Document ID: EPA-R09-OAR-2013-0588-0063
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2014-06-27T04:00Z

TECHNICAL REVIEW AND EVALUATION
                              OF APPLICATION FOR
                         AIR QUALITY PERMIT NO. 58409
             (SIGNIFICANT REVISION TO OPERATING PERMIT NO. 53592)
                 FREEPORT MCMORAN MIAMI INC.  -  MIAMI SMELTER
INTRODUCTION
       This Class I Significant Permit Revision No. 58409 (Revision to Permit No. 53592) is issued to Freeport McMoRan Miami Inc. (FMMI) for the implementation of various upgrades to the smelter emissions capture and control systems to better control facility emissions, and to increase the allowable annual throughput from 850,000 tons per year of New Metal Bearing Material (NMBM) to 1,000,000 tons per year. 
       This revised permit incorporates all the permit revisions since issuance of operating Permit No. 53592
Company Information
Facility Name:		Freeport-McMoRan Miami Inc.
                   Mailing Address:	P.O. Box 4444									Claypool, Arizona 85532
Facility Address:	5701 New Street
             				Miami, Gila County, Arizona 85532
Background 
             In 2010, the U.S. Environmental Protection Agency (EPA) promulgated a new 1-hour SO2 National Air Quality Standard (NAAQS).  Ambient monitoring data around the Miami Smelter show that the portion of Gila County where the Miami Smelter resides does not meet the new 1‐hour SO2 NAAQS and is currently classified as "non-attainment" for that standard.  FMMI has proposed upgrades to the Miami Smelter emissions capture and control systems to better control SO2 emissions.
Attainment Classification
             Miami area is currently designated as a non-attainment area for Particulate Matter less than 10 microns (PM10) and SO2 (1-hour, 75 ppb standard).
REVISION DESCRIPTION
       FMMI has proposed to implement upgrades to the Miami Smelter emissions capture and control systems to better control facility emissions and to increase the allowable throughput to 1,000,000 dry tons per year of New Metal Bearing Material (NMBM).  The changes are scheduled to be implemented during 2017.  The proposed changes are as follows:
Concentrate Storage
             Enclose the temporary on‐site concentrate storage piles with a tent or dome to reduce particulate matter emissions.
Bedding Plant 
Add one new paddle mixer in parallel with the existing paddle mixer 
Add three new paddle mixer feed conveyors and one new hopper
               
IsaSmelt(R) Furnace and Cooling Water System
Replace the existing 12 feet diameter vessel with 15 feet diameter vessel for increased throughput and reduced maintenance.
Shift the existing process off‐gas uptake hood to accommodate the larger furnace.
Change the cooling circuit for increased steam recovery.
Upgrade the IsaSmelt(R) furnace cooling water system to provide more intense cooling to extend refractory life.
Add a seal to the lance to reduce process fugitive emissions.
Install a new feed port hood to capture emissions from the IsaSmelt(R) furnace feed port, and route the emissions to the existing vent fume control system.
Replace tapping hoods to accommodate the larger furnace
Upgrade the oxygen line to meet the oxygen transport velocity specifications into the smelter for safety purposes, which reduces natural gas and blast air flows down the lance.
Converter Aisle
Reconfigure the roofline to improve capture of process fugitive emissions that currently exit through roofline monitors, and routing of the captured emissions to the new aisle scrubber before release through the integrated stack.
Install the new aisle scrubber with caustic for enhanced SO2 control.
Anode Furnaces and Utility Vessel 
Add process gas hoods and mouth covers to each vessel to improve process gas capture and reduce process fugitive emissions;
Route process gases to an evaporative spray‐cooler and a new baghouse for control of particulate matter and metals emissions; and
Route the off gases from the new baghouse to the new aisle scrubber for SO2 removal. 
Acid Plant
Replace the existing 4-pass converter bed to increase the capacity of double contact acid plant.
Other major process equipment changes include:
Replace final SO3 coolers;
Replace hot heat exchangers;
Replace hot re‐heat exchangers;
Replace intermediate absorption tower acid coolers and pumps;
Install new (third) cold gas blower; and
Upgrade cooling water and utilities as required.
Other Changes
Upgrade the vent fume Scrubber and acid plant tail gas scrubber to caustic use for enhanced control of SO2 emissions;
Add three new wet electrostatic precipitators (WESP) modules at the vent fume control system; and
Replace vent fume and tail gas stacks with taller stacks in accordance with Good Engineering Practices.
EMISSIONS
Potential Emissions 
             Table-1 provides the summary of smelter facility potential emissions after the completion of the smelter upgrades:
               Table-1  -  Smelter Facility Potential Emissions
                                   Pollutant
                       Post-Project Potential Emissions 
                               (Tons per year)*
                                      PM
                                     562.2
                                     PM10
                                     362.2
                                     PM2.5
                                     233.7
                                      SO2
                                     552.3
                                      NOX
                                     286.0
                                   Lead (Pb)
                                     5.17
                                      CO
                                     89.5
                                      VOC
                                     12.6
                                     H2SO4
                                     92.0
                                     CO2e
                                    98,852
             *Post-project potential emissions includes enforceable limits over the estimated calculations for PM, PM10, PM2.5, SO2, NOX and Lead.
Basis of Emission Calculations
Particulate Matter
PM emissions for tail gas stack and vent fume stacks are based on extrapolations from 2011-2012 performance test data and prorating the emissions for increase in throughput to 1,000,000 tons/year.
Fugitive PM emissions from IsaSmelt(R), Electric Furnace, Converters and Anode Furnace are based on extrapolations from the year 2000 fugitive study data and prorating the emissions for increase in throughput to 1,000,000 tons/year.  Further, the following improvements will result in reduction of fugitive emissions: 
Add a new feed port hood to capture process fugitive emissions from the IsaSmelt(R) furnace feed port, and routing the captured emissions to the existing vent fume control system.  -  expected reduction 53.6%.
Capture of process fugitive emissions from converters.  -  the capture system is expected to reduce emissions by 84.7%.
Capture of process fugitive emissions from anode furnaces.  -  the capture system is expected to reduce emissions by 90.5%.  Further, anode furnace baghouse with capture efficiency of 95% will result in reduction of particulate matter emissions.
Calculations for particulate matter emissions from fugitive dust sources (paved/unpaved roads) and storage piles wind erosion, emissions are based on AP-42 emission factors.
Non-fugitive particulate emissions from other sources (boilers, heaters, engines, and cooling towers) are based on AP-42/manufacturers' emission factors.  Emissions for emergency engines are conservatively estimated based on 500 hours of operation per engine per year.
SO2
Acid plant tail gas  - The emissions are based on operation of the caustic scrubber designed for 2.24 ppm SO2 concentration in the tail gas stack. 
Vent fume stack- The emissions are based on operation of the caustic scrubber designed for 4.00 ppm SO2 concentration in the vent fume stack.
Aisle scrubber stack - Fugitive SO2 emissions from IsaSmelt(R), Electric furnace, Converters and anode furnace are based on the 2012 fugitive study and prorating the emissions for future throughput of 1,000,000 tons/year.  Emissions from converters and anode furnaces are captured by the capture systems and further controlled by the new aisle scrubber using caustic (designed for 1.00 ppm SO2 concentration).
Fugitive emissions from converter roofline  -  The emissions are extrapolated from the June 2012 roofline emissions study data.  
SO2 emissions from other sources (boilers, heaters, engines) are based on AP-42/manufacturers' emission factors.  Emissions for emergency engines are conservatively estimated based on 500 hours of operation per engine per year.
NOX
NOX emissions from tail gas stack are based on extrapolations from performance test data and prorated emissions for 1,000,000 ton/year throughput, expected reduction in natural gas usage due to upgrade of oxygen line to meet the oxygen transport velocity specifications into the smelter for safety purposes (expected to reduce natural gas consumption), and reduction in NOX due to caustic scrubber in the tail gas stack (expected reduction: 25%).  
NOX emissions from other sources (boilers, heaters, engines) are based on AP-42/manufacturers' emission factors.  Emissions for emergency engines are conservatively estimated for 500 hours of operation per engine per year.
NEW SOURCE REVIEW ANALYSIS
       Major modifications at existing major sources require New Source Review.  The proposed physical changes and changes in the method of operation therefore must be reviewed to determine if they would constitute a major modification. The current permit has an enforceable limitation of 850,000 tons per year on the throughput.  Therefore, an increase in throughput to 1,000,000 tons per year meets the definition of modification. 
       A project is a major modification under the Prevention of Significant Deterioration ("PSD") and Nonattainment New Source Review ("NNSR") regulations only if it will cause both a significant emissions increase and a significant net emissions increase in a regulated pollutant. With respect to a particular pollutant, if the project will not cause a significant emissions increase, quantification of net emissions increase for that pollutant is not required.

	Table-2 below compares past actual emissions with post-project potential emissions.  The increase in post-project emissions for all pollutants is less than the significance level for all applicable pollutants.  Hence the project is not subject to new source review. 

                                    Table-2
                                   Pollutant
                    Post-Project Potential Emissions (tpy)
                                  Past Actual
                          (Average of 2011 and 2012)
                                     (tpy)
                              Emission Increase/
                                   Decrease
                                      PM
                                     562.2
                                      563
                                     -0.8
                                     PM10
                                     362.2
                                      360
                                     +2.2
                                     PM2.5
                                     233.7
                                      229
                                     +4.7
                                      SO2
                                     552.3
                                     6383
                                    -5830.7
                                      NOX
                                     286.0
                                     251.0
                                      +35
                                     Lead
                                     5.17
                                     4.72
                                     +0.45
                                      CO
                                     89.5
                                     48.9
                                     +40.6
                                      VOC
                                     12.6
                                     8.65
                                     +3.95
                                     H2SO4
                                     92.0
                                     133.0
                                     -41.0
                                     CO2e
                                    98,852
                                    74,658
                                    +24,194
PERMIT EMISSION LIMITS
Considering the nature of emissions and potential variability of emissions from main process emission sources (acid plant tail gas stack, vent fume stack, aisle scrubber stack, and roofline fugitive emissions), the facility will be subject to emission limits in Table 3 below. Justification for the combined emission limit for SO2 is provided in Section V.B of this document.  The facility will be required to demonstrate compliance with these emission limits based on CEMS for SO2, continuous monitoring for roofline fugitives, addition of a NOx CEMS at the Tail Stack, and performance tests for particulate matter and lead. 
                                    Table-3
                                   Pollutant
                               Emission Sources
                                Emission Limit
                               Averaging Period
                                      SO2
Acid Plant Tailgas stack
Vent Fume Stack 
Aisle Scrubber Stack
                               128 tons per year
                             365-day rolling total
                                       
                                       
Acid Plant Tailgas stack
Vent Fume Stack 
Aisle Scrubber Stack 
Roofline Fugitives
                               477 tons per year
                                       
                                       
Bypass Stack
                               75 tons per year
                                       
                              Particulate Matter
Acid Plant Tail Gas stack
Vent Fume Stack 
Aisle Scrubber Stack 
Roofline Fugitives
                             PM: 364 tons per year
                            12-month rolling total
                                       

                            PM10: 287 tons per year
                                       
                                       

                           PM2.5: 221 tons per year
                                       
                                     Lead
Acid Plant Tail Gas stack
Vent Fume Stack 
Aisle Scrubber Stack 
Roofline Fugitives
                              5.17 tons per year
                            12-month rolling total
                                      NOX
Acid Plant Tail Gas stack
                               175 tons per year
                             365-day rolling total
             Emissions from other sources (boilers/heaters, engines, cooling towers, paved/unpaved roads, wind erosion from storage piles etc.) are based on AP-42/manufacturers' emission factors, and hence fairly conservative.  
Justification for Proposed Emission Limits for SO2
             FMMI performed modeling analysis of SO2 to demonstrate compliance with 1-Hr SO2 NAAQS.  The modeling analysis was based on the following emission rates:
               * 128 tons per year for three main stacks (tail gas, vent fume and aisle scrubber stack),
               * 349 tons per year for roofline fugitive emissions, and 
               * 75 tons per year for the bypass stack.   
             These modeled emissions rates were used for developing the SO2 emission limits for FMMI. 
             Considering the need of FMMI for operational flexibility, particularly a much larger range of potential variability associated with roofline fugitive emissions, ADEQ further performed numerous AERMOD runs to investigate the viability of establishing a combined emission limit for three main stacks emissions and roofline fugitive emissions.   The modeling analyses were conducted by altering the relative ratios of stack and roofline emissions but maintaining the collective emission limit of 477 tons per year (128 + 349 tons per year) constant.  The AERMOD runs indicated that any increase in stack emissions increased air quality impact, while any increase in roofline fugitive emissions resulted in equivalent or lower air quality impacts than those modeled by FMMI.   An extreme scenario assuming the total emissions of 477 tons per year are emitted through roofline predicted the lowest model concentration among all scenarios tested.  Even if the roofline potentially emits more than the 349 tons per year SO2 that FMMI modeled, the NAAQS can still be protected with the imposed combined emission limit of 477 tons per year for stacks and roofline fugitives.  In other words, offsetting any roof top fugitive increases with lower emissions from the stacks is protective of the NAAQS as long as the total emission limit of 477 tons per year is not exceeded.  
             Based on the AERMOD modeling analyses, the following emission limits are proposed:
               * A combined emission limit of 128 tons per year for the three main stacks; and 
               * A combined emission limit of 477 tons for the three main stacks and roofline fugitives.  

ADEQ also establishes an individual emission limit of 75 tons per year for the bypass stack, to maintain its status as an intermittent source. NEW APPLICABLE REQUIREMENTS
IsaSmelt(R) furnace was constructed or modified after October 16, 1974 and therefore it is the only "affected facility" at FMMI subject to NSPS Subpart P.   Emissions from the IsaSmelt(R) furnace are currently vented to the acid plant tail gas stack.  Thus, in the current permit, only acid plant tail gas stack is subject to emission limitation of 0.065 percent by volume for sulfur dioxide (SO2) under NSPS Subpart P.  
       	Some process fugitive emissions from the IsaSmelt(R) furnace will be captured and vented to the vent fume stack after upgrades are implemented.  Therefore, the NSPS Subpart P emission limitation of 0.065 percent by volume SO2 will become applicable to vent fume stack also. 
Emissions from anode furnace are currently not captured.  On implementation of the proposed, the emissions from anode furnaces will be captured, and routed to a baghouse for control of particulate matter emissions.  The anode furnaces are, thus, subject to CAM requirements.
DESCRIPTION OF CHANGES TO OPERATING PERMIT NO. 53592
On implementation of the proposed project, the New Metal Bearing Material (NMBM) processing limit is revised to 1,000,000 tpy from existing 850,000 tons per year.  Also, monthly reporting requirement for NMBM is deleted. The Permittee is required to maintain records of daily monthly and rolling 12-month total of concentrate feed.  

Particulate matter testing requirements are updated to include Method 5/Method 202/201A for monitoring of total particulate matter (filterable + condensable), PM10 & PM2.5.
Tail gas stack  -  Compliance with NOX emission limit for tail gas stack will be based on the addition of a new NOX CEMS.
Vent fume stack-Air Pollution Control requirements for ESPs are revised.  Requirements for maintaining the hourly average values for primary and secondary voltage, amperage are deleted as monitoring of power for ESPs, which is function of voltage and current is considered adequate.
Vent fume stack is now subject to an emission limitation of 0.065 percent by volume for sulfur dioxide (SO2) under NSPS Subpart P.  The revision also includes NSPS monitoring requirements using SO2 CEMS.
The revised permit includes new requirements for aisle scrubber stack for capture and control of fugitive emissions from converter aisle and anode furnace.  These include:
CAM requirements for anode furnace baghouse
Semiannual performance test requirements for PM and lead emissions from the aisle scrubber stack
SO2 CEMS requirements for the aisle scrubber stack
New SO2 CEMS requirements for bypass stack.
Monitoring of Fugitive Emissions from Roofline
             The Permittee is required to monitor the fugitive particulate matter, lead and SO2 emissions from the converters roofline.  The emission monitoring system for PM and lead shall be based on Method 14 and Method 5 (for PM)/Method 29 (for lead).  SO2 emissions shall be monitored by roofline emission monitors.  The system shall be developed in accordance with the enclosed concept plans, and in consultation with ADEQ.  The concept plans and clarification memo are attached to the TSD. The Permittee is required to submit a protocol for measurement of PM, lead and SO2 emissions at least 180 days before Project startup for ADEQ's approval.
Engines
The requirements for engines are revised due to replacement of some engines with new ones, and addition of new emergency engines.  Also, the requirement from NSPS Subpart IIII and JJJJ, and NESHAP requirements from Subpart ZZZZ are updated to include the most recent updates.
Best Available Control Technology (BACT) limit of 29 lb/hr for NOX for IsaSmelt(R) emergency engine is deleted as the engine is replaced with a new engine with much lower NOX emissions (4.54 lb/hr).  This new engine is subject to NSPS Subpart IIII requirements.
Ambient Monitoring Requirements  -  requirements for the Miami Golf Course PM monitor are deleted as this is now done by ADEQ monitors.
AMBIENT AIR IMPACT ANALYSIS
       As per ADEQ modeling guidelines, modeling analysis is required for permit revisions where the increase in the potential to emit is greater than the permit exemption thresholds.  
            
      Following table compares current permitted emissions from the facility with the future emissions from the facility:
      
                                    Table-4
                                   Pollutant
                       Current Potential Emissions (tpy)
                    Post-Project Potential Emissions (tpy)
                          Emissions Difference (tpy)
                                      PM
                                      764
                                     562.2
                                    -201.8
                                     PM10
                                      588
                                     362.2
                                    -225.8
                                     PM2.5
                                      436
                                     233.7
                                    -202.3
                                      SO2
                                    10,368
                                     552.2
                                    -9815.8
                                      NOX
                                      548
                                     286.0
                                     -262
                                      CO
                                     91.7
                                     89.5
                                     -2.2
                                      VOC
                                     12.7
                                     12.6
                                     -0.1
                                     H2SO4
                                      173
                                      92
                                      -81
                                      Pb
                                      150
                                     5.17
                                    -144.83
                                     CO2e
                                    110,051
                                    98,852
                                    -11199
       Since post-project emissions for all pollutants are less than the current potential to emit based on the current permit limits, no modeling analysis was necessary for any of the pollutants.  However, to demonstrate that the smelter facility's emissions would not interfere with attainment or maintenance of the new 1-hour NAAQS standard, modeling was performed for SO2.  
       FMMI performed dispersion modeling to determine if the facility's emissions of sulfur dioxide (SO2) after the smelter's expansion and enhanced control project will cause or contribute to an exceedance of the National Ambient Air Quality Standards (NAAQS) for SO2.  This chapter includes a discussion of air dispersion modeling methods and results.  
Model Selection 
             As outlined in Applicability of Appendix W Modeling Guidance for the 1-hour SO2 National Ambient Air Quality Standard" (EPA's August 23, 2010 memo), the American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) is the preferred model for single source modeling to address the 1-hour SO2 NAAQS as part of the NSR/PSD permit programs.   AERMOD should be used unless the use of an alternative model can be justified, such as the Buoyant Line and Point Source Dispersion Model (BLP). 
Modeling Fugitive Emissions from Ridge Vents  
                   The fugitive emissions from ridge vents are one of the most significant sources in the FMMI facility.  Per Appendix W A.2, BLP is the EPA's preferred model for industrial sources where plume rise from stationary line sources (such as ridge vents) are important.  However, Appendix W recommends using BLP for simple terrain but the FMMI facility's surrounding areas have complex terrain features.  
                   To handle such unique modeling problems associated with the ridge vents, the BLP model was used to estimate hourly line source final plume rise and sigma-Z and then apply the BLP-predicted final plume heights and sigma-Z in AERMOD with hourly volume source approach.  To do so, the BLP code was modified to calculate hourly predicted final plume rise values for each roofline vent with Sigma-z and save the results to an ASCII output file.  It should be addressed that the modification did not change the BLP's algorithms and thus its preferred status.  
Modeling Other Sources 
                   AERMOD was used for modeling all other sources, including three main stacks as well as other industrial sources. 
AERMOD/AERMET Version
                   The most recent version of AERMOD and its meteorological data preprocessor AERMET is Version 13350.  However, EPA has identified several bugs within the program that need to be addressed.  In particular, the bugs found in AERMET Version 13350 could be significant.   Therefore, the AERMOD/AERMET Version 12345 was used to do the modeling analysis.  ADEQ reran the model with AERMOD Version 13350 and AERMET Version 12345 and determined that the new features added in Version 13350 will not affect the modeled concentrations for FMMI.  
Source Inputs
             This section provides a discussion on source characterization to develop appropriate source inputs, including the treatment of intermittent sources, source configuration and source types, Good Engineering Practice (GEP) stack heights, and urban/rural determination of the sources.  
Treatment of Intermittent Sources
                   Per Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1-hour NO2 National Ambient Air Quality Standard (EPA's March 1, 2011 memo), the reviewing agency, at their discretion, may exempt intermittent units from model requirements for 1-hour NAAQS under appropriate circumstances.  Currently ADEQ allows an exemption from 1-hour SO2 modeling for the emergency generators that operate up to 500 hours per year and no more than 100 hours per year for maintenance and readiness testing purposes.  As the FMMI's emergency generators fall into this category, emissions from the emergency generators were not modeled for 1-hour SO2.  However, these emissions were incorporated into the modeling analysis for the NAAQS for 3-hour SO2.   
                   Upon reviewing the most recent three-year (2011-2013) bypass data FMMI provided, ADEQ has determined that the bypass events in the FMMI facility are frequent and the associated emissions are significant.  Therefore, the bypass emissions were incorporated into the 1-hour SO2 modeling.  As the time periods for bypass events are uncertain and cannot be specifically defined in the model, the bypass emissions were modeled based on the annualized hourly emission rate (average hourly emissions over the year) rather than the maximum hourly emission rate Per the EPA's March 1, 2011 memo.  
Source configurations and source types
                   All stacks were modeled as point sources with maximum allowable emission limits.  The stack's parameters such as exit temperature, diameter, and exit velocity reflected those emissions levels. 
                   Fugitive emissions from ridge vents were modeled as volume source with hourly release heights and vertical dimensions, which were derived from the BLP model.    One of the critical modeled inputs for the BLP model is the average line source buoyancy parameter.  To calculate this parameter, the 2013 roofline study data (temperature, flow rate, exit velocity) were reviewed and validated, and the physical dimensions were modified to reflect the actual dimensions after the project.    
Good Engineering Practice (GEP) stack heights
                   For all stacks, the proposed stack height is less than the corresponding calculated formula GEP height.  Therefore, stacks were modeled with actual heights.  Building downwash was evaluated using building and stack location and dimensions, and the EPA approved Building Profile Input Program Plume Rise Model Enhancements (BPIP-PRME).
Urban/rural determination  
                   The FMMI facility area was determined as "Rural" based on the land use method in Appendix W.  The SO2 half-life for urban sources was not considered in the modeling analysis.  
Meteorological Data
             This section provides a discussion on selecting and processing meteorological data for input into AERMOD and BLP.  The meteorological data files for BLP must be prepared separately because the AERMET output files do not support BLP.   
Representativeness of Meteorological Data
                   Per Appendix W Section 8.3, the selection of data should be based on spatial and climatological (temporal) representativeness.  A meteorological tower located approximately 0.3 kilometers of the project site was selected as the most representative monitor.  In spite of complex winds in the facility's surrounding areas, meteorological data collected from this tower was determined to be representative of transport and dispersion conditions between the sources of concern and areas where maximum design concentrations are anticipated to occur.  Following the EPA's Meteorological Monitoring Guidance for Regulatory Modeling Applications, the site-specific data meet QA/QC and completeness requirements.  
Meteorological Data for AERMOD 
                   Four-years of site-specific data, in combination with concurrent surface data obtained from the Safford National Weather Service (NWS) site and Globe Remote Automated Weather Stations (RAWS) site, and concurrent upper air radiosonde data obtained from the Tucson NWS site, were processed with the AERMET meteorological preprocessor.  The EPA's AERSURFACE tool was used to calculate surface characteristic parameters required by AERMET.  The use of four-years of site-specific data exceeds the EPA's recommendation of one year for site-specific data. 
 Meteorological Data for BLP 
                   There were two steps in processing meteorological data for input into BLP.  Based on surface data and radiosonde data as previously discussed, the EPA's MIXHTS program was first used to calculate twice daily mixing heights.  The EPA's Meteorological Processor for Regulatory Models (MPRM) then combined the twice daily mixing heights, site-specific meteorological data, and surface data, into an Industrial Source Complex (ISC) compatible meteorological file.  While the ISC model is not used anymore for regulatory purposes, BLP can utilize the ISC compatible meteorological file for model calculation.  Since MPRM does not allow any missing data, the missing data were substituted following appropriate procedures.
Receptor Network 
             The receptor grid has a total coverage of 110 kilometers by 108 kilometers, covering the whole model domain.  The AERMAP terrain processor was used to process the National Elevation Data (NED) data to generate the receptor elevations and hill heights.  
             A unique situation FMMI encountered was how to define the ambient air boundary, as Highway 60 passes through portions of the facility.  Following the EPA's interpretation of ambient air, receptors were placed along sections of Highway 60 within the facility.  Moreover, additional receptors were placed in the areas between Highway 60 and the property boundary where the public may access.  
             The model was run twice to ensure that the maximum modeled concentrations were detected.  The first model run used all receptors within the model domain and the second model run used more dense receptors in areas showing potential for high concentrations as indicated by the results of the first model run.  
Background Concentration 
             FMMI has reviewed the most recent four years of monitoring data obtained from three monitors that are located in the facility's surrounding areas.  It was concluded from the monitoring data that the smelter operations dominate the ambient air quality measured at these monitors.  Per Appendix W Section 8.2, the determination of background concentrations should exclude values when the source in question is impacting the monitor.  Therefore, the data collected during the shutdown of smelter operations were used to calculate the background concentration of SO2.  
Model Results 
             The model results are presented in Table below.  The results indicate that the smelter's expansion and enhanced control project will not cause or contribute to an exceedance of the NAAQS for SO2.	
                                           Table-5
                               Averaging Period
                       Modeled Concentration (ug/m[3])
                           Background Concentration
                                  (ug/m[3])
                        Total Concentration (ug/m[3])
                             SO2 NAAQS (ug/m[3])
                                    1-hour
                                     169.2
                                     23.3
                                     192.5
                                      196
                                    3-hour
                                     196.6
                                     23.3
                                     219.9
                                     1300
LIST OF ABBREVIATIONS
      
      AAAQG	Arizona Ambient Air Quality Guideline
      A.A.C.	Arizona Administrative Code
      ADEQ	Arizona Department of Environmental Quality
      BACT	Best Available Control Technology
      ADEQ	Compliance Assurance Monitoring
      CO	Carbon Monoxide
      CO2	Carbon Dioxide
      g/m[3]	Microgram per Cubic Meter
      NAAQS	National Ambient Air Quality Standard
      NESHAP	National Emission Standards for Hazardous Air Pollutants
      NSPS	New Source Performance Standards
      NOx 	Nitrogen Oxide
      NO2	Nitrogen Dioxide
      O3 	Ozone
      Pb	Lead
      PM	Particulate Matter
      PM10	Particulate Matter Nominally less than 10 Micrometers
      PM2.5	Particulate Matter Nominally less than 2.5 Micrometers
      PTE	Potential-to-Emit
      SO2	Sulfur Dioxide
      TPY	Tons per Year
      USEPA 	United States Environmental Protection Agency
      VOC	Volatile Organic Compound