Page 1 of 212 **December 1 6**  **, 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 fo r 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 Mercu ry ........................... 207Page 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
............................... 211Page 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

- 0 149 M. Brady Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 150 M.G. Miller Concer ned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 177 J. Wise Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 178 E. E. Eigbokhan Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 180 C. Redstone Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 181 A. Zeigler Concerned citizen EPA

- HQ

- OAR

- 2 010

- 0239

- 0 182 L. Johnson Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 183 J. Public Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 184 H. G. Ehrbar Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 194 C. Ralph ICMJ Mining Journal EPA

- HQ

- OAR

- 2010

- 0239

- 0 195 D. Ingraham C oncerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 196 Anonymous Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 203 Anonymous Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 204 R. F. Carter Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 205 J. Cummings Concerned citizen EPA

- HQ

- OA R

- 2010

- 0239

- 0 206 M. Warner Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 207 Mass Comment Concerned citizen; mass e

- mail campaign EPA

- HQ

- OAR

- 2010

- 0239

- 0 208 Chris Ralph ICMJ Mining Journal
EPA

- HQ

- OAR

- 2010

- 0239

- 0 209 J. Saunders Concerned citizen; mass e

- mai l campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 210 L. Lamberth Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 211 M. Sage Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 212 M. Engelman Concerned citizen; mass e

- mail campaign
EPA

- HQ

- O AR

- 2010

- 0239

- 0 213 M. McLaughlin Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 214 M. Donian Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 215 M. Hauck Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 216 N . O. Rolon Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 217 P. Matejcek Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 218 P. Rizzo Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 219 A. Fulmer Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 220 P. Chaiken Concerned citizen; mass e

- mail campaignPage 4 of 212 Docket Item Commenter Affiliation
EPA

- HQ

- OAR

- 2010

- 0239

- 0 221 R. J. Goff Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 222 R. Tafanelli Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 223 R. Kofler Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 224 R. Bienek Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 225 S. Ecolano Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 226 S. Anderson Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 227 S. Roth Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 228 S. Bragg Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 229 S. Lacy Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 230 A. Sherwood Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 231 T. Palmer Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 232 T. Kelley Concerned citi zen; mass e - mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 233 V. Brandt Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 234 C. Mead Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 235 J. Gintzler Concerned citizen; mass e

- mail campa ign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 236 M. A. McDonald Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 237 M. Reed Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 238 B. Deckard Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 20 10

- 0239

- 0 239 B. Feiss Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 240 B. Johnson Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 241 C. Brady Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 242 C. Okstel Concerned citizen; mass e

- mail campaign EPA

- HQ

- OAR

- 2010

- 0239

- 0 243 R. Grimmer Concerned citizen
EPA

- HQ

- OAR

- 2010

- 0239

- 0 244 C. Ralph ICMJ Mining JournalPage 5 of 212 Docket Item Commenter Affiliation
EPA

- HQ

- OAR

- 2010

- 0239

- 0 245 A. Dattner Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 246 C. Boehle Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 247 D. Splisbury Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 248 E. Rodgers Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 249 F. De Nicola Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 250 I. Cree Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 251 J. Klein Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 252 J. G. Garey Concerned citizen; mass e - mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 253 J. Netson Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 254 A. Berenzy Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 255 G. Stradtman Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 256 J. Archuleta Concerned citizen; mass e

- mail campaign EPA

- HQ

- OAR

- 2010

- 0239

- 0 257 Anonymous Concerned citizen

EPA

- HQ

- OAR

- 2010

- 0239

- 0 258 Sharon G. Cox On behalf of Steven C. Borell, Executive Director, Alaska Miners Association ( AMA)

EPA

- HQ

- OAR

- 2010

- 0239

- 0 259 Kevin Pylka Manager Environmental Permitting and Compliance, Polymet Mining

EPA

- HQ

- OAR

- 2010

- 0239

- 0 260 Sharon G. Cox On behalf of Steven C. Borell, Executive Director, Alaska Miners Association, Inc. EPA

- HQ

- OAR

- 2010

- 0239

- 0 261 C. Lish Concerned citizen
EPA

- HQ

- OAR

- 2010

- 0239

- 0 262 Rob Dubuc Staff Attorney, Western Resource Advocates EPA

- HQ

- OAR

- 2010

- 0239

- 0 263 G. Bloss Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 264 S. Ogata Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 265 Anonymo us Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 266 Anonymous Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 267 J. Varner Concerned citizenPage 6 of 212 Docket Item Commenter Affiliation

EPA

- HQ

- OAR

- 2010

- 0239

- 0 268 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

- 0 269 Benjamin L. Brandes Director, Air Quality, National Mining Association EPA

- HQ

- OAR

- 2010

- 0239

- 0 270 Bonnie Gestring Earthworks

EPA

- HQ

- OAR

- 2010

- 0239

- 0 271 John R. Jacus Attorne y, Davis Graham and Stubbs LLP, on behalf of Great Basin Gold Inc. and Rodeo Creek Gold, Inc.

EPA

- HQ

- OAR

- 2010

- 0239

- 0 272 Glenn C. Miller Professor, Department of Natural Resources and Environmental Science, University of Nevada

EPA

- HQ

- OAR

- 2010

- 0239

- 0 273 F rank Ongaro Executive Director, Mining Minnesota

EPA

- HQ

- OAR

- 2010

- 0239

- 0 274 Michael J. Tomko Parsons Behle and Latimer on behalf of Barrick Goldstrike Mines, Inc. and Barrick Cortez, Inc.

EPA

- HQ

- OAR

- 2010

- 0239

- 0 275 Alice Edwards Acting Director, Division of Air Quality, Alaska Department of Environmental Conservation
EPA

- HQ

- OAR

- 2010

- 0239

- 0 276 S. Sanderson President, Colorado Mining Association (CMA)

EPA

- HQ

- OAR

- 2010

- 0239

- 0 277 Brook M. Brisson Clean Water and Mining Program Director, Northern Alaska Envir onmental Center (NAEC)
EPA

- HQ

- OAR

- 2010

- 0239

- 0 278 K. Zamzow Center for Science in Public Participation

EPA

- HQ

- OAR

- 2010

- 0239

- 0 279 Luke Russell Vice President Environmental Services, Coeur d'Alene Mines

EPA

- HQ

- OAR

- 2010

- 0239

- 0 280 Peter O'Connor Vice Pres ident Environmental Law & Government, AngloGold Ashanti North America Inc. (AGANA)
EPA

- HQ

- OAR

- 2010

- 0239

- 0 281 D. Chambers Center for Science in Public Participation (CSP2)
EPA

- HQ

- OAR

- 2010

- 0239

- 0 282 Justin Hayes Program Director, Idaho Conservation Leagu e EPA

- HQ

- OAR

- 2010

- 0239

- 0 283 James Pew Sierra Club and EarthjusticePage 7 of 212 Docket Item Commenter Affiliation

EPA

- HQ

- OAR

- 2010

- 0239

- 0 284 Kendra Zamzow Center for Science in Public Participation (CSP2) on behalf of Joel Reynolds, Solutions Statistical Consulting (SSC)

EPA

- HQ

- OAR

- 2010

- 0239

- 0 285 Mi chael J. Tomko Counsel, Parsons Behle & Latimer on behalf of Kinross Gold USA, Inc.
EPA

- HQ

- OAR

- 2010

- 0239

- 0 286 C. Cullen Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 287 D. Inouye Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 201 0

- 0239

- 0 288 J. Wheeler Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 289 M. Santarelli Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 290 M. Bresnan Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 291 B. Pelts Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 292 M. Rausch Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 293 M. Heaviland Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 294 D. Conrey Concerned ci tizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 295 A. Nowak Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 296 E. McCabe Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 297 E. Kompanek Concerned citizen; mass e

- mail ca mpaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 298 N. Bartol Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 299 R. DeWald Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 300 R. Krousoff Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2 010

- 0239

- 0 301 D. Hudson Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 302 E. Pearlman Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 303 R. Rutemoeller Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 304 G . Goffe Concerned citizen; mass e

- mail campaignPage 8 of 212 Docket Item Commenter Affiliation
EPA

- HQ

- OAR

- 2010

- 0239

- 0 305 G. Fairbanks Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 306 G. Wingard Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 307 H. Savage Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 308 R. Lauster Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 309 D. Diegoli Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 310 A. Rapalyea Concerned citizen; mass e

- m ail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 311 A. Page Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 312 D. Deming Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 313 D. Mack Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2 010

- 0239

- 0 314 D. Schmitt Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 315 Dr. D. Kyte Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 316 E. Mosimann Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 317 H. Carr Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 318 H. Peach Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 319 J. Carter Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 320 J. Unruh Concerned citizen; mass e - mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 321 J. Allen Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 322 J. and V. Wagner Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 323 J. Eakins Concerned citizen; mass e

- mail cam paign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 324 K. Ramsey Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 325 AC 6.30 54 Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 326 M. Kelner Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 201 0

- 0239

- 0 327 S. Buesing Concerned citizen; mass e

- mail campaignPage 9 of 212 Docket Item Commenter Affiliation
EPA

- HQ

- OAR

- 2010

- 0239

- 0 328 T. Robinson Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 329 T. Kane Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 330 B. Campbe ll Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 331 V. Phillips Concerned citizen; mass e

- mail campaign

EPA

- HQ

- OAR

- 2010

- 0239

- 0 332 Mark Compton Manager, Government Affairs on behalf of Laura Skaer, Executive Director, Northwest Mining Association (NWMA)
EPA

- HQ

- OAR

- 2010

- 0239

- 0 333 V. Olson Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 334 W. Evans Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 335 W. Davis Concerned citizen; mass e

- mail campaign
EPA

- H Q

- OAR

- 2010

- 0239

- 0 336 B. Dickinson Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 337 C. Jackson Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 338 C. Harris Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 3 39 C. Lawrence Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 340 K. Nezelek Concerned citizen; mass e

- mail campaign
EPA

- HQ

- OAR

- 2010

- 0239

- 0 341 T. Crowley President, Nevada Mining Association

EPA

- HQ

- OAR

- 2010

- 0239

- 0 342 Denise Kennedy Holl and & Hart LLP on behalf of the Newmont Mining Corporation EPA

- HQ

- OAR

- 2010

- 0239

- 0 343 Anonymous Concerned citizen
EPA

- HQ

- OAR

- 2010

- 0239

- 0 344 Ryan Deshon President, A&B Prospecting Supplies, Inc. EPA

- HQ

- OAR

- 2010

- 0239

- 0 345 S. Justice Concerned citizen EP A

- HQ

- OAR

- 2010

- 0239

- 0 346 R. Maddox Concerned citizen
EPA

- HQ

- OAR

- 2010

- 0239

- 0 347 A. Buster Concerned citizen; mass e

- mail campaign EPA

- HQ

- OAR

- 2010

- 0239

- 0 348 L. Brown Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 349 A. Evenson Concerned citizen EPA

- HQ

- OAR

- 2 010

- 0239

- 0 350 S. D. Barry Concerned citizenPage 10 of 212 Docket Item Commenter Affiliation

EPA

- HQ

- OAR

- 2010

- 0239

- 0 351 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

- 0 352 N. Pastos Concerned citizen
EPA

- HQ

- OAR

- 201 0

- 0239

- 0 353 C. Wassilie Concerned citizen; mass e

- mail campaign EPA

- HQ

- OAR

- 2010

- 0239

- 0 354 A. Jackson Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 357 J. and K. Mitchell Concerned citizen EPA

- HQ

- OAR

- 2010

- 0239

- 0 358 B. Whittenberg Concerned citizenPage 11 of 212 **1. Listing of the Gold Mine Ore Processing and Production**  **Source Category Under Section 1**  **12(c)(6) A.**  **Statutory Requirements**

**Comment :**  Several commenters (0277, 0282, 0283) stated that adding the gold mine ore processing and production category to the li st 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 bePage 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 subj ect 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 pro duction 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 limi ted 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), how ever, 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 purpos e 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 i n 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 sp ecified 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 i nitial 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 a n 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 concernin g 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 mee t 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

resu lt 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 precl udes 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 E PA 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. Ca lc**  **ulation of Mercury Emis sions 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 1990Page 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 20 10, 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 sec tion 112(c)(6), the A gency 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 ofPage 17 of 212 the Emission Standards Division sent a memorandum 1

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 tha n 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 t he 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 “currentl y 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 atta ched a m emo 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 N evada 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

n ational 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 well

controlled when EPA still has not met its obligation to issue standards for thos e sources listed more than 10 years ago. **Response :**  As explained above, w e 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 fo r 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 fromPage 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., Alas ka). 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 Standa rds for HAP Other**  **t han 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 commenter s 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), EP A 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)). ThePage 20 of 212 commenter s 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 commenter s said that EPA appears to believe that because gold mines are needed only to reac h 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 commenter s said that secti on 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 emissi on standards for each HAP that a source category emits. The commenter s continued by stating that nothing in the CAA exempts EPA from this requirement. The commenter s concluded that, had Congress wished to give EPA discretion to set standards for only som e 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 spec ified in that section, EPA mustPage 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 be cause 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 liste d source categories must address all HAP or only the section 112(c)(6) HAP for which the source category was listed. Section 112Page 22 of 212 (c)(6) requires that “sources accounting for not less than 90 per centum of the aggregate emissions of each such [specific]
po llutant 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 pro vision 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 emit s 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

r equired 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 categor y 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 gen erally 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 ob ject of section 112(c)(6), which is control of the specific persistent, bioaccumulativePage 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, sin ce 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 sec tion 112 must be subject to MACT standards for all HAP emitted from the source category consistent with National Lime

. **:** Several commenter s (0270 , 0283 ) stated that it is well known that gold mines have significant fugitive emissions

o f mercury and other HAP , but that EPA did not propose standards for these emissions or mention them in its p roposal. The
commenter s 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

ca tegory. The commenter s 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 commenter s , EPA may not choose to setPage 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 commenter s 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 commenter s 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 e mission 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 commenter s stated that means to control fugitive emissions are available, suc h 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 commenter s (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 commenter s recommended that EPA evaluate the use of sulfur

- based complexing agents, such as dimethyldithiocarbamate orPage 26 of 212 diethyldithiocarbamate, for removing mercury during cyanidization of gold. According to the commenter s , research indicates that these products appear useful for substan tially 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 th e 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 minin g disturbances are approximately 20 percent of the total mercury emitted. C ommenter s 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

em issions are not part of the source category we are listing and regulating in this final rule. Other than the recentPage 27 of 212 preliminary research at two facilities, we have no data on fugitive mercury emissions at gold mine facilities. The recent preliminary rese arch 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 publis hed 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 c ompounds 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 impa cts 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 leac hing 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 ope rations (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 s ource 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 a ny 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 cyan ide (HCN) at a few facilities are near the major source threshold. The commenter continued by saying that “by basing its evaluationPage 29 of 212 of whether gold mines are major sources on their actual emissions instead of their potential emissions, EPA violates both t he 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 arb itrary 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 “manageme nt 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,” “restrictio ns 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 aPage 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 a pproximately 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 s tandards. 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
commenter s 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 sol ution 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 thes e work practice standards and the annual TRIPage 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 propose d 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 calcul ations 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 wi thout applying the surface area correction factor, and those calculations resulted in a conservative potential to emit estimate of 9 tons of HCN perPage 32 of 212 year for the largest source. The emission estimates for the remaining large facilities were all below 9 ton s. The commenters correctly point out that i n 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 no t 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 tp y 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, madePage 33 of 212 only co nclusory 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 emi t 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 e missions 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 i ssue 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 Internati onal 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 sugges ts that the facilities would be major sources if they failed to employ the management practices. Accordingly, we are taking finalPage 34 of 212 action today to list the gold mine ore processing and production area source category and regulate its mercury emissions purs uant 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 bel ow 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 capri cious. **Response** : W e 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.
I n 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 mea n 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 bestPage 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 calcula tion, 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 saidPage 3 6 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 se ction 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 appl y 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) f or 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 establis h 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 aPage 38 of 212 “permissible” reading of t he 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 contai ned 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) sh ould 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 liste d 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 andPage 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 proce ssing 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 emiss ions 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

- controlle d 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 effectivenessPage 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 controll ed 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). S ection 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 provisio n ] **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 le gislative 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 wou ld 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 p rovides 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 interpret ation 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 obta in a title V permit. **:** In the proposal preamble, EPA solicited comment on whether a tit le 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 no t 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 permitti ng 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 madePage 43 of 212 that compliance with title V would be “unnecessarily burdensome.”

The comme nter 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 sai d 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 permittingPage 44 of 212 i nformation 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 ou tweigh 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 standa rds. 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 comment er points out that major sources of criteria pollutant emissions are currentlyPage 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. I n addition , the N MCP 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 s ubpart EEEEEE not require that all gold mine ore processing and production facilitie s 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 tit le 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 A gency discretion, and the commenters be lieve 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 aPage 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 ex e mption. In discussing the first factor of the Exemption Rule, whether title V would result in significant improv ements 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. T hus, 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 source s 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 NE SHAP 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 req uirements 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 notif ication 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 Exemptio n 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. ThePage 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 g uidance 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 submittin g 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 an d 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 byPage 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 f actor 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

a ny 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 substantia l 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 witho ut 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 t hat 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 ar ea sources for the gold mine ore processing and production are already permitted under State permit programs. According to the commenters, all non

title V sources in Nevada are required to hold “Class II” operating permits that must contain, among other t hings, 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 t he 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

so urces 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 ofPage 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, pain ts 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 cert ain 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 in dustrial, 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 techn ology 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 morePage 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
comment ers 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 S tate 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 potent ial of adversely affecting public health, welfare, or the environment by shifting State agency resources away from ensuring compliance with a program t h at 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 unnecessarilyPage 53 of 212 burdensome, and at a minimum, EPA should exempt area source gold mines that are subject to Nevada’s comprehensive mercury control
pr ogram 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 exclus ively 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 subjecti ng 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 sourc e 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, multi

national, corporations. Therefore, we conclude that the argument of financial burden, which has supported ti tle V exemption for other source categories, does not apply to the gold mining industry (see E conomic 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 t he 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 a re more facilities in Nevada that will be subject to the final rule, as thePage 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 Provisio**  **ns 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 explain ed that the regulatory requirements of 40 CFR part 63, subpart D outline a process at the S tate level for section 112 delegated programs for demonstration of a 90 percent reduction from a baseline emi ssions estimate. The commenter expects that Nevada will receive expedited delegation of this proposed NESHAP, and the commenter requests clarification that Nevada gold miningPage 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 commenter s ( 0341 , 0342 ) believe that EPA’s rule will have federalism issues concerning the trust between S tate air agencies and the EPA. The commenter s 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 supporti ve of the program and would not promulgate MACT standards if the NMCP was adopted and implemented. The commenter s believe that if a S tate cannot rely on EPA’s representations, as an agent of the federal government,
S tates like Nevada will be much less wil ling to step up and commit necessary resources to address a problem in a timely and efficient matter. The commenter s concluded that not only is this detrimental to the cooperation required between federal andPage 57 of 212 S tate government for successful government ope ration and notions of federalism, but it is detrimental to the environment, because it creates a disincentive for S tates (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 proc ess, 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 separ ate 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 appropr iate 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 Par tPage 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
reconstruc tion 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 e ncompassed 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 c onstitute 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 comme nters provided three examples and said that consideration of whetherPage 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 replaceme nt 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.
Ac cording 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 c ommenters 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. ThePage 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 tha t 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 c ommenters, 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 the y 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 reasonab le 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 reason able” ( citing 66 FR 16322, MarchPage 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 feasib le 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 c ontrol 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 bec ause 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, elect rostatic 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 followin g 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 consider ed 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 nonaffecte d 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 f or 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 re levant 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 collecti on 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 a ll 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 wou ld 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 a n 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 fixe d 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 pr ocesses. 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 neces sity to provide criteria for this final rule that are different from the requirements in the General Provisions for determining what constitutes aPage 65 of 212 reconstruction. We also think it is appropriate to exclude the cost of emission control equipment from the c ost 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

ur ged 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 ex emptions 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 numbe r 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 categ ory 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

we re 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 defin ed 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 contra st, 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 operati ons. 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
concentrat e 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 commenter s ( 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 facil ity.Page 68 of 212 commenters s aid 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. T he 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 Go ld 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 poi nt 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 commenter s ( 0283, 0284) acknow ledged 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 le vel. The commenter s claim such an approach ignores the reality thatPage 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 99 th percentile), that does not mean that a well

operated 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 co ntrol measures, but also use those control measures consistently to minimize emissions. The commenter s 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 commenter s believe that those dicta have no precedential value and do not bind EPA’s rulemaking in any way. In addition, the commenter s stated that the underlying

as sumption, 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 hi gher levels if it is not run properly. According to the
commenter s , the high emissions that occur when a source is poorly operated should violate emission standards, even thoughPage 71 of 212 it is “foreseeable” that periods of sloppy or negligent operation may occur e ven at the source with the lowest emission tests. The commenter s 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 appro ach violates section 112(d)(3). The
commenter s 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 commenter s s aid 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 explana tion 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’ perfor mance 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 variat ions 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 t he best performing sources).

4

4 Run

- to

- run variability is essentially within

- test variability, a nd 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

v ariance 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 be st 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) c alculated 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 observati ons (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 testPage 74 of 212 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

- tes t 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 exceed ing 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 lo wer 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); s ee also 70 FR at 59438 (Oct. 12, 2005)Page 75 of 212 (ex plaining 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 incor rect. 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 f ive 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 t he 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 mate rials)
. 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 emis sions, 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 stand ards 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 prov ide 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 th ese 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 addit ional data from test reports not available at the time ofPage 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 **.** T herefore, 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 perfor mers 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 fa cilities (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 limitPage 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 w as 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 prec edent. 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 calcu lations 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 usePage 79 of 212 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 measur es are applied consistently to minimize emissions.
**Comment:** Several commenter s (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 s ource - 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 commenter s said this is a fundamental d ifference between setting a prediction interval or a tolerance interval. According to the commenter s , setting the floor at a level that the best performing source can meet every day and under all operating conditions requires estimating the distribution o f possible emissions rates from that source's production process and setting the threshold just beyond the maximum possible emission rate. The commenter s stated that this is an impossible standard to quantify, and it requires assuming a specific mathemati cal distribution as an adequate description of the emissions rate distribution. The commenter s claim that even then, most common feasible mathematical distributions havePage 80 of 212 infinite upper thresholds, and the floor would logically be set to infinity, an oper ationally useless threshold. The commenter s 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 commenter s recommend accounting for the uncertainty in this estimate by providing an interval estimate, or specifically, a tolerance interval that brackets a portion o f the full population distribution, such as the smallest 99 percent of the population of emissions rates from this source. Thus, concluded the commenter s , a one - sided upper 99 percent tolerance interval with 95 percent confidence is a threshold expected w ith 95 percent confidence to be exceeded by only 1 percent of the observations from the emissions rate process. The commenter s 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 commenter s interpret the approach used in the proposal as setting the objective to estimate a threshold under which the nex t source's estimated total emission rate will liePage 81 of 212 and to estimate it with 99 percent confidence (i.e., a 99 percent prediction interval). According to the commenter s , past EPA practice appears to have adopted prediction intervals, while the tolerance inte rval 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 commenter s 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 commenter s also stated that the choice of a 99 percent confidence level appears arbitrary and capricious, and very sound argumen ts could be made for a precautionary approach using 97.5 percent, 95 percent, or even 90 percent. The commenter s believe that a 99 percent level places much greater emphasis on avoiding “Type I” errors of accidentally claiming a source is “out of complian ce”, which makes it necessary to accept a much higher emission rate as “in compliance.” The commenter s 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 175Page 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., 99 th percentile) is expected to lie with a stated level of confiden ce. 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 99 th 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 set s and proportions close to 100 percent, the sample percentile typically underestimates the corresponding population percentile. Therefore, the UTL is ordinarily u sed 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 who se 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 actu al 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 t est runs that are averaged to determine compliance) from 3 toPage 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 estima te 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 mate rials, 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 select ion 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 rulemaking s , 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 measure ment 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 compl i ancePage 86 of 212 t e st 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 mo nitoring of control devices provide a means of ensuring continuing compliance for those periods of time when manual stack testing is not perf ormed
. 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 th e 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. I f the measures of variability of the top performing sources are similar, th e n this would be an appropriate approach; however, if they are not similar, then this wou ld not be an appropriate approach. A test to check thePage 87 of 2 12 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 t o 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 beli eve 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 commenter s (0278 , 0281 ) stated that consideration should be given to defi ning the inherent range of measurement error and to requiring more runs in order to reduce variability due to process variation. The commenter s said that this would also better clarify when variability was due to operational controls, which could be addre ssed, rather than due to factors that cannot be controlled, such as mercury content in the ore. The commenter s noted that one set of dry grinding/preheater data shows an order of magnitude difference across each of the 3 runs. The commenter s asked for cl arification on how inconsistent runs should be treated, whatPage 88 of 212 defines an acceptable set of runs, and at what point would more runs be required to provide reliable data. The commenter s 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
commenter s pointed out that for new carbon process sources, the variability is much lower than the variabilit y 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 commenter s believe that th e 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 commenter s

recommended that if EPA continues to use Goldstrike as the best performing source for new source MACT, then they should re

evaluate and reduce the variability to be equal to or less than the variability for existing sources. **Response:** We agree with the comme nter that the testing process would be more accurate if the number of test runs was increased. However, we balance several factors in determiningPage 89 of 212 the minimum number of runs required, and because the compliance testing is supplemented by various types of c ontinuous 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 rev iews 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

ru ns, 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 o f 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 non

carbon concentrate processes. We agree with the commenterPage 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., aut oclaves) 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 te sts 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 t he 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 MAC T 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 commenter s (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 ofPage 91 of 212 ore, but the floor limit for new sources wa s 163 lb/million tons of ore ( 250 percent higher ) , and even the proposed beyond

- the

floor limit wa s 149 lb/million tons of ore ( 200 percent higher )
. The commenter s 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 c ommenter s recommend ed an alternative efficiency standard based on a minimum 99 percent mercury removal. The commenter s believe that an alternative efficiency limit would be appropriate for mines that have lower mercury concentrations in the ore because ot herwise they w ould not be held to the same level of emissions control as mines with high mercury concentrations in the ore. The commenter s concluded that mines should have to meet either a throughput

- based emission limit or the efficiency

- based emission l imit, 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 howPage 92 of 212 exactly facilities would demonstrate compliance. Mo reover, 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
ag ency (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 pursuan t to section 112 of the Act. Each relevantPage 93 of 212 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 controlli ng 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 facilitie s that are the basis for the MACTPage 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 emis sion 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 facili ties 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 thePage 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 comment er s ( 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. T he commenter s 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 inspector s 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 thr ough 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 thePage 96 of 212 proposal. On the other hand s everal 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 emissio ns. 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.
Ac cording to the commenter s , 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 tempera ture 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 differentPage 97 of 212 affected s ources, 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 th at 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 equipme nt, 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:** Se veral commenter s (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 commenter s cl aim that EPA has a statutory obligation to ensure that its new source standards reflect thePage 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 evalua te 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. C ommenter s (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 commenter s stated that the beyond

the

- floor st andard 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 thanPage 99 of 212 0.6 lb/MM tons to reflect a 99.5 percent reduction or 6 lb/MM tons to reflec t a 90 percent reduction). The commenter s 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 commenter s 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 l evel that is achievable after a 99.5 percent reduction from floor levels. The commenter s 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 commenter s also stated that EPA provided no reason to explain why it needs to add a nother 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 th at already has been inflated to accountPage 100 of 212 for variability. The commenter s 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 inves tigate 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 facili ty 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 wit h 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 refrigerat ion 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 the ir 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, wePage 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 mer cury. 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 th at this is an acceptable beyond

- the

- floor control technology for existing roaster preheaters/ore dryers. Therefore, we included the beyond

- the

floor control for ore preheaters/dryers, as well as the beyond

the

- floor control for autoclaves, in determining the MACT standard in this final rule for existing sources of ore pre

treatment 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 menti oned 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 analys is because we did not identify aPage 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 commenter s ( 0 274, 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 carbo n adsorber on autoclaves. One commenter (0342) note s 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 explain s that they contin ued 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 f rom $2 million to $60 million, depending on which controls, if any, are determined to be technically feasible. The commenter believesPage 104 of 212 that based on these cost estimates, beyond

- the

- floor MACT controls would be cost prohibitive and are not justified for th e 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. OurPage 105 of 212 revised estimates are that the capital cost f or 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 ne w 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

so urce 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 proce ssed inPage 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 describe d 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
auto claves (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 e stimate 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 C ourt 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 quantiti es 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

s ection 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, a nd 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 inp uts, 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 cons ider 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

r esult 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 Facil ity M isPage 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 requir ed 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 f or 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 chara cteristics 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 d o not use retorts to process concentrate, then they should subcategorize them. The commenter explain ed that thePage 110 of 212 subcategorization should be based on ore and process differences that would fit within EPA’s authority to distinguish among “classes” and “type s” 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 re

examination of the design of the facilities at issue, the emission controls, and other factors affecting emissions from the carbon processes at Facility M, we agr ee 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 mercur y 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 with out 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 th ose, 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 emiss ion 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 with out 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 mercu ry. 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 beyond

the

- floor options for new carbon proces ses without mercury retorts, but concluded these options were not cost

- effective orPage 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 pa rt 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 proposa l. Two facilities with newly

installed 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 withPage 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 op tions 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 emissi on 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

re duction 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 S everal commenter s ( 0341 , 0342 ) supported EPA’s use of the percent control alternative to the new source MACT for the carbon group. The commenter s 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 gr oup. The commenter s 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 commenter s ( 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 commenter s 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 commenter s stated that EPA took t he 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 commenter s claimed that emissions reductions are significantly higher the first year after control technology is newly

- installed than they are inPage 115 of 212 subsequent years, and this skews the data. The commenter s recommended that in order for this compliance alternative to be representative of controlled emissions at the source, EPA should, a t 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 ha s 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 perfo rmed 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 withPage 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 ope rate 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 t he 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 commenter s (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 rev iewing 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 differe nt 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 r eduction 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 proces ses 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 i s 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 th at beyond the floor controls would be prohibitively costly for the carbon process group. The
commenter s 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 t ype 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 adsor bers 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 indus try recommended that the compliance deadline for existing sources be three years after the effective date of the rule, not the twoPage 119 of 212 years as proposed. The commenters noted that several facilities will have to install control devices to achieve the MACT flo or 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 des igning, 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 n ew 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 estab lished 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. Secti on 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 thre e 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 conduc t 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 t hat the proposed rule be revised to require initial testing within 12 months of the compliance datePage 122 of 212 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 determin e 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

annu al 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 yea r 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 cond ucted 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. Howeve r, 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 c ompliance 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 comp liance 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 compliancePage 124 of 212 determinations will also be occurring at different times througho ut 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 rul e 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 cale ndar 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 duringPage 125 of 212 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 calend ar 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 iden tify 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 c ompleted 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 a nd 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 s ource is in compliance in a timely manner. (This is consistent with the way compliance determinations are made in another MACT rule that uses a similarPage 126 of 212 format

- National Emission Standards for Hazardous Air Pollutants for Primary Lead Smelting, 40 CFR par t 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 h ave 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.
Mo reover, 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 Ne vada State Phase 2 permits are (or will be) based on concentration in the stacks (e.g., micrograms per cubic meter (μg/m 3 )). 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 conce ntrate. 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 determin ation 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 p rovide 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 proble m 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 mo nths 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 probl em for the permittingPage 128 of 212 authority because that is the case for many other source categories subject to annual compliance testing.
**Comment:** Several commenter s (0341 , 0342 ) asked for confirmation of the basis for compliance determinations relative to part ial calendar months and suggested that the compliance period would be based on full calendar months. The commenter s 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 commenter s and have clarified in the final rule that the production data used in the compl iance 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 month s prior t o 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 b e determined before sampling isPage 129 of 212 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 de termine 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
concentrat ions, 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 demonstrati ng 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 speci fying 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 t ime 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 thePage 131 of 212 outlet lower than expected. If the emission testing results for any of the emission points yield a non

- detect value, the n 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

r esulting 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

resu lts 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., the re 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 sourc e 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 ),Page 132 of 212 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 2 9 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 stil l 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 ch ances 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 dscfPage 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 requir ed 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 vo lume 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 f inal rule does not require any sampling at the inlet to the mercury emission control device.Page 134 of 212 **Comment:** Several commenter s (0341 , 0342 ) noted that there are acetone rinse procedures, cyclonic flow testing procedures, and specific requirements on the numbe r of test runs, test run duration and sample volume in addition to the required EPA reference test methods. The commenter s recommended that these additional test procedures be removed because the proposed test methods already contain the testing procedure s necessary to measure emissions. The commenter s 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 i n 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 re quiring 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 proposa l, we requested comment on the possible use of carbon rather than c oncentrate 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 pr ocessed 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 reporte d 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 b elieve 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) u sing aPage 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 moistur e 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 quanti ty 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 t ested 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 t he 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 te stingPage 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 ki ln 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 fl oors 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 prom ulgating the methodology as proposed.Page 138 of 212 **5. Compliance Calculations and Procedures**
**Comment:** Several commenter s (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 comment er s 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 formula s provided in the pro posed 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 t hree 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 lan guage from “hours” to “one

- hour periods.” Several commenter s (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 commenter s explai ned that this change would allow the flexibility to monitor the density and volumetric flowPage 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 ox idized 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 average d 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 agr ee 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 madePage 140 of 212 the change requested by the commenter to ensu re 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
sug gested 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 sh ould 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 startPage 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 electrowi nning, 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 dete r mi ned 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 e mission 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
op erator 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 determina tion. As an alternative, the operator may perform multiple tests with units operating in the various modes thatPage 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 wer e 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 stan dards

– even if that test showed that the source likely violated its emission limit on an ongoing basis throughout the year. GivenPage 143 of 212 that the penalties for a single violation of emission standards are capped by the CAA, the commenter believes that the propo sal 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 comment er 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 n ot 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; ho wever, 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 toPage 144 of 212 operat ing 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 al l 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 w ill 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 compl iance 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 compliance

based 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 adequat e 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 a pproach 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 hasPage 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 appropr iate 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 de vices 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 do es 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 allPage 147 of 212 these other units would be quite costly and burdensome. Moreover, most of these other units are, or will be, control led 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 b reakthrough 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 p roperly 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 suff icient 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 commente r 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 no t 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 wouldPage 149 of 212 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 emi ssion 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 tha t 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 th e different facil i ties be cause of differences in the desi gn 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 c oncentration limits forPage 150 of 212 certain combustion units, and they are acceptable for combustion units because the results can be adj usted to 7 percent oxygen to account for dilution and provide a uniform standard
. When
oxyg en levels are at or near ambient levels, an oxygen correction factor is ineffective at detecting and ac c ounti ng for dilution. Also note that concentration is not a direct measure of emissions; emissions must be calculated by multiplying concentration by t he 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 o ur 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 develop ing 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 o perating limits for roasters and for carbon adsorbers are inappropriatePage 151 of 212 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 aff ects 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 ch ange 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 re commended 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 thePage 152 of 212 permitting authority and not based on values measured during source compliance testing. **Response:** We proposed the me rcury 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 emissio n 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

no tification 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
ope rators 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 2 12 Regarding specific comments about monitoring the carbon ad sorber, 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. T his 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
appro ach 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 prov ide 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 man ufacturer specifications and/or inPage 154 of 212 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 as sociated 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 tha t 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 requirin g 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 als o 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 e xperience of the permit authority with addressing these sources. Therefore, this final rule allows three options for establishing parameter limits: (1) based onPage 155 of 212 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 c ommenters 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 commenter s 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 n either improve the operation of these current controls, nor is it likely that mercury emissions would be significantly improved. The
commenter s concluded that the operating parameters monit ored 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 optimumPage 156 of 212 ranges ensures that mercury emissions are being effective ly 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 th e 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

an d 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 conti nuous 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.Page 157 of 212 **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 re

establish these limits during subsequent compliance tests. **3 . Mercury Concentration Moni**  **toring 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 conce ntration 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 conditionsPage 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 concentra tion 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 contro l 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 r oaster 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 aPage 159 of 212 reasonable indication of overall emissions from the affected

so urce. 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 wit h 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 forPage 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 u sing 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

com pared 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 c arbon 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 problemPage 161 of 212 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 rul es 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 fo r 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 operabil ity 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

u navailability of National Institute of Standards and Technology (NIST) traceable calibration gas; NIST certifies methods andPage 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 p rovisions 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 mercu ry 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 umbilica l 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 SO 2 , NO x , or CO 2 ) 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 f unctionPage 163 of 212 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 ab sorption 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
prema ture 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 operati ng 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 w ould 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 conclud ed 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 d emonstrated for process units similar to roasters (e.g., coal

fired 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 C oal

- 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. Howeve r, we realize that mercury concentrations in the exhaust gases from roasters can be higher than the range of concentrations forPage 165 of 212 coal

- fired power plants, and that the calibration standards traceable to NIST, that have been available in the past, have not ap plied 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

roas ters. 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/m 3 . 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 measuremen ts 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 threePage 166 of 212 monitoring options. The other two options that we are promulgating for monitori ng 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 roas ters 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 fa cility 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 yea rs to comply withPage 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 mon itoring 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 t he 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 no ted 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

em issions. The commenter stated that the operating limit does not take into account changes in production that may vary thePage 168 of 212 allotted emissions even though the emission limit is dependent on tons of plant production. The commenter concluded that any exceede nce 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 monit oring 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 succe ssfully 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 investigationPage 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. **Commen t:**  One commenter (0341) requested that EPA reduce the Method 12B monitoring frequency to quarterly or at most monthly. The commenter also request ed that EPA include a provision that allows for a source to demonstrate a correlation or consistency of perfor mance such that the Method 12B sampling frequency can be further reduced based on the permitting authority’s acceptance of the demonstration. The commenter

s uggested that if multiple Method 12B samples are collected in a single day or over multiple days i n 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 , a nd 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 monito ring option, the final rule requiresPage 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 monit oring 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 sequen ce of air pollution control devices that interact to control mercury emissions and, therefore, monitoringPage 171 of 212 parameters that may be appropriate for one roaster may not be applicable to another. The commenter s noted that scrubber liquor flow rate, scrubber pr essure 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 commenter s said that the scrubber liquor flow rate is not currently monitored, nor is it consid ered a critical parameter in the daily operation of the scrubber mercury removal tower associated with its roasters. The commenter s further explained that the scrubber is not a spray tower where water flow rate is critical, instead the liquor is recircula ted in the tower, so the pump is monitored to insure it is operational. The commenter s 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 exitPage 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 t o 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 comme nter (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 commenter s ( 0274, 0341) also stated that the requirement to est ablish 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 commenter s noted that the scrubbers on roasters often include chemical reaction rather t han 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 monitoringPage 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 adequ ate 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 e stablished 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 limi ts 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 thePage 174 of 212 compliance test. The final rule requires hourly monitoring and th at 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 scr ubbers 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 emiss ions measurement methodology is used. The commenter concluded that these parameters are not deemed critical in the effective operation of a mercury calomel scrubber. O ther
commenter s ( 0274, 0341) added that their Compliance Assurance Monitoring (CAM) pla n provides for an inlet gas temperaturePage 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 commenter s stated that mercury scrubbers remove mercury from the gas stream throu gh a chemical reaction and not a condensation mechanism and that lower temperatures will not remove (via condensation) additional mercury. The commenter s 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 commenter s stated that if EPA continues to require inlet gas temperatur e 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 perm its 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 bounde d to prevent damage to equipment, which in turn could lead to excess emissions. In addition, we have learned that this temperaturePage 176 of 212 is dependent on the cooling tower water temperature used in the process, and this water temperature can vary quite widely fr om 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 establish ed 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 comp liance 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 commenter s ( 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 (HgCl 2 ) concentration at the exit of the scrubber on a frequency of “one time d aily.” The commenter sPage 177 of 212 stated that they have historically used daily analyses of the exit concentration of HgCl 2 to maintain control performance. The
commenter s continued to explain that the primary reactant of concern is HgCl 2 in the removal of mercury r eaction and that an excess of HgCl 2 in the solution exiting the mercury scrubber ensures there is sufficient HgCl 2 in the mercury scrubber liquor for reaction with the incoming mercury. The commenter s noted that the underlying purpose of HgCl 2 sampling is for adjusting the mercury scrubber HgCl 2 feed rate and that the target concentration is 1.0 gram of HgCl 2 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 author ity prior to the proposed rule as part of an existing regulatory requirement (Title V, Compliance Assurance Monitoring, NevadaPage 178 of 212 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 perm itting authority under this rule. **5 . Exceed**  **ing the Operating Limits for Roasters** 
**Comment:** Several commenter s ( 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 eco nomic 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 rang es 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 perf ormance 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 emiss ions above 10 lb/million tons of ore are allowed 48 hours for investigation and corrective action. The commenter s stated that it is arbitrary that corrective action response time allowed for a parametric deviation, which may not significantly affect merc ury 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 commenter s believe that elevated mercury concentrations, if verified, should be the greater environmental concern. The commenter s 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 becau se they do not take into account the time necessary for analytical procedures, dataPage 180 of 212 assimilation and interpretation, process adjustments, data validation, investigation and troubleshooting, and confirmation that corrective action was effective.
One comment er (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 f or 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 op erating 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 param etric limits, or provide the permitting authority with a compliance plan that details corrective actions taken to date and the plan andPage 181 of 212 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 me thods 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 c hoose 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 parametri c 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 co mpliance 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 sourc ePage 182 of 212 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 investi gated 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 meas ured 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 requireme nts 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 act ions do not result in the parameter reading being corrected and verified within 48 hours, a mercuryPage 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 e xceeded. 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 ac tions 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. I f, 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 concentrati on 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 persis ts, thePage 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 th e 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

o perating 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 s ample 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 ton s 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 l imit 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 deviat ion 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, Me thod 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 th ese 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 comp liance, the compliance test may also be used to establish a new operatingPage 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 ran ge 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 monitoringPage 188 of 212 by having demonstrated that their roaster emissions are less than 10 lb/million ton s 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 hou rs 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 initi al 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 “C trap ” in Equat ion 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 addit ion, 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 reportPage 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 commenter s (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 commenter s proposed that only the scrubber water flow rate monitoring be req uired 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 f lash 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 l ow, 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 negativePage 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
proce sses, 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 eff iciently. 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 includedPage 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 recomm ended 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

m onitoring 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 fo r 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 r equirements 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 commenter s ( 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 commenter s wanted to confirm that wet scrubber monitoring does not apply to wet scrubbers or condensers onPage 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 ga uges 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 c ommenter 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
capa ble 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 performa nce 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 Proce ssing 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 ave rage 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 monito r 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 SO 2 ) 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 t he only control device for mercury emissions, the final rule requires that it be monitored once per shift per operating day (e.g., minimum of twoPage 194 of 212 times per day) for pressure drop and flow rate with operating limits that are either established during the in itial 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 ca rbon 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

sc rubbers that are used to remove PM and SO 2 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 pressur e 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 me rcury. 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 systemPage 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 comment er. 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 . C**  **arbon 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 temperatu re 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 merc ury 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 commentersPage 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 incre ase 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 o perating 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 inle t 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 proposedPage 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 recommen ded 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 va lue of “C trap ” 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 conc entration 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 thePage 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 tempera ture 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.Page 199 of 212 Further, the final rule requires facilities to monitor inlet temperature once per shift rather than continuously, as was proposed. Because inlet temperat ures 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 determin ed, 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 monit oring 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, thePage 200 of 212 bed inlet is at the bottom, rather than the top, of the bed. The commenter recommended that the rule state “A represent ative 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 sam pling 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.
O ther commenter s (0341 , 0342 ) recommended tha t during Method 30B monitoring of carbon adsorbers, the sampling shouldPage 201 of 212 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.
**Re sponse:**  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 commente rs. 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 th e 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 toPage 202 of 212 require that the inlet and outlet be sampled for mercury cont ent 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 b ed 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

owner s or operators may request that EPA approv e alternative methods rather than using Method 7471A.) Finally, we are not specifying a priori ty that the carbon capacity is 20 percent. Carbon capacity can vary with the type of carbon and is dependent on such f actors 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 designe d, 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.Page 203 of 212 However, we agree with the commenter that the Method 30B sampling s hould 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 operatin g 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,Page 204 of 212 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) u nder what circumstances a facility must re

establish 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) tha t the triggering event for re

establishing 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, an d (3) if the carbon loading exceeds 90 percent, the facility would need to re

establish 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.Page 205 of 212 **8 . Monitoring of Mult**  **iple 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 comb ined 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 combi ned 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 u nits 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
concentrat ion operating limit can be based on both roastersPage 206 of 212 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 specif ied 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 concentr ation 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 contr ols, 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 significanc e would be used to show an increase in ore mercury content occurred. The commenterPage 207 of 212 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 requ irement (§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 elementa l 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 ensur e 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 facili ties should be required to provide data to fully account (mass balance) for mercury in all product andPage 208 of 212 waste streams at regulated units. The commenters believe that it is critical that the mercury captured by emissions controls are appropriately managed a nd stored over the long term.
C ommenter s (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 process es; 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 ai r 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 toPage 209 of 212 autoclaves. There are existing requirements for th e 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 t otal 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 th at 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 t he 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 th at is chosen. WePage 210 of 212 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. De finitions** 
**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 pr otection, 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 r isk 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** Page 211 of 212 **Comment** : Several commenter s (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 Clari fications** 
**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 discharg e in the off gas, and a loss of 0.4 to 0.7 percent of mercury from the condenser has been reported , ” and t hen the preamble further noted that “all retorts employ a carbon adsorption filterPage 212 of 212 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.