, which can have significant 

emissions of mercury. However, as mentioned above we are 

clarifying that this final rule does not apply to these very 

small scale operations. 

Comment:

Commenters (0273, 0259) representing a proposed mine in 

Minnesota requested that EPA clarify that their proposed 

facility would not be subject to the proposed rule because it is 

not a gold mine ore processing and production facility. The 

 Several commenters (0332, 0341, 0342) supported 

EPA’s exclusion of facilities that produce primarily copper, 

where copper is 95 percent or more of the total metal 

production. The commenter suggested that the exclusion be 

clarified to apply whether final metal production occurs onsite 

or at an offsite facility.
Page 68 of 212

commenters said the proposed facility would process low-grade 

sulfide-bearing ore into finished copper metal and various 

copper, nickel, cobalt, and precious metal concentrates and 

precipitates. The commenters explained that the facility is 

classified under the NAICS code 212234 – Copper Ore and Nickel 

Ore Mining and is not classified under the NAICS code 212221 for 

Gold Ore Mining. According to the commenters, the projected 

annual production would be 80 percent copper, 19 percent nickel, 

and the remaining 1 percent would be byproduct precious metals 

(platinum, palladium, and gold). The commenters requested that 

the definition of the gold mine ore processing and production 

source category be revised to clearly indicate that their 

proposed copper and nickel processing facility would not be 

subject to the proposed rule.

Another commenter (0281) stated that EPA should apply this 

rule to all mine processing that has the potential to emit 

mercury in significant amounts due to mineral processing, not 

just for gold mines. The commenter explained that under the 

proposed rule, the mercury emissions from the autoclaves at the 

mining project in Minnesota (discussed above) would not be 

regulated because the mine is not processing gold ore through 

the autoclave. 
Page 69 of 212

Response: The Gold Mine Ore Processing and Production 

source category includes facilities that have a primary purpose 

of processing gold ore, and only these facilities were included 

in the section 112(c)(6) inventory that was the basis of the 

listing. To clarify this point in the proposed rule, we defined 

“gold mine ore processing and production facility” to exclude 

facilities where copper is 95 percent or more of the total metal 

production. We agree with the commenter that the exclusion 

would be more properly expressed as those facilities whereby 95 

percent or more of total mass of metals produced are metals 

other than gold and that this would apply whether final metal 

production was onsite or offsite. In other words, if the mass 

of gold produced at a facility comprises 5 percent or less of 

the total mass of metals produced at the facility per year then 

the facility is not a part of the source category.

1. Consideration of Variability in Determining Floors

C. MACT Floors

Comment: Several commenters (0283, 0284) acknowledged that 

EPA may consider variability in calculating the best sources’ 

performance, but stated that EPA’s method of considering 

variability seeks to assure that none of the sources among those 

identified as best performers would ever exceed the floor level. 

The commenters claim such an approach ignores the reality that 
Page 70 of 212

sources’ emission levels are largely within their control, and 

although a great deal of variability may be statistically 

conceivable if EPA chooses a high enough prediction limit (in 

this case the 99th percentile), that does not mean that a welloperated source actually would experience such variability. The 

commenter said that one of the main points of having emission 

standards is to ensure that sources not only deploy the 

appropriate control measures, but also use those control 

measures consistently to minimize emissions. 

The commenters stated that industry groups have argued that 

EPA must set weak standards to accommodate sources’ worst 

reasonably foreseeable performance (citing dicta in a D.C. 

Circuit decision, Sierra Club v. EPA, 167 F.3d 658, 665 (D.C. 

Cir. 1999)). The commenters believe that those dicta have no 

precedential value and do not bind EPA’s rulemaking in any way. 

In addition, the commenters stated that the underlying 

assumption, that if a particular standard reflects what a given 

source achieves in practice, that source will never violate the 

standard, is plainly flawed because no matter what level a given 

source normally achieves in practice, that source may emit far 

higher levels if it is not run properly. According to the 

commenters, the high emissions that occur when a source is 

poorly operated should violate emission standards, even though 
Page 71 of 212

it is “foreseeable” that periods of sloppy or negligent 

operation may occur even at the source with the lowest emission 

tests. The commenters stated that floors should not be set at 

a level that the best performers could never exceed even when 

they operate poorly or fail to maintain their control equipment, 

and that such an approach violates section 112(d)(3). The 

commenters believe that floors must be set at the average 

emission level achieved by the best performers when they are 

operating properly (i.e., in the way that identified them as the 

best performers). The commenters said that using an upper 

prediction limit to set standards reflecting the statistical 

worst performance these sources could have does not yield an 

accurate picture of the best sources performance, and it is 

especially arbitrary in the absence of any explanation of why 

EPA thinks that the relevant best sources’ performance would 

ever be so bad, other than the fact that it is statistically 

possible. 

Response: As described previously, the MACT floor limits 

are calculated based on the performance of the lowest emitting 

sources in each of the MACT floor pools. We ranked all of the 

sources for which we had data based on their emissions and 

identified the lowest emitting sources.
Page 72 of 212

As the commenter concedes, EPA can consider variability in 

assessing sources’ performance when setting MACT standards. See 

Brick MACT, 479 F. 3d at 881-82; and Mossville Envt’l Action Now 

v. EPA

Variability in facilities’ performance has various causes. 

One source of variability for these facilities is the differing 

mercury concentrations in the input materials. Another source 

of variability is due to normal variations in performance of the 

control devices for which both run-to-run and test-to-test 

variability must be accounted.

, 370 F.3d 1232, 1241–42 (D.C. Cir 2004) (reaffirming that 

EPA can assess variability in determining the level of emissions 

control achieved by the best performing sources). 

4

 4 Run-to-run variability is essentially within-test variability, and encompasses variability in individual runs 

comprising the compliance test, and includes uncertainties in correlation of monitoring parameters and emissions, 

and imprecision of stack test methods and laboratory analysis. 72 FR at 54877 (Sept. 27, 2007). Test-to-test 

variability results from variability in pollution device control efficiencies over time. Test-to-test variability can be 

termed long-term variability. 72 FR at 54878. 

 A review of the run-by-run 

emissions data in the record shows that emission rates from one 

run to the next for well-operated sources can vary by as much as 

a factor of 8. We need to account for sources’ variability 

(both due to control device performance and variability in 

inputs) in assessing sources’ performance when developing 

technology-based standards. Accordingly, EPA accounts for 

variance in test data, between units, and among facilities when 

developing the MACT standard.
Page 73 of 212

In determining the MACT floor limits, we first determine 

the average emissions of the top performers based on available 

data. We then assess variability of the best performers by 

using a statistical formula designed to estimate a MACT floor 

level that is equivalent to the average of the best performing 

sources based on future compliance tests. Specifically, the 

MACT floor limit is an upper prediction limit (UPL) calculated 

with the Student’s t-test. The Student’s t-test has also been 

used in other EPA rulemakings (e.g., NESHAP for Cement 

Manufacturing, NSPS for Hospital/Medical/Infectious Waste 

Incinerators, and NESHAP for Industrial, Commercial, and 

Institutional Boilers and Process Heaters) in accounting for 

variability. A prediction interval for a future observation is 

an interval that will, with a specified degree of confidence, 

contain the next (or some other pre-specified) randomly selected 

observation from a population. In other words, the prediction 

interval estimates what the upper bound of future values will 

be, based upon present or past background samples taken. The 

UPL consequently represents the value which we can expect the 

mean of future observations (i.e., emission test runs) to fall 

below within a specified level of confidence, based upon the 

results of an independent sample from the same population. In 

other words, if we were to randomly select a future test 
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condition from any of these sources (e.g., average of 3 runs) we 

can be 99 percent confident that the reported level will fall at 

or below the 99 percent UPL value. We note that the methodology 

accounts for both short-term and long-term variability and 

encompasses run-to-run and test-to-test variability.

For this rule, we used the 99 percent UPL analysis on the 

emissions data for the top performing sources to account for the 

variance. In the context of determining the MACT floor, the 99 

percent UPL represents the value below which the mean of future 

compliance tests (based on, for example, a 3-run average) would 

fall 99 percent of the time. A 99 percent level of confidence 

means that a facility, whose emissions are consistent with the 

best performing sources, has one chance in 100 of exceeding the 

emission standard. 

We believe that using the 99 percent UPL is appropriate for 

this rule. As noted above, this approach is consistent with 

several other previous rulemakings. It also makes sense from a 

practical standpoint. If we selected a lower number (e.g., 95 

percent UPL) this would mean that a best performing source that 

is performing at the MACT level of control would potentially 

exceed the limit 5 percent of the time - which we do not believe 

is a reasonable approach for this rule. See Mossville, 379 F. 

3d at 1241-42); see also 70 FR at 59438 (Oct. 12, 2005)
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(explaining use of 99th percentile). With regard to the 

commenter’s statement that no sources among the best performers 

would ever exceed the MACT standard, we believe this is 

incorrect. The commenter provided no basis for this statement, 

and we do not believe the commenter based this statement on an 

analysis of the variability in the data. 

We do not believe that the UPL analysis reflects the 

statistical worst performance the top five performing sources 

could have. The UPL calculation is dependent on the data that 

we have, and reflects the actual variability in the test data 

for the best performing sources. It does not reflect worst-case 

performance. We continue to believe that the UPL does yield an 

accurate picture of the best sources' performance as best as 

possible with taking into account variance between the 

facilities, units at the facilities, and between test runs for 

the different units (including variability in input materials). 

Furthermore, although the average of several data sets may 

show a top performing source meeting the emission standard by a 

significant margin, the variability in emissions inherent in any 

one compliance test could easily indicate much higher emissions, 

and, in some cases, an exceedance of the emission standard. We 

continue to believe that the UPL analysis evaluated at 99 

percent confidence is appropriate for this source category. 
Page 76 of 212

Moreover, we believe the data we used to calculate the MACT 

standards are representative of the normal performance of the 

best performing sources for several reasons. First, the test 

results that we are using in our MACT database are tests 

conducted under Nevada’s mercury emission control program, and 

are conducted to determine whether a facility is in compliance 

with State requirements. Facilities typically try to perform as 

well as they can during such tests. State (and often EPA) 

permitting authority staff are notified before a performance 

test is conducted to provide an opportunity to attend and 

observe the test, and they often attend to ensure the source is 

operating properly and that the testing is performed according 

to the strict requirements in the codified test methods.

Test reports are carefully reviewed by the permitting 

authority, and any failure to follow the test method or abnormal 

operation of a source is flagged. These data are usually 

invalidated, and invalidated tests are not used in our MACT 

standard calculations. For example, several tests from these 

facilities were invalidated by the NDEP because the specified 

testing procedures were not followed or the emission control 

device was not operating properly, and we have not used those 

results in our analysis for those reasons. We have collected 

additional data from test reports not available at the time of 
Page 77 of 212

proposal, and one of those tests was invalidated because NDEP 

representatives discovered that the emission control device was 

not operating properly during the test. Therefore, we also did 

not use those test data.

The commenter believes that floors must be set at the 

average emission level achieved by the best performers when they 

are operating properly. We agree that the performance data 

characterizing the emission level achieved by the top performers 

must be data obtained when they are operating properly, and we 

believe that is the case for our current database for this 

source category. 

As described above, the MACT floor is based on the average 

performance of the top performers plus an amount to account for 

variability. We have appropriately developed a MACT standard 

based on emissions from the top 5 best performing sources that 

accounts for variability because, over an extended period of 

time, the emissions from each of these best performing 

facilities (even the best controlled) will vary above and below 

the facility average. For example, we expect that about half of 

the duration of the year the emissions from a best performing 

facility would be somewhat below their average and that about 

half of the duration of the year their emissions would be 

somewhat higher than their average. If we set the MACT limit 
Page 78 of 212

exactly equal to the average emissions level achieved by the 

best performers (without accounting for variability), and we had 

a source that was performing at exactly the MACT level over the 

course of the year, the measured emissions level on roughly half 

the days of the year would suggest that the source is emitting 

at levels above the MACT limit, and on about half of the other 

days of the year the measured emissions level would suggest that 

the source is emitting at levels less than the MACT limit. We 

reasonably and appropriately accounted for variability in the 

data consistent with established statistical theory and practice 

and judicial precedent. Finally, ignoring variability of the 

best performing sources and using only the average performance 

would virtually guarantee that some of even the best performers 

would exceed the floor limit at least some of the time. 

Thus, we developed a MACT standard based on the average of 

the best performing sources that accounts for variability. We 

accomplished this by calculating the MACT standard from this 

average performance and accounting for variability by using the 

99 percent UPL. The specific calculations are presented in the 

MACT floor document in the docket for this rulemaking. 

Furthermore, we agree with the comment that one of the 

points of having emission standards is to ensure that sources 

not only deploy the appropriate control measures, but also use 
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those control measures consistently to minimize emissions. We 

believe that the MACT standards established in this rule along 

with the requirements to monitor and maintain control device 

parameters within certain ranges will ensure control measures 

are applied consistently to minimize emissions. 

Comment: Several commenters (0281, 0284) stated that the 

statistical analysis used in the proposed rulemaking is unclear 

as to whether the limit to be met is one under which 99 percent 

of all future source-specific total emission rates will lie (at 

some unstated confidence level), or whether the threshold is one 

that the next source's estimated emissions will lie as estimated 

at a 99 percent confidence level. The commenters said this is a 

fundamental difference between setting a prediction interval or 

a tolerance interval. According to the commenters, setting the

floor at a level that the best performing source can meet every

day and under all operating conditions requires estimating the

distribution of possible emissions rates from that source's 

production process and setting the threshold just beyond the 

maximum possible emission rate. The commenters stated that this 

is an impossible standard to quantify, and it requires assuming 

a specific mathematical distribution as an adequate description 

of the emissions rate distribution. The commenters claim that 

even then, most common feasible mathematical distributions have 
Page 80 of 212

infinite upper thresholds, and the floor would logically be set 

to infinity, an operationally useless threshold.

The commenters believe that a reasonable approach would be 

to develop a threshold that is only exceeded under standard 

operating conditions for a specified percent of the time, which 

requires a decision as to what percentile of the emissions rate 

distribution to use as the threshold (e.g., 90 to 99 percent?). 

The commenters recommend accounting for the uncertainty in this 

estimate by providing an interval estimate, or specifically, a 

tolerance interval that brackets a portion of the full 

population distribution, such as the smallest 99 percent of the 

population of emissions rates from this source. Thus, concluded 

the commenters, a one-sided upper 99 percent tolerance interval 

with 95 percent confidence is a threshold expected with 95 

percent confidence to be exceeded by only 1 percent of the 

observations from the emissions rate process. The commenters

recommend setting the objective to estimate a threshold under 

which x percent (where the value of x needs to be agreed upon) 

of all future source-specific estimated total emission rates 

will lie, and to estimate it with some confidence level. In 

contrast, the commenters interpret the approach used in the 

proposal as setting the objective to estimate a threshold under 

which the next source's estimated total emission rate will lie 
Page 81 of 212

and to estimate it with 99 percent confidence (i.e., a 99 

percent prediction interval). According to the commenters, past 

EPA practice appears to have adopted prediction intervals, while 

the tolerance interval approach seems closer to the objective’s 

language, provides greater regulatory control of emissions, and 

provides a statistically feasible regulatory standard for 

clearly assessing violations. The commenters note that adopting 

the tolerance interval perspective would require agreeing on the 

percentage for the threshold and the confidence level desired 

for the estimation.

The commenters also stated that the choice of a 99 percent 

confidence level appears arbitrary and capricious, and very 

sound arguments could be made for a precautionary approach using 

97.5 percent, 95 percent, or even 90 percent. The commenters

believe that a 99 percent level places much greater emphasis on 

avoiding “Type I” errors of accidentally claiming a source is 

“out of compliance”, which makes it necessary to accept a much 

higher emission rate as “in compliance.” The commenters pointed 

out that as the value of “t” in the statistical equations goes 

down as the confidence level goes down (for example, from 2.36 

at 99 percent to 1.29 at 90 percent), and the resulting emission 

limit for the ore pretreatment group would drop from 175 
Page 82 of 212

lb/million tons of ore (at 99 percent) to 140 lb/million tons 

(at 90 percent).

Response: The UPL is the value below which a single test 

observation (or average of several test observations) from the 

source to be tested for compliance is expected to fall with a 

stated level of confidence (e.g., 99 percent). The Upper 

Tolerance Limit (UTL) is the value below which a specified 

proportion (e.g., 99 percent) of the population is expected to 

lie with a stated level of confidence. In other words, the UTL 

is the value below which the population percentile corresponding 

to that proportion (e.g., 99th percentile) is expected to lie 

with a stated level of confidence. Operationally, the sample

The level of confidence represents the level of protection 

afforded to facilities whose emissions are in line with the best 

performers, and consequently, the level of confidence is not 

percentile derived from the test runs (e.g., the 99th sample 

percentile for small data sets is the largest observation) must 

be smaller than the UTL to be in compliance. The problem with 

this method is that for small data sets and proportions close to 

100 percent, the sample percentile typically underestimates the 

corresponding population percentile. Therefore, the UTL is 

ordinarily used for large data sets (i.e., data sets much larger 

than those that we have for gold mines).
Page 83 of 212

arbitrary. A 99 percent level of confidence means that a 

facility whose emissions are in line with the best performers 

has one chance in 100 of exceeding the floor limit.

Comment: One commenter said that the stated objective of 

accounting for variability does not discriminate between the 

reasons behind variation, which may include variation in 

processes as well as variation in measurement error. The 

commenter believes that variation in measurement error is one 

that the EPA should put some effort into resolving so that it 

will be clearer in future measurements what the actual process 

variation is. The commenter noted that the variance used by EPA 

reflects both process variation and measurement error and 

suggested that EPA should consider improving both precision and 

accuracy by (1) increasing the required minimum number of runs 

and batches of runs per unit so as to more precisely estimate 

the process variance (say from 3 to 12 or more), thus leading to 

more reliable MACT floor values (better accuracy), and (2) 

developing methods of estimating the measurement error component 

and removing it, leaving a more precise estimate of the process 

variation which is the real focus of accounting for variability. 

The commenter explained that changing the value of “m” (the term 

in the statistical equations that account for the number of test 

runs that are averaged to determine compliance) from 3 to 
Page 84 of 212

something on the order of 5 to 10 would greatly reduce the 

estimate of within source variance.

The commenter also stated that ranking sources by their 

specific mean total emission rates ignores their variation in 

total emissions rates and could result in an inflated MACT 

floor. According to the commenter, the MACT for new sources is 

based strictly on the best performing source, but given the 

limited information on process variation at any given single 

source and the difficulty in getting reliable estimates of 

variance (rather than just means or totals), it might be more 

reasonable to use a pooled estimate of “within source process 

variation” from all the available data rather than just the 

estimate based on runs from the single “best” source. The 

commenter believes “best performing” should be based both on a 

source's average total emissions rate and also on the source's 

variability in emissions rate (presumably mainly due to 

variation in raw materials, processing procedures, etc.). The 

commenter said that ranking on the average total emissions rate 

would ignore variation, and thus potentially undermine the 

intent of “best performing.” The commenter noted that it is an 

open question as to how to account for both of these aspects, 

whether by a tolerance interval or the source's total emissions 

rate distribution.
Page 85 of 212

Response:

Although the calculation of the floor limit should account 

for variability (which it does), the actual selection of best 

performing sources should be based only on their average 

emissions (i.e., the group with the lowest average emissions 

should be selected), which is consistent with the CAA mandate. 

For the development of MACT floors in previous MACT rulemakings, 

we have characterized emissions and ranked the sources from 

lowest to highest based on their average emissions.

 The variation used in calculating the MACT floor 

is within unit variation, which captures both "process" 

variation and measurement error variation. The commenter 

suggests that measurement error variation should be filtered out 

of the calculation. We disagree for two reasons: (1) separating 

out measurement error variation is not a trivial exercise, and

(2) there appears to be no need to do so because the variability 

of all sources (i.e., best performing and tested sources) can be 

based on comparable within unit variation.

We agree with the commenter that the testing process would 

be more accurate if the number of tests was increased from 3 to 

12 runs. However, based on our experience with the development 

of compliance test requirements for many rules and the 

historical success in providing reasonable means of determining 

compliance, we have traditionally required that a compliance 
Page 86 of 212

test be composed of 3 sampling runs, and the compliance 

determination is based on the average of the three runs. For 

example, we specify a minimum of three runs in part because it 

provides a measure of variability (e.g., from the calculation of 

standard deviation or variance). Manual stack testing is 

expensive and not practical on an ongoing basis for monitoring 

and continuous compliance; however, we have found that periodic 

stack testing coupled with operating limits developed for 

mercury concentration monitoring and/or parametric monitoring of 

control devices provide a means of ensuring continuing 

compliance for those periods of time when manual stack testing 

is not performed.

MACT for new sources “shall not be less stringent than the 

emission control that is achieved in practice by the best 

controlled similar source” (section 112(d)(3) of the CAA). The 

commenter suggests that in the case of the single best 

controlled source, a pooled measure of variability based on the 

pool of best performing sources (i.e., top 5 performers in this 

case) should be used instead of the variability based only on 

the best performing source. If the measures of variability of 

the top performing sources are similar, then this would be an 

appropriate approach; however, if they are not similar, then 

this would not be an appropriate approach. A test to check the 
Page 87 of 212

homogeneity of variance (e.g., Bartlett test) among the top 

sources would need to be conducted to determine if it might be 

appropriate to apply the pooled variability of the top 5 

performing sources to the average performance of the single best 

controlled source. However, we do not feel that it is necessary 

to apply pooled variability in this manner because we have 

sufficient data to determine the variability of the best 

controlled source, and we believe it is appropriate to apply the 

variability calculated from the best controlled source to the 

average of the best controlled source to determine new source 

MACT.

Comment: Several commenters (0278, 0281) stated that 

consideration should be given to defining the inherent range of 

measurement error and to requiring more runs in order to reduce 

variability due to process variation. The commenters said that 

this would also better clarify when variability was due to 

operational controls, which could be addressed, rather than due 

to factors that cannot be controlled, such as mercury content in 

the ore. The commenters noted that one set of dry 

grinding/preheater data shows an order of magnitude difference 

across each of the 3 runs. The commenters asked for 

clarification on how inconsistent runs should be treated, what 
Page 88 of 212

defines an acceptable set of runs, and at what point would more 

runs be required to provide reliable data.

The commenters also stated that the degree of variability 

allowed in the development of the new source limit for ore 

pretreatment appears to be out of line with the new source 

limits for carbon processes and non-carbon processes. The 

commenters pointed out that for new carbon process sources, the 

variability is much lower than the variability for existing 

sources; for non-carbon process new sources, the variability is 

about the same as for existing sources; however, for ore 

pretreatment new sources, the variability is much higher than 

that for existing sources. The commenters believe that the ore 

pretreatment variability for new sources is higher than existing 

sources because low thermal units were included in the same 

category, high emissions were allowed in the data set, and 

variable emissions were allowed in data set. The commenters

recommended that if EPA continues to use Goldstrike as the best 

performing source for new source MACT, then they should reevaluate and reduce the variability to be equal to or less than 

the variability for existing sources. 

Response: We agree with the commenter that the testing 

process would be more accurate if the number of test runs was 

increased. However, we balance several factors in determining 
Page 89 of 212

the minimum number of runs required, and because the compliance 

testing is supplemented by various types of continuous or 

periodic parametric monitoring, we have concluded that three 

test runs are appropriate for this final rule. Although we have 

not proposed a formal procedure to assess the consistency of 

test runs, the permitting authority performs routine reviews of 

compliance test data to identify potential outliers and results 

that suggest further investigation is needed. For example, a 

routine review tracks trends in performance, and in particular, 

flags any trends in deteriorating performance over time. An 

unusually high run among the three runs also attracts attention 

and would be examined to determine if it might have been caused 

by a problem with the process, control device, sampling, or 

analysis. If the permitting authority identifies inconsistent 

runs, they have the authority to invalidate any or all runs. A 

source would be required to perform more runs to provide 

reliable data if two to three runs were invalidated.

We agree with the commenter that the degree of variability 

used in the development of the proposed new source MACT standard 

for the ore pretreatment group appeared to be inconsistent with 

the degree of variability used in the development of the 

proposed new source MACT standard for carbon processes and noncarbon concentrate processes. We agree with the commenter 
Page 90 of 212

that the ore pretreatment degree of variability at proposal for 

new sources was higher than the degree of variability for 

existing sources. We do not believe that the variability was 

higher because low thermal units (i.e., autoclaves) were 

included in the same category, but because two tests of the ore 

preheater/dry grinding processes at Goldstrike were allowed in 

the data set. These tests had, as the commenter identified, 

inconsistently high emissions (as compared to other tests at 

other times for the same units) and inconsistent variability 

between the runs. We have determined that the tests the 

commenter is referring to are not representative of normal 

operation, and those tests have been removed from our database 

because the NDEP invalidated the tests due to possible sample 

contamination. (See the MACT Floor Document in the docket for 

the final rulemaking for more details). We continue to use 

Goldstrike as the best performing source for the ore 

pretreatment new source MACT and the variability for new source 

MACT is now less than that of the variability for existing 

source MACT, and is less than the variability calculated at the 

time of proposal. 

Comment: Several commenters (0270, 0277, 0278, 0282) noted 

that the best performing ore pretreatment facility’s average 

emission level in the proposed rule was 62 lb/million tons of 
Page 91 of 212

ore, but the floor limit for new sources was 163 lb/million tons 

of ore (250 percent higher), and even the proposed beyond-thefloor limit was 149 lb/million tons of ore (200 percent higher). 

The commenters noted that the CAA requires that emission limits 

for new sources “shall not be less stringent than the emission 

control that is achieved in practice by the best controlled 

similar source.” The commenters recommended an alternative 

efficiency standard based on a minimum 99 percent mercury 

removal. The commenters believe that an alternative efficiency 

limit would be appropriate for mines that have lower mercury 

concentrations in the ore because otherwise they would not be 

held to the same level of emissions control as mines with high 

mercury concentrations in the ore. The commenters concluded 

that mines should have to meet either a throughput-based 

emission limit or the efficiency-based emission limit, whichever 

is more stringent. 

Response: As discussed above, we have significantly 

revised the new source limit for ore pretreatment processes for 

a number of reasons, including the availability of additional 

test data and additional beyond-the floor analyses. We do not 

think it is appropriate to establish a percent reduction 

alternative because we do not have adequate information to do so

and because of the complexities and uncertainties as to how 
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exactly facilities would demonstrate compliance. Moreover, even 

if we did establish a percent reduction alternative, we are 

uncertain, at this time, whether we could assure that it would 

be equivalent, in all cases for this source category, to our 

determination of the new source MACT limit expressed as 

lb/million tons of ore.

2. General Comments on MACT

Comment:

Numerous industry commenters (0341, 0342) and a State 

agency (0268) supported the three groups of affected sources as 

proposed for the reasons explained in the proposal preamble.

 One commenter (0278) noted that in the proposed 

rule the definition of a source is referred to both as a mining 

facility and as an individual process unit. The commenter 

believes that the best 5 performing sources could be the best 5 

units complexes venting to the same stack and that EPA should 

consider the 5 best unit complexes venting to the same stack for 

the emissions floor calculations.

Response: As stated in the General Provisions (40 CFR part 

63, subpart A):

Affected source, for the purposes of this part, means 

the collection of equipment, activities, or both 

within a single contiguous area and under common 

control that is included in a section 112(c) source 

category or subcategory for which a section 112(d) 

standard or other relevant standard is established 

pursuant to section 112 of the Act. Each relevant 
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standard will define the “affected source,” as defined 

in this paragraph... 

We explained in detail in the proposal preamble (section V. 

“Rationale for the Proposed Standards” subsection A. “How did we 

select the affected source,” 75 FR 22480, April 28, 2010) our 

rationale for selecting three groups of process equipment as the 

affected sources for the source category. After review and 

consideration of comments, we believe that the choice of the 

three groupings is appropriate for the many reasons described in 

the proposal. 

Comment: One commenter (0342) stated that the MACT floor 

already represents installation and operation of MACT controls, 

and the use of emissions data from facilities that are already 

controlling their mercury emissions creates an artificially low 

MACT floor. The commenter said that the low MACT floor 

penalizes facilities that voluntarily invested in pollution 

control technology and creates a substantial disincentive for 

industry and States to move ahead of EPA in reducing emissions 

of HAP. 

Response: We acknowledged at proposal that many gold mine 

facilities are already well controlled for many reasons, 

including participation in the NMCP. We also acknowledge that 

the top performing facilities that are the basis for the MACT 
Page 94 of 212

floor calculation are the top performers because they have 

installed controls. CAA section 112(d)(3)(B) requires that, for 

a category with fewer than 30 sources, the MACT floor not be 

less stringent than “the average emission limitation achieved by 

the best performing 5 sources (for which the Administrator has 

or could reasonably obtain emission information).” (Emphasis 

added). EPA has information on the well-controlled facilities 

and used the information to conduct MACT floor analysis, as 

required by the CAA. Although the MACT floor may be considered 

more stringent in comparison to floors that would have been 

established if no facilities had mercury emission controls, we 

do not consider the floor to be “artificially low” because 

consistent with the statute, it reflects the level achieved in 

practice by the best performing sources. See 112(d)(3). We do 

not believe that the MACT floor penalizes facilities that 

invested in pollution control technology because those 

facilities will be able to meet the MACT standards. We do not 

consider that this final rule creates a disincentive for 

industry and states to move ahead of EPA in reducing HAP 

emissions because as facilities reduce mercury emissions by 

adding controls required by state programs, they will be able to 

meet the NESHAP. Most of the facilities that will not meet the 
Page 95 of 212

current final standards have already proposed to add controls to 

their units in their Phase 2 applications for the NMCP. 

Comment: Several commenters (0274, 0341, 0342) stated that 

emissions from the roaster quenching unit at Facility E have not 

been measured, but an estimate of the emissions should be 

included to characterize the total emissions from the ore 

pretreatment processes at Facility E. The commenters suggested 

using data from other roasters that have measurements of 

quenching emissions to estimate the quenching emissions from 

Facility E.

Response:

3. MACT for the Ore Pretreatment Group

 We reviewed the roaster process at Facility E 

(Jerritt Canyon) and consulted with inspectors at the State 

agency and found that the quenching operation at Facility E is 

quite different from the quenching operation at other facilities 

with roasters. The offgases from quenching are contained within 

the roaster exhaust system and are processed through the same 

sequence of emission control devices as used for the roaster 

emissions. Consequently, the quenching emissions are included 

in the roaster emissions, and no additional adjustments are 

needed to account for quenching emissions at Facility E.

Comment: Several commenters supported EPA’s general 

approach to establish three groups of affected sources in the 
Page 96 of 212

proposal. On the other hand several commenters (0270, 0278, 

0281) suggested that EPA develop separate emission limits for 

roasters and autoclaves for existing and new sources. One 

commenter stated that roaster and autoclave processes are 

different from each other based on the mercury species released, 

controls utilized, and their rates of mercury emissions. The 

commenter said that roasters commonly reach temperatures of 400-

700°C, releasing gaseous elemental mercury, whereas autoclaves 

commonly reach temperatures of 175-230°C producing reactive 

gaseous mercury and sulfate and forming mercury sulfate. 

According to the commenters, autoclaves are expected to be able 

to improve efficiency over time. The commenter noted that 

roasters produce one to two orders of magnitude higher emissions 

than do autoclaves. The commenter believes that facilities that 

only use autoclaves should not be allowed the leeway to emit at 

the rate that facilities employing roasters are allowed. The 

commenter recommends that the ore pretreatment group be divided 

into high temperature pretreatment processes (roasters) and low 

temperature pretreatment processes (autoclaves and ancillary 

roaster processes, such as dry grinding, pre-heating, and 

quenching).

Response: We discussed in section V.A. of the preamble to 

the proposed rule our rationale for establishing the different 
Page 97 of 212

affected sources, including the ore pretreatment processes 

affected source. We believe it is appropriate to maintain the 

ore pretreatment group affected source, as we had proposed. We 

do not agree with the comment that roasters necessarily have 

higher emissions that are one to two orders of magnitude higher 

than emission from autoclaves. The available data show a wide 

range in emissions from autoclaves (from 0.4 to 115 lb/million 

tons of ore). This range overlaps the range for roasters and 

their ancillary equipment, which have combined emissions between 

42 to 71 lb/million tons of ore. Regardless of the mercury 

species released, controls utilized, operating temperatures, or 

control efficiency over time, autoclaves and roasters process 

the same input material (i.e., ore) and are intended for the 

same purpose (i.e., to oxidize the ore). Therefore, we believe 

that it is appropriate to maintain the ore pretreatment affected 

source as we had proposed, keeping roasting operations and 

autoclaves together. 

Comment: Several commenters (0270, 0283) stated that 

although EPA’s standard for new ore pretreatment facilities is 

as high as its standard for existing facilities, EPA does not 

propose or discuss setting beyond-the-floor standards for new 

sources. The commenters claim that EPA has a statutory 

obligation to ensure that its new source standards reflect the 
Page 98 of 212

maximum achievable reduction in emissions, and that by failing 

to consider such a standard, EPA violates the CAA.

Another commenter (0270) suggested that EPA evaluate the 

mercury emission reductions based on the installation of a 

second carbon adsorption system for both existing and new source 

autoclaves. The commenter believes that if a second adsorber 

could achieve an additional reduction of 90 percent, then that 

would be a significant reduction.

For the ore pretreatment group, one commenter (0283) 

claimed that EPA did not explain its statement that sources 

could achieve an average standard of only 90 lb/million (MM) 

tons of ore by installing a carbon adsorber and refrigeration 

unit. According to the commenter, the three autoclave 

facilities are currently achieving emission levels of 62, 63, 

and 64 lb/MM tons respectively, and carbon adsorbers and 

refrigeration units should be able to provide reductions of 

greater than 90 percent. Commenters (0270, 0283) also claim 

that Barrick Corporation has indicated that the carbon scrubbers 

deployed at its Goldstrike mine achieve a 99.5 percent reduction 

in mercury emissions. The commenters stated that the beyondthe-floor standard for mercury must reflect the “maximum” degree 

of reduction that can be achieved by carbon scrubbers, and that 

level is plainly far below 90 lb/MM tons (e.g., no higher than 
Page 99 of 212

0.6 lb/MM tons to reflect a 99.5 percent reduction or 6 lb/MM 

tons to reflect a 90 percent reduction). The commenters said 

that EPA failed to explain why it did not consider the carbon 

scrubbers that Barrick has deployed at its Goldstrike mine, 

which can achieve a 99.5 percent reduction, and that EPA 

provided no reason to believe that it would be too costly to be 

economically achievable. The commenters concluded that EPA must 

set beyond-the-floor standards that either require all sources 

to reduce their mercury emissions by 99.5 percent or set a 

standard reflecting the emission level that is achievable after 

a 99.5 percent reduction from floor levels. 

The commenters also stated that EPA failed to consider 

beyond-the-floor standards for roasters and that if additional 

reductions are achievable at roasters (e.g., by adding venturi 

scrubbers or any other control technology), then EPA must set 

additional beyond-the-floor standards for roasters reflecting 

the maximum achievable degree of reduction. The commenters also 

stated that EPA provided no reason to explain why it needs to 

add another level of variability to its beyond-the-floor 

analysis, and if EPA is applying some presumption about the 

reductions that are achievable through the use of carbon 

adsorbers to the floor level, it is necessarily applying that 

presumption to a level that already has been inflated to account 
Page 100 of 212

for variability. The commenters said that because the baseline 

number already has been inflated, EPA does not need to inflate 

the beyond-the-floor number as well.

Response

Based on the addition and change described above with 

respect to our available data, we revised the MACT floor 

analysis for the ore pretreatment processes. The revised MACT 

floor for existing sources decreased from 175 lb/million tons at 

: Following proposal, we continued to investigate 

the performance of facilities with ore pretreatment processes 

and opportunities for additional control. We collected data 

from more recent tests that were not available at proposal, and 

these new data show that emission control performance at these

facilities has continued to improve. We identified two previous 

tests in the proposal database that were suspect, and we 

confirmed with NDEP that these tests should be invalidated and 

not used in the analysis because of possible sample 

contamination. We have also dropped the data for one facility 

from the analysis because their autoclave was shutdown in 2007 

and dismantled, and we only had one test of the autoclave when 

it was operating in 2006. For these reasons, we did not include 

data for that facility in the analysis, which is now based on 

the only four facilities currently operating.
Page 101 of 212

proposal to 158 lb/million tons, and the new source MACT floor 

dropped from 163 lb/million tons to 84 lb/million tons. 

The MACT floor limit for existing ore pretreatment 

processes is based on the use of calomel-based mercury scrubbers 

on roasters and wet scrubbers on autoclaves and ancillary 

roaster operations. We conducted a beyond-the-floor analysis 

during the development of the proposed rule. The roasters were 

already equipped with very good mercury controls (condensers and 

calomel-based mercury scrubbers), and we did not identify any 

beyond-the-floor options for the roasters. However, we 

identified as a beyond-the-floor control for autoclaves the 

installation of both a refrigeration unit (or condenser) and a 

carbon adsorber. We continue to believe that the roasters 

stacks are well controlled, but since our proposal, we have 

identified a beyond-the-floor control option (carbon adsorption) 

for the ore pre-heaters/dryers (ancillary roaster operation) 

that could achieve additional emissions reductions of 

approximately 70 percent (or more) for those units. Two of the 

three facilities with roasters have already proposed in their 

NMCP Phase 2 permit applications to apply controls to their 

preheaters/ore dryers, and these two companies have submitted 

cost estimates for applying a carbon adsorption system. Using 

the cost estimates submitted by the affected facilities, we 
Page 102 of 212

estimate the capital costs for control of roaster 

preheaters/dryers for the three facilities with roasters as $3 

million with a total annualized cost of $1.6 million per year. 

We also estimate a reduction of 118 lb/yr of mercury emissions 

would be achieved at an overall cost effectiveness of about 

$13,800 per pound of mercury. We believe that these costs and 

cost effectiveness are reasonable. As required under CAA 

section 112(d)(2), we have also considered non-air quality 

health and environmental impacts and energy requirements of this 

additional control. We conclude that this is an acceptable 

beyond-the-floor control technology for existing roaster 

preheaters/ore dryers. Therefore, we included the beyond-thefloor control for ore preheaters/dryers, as well as the beyondthe-floor control for autoclaves, in determining the MACT 

standard in this final rule for existing sources of ore pretreatment processes. After applying the appropriate variability 

analyses to the data, we determined that the MACT standard for 

existing sources is 127 lb/million tons of ore. 

As mentioned above, we have revised the new source 

MACT floor. We also did a beyond-the-floor analysis for new 

sources in the ore pre-treatment processes group. However, we 

did not establish the MACT standard for new sources based on 

this beyond-the-floor analysis because we did not identify a 
Page 103 of 212

feasible and cost-effective option to achieve reductions greater 

than the new source MACT floor. Therefore, for new sources of 

ore pretreatment processes, the MACT “floor” is the MACT 

standard for the affected source. The final new source MACT 

standard is 84 lb/million tons of ore, which is considerably 

more stringent compared to the proposed standard of 149 

lb/million tons of ore and reflects the maximum achievable 

reduction in emissions. 

Comment: Several commenters (0274, 0341, 0342) stated that 

the proposed estimated capital costs of $890,000 and total 

annualized cost of $720,000 for beyond-the-floor autoclave 

controls are not representative of actual costs of installing a 

refrigeration unit (or condenser) and a carbon adsorber on 

autoclaves. One commenter (0342) notes that the EPA’s cost 

estimate was based on information provided in the commenter’s 

Phase 2 operating permit application for autoclaves submitted in 

February 2008. The commenter explains that they continued to 

investigate control options for the autoclaves and based on this 

new information, the commenter estimates that capital costs for 

autoclave controls will range from $18 million to $30 million, 

and even higher, and annual operating costs could range from $2 

million to $60 million, depending on which controls, if any, are 

determined to be technically feasible. The commenter believes 
Page 104 of 212

that based on these cost estimates, beyond-the-floor MACT 

controls would be cost prohibitive and are not justified for the 

ore pretreatment affected source group. The commenter 

recommends that EPA set the MACT emission limit for the ore 

pretreatment group at the MACT floor of 175 lbs/million tons of 

ore.

Another commenter (0274) estimated that for the 

installation of carbon adsorbers on their autoclaves to control 

mercury emissions, the capital costs will range from $30 million 

to $35 million, annual operating costs would be $2 million per 

year, and the annual energy requirements would be 11,400 

megawatt-hours per year with an annual energy cost of $900,000.

Response: After reviewing the new cost estimates provided 

by the commenters, we agree that capital and total annualized 

cost estimates of the beyond-the-floor controls on autoclaves in 

the proposal were underestimated. We evaluated the detailed 

cost estimate based on an engineering study for a carbon 

adsorption system provided by one of the commenters (see details 

in the comment above on capital, operating, and energy costs), 

and our review of these details indicates it to be a reasonable 

cost estimate and more representative. Therefore, we have used 

this estimate as the basis for our estimate of the costs of the 

beyond-the-floor mercury emission controls for autoclaves. Our 
Page 105 of 212

revised estimates are that the capital cost for installing 

carbon adsorbers on autoclaves would be $29.3 million, with a 

total annualized cost of $4.9 million per year, which would 

result in an estimated reduction of 431 lb/yr of mercury 

emissions per year and an overall cost effectiveness of about 

$11,000 per pound of mercury. Based on these new costs and 

estimated reductions we conclude that the beyond the floor 

controls are affordable and justified for the ore pretreatment 

affected source. 

Comment: Over one hundred commenters stated that the new 

source limit for the ore pretreatment group is too high and 

would allow an unacceptable amount of mercury to be released by 

new mines. The commenters noted that at the proposed new source 

MACT limit of 149 pounds/million tons of ore, the proposed new 

source Donlin Creek Mine, located in Alaska, would be allowed to 

emit 3,200 lbs of mercury based on a projected production rate 

of 22 million tons of ore per year.

Response: With respect to this proposed new gold mine in 

Alaska, the commenters’ estimate of 3,200 lb/yr of mercury 

emissions is inaccurate and a significant overestimate for a 

number of reasons. The two primary reasons are that, based on 

available information, if the facility is built, only an 

estimated 15 percent of the ore mined will be processed in 
Page 106 of 212

autoclaves (not 100 percent as assumed by the commenters), and 

that the commenters’ estimate is based on assuming that the 

average emissions level for the facility throughout the year 

would be at the maximum allowed at the proposed new source limit

(149 lb/million tons of ore), which has been significantly 

reduced since proposal. 

With the new source MACT standard in the final rule that is 

about two times more stringent (i.e., lower) than the proposed 

MACT standard, along with corrections described above, we 

estimate that far less than 3,200 lb/yr would be emitted from 

this new source if it is ever built. Assuming continuous 

operation for 365 days per year, an estimated 21.5 million 

tons/yr of ore mined, about 3.2 million tons/yr processed in 

autoclaves (15 percent), and assuming the source would emit at 

the average emission level used to calculate the revised new 

source MACT (45 lb/million tons of ore), we calculate that 

mercury emissions would be about 144 lb/yr, which is about 5 

percent of the estimate provided by the commenters. Considering 

that the facility has yet to go through the permitting process 

and that, if it is built, it will likely include emissions 

controls that would reduce the emissions below 45 lb/million 

tons of ore, we believe that, if the facility is built, 

emissions would quite likely be lower than 144 lb/yr. 
Page 107 of 212

4. MACT for Carbon Processes

Comment: Several commenters (0258, 0260, 0271, 0280, 0341, 

0342, 0351) objected to including Facility M in the MACT floor 

determination for new and existing sources in the carbon 

processes group because it has unusually low mercury 

concentrations in its ore, and it does not need a retort to 

remove and recover mercury. They noted that because the mercury 

content of the gold ore is fixed, the only way for other 

facilities to reduce emissions of mercury is to apply mercury 

emission controls, but for many facilities, emission controls 

will not be enough to meet the MACT standards. The commenters 

stated they were aware that the D.C. Circuit Court had 

constrained EPA’s discretion to set floors that fail to consider 

material inputs, but they said gold mines were different from 

the remanded source categories (brick kilns and cement kilns) 

because gold mining operations process very large quantities of 

ore, and the ore is the only material input that results in 

mercury emissions. According to the commenters, brick kilns and 

cement kilns have more than one material input that results in 

HAP emissions. The commenter (0341) stated that in adopting 

section 112, Congress expressly cautioned EPA against setting 

standards that would require mining operations to change the ore 

used as essential feedstock:
Page 108 of 212

For categories and subcategories of sources of [HAPs] 

engaged in mining, extraction, beneficiation, and 

processing of nonferrous ores, concentrates, minerals, 

metals, and related in-process materials, the 

Administrator shall not consider the substitution of, 

or changes in, metal- or mineral-bearing raw materials 

that are used as feedstocks or material inputs, or 

metal- or mineral bearing materials processed or 

derived from such feedstocks or materials in setting 

emission standards, work practice standards, operating 

standards, or other prohibitions or requirements or 

limitations under this section for such categories and 

subcategories. (See H.R. Rep. No. 101-952, at 339 

(1990))

The commenters said that by ignoring the mercury content in 

the ore being mined and processed at the facilities in the MACT 

floor determination, EPA is requiring facilities to consider the 

substitution of, or changes in, the ore that is processed 

because there is no other way to achieve the standard. The 

commenter recommended that EPA address as a threshold matter the 

differences in processing and emissions across facilities that 

result from the variable concentration of mercury in ore. As 

discussed in more detail below, their recommendations were to 

either exclude Facility M from the source category or to 

subcategorize such facilities. 

The commenters stated that Facility M is not representative 

of or similar to other sources in the carbon processes group and 

should not be used in the determination of the MACT floor for 

existing sources or as the basis for new source MACT. The 

commenters noted that the average performance of Facility M is 
Page 109 of 212

an order of magnitude below the performance of the next lowest 

emitting facility and explained that the concentration of 

mercury in Facility M’s ore is so low that a mercury retort is 

not required prior to refining the concentrate in the furnace. 

Data supplied by the commenters indicated the mercury 

concentration in the ore is 0.1 ppm for Facility M compared to 

1.6 to 38 ppm for other facilities in the top 5 performing 

sources. The commenters also believe that the fact that a 

retort is not required as part of Facility M’s carbon process to 

safely melt the concentrate distinguishes it from other gold 

mine carbon processes and demonstrates that it is not 

appropriate to include mercury emission data from that facility 

in the MACT floor calculations for the industry as a whole. 

The commenters recommended that Facility M not be 

considered the “best controlled similar source” for purposes of 

setting the new source MACT floor because they are not similar 

to other sources, i.e., they have different characteristics and 

operations, low mercury concentrations in the ore, and do not 

need a retort to recover mercury prior to processing the 

concentrate in the furnace. The commenters stated that if EPA 

does not exclude from the source category facilities that do not 

use retorts to process concentrate, then they should 

subcategorize them. The commenter explained that the 
Page 110 of 212

subcategorization should be based on ore and process differences 

that would fit within EPA’s authority to distinguish among 

“classes” and “types” of facilities under section 112(d)(1).

Response:

As part of our re-analysis of the MACT floor and the MACT 

for sources that are in the carbon processes with mercury 

After consideration of comments and a reexamination of the design of the facilities at issue, the 

emission controls, and other factors affecting emissions from 

the carbon processes at Facility M, we agree that this facility 

is quite different and unique compared to most other gold mine 

ore processing and production facilities, including other 

facilities in Nevada, in its carbon process. The difference is 

manifested in the processing train in that mercury retorts are 

not needed or used at Facility M to recover mercury. As the 

commenter notes, the CAA allows EPA to “distinguish among 

classes, types and sizes of sources within a category” in 

developing MACT emission standards, and gold mine facilities 

without mercury retorts are different in both class and type 

from those with mercury retorts. Accordingly, in the final 

rule, we identify and set separate MACT standards for these two 

different types of carbon processes: those that use mercury 

retorts; and those, such as the carbon process at Facility M, 

that do not use mercury retorts. 
Page 111 of 212

retorts group and sources that are in the carbon processes

without mercury retorts group, we considered new data that were 

not available at the time of proposal. Over the past one to two 

years since our data collection effort for the proposal, 

facilities in Nevada have continued to add controls and improve 

emission control as part of the NMCP. The new data indicate 

there were two facilities with carbon processes without mercury 

retorts operating in 2009. Using the data from these two 

facilities, we determined that the MACT floor limits for carbon 

processes without mercury retorts are 0.17 lb/ton of concentrate 

for existing sources and 0.14 lb/ton of concentrate for new 

sources (based on the best performing facility, Facility M). 

In our beyond-the-floor analysis, we considered the 

addition of a carbon adsorber on an uncontrolled emission unit 

within an existing affected source. We estimate the capital 

cost as $210,000 with a total annualized cost of $72,000 per 

year, an emission reduction of 1.63 lb/yr of mercury, and a cost 

effectiveness of $44,000/lb of mercury. We do not believe that 

the small emission reduction that this control option would 

achieve is justified in light of its cost. We therefore decided 

not to go beyond-the-floor. We also considered possible beyondthe-floor options for new carbon processes without mercury 

retorts, but concluded these options were not cost-effective or 
Page 112 of 212

feasible. Therefore, for new and existing sources of carbon 

processes without mercury retorts, the MACT floor limit is the 

MACT standard for this affected source. 

As part of our re-analysis for the carbon group processes 

with mercury retorts, we collected and evaluated additional 

data. As discussed above, several of the facilities have 

improved emission control over the levels observed in the 

database we used at proposal. Two facilities with newlyinstalled controls replaced two higher-emitting facilities that 

were in the top 5 at proposal, and all three of the other 

facilities that remained in the top 5 had lower levels of 

emissions after considering the new data. The results are that 

the MACT floor limits for carbon processes with mercury retorts 

are 2.2 lb/ton of concentrate for existing sources and 0.8 

lb/ton of concentrate for new sources (based on the best 

performing facility, Facility N). In the beyond-the-floor

analysis, we evaluated the impacts of adding a second carbon 

adsorber in series with the controls applied to achieve the MACT 

floor level of control. We estimate the capital cost would be 

$3 million with a total annualized cost of $1.3 million per 

year, an emission reduction of 9 lb/yr of mercury, and a cost 

effectiveness of $150,000/lb of mercury. Because of the small 

emission reduction and high cost effectiveness associated with 
Page 113 of 212

this additional control, we decided not to go beyond the floor. 

Therefore, for existing sources of carbon processes with mercury 

retorts, the MACT floor limit is the MACT standard for this 

affected source. We also considered possible beyond-the-floor 

options for new carbon processes with mercury retorts, but 

concluded these options were not cost-effective or feasible. 

5. Compliance Alternative for New Carbon Process Sources

Comment: One commenter (0283) noted that EPA seeks comment 

on a “compliance alternative” that would allow a 97 percent 

reduction instead of an emission standard for new sources in the 

carbon group. According to the commenter, such an 

“alternative” would be unlawful unless EPA specified that carbon 

sources had to meet the more stringent of either the floor 

standard or a 97 percent reduction standard. The commenter 

stated that because floors must reflect the emission level 

achieved by the best performing sources, a level that 

necessarily reflects not just the amount of mercury reduced but 

also the mercury input, allowing sources to meet a 97 percent 

reduction standard that was less stringent than the emission 

level actually achieved by the relevant best sources would 

contravene section 112(d)(3) and well-established D.C. Circuit 

court precedent.
Page 114 of 212

Several commenters (0341, 0342) supported EPA’s use of the

percent control alternative to the new source MACT for the 

carbon group. The commenters believe that the percent control 

alternative for new source carbon group MACT should also be 

available as an alternative to the existing source MACT for the 

carbon group. The commenters note that allowing an existing 

source to meet the more stringent new source MACT can only 

further the air quality benefits of the MACT standard. 

Several commenters (0258, 0260, 0341, 0342) stated that 

they support EPA’s proposal of a compliance alternative based on 

percent reduction as a means of recognizing that Facility M is 

an outlier and its emissions are not representative of other 

sources in the proposed subcategory. The commenters said that 

the compliance alternative is based on the average of Facility 

M’s mercury emission reductions for the first two years of 

operation of brand new control technology, which are not 

representative of long-term emissions reductions achievable at 

the source. The commenters stated that EPA took the average of 

the 99.6 percent mercury reduction in 2008 and the 93.5 percent 

mercury reduction in 2009 to get the compliance alternative of 

97 percent mercury reduction. The commenters claimed that 

emissions reductions are significantly higher the first year 

after control technology is newly-installed than they are in 
Page 115 of 212

subsequent years, and this skews the data. The commenters

recommended that in order for this compliance alternative to be 

representative of controlled emissions at the source, EPA 

should, at a minimum, provide a compliance alternative 

consistent with Facility M’s second year of operations, which 

would be 93.5 percent reduction in mercury emissions.

Another commenter (0270) stated that the Marigold mine 

(Number 2 in the top 5) represents the “best controlled” similar 

source for the carbon process group more appropriately than 

Facility M (Round Mountain) because it reportedly has emission 

controls that achieve a higher mercury removal efficiency. The 

commenter claimed that the Marigold mine has an average mercury 

reduction efficiency level of 99.995 percent achieved from 2007-

2009. The commenter recommended that EPA use the Marigold mine 

percent reduction of 99.995 percent for the alternative limits 

for new carbon processes.

Commenters (0341, 0342) requested clarification of the way 

in which compliance with the alternative for percent reduction 

is demonstrated for new source MACT for carbon processes. The 

commenters believe that the proposed rule should clarify that 

outlet testing can be performed at the end of all of the control 

devices when there are multiple control devices on an emission 

unit. The commenters also said that for facilities with 
Page 116 of 212

multiple emission units ducted to a common stack, the facility 

should be able to measure the inlet mercury emissions to the 

first emission control unit in the series and the outlet stack 

following applicable control equipment to determine the percent 

emission reduction achieved. The commenters concluded that the 

condenser and chiller on the retort operate as a control device 

and that retort inlet emissions testing should be before both 

the chilled water condenser and the carbon adsorber. The 

commenters explained that a retort configuration may not allow 

direct measurement of mercury emissions before the condenser, 

but it is possible to measure the mercury concentration in the 

concentrate before and after retorting to account for any 

mercury reductions attributed to the control devices at the 

retorts. 

Several commenters (0268, 0277) suggested that the 

requirements for new carbon processes to be clarified: the 

emissions standard of 0.14 pounds per ton of concentrate 

processes applies to the entire carbon processes group whereas 

the 97 percent reduction from installing a mercury emissions 

control device on any new process unit applies specifically to 

the individual new process unit and not to the entire carbon 

processes group.
Page 117 of 212

Response: We eliminated in the final rule the compliance 

alternative of 97 percent reduction for new carbon processes. 

After reviewing the comments received on this standard and 

giving further consideration to the practicality of how it would 

be measured, we concluded that this option would be difficult to 

implement, particularly when multiple processes that are 

operated at different times vent to a single control device and 

stack. In addition, we have limited data supporting this 

compliance alternative. In proposing this alternative for 

comment, we had hoped to, but did not receive additional data 

indicating that the 97 percent reduction option would be 

equivalent in stringency to the proposed new source limit of 

0.14 pounds of mercury per ton of concentrate. Largely due to 

the reasons stated above, we have eliminated the 97 percent 

control efficiency option for new carbon processes in the final 

rule. In addition we are not allowing this percent reduction to 

be used for existing carbon sources. We also note that the 

facility that one commenter identified as having an average 

mercury reduction efficiency level of 99.995 percent is now 

being used as the “best controlled” similar source for the final 

MACT standard for new carbon processes with mercury retorts.
Page 118 of 212

6. Beyond the Floor for the Carbon Group

Comment: Several commenters (0258, 0260, 0342) supported 

EPA’s determination that beyond the floor controls would be 

prohibitively costly for the carbon process group. The 

commenters believe that the actual costs of adding a second 

carbon adsorber would exceed EPA’s cost estimates of capital and 

annualized costs depending upon the type of system designed, 

exhaust flow fate, and site-specific constraints on geometry and 

size. 

Response: At proposal, we concluded that beyond-the-floor 

was not appropriate for the carbon group and provided our 

explanation. We have not received adverse comments on that 

conclusion and have no reason to change it. The commenters 

provided no cost or other information and no substantive reasons 

to increase the cost estimates; consequently, we are not 

revising the estimated costs for additional carbon adsorbers on 

process units that are already equipped with carbon adsorbers.

1. Timing for Compliance Determinations

D. Compliance Determinations

Comment: Commenters (0269, 0271, 0274, 0279, 0280, 0285, 

0332, 0341, 0342, 0351) representing the gold mine industry 

recommended that the compliance deadline for existing sources be 

three years after the effective date of the rule, not the two 
Page 119 of 212

years as proposed. The commenters noted that several facilities 

will have to install control devices to achieve the MACT floor 

limits that have been proposed. The commenters explained that 

the controls must be custom designed for the unique 

characteristics of each process and associated process streams 

at each facility and stated that it can be time consuming and 

difficult to design, procure, construct, and implement emission 

controls to ensure effective operation for the particular 

source. The commenters suggested that there are additional 

technical challenges involved in designing new control 

technologies because of the gas stream chemistry involved, and 

that the engineering challenges are not trivial to overcome and 

it will take time to research new technology, conduct testing, 

and evaluate possible solutions. The commenters also noted that 

some of the compliance monitoring methods cannot be implemented 

in a reliable fashion within the proposed two-year compliance 

period and concluded that EPA should grant a three-year 

compliance period.

Response: After reviewing the information provided in 

public comments on the challenges of retrofitting new controls, 

we believe that allowing 3 years for existing sources to comply 

is appropriate. Given the complexity of the sources, the 

combinations of control devices that are needed in many cases, 
Page 120 of 212

and the amount of time necessary for designing, installing, 

testing, and commissioning additional emission controls for 

mercury, we conclude that 2 years may not provide adequate time 

for existing sources to comply with the final emission 

standards. 

Comment: One commenter (0268) stated that new affected 

sources that startup between the proposed rule publication date 

and the final rule publications date will not have adequate time 

to comply with the new regulatory standards because they will 

not know what the final rule requirements are before their 

operations have begun. The commenter recommends that the 

compliance date for this type of new affected source be within 

180 days of the date of publication of the final rule in the 

Federal Register. The commenter supported the compliance date 

established for existing affected sources and new affected 

sources that begin operating after the date of publication of 

the final rule.

Response: The CAA prescribes compliance schedule for both 

new and existing sources subject to section 112 standards. 

Section 112(a)(1) defines a new source to include a source that 

is constructed or modified after EPA proposes an emission 

standard applicable to that source, which would include sources 

with startup between a proposed and final rule.
Page 121 of 212

For these new sources, the compliance date is the 

standard’s effective date. See CAA section 112(i) and 40 CFR 

63.6(b)(1). The CAA does not give EPA discretion to change this 

compliance schedule. However, EPA notes that many of the 

standards in this final rule are more stringent than the 

standards in the proposed rule. Under the CAA, a new source for 

which construction is commenced after proposal is allowed up to 

3 years for compliance if the final standards are more stringent 

than the proposed standards and the owner or operator complies 

with the proposed standards during the 3-year period. See CAA 

section 112(i)(2) and 40 CFR 63.6(b)(3). Therefore, to the 

extent that the applicable standards are more stringent in the 

final rule than in the proposed rule, these sources have three 

years to comply with the final standards as long as they are in 

compliance with the proposed standards during this period.

Comment: Commenters (0341, 0342) stated that it will not 

be physically possible for all gold mining operations in Nevada 

to conduct source testing in the first 180 days after the 

compliance date because of the numerous gold mine facilities and 

units that would need to be tested and the limited number of 

testing companies qualified to perform the testing. The 

commenters recommended that the proposed rule be revised to 

require initial testing within 12 months of the compliance date 
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to ensure that future annual testing does not occur in the same 

quarters of the year for all facilities. One commenter (0268) 

stated that they support the concept that affected units 

initially determine compliance with the emissions standards for 

a period of time that is less than a full year. 

Response: We disagree and believe 180 days, which is a 

standard provision in the Part 63 General Provisions, is an 

adequate amount of time to schedule and perform the initial 

compliance test.

Comment:

One commenter (0341) suggested adding the following, “If 

the initial compliance test is conducted in the same calendar 

 Several industry commenters (0341, 0342) 

recommended that the source testing results should determine 

compliance for the calendar year in which the test was conducted

rather than to determine compliance for the prior 12 months. 

The commenters suggested that the source test results be applied 

to the hours of operation at the end of the calendar year to 

determine the source’s compliance with the MACT standard on an 

annual basis, just as required in the Nevada Mercury Control 

Program. The commenters suggested that if more than one source 

test is conducted in a year, the facility should average the 

mercury emission test results to determine compliance for the 

calendar year in which the tests were conducted.
Page 123 of 212

year as the end of the initial compliance period, then the first 

annual compliance test will be conducted in the following 

calendar year, and the annual compliance determination 

corresponding to the calendar year of the initial compliance 

test will use the initial compliance test and the number of 

hours each process unit operated during the calendar year of the 

initial compliance test.”

One commenter (0268) stated that they supported having 

affected sources determine compliance on an annual basis because 

this is consistent with the averaging period established for the 

proposed emissions standards. However, the commenter believes 

that it is important to have all affected source annual 

compliance determinations occur at the same time and on a 

calendar year basis. 

The commenter noted that the proposed rule requires an 

affected source to determine initial compliance for a 6-month 

period following the compliance date and that the initial 6-

month period will be triggered by existing and new affected 

sources at different times throughout the calendar year. The 

commenter stated that this occurs because the compliance date 

for new and existing affected units is not the same, and since 

the annual compliance determination is tied directly to the 

initial compliance period, subsequent annual compliance 
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determinations will also be occurring at different times 

throughout the calendar year. According to the commenter, 

facility owner or operators of affected sources, as well as 

permitting authorities, will be required to track the resulting 

myriad of different compliance dates. 

The commenter urged EPA to revise the rule so that the 

annual compliance determinations occur on a calendar year basis 

and be the same for all affected sources. The commenter 

suggested that the initial compliance determination remain, but 

be separated from the annual determination. According to the 

commenter, the initial compliance determination would continue 

to be based on the initial mercury compliance emissions test and 

be for a 6-month period, consistent with the proposed rule; 

however, the annual compliance determination for the first 

calendar year should also be based on the initial mercury 

compliance emissions test, if that test was conducted within the 

calendar year. The commenter believes this will result in 

having all annual compliance determinations on the same time 

interval, and all subsequent annual compliance determinations 

would be based on the required annual mercury emissions tests.

The commenter stated that the annual compliance testing 

should not be constrained to the same calendar quarter each 

year. The commenter stated that this can lead to testing during 
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periods of operation that may not represent normal (or elevated) 

production capacities. The commenter believes that mercury 

emissions testing should be scheduled for the most appropriate 

time interval throughout the calendar year. The commenter 

supported the requirements for annual compliance emissions 

testing for mercury, as well as the requirement to conduct an 

initial emissions test within 180 days of the compliance date, 

but would like the proposed rule to clearly identify when the 

initial mercury compliance test is referenced and when the 

annual mercury compliance test is referred to. 

Response: The permitting authority needs to be able to 

determine compliance with the NESHAP as soon as possible after 

the tests are completed and test results are available. 

Consequently, the final rule requires that initial compliance be 

determined based on production data and operating hours for all 

full calendar months between the date the rule is published in 

the Federal Register and the date of the compliance test, and 

subsequently, annual compliance must be based on production data 

and operating hours for the 12 full calendar months preceding 

the compliance test. This allows the permitting authority to 

determine if the affected source is in compliance in a timely 

manner. (This is consistent with the way compliance 

determinations are made in another MACT rule that uses a similar 
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format - National Emission Standards for Hazardous Air 

Pollutants for Primary Lead Smelting, 40 CFR part 63, subpart 

TTT.) If compliance was based on a calendar year, as suggested 

by the commenter, then we would not know if a source is in 

compliance until after December each year. For example, if a 

source conducted its compliance test in March, we would have to 

wait about 9 more months before we could determine if that 

source was actually in compliance. After those 9 months, if the 

source was not in compliance, it would mean that the source 

could have been out of compliance for the previous 9 months. 

Moreover, we do not believe that compliance with the NESHAP 

based on the production data from the 12 months prior to the 

compliance test would cause problems with reporting under the 

State program. It is our understanding that the emissions 

limits in the Nevada State Phase 2 permits are (or will be) 

based on concentration in the stacks (e.g., micrograms per cubic 

meter (μg/m3

)). The limits in this final rule are based either 

on pounds of mercury per million tons of ore or pounds of 

mercury per tons of concentrate. Therefore, the companies can 

continue to report the annual emissions as required under the 

TRI program and the State program without conflict with this 

rule. 
Page 127 of 212

If multiple compliance tests are conducted during the year, 

then a compliance determination must be made for each separate 

compliance test based on the production data and hours of 

operation for the 12 full calendar months preceding each test 

(i.e., the results of multiple compliance tests conducted 

throughout the year are not averaged to provide a single 

compliance determination for the year).

We understand that the rule, as proposed, may have required 

all existing sources to conduct their subsequent annual 

compliance tests in the same calendar quarter, and this may pose 

a scheduling problem because of the large number of facilities 

located in the same State (e.g., Nevada). Our concern was that 

subsequent annual compliance tests, if not separated in time, 

could be conducted for two different years with little time 

between the two tests (e.g., only a few days apart for the 

extreme case where the first test is conducted in late December 

and the second one in early January of the following year). We 

are providing scheduling flexibility by requiring that annual 

compliance tests be at least 3 months apart and no more than 15 

months apart, and we are providing a similar separation for the 

period between the initial compliance test and the first annual 

compliance test. We do not believe that tracking multiple 

compliance dates is a particular problem for the permitting 
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authority because that is the case for many other source 

categories subject to annual compliance testing. 

Comment: Several commenters (0341, 0342) asked for 

confirmation of the basis for compliance determinations relative 

to partial calendar months and suggested that the compliance 

period would be based on full calendar months. The commenters

explained that, for example, if the compliance date is September 

15, 2012, then the first annual testing would be the full 

calendar months of October 2012 through September 2013, and 

operating hours and production would be totaled from these 12 

months for calendar year 2013.

Response: We agree with the commenters and have clarified 

in the final rule that the production data used in the 

compliance determination is based on full calendar months. For 

the initial compliance test, this would be the 6 full calendar 

month prior to the initial compliance test. For subsequent 

annual compliance tests, this would be the 12 full calendar 

months prior to the annual compliance test.

2. Test Methods

Comment: One commenter (0268) noted that they support 

EPA’s requirement to use Method 29 as an emission test method, 

but recommended two revisions. The commenter suggested that the 

absence of cyclonic flow be determined before sampling is 
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conducted and that the minimum sampling time for each test run 

be 90 minutes. The commenter also stated that they do not 

support the use of the Ontario Hydro Method (ASTM D6784-02), 

Method 30A, or Method 30B as mercury test methods. The 

commenter believes that the methods of demonstrating compliance 

with the emissions standards should be consistent with the 

methods utilized to establish the emission limits; the test 

results from these alternative methods were not used to 

determine the mercury emissions standards proposed for this rule 

and only data from Method 29 test results were used. The 

commenter said that the typical gas streams associated with the 

mining industry have high particulate loadings, high mercury 

concentrations, sulfur dioxide, and contain particulate-bound 

mercury. The commenter also stated that the alternative methods 

were not developed specifically for the gold mining industry and 

their typical gas streams and concluded that the results from 

the various alternative methods will yield varying results, will 

not be comparable, and will provide inconsistent reporting of 

overall mercury emissions.

Several industry commenters (0341, 0342) supported EPA’s 

proposal of alternate Methods 30A and 30B for demonstrating 

compliance with the MACT emission limits. 
Page 130 of 212

Response: Method 29 references Method 1, which requires 

cyclonic flow checks under certain circumstances. Consequently, 

in the final rule, we have removed the specific requirements for 

cyclonic flow checks prior to every stack test that were in 

§63.11646(a)(1)(vi) of the proposed rule. Owners or operators 

should follow the requirements in the applicable EPA reference 

method and any additional requirements specified by the 

permitting authority. 

When specifying the minimum requirements for compliance 

tests, it is more important to specify a minimum sampling volume 

than a minimum sampling time because the detection of a 

regulated pollutant is a function of the volume of the sample 

rather than the length of time taken to collect the sample. 

Thus, the final rule does not specify a minimum sampling time. 

We are also changing the required minimum sampling volume to be 

30 dscf rather than the 60 dscf as proposed in §63.11646(a)(2) 

because we believe that 30 dscf generally will be adequate for 

detecting mercury emissions for this industry. Affected 

facilities should be aware, however, that the minimum sample 

volume may sometimes result in a failure to detect any mercury 

(a non-detect) emitted from a process unit subject to the 

emission standard (for the group of process units within the 

affected source) because of a mercury concentration at the 
Page 131 of 212

outlet lower than expected. If the emission testing results for 

any of the emission points yield a non-detect value, then the 

minimum detection limit (MDL) must be used in calculating the 

emissions for that emission point and, in turn, for calculating 

the sum of the mass emissions for all emission points subject to 

the emission standard for determining compliance. If the 

resulting mercury emissions (in pounds of mercury per ton of 

concentrate, or pounds of mercury per million tons of ore) for 

the affected source are greater than the MACT emission standard, 

the owner or operator may use procedures that produce lower MDL 

results and repeat the mercury emissions testing one additional 

time for any emission point for which the measured result was 

below the MDL. If this additional testing is performed, the 

results from that testing must be used to determine compliance 

(i.e., there are no additional opportunities allowed to lower 

the MDL).

After reviewing the information provided by the commenter 

about Method 29, we agree with the commenter that Method 29 is 

the most appropriate method for compliance determinations for 

this source category because of the unique characteristics of 

these sources. Therefore, we are promulgating Method 29 as the 

main method for compliance in this rule. Alternative methods, 

such as 30B and the Ontario Hydro method (OHM; ASTM D6784-02), 
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could be used to demonstrate compliance for this source category 

if approved by the permitting authority. These alternative 

methods (such as 30B and OHM) may prove to be more appropriate 

under certain circumstances. However, we have omitted Method 

30A as an option in the final rule, as it is not yet in general 

use. 

Comment: Several commenters (0341, 0342) expressed concern 

with the testing requirement that each test run must collect a 

minimum sample volume of 60 dscf and noted that this is not part 

of the Method 29 requirements. The commenters stated that in 

Nevada sources are required to collect a minimum sample volume 

of 60 dscf or sample for at least 2 hours in an attempt to get 

60 dscf, and if the source fails to collect 60 dscf after 2 

hours, the test is still a valid test. The commenters believe 

it will be virtually impossible for autoclaves to meet the 60 

dscf requirement because of the high moisture level in the gas 

stream, and this would cause disruptions in the sampling 

impinger train and increase the chances of contamination. The 

commenters continued by explaining how the requirement for 60 

dscf would be problematic for Method 30B because the method 

requirement to use a small dry gas meter and sampling pump will 

result in a 14-hour test run to meet the 60 dscf volume 

requirement. The commenters also stated that sampling 60 dscf 
Page 133 of 212

at inlet locations for the alternative percent reduction option 

for new source MACT for carbon processes would be difficult 

because of the higher concentrations and high moisture content 

of the gas stream. The commenters recommended that EPA require 

compliance with the specified methods without any adjustment or 

requirement for a minimum sample volume of 60 dscf. The 

commenters also recommended that for the outlet testing required 

by the alternative percent reduction option, each test run 

should be conducted for at least 2 hours or collect a minimum 

sample volume of 60 dscf, whichever comes first. 

Response: We agree that 30 dscf is an adequate minimum 

sample volume for Method 29. We discussed above how the final 

rule would deal with non-detect values. The minimum sample 

volume is not applicable to Method 30B because Method 30B 

includes performance-based criteria for determining sample time 

and volume – the minimum sampling volume is a requirement for 

Method 29 only. The Ontario Hydro Method has its own testing 

criteria.

We discussed above we are not promulgating the compliance 

alternative of a 97 percent reduction for the carbon group of 

affected sources. Consequently, the final rule does not require 

any sampling at the inlet to the mercury emission control 

device. 
Page 134 of 212

Comment: Several commenters (0341, 0342) noted that there 

are acetone rinse procedures, cyclonic flow testing procedures, 

and specific requirements on the number of test runs, test run 

duration and sample volume in addition to the required EPA 

reference test methods. The commenters recommended that these 

additional test procedures be removed because the proposed test 

methods already contain the testing procedures necessary to 

measure emissions. The commenters also noted that some of the 

additional test procedures are incompatible with certain process 

units such as the high moisture in autoclave exhaust, which 

prevents the collection of 60 dscf of sample volume in a 

reasonable time frame, and melt furnace batch times that are 

than two hours, which prevents conducting two hour test runs.

Response: We agree that the acetone rinse is an option and 

that Method 1 addresses cyclonic flow, and they are not 

requirements in the final rule. It is important that the final 

rule specify the number of test runs for a compliance 

demonstration, which is the three runs per emission point in 

this final rule. However, this does not preclude States or 

permitting authorities from requiring additional procedures for 

testing in their own programs. In other words, State or local 

permitting authorities can have more stringent requirements than 

our NESHAP requirements.
Page 135 of 212

3. Emission Limits Based on the Quantity of Concentrate 

At proposal, we requested comment on the possible use of 

carbon rather than concentrate or as an alternative to 

concentrate, as the metric for the emission limit for the carbon 

processes group of affected sources (i.e., where the quantity of 

concentrate or carbon processed would be used as the denominator 

in the calculation of emissions in pounds per ton to determine 

compliance). We also requested comment on whether the 

concentrate should be measured “as fed” or on a dry basis.

Comment: Commenters (0282, 0341, 0342) supported EPA’s use 

of concentrate as the metric for the carbon group for the 

reasons set forth in the proposal, including its close 

correlation to the final product of gold, the fact that the 

facilities already measure it, and that it is already reported 

to NDEP as part of the NMCP.

Commenters also supported EPA’s proposal to use “as fed” as 

the method for determining the level of concentrate in the MACT 

emission standard for the carbon group and the non-carbon 

concentrate group. The commenters do not believe that the 

concentrate should be measured on a dry basis for the following 

reasons: (1) it would be difficult to accurately measure the 

dry weight of the concentrate because it contains not only 

moisture, but also mercury in an elemental state; (2) using a 
Page 136 of 212

dry basis would require additional sampling of concentrate 

and/or mercury from the retort’s condenser, which would increase 

mercury exposure for those workers performing the sampling; (3) 

current Nevada regulatory requirements do not require moisture 

determinations, and (4) the data used to develop the MACT 

standards was based on “as fed” concentrate. 

Response: In general the commenters supported our position 

at proposal on these issues, and we are promulgating the rule as 

proposed with the quantity of concentrate determined on an “as 

fed” basis.

4. Alternative Calculation for Determining Compliance

At proposal, we requested comment on an alternative 

calculation procedure to determine compliance based on the 

process throughput for the unit being tested as measured during 

the compliance test rather than the amount of throughput 

processed annually. We received several comments on this 

potential alternative procedure for compliance calculations.

Comment: Several commenters (0341, 0342) stated that the 

methodology in the proposal is a more appropriate approach than 

the alternate for which comments were requested for the 

following reasons:

• Roaster throughput is measured differently (less accurately 

but more correlative for short time periods) during testing 
Page 137 of 212

than for annual tons. Annual hours of operation as applied 

to a lb/hr emission factor from a source test is more 

representative of actual emissions than would be the 

alternate methodology.

• Correlation between an individual source test of a carbon 

kiln or pregnant tank is not directly correlative to an 

amount of concentrate added to the retort over the same 

time period and for this reason, a lb/hr emission factor 

times annual hours is more representative of actual source 

emissions.

• Because the MACT floors were determined based on hours of 

operation, the compliance mechanism should take the same 

approach.

• The proposed rule approach reflects control and actual 

operation of the affected source and is, therefore, more 

representative of emissions from each affected source.

• EPA’s proposed methodology is consistent with the source 

category’s current reporting requirements to NDEP.

Response: We agree with the commenters for the reasons 

they suggested and the explanation we provided at proposal, and 

we are promulgating the methodology as proposed.
Page 138 of 212

5. Compliance Calculations and Procedures

Comment: Several commenters (0341, 0342) stated that the 

proposal does not address how to average two or more compliance 

tests for a given year and process unit. The commenters

recommend that EPA clarify that mercury emissions in lb/hr from 

the compliance tests conducted in the same calendar year for the 

same process unit should be arithmetically averaged.

Another commenter (0268) recommended that formulas provided 

in the proposed rule for calculating emissions only include 

English units and not the mix of English and metric units to 

avoid errors in the calculations. The commenter also 

recommended clarifying that the mercury emission rate must be 

based on the average of the three test run values obtained from 

the corresponding mercury emissions test. 

The same commenter recommended that EPA revise the proposed 

rule to be consistent with the definition of one-hour period as 

defined in the General Provisions by changing the language from 

“hours” to “one-hour periods.” 

Several commenters (0341, 0342) recommended that the weight 

or the density and volumetric flow rate of the ore slurry be 

allowed to be measured as it is fed or as it exits the 

autoclave(s). The commenters explained that this change would 

allow the flexibility to monitor the density and volumetric flow 
Page 139 of 212

rate of the ore slurry either before or after the autoclave, 

which is the same mass flow for all practical purposes.

A commenter (0268) stated that measuring the oxidized ore 

slurry as it “exits” a roaster oxidation circuit is not 

consistent with the data used to establish the corresponding 

emissions standard. They recommend that the gold mine ore be 

measured as it is fed to the roaster oxidation circuit.

Response: Compliance is determined based on a test that 

uses the average of three runs. If multiple compliance tests 

are performed during the year, the rule requires they be 

submitted as additional compliance tests for the year, and 

multiple tests are not averaged and submitted as one compliance 

determination. We agree that English units should be used, and 

we have incorporated them into the final rule. We agree with 

the comment about “one-hour periods” and have made this change 

in the final rule. We do not agree that an option of measuring 

either ore fed or exiting the autoclave should be included 

because the calculation must be consistent with the way the data 

were presented to develop the emission limits; consequently, 

this provision remains as proposed (i.e., ore as fed to the 

autoclave). We consulted with owners or operators on how the 

original data were developed for roasters and found that it was 

reported based on the ore exiting the roaster. We have not made 
Page 140 of 212

the change requested by the commenter to ensure we are 

consistent with the way the emission limits were developed.

Comment: One commenter (0342) explained that in general, 

hours of operation are based on either when the process feed (or 

throughput) is on or the heat is on; however, the commenter 

suggested that the determinations of operating hours should be 

based on the type of operation because only those hours that 

have the potential for mercury emissions should be counted, and 

as a result, the hours of operation for roasters, carbon kilns, 

retorts, and furnaces would all be different. The commenter 

provided the following suggestions:

• For roasters and carbon kilns, feed is not added until the 

heat is on, so the operating hours should be based on 

throughput hours.

• For retorts, the operating hours should begin at startup 

when both feed and heat are started and continue through 

cool down.

• For melt furnaces operated as a batch process, operating 

hours should start when both the batch is in the furnace 

and the heat is on and end when the melted material is 

poured and cooled and the furnace is off. For melt 

furnaces that are screw fed, operating hours should start 
Page 141 of 212

when the feed is started and end when the melted material 

is poured and cooled and the furnace is off.

• For solution processes such as electrowinning, operating 

hours should not include the time that the unheated 

solution is circulated and has been cooled to ambient 

temperature.

Response: We have clarified in the final rule how 

operating hours must be measured and reported, and the final 

rule is consistent with the way operating hours were determined 

in the data analysis used to develop the emission limits.

6. Multiple Emission Units

Comment: One commenter (0342) requested clarification of 

how compliance should be determined when more than one emission 

unit is ducted to a common stack, and the emission units may 

have operated for different periods of time in the year. 

Response: The final rule clarifies how testing of multiple 

units vented to a common control device and stack. The owner or 

operator may test for emissions with all units operating and may 

use the operating hours associated with the process that 

operates for the longest period of time during the year to 

calculate emissions and determine compliance. This is a worst 

case determination. As an alternative, the operator may perform 

multiple tests with units operating in the various modes that 
Page 142 of 212

occur during the year (for example, a test with all units 

operating, a test with two units operating, a test with three 

units operating, etc.) and calculate emissions based on the 

number of hours during the year that each mode of operation 

occurs.

E. Monitoring

1. Continuous Compliance

Comment: One commenter (0283) noted that EPA’s proposed 

mercury standards are expressed in a format of pounds of mercury 

per million tons of ore processed and observed that the proposed 

rule requires stack testing only once a year. The commenter 

claims that EPA’s proposed monitoring requirements are designed 

to measure compliance with certain “operating limits” and would 

not demonstrate whether sources are in or out of compliance with 

their emission standards, which renders the rule unenforceable. 

According to the commenter, the once-a-year stack test would 

provide no indication as to what a mine’s emissions were the 

rest of the year, and a source could pass the stack test even if 

its emissions exceeded the limit in pounds per million tons of 

ore processed. The commenter said that a source that failed its 

stack test would have only one violation of emission standards –

even if that test showed that the source likely violated its 

emission limit on an ongoing basis throughout the year. Given 
Page 143 of 212

that the penalties for a single violation of emission standards 

are capped by the CAA, the commenter believes that the proposal 

effectively gives gold mine operators an easy choice: (1) comply 

continuously with emission standards, as the CAA requires, or 

(2) violate the standards and then either come into compliance 

on test day or pay one $25,000 penalty each year. 

The commenter stated that the D.C. Circuit court has made 

clear that monitoring requirements in a title V permit must be 

sufficient to “assure” compliance with all applicable 

requirements, but the commenter believes that EPA’s proposed 

monitoring requirements would not assure compliance with the 

proposed emission standards. The commenter noted that EPA 

proposes to require sources to monitor their mercury emissions 

either with continuous emission monitors (CEMs), sampling, or 

various types of parametric monitoring; however, these methods 

provide information either about stack gas concentration or 

about the operation of certain control devices rather than 

direct information about the pounds of mercury emitted, and 

consequently, none of these monitoring methods could be used to 

demonstrate whether a source is in or out of compliance with the 

proposed emission standards at any given time. The commenter 

said that EPA recognizes this point by tying the proposed 

monitoring requirements not to the emission limit but to 
Page 144 of 212

operating limits that do not purport to implement or satisfy the 

requirements for emission standards in section 112(d)(2) and 

(3). 

According to another commenter (0282), all three affected 

source categories should be required to use CEMS at all times 

and at all emission points. The commenter stated that the ore 

pretreatment group especially needs CEMS because of variable 

levels of mercury in the ore and different operational measures 

within the control of the facility. The commenter believes that 

facilities will find low mercury ore and use it during the 

annual compliance test to show compliance with the emission 

limit.

Other commenters (0270) supported EPA’s decision to require 

continuous monitoring and said that the CEMS should be 

incorporated into the compliance regime as well. The commenters 

believe that if the monitoring results indicate that the mine is 

consistently out of compliance for a period of one week without 

correction, the process unit should be subject to compliancebased penalties and/or shut down until corrections are made and 

the process unit is back in compliance. According to the 

commenters, quarterly stack testing should still be required to 

demonstrate that the CEMS is working.
Page 145 of 212

Response: We recognize the importance of requiring 

adequate monitoring to assure compliance with the emission 

standards. Because of the higher mercury emitting potential of 

the roaster, we proposed the option of mercury monitoring using 

CEMS or weekly monitoring with PS 12B with associated parametric 

monitoring as well. We are including in the final rule the 

option to perform continuous PS 12B monitoring, and, as with the 

CEMS, associated parametric monitoring would not be required. 

We are changing the frequency of the proposed weekly 

concentration monitoring approach for roasters to twice per 

month (at least 11 days apart) and would allow a facility to 

conduct a Method 30B test (as an alternative to a PS 12B test), 

supplemented with continuous parametric monitoring. We changed 

the frequency because we believe that sampling twice per month, 

coupled with continuous parametric monitoring, is sufficient for 

determining that the roaster control devices are operating 

properly. We added the alternative of using Method 30B because 

this method directly measures mercury concentration and is a 

valid means of determining whether the concentration is below 

the operating limit established during the initial performance 

test. The twice per month Method 30B measurements will provide 

a concentration value that can be compared to that operating 

limit to determine if an exceedance of the operating limit has 
Page 146 of 212

occurred. Also, if the twice monthly sampling shows repeated 

deviations over time, EPA could decide at a later date that CEMs 

or continuous monitoring with PS 12B are appropriate and 

necessary for roasters. 

We disagree with the commenter that the proposed monitoring 

requirements render the rule unenforceable. Although the 

mercury concentrations monitoring for roasters along with the 

parametric monitoring of all control devices on all units do not 

directly measure pounds of mercury per ton of input, we believe 

that these actions, along with the annual emissions compliance 

tests, is still an acceptable approach to assure compliance with 

the emission standards all year long. Parametric monitoring of 

control devices assures that the control devices are operating 

properly (and reducing emissions) on an ongoing basis. Any 

exceedance of the parameter limits or operating limits triggers 

corrective action. If corrective action does not return the 

mercury concentration within the established limits, the plant 

must conduct a full compliance test and determine if the source 

is meeting the mass-based (lb/million tons of ore) emission 

standard.

We do not believe that we should include CEMS as a 

monitoring option for the non-roaster sources. These sources 

have less potential mercury emissions, and requiring CEMS on all 
Page 147 of 212

these other units would be quite costly and burdensome. 

Moreover, most of these other units are, or will be, controlled 

with carbon adsorbers, and the carbon adsorber monitoring 

required by the final rule is an effective means of ensuring the 

controls are working effectively on a continuing basis. We 

consider that either frequent testing of carbon beds to monitor 

for breakthrough using Method 30B, or frequent adsorbent 

sampling for mercury content, is an effective way to ensure 

these mercury control systems are operating properly on a 

continuing basis. The final rule also requires parametric 

monitoring of wet scrubbers that are considered the final 

mercury control (i.e., not followed by a carbon adsorber or 

calomel mercury scrubber). We believe that annual tests coupled 

with appropriate parametric monitoring of the wet scrubbers are 

sufficient to ensure emissions are properly controlled on a 

continuing basis. 

With regard to the comment that quarterly stack testing 

should be required for facilities using a CEMS, we believe that 

following the Quality Assurance (QA) procedures detailed in 40 

CFR 60, Appendix F, are sufficient to ensure the CEMS continues 

to operate as designed, and in this case, additional stack 

sampling is not necessary. 
Page 148 of 212

Comment: One commenter (0283) stated that the CAA mandates 

that emission standards require “continuous” compliance (citing 

42 U.S.C. section 7602(k)), but claims that the proposed rule, 

which requires compliance only once a year during stack tests, 

fails to satisfy this requirement. The commenter believes that 

EPA needs to select a format that can be measured on a 

continuous basis to establish standards that do require 

continuous compliance and has emissions data that will allow it 

to do so (e.g., mercury emissions test data expressed in a stack 

gas concentration format of grains of mercury per dry standard 

cubic foot). The commenter recommended that EPA use these data 

to set floors and final standards that are expressed in a 

concentration format, that these standards would apply 

continuously, and that any exceedance of them would be a 

violation. The commenter stated that EPA did not discuss a 

stack gas concentration standard even though the stack tests on 

which it would base floors are expressed in this format, and 

many of EPA’s other section 112(d) standards use this format. 

The commenter also said the proposal did not discuss the

relationship between the choice of format for the standards and 

the continuous compliance requirement in section 302(k). 

According to the commenter, the choices EPA considered would 
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neither require continuous compliance nor be enforceable on a 

continuous basis, unlike a stack gas concentration standard.

The commenter also believes that if EPA changed the format of 

its emission standards to a stack gas concentration format, some 

of the proposed monitoring methods could be used to assure 

compliance with emission standards and to enable operators to 

meet their compliance certification requirements. The commenter 

concluded by stating that EPA must adopt monitoring requirements 

that assure compliance with its emission standards, not just 

operating limits, and that allow operators to certify whether 

they are in continuous compliance with emission standards and to 

identify and report all deviations from emissions standards, as 

required by sections 114 and 504 of the CAA. 

Response: There are several reasons that a concentration 

format is not appropriate for the emission points subject to 

this rule. The primary concern is that dilution air directly 

affects concentration measurement, and there is variation in the 

amount of dilution air the different facilities because of 

differences in the design and operation of their processes. 

These process units are not like combustion units, where the 

level of oxygen in the exhaust stream is low (e.g., 7 percent 

rather than the ambient level of 19 percent found for many gold

mine emission points). We have used concentration limits for 
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certain combustion units, and they are acceptable for combustion 

units because the results can be adjusted to 7 percent oxygen to 

account for dilution and provide a uniform standard. When 

oxygen levels are at or near ambient levels, an oxygen 

correction factor is ineffective at detecting and accounting for 

dilution. Also note that concentration is not a direct measure 

of emissions; emissions must be calculated by multiplying 

concentration by the volumetric flow rate, and the volumetric 

flow rate depends in part on the amount of dilution air entering 

the system.

We have used emission limits in the format of pounds per 

ton of throughput or product in several other NESHAP, and this 

is generally our preferred approach when appropriate. This 

format is appropriate for gold mines because it accounts for 

variations in the sizes of facilities, and it provides a uniform 

basis and level playing field for assessing emission control 

performance and developing emission limits.

The discussions below address the commenter’s concern about 

continuous compliance and appropriate monitoring for gold mine 

ore processing and production facilities.

2. Operating Limits

Comment: One commenter (0342) stated that the operating 

limits for roasters and for carbon adsorbers are inappropriate 
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and set up a second set of MACT standards. The commenter 

claimed that the operating limits do not take into account the 

following: changes in hours of operation of a process unit 

affects its overall mercury emissions; the reduction in 

performance of an individual process unit may be entirely 

compensated for by an improvement in performance of another 

process unit; variability in the exhaust gas flow rate may 

result in a significant change in mercury concentration with no 

appreciable effect on the corresponding mercury emission rate; 

and variability in the inlet mercury concentration to a carbon 

adsorber results in variability in the mercury concentration in 

the exhaust gas stream. The commenter also noted that using the 

operating limit methodology many not adequately represent the 

health of the carbon adsorber and that carbon could then be 

changed out prematurely, potentially resulting in the generation 

of more waste. The commenter recommended that EPA defer to the 

Nevada state monitoring requirements for Nevada facilities, and 

only provide for monitoring of throughput and annual mercury 

emission testing to demonstrate compliance with the MACT 

emission standard. The commenter believes that any operating 

limit parameters must be established based on manufacturer 

specifications and recommendations in coordination with the 
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permitting authority and not based on values measured during 

source compliance testing.

Response: We proposed the mercury operating limits as a 

monitoring tool to ensure that the processes within individual 

affected sources and their associated control devices are 

functioning properly on a continuing basis and not as a second 

set of MACT standards. We developed emission standards for four 

affected sources, and the emission standard for an affected 

source applies to the sum of emissions from all process units 

within the affected source. One unit could have an upward 

fluctuation in mercury concentration, but the group of process 

units could still meet the MACT limit. We see the value of the 

operating limit approach as sufficient to detect significant 

increases in emissions and as a valuable tool to ensure the 

control devices are operating effectively and provide quick 

notification of a potential problem with controls or emissions. 

The monitoring parameters are used as compliance indicators, and 

the relevant mercury operating limits are the main “triggers” of 

a possible emissions increase and are set to alert facility 

operators when emissions are greater than the corresponding 

mercury operating limit. We believe it is important to have 

such monitoring in the rule to ensure the control devices are 

working properly.
Page 153 of 212

Regarding specific comments about monitoring the carbon 

adsorber, the State of Nevada has had good results with 

conducting sampling of the carbon adsorber to maintain its 

performance. The final rule offers an additional option of 

measuring the mercury concentration exiting the carbon adsorber 

that also achieves the same objective of avoiding breakthrough 

of the bed. We do not expect sudden dramatic failures of this 

technology. Instead, we expect to obtain close control of 

performance by ensuring that the carbon is changed in a way that 

prevents breakthrough. This monitoring methodology should also 

prevent premature replacement of the bed.

We disagree with the comments that only monitoring for 

throughput and annual emissions testing are sufficient to 

demonstrate compliance with the MACT standards. Such an 

approach does not yield sufficient data to assure compliance 

with the emission standards either directly or indirectly by 

assuring that the control devices are operating properly. The 

parametric monitoring and operating limits specified in this 

final rule provide assurance that control devices are properly 

operated and maintained between emissions tests, and exceedances 

of the operating limit require corrective action. With regard 

to the comment that any operating limit parameters should be 

based solely on manufacturer specifications and/or in 
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consultation with the permitting authority, we have provided 

various options in this rule for establishing control device 

parameter limits. Control device operating parameter values 

sometimes are site-specific and are associated with a level of 

emissions from the source. Therefore, it is generally 

preferable for certain control device parameter limits to be 

associated with an emissions test that demonstrates compliance 

with the emissions standards. However, we agree that certain 

parameters for mercury scrubbers applied to roasters, such as 

the ranges associated with ensuring the proper chemistry of the 

scrubber, are best provided by the system’s manufacturer. 

Guarantees of performance are usually conditioned by requiring 

that the system be operated as designed and specified by the 

manufacturer, and there is no assurance that a potentially 

narrow range that would be established during a short 

performance test reflects the full applicable range of proper 

operation. We also realize that it may be preferable that the 

permit authority establish the parameter limits for some of the 

control devices in this industry because of some of the unique 

characteristics of the processes and control devices used in 

this industry and the experience of the permit authority with 

addressing these sources. Therefore, this final rule allows 

three options for establishing parameter limits: (1) based on 
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the initial compliance test; (2) according to the manufacturer’s 

specifications; or (3) based on limits established by the 

permitting authority 

Comment: Some commenters (0341, 0342) stated that their 

established parametric monitoring programs are sufficient to 

confirm that mercury emission controls are functioning properly 

for roasters. The commenters noted that some of the parameters 

currently being monitored are gas stream temperatures, voltages 

of wet electrostatic precipitators, the mercuric ion 

concentrations of the calomel scrubber solution, and the mercury 

concentration of sulfuric acid product. The commenters

explained that when control devices are not operating properly, 

corrective actions are taken (including shutting off the feed to 

the roaster). The commenters also stated that the NMCP Phase 1 

and 2 permits have parametric limits that must be followed and 

that additional CEMS for mercury would neither improve the 

operation of these current controls, nor is it likely that 

mercury emissions would be significantly improved. The 

commenters concluded that the operating parameters monitored on 

a regular basis are key parameters for measuring the efficiency 

and operation of the mercury controls in the off-gas cleaning 

system and that operating each of these units within the optimum 
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ranges ensures that mercury emissions are being effectively 

controlled. 

Response: As discussed above, we do not believe parametric 

monitoring alone is sufficient for roasters because of the very 

high mercury emission potential, unless the facility has 

adequately demonstrated that the mercury emissions from the 

roasters are consistently very low (e.g., less than 10 pounds 

per million tons). We have concluded that the combined approach 

of annual stack compliance testing along with the mercury 

concentration monitoring and parametric monitoring requirements 

and options outlined in this rule are necessary to detect excess 

emissions and to ensure controls are working effectively on a 

continuous basis. We note that for facilities that choose to 

monitor the mercury concentration from the roaster with CEMS or 

continuous PS 12B sampling, they do not have to do parametric 

monitoring. For facilities that can demonstrate their mercury 

emissions are less than 10 lbs per million tons of ore, they 

only have to do parametric monitoring, no mercury concentration 

monitoring. 

Comment: One commenter (0341) requested clarification that 

establishing the mercury concentration limits for monitoring 

roasters and carbon adsorbers and the carbon bed inlet 

temperature will first be during the “initial” compliance test.
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Response: We have clarified in the final rule that these 

monitoring limits must first be established during the initial 

compliance test. The owner or operator may choose to reestablish these limits during subsequent compliance tests.

3. Mercury Concentration Monitoring for Roasters

Comment: One commenter (0268) stated that the provisions 

for monitoring the mercury concentration in roaster emissions 

are not based on roaster process and pollution control device 

operational parameters, and thus do not yield reliable

information that can be used for detecting and correcting 

problems that may occur in the roaster circuit process. The 

commenter also stated that the formula for establishing the 

operation limit for roasters is not appropriate because it uses 

the emission limit of 149 lb/million tons of ore for ore 

pretreatment processes, which is based on emission test data 

from several process units in addition to the roaster. 

The commenter recommended removing the proposed 

requirements for monitoring the mercury concentration in roaster 

emissions and instead use the methods proposed for parametric 

monitoring of roaster emission control devices for all roasters. 

The commenter also has concerns about utilizing Performance 

Specification (PS) 12A (mercury CEMS) and PS 12B for emissions 

monitoring purposes because there are terms and conditions 
Page 158 of 212

listed in the proposed rule that are not fully defined, such as 

how to determine the daily average mercury concentration and 

what specifically must be included in the monitoring plan. The 

commenter also recommended deleting the emissions monitoring 

requirements for mercury concentration for carbon adsorbers for 

the same reasons described above for roasters.

Response: We disagree with the comment that monitoring the 

mercury concentration in roaster emissions would not yield 

reliable information that can be used for detecting and 

correcting problems. An elevated mercury concentration in the 

roaster stack gas indicates that there could be a problem with 

either the process or the control device, which could result in 

excess mercury emissions from that unit. Monitoring the mercury 

concentration in roaster emissions provides a direct measure of 

the regulated pollutant (mercury). The commenter is correct 

that the formula for establishing the mercury operating limit 

for roasters is based on emission tests performed on several 

processes units in addition to the roaster. However, for the 

facilities with roasters that will be subject to the 

requirements to monitor mercury concentration, the roaster is 

the biggest source of potential mercury emissions within the 

affected source. Therefore, we conclude that changes in the 

mercury concentration in the roaster exhaust gases provide a 
Page 159 of 212

reasonable indication of overall emissions from the affected 

source. In addition, the operating limit is not used directly 

to determine compliance with the MACT emission standard. As 

mentioned above, it is designed to detect elevated mercury 

concentrations in the roaster stack gas, which could indicate a 

problem with either the process or the control device. We 

continue to believe that it is necessary and appropriate to 

monitor mercury concentration for the largest source of 

potential mercury emissions in the source category (i.e., the 

roaster) to detect excursions in emissions that must be 

addressed when the operating limit is exceeded. By developing 

the mercury operating limit from the emission standard and 

compliance test results, an exceedance of the mercury operating 

limit will indicate a potential increase in emissions and that 

corrective actions are needed. 

As described above, we believe that either continuous 

mercury sampling or mercury sampling twice per month (coupled 

with continuous parametric monitoring of the control device) 

should be required for the roaster emissions. If a CEMS is 

used, the daily average mercury concentration is calculated by 

averaging the hourly emissions concentrations during that day. 

The final rule includes continuous sampling with PS 12B as an 

option for monitoring roasters. If PS 12B is used for 
Page 160 of 212

continuous integrated sampling (i.e., without parametric 

monitoring), the daily average concentration is determined by 

assigning the mercury concentration measured by the sorbent trap 

monitoring system (total mass of mercury collected during the 

sampling period divided by the sample volume) as the daily 

average value to each of the days covered by the integrated 

sample.

 A third option is based on short-term sampling twice per 

month (at least 11 days apart) for mercury concentration using 

either PS 12B or Method 30B, and if this option is chosen, 

continuous parametric monitoring of the mercury scrubber must 

also be performed. For this short-term sampling option (twice 

per month sampling) each measured mercury concentration must be 

compared to the operating limit to determine if an exceedance 

has occurred. For the contents of the monitoring plan, see 40 

FR 63.8(d)(3) and 40 CFR 60, Appendix F.

We also disagree that parametric monitoring alone is 

sufficient for carbon adsorbers. For carbon adsorbers, 

measuring the mercury concentration exiting the carbon bed is 

also a direct measure of the pollutant of interest. (The other 

option as established for years in NDEP operating permits 

involves sampling the carbon for mercury content.) An elevated 

mercury concentration indicates that there could be a problem 
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with either the process or the control device, which could 

result in excess mercury emissions from that unit. We have 

established exit concentration monitoring requirements in many 

rules for emissions of organic compounds exiting carbon 

adsorbers. That monitoring has proven to be effective to 

prevent or detect breakthrough, and the same principles apply 

here for mercury. 

Comment: Commenters (0274, 0341, 0342) stated that CEMS 

for gold mining operations are not capable of accurately 

measuring mercury emissions and that there are three major 

challenges with the feasibility of mercury CEMS for the gold 

mining industry: mercury CEMS calibration, sample transport, 

and system operability and reliability.

The commenters are concerned with the unavailability of a 

means to calibrate the CEMS for roasters, resulting in data of 

limited and suspect value. The commenters stated that all 

vendors would have to modify their existing head-space 

calibrator units because existing calibrator designs are simply 

not capable of generating mercury concentrations high enough to 

provide meaningful upscale calibration points that correspond to 

gold mining source characteristics. The commenters noted the 

unavailability of National Institute of Standards and Technology 

(NIST) traceable calibration gas; NIST certifies methods and 
Page 162 of 212

gases used for calibrating monitors, an important and necessary 

procedure for ensuring that measured data is accurate and 

reliable. The commenters stated that 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 

of roasters. The commenters believe that promulgating a rule 

that includes provisions for mercury CEMS that cannot be 

calibrated with NIST-traceable reference gas standards directly 

contradicts existing EPA requirements. The commenters concluded 

that the lack of a NIST-traceable standard is a fatal flaw that 

precludes using mercury CEMS to monitor roaster emissions.

The commenter were also concerned with the transport of the 

sample from the stack to the analyzer and said that current 

designs of mercury CEMS for coal-fired electric generating units 

require high temperature umbilical lines to transport the sample 

from the stack to the analyzer. The commenters noted that the 

mercury sample transport lines must be maintained at a higher 

temperature than sample lines for conventional CEMS (i.e., CEMS 

used for SO2, NOx, or CO2) because mercury is a “sticky” 

molecule, especially the oxidized form. The commenters stated 

that CEMS on coal-fired electric generating units have seen 

umbilical failures occur and concluded that the umbilical 

failures represent another challenge to having CEMS function 
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consistently for the continuous monitoring of mercury from 

industrial sources.

The commenters were also concerned with the CEMS 

operability and reliability and stated that because only 

elemental mercury can be “seen” or detected by either atomic 

absorption or atomic fluorescence, mercury CEMS must contain 

some type of converter to reduce oxidized mercury to elemental 

mercury. The commenters noted that most mercury CEMS suppliers 

use a thermal catalytic process for mercury conversion, although 

premature catalytic failures periodically occur in these units 

resulting in several days of missing data. The commenters 

continued by stating that users reported mercury CEMS to be 

unavailable as much as 30 to 40 percent of the electric 

generating unit operating time. The commenters believe that 

because of the complexities of applying this technology to a new 

source category and the stream differences from electric utility 

generating units, the amount of downtime to be expected from 

these systems on roasters would likely be even higher. The 

commenter concluded that the breakdown events, combined with the 

other types of failures, result in data availability that is 

substantially inferior to parametric monitoring and therefore 

cannot justify the significant cost and resource investment 

necessary to install, operate, and maintain these devices.
Page 164 of 212

The commenters believe that to rely on CEMS for the limited 

purpose of verifying proper emission control operation ignores 

the real concern that is presented by continuous data reports of 

mercury emissions that are not accurate, reliable, or credible. 

The commenters are concerned that the uncertifiable CEMS data 

from the proposed monitoring will be offered as “credible 

evidence” to assert a violation. The commenter concluded by 

stating that this concern was particularly troubling in Nevada, 

where there are separate mercury limits established pursuant to 

State law.

Response: Regarding the feasibility of using CEMS to 

monitor mercury emissions from roasters, CEMS have been 

demonstrated for process units similar to roasters (e.g., coalfired power plants), and we believe there is no technical reason 

why they will not work for the roasters. (See NESCAUM, 2010. 

Technologies for Control and Measurement of Mercury Emissions 

from Coal-Fired Power Plants in the United States: A 2010 Status 

Report Northeast States for Coordinated Air Use Management 

(NESCAUM) July 2010).

Many of the issues with mercury CEMS have been resolved as 

facilities have gained experience with their use. However, we 

realize that mercury concentrations in the exhaust gases from 

roasters can be higher than the range of concentrations for 
Page 165 of 212

coal-fired power plants, and that the calibration standards 

traceable to NIST, that have been available in the past, have 

not applied to the full range of mercury concentrations that can 

be present in the exhaust gases from roasters. Nevertheless, as 

we discussed in the proposal preamble, CEMS manufacturers supply 

calibration standards for the ranges of concentrations seen at 

roasters.

In addition, the NIST has recently completed certification 

of a ‘NIST Prime’ elemental mercury gas generator at 

concentrations of 41, 68, 85, 105, 140, 185, 230, 287, and 353 

μg/m3

. Mercury gas generator vendors may now submit elemental 

mercury gas generators for certification to serve as ‘Vendor 

Primes’ in a wide range of concentrations. Therefore NIST 

traceable mercury gas standards can now be made available in 

concentrations that cover the full range of the concentrations 

typically measured from roasters.

After consideration of public comments, we continue to 

believe CEMS are a valuable tool and a reasonable option for 

monitoring mercury concentrations and comparing those 

concentrations to the operating limit that is established by 

CEMS measurements made during the compliance test. However, we 

also point out that the final rule does not require the use of 

CEMS; instead, the final rule includes CEMS as one of the three 
Page 166 of 212

monitoring options. The other two options that we are 

promulgating for monitoring mercury from roasters are: (1) 

continuous monitoring using PS 12B; and (2) twice per month 

sampling using PS 12B or Method 30B coupled with parametric 

monitoring. All three of these monitoring options are intended 

to ensure that emissions from the roasters are not exceeding 

operating limits, or if they do exceed the operating limits, 

that corrective actions are taken in a timely manner to bring 

the emissions down to within the operating limits. If these 

corrective actions are not successful then the facility must 

perform a complete compliance test using the methods in section 

63.11646 to determine whether the affected source is in 

compliance with the MACT standard. The CEMs can also be used to 

help identify problems with control systems and ensure that

corrective actions are taken immediately to fix such problems. 

The exceedance of the operating limit is not intended to 

determine if the source in violation of the MACT standard. 

Rather, it would be the subsequent compliance test pursuant to 

section 63.11646 that would be used to determine if the source 

is in compliance with the MACT standard.

We understand the commenter’s concerns regarding the 

transport of samples and converter failures. However, we have 

revised the final rule to give facilities 3 years to comply with 
Page 167 of 212

the rule which will allow extra time to successfully set-up and 

operate controls and monitoring equipment to be able to comply 

with the MACT standards. We believe this will provide 

sufficient time, for facilities that choose the CEMs monitoring 

option, to identify and resolve issues with the transport of 

samples and converters. 

Comment: One commenter (0342) stated that the regulated 

industry has no experience with direct measurements of mercury 

concentrations at the roaster exhaust gas stream. As a result, 

the commenter believes that there will be problems in collecting 

data, establishing appropriate timeframes for sampling under PS 

12B, maintaining instrument reliability for CEMS, and in 

establishing confidence in the accuracy of the results reported 

by these methods. The commenter claimed that the calculated 

operating limit based on source testing and simultaneous direct 

measurements may not be reflective of the future daily 

operations of all the stack emissions. The commenter noted that 

flow rate measurements are critical in verifying compliance with 

actual emission limits because sometimes lower flow rates of the 

stack exhaust gas flow can artificially elevate the mercury 

concentration in the gas stream with no real effect on 

emissions. The commenter stated that the operating limit does 

not take into account changes in production that may vary the 
Page 168 of 212

allotted emissions even though the emission limit is dependent 

on tons of plant production. The commenter concluded that any 

exceedence in mercury concentration should be verified first 

with a compliance test before halting the roaster production.

Response: We have learned from the comments received that 

there may be a learning curve for facilities to implement the 

concentration monitoring procedures. As described in section 

V.D. of this preamble, we have established in the final rule a 

compliance date that is 3 years after the effective date of the 

final rule for existing sources, partly to allow sources time to 

ensure they can successfully comply with the monitoring 

requirements, but mainly to allow time to install new mercury 

emission controls that we believe will be necessary to meet the 

emission standards in the final rule.

We agree that mercury concentration measurements are not 

direct measurements of the emissions rate from the affected 

source and that flow rate, production, and other factors need to 

be considered. These are some of the reasons that the operating 

limit is not being used as a direct measure of compliance with 

the MACT standards. However, concentration measurements above 

the operating limit should indicate that either controls are not 

working effectively or other problems are occurring. In either 

case, exceedances of the operating limit require investigation 
Page 169 of 212

and may require corrective actions. The requirement to shut 

down the roaster has been removed from this final rule. However 

an exceedance of the mercury concentration does trigger 

corrective action, and if not corrected requires a compliance 

test. 

Comment: One commenter (0341) requested that EPA reduce 

the Method 12B monitoring frequency to quarterly or at most 

monthly. The commenter also requested that EPA include a 

provision that allows for a source to demonstrate a correlation 

or consistency of performance such that the Method 12B sampling 

frequency can be further reduced based on the permitting 

authority’s acceptance of the demonstration. The commenter 

suggested that if multiple Method 12B samples are collected in a 

single day or over multiple days in the calendar week, then the 

samples should be averaged, and this average concentration would 

be compared to the operating limit. The commenter said that for 

stacks with high mercury concentration, the sample collection 

time may be only an hour or two, and in this case, it may be 

important to collect more than one sample in a single day or 

over multiple days to obtain a representative mercury 

concentration measurement.

Response: After taking into consideration the commenter’s 

rationale, under this monitoring option, the final rule requires 
Page 170 of 212

the sampling of mercury concentration at least twice per month 

(with 2 samples taken at least 11 days apart) instead of weekly 

sampling as proposed. If multiple samples are taken during the 

twice per month period, each result must be compared to the 

operating limit separately (i.e., not averaged). Otherwise, a 

high result from a sample taken near the end of the sampling 

period might not trigger corrective actions to correct a problem 

that developed at that time if the results are averaged with 

previous samples during periods of good performance. We do not 

agree with the suggestion to allow the monitoring frequency to 

be reduced if the monitoring results demonstrate consistency 

over the long term. We believe that monitoring the mercury 

concentration at least twice per month is necessary for roasters 

to ensure that potential problems with control systems are 

identified quickly and corrective actions are taken in a timely 

manner. 

4. Parametric Monitoring of Roasters

Comment: Some commenters (0341, 0342) recommended that EPA 

remove the provisions requiring monitoring of the mercury 

scrubber liquor flow rate and scrubber pressure drop and related 

requirements because each facility that has a roaster has a 

unique sequence of air pollution control devices that interact 

to control mercury emissions and, therefore, monitoring 
Page 171 of 212

parameters that may be appropriate for one roaster may not be 

applicable to another. The commenters noted that scrubber 

liquor flow rate, scrubber pressure drop, and inlet gas 

temperature are not required in the title V or NMCP Phase 1 

permits issued by NDEP for the roasters at the commenter’s 

facility. The commenters said that the scrubber liquor flow 

rate is not currently monitored, nor is it considered a critical 

parameter in the daily operation of the scrubber mercury removal 

tower associated with its roasters. The commenters further 

explained that the scrubber is not a spray tower where water 

flow rate is critical, instead the liquor is recirculated in the 

tower, so the pump is monitored to insure it is operational. 

The commenters stated that the pressure drop across the mercury 

removal tower at its roasters is monitored, but is not 

considered a critical parameter to the operation of the mercury 

scrubber and that the mercuric ion and chloride ion 

concentrations are the critical parameters that define the 

effectiveness of the mercury scrubber. 

Another commenter (0341) added that calomel-based mercury 

scrubbers are not similar to venturi scrubbers. The commenter 

explained that the key control performance parameter for the 

calomel-based mercury scrubbers is the reagent concentration in 

the solution exiting the scrubber and that maintaining the exit 
Page 172 of 212

reagent concentration ensures there is sufficient reagent to 

react with the mercury vapor. The commenter noted that low exit 

concentrations indicate that either the liquor flow rate is too 

low or the fresh reagent addition rate is too low thus, liquor 

flow rate does not need to be monitored in addition to reagent 

exit concentration. The commenter stated that if EPA continues 

to require then the ranges should be based on the manufacturer’s 

specification or an alternative value approved by the permitting 

authority, as opposed to three test runs. One commenter (0342) 

recommended that the corresponding range or limit for parametric 

deviations be applied to a daily average value rather than 

continuous instantaneous values or single samples. 

The commenters (0274, 0341) also stated that the 

requirement to establish the minimum water flow rate and 

pressure drop of the wet scrubber on readings taken during the 

performance test should not apply to scrubbers on roasters. 

The commenters noted that the scrubbers on roasters often 

include chemical reaction rather than the physical processes 

that these parameters were intended to monitor for. 

Response: We agree that pressure drop is not relevant to 

mercury scrubbers because, unlike venturi scrubbers applied to 

control PM emissions, it is not related to its mercury emission 

control performance. We have removed pressure drop monitoring 
Page 173 of 212

from the final rule for mercury scrubbers. However, we continue 

to believe that it is important to monitor the scrubber flow 

rate to ensure the scrubber solution is being delivered to the 

system and that the flow is adequate, which is related to the 

system’s performance. We understand that some facilities 

monitor mercury scrubber solution line pressure (solution header 

pressure) as an indicator of flow rate, and we agree this is 

adequate to ensure proper flow. Consequently, the final rule 

requires hourly monitoring of scrubber flow rate (or line 

pressure) for mercury scrubbers on roasters. As with the inlet 

temperature operating range, the minimum flow rate or line 

pressure must be established by one of the following three ways: 

(1) during the initial compliance test, (2) from the 

manufacturer’s specifications, or (3) based on the limits 

established by the permitting authority. If the facility 

chooses the option to establish the limits during initial 

compliance, the final rule requires the scrubber flow rate 

operating limit to be based on either the lowest value for any 

run of the initial compliance test or 10 percent less than the 

average value measured during the compliance test and the inlet 

gas temperature operating limit to be based on either the 

highest value for any run of the initial compliance test or 10 

percent higher than the average value measured during the 
Page 174 of 212

compliance test. The final rule requires hourly monitoring and 

that corrective action is triggered if the flow rate or line 

pressure falls below the established parameter limit.

Regarding the acceptability of scrubber flow rate and inlet 

gas temperature parameter values that were approved by 

permitting authorities prior to this final rule, such values 

must be established as specified in the final rule and are not 

presumed in advance to be acceptable. Note that the monitoring 

requirements for wet scrubbers in §63.11647 of the final rule 

would not apply to the mercury scrubbers on roasters, or any wet 

scrubber prior to the mercury scrubber on the roasters.

Comment: One commenter (0342) believes that establishing a 

maximum operating temperature for inlet gas concentrations by 

artificially increasing this temperature during compliance 

testing may destroy the control equipment, conflict with 

recommended operating temperatures, artificially increase the 

reported mercury emissions, and artificially decrease the 

allowable operating limit for mercury concentration if direct 

emissions measurement methodology is used. The commenter 

concluded that these parameters are not deemed critical in the 

effective operation of a mercury calomel scrubber. Other 

commenters (0274, 0341) added that their Compliance Assurance 

Monitoring (CAM) plan provides for an inlet gas temperature 
Page 175 of 212

range of 32 to 134°F to prevent water freezing problems or 

extremely hot gas temperatures that could damage the mercury 

scrubber. The commenters stated that mercury scrubbers remove 

mercury from the gas stream through a chemical reaction and not 

a condensation mechanism and that lower temperatures will not 

remove (via condensation) additional mercury. The commenters

explained that although mercury scrubber inlet gas temperature 

is not a relevant control performance parameter, their facility 

maintains the inlet gas temperature below 134°F and monitors 

daily to prevent damage to the controls system from excessively 

low or high gas temperatures. The commenters stated that if EPA 

continues to require inlet gas temperature monitoring, then the 

maximum temperatures should be based on the manufacturer’s 

specification (or an alternative value approved by the 

permitting authority, i.e., 134°F), as opposed to three test 

runs.

Response: After additional review of operating permits and 

consideration of public comments, we have found that the inlet 

temperature of the mercury scrubber is monitored and maintained 

within a range to provide operational flexibility with the lower 

end bounded to prevent freezing and the upper end bounded to 

prevent damage to equipment, which in turn could lead to excess 

emissions. In addition, we have learned that this temperature 
Page 176 of 212

is dependent on the cooling tower water temperature used in the 

process, and this water temperature can vary quite widely from 

winter to summer. Facilities may not be able to address the 

issues described above if they can only use initial compliance 

testing to establish the inlet temperature operating range, as 

we proposed. Consequently, the final rule provides the 

following three ways for a facility with a roaster to establish 

an operating range for inlet temperature: (1) based on the 

maximum inlet temperature during the initial compliance test; 

(2) from the manufacturer’s specifications; or (3) based on the 

limits established by the permitting authority. If the facility 

chooses the option to establish the limits during initial 

compliance, the final rule requires the inlet gas temperature 

operating limit to be based on either the highest value for any 

run of the initial compliance test or 10 percent higher than the 

average value measured during the compliance test. The facility 

must monitor the temperature hourly, and any exceedance of the 

upper limit for temperature would trigger corrective action. 

Comment: Several commenters (0274, 0341) recommended a 

third option for monitoring the mercury scrubber reagent 

solution chemistry be added that would allow for the monitoring 

of mercuric chloride (HgCl2) concentration at the exit of the 

scrubber on a frequency of “one time daily.” The commenters
Page 177 of 212

stated that they have historically used daily analyses of the 

exit concentration of HgCl2 to maintain control performance. The 

commenters continued to explain that the primary reactant of 

concern is HgCl2 in the removal of mercury reaction and that an 

excess of HgCl2 in the solution exiting the mercury scrubber 

ensures there is sufficient HgCl2 in the mercury scrubber liquor 

for reaction with the incoming mercury. The commenters noted 

that the underlying purpose of HgCl2 sampling is for adjusting 

the mercury scrubber HgCl2 feed rate and that the target 

concentration is 1.0 gram of HgCl2 per liter or greater. 

Response: The parameters to be monitored and the frequency 

are based on recommendations from NDEP and their experience with 

parametric monitoring of roasters. In addition, this monitoring 

has been applied at the facility with the best controlled 

roasters in the industry. Consequently, we do not accept the 

suggestion of less stringent monitoring and maintain these 

requirements as proposed.

Comment: One commenter (0341) is seeking confirmation that 

the approval language for the mercury control operating limits 

(i.e., “may be approved by your permitting authority”) includes 

operating limit approvals made by the permitting authority prior 

to the proposed rule as part of an existing regulatory 

requirement (Title V, Compliance Assurance Monitoring, Nevada 
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Mercury Control Program, etc.) provided the approval and 

operating limit were specific to the control of mercury.

Response: All approvals of operating limits must be made 

under the conditions specified in this final rule, and prior 

approvals are not assumed to be adequate in advance to meet the 

rule requirements, although they may subsequently be accepted 

when submitted to the permitting authority under this rule.

5. Exceeding the Operating Limits for Roasters

Comment: Several commenters (0274, 0341, 0342) was 

concerned with the monitoring required to demonstrate compliance 

with the alternative to monitoring mercury concentration from 

roasters and provided the following comments:

• Roaster shutdown for merely exceeding a monitoring 

parameter without evidence of an ongoing, intentional 

emission limit exceedance is arbitrary and capricious, 

unnecessarily punitive, and threatens the economic 

viability of the regulated sources.

• The ranges of parameters measured during source testing are 

not necessarily the only ranges within which the unit can 

operate and remain below the threshold of 10 lb/million 

tons of ore. Parametric monitoring ranges should be based 

on manufacturing specifications and permitting authority 

review. 
Page 179 of 212

• The parameters selected by EPA are not the best parameters 

for monitoring roaster emissions and do not directly 

correlate to mercury emissions or proper operation and 

performance of the mercury control system. 

• A period of 45 minutes is too short to allow investigation 

and corrective action, especially for an annual standard 

and for a complex system like a roaster. The roaster 

monitoring alternative for systems with emissions above 10 

lb/million tons of ore are allowed 48 hours for 

investigation and corrective action. 

The commenters stated that it is arbitrary that corrective 

action response time allowed for a parametric deviation, which 

may not significantly affect mercury emissions and given the 

multiplicity of control devices, would be only 45 minutes when 

the response time allowed for a deviation in mercury 

concentration is 48 hours. The commenters believe that elevated 

mercury concentrations, if verified, should be the greater 

environmental concern.

The commenters continued by stating that the corrective 

action response times of 45 minutes for parametric deviations 

and 48 hours for mercury concentration measurement following 

deviations is arbitrarily inaccurate because they do not take 

into account the time necessary for analytical procedures, data 
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assimilation and interpretation, process adjustments, data 

validation, investigation and troubleshooting, and confirmation 

that corrective action was effective.

One commenter (0342) recommended that the corrective action 

response time be extended minimally to 48 hours after daily 

average values are processed and available for review 

(presumably the next day) plus an additional 24 hours to collect 

verification data to see if the daily average parametric value 

was below the operating limit or within the required operating 

range. 

For facilities that conduct PS 12B sampling and a daily 

average parametric deviation persists for 96 hours (24 hours of 

deviation plus the 48 hours for corrective actions plus the 24 

hours allowed for verification), the commenter recommended that 

the facility be required to sample the roaster’s exhaust using 

PS 12B within the next 24 hours, then evaluate the mercury 

concentration results against the operating limit. The 

commenter stated that if the mercury concentration is below the 

operating limit, then within 10 days of receiving the analytical 

results the facility will be required to either petition the 

permitting authority for a change in the parametric limits, or 

provide the permitting authority with a compliance plan that 

details corrective actions taken to date and the plan and 
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schedule for bringing the parameter back within range (the 

compliance plan would require concurrence on the part of the 

permitting authority). The commenter said that if the mercury 

concentration is above the operating limit, the facility will be 

required to schedule an independent source testing firm to 

perform a compliance test within 45 days using one of the 

approved methods described in the rule. The commenter noted 

that the Nevada State agency requires 30 days to review the 

testing protocol, and source testing companies typically require 

30 days or more advanced notice. The commenter suggested that 

the facility may choose to test the remaining ore pretreatment 

group process units to show compliance with the overarching 

emission limit expressed in lb/million tons of ore.

For roasters where direct concentration measurements are 

not required and a daily average parametric deviation persists 

for 96 hours (24 hours of deviation plus the 48 hours for 

corrective actions plus the 24 hours allowed for verification), 

the commenter recommended that within 48 hours, the facility 

would (1) provide the permitting authority with a compliance 

plan that details corrective actions taken to date and the plan 

and schedule for bringing the parameter back within range (the 

compliance plan would require concurrence on the part of the 

permitting authority); or (2) schedule an independent source 
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testing firm to perform a compliance test within 45 days using 

one of the approved methods described in the rule. The 

commenter concluded that once the test results are received, 

calculations will be made to demonstrate emissions are below the 

threshold of 10 lbs/million tons of ore, and if not, the 

facility would be required to implement direct mercury 

concentration measurements.

One commenter (0341) requested that EPA provide an 

exception from the shutdown requirement when it can be 

demonstrated that, notwithstanding an exceedance of the 

parametric operating range, the roaster mercury emissions are 

less than the operating limit for mercury concentration. The 

commenter stated that the mercury concentration measurement is a 

more direct indication of the ultimate mercury emissions that 

the parametric monitors are designed to address. The commenter 

believes that this option will make it less likely that an 

unnecessary shutdown is triggered based on an out-of-range 

incident that does not accurately reflect scrubber performance. 

The commenter requested that EPA provide this option and allow a 

source ample time to conduct a Method 30B or PS 12B test to 

provide a more accurate assessment of scrubber performance and 

mercury emissions. 
Page 183 of 212

Response: We have investigated in greater detail the 

issues associated with monitoring roasters, and we have 

consulted with NDEP and the owners and operators of roasters to 

learn more about appropriate roaster monitoring. We understand 

that sometimes the ranges of parameters measured during source 

testing are not necessarily the only ranges within which the 

unit can operate effectively, that is why in the final rule we 

are offering two other options for establishing the ranges: (1) 

based on manufacturer’s specifications; and (2) ranges approved 

by the permitting authority. We believe that monitoring the 

scrubber flow rate, inlet gas temperature, and scrubber liquid 

chemistry, as required in the final rule, are appropriate 

parameters to monitor. We have also revised the requirements of 

this final rule to provide assurance that timely corrective 

actions are taken when a monitoring parameter is exceeded, and 

we have included requirements for testing for mercury 

concentrations to determine if the corrective actions were 

successful or if a deviation has occurred. The final rule 

includes parametric monitoring of the mercury scrubbers applied 

to roasters to control mercury. If a parameter is outside of 

the established range or limit, corrective actions are 

triggered. If corrective actions do not result in the parameter 

reading being corrected and verified within 48 hours, a mercury 
Page 184 of 212

concentration measurement (using CEMs, Method 30B, 29, OHM, or 

PS 12B) must be made to determine if the operating limit for 

mercury concentration is being exceeded. The measurement must 

be performed and the concentration determined within 48 hours 

(after the initial 48 hours, or a total of 96 hours). If the 

measured mercury concentration meets the operating limit for 

mercury concentration, the corrective actions are deemed 

successful. In addition, the owner or operator may request 

approval from the permitting authority to change the parameter 

range or limit based on measurements of the parameter at the 

time the mercury concentration measurement was made. If, on the 

other hand, the operating limit is exceeded, the exceedance must 

be reported as a deviation and the facility must conduct a full 

compliance test within 40 days to determine if the source is in 

compliance with the MACT limit. See §63.11647(d) of final rule. 

Comment: For facilities that monitor roasters with a CEMS, 

one commenter (0342) proposed that corrective action be required 

within 48 hours of receiving and processing the results from the 

CEMS data into a daily average mercury concentration for review 

(presumably by the next day), plus an additional 24 hours would 

be allowed to collect verification data to see if the daily 

average concentration was restored below the operating limit. 

The commenter recommended that if the exceedance persists, the 
Page 185 of 212

facility would be required to schedule an independent source 

testing firm to perform a compliance test within 45 days using 

one of the approved methods described in the proposed rule. The 

commenter suggested that the facility may choose to test the 

remaining ore pretreatment group process units to show 

compliance with the overarching emission limit in lb/million 

tons of ore.

For facilities that choose PS 12B monitoring, the commenter 

recommended that a deviation be considered an exceedance of the 

operating limit if the average of three consecutive sampling 

results (three weeks) were above the established limit. The 

commenter proposed that the facility would then have one week to 

take corrective actions, an additional week to take the 

verification sample using PS 12B, with receipt of results the 

following week (three weeks total). The commenter stated that 

if the exceedance persists, the facility would be required to 

schedule an independent source testing firm to perform a 

compliance test within 45 days using one of the approved methods 

described in the proposed rule. The commenter suggested that 

the facility may choose to test the remaining ore pretreatment 

group process units to show compliance with the overarching 

emission limit in lb/million tons of ore.
Page 186 of 212

Response: After considering these comments on the mercury 

concentration operating limit and the above discussion on 

parametric monitoring of roasters, we have made several 

clarifications in the final rule. If a mercury concentration 

operating limit is exceeded from either daily average 

measurements from a CEMS, continuous sampling using PS 12B, or 

from sampling twice per month (at least 11 days apart) using PS 

12B or Method 30B, the exceedance must be reported to the permit 

authority as a deviation and corrective actions must be 

implemented within 48 hours upon receipt of the sampling results 

that show the deviation. Moreover, within 96 hours of the 

exceedance, the owner or operator must measure the concentration 

again (with the CEMS, PS 12B, Method 30B, Method 29, or OHM) and 

demonstrate to the permit authority that the operating limit for 

mercury concentration has been met, or inform the permit 

authority that the limit continues to be exceeded. If the 

operating limit is still exceeded after these 96 hours, the 

owner or operator must conduct a full compliance test for the 

ore pretreatment affected source within 40 days to determine if 

the affected source is in compliance with the MACT emission 

standard. If the source is determined to be in compliance, the 

compliance test may also be used to establish a new operating 
Page 187 of 212

limit for mercury concentration. See §63.11647(a)(1)(ii), 

(a)(2)(ii), and (a)(3)(ii) of the final rule. 

Comment: One commenter (0341) requested that EPA provide 

an exception to the shutdown requirement for facilities that 

have well-controlled roasters and elect to monitor under Option 

3. The commenter believes a facility should have time (45 days) 

to demonstrate that, notwithstanding an exceedance of the 

parametric operating range that remains uncorrected for more 

than 48 hours, the roaster’s mercury emissions remain less than 

10 lbs of mercury per million tons of ore. The commenter stated 

that this would be achieved by scheduling an independent source 

testing firm to perform a compliance test using methods 

described in the rule, and when the test results are received, 

calculations will be made to demonstrate compliance with the 

limit of 10 lbs per million tons of ore. 

Response: As we have discussed above, the final rule 

relies in part on parametric monitoring of mercury scrubbers 

used on roasters to assure compliance with the applicable 

emission standards, and when the measured parametric values are 

out of the established operating range, corrective actions must 

be taken. This is no different for facilities that qualify for 

the exemption described in §63.11647(a)(5) of the final rule 

(i.e., facilities exempt from mercury concentration monitoring 
Page 188 of 212

by having demonstrated that their roaster emissions are less 

than 10 lb/million tons of ore). For these facilities, the 

final rule similarly requires that corrective actions be taken 

to restore the scrubber operating parameters to the established 

operating range. If the parameters are not restored to the 

established range within 48 hours of triggering the corrective 

actions, the owner or operator must perform mercury 

concentration sampling of the roaster emissions using PS 12B, 

Method 30B, Method 29, CEMS or OHM and determine the mercury 

concentration within 48 hours following the initial 48 hours (or 

a total of 96 hours from the time the parameter range was 

exceeded). The measured concentration must be compared to a 

mercury concentration operating limit that is based on Equation 

2 in the final rule, where the value for “Ctrap” in Equation 2 is 

based on the mercury concentration for the roaster measured 

during the most recent compliance test. If the measured mercury 

concentration meets the operating limit for mercury 

concentration, the corrective actions are deemed successful. In 

addition, the owner or operator may request approval from the 

permitting authority to change the parameter range or limit 

based on measurements of the parameter at the time the mercury 

concentration measurement was made. If the operating limit is 

exceeded, the facility must take corrective actions and report 
Page 189 of 212

it to the permit authority as a deviation. The owner or 

operator must also conduct a compliance test within 40 days to 

determine if the roaster operations are in compliance with the 

emission standard. See §63.11647(d) of the final rule. We also 

note that the requirement to shut down the roaster has been 

removed from this final rule. 

6. Monitoring Wet Scrubbers

Comment: Several commenters (0341, 0342) stated that 

monitoring the pressure drop during the performance test is not 

appropriate for autoclave wet scrubbers due to the design of 

these scrubbers, which is incompatible with a minimum operating 

limit for pressure drop. The commenters proposed that only the 

scrubber water flow rate monitoring be required for autoclave 

wet scrubbers and provided the following technical details:

The autoclave and high temperature slurry heater 

exhaust to the wet scrubber (venturi) through release 

valves. To prevent steam loss from the autoclave and 

the high pressure flash tank, the release valves on 

these vessels are kept as closed as possible. By 

limiting the release of steam from the autoclave and 

high pressure flash tank, the autoclave system can 

operate more efficiently by requiring less heat input. 

When off-gas does exit the autoclave and high 

temperature slurry heater it passes through the wet 

scrubber before being released to the atmosphere. Due 

to the small amount of off-gas passing through the wet 

scrubber, the pressure before the wet scrubber is 

typically low, resulting in a small drop in pressure 

across the scrubber. In addition, the low temperature 

slurry heater is vented downstream of the wet scrubber. 

This results in some pressure buildup at the scrubber 

outlet, which can at times result in a negative 
Page 190 of 212

pressure drop across the scrubber. Due to these unique 

design characteristics of the autoclave and associated 

wet scrubber, establishing a minimum pressure drop 

operating limit is incompatible with the process. For 

this wet scrubber, a low (or negative) pressure drop is 

an indication of low emissions because it occurs when 

there is little or no exhaust from the autoclave and 

high temperature slurry heater. Scrubber water flow 

rate, on the other hand, is compatible with the 

autoclave wet scrubber process.

Response: We understand that the operation of scrubbers on 

autoclaves is quite different from the typical and traditional 

application of venturi scrubber to control particulate matter on 

other industrial processes. For example, in other types of 

processes, the gas exhaust flow rate is relatively constant, as 

is the scrubber flow rate and pressure drop across the venturi. 

For those systems, the pressure drop is a measure of the energy 

applied to the system to achieve the desired removal efficiency 

for particulate matter. On the other hand, the autoclave 

exhaust flow rate is intermittent and not constant, it is a low 

flow compared to other types of process units, and the pressure 

drop can fluctuate significantly while the scrubber is still 

operating efficiently. We agree with the commenter that 

establishing a minimum pressure drop for scrubbers applied to 

autoclaves during the performance test is problematic. However, 

our review of the commenter’s application for a mercury air 

quality operating permit to NDEP (Phase 2 application) indicated 

that the proposed monitoring for the autoclave scrubber included 
Page 191 of 212

daily monitoring and recording of the scrubber pressure drop and 

recording any occurrences when the pressure drop was outside the 

manufacturer’s recommended operating range, and recording 

corrective actions taken if this occurs. We are including 

similar requirements for pressure drop monitoring for scrubbers 

applied to autoclaves in the final rule.

Another important consideration to this discussion of 

monitoring for autoclaves is that the beyond-the-floor analysis 

for autoclaves discussed earlier in this preamble indicates that 

significant mercury emission reductions will be required for the 

commenter’s autoclaves. We expect that it will be necessary for 

carbon adsorbers (or other additional mercury controls) to be 

installed on the autoclaves to meet the emission limits in the 

final rule based on the beyond-the-floor technology. In that 

event, monitoring the carbon adsorber according to the final 

rule requirements will be the fundamental and necessary 

monitoring for mercury controls on the autoclaves, and the rule 

would not require any monitoring of the scrubber. 

Comment: Several commenters (0274, 0341, 0342) proposed 

that only the scrubber water flow rate monitoring be required 

for wet scrubbers on the quenching circuits associated with the 

roaster. The commenters wanted to confirm that wet scrubber 

monitoring does not apply to wet scrubbers or condensers on 
Page 192 of 212

roasters. The commenter (0342) asked that EPA confirm that the 

term “wet scrubbers” does not include condensers, which are used 

throughout the mining processes for gas cooling to condense 

water or (in the case of retorts) mercury. The commenter noted 

that in many cases, chilled water is used as the cooling media. 

The commenter also asked EPA to confirm that wet scrubber 

monitoring does not apply to wet scrubbers associated with ore 

preheaters.

One commenter (0342) noted that continuous readings on wet 

scrubbers are unreliable because pressure gauges on scrubbers 

tend to become blocked, and many mines do not have continuous 

data recording capability. The commenter proposed to monitor 

the water flow rate and pressure drop once per shift, not 

continuously, and compare to the operating limit. The commenter 

noted that if any water flow rate or pressure drop reading 

exceeds the operating limit, the facility should follow the 

procedures for operating limit exceedances. The commenter 

stated that many facilities do not have Data Acquisition Systems 

capable of recording continuous data and that wet scrubbers are 

primarily used to control particulates. The commenter concluded 

by stating that wet scrubbers are not key mercury controls and 

monitoring once per shift is sufficient to maintain control 

performance on a continuing basis. 
Page 193 of 212

One commenter (0342) wanted to confirm that the limits 

established during testing would not be more stringent than the 

requirements set forth in the Standards of Performance for New 

Stationary Sources for Metallic Mineral Processing Plants, which 

allows for plus or minus 30 percent. Another commenter (0341) 

recommended that the operating limit for wet scrubber monitoring 

be based on either the lowest average value during any test run 

or as no lower than 10 percent below the average value measured 

during the test.

Response: We are clarifying in the final rule that 

§63.11647(h) applies only to wet scrubbers not followed by a 

mercury control system (i.e., carbon adsorber, calomel mercury 

scrubber, etc.). It is necessary to monitor the primary mercury 

emission control device, which is the last stage of the exhaust 

gas cleaning treatment train, to ensure it is operating properly 

and controlling mercury emissions, and the rule does not require 

that wet scrubbers in the gas treatment train (typically used 

for control of PM and/or SO2) prior to the primary mercury 

emission control device be monitored under this rule for mercury 

emissions. However, if there is no carbon adsorber or mercury 

scrubber, and the wet scrubber in question is the only control 

device for mercury emissions, the final rule requires that it be 

monitored once per shift per operating day (e.g., minimum of two 
Page 194 of 212

times per day) for pressure drop and flow rate with operating 

limits that are either established during the initial compliance 

test, from the manufacturer’s specifications, or based on 

approval from the permitting authority (except for pressure drop 

for autoclaves as discussed above). This applies to wet 

scrubbers on ore preheaters and quenching if there is no carbon 

adsorber or mercury scrubber in the exhaust gas treatment train. 

As discussed above, the scrubber monitoring for roasters applies 

to the mercury scrubber (located at or near the end of the 

exhaust gas treatment train) and does not apply to the wet 

scrubbers that are used to remove PM and SO2 prior to the mercury 

scrubber. 

We are clarifying in the final rule that condensers, such 

as those found at roasters and mercury retorts, are not wet 

scrubbers. We agree that monitoring and recording the pressure 

drop once per shift is adequate for monitoring these wet 

scrubbers to ensure they are operating properly. We disagree 

that a buffer of +/- 30 percent based on a certain New Source 

Performance Standard (NSPS) subpart is appropriate for this 

NESHAP for mercury. The comment suggesting an option of a +/-10 

percent buffer around the average value during the performance 

test has merit as an option to only using the lowest value 

during any individual run as the operating limit. If the system 
Page 195 of 212

is so stable that it shows very minimal variability during the 

performance test, we agree that it is appropriate to add +/-10 

percent to account for potential future variability. 

Consequently, we are incorporating this option in the final 

rule, as suggested by the commenter. However, we are using +/-

10 percent rather than +/- 30 percent. We are also clarifying 

for the final rule for wet scrubbers on an autoclave, that 

facilities must establish the pressure drop range according to 

manufacturer’s specifications. 

7. Carbon Adsorber Monitoring

Comment: Several commenters (0341, 0342) stated their 

concern with the proposed requirement of monitoring gas steam 

temperature at the inlet to the carbon adsorber and maintaining 

the inlet temperature below the maximum temperature established 

during the compliance test and noted that the primary purpose 

for monitoring the inlet gas stream temperature of carbon 

adsorbers is to prevent spontaneous combustion of the sulfidized 

carbon in the adsorber, not to detect excursions in mercury 

emissions. The commenters also stated that some carbon 

adsorption systems heat the gas stream prior to the carbon 

adsorber to prevent moisture buildup and/or subsequent 

condensation in the carbon, which is unrelated to the mercury 

emissions contained within the gas stream. The commenters 
Page 196 of 212

explained that the NMCP already requires that the exit gas 

temperature of condensers prior to the carbon adsorbers be 

established to minimize mercury emissions from the condenser. 

The commenters believe that an increase in inlet gas temperature 

to a carbon adsorption unit is not indicative of an increase in 

inlet gas stream mercury emissions because the high operating 

temperatures of the processes volatilize approximately 100 

percent of mercury. The commenters stated that establishing a 

maximum operating temperature for inlet gas concentrations by 

artificially increasing this temperature during compliance 

testing may destroy mercury control equipment; conflict with 

NMCP requirements and/or manufacturer’s recommended operating 

temperatures; artificially increase the reported mercury 

emissions; or artificially decrease the allowable operating 

limit for mercury concentration. The commenters concluded by 

recommending that EPA remove the requirement for monitoring the 

inlet gas stream temperature.

The commenters continued by stating that if EPA was 

persistent in requiring the monitoring of the gas stream inlet 

temperature, the maximum inlet temperature limit should be 

established by either the manufacturer’s recommendation and/or 

concurrence with the permitting authority, but not by values 

measured during compliance testing. The commenters proposed 
Page 197 of 212

monitoring the inlet temperature once per shift as an option to 

continuously monitoring the inlet temperature and comparing the

daily averages rather than the hourly averages to the operating 

limit. The commenters noted that many facilities do not have 

Digital Acquisition Systems capable of recording continuous 

data, and monitoring once per shift is sufficient to maintain 

control performance. The commenters suggested that if 

corrective action is needed, the facility should be allowed to 

sample the carbon loading to demonstrate that the effectiveness 

of the carbon adsorber has not been adversely impacted. 

The commenters recommended that if an hourly average inlet 

temperature exceeds the temperature operating limit and Method 

30B was not used during the last performance test, then the 

facility would use the mercury concentration measured during the 

last performance test for the value of “Ctrap” in Equation 3 of 

the proposed rule. The commenters stated that the concentration 

measured during the last performance test must be used in order 

to establish the mercury concentration operating limit to 

compare to the Method 30B outlet concentration measurement made 

after the temperature excursion.

Response: The purpose of monitoring the inlet temperature 

to carbon adsorbers is not to provide an indication of higher 

mercury concentrations in the inlet stream as suggested by the 
Page 198 of 212

commenters. The purpose is related to the fact that temperature 

is a fundamental parameter that affects the efficiency and 

capacity of carbon adsorbers. Generally, higher temperatures 

result in lower capacity and earlier breakthrough and, in fact, 

high temperatures are used to desorb adsorbed pollutants to 

regenerate carbon. In the extreme of temperature, the carbon 

adsorber might actually be desorbing rather than acting as a 

control device. This is particularly important for those carbon 

adsorbers applied to high temperature thermal processes, such as 

carbon kilns and melt furnaces, where it is possible for the 

exhaust temperature to rise above the normal operating 

temperature or above the temperature at which the carbon 

adsorber was designed to operate. For high temperature 

processes (such as furnaces), and not those such as 

electrowinning where the temperature may be near ambient 

conditions, we continue to require monitoring the inlet 

temperature. Owners or operators must establish an operating 

limit for temperature based on one of the following: (1) the 

maximum temperature during the initial compliance test; (2) from 

the manufacturer’s specifications; or (3) based on limits 

established by the permitting authority. If this established 

operating limit is exceeded corrective action must be taken and 

the exceedance reported as a deviation to the permit authority. 
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Further, the final rule requires facilities to monitor inlet 

temperature once per shift rather than continuously, as was 

proposed. Because inlet temperatures should not vary greatly 

over the course of an 8 to 12-hour period, we believe monitoring 

once per shift is adequate. We also conclude that if a 

temperature exceedance has occurred, the carbon bed should be 

sampled or the outlet concentration determined, depending on the 

monitoring option chosen, within 48 hours to ensure no permanent 

damage to the carbon adsorber occurred as a result of the 

deviation. We believe the temperature exceedance should be 

reported as a deviation even if the subsequent monitoring shows 

that the carbon bed is operating properly because the subsequent 

monitoring would not necessarily detect if mercury had been 

desorbed and excess emissions occurred. 

Comment: Several commenters (0341, 0342) provided specific 

suggestions for changes to the monitoring requirements for 

carbon adsorbers:

• The proposed rule only addressed a single carbon bed; 

however, it does not address carbon columns, filter packs, 

modules, and other units that are also forms of carbon 

emission controls at gold mining operations.

• Clarify or confirm that the word “top” in 63.11647(f)(2) 

refers to the “inlet” of the bed because in many cases, the 
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bed inlet is at the bottom, rather than the top, of the 

bed. The commenter recommended that the rule state “A 

representative sample must be collected from either the 

middle of the bed or collected from the top of the bed and 

the exit of the bed and analyzed using EPA Method 7471A, 

7471B, 6020, 6020A or alternate method approved by your 

permitting authority.” The added sampling location is to 

provide additional flexibility because some existing carbon 

beds or carbon columns already have sampling ports near the 

middle of the carbon adsorption system. The analysis 

methods in addition to the proposed Method 7471A are also 

for additional flexibility (e.g., Method 6020 is commonly 

used by mines for mercury analyses, and new analysis 

techniques that are more specific to this particular 

application may be developed).

• Increase the monitoring frequency from quarterly to monthly 

at 75 percent loading rather than at 50 percent loading as 

proposed.

• Define the design capacity as 20 percent mercury by weight 

(0.2 lb Hg per lb carbon), which is the default value used 

by NDEP in its NMCP permits.

Other commenters (0341, 0342) recommended that during 

Method 30B monitoring of carbon adsorbers, the sampling should 
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last up to one week instead of a full week as proposed because a 

full week could result in breakthrough of the sampling trap from 

exhaust streams with high mercury concentrations. 

Response: We are clarifying in the final rule that the 

mercury control system discussed in the comment is a “carbon 

adsorber”, which may be a fixed carbon bed, carbon filter packs 

or modules, carbon columns, and other variations as described by 

the commenters. The emissions points for which the industry 

uses carbon adsorbers are quite varied in terms of their 

characteristics and the exhaust configurations, and these 

variations result in different designs for carbon adsorbers to 

best accommodate the specific process unit.

We are clarifying the language in the final rule to use the 

terms “inlet” and “exit” rather than “top” and “bottom” for the 

reasons cited by the commenters. However, we are not making the 

other changes requested by the commenters because the monitoring 

and sampling requirements are based on the most prevalent ones 

in NDEP operating permits and in permit applications at the time 

of the proposed rule. This monitoring option is based on the 

experience of NDEP in applying it, and we do not feel it is 

necessary to make deviations in this established procedure 

without assurances that the changes would not have a potentially 

adverse effect on emissions. In the final rule, we continue to 
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require that the inlet and outlet be sampled for mercury content 

and the average results be used to determine mercury content as 

a percent of the carbon capacity. However, to accommodate other 

designs where there may be multiple carbon columns or beds, we 

are also allowing sampling of the first and last column or bed 

rather than the inlet or outlet. We are promulgating Method 

7471A as proposed because that is the method used in the NDEP 

permits, and we are not making the monitoring frequency and 

loading triggers less stringent for the same reason. (Note that 

owners or operators may request that EPA approve alternative 

methods rather than using Method 7471A.) Finally, we are not 

specifying a priority that the carbon capacity is 20 percent. 

Carbon capacity can vary with the type of carbon and is 

dependent on such factors as internal surface area, particle 

size, whether there is an impregnated chemical to improve 

mercury adsorption (such as sulfur), and if so, its 

concentration. Carbon manufacturers rely on quality control to 

ensure their product performs as designed, and the best 

information on carbon capacity for mercury is from 

specifications guaranteed by the manufacturer, which is the 

requirement for specifying carbon capacity in the final rule.
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However, we agree with the commenter that the Method 30B 

sampling should last up to a week rather than specifying a week 

for the reasons given by the commenter.

Comment: One commenter (0277) stated that EPA should not 

allow option 3 (changing out the carbon bed based on a fixed 

period of time based on historical operating experience) for 

carbon adsorber monitoring. The commenter believes that there 

is not enough data to support the method and that industry has 

problems with reporting self-monitoring and mercury levels. The 

commenter recommends that the rule require all units that are 

capable of emitting mercury, in pre-treatment and carbon 

processes, be running when the initial compliance test is done.

 Another commenter (0268) recommended deleting the 

monitoring option that is based on establishing an estimated 

life of the carbon bed because a uniform mercury loading cannot 

be predicted due to the great variability in the mercury content 

of ore.

Response: We agree with the commenters that establishing a 

change out period based on the estimated life of the carbon is 

not adequate to ensure that breakthrough does not occur earlier 

than expected. Mercury loading can change over time for many 

reasons and may be unpredictable. We retain our two monitoring 

options for carbon beds based on actual mercury measurements, 
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but we have dropped the third option because it may not result 

in carbon replacement before it is needed, and conversely, it 

could result in replacing the carbon bed before it is necessary.

Comment: One commenter (0342) asked that EPA clarify in 

63.11647(f)(3) under what circumstances a facility must reestablish the time period for changing out the carbon bed 

because the following language in the proposed rule is too vague 

and does not provide any guidelines as to what would trigger a 

reanalysis: ”if you change the process or inputs in such a 

manner that mercury emissions might increase (e.g., increase 

throughput), you must re-establish the change out period based 

on two years of historical data as described in this paragraph.” 

The commenter suggested: (1) that the triggering event for reestablishing the change out period is a significant modification 

event at a facility, (2) that when that triggering event occurs, 

the facility is required to sample the carbon at its next 

regularly schedule change out time, and (3) if the carbon 

loading exceeds 90 percent, the facility would need to reestablish the change out period.

Response: As discussed above, the final rule no longer 

allows the option that is the subject of the commenter’s 

comments.
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8. Monitoring of Multiple Units Ducted to One Stack

Comment: Commenters (0341, 0342) requested clarification 

that for facilities that have two roasters ducted together 

through a shared mercury control system, the mercury 

concentration monitoring would be conducted on the combined 

exhaust stream. The commenters also requested clarification 

that the mercury concentration operating limit for two roasters 

that share a control system would be established during the 

simultaneous operation of the roasters in order to account for 

the combined mercury emissions from both roasters. 

Commenters also requested clarification that for facilities 

with multiple process units ducted together through a shared 

carbon adsorber, the mercury concentration monitoring would be 

conducted on the combined exhaust stream. The commenters also 

requested clarification that the mercury concentration operating 

limit for a carbon adsorber for multiple units that share the 

carbon adsorber would be established during the simultaneous 

operations of all process units in order to account for the 

combined mercury emissions. 

Response: We agree with the commenters in general and have 

made the following clarifications in the final rule. If two 

roasters share a common control device and stack, the mercury 

concentration operating limit can be based on both roasters 
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operating if possible. However, monitoring for mercury 

concentration must be performed at the frequency specified in 

the final rule whether only one or both roasters are operating. 

We also have clarified that, for multiple process units vented 

to a common carbon adsorber, the mercury concentration operating 

limit can be based on all units operating if possible. However, 

the ongoing mercury concentration monitoring must be performed 

at the frequency specified in the final rule for whatever units 

are operating at the time. 

9. Monitoring Mercury Concentration in Roaster Ore

Comment: One commenter (0342) objected to the proposed 

requirement to conduct additional compliance testing if the 

mercury concentration in the ore fed to the roaster is higher 

than any concentration measured in the previous 12 months. The 

commenter stated that there would not be an increase in the 

mercury emissions from their roasters because of the extensive 

series of mercury controls, some of which operate more 

efficiently at higher mercury loadings with unchanged stack 

emissions. In addition, the commenter noted that the rule does 

not provide details on how to measure the mercury ore 

concentration or what threshold of significance would be used to 

show an increase in ore mercury content occurred. The commenter 
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concluded that the requirement would only provide extra cost and 

burden without any environmental benefit.

Response: We agree with the commenter and have removed 

this requirement (§63.11647(a)(4)(iii) of proposed rule) from 

the final rule. We have no data showing that the mercury 

content of the ore has a significant effect on the performance 

of mercury scrubbers applied to roasters, which are designed to 

handle and operate efficiently for a range of mercury inlet 

concentrations. In addition, roasters condense and recover 

elemental mercury prior to the mercury scrubber, and any 

increase in mercury loading would likely result in an increase 

in the recovery of liquid elemental mercury. We have identified 

and require the monitoring of parameters associated with the 

scrubber chemistry, and maintaining these parameters within the 

established range for which the mercury scrubber was designed. 

This monitoring approach helps ensure that the mercury scrubbers 

are controlling mercury emission independent of variations in 

ore mercury content. 

F. Miscellaneous Comments

1. Tracking the Fate of Mercury 

Comment: Over one hundred environmental group commenters 

said that all facilities should be required to provide data to 

fully account (mass balance) for mercury in all product and 
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waste streams at regulated units. The commenters believe that 

it is critical that the mercury captured by emissions controls 

are appropriately managed and stored over the long term. 

Commenters (0270, 0277) stated that the proposed rule 

should include reducing the volume of, or eliminating pollutants 

through process changes, substitution of materials, or other 

modifications and enclose systems or processes; and reduce 

mercury through the collection or treatment of pollutants when 

released from a process or stack. The commenter noted that 

mines dispose of mercury captured by control devices into 

tailings ponds where the mercury can volatize back into the 

atmosphere. The commenter believes that fugitive emissions 

(from wet heaps and tailings impoundments) are a significant 

source of mercury air emissions at some mines and that some of 

the tailings impoundments are leaky. The commenter recommends 

that the proposed rule require the mines to collect the mercury 

captured from the pollution control devices, and provide for the 

long term enclosure of this mercury where it cannot be released 

back in the environment. 

Response: The mercury that is removed by air emission 

control devices is captured as calomel from mercury scrubbers on 

roasters, adsorbed on carbon when carbon adsorption is used, or 

captured in the scrubber water from venturi scrubbers applied to 
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autoclaves. There are existing requirements for the proper 

management of these materials, either by the beneficial use or 

recovery of mercury, or by proper disposal as waste materials.

2. Costs, Economic, and Environmental Impacts

Comment: One commenter (0342) believes that EPA’s 

estimated capital and total annualized costs of emissions 

controls, monitoring, reporting, and recordkeeping are 

underestimated. The commenter stated that the estimate of 

energy requirements (2100 MW hours) is low. The commenter noted 

that the impact on small mining operations will be substantial 

and is underestimated by EPA. The commenter believes that the 

monitoring, recordkeeping and reporting requirements go beyond 

the bare minimum. 

Response: After reviewing the new cost estimates provided 

by the commenter, we agree that the estimated capital and total 

annualized costs of emissions controls, monitoring, reporting, 

and recordkeeping are underestimated. We have revised the cost 

estimates in the final rule the capital cost of emission 

controls is estimated as $36 million with a total annualized 

cost of $8 million per year. The capital costs for monitoring, 

reporting, and recordkeeping are estimated as $0.5 to $1.0 

million with a total annualized cost of $0.7 to $1.5 million per 

year, depending on the monitoring option that is chosen. We 
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have also revised the estimate of energy requirements to be 

about 12,600 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. 

3. Definitions

Comment: One commenter (0268) recommended that EPA revise 

the definition of “retort” and any reference to “retorting” to 

“mercury retort” and “mercury retorting” because the proposed 

rule is specific to this type of retort. 

Response: We agree and have made the suggested change.

4. Roasters Are Well Controlled

Comment: One commenter (0342) asked that EPA acknowledge 

that the exhaust gas flow and its interactions with control 

devices, redundancies of controls, extensive monitoring, 

equipment protection, and title V and NMCP permit requirements 

that already exist to prevent operating roasters in an 

uncontrolled state, and ensure continuation of de minimis 

mercury emissions from their Gold Quarry roaster. The commenter 

believes that there is no risk of any significant excursions of 

elevated mercury emissions for any extended period of time from 

the exhaust gas stream of the roasters at Gold Quarry. 

Response: We agree.

5. Record Keeping and Reporting 
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Comment: Several commenters (0277, 0278) stated that 

testing and monitoring reports should be made publicly available 

in a categorized and searchable database. According to another

commenter, EPA should require that records of mercury sold (as 

elemental, or calomel, tonnage, and to whom) be kept and 

available in a database similar to the one maintained by Nevada. 

The commenter believes this would allow the EPA to determine how 

many mining facilities are able to manage their mercury waste 

and would discourage the less costly route of disposing of

captured mercury in tailings facilities. 

Response: This final rule is one of the first to require 

entering test data into EPA’s WebFIRE database using EPA’s 

Electronic Reporting Tool, and this information will be publicly 

available. 

6. Technical Clarifications

Comment: One commenter (0341) noted that roasters at 

Goldstrike did not start up until 2000, not in the mid-1990s as 

the proposal stated.

According to the commenter the preamble stated that the 

retort condensers “allow some mercury to discharge in the off 

gas, and a loss of 0.4 to 0.7 percent of mercury from the 

condenser has been reported,” and then the preamble further 

noted that “all retorts employ a carbon adsorption filter 
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downstream of the condenser.” The commenter stated that is 

should be clearly noted that the gas stream from the condenser 

is not discharged directly into the atmosphere because it first 

passes through the carbon adsorption filter. 

Response: We thank the commenters for the clarifications.