Technical Memorandum. 1.0 Deposition Algorithm. 2.0 Ustar Adjustment Option

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1 Technical Memorandum To: Jim Sullivan, Minnesota Pollution Control Agency From: Pat Sheehy; Todd Fasking and Eric Edwalds, Barr Engineering Subject: NorthMet Mine Site Class II Protocol Addendum Date: July 6, 2016 Project: c: Kevin Pylka, PolyMet; Steve Sommer, Minnesota Pollution Control Agency This purpose of this memo is to provide an addendum to the Class II modeling protocol submitted for the NorthMet Project (Project) Mine Site on April 15, This addendum addresses comments received from the Minnesota Pollution Control Agency (MPCA) on the protocol and provides additional requested information. The following sections describe the proposed procedure for addressing the effects of particulate deposition on modeled ambient PM 10 concentrations, the use of the Adjusted u* beta option in AERMOD to address low wind speed conditions and the proposed approach for maintaining the ambient air boundary for the Mine Site. These items are described in Section 1, 2 and 3 below, respectively. 1.0 Deposition Algorithm The default AERMOD deposition algorithm is proposed for the particulate matter less than 10 microns in aerodynamic diameter (PM 10) modeling to be submitted with the air emission permit application. Where AP-42 emission factors are used in emissions calculations and different emission factors are used for PM 10 and particulate matter less than 2.5 microns in aerodynamic diameter (PM 2.5), the fraction of particulate in each size category, based on the emission factors, will be used in the modeling. Where AP-42 emission factors are calculated through the use of correlation equations, such as for unpaved roads and outdoor material handling sources (from AP-42 Sections and respectively) the ratio of the particle size multipliers for the fractions equivalent to PM 10 or smaller will be used to calculate the relative fraction of emissions in each size category. In the case of sources for which all particulate emissions are assumed to be PM 2.5, all emissions will be assigned to the PM 2.5 size category. 2.0 Ustar Adjustment Option The preferred air quality model AERMOD has a bias to overestimate concentrations for surface releases under low-wind stable conditions (Paine and Connors, 2013). A major reason for AERMOD s bias to overestimate atmospheric concentrations is that a default algorithm in AERMET underestimates the surface fraction velocity (u* or Ustar) for low-wind stable conditions. Recent versions of AERMET (version and later) provide an optional method for calculating u* for low-wind stable conditions (U.S. EPA, 2014). For the low-level volume sources and ground-level area sources found at PolyMet s Mine Site, the use of the ADJ_U* beta option in AERMET greatly reduces, but does not completely eliminate, the bias for the AERMOD/AERMET modeling system to overestimate atmospheric concentrations. Because the Barr Engineering Co MarketPointe Drive, Suite 200, Minneapolis, MN

2 To: Jim Sullivan, Minnesota Pollution Control Agency From: Pat Sheehy; Todd Fasking and Eric Edwalds, Barr Engineering Subject: NorthMet Mine Site Class II Protocol Addendum Date: July 6, 2016 Page: 2 preferred air quality model (the default AERMOD/AERMET 3 modeling system) is less appropriate than using the ADJ_U* beta option in AERMET for modeling emissions from the Mine Site, the Mine Site Air Quality Modeling Protocol proposes the use of the ADJ_U* beta option in AERMET in the preparation of weather input files. See the separate technical memorandum submitted with this addendum NorthMet Class II Air Quality Modeling Protocols Ustar Adjustment Option for additional detail on the application of the u* Adjustment Option for the Plant Site air quality modeling. 3.0 Ambient Air Boundary The proposed ambient air boundary for the Mine Site is unchanged from the protocol previously submitted. Access to the area excluded from ambient air will be restricted through a combination of locked or monitored gates, posting, patrols, security cameras, access agreements with other entities and natural barriers such as terrain and vegetation. A detailed description of the how the ambient air boundary will be controlled will be provided in a separate technical memo NorthMet Ambient Air Boundary. Reference: Paine, B. and Connors J AERMOD low wind speed issues: Review of new model release. EPA Regional/State/Local Modelers Workshop, April 22-25, Dallas, TX. USEPA, Addendum. User s Guide for the AERMOD Meteorological Preprocessor (AERMET). U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Research Triangle Park, NC. EPA-454-B P:\Mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\With Adjusted U star\protocol Addendum\Mine Site Prot Addendum C2 memo.docx

3 POLYMET 11-l! N l l\g April 15, 2016 Air Quality Permit Document Coordinator Minnesota Pollution Control Agency 520 Lafayette Road North St. Paul, MN Dear Sir/Madame, Please find attached two paper copies of the completed Air Quality Dispersion Modeling Protocol form (AQDM-01) submitted for the Poly Met Mining, Inc. Mine Site as part of the North Met Project. If you have any questions regarding this submittal, please contact me at Sincerely, Kevin Pylka Manager of Environmental Permitting and Compliance

4 Mine Site Class II Air Quality Dispersion Modeling Protocol Version 3 April 2016 NorthMet Project PolyMet Mining Incorporated Hoyt Lakes, MN This document provides the Class II dispersion modeling protocol for the Mine Site in the format requested by the Minnesota Pollution Control Agency (MPCA). This includes MPCA form AQDM-01, two figures and two attachments. The figures and attachments are listed below: Figures: Large Figure 1 Mine Year 8 Source Layout Large Figure 2 Mine Year 13 Source Layout Attachments (name references corresponding section of the AQDM-01 form): Attachment C Non-Default Modeling Options Attachment J Background Concentrations and Determination of Nearby Sources to be Modeled The AQMD-02 spreadsheet is incorporated in the Emission Inventory spreadsheet which was previously submitted to MPCA on March 26, Supporting files to accompany the protocol are posted to the project website. \\barr.com\projects\mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\...\Cover Page.docx

5 AQDM-01 Air Quality Dispersion Modeling Protocol Protocol Form for Criteria Pollutant Modeling (Previously AQDMP-01) Doc Type: Air Dispersion Modeling Guidance Information on Page 14 Instructions: Permit applicants required to conduct air dispersion modeling should submit two paper copies of the completed Air Quality Dispersion Modeling Protocol form (AQDM-01), the Air Quality Dispersion Modeling Protocol Spreadsheet (AQDM-02), and all accompanying files to: Air Quality Permit Document Coordinator Minnesota Pollution Control Agency 520 Lafayette Road North St. Paul, MN Applicants may also submit an electronic version, in addition to the two required paper copies. Please note that all assumptions made in the air dispersion modeling analysis could result in air permit requirements. Electronic copies of the forms and accompanying files should be sent to: Only use the most current version of this form that is on the website versions prior to 01/24/2012 will not be accepted. Facility Information AQ facility/permit ID no.: Today s date (mm/dd/yyyy): 04/15/2016 Three-letter modeling facility ID (ex., XEK = Xcel Energy Allen S. King, MEC = Mankato Energy Center, etc.): Facility name: PolyMet Mining Inc.- Mine Site Facility street address: 6500 County Road 666 City: Hoyt Lakes County: St. Louis Zip code: State: MN Facility contact: Kevin Pylka Protocol prepared by: Eric Edwalds (Barr Engineering Co.) Facility contact phone: (218) Preparer phone: (952) Facility contact address: kpylka@polymetmining.co m Preparer address: eedwalds@barr.com *UTM coordinates of facility (NAD83, zone 15 extended ONLY): x = 577, m East, y = 5,273, m North *This should be the central location of the facility/source. PMM Files to accompany protocol Use the checkboxes to indicate that the following required files are included with the completed protocol form (unless otherwise noted). Please do not use spaces or special characters in the file names and pathways. 1. Sample AERMOD input files for each modeled criteria pollutant (*.inp, *.adi, *.ami) *Note: Input file should include receptor grid and building downwash (if applicable) 2. AQDM-02 form (spreadsheet) 3. BPIPPRM input file (*.bpi) (if applicable) 4. Elevation files for input into AERMAP (*.tif [NED files]) (if applicable) 5. Background data files with concentrations for each applicable pollutant (annual, seasonal, monthly, and daily, etc.) (if applicable) 6. Optional, but recommended, files and supporting documents Please list below: Examples include: sample AERMOD output files (with CO RUNORNOT NOT ), hourly emissions file, images and figures, SIL analysis and/or paved roads fugitive dust modeling output files, etc TTY or Available in alternative formats aq2-40 7/10/13 Page 1 of 16

6 Large Figure 1 Year 8 Source Layout; Large Figure 2 Year 13 Source Layout; Attachment C - Non-Default Model Options; Attachment J Background Concentrations and Determination of Nearby Sources to be Modeled; The AQMD-02 spreadsheet is incorporated in the Emission Inventory spreadsheet which was previously submitted to MPCA March 26, Modeling files (AERMOD output CO RUNORNOT NOT, BPIP, receptor grids, hourly emission rate files) are posted to the Project Website. Section A. Purpose for Air Dispersion Modeling and Related Information 1. What is the purpose for conducting the ambient air dispersion modeling? (check all that apply) EAW EIS SIP PSD Permit requirement please specify permit requirement information (i.e., equivalent dispersion demonstration): Other please explain: Discretionary request from MPCA. a. If EAW and/or EIS are selected, please specify the regulatory trigger for modeling (ex., air emissions increase of 250 TPY, 25 MW operating capacity or design, petition, voluntary, etc. see Minn. R. ch for more information) and the name of MPCA Environmental Review staff consulted with (N/A if not applicable or if no Environmental Review staff were consulted): MPCA EAW staff name(s): Date of consultation (mm/dd/yyyy): *Note: If EAW and/or EIS are to be performed and air modeling will be conducted, a cumulative effects analysis will need to be addressed, as per the CARD decision. Please then select NAAQS/MAAQS in question 8 (A.8). Contact the Environmental Review Unit Supervisor for any questions regarding applicability and requirements. 2. Were MPCA air dispersion modeling staff consulted while completing this form? Yes No a. If yes, please provide the following consultation information: MPCA modeling staff name(s): Jim Sullivan, Daniel Dix Date of consultation (mm/dd/yyyy): Multiple Topic of consultation: Expectations for protocol including meteorological data, pollutant receptor grids,and protocol elements. 3. What type of air emission permit does this facility currently hold? No current permit Federal (Title V/Part 70) State State Registration Capped General Other: 4. Will you be applying for a permit or a permit amendment for the project? Yes No 5. Please provide a project title and a description of the proposed project: a. Project title (10 words or less): NorthMet Project - Mine Site b. Project description (50 words or less): (Additional information can be provided in question 9 below) PolyMet plans to construct and operate a mine, to reactivate portions of the LTV Steel Mining Company facility and to build a hydrometallurgical concentrate processing facility at the former LTVSMC site. This protocol covers the Mine Site. More detail is available in the NorthMet Project Description Version 9 Submitted February 19, Is the proposed project subject to PSD? Yes No a. If yes, list pollutants: b. Is this facility considered a major source for PSD: Yes No 7. Has the PSD minor source baseline been set for: St. Louis County? Yes No a. If yes, for which pollutant(s) and the year(s) it was set (check all that apply)? NO PM PM2.5 SO PSD major source baseline (PM2.5 trigger date will be on Oct. 20, 2011, 1 year after F.R. publication date.) NO PM PM SO What type of analysis will be conducted? (check all that apply) NAAQS/MAAQS PSD Class II Increments PSD Class I Increments SIL Analysis Screening Other: AERA TTY or Available in alternative formats aq2-40 7/10/13 Page 2 of 16

7 9. Additional information for this section that was not included above (if not applicable, place N/A in field): (Examples include: more information about the proposed project, whether the facility is in any SIP non-attainment or reclassified areas, etc.) The Project is a PSD synthetic minor and therefore the project does not trigger PSD modeling. The modeling approach in this protocol follows the approved methodologies used in the discretionary modeling completed for the Draft and Supplemental Draft EIS with updates that are limited to changes in guidance and software. Section B. EPA Pre-Processors and EPA Post-Processors 1. Will AERMAP be used? Yes No If no, please explain: High-resolution elevation data obtained from the Arrowhead Region LiDAR aerial survey will be used as it is more current and of higher resolution than the NED 1/3 are second data. However, there may be file formatting issues such that AERMAP would not be able to execute and provide hill height (Zhill) values from the lidar data. a. What version of AERMAP is proposed to be used: AERMAP version If other, please explain: b. What type of elevation data will be used: NED 1/3 arc second NED 1 arc second Other - Please describe: MN DNR LiDAR aerial survey 2011 ftp://ftp.gisdata.mn.gov/pub/gdrs/data/pub/us_mn_state_mngeo/elev_lidar_arrowhead2011/metad ata/metadata.html All UTM coordinates must be in NAD83, Zone 15 Extended (not NAD27). 2. Will BPIP-PRIME version be used? Yes No If no, please explain: Tiering of buildings must follow MPCA s modeling guidance from the How To Model section of the April 2013 MPCA Air Dispersion Modeling Guidance For Minnesota Title V Modeling Requirements And Federal Prevention of Significant Deterioration (PSD) Requirements. (aq2-58) 3. Will MPCA pre-processed AERMET data be used? Yes No If yes, proceed to question 4. Note MPCA s pre-processed meteorological data with AERMET incorporates the following details: AERSURFACE version (or version 13016) is used to determine surface characteristics using 1992 LULC data. Yearly-averaged moisture conditions (wet, dry, or average) based on historical ranks are accounted for in AERSURFACE to aid in the determination of Bowen ratio values. Default 1.0 km radius for surface roughness and 10 km by 10 km domain for albedo and Bowen ratio used in AERSURFACE a. If no, will on-site meteorological data be processed and used? Yes No * If no, skip to question 4 and provide additional information in question 6. b. If yes to question a, please answer the following questions. i. Will AERSURFACE be used to determine surface characteristics around the meteorological tower? (Default is Yes ) Yes No ii. What version of AERSURFACE is proposed to be used: [Select from list] iii. What LULC data will be used? [Select from list] iv. If other, please explain: Will yearly-averaged moisture conditions (wet, dry, or average) based on historical ranks be accounted for in AERSURFACE (for the Bowen Ratio)? (Default is Yes ) Yes No v. Will the default 1.0 km radius for surface roughness, and 10 km by 10 km domain for albedo and Bowen ratio be used? (Default is Yes ) Yes No vi. If no, please explain: Please provide any additional processing details of the on-site meteorological data that is not provided above: 4. Are any EPA post-processors (such as LEADPOST) proposed to be used in the analysis? Yes No a. If yes, what post-processor(s) and version(s): TTY or Available in alternative formats aq2-40 7/10/13 Page 3 of 16

8 5. Are any user-developed pre-processors or post-processors proposed to be used in the analysis? Yes No a. If yes, what pre-processors or post-processors, and describe their functions: 6. Additional information for this section that was not included above (if not applicable, place N/A in field): The meteorological data set is Hibbing processed using AERMINUTE The MPCA reviewed and approved (3/25/2016 from Daniel Dix to Eric Edwalds; cc: Jim Sullivan) this data set for this modeling analysis. Section C. Model Selection and Options (Key CO Pathway Inputs) 1. Identify the air dispersion model and version proposed to be used in the analysis: [Select from list] a. If other, please list: AERMOD Version What criteria pollutants are required and will be modeled (check all that apply)? CO NO2 PM2.5 PM10 SO2 Pb Other: Please refer to Tables App.1 and App.2 in the Appendix for averaging times and form of standard for each criteria pollutant(s). Refer to the most recent version of the EPA s AERMOD User s Guide for correct pollutant IDs to use. Use EPA s most recent modeling guidance methods for PM What model options (CO pathway keywords) are proposed to be used in the analysis for the source under review (check all that apply)? (See Tables B-1 and B-2 of the AERMOD User s Guide Addendum ) Regulatory Default - list pollutants: PM2.5 Non-Default - List pollutants: PM10 Concentration Rural Urban ELEV FLAT BETA PVMRM OLM FLAGPOLE Other(s) not listed: a. If Urban, please specify population area, population, and surface roughness radius: Population area: Population: Surface roughness height: km b. If Non-Regulatory Default, please specify non-default options: Deposition algorithm using AERMOD half-life function for PM10; see Attachment C for more detail c. If BETA is selected, please specify BETA options: (BETA options LOWWIND1 and LOWWIND2 are not to be used for regulatory purposes, and will not be accepted or review by the MPCA.) 4. Will alternative air dispersion models and/or methods, as specified by Appendix W, or applicable guidance, be applied (e.g., parallel version(s) of model, PVMRM, OLM, secondary formation coefficients, etc.)? Yes No Skip to question 5. If yes, please explain: a. If yes, will approval be required by MPCA and/or EPA Region V air modeling staff? Yes No If yes, please select: MPCA (State-only action) EPA Region V (PSD/SIP action) If no, please explain: 5. If NO2 is required to be analyzed for the one-hour and annual NAAQS, what tier methodology(s) is proposed? N/A, NO2 not required (skip to question 6) Tier 1 (100% NOx to NO2 conversion, most conservative) Tier 2 (Default ambient ratio of 0.80, or an appropriate ratio value) Tier 3 (OLM, requires justification and approval by MPCA and/or EPA Region 5)* Tier 3 (PVMRM, requires justification and approval by MPCA and/or EPA Region 5)* *For Tier 3 options, please fill-out the NO2 questions in Section K: Pollutant-based Considerations. a. If Tier 2, please provide the ambient ratio proposed (default = 0.80): b. If Tier 2, please provide justification for proposed ambient ratio: TTY or Available in alternative formats aq2-40 7/10/13 Page 4 of 16

9 6. If an alternative refined model is proposed for use (including non-default options like PVMRM or OLM), will the following criteria from Appendix W, section 3.2.2, paragraph (e), be met in this protocol? Yes No N/A If no, please explain: e. Finally, for condition (3) in paragraph (b) of this subsection an alternative refined model may be used provided that: i. The model has received a scientific peer review; ii. iii. iv. The model can be demonstrated to be applicable to the problem on a theoretical basis; The data bases which are necessary to perform the analysis are available and adequate; Appropriate performance evaluations of the model have shown that the model is not biased toward underestimates; and v. A protocol on methods and procedures to be followed has been established. 7. Additional information for this section that was not included above (including justification for non-default options, additional CO pathway keywords not mentioned above, values for options selected, etc.): Attachment C to this protocol describes the PM10 deposition half-life calculation. While the BETA option of adjusted ustar is available and has been approved for similar sources (EPA Region 10), PolyMet has chosen at this time not to pursue approval and application of this method. The sources (fugitive emissions generated near the ground) and the meteorological conditions (all of the maximum modeled impacts from the Mine Site sources occur for wind speeds < 1 m/s) are consistent with conditions for which the adjusted ustar BETA option was developed. While we would expect to model even lower levels of impact if we used the adjusted ustar BETA option, we expect to successfully model compliance without using this methodology. This approach applies an additional level of conservativism to modeled impacts associated with the described sources and conditions. SO2 is not part of this protocol as propane is the fuel for the space heater at the wastewater treatment plant. Previous modeling analyses using these sources and fuel types showed NO2 impacts were well below the SIL and therefore NO2 is not included in this protocol. Section D. Emission Source Characterizations and Parameters (Key SO Pathway Inputs) Include and list the facility s modeling parameters for all source types in the MPCA s Modeling Parameters Spreadsheet (Form AQDM-02). For background sources listed within SO Pathway, please see Section I. 1. Please indicate which of the following source characterizations are present at your facility and will be included for modeling analysis (check all that apply ): N/A = Source-type not present; Yes = Source-type present and will model; No = Source-type present but will not model. a. Point sources: N/A Yes No-please explain: i. Are any of the point sources capped and/or horizontal stacks (see guidance in section 6.1, AERMOD Implementation Guide (03/19/2009)) and, if yes, accounted for in the following? ii. No Yes exit velocity(s) = m/s Yes Non-Default POINTCAP and /or POINTHOR* *Please provide justification for use of non-default option in question ii, below. If using third-party software, please check with the vendor to determine if there are any issues with the use of BETA options POINTCAP and POINTHOR. Additional information for this subsection (if not applicable, place N/A in field): There are 2 point sources that will be modeled at the NorthMet mine site: lime silo (SV425) and space heater at the wastewater treatment plant (WWTSH). b. Volume sources: N/A Yes No -please explain: Tip: Please refer to Figure App.1 in the appendix on calculating the lateral and vertical dimensions. i. Will there be any volume source(s) overlapping or within (2.15 * sigma Y) meters of any receptors? ii. No Yes * * Volume source should then be converted to an area source of commensurate size (per section 6.2 of EPA s AERMOD Implementation Guide (03/19/2009) or be further refined. Also see EPA s Haul Road Workgroup Guidance (03/02/2012). Additional information for this subsection (if not applicable, place N/A in field): TTY or Available in alternative formats aq2-40 7/10/13 Page 5 of 16

10 The mine site volume sources represent the fugitive dust from the unpaved roads and stockpile handling. c. Area sources (includes AREACIRC and AREAPOLY): N/A Yes No-please explain: i. Additional information for this subsection (if not applicable, place N/A in field): d. Open pit sources: N/A Yes No-please explain: i. Additional information for this subsection (if not applicable, place N/A in field): There are two open pit sources at the NorthMet mine site for both the Year 8 and Year 13 modeled scenarios. e. Line sources: N/A Yes No please explain: i. Additional information for this subsection (if not applicable, place N/A in field): N/A 2. Are fugitive emissions emitted from the source, and if yes, will they be accounted for in the modeling analysis? (Examples of fugitive emissions include but are not limited to: traffic on paved and/or unpaved roads, stockpiles of various materials, wind erosion, loadout, unloading, etc.) (N/A = no fugitive emissions are emitted; Yes = fugitive emissions are emitted AND will be included in modeling analysis; No = fugitive emissions are emitted and will NOT be included in modeling analysis) N/A Yes No-please explain*: * Please provide justification for excluding any fugitive emission sources within the modeling, including the use of the Paved Roads Fugitive Dust Policy. a. If yes, please list the facilities fugitive sources: material handling, unpaved road traffic, crushing/screening Note: If modeling for paved road fugitive dust, please read and complete Section E. 3. Will all insignificant activities emitted from the source for PM10 (with emissions over 0.1 lb/hr), PM2.5 (with emissions over 0.02 lb/hr), or other pollutants be accounted for in the modeling? (N/A = no insignificant activities are emitted from the source; Yes = insignificant activities are emitted AND will be included in modeling analysis; No = insignificant activities are emitted and will NOT be included in modeling analysis) N/A Yes No a. If no, please provide justification for excluding any insignificant activities within the modeling: Refer to guidance under the General Modeling Information section of the April 2013 MPCA Air Dispersion Modeling Guidance For Minnesota Title V Modeling Requirements And Federal Prevention of Significant Deterioration (PSD) Requirements (aq2-58), under the Insignificant Activities subsection. 4. Are intermittent emissions sources (as described in the Intermittent Emissions subsection of the MPCA Air Dispersion Modeling Guidance) present at the facility? Yes No Skip to question 5. a. If yes, please provide detail on the types and operations of the intermittent emission source(s) for each applicable source (include the source IDs, any regular uses, testing frequencies, emergency uses, peaking vs. non-peaking units, days and hours of operation or testing, etc.): SV 068 is the wastewater treatment facility backup generator and SV 069 is a portable generator that is used to move electrical equipment. b. If yes to question 4, will intermittent emission sources be included in the modeling analysis? Yes please list the source ID(s): No please list the source ID(s): SV 068, SV TTY or Available in alternative formats aq2-40 7/10/13 Page 6 of 16

11 i. If no, please provide an explanation for not including the above sources in the modeling analysis: When these sources are operating, primary sources (drill, excavator) will not be operating. Intermittent sources will use Best Management Practices (BMPs) for minimizing emissions and therefore can be excluded from the modeling analysis. 5. Does your facility have alternative operating scenarios? Yes No Skip to question 6. a. If yes, will multiple operating scenarios be modeled? Yes - # of scenarios to be modeled: 2 No most conservative scenario will be modeled b. If yes to 5a above, please describe the operating scenarios and the differences between them: There will be two main phases of Mine Site operation: 1) temporary stockpile phase and 2) in-pit disposal/stockpile reclaimation phase. The change in mining phase is scheduled to occur during Year 11 of mine operation in this year the East Pit will be mined out and newly mined wasterock will be placed in the East Pit and rock from the temporary stockpiles will begin to be relocated to the pit. A worst case year for each phase was determined as described in the emission inventory spreadsheet and the two worst case years will be modeled. The two mining phases are not consistent with the definition of alternative operating scenario for permitting purposes, but this question was the most applicable place on the protocol form to discuss the modeling scenarios. Note: If multiple scenarios will be modeled, please list the scenarios in the AQDM-02 spreadsheet. 6. Will emission factors/scalars (SO EMISFACT) be used to demonstrate compliance in the air dispersion modeling analysis? Yes No Skip to question 7. a. If yes, describe for which sources and the types of emission factors/scalars that will be applied: Overburden crushing, screening and overburden hauling sources will be modeled for 12 hours/day during November April using the MHRDOW keyword. 7. Will hourly emissions file(s) be used for this analysis (HOUREMIS)? Yes* No *If yes, please provide the hourly emission file(s) with the submittal of this form and list file in question 6 under the Files To Accompany Protocol section. 8. Will all applicable PSD increment consuming and/or expanding sources be modeled for your source? Yes No-please explain (SIL-only, NAAQS-only, etc.): 9. Additional information for this section that was not included above, including discussion of options (if not applicable, place N/A in field): AQDM-02 spreadsheet is included with the emission inventory. As described in the emission inventory, Year 8 emissions are worst-case for the temporary stockpile phase. Large Figure 1 shows the Year 8 modeled source layout. Similarly, Year 13 emissions are worst-case for the in-pit disposal/stockpile reclamation phase. Large Figure 2 shows the Year 13 modeled source layout. Section E. Paved Roads Fugitive Dust Current MPCA policy regarding modeling of paved road fugitive dust emissions, in support of air quality permitting or environmental review, recommends that: New facilities or facilities undergoing physical expansions will not be required to model paved road fugitive dust emissions if a facilities predicted ambient impacts for PM10 and PM2.5 are less than a specified percent of the NAAQS and/or PSD Class II Increment. Physical expansions do not include increases in emission limits (emphasis added). This policy does not apply to modeling that supports permitting in maintenance areas or the development of State Implementation Plans. Exceptions to the policy can and will occur. Please see the MPCA air modeling webpage for policy. If paved road fugitive dust emissions are proposed to be included in your modeling analysis and you did not answer Neither to question 1b, MPCA guidance recommends that the source in question first model its facility (without including paved road fugitive dust emissions) plus nearby sources plus background (i.e., FAC w/o paved roads + nearby source impacts + background impacts). If your facility has multiple paved roads operating scenarios, results recorded in Table E-01 must reflect the most conservative scenario. Results can be recorded using Table E-01 below for PM10 and PM2.5. If not elected to include results with this protocol (using the methodology above), then please provide the results in the AQDM-06 (modeling report) form. 1. Does your facility have paved road fugitive dust emissions for PM10 and PM2.5? Yes No Please continue to the next section (F) a. Will your facility include paved road fugitive dust emissions in the modeling analysis? Yes No b. Is your facility either a new facility or an existing facility undergoing a physical expansion? New facility Existing w/ phys. expan. Neither * * If neither, policy does not apply. Please answer questions 2 4, and proceed to the next section (F) without filling in TTY or Available in alternative formats aq2-40 7/10/13 Page 7 of 16

12 Table E-01. c. If yes to question 1 and no to question 1a, please provide justification for not including paved road fugitives: 2. How many vehicles per day drive on and off your facility s property? (Provide the maximum number from all scenarios.) Employee traffic and parking: Third-party truck traffic: 3. Does your facility have multiple operating scenarios for traffic on your property (i.e., seasonal traffic changes)? Yes No a. If yes, please provide additional details for the operating scenarios, such as changes in traffic counts, types of vehicles, silt loadings, cleaning frequencies, etc. 4. Additional information for this section that was not included above or below, including discussion of options and how paved road fugitive sources will characterized in the model (if not applicable, place N/A in field): N/A Note: If completing Table E-01, modeling output files must then be submitted. Table E-01 (Use max modeled concentrations from all operating scenarios) Averaging Period NAAQS (μg/m 3 ) Modeled NAAQS Impact Concentrations w/ Background and Nearby Sources(μg/m 3 ) % of NAAQS/MAAQS PSD Class II Increments (μg/m 3 ) Modeled Class II Increment Impact Concentrations (μg/m 3 ) % of Class II Increments PM10 PM hour % % Annual % % 24-hour % % Annual % % Table E-02 indicates the resultant category(s) for your facility, based on the % of the standard(s) for PM 10 and PM 2.5 (see results in columns % of NAAQS and % of Class II Increments in Table E-01 above). This uses the highest % from all averaging periods for each pollutant and standard. The category descriptions are provided in Table E-03. Answers to question 2 above will help determine permit conditions if modeled concentrations result in a category 2 designation. Table E-02 NAAQS NAAQS/MAAQS Result(s) w/ Background and Nearby Sources (%) Cat. 1 Cat. 2 Cat. 3 PSD Class II Increments PSD Class II Result(s) (%) Cat. 1 Cat. 2 Cat. 3 PM % # < 60% 60% < # < 95% 95% < # 0.00% # < 35% 35% < # < 75% 75% < # PM % # < 80% 80% < # < 95% 95% < # 0.00% # < 40% 40% < # < 80% 80% < # Table E-03 Cat 1: Cat 2: Cat 3: Paved road fugitive emissions not required to be modeled, and no paved road fugitive dust permit conditions. Requirements in Minn. Rule apply. Paved road fugitive emissions not required to be modeled, with paved road fugitive dust permit conditions determined by levels of traffic at the facility. Paved road fugitive emissions are required to be modeled, with site-specific paved road fugitive dust permit conditions. Re-modeling and/or addition of paved road fugitive emissions source group required. Section F. Receptors (RE Pathway) Please refer to guidance from Tables 11, 12, and 13 of the April 2013 MPCA Air Dispersion Modeling Guidance for Minnesota Title V Modeling Requirements and Federal Prevention of Significant Deterioration (PSD) Requirements (aq2-58), as well as federal guidance TTY or Available in alternative formats aq2-40 7/10/13 Page 8 of 16

13 1. What type of receptor grid will be used? Discrete Cartesian a. If other, or a combination, please describe: Multiple grids will be used b. Will grid be converted to discrete Cartesian? Yes No N/A 2. What will be the grid dimensions? (Ex., radius of 10 km, 5 km by 5 km, etc.) 20.5 km x 20.5 km; 50 km radius 3. What is the proposed spacing of receptors for? a. Inside the property boundary(s): NA meters b. On the fenceline(s): NA meters c. On the property line(s): 25, 100 meters d. Beyond the property line(s): 50, 100, 500, 1000, 5000 see 5 meters 4. Will FLAGPOLE receptors be included in the receptor grid? (N/A = No high-rise structures w/ ambient air within 3 miles of source; No = High-rise structures w/ ambient air exist within 3 miles of source, but will not include in receptor grid.) Yes N/A No Please continue to the next question (6) 5. Additional information for this section that was not included above, including discussion of options (if not applicable, place N/A in field): This protocol includes a SIL grid for PM10 which is 20.5 km x 20.5 km with 500 m receptor spacing at distance and 100 m spacing along the property line. The PM2.5 grid uses the Class II Cumulative NAAQS and Increment Mine Site receptor grid used for the SDEIS modeling assumes a 100 meter space grid around the ambient air boundary with a 25 meter spaced area south of the unloading area where initial modeling showed maximum impacts. From the boundary out 1km the receptors are spaced 100 meters, except in the area of maximum impacts, which are spaced at 50 meters. From 1 km out to 5 km the receptors are spaced every 500 meters. From 5 km to the maximum extent of the grid, 15 km, the receptors were spaced every kilometer. Additionally for the PM2.5 SIL analysis, polar grid receptors extend from 12 to 25 km at 1 km spacing and from km at 5 km spacing. The SIL modeling results (discussed in Attachment J) will be used to develop the cumulative NAAQS receptor grids for the permit modeling submittal. Separate receptor grids extending to the SIL extents will be developed for PM10 and PM2.5. Section G. Meteorological Data (ME Pathway) Note: If modeling with more than one meteorological data set (i.e., portable facility), please list in question 8 the information requested in questions 1-4 for the additional data sets. 1. What meteorological surface station is proposed for use? Please indicate the station name, the state the surface station is located in, and the three letter call sign\identifier. (Ex.: Minneapolis/St. Paul Int l Arpt; MN; MSP) Or check the box to indicate that on-site surface meteorological data will be used instead of NWS surface meteorological data. Surface station name: Hibbing Airport State: MN Three-letter call sign/identifier: HIB Onsite surface data 2. What meteorological upper air station is proposed for use? Please indicate the station name, the state the surface station is located in, and the three letter call sign\identifier. (Ex.: Chanhassen; MN; MPX) Upper air station name: International Falls State: MN Three-letter call sign/identifier: INL 3. What consecutive 5- year period will be used? 2009 to Were the proposed AERMET files pre-processed by MPCA staff? Yes No a. If yes, please provide the name of the met data zip file that was received or obtained from the MPCA and the date it was obtained: Name:.zip Date (mm/dd/yyyy): b. Please indicate what version of AERMET will be used: Other If other, please explain: AERMET; AERMINUTE 5. Will on-site meteorological data be used, instead of NWS meteorological data processed by MPCA staff? Yes No Note: If site-specific meteorological data will be collected and used, please follow the federal guidance (EPA s), as specified in section 8.3 and section (QA/QC) of 40 CFR Part 51 dated 11/09/2005 (Appendix W). a. If site-specific surface meteorological data will be collected and used, where will the location of the meteorological tower be set (city and state, coordinates, etc.)? N/A TTY or Available in alternative formats aq2-40 7/10/13 Page 9 of 16

14 b. If site-specific meteorological data will be collected and used, what year of data is proposed to be used? N/A 6. What justification(s) applies for the proposed surface and upper air stations identified above? (Check all that apply) Similar surface characteristics as meteorological tower Similar wind patterns/characteristics Other Please describe: a. Please provide detail for your justifications (required): Similar land use characteristics Proximity to surface and/or upper air station(s) Hibbing has AERMINUTE data. Other nearby airports do not have AERMINUTE data. The Hibbing meteorological data set is the primary meteorological data set for dispersion modeling use on the Mesabi Iron Range. 7. Will wind speed categories and/or wind speed emission factors be used? No Skip to question 8. Yes for which pollutants: a. Please specify the wind speed categories (m/s) to be used for the ME WINDCATS keyword: User-specified ME WINDCATS: m/s m/s m/s m/s m/s Default ME WINDCATS: 1.54 m/s 3.09 m/s 5.14 m/s 8.23 m/s m/s b. Please list the user-specified wind speed emission factors for the SO EMISFACT WSPEED pathway. Include the source ID or range, pollutant, and six wind speed emission factors. This does not need to be an exhaustive list. 8. Additional information for this section that was not included above (if not applicable, place N/A in field): As described in Section B.6, the meteorological data set is and processed using AERMINUTE AERMINUTE was required to processs the 5-minute AERMINUTE data from Hibbing for the last 7 months of The MPCA approved the AERMET / AERMINUTE data processing in an from 3/26/2016 from Daniel Dix (MPCA) to Eric Edwalds (Barr), cc: Jim Sullivan (MPCA). Section H. SIL Analysis and Results 1. Will a SIL or impact area analysis be conducted in conjunction with this project, in order to determine if a cumulative analysis is required and to determine the extent of the modeling domain? No Will not model against SILs and instead proceed directly to conducting a cumulative analysis, with a modeling domain of 50km x 50km. Yes List for which pollutants: PM10, PM2.5 N/A Proceed to the next section (I) 2. If a preliminary SIL analysis has been conducted for this project, it is optional but highly recommended that results be provided (in the Table H-01 below), as well as including corresponding model output files. Note: Refer to the MPCA s Air Modeling Guidance, How To Model, Part II: Setting Up the Model, Step one Impact Area Evaluation for guidance. Table H-01, Class II Significant Impact Levels Modeling Results for: Pollutant SO2 PM10 Averaging Time Modeled Impacts (H1H) (μg/m 3 ) SILs (μg/m 3 ) *As of 10/26/2010 % of SIL Exceed SIL? 1-hr % 3-hr % 24-hr % Annual % 24-hr % Annual % (blank) Yes - Refined Modeling Radius of Impact (If exceeds SIL) km 5, 2 km TTY or Available in alternative formats aq2-40 7/10/13 Page 10 of 16

15 Pollutant PM2.5 NOx CO Averaging Time Modeled Impacts (H1H) (μg/m 3 ) SILs (μg/m 3 ) *As of 10/26/2010 % of SIL Exceed SIL? 24-hr % Annual % 1-hr % Annual % 1-hr % 8-hr % Yes - Refined Modeling (blank) (blank) Radius of Impact (If exceeds SIL) 25.8, 10 km km km 3. Additional information for this section that was not included above (if not applicable, place N/A in field): The maximum SIL extent for each pollutant will be used to develop the NAAQS and increment receptor grids for each pollutant separately. Attachment J provides a detailed discussion of the SIL results.. Section I. Background Values Please refer to Section 2.4 and Table B-4 of the latest version of the AERMOD User s Guide, Addendum for guidance as well as the latest version of the MPCA s Air Dispersion Modeling Guidance for Title V and PSD. 1. Are background concentrations required for your analysis? *Tip: If NAAQS/MAAQS was selected in question A.8, the answer is Yes. Yes List pollutants required for: PM10, PM2.5 No Please explain (e.g., SIL analysis-only, etc.) and then proceed to question 2: Note: All background concentrations, including uniform and temporally varying concentrations, will need to be specified in the input file(s). a. If yes, please provide a description below of the background concentration(s) and any considerations given to the methodology: The Virginia, MN monitor is a site representative of the Iron Range. The background concentrations will be developed from : PM hour 3-year average of 98 th %ile = ( )/3 = 18 µg/m 3 PM2.5 Annual 3-year average of annual conc = ( )/3 = 7.5 µg/m3 PM10 24-hour 3-year average of H2H conc = ( )/3 = 33 µg/m 3 PM10 Annual 3-year average of annual conc = To be determined Note PM10 annual is a MAAQS only standard. b. Background data sources (check all that apply): MPCA website EPA website Other explain: MPCA provided data for PM10 and PM2.5 Virginia data for for developing background c. Examined monitors out to a distance of: NA km d. Monitors excluded from consideration and reasons why: NA e. Facility characteristics: i. Facility land use (industrial, residential, agricultural, cropland, mixed, etc.): forested ii. Facility setting: Urban Suburban Rural f. Ambient air monitor(s) characteristics: i. Monitor land use (industrial, residential, agricultural, cropland, mixed, etc.): Virginia city hall ii. Monitor setting: Urban Suburban Rural g. Form of background value(s) for each applicable pollutant (maximum, 98 th percentile, etc.): PM10 24 Hour 3-year average of High-2 nd -high; PM10 annual 3-year average of annual concentrations PM Hour 3-year average of 98 th percentile; PM2.5 annual 3-year average of annual concentrations h. Please check user-generated background concentrations option(s) to be used for each applicable pollutant (check all TTY or Available in alternative formats aq2-40 7/10/13 Page 11 of 16

16 that apply): SO BACKGRND BGflag i. File name(s): ii. iii. File creation date(s): BGflag(s) List all that apply and for which pollutant: SO BACKGRND HOURLY i. File name(s): (BGflag can be defined as ANNUAL, SEASON, MONTH, etc. See Table B-4, Appendix B, of the AERMOD User s Guide Addendum) 2. Additional information for this section that was not included above (if not applicable, place N/A in field): Seasonal background values for PM2.5 may be developed as a possible refinement to the analysis. The PM10 24-hour increment is the most restrictive standard for the PM10 modeling, so further refinement to the PM10 monitored background concentrations will not be employed. Attachment J provides a detailed discussion of the sources influencing the background monitors and the combined use of background concentrations and explicitly modeled nearby sources. Section J. Nearby Sources *Contact MPCA air dispersion modeling staff for MPCA-generated products. Also, refer to the How to model, Part II section, Step four Compliance demonstration subsection in the MPCA s Air Dispersion Modeling Guidance. 1. Will any nearby sources be modeled explicitly for the analysis? N/A No* Yes List pollutants required for: PM10, PM2.5 *If no, please skip ahead to Section K: Pollutant-based Considerations. 2. Please select the methodology for selecting nearby sources (check all that apply): MNLookup Table ROI SQRM-D Tool* Other Please explain: USEPA March 1, 2011 Clarification Memorandum: Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1-hour NO2 National Ambient Air Quality Standard *This is the MPCA-generated GIS Tool a. Please provide additional information on the selection process used to obtain the initial and final nearby source emission inventory, including any deviations from or additional work to MPCA approved approaches: *Nearby sources out to 50 km away from the subject source should be examined. *Please include facility ID s and/or names in the modeling input files of all nearby sources. Attachment J provides a detailed discussion of background concentrations and nearby sources to be explicitly modeled. Northshore Peter Mitchell Mine will be modeled explicitly for cumulative NAAQS impacts for PM10 and PM2.5. b. Are there any nearby sources that are being omitted that were identified by MPCA approved methods? No Yes c. If yes to question b above, please provide the names of the sources omitted and the justification: See Attachment J for a discussion of the omitted sources. d. What emission inventory year(s) is being used? N/A - using permitted emission rates 3. Describe the emission s type(s) that will be used in the nearby source modeling (check all that apply): Allowables (PTE s) Actuals User-collected Other a. Where does the emissions data come from (for each source)? *Example: Permit ID and action #, MPCA emissions inventory, stack tests, etc. For Northshore Peter Mitchell Mine June 2005 Title V Air Permit and associated permit application, 2009 permit reissuance application and Stack Test Data. b. Please describe how the emissions are calculated (for each source): *Example: Process-based emissions, permitted value, merged-stack calculation, scaled emissions, etc. See Attachment J and NorthMet Plant Site emission inventory for specific emission calculation methods TTY or Available in alternative formats aq2-40 7/10/13 Page 12 of 16

17 4. How will the nearby source(s) be characterized? (Check all that apply) Explicit Merged Parameters Other a. If other was selected for question 4 above, please provide further details: 5. Additional information for this section that was not included above (if not applicable, place N/A in field): Attachment J provides a detailed discussion of the sources influencing the background monitors and the combined use of background concentrations and explicitly modeled nearby sources. Section K. Pollutant-based Considerations *Please refer to the April 2013 MPCA Air Dispersion Modeling Guidance for Minnesota Title V Modeling Requirements and Federal Prevention of Significant Deterioration (PSD) Requirements. (aq2-58) Secondary Formation of PM2.5 (PM2.5, NOx, and SO2): 1. Will this source have direct PM2.5 emissions? Less than (<) 10 TPY SER (including no direct PM2.5 emissions) 2. Will this source have NOx emissions? Less than (<) 40 TPY SER (including no NOx emissions) 3. Will this source have SO2 emissions? Less than (<) 40 TPY SER (including no SO2 emissions) Greater than (>) 10 TPY SER Greater than (>) 40 TPY SER Greater than (>) 40 TPY SER 4. Please select the assessment case that applies to your facility for the secondary formation of PM2.5? (Refer to answers given above for questions 1 3. Also refer to the Secondary Formation of PM2.5 section of the April 2013 MPCA Air Dispersion Modeling Guidance.) Case 1 (No air quality analysis): Direct PM2.5 emissions < 10 TPY, NOx and/or SO2 emissions < 40 TPY Case 2 (Primary air quality impacts only): Direct PM2.5 emissions 10 TPY, NOx and/or SO2 emissions < 40 TPY Case 3 (Primary and secondary air quality impacts): Direct PM2.5 emissions 10 TPY, NOx and/or SO2 emissions 40 TPY Case 4 (Secondary air quality impacts only): Direct PM2.5 emissions < 10 TPY, NOx and/or SO2 emissions 40 TPY 5. Please describe the qualitative and/or quantitative approach to be used to address cases 3 or 4, selected in question 4 above (if applicable to your facility if not, then place N/A in field): N/A NO2: 1. Is NO2 proposed to be modeled? Yes No* *If no, skip the rest of the NO2-related questions. 2. If Tier 3 is anticipated to demonstrate compliance in the modeling analysis (OLM or PVMRM), please provide the following details now to expedite MPCA s review: a. In-stack ratio of NO2/NOx (CO NO2STACK) (default=0.50): b. Equilibrium ratio (CO NO2EQUIL) (default=0.90): 3. If Tier 3 is anticipated, please provide details below regarding ozone values (Please check all option(s) proposed to be used): a. CO OZONEFIL (hourly): i. O3FileName: ii. O3Units: UG/M3 PPM PPB iii. O3Format: TTY or Available in alternative formats aq2-40 7/10/13 Page 13 of 16

18 b. CO O3VALUES O3flag: OZONUNIT: PPB PPM UG/M3 Note: O3flag can be defined as ANNUAL, SEASON, MONTH, etc. PPB is the AERMOD default for OZONUNIT. See Table B-2, Appendix B, of the AERMOD User s Guide, Addendum for Version i. Please input the O3values (i=1,n) for the O3flag specified above (C.5.d.ii): Example: For CO O3VALUES SEASON, n=4 values (winter #, spring #, summer #, fall #) c. CO OZONEVAL (monitored value): O3Units: UG/M3 PPB PPM Note: UG/M3 is the AERMOD default for OZONEVAL O3units. 4. Will separate NO2/NOx ratios (SO NO2RATIO SrcID) be used for specific sources while using the OLM or PVMRM options? Yes No 5. Will SO OLMGROUP ALL be used for the OLM option? N/A Yes No 6. Is EPA approval needed for the modeling protocol (e.g., Tier 3 NO2)? Tier 3 NO2 methodologies that require approval by Region 5 modeling staff need to have said approval before submission of the AQDM-06 report form and attach approval. Yes PSD/SIP permit action No State-only action 7. Additional information for this subsection that was not included above (if not applicable, place N/A in field): N/A TTY or Available in alternative formats aq2-40 7/10/13 Page 14 of 16

19 Appendix Figure App.1 Table App.1 Modeled Form of the NAAQS/MAAQS by Averaging Periods Pollutant 1-hour 3-hour 8-hour 24-hour Monthly Annual CO H2H - H2H NO 2 98 th percentile of the daily max. 1-hour values H1H Pb H1H - PM H6H of the multiyear values - H1H PM th percentile of daily max. 24-hour values - H1H SO 2 99 th percentile of the daily max. 1-hour values H2H - H2H - H1H Table App.2 Modeled Form of PSD Increment by Averaging Periods Pollutant 1-hour 3-hour 24-hour Annual NO H1H PM H2H H1H PM H2H* H1H SO 2 - H2H H2H H1H Criteria pollutants modeled for SIL analyses should be modeled as H1H s. Helpful Webpages, Documents/Guidance, and Modeling Tips Please consult the following webpages and documents for the most current modeling guidance and recommendations when filling out this form: U.S. EPA s Support Center for Regulatory Atmospheric Modeling: Please check the SCRAM webpage regularly for the most recent updates to guidance, models, and standards; especially, for modeling guidance related to: 24-hour PM2.5, 1-hour NO2, and 1-hour SO2 NAAQS. U.S. EPA s 40 CFR Part 51 Appendix W: U.S. EPA s AERMOD Implementation Guide: U.S. EPA s AirData: MPCA s Air Dispersion Modeling: MPCA s Ambient Air Monitoring Network Plan: MPCA s Environmental Review: USGS National Map Seamless Viewer (NED data): For questions on this form, or data requests from MPCA air dispersion modeling staff, please send an to: AirModeling.PCA@state.mn.us. Please be sure to include with your questions or requests: the form ID (ADQMP-01), facility name and permit #, and contact information TTY or Available in alternative formats aq2-40 7/10/13 Page 15 of 16

20 Questions can also be asked by calling one of the MPCA s air dispersion modeler s (phone numbers are listed on the MPCA s Air Dispersion Modeling webpage, link above). Tip: Please be sure to use UTM Coordinates, NAD83, Zone 15 Extended for all locational data. Zone 14 or 16 will not be acceptable. This is to keep consistency between coordinates of all Minnesota sources. Tip: For NAAQS modeling, please include the following source groups: SO SRCGROUP ALL BACKGROUND SO SRCGROUP BKG BACKGROUND SO SRCGROUP FAC [FAC sources) Tip: Plot files with combined averaging times for the same pollutant, and extensions such as *.grf, should be separated into individual *.plt files. For example, PM10 should have at least two individual plot files: one for the 24-hour averaging period for source group ALL and a second for the annual averaging period for source group ALL. Group ALL should include BACKGRND if conducting NAAQS modeling (e.g., SO SRCGROUP ALL BACKGRND ). Acronyms μg/m 3 AERMAP AERMET AERMINUTE AERMOD AERSURFACE AQ AQDMP-01 AQDMPS-01 BPIP-PRIME CO DEM EAW EIS EPA FAC FAR H1H H2H H6H H 2 S km LULC MAAQS MPCA NAAQS Micrograms per cubic meter AERMOD Terrain Preprocessor AERMOD Meteorological Preprocessor AERMOD 1-Minute ASOS Wind Data Processor AMS/EPA Regulatory Model AERMOD Surface Characteristic Tool Air Quality Air Quality Dispersion Modeling Protocol form Air Quality Dispersion Modeling Protocol Spreadsheet Building Profile Input Program for PRIME Carbon Monoxide Digital Elevation Model Environmental Assessment Worksheet Environmental Impact Statement U.S. Environmental Protection Agency 3-letter facility ID First-Approximation Representative High-first-high value High-second-high value High-sixth-high value Hydrogen Sulfide Kilometer Land Use Land Cover Minnesota State Ambient Air Quality Standard Minnesota Pollution Control Agency National Ambient Air Quality Standard NAD North American Datum of 1983 NED NO 2 NWS OLM Pb PM 10 PM 2.5 POINTCAP POINTHOR PPB PPM PRIME PSD PTE s PVMRM SCRAM SER SIL SO 2 SIP SMS National Elevation Dataset Nitrogen Dioxide National Weather Service Ozone Limiting Method Lead Particulate Matter less than 10 um in size Particulate Matter less than 2.5 um in size Capped-release point source (AERMOD beta, nondefault) Horizontal-release point source (AERMOD beta, non-default) Parts Per Billion Parts Per Million Plume Rise Model Enhancements Prevention of Significant Deterioration Program Potential to Emit Plume Volume Molar Ratio Method Support Center for Regulatory Atmospheric Modeling Significant Emission Rate Significant Impact Level Sulfur Dioxide State Implementation Plan Standardized Mobile Source UG/M3 Micrograms per cubic meter (μg/m 3 ) UTM Universal Transverse Mercator TTY or Available in alternative formats aq2-40 7/10/13 Page 16 of 16

21 Barr Footer: ArcGIS 10.4, :36 File: I:\Client\PolyMet_Mining\Work_Orders\Permitting\Air_Permit_Application\Maps\Report\AQDM_01_MineSite_Protocol\Large Figure 1 Mine Year 8 Source Layout.mxd User: arm2 CATEGORY 1 WEST PIT OVERBURDEN STORAGE & LAYDOWN AREA WWTSH!(!( SV425 ORE SURGE PILE RAIL TRANSFER HOPPER EAST PIT WASTE WATER TREATMENT FACILITY (WWTF) CATEGORY 2/3!( Point Sources Open Pit Sources Volume Sources Ambient Air Boundary Mine Pit Haul Roads Active Stockpile Removed Stockpile Dunka Road I ,500 3,000 Feet MINE YEAR 8 SOURCE LAYOUT NorthMet Project Poly Met Mining Inc. Large Figure 1 NorthMet Mine Site Dispersion Modeling Protocol

22 Barr Footer: ArcGIS 10.4, :14 File: I:\Client\PolyMet_Mining\Work_Orders\Permitting\Air_Permit_Application\Maps\Report\AQDM_01_MineSite_Protocol\Large Figure 2 Mine Year 13 Source Layout.mxd User: crr CATEGORY 1 WEST PIT OVERBURDEN STORAGE & LAYDOWN AREA CATEGORY 4 - REMOVED WWTSH!(!( SV425 ORE SURGE PILE RAIL TRANSFER HOPPER EAST PIT WASTE WATER TREATMENT FACILITY (WWTF) CATEGORY 2/3 - REMOVED AND RECLAIMED!( Point Sources Open Pit Sources Volume Sources Dunka Road Ambient Air Boundary Mine Pit Active Stockpile Removed and Reclaimed Stockpiles Removed Stockpile Open Stockpile Covered Stockpile Haul Roads Reclaimed Haul Roads I ,500 3,000 Feet MINE YEAR 13 SOURCE LAYOUT NorthMet Project Poly Met Mining Inc. Large Figure 2 NorthMet Mine Site Dispersion Modeling Protocol

23 Attachment C Non-Default Modeling Options This attachment provides additional information on the non-default modeling options described in Section C of the MPCA AQMD-01 form. The non-default options include a deposition algorithm used for PM 10 modeling. This option is described below. I. Deposition Algorithm a. PM10 Particulate Deposition An alternative to the default AERMOD deposition algorithm was proposed and approved for the PM 10 modeling completed for the Mine Site for the Draft Environmental Impact Statement and the Supplemental Draft Environmental Impact Statement. The same approach is proposed for the modeling to be submitted with the air emission permit application. In this alternative approach, particulate deposition is represented by the Decay Term (D). As stated in the model user s guide: The Decay Term in Equation (1-1) is a simple method of accounting for pollutant removal by physical or chemical processes. The decay term is calculated as a half-life as follows: D = exp [ - ψ x / u s ] Where: ψ = decay coefficient (s -1 ) x = downwind distance (m) u s = wind speed (corrected for release height) and ψ = / T 1/2 T 1/2 = pollutant half-life (s) Example: T 1/2 = 900 s x = 1000 m u s = 4 m/s D = exp [ - (0.693/900) 1000 / 4 ] = In this case, 17.5% of the plume would be removed for a receptor at 1 km distance from the source. The model applies the Decay Term after conducting the other dispersion calculations. P:\Mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\Without Adjusted U star\attachment C-Non-Default Model Options.docx 1

24 The pollutant half-life (T 1/2 ) is used to represent the various physical mechanisms which remove particulate mass from the plume. Deposition occurs from gravitational settling, removal by vegetation, particle agglomeration, and other mechanisms. The pollutant half-life was estimated using the gravitational settling velocity (Stoke s Law) term as described in the model user s guide (Equation 1-84), as follows. v g = (ρ ρ air ) g d p 2 c 2 / [ 18 µ ] * S CF Where: v g = gravitational settling velocity (cm/s) ρ = particle density (g/cm 3 ) = 2.7 for haul roads (crushed ore) ρ air = air density (= 1.2 x 10-3 g/cm 3 ) d p = particle diameter (µm) = 7.4 for mass-mean particle size c 2 = units conversion constant (1 x 10-8 cm 2 /µm 2 ) µ = viscosity of air (1.81 x 10-4 g/cm/s) S CF = slip correction factor (see Equation 1-85; for a 7.4 µm particle S CF = 1.02) g = acceleration due to gravity (981 cm/s 2 ) For the particle characteristics given above (7.4 µm diameter, 2.7 g/cm3 density), the gravitational settling term v g = cm/s. The derivation of the 7.4 µm diameter is described in Exhibit 1. To calculate the pollutant half-life, it was assumed that the time required for a 7.4 µm particle to settle from an average release height of 5 m would approximate the time-dependent component of deposition. For a 5 m release height, the settling time is T = 5 m x 100 cm/m / cm/s = 1,100 s. The calculation of pollutant half-life and use of the decay coefficient to represent deposition was used in Midwest Research Institute s report prepared for the MPCA entitled: Iron Range Air Quality Analysis (June 1979). The MRI report also provided detailed emission inventories and modeling analysis (including model calibration) which were required for EPA approval of Minnesota s State Implementation Plan (SIP). During the late 1970s, the Iron Range was in nonattainment for TSP, and the 1979 modeling analysis was part of determining the actual attainment status and identifying mitigation measures and future attainment status. An important component of the modeling analysis was to adequately address particulate deposition so that the model results could be directly compared to monitoring data. To account for particle deposition, the 1979 modeling assumed a particle density of 3 g/cm 3, a particle diameter of µm, and a release height of 5 m, for a half-life of 370 s. The proposed pollutant half-life of 1,100 s is 3 times greater than was assumed in the MRI study, with the greatest difference in the half-life resulting from the smaller particle diameter used in this analysis. The 1979 analysis also assumed that particles less than 5 µm did not settle out. For this analysis, we propose to model particles less than 2.5 µm as though they do not deposit. For the mining fugitive dust sources, PM 2.5 accounts for 10% of the total PM 10. Therefore, the modeled emission rate will be scaled by a factor of 1.1 to account for the PM 2.5 portion of the PM 10 that would not be predicted to settle out. P:\Mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\Without Adjusted U star\attachment C-Non-Default Model Options.docx

25 b. PM10 Half-Life Modeling Analysis The AERMOD model is setup that when the half-life option is selected it is applied to every source in the input file and does not allow the user to specify which sources it can be applied to (similar to the urban source option). The purpose of modeling PM 10 with half-life is to account for the deposition of particulate matter from mechanically generated fugitive dust sources. There are numerous sources included in the Mine Site modeling analysis that are not considered mechanically generated. In order to model all of the PM 10 Mine Site sources together, the LAKES AERMOD-View Multi-Chem utility will be used to combine the post-files of the mechanically generated half-life sources and the non-half-life sources together by each hour and receptor to determine the combined 24 hour and annual PM 10 NAAQS and Increment concentration results. The LAKES Multi-Chem utility allows the user to model multiple emission rates for the same input file by splitting out a single AERMOD input file into individual source, unitized model runs. Each source is modeled individually at 1 g/s with an output plot file and post file for the maximum 1hour concentration. Multi-Chem then post-processes the individual source files, combining them together by hour and receptor and multiplying each source s individual concentration results by an emission rate specified in a text file input to the software. Using this utility creates a significant amount of data files due to a post file created for every individual source. Since the format of the post-files is the same whether for a single source or a combination of sources, PolyMet is proposing to use the Multi-Chem post-processing capabilities, but not for individual source, unitized post file runs. The PM 10 modeling for the Mine Site will be divided into two separate modeling files. The first file will model the non-half-life sources listed in the paragraph above in regulatory default mode using the hourly PM 10 emission rates calculated in the emission inventory. The input file will be setup to model the 1 hour concentration and output the maximum 1 hour high 1 st high concentration plot file and post file. The second file will model the mechanically generated fugitive dust sources using the half-life option using the hourly PM 10 emission rates calculated in the emission inventory multiplied by 1.1 to account for the 10% of the PM 10 that is made up of PM 2.5 and is not subject to deposition. The output will be the maximum 1 hour high 1 st high concentration plot file and post file similar to the first input file. Using the Multi-Chem post-processing utility, these post files will be combined on an hour by hour basis for each receptor. Since the actual modeled hourly PM 10 emission rates will be accounted for in the post files, the emission rate text file that is required for the Multi-Chem utility will list the emission rates for the two post-files as 1 g/s. In this way, the half-life and non-half-life sources will be combined in time and space and the 24 hour PM 10 high 2 nd high plot file can be produced for determining the Increment results and the high 1 st high through high 6 th high plot files can be produced for determining the NAAQS results. Using this method provides the option of modeling half-life for specific sources without the necessity of creating individual input files and an overwhelming number of post files. Reference: Midwest Research Institute, Iron Range Air Quality Analysis. Draft Final Report. MRI Project No L(2). June 5, Prepared for Minnesota Pollution Control Agency. P:\Mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\Without Adjusted U star\attachment C-Non-Default Model Options.docx

26 USEPA, User s Guide for the Industrial Source Complex (ISC3) Dispersion Models. Volume II Description of Model Algorithms. USEPA OAQPS. RTP, NC. September USEPA, AERMOD Deposition Algorithms Science Document (Revised Draft). March 19, P:\Mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\Without Adjusted U star\attachment C-Non-Default Model Options.docx

27 Exhibit 1 Determination of the mass mean particle diameter of 7.4 µm A size distribution curve representative of mechanically generated particulates is shown in Figure 2 on the Particle Size Categories page appended at the end of this discussion as Attachment 1.1 or can be accessed at the following website. ( This Figure 2 shows the frequency % particle by mass for three types of atmospheric particulates (ultrafine, fine, and coarse - supercoarse). The Particle Formation page ( goes into some detail over the mechanisms associated with formation of the three classes of atmospheric particulates shown in Figure 2. As described on the Particle Formation page, physical attrition (mechanically generated) particles are shown to be primarily greater than PM 10 and correspond to the coarse - supercoarse curve on Figure 2. The mass mean particle diameter used in the proposed decay coefficient reflects mechanically generated particulate. EPA s size spectrum shown in Figure 2 was used to apportion the particulate matter between 3 and 10 microns and develop the mass mean particle diameter. Figure 2 is generic in that it is representative of atmospheric particulates and is not specific to any industry or source type. Using Figure 2 for this calculation was recommended by MPCA on a previous project. Interpolation of the coarse - supercoarse curve for the coarse particle size range (between 2.5 and 10 microns which is representative of the fugitive PM 10 modeling) of Figure 2 leads to a mass mean diameter of 7.4 microns as shown below in Table 1 and Figures 3 and 4: Table 1 PM10 Mass Percent from EPA Figure 2 Particle Size Frequency % Particles by Mass 1 Normalized Mass % Cumulative Normalized Mass % % 2.7% % 8.0% % 16.0% % 28.0% % 43.1% % 60.0% % 77.8% % 100.0% 1 Interpolated from Figure 2 for the midpoint of the category (e.g., 10 micron frequency % is midpoint between 9 and 10 microns). P:\Mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\Without Adjusted U star\attachment C-Non-Default Model Options.docx

28 Figure 3 shows the cumulative mass % (normalized to 100%) derived from EPA s Figure 2. Note that Figure 3 did not use a mathematical representation of EPA s Figure 2 as one was not provided in EPA s references. Instead, Figure 3 was obtained by selecting the particle size and reading the mass % off of the Y-axis in Figure 2. The total mass % was normalized to 100% as shown in Table 1 above. Figure 4 shows the linear interpolation for the cumulative mass percent between the 7 and 8 µm particle sizes in Figure 3. As shown in Figure 4, the 50% cumulative mass percent intersects the 7.4 µm particle size. Figure 3 - PM10 Cumulative % Mass 100% 90% 80% 70% Cumulative % 60% 50% 40% 30% 20% 10% 0% Particle Size Category (microns) Figure 3 is derived from EPA s Figure 2 for the coarse particle size distribution curve. P:\Mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\Without Adjusted U star\attachment C-Non-Default Model Options.docx

29 Figure 4 - PM10 Particle Size Distribution 7-8 um 62% 60% 58% 56% Cumulative % 54% 52% 50% 48% 46% 44% 42% 40% Particle Size (microns) Figure 4 shows the linear interpolation between the 7 and 8 µm particle size categories from Figure 3 to determine the 7.4 µm mass mean particle size. P:\Mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\Without Adjusted U star\attachment C-Non-Default Model Options.docx

30 Attachment 1.1 Basic Concepts in Environmental Sciences Module 3: Characteristics of Particles - Particle Size Categories EPA Particle Size Terminology Since the range of particle sizes of concern for air emission evaluation is quite broad it is beneficial to divide this range into smaller categories. Defining different size categories is useful since particles of different sizes behave differently in the atmosphere and the respiratory system. The EPA has defined four terms for categorizing particles of different sizes. Table 1 displays the EPA terminology along with the corresponding particle sizes. Figure 1 provides a visual comparison of the size of a fine particle (1.0 µm), coarse particle (10 µm), and a supercoarse particle (100 ). There is a substantial difference in size between these particles, all of which are considered moderate-to-large in air pollution control. P:\Mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\Without Adjusted U star\attachment C-Non-Default Model Options.docx

31 Regulated Particulate Matter Categories In addition to the terminology provided in Table 1 the EPA also categorizes particles as follows: Total Suspended Particulate Matter (TSP) PM 10 PM 2.5 Particles less than 0.1 Condensable Particulate Matter These particle categories are important because particulate matter is regulated and tested for under these categories. The National Ambient Air Quality Standard for PM 2.5 was remanded by a District of Columbia court in May of 1999 and is under litigation as of the writing of these modules (December 1999). Air quality standards are presented in these modules as they were promulgated by the EPA, with no presumptions made regarding the outcome of the pending litigation. Figure 2 displays a typical size distribution of atmospheric particulate matter that combines the two classification schemes discussed above. P:\Mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\Without Adjusted U star\attachment C-Non-Default Model Options.docx

32 Total Suspended Particulate Matter Particles ranging in size from 0.1 micrometer to about 30 micrometer in diameter are referred to as total suspended particulate matter (TSP). TSP includes a broad range of particle sizes including fine, coarse, and supercoarse particles. PM 10 The U.S. EPA defines PM10 as particulate matter with a diameter of 10 micrometers collected with 50% efficiency by a PM10 sampling collection device. However, for convenience in these modules, the term PM10 will be used to include all particles having an aerodynamic diameter of less than or equal to 10 micrometers. PM10 is regulated as a specific type of "pollutant" because this size range is considered respirable. In other words, particles less than approximately 10 micrometers can penetrate into the lower respiratory tract. The particle size range between 0.1 and 10 micrometers is especially important in air pollution studies. A major fraction of the particulate matter generated in some industrial sources is in this size range. PM10 is discussed in more detail in Module 6. P:\Mpls\23 MN\69\ \WorkFiles\APA\Permitting\Air Permitting\Class II Modeling Mine Site\Protocol\Without Adjusted U star\attachment C-Non-Default Model Options.docx

33 Attachment J to AQDM-01 - NorthMet Mine Site Protocol Background Concentrations and Determination of Nearby Sources to be Modeled This attachment provides a detailed discussion of background concentrations and the nearby sources to be explicitly modeled for the NorthMet Mine Site Class II Area air dispersion modeling cumulative impact assessment. The approach presented herein follows directly from EPA s March 1, 2011 Memorandum Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1-hour NO 2 National Ambient Air Quality Standard. The Determining Background Concentrations section of the EPA memorandum (starting on p.12) provides guidance applicable to all pollutants and is not limited to the NO 2 NAAQS. Relevant excerpts from EPA s March 2011 Memorandum are reiterated (bold added) as they provide the foundation for the proposed approach: p. 12 goal of cumulative impact analysis: The goal of the cumulative impact assessment should be to demonstrate with an adequate degree of confidence in the result that the proposed new or modified emissions will not cause or contribute to violations of the NAAQS. In general, the more conservative the assumptions on which the cumulative analysis is based, the more confidence there will be that the goal has been achieved and the less controversial the review process will be from the perspective of the reviewing authority. p.12 nearby sources to include: As noted in the June 29, 2010 memo, Section of Appendix W emphasizes the importance of professional judgment by the reviewing authority in the identification of nearby and other sources to be included in the modeled emission inventory, and establishes a significant concentration gradient in the vicinity of the source under consideration as the main criterion for this selection. Appendix W also suggests that the number of such [nearby] sources is expected to be small except in unusual situations. p. 13 monitoring data: Section b of Appendix W states that [t]ypically, air quality data should be used to establish background concentrations in the vicinity of the sources(s) under consideration. Section c further states that [i]f the source is not isolated, it may be necessary to use a multi-source model to establish the impact of nearby sources. While many applications will be required to include both monitored and modeled contributions to adequately account for background concentrations in the cumulative analysis, we believe that these statements imply a preference for use of ambient air quality data to account for background concentrations where possible.

34 p. 13 double counting: Many of the challenges and more controversial issues related to cumulative impact assessments arise in the context of how best to combine a monitored and modeled contribution to account for background concentrations. Addressing these issues requires an assessment of the spatial and temporal representativeness of the background monitored concentrations for purposes of the cumulative impact assessment and the potential for double counting of impacts from modeled sources that may be contributing to monitored concentrations. p. 16 concentration gradients: Even accounting for some terrain influences on the location and gradients of maximum 1-hour concentrations, these considerations suggest that the emphasis on determining which nearby sources to include in the modeling analysis should focus on the area within about 10 kilometers of the project location in most cases. The routine inclusion of all sources within 50 kilometers of the project location, the nominal distance for which AERMOD is applicable, is likely to produce an overly conservative result in most cases. The March 2011 memo also provides a methodology for the analysis which includes: Identify nearby sources to be included in the modeled inventory o The MPCA s SQRMD tools provides the first step in this inventory by identifying all permitted sources within 50 km of the project site as shown in Large Figure J-1. The tool uses 2013 actual emissions to provide a first-cut on sources which may cause a significant concentration gradient in the vicinity of the source. Large Figure J-1 also depicts those sources which exceed the SQRMD thresholds and would potentially be considered as nearby sources to explicitly model. Determine the source characteristics and local meteorological and topographical factors that determine the spatial and temporal patterns of the source s ambient impacts. A three step process is identified which includes preparation of modeled concentration contour plots, identifying meteorological conditions associated with maximum modeled concentrations, and preparation of a wind rose to depict general flow characteristics. o o Significant Impact Level (SIL) results figures, meteorological conditions and other factors contributing to maximum modeled concentrations are discussed by pollutant below. The primary topographical formation near the NorthMet Mine Site is the ridge along the Mesabi Iron Range formation. Also of topographical importance are the landscape changes due to former (and future) mining activities including open pits and waste rock stockpiles.

35 o The wind rose for Hibbing, Minnesota is shown in Large Figure J-2. Predominant winds are from the northwest and southeast. As discussed further below, these wind directions do not line up with sources west of the Mine Site. Determine the location and magnitude of air quality data from ambient monitors located within the area. o The Virginia, Minnesota (pop. 8,700) ambient monitor (MPCA ID 1300) was established in 1968 to measure dust impacts from taconite mining and related activities. The site currently monitors Total Suspended Particulate (TSP), PM 10, and PM 2.5. The monitor is located approximately 32 km west-southwest of the Plant Site roughly equidistant to United Taconite Thunderbird Mine, U.S. Steel MinnTac, and ArcelorMittal Minorca Mine. Notably, the monitor is located downwind of MinnTac for the predominant northwest wind direction. The monitor also is influenced by Virginia Public Utilities as well as population-related sources. PM 10 Large Figures J-3 and J-4 show the PM Hour and annual SIL analysis results for the Year 8 Mine Site layout. 1 The receptors which exceed the SIL are similar for both runs, with the 24-hour SIL having a slightly larger extent and receptors over the SIL just to the north and south of the Mine Site boundary. Maximum modeled results at the Mine Site occur during low wind speeds (<1 m/s) and stable atmospheric conditions. The MPCA SQRMD Tool identified four PM 10 sources (ArcelorMittal Minorca Mine, Mesabi Nugget, Northshore Peter Mitchell Mine, and Laskin Energy Center) within 50 km of the Mine Site which exceed the SQRMD threshold value and could potentially be explicitly modeled. 2 Laskin Energy Center now only burns natural gas and so is no longer a significant PM 10 source. ArcelorMittal Minorca Mine is located close to the Virginia monitor and the Virginia monitored concentrations would include the contributions from this source. Mesabi Nugget and NorthMet Plant Site are located over 10 km due west of the Mine Site and would not have combined impacts during the meteorological conditions associated with maximum modeled concentrations from Mine Site sources which occur during low wind speeds (<1 m/s) and either southerly or northerly winds. Additionally, Mesabi Nugget and NorthMet Plant Site are source types similar to those sources captured by the Virginia monitor. So explicitly modeling Mesabi Nugget and the NorthMet Plant Site would be in essence double counting the impacts from these sources when using the NAAQS design value from the Virginia monitor as the representative background concentration. Northshore Peter Mitchell Mine is the only source with a potential for combined PM 10 impacts with the Mine Site sources. Note that the receptors exceeding the PM 10 SIL on the north side of the Mine Site are on Northshore Peter Mitchell Mine property, so the Northshore sources would not be included in a cumulative impact analysis at those receptors. The model input parameters for the Northshore sources 1 Previous modeling has shown Year 8 to have higher modeled concentrations than Year 13. Only Year 8 results are included for the SIL modeling analysis. 2 The SQRMD tool requires a source to exist to determine distance to other nearby sources. The SQRMD tool s coordinates for Northshore s Peter Mitchell Mine were used for the NorthMet Mine Site location.

36 are included in the spreadsheet NorthMet Mine Site Nearby Source Model Inputs Northshore Peter Mitchell Mine.xlsx posted on the Project Website. Additional discussion of Northshore Peter Mitchell Mine modeling inputs is presented below. The Virginia PM 10 monitored NAAQS concentration (3-year average of the high-2 nd -high monitored concentration for 24-hour NAAQS, and 3-year average concentration for annual MAAQS) will be used as a conservative single value background in the cumulative PM 10 NAAQS model results. As an additional measure to account for potential combined impacts from Mesabi Nugget and NorthMet Plant Site sources, the design value modeled concentration (high-6 th -high of 5 years for 24-hour NAAQS and maximum annual concentration for MAAQS) from the Plant Site modeling which occurs on the western Mine Site boundary will also be added to the background concentration. For example, the SDEIS modeling showed a H6H 24-hour PM 10 modeled concentration of 5 µg/m 3 at the western Mine Site boundary. Adding 5 µg/m 3 to the Virginia monitored background concentration of 33 µg/m 3 would result in a 38 µg/m 3 concentration being added to the modeled concentration at each receptor for comparison to the 24-hour PM 10 NAAQS. The PM hour PSD increment of 30 µg/m 3 is the limiting (i.e., most restrictive) standard for the Mine Site PM 10 modeling. Only the Mine Site sources will be modeled for demonstrating compliance with the PM 10 increments based on the following considerations: The increment consuming and expanding sources at the Plant Site (Mesabi Nugget, NorthMet Plant Site, and LTVSMC) do not have combined impacts with the Mine Site maximum modeled concentrations. The SDEIS Plant Site increment modeling showed no increment consumption at the western Mine Site boundary (eastern Plant Site boundary) and would not show increment consumption at receptors further to the east. Northshore Peter Mitchell Mine was active at the PSD increment minor source baseline date and is therefore not an increment consuming source. This protocol does not propose to develop emission expansion credits due to any enforceable emission reductions at Northshore s facility. PM 2.5 Large Figures J-5 and J-6 show the Mine Site PM Hour and annual SIL analysis results. The 24 PM 2.5 SIL is exceeded in all directions from the Mine Site, with the furthest SIL exceedance 24 km to the southeast of the Mine Site. Model concentrations exceeding the SIL occur during very light winds (< 1 m/s) for all wind directions. The annual PM 2.5 SIL is also exceeded but to a lesser extent than the 24-hour PM 2.5 SIL. The MPCA SQRMD Tool identified two PM 2.5 sources (Mesabi Nugget and Northshore Peter Mitchell Mine) within 50 km which exceed the SQRMD threshold value and could potentially be explicitly modeled. 3 Mesabi Nugget is located over 10 km due west of the Mine Site and would not have 3 The SQRMD tool requires a source to exist to determine distance to other nearby sources. The SQRMD tool s coordinates for Northshore s Peter Mitchell Mine were used for the NorthMet Mine Site location.

37 combined impacts during the meteorological conditions associated with maximum modeled concentrations from Mine Site sources which occur during very low wind speeds (<1 m/s). Northshore Peter Mitchell Mine is the only source with a potential for combined PM 2.5 impacts with the Mine Site sources. Note that the receptors exceeding the PM 2.5 SIL on the north side of the Mine Site are on Northshore Mine property, so the Northshore sources would not be included in a cumulative impact analysis at those receptors. The model input parameters for the Northshore sources are included in the attached spreadsheet and additional discussion of Northshore Peter Mitchell Mine modeling inputs is presented below. The Virginia monitor will be used to develop background PM 2.5 concentrations. The PM 2.5 NAAQS concentration value (3-year average of the 98 th percentile monitored concentration for the 24-hour averaging period, and 3-year average concentration for the annual averaging period) may be used as a conservative single value to determine the total PM 2.5 NAAQS model results. A potential refinement to the 24-hour PM 2.5 background concentration will be to use the 98 th percentile value of the seasonal concentrations. Northshore Peter Mitchell Mine: The Northshore Mining Company Peter Mitchell Mine operates under Air Emission Permit No This facility will be included in the cumulative NAAQS evaluation for the Mine Site. The facility was in operation at the baseline date, so it does not consume increment and will not be included in the increment assessment. Emission rates were taken from the June 2005 Title V Air Permit and associated permit application, the 2009 permit reissuance application and stack test results as analyzed by MPCA. The model inputs, data sources, and calculations are shown in detail in the attached NorthMet Mine Site Nearby Source Model Inputs spreadsheet. A project was proposed by Northshore Mining Company in a September 2, 2014 Environmental Assessment Worksheet (EAW) titled Northshore Mining Company Progression of the Ultimate Pit Limit. The Project Description from the EAW reads as follows: Northshore Mining Company proposes to progress the Ultimate Pit Limit within its Permit to Mine at its Peter Mitchell Mine to access additional economic taconite ore, consistent with Northshore s long-term development plan for the mine. In this 108 acre progression, the taconite ore is overlain by Type II Virginia Formation (VF) rock that will be mined and stockpiled to access the ore. Northshore will permanently stockpile Type II VF rock from the progression on-site following a stockpile plan that minimizes contact of groundwater and runoff with stockpiled rock. Per the EAW discussion of potential air impacts: 1. The Ultimate Pit Progression Project involves only fugitive mining emissions (crushing and railcar loading are unaffected); 2. The mining is in same general pit area; 3. The expansion area is small compared to the overall site footprint;

38 4. No increase over historic production levels will occur; 5. Emissions are controlled; and 6. The proposed expansion area is closer to stockpiles and the crushing plant, so haul distances will not increase. Therefore, no adjustment to the modeling parameters is warranted or proposed as a result of the Ultimate Pit Progression Project.

39 50 km Barr Footer: ArcGIS 10.4, :12 File: I:\Client\PolyMet_Mining\Work_Orders\Permitting\Air_Permit_Application\Maps\Report\AQDM_01_MineSite_Protocol\Figure J-1 Nearby Source Locations MPCA SQRMD Tool.mxd User: arm2 u n t y y ArcelorMittal Minorca Mine Inc Hoover Construction Co - Nonmetallic Virginia Department of Public Utilities! ")!! S t. L o u i s C o u n t y Virginia PM Monitor Mesabi Nugget Delaware LLC!(!!! Cliffs Erie LLC - Hoyt Lakes!( Minnesota Power - Laskin Energy Center! Northshore Mining Co - Babbitt* Louis Leustek & Sons Inc - Nonmetallic L a k e C o u n t y L a k e S u p e r i o r! PM 10 All Nearby Sources!( PM 2.5 Sources That Exceed SQRMD PM 10 Sources That Exceed SQRMD ") Ambient Monitoring Site *Note: SQRMD Tool requires source to exist. NorthShore Mining Co - Babbitt was used for mine site location. Ambient Air Boundary (AAB) MnDNR Mine Featues, 2015 I Kilometers NEARBY SOURCE LOCATIONS MPCA SQRMD TOOL NorthMet Project Poly Met Mining Inc. Large Figure J-1 NorthMet Mine Site Dispersion Modeling Protocol

40 Large Figure J-2 Hibbing Wind Rose

41 Barr Footer: ArcGIS 10.4, :19 File: I:\Client\PolyMet_Mining\Work_Orders\Permitting\Air_Permit_Application\Maps\Report\AQDM_01_MineSite_Protocol\Figure J-3 PM10_SIL_24HR.mxd User: crr PM Hour SIL Radius = 5 km PM Hour SIL Concentrations (µg/m 3 )!( !( !( !(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!( NorthMet Ambient Air Boundary (AAB) Approximate Northshore Ambient Air Boundary (AAB) Approximate LTVSMC Ambient Air Boundary (AAB) Approximate Mesabi Nugget Ambient Air Boundary (AAB) MnDNR Mine Featues, 2015 I Kilometers 24-HR PM 10 MODELED CONCENTRATIONS MINE SITE YEAR 8 - SIL ANALYSIS NorthMet Project Poly Met Mining Inc. Large Figure J-3 NorthMet Mine Site Dispersion Modeling Protocol

42 Barr Footer: ArcGIS 10.4, :19 File: I:\Client\PolyMet_Mining\Work_Orders\Permitting\Air_Permit_Application\Maps\Report\AQDM_01_MineSite_Protocol\Figure J-4 PM10_SIL_ANN.mxd User: arm2 PM 10 Annual SIL Radius = 4.4 km PM Hour SIL Radius = 5 km PM 10 Annual SIL Concentrations (µg/m 3 )!( !( !( !(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!( NorthMet Ambient Air Boundary (AAB) Approximate Northshore Ambient Air Boundary (AAB) Approximate LTVSMC Ambient Air Boundary (AAB) Approximate Mesabi Nugget Ambient Air Boundary (AAB) MnDNR Mine Featues, 2015 I Kilometers ANNUAL PM 10 MODELED CONCENTRATIONS MINE SITE YEAR 8 - SIL ANALYSIS NorthMet Project Poly Met Mining Inc. Large Figure J-4 NorthMet Mine Site Dispersion Modeling Protocol

43 S t. L o u i s C o u n t y Barr Footer: ArcGIS 10.4, :23 File: I:\Client\PolyMet_Mining\Work_Orders\Permitting\Air_Permit_Application\Maps\Report\AQDM_01_MineSite_Protocol\Figure J-5 24HrPM25SIL_noustar mxd User: arm2 L a k e C o u n t y L a k e S u p e r i o r PM Hour SIL Radius = 25.8 km PM Hour SIL Concentrations (µg/m 3 ) NorthMet Ambient Air Boundary (AAB) Approximate Northshore Ambient Air Boundary (AAB) Approximate LTVSMC Ambient Air Boundary (AAB) Approximate Mesabi Nugget Ambient Air Boundary (AAB) US Forest Service Class I Areas MnDNR Mine Featues, 2015 I Kilometers 24-HR PM 2.5 MODELED CONCENTRATIONS SIL Analysis NorthMet Project Poly Met Mining Inc. Large Figure J-5 NorthMet Mine Site Dispersion Modeling Protocol

44 S t. L o u i s C o u n t y Barr Footer: ArcGIS 10.4, :33 File: I:\Client\PolyMet_Mining\Work_Orders\Permitting\Air_Permit_Application\Maps\Report\AQDM_01_MineSite_Protocol\Figure J-6 AnnPM25SIL_noustar mxd User: crr PM 2.5 Annual SIL Radius = 25.8 km PM Hour SIL Radius = 10 km PM 2.5 Annual SIL Concentrations (µg/m 3 ) NorthMet Ambient Air Boundary (AAB) Approximate Northshore Ambient Air Boundary (AAB) Approximate LTVSMC Ambient Air Boundary (AAB) Approximate Mesabi Nugget Ambient Air Boundary (AAB) US Forest Service Class I Areas MnDNR Mine Featues, 2015 I Kilometers L a k e C o u n t y L a k e S u p e r i o r ANNUAL PM 2.5 MODELED CONCENTRATIONS SIL Analysis NorthMet Project Poly Met Mining Inc. Large Figure J-6 NorthMet Mine Site Dispersion Modeling Protocol