for draft air emission permit no. 13700345 101

Technical Support Document, Permit Action Number: 13700345‐101 of 234

Technical Support Document for

Draft Air Emission Permit No. 13700345‐101 This technical support document (TSD) is intended for all parties interested in the draft permit and to meet the requirements that have been set forth by the federal and state regulations (40 CFR § 70.7(a)(5) and Minn. R. 7007.0850, subp. 1). The purpose of this document is to provide the legal and factual justification for each applicable requirement or policy decision considered in the preliminary determination to issue the draft permit. 1. General Information

1.1 Applicant and Stationary Source Location

Table 1. Applicant and Source Address

Applicant/Address Stationary source/Address

(SIC Code: 1021)

PolyMet Mining, Inc. 6500 County Road 666 Hoyt Lakes, Minnesota 55750

PolyMet Mining, Inc. 6500 County Road 666 Hoyt Lakes, MN 55750

Contact: Kevin Pylka Phone: 218‐471‐2162

1.2 Facility Description

PolyMet Mining, Inc. (PolyMet) is proposing to develop the NorthMet copper‐nickel‐gold/platinum‐group‐metal (AuPGM) mine and associated processing facilities in northeastern Minnesota for the NorthMet Project (Project). The mining and processing operations will be located in an existing mining region and will use existing infrastructure as much as possible. The Project area, which includes the Mine Site, Plant Site, and the Transportation and Utility Corridors (primarily Dunka Road), is located in St. Louis County, Minnesota, at the eastern end of the Mesabi Iron Range. The Mine Site is located within the Superior National Forest in an area that has not previously been mined. It is located approximately 6 miles south of the City of Babbitt and directly south of the Peter Mitchell Mine, which is an active taconite/iron mine. The Plant Site is located southwest of the Mine Site at the former LTV Steel Mining Company (LTVSMC) taconite facility, which PolyMet purchased from Cliffs Erie LLC. The Project design basis is to mine and process an average of 32,000 tons of ore per day (11,680,000 tons of ore per year). PolyMet will restart and use existing portions of the LTVSMC infrastructure and crushing and grinding capability with upgraded pollution control equipment. Construction of the Project may occur in phases, with the Crusher/Concentrator/Flotation portion of the Plant Site likely completed and operating prior to the construction of the Hydrometallurgical Plant. Operations at the Mine Site will include point and fugitive sources of air emissions. Point source emissions from support activities associated with mining operations include heaters, emergency generators, and lime storage and handling. Fugitive source emissions from mining operations include waste rock, ore, and overburden loading/unloading and truck traffic. Portable crushing and screening equipment will also be operated at the Mine Site to prepare approved material for use in construction, for blast hole stemming, and for use as railroad ballast.


Mining preparation begins by removing overburden with diesel‐hydraulic shovels, haul trucks, and other excavating equipment. Overburden is stored in temporary and permanent stockpiles near the mine pits to minimize the time and travel distance for haul truck round trips. After overburden stripping, waste rock and ore is blasted and then loaded into mine trucks by diesel‐hydraulic shovels. The mine is considered operational upon the commencement of blasting of waste rock and ore or 15 days after the commencement of blast hole drilling, whichever occurs first. The ore is hauled by mine trucks out of the pits to the rail transfer hopper to be delivered to the Plant Site. An ore surge pile is located near the rail transfer hopper to allow ore shipment to continue during a temporary interruption in ore mining. Waste rock is transported to a temporary or permanent stockpile or transported to a mined out pit for disposal. Plant Site operations include point and fugitive sources of air emissions. Point source emissions from the Plant Site operations include crushing, grinding, and screening operations; material handling and storage; and mineral processing operations including an autoclave and hydrometallurgical process tanks. There are also combustion‐related emissions from space heaters, emergency engines, and a startup boiler for the autoclave. Fugitive sources of emissions at the Plant Site include construction activities at the flotation tailings basin and the hydrometallurgical residue cells along with wind erosion during flotation tailings basin operation. Other fugitive emission sources at the Plant Site include outdoor process consumable storage and handling and miscellaneous truck traffic. Ore from the Mine Site is delivered by rail to the Coarse Crusher building where it undergoes two stages of crushing and screening before it is transferred to a semi‐autogenous grinding (SAG) mill and ball mill for further size reduction. The ground ore is fed to the flotation process, which separates the nickel, copper, cobalt, and AuPGM bearing minerals into a concentrate streams and sends the remaining material (flotation tailings) to the flotation tailings basin. The flotation process produces separate copper‐rich and nickel‐rich flotation concentrate streams that can be sold or, after construction of the Hydrometallurgical Plant, the nickel‐rich concentrate can be further processed to produce a higher quality nickel/cobalt concentrate product and an AuPGM concentrate product. The operation of the hydrometallurgical plant also allows for enrichment of the copper concentrate product.

1.3 Description of the Activities Allowed by this Permit Action This permit action is an initial Part 70 Permit. The Minnesota Pollution Control Agency (MPCA) has a combined operating and construction permitting program under Minnesota Rules Chapter 7007, and under Minn. R. 7007.0800. Under that authority, this permit action authorizes construction. The PolyMet process flow diagrams documenting the intended facility configuration is included as Attachment 5 to this TSD.


1.4 Facility Emissions

Table 2. Total Facility Potential to Emit Summary

PM tpy

PM10 tpy

PM2.5 tpy

SO2 tpy

NOx tpy

CO tpy

CO2e tpy

VOC tpy

Single HAP tpy

All HAPs tpy

Total Facility Limited Potential Emissions (with fugitive emissions)

2,530.3 885.43 266.65 8.28 107.34 114.45 160,679 49.52 5.33

(Nickel) 19.37

Total Facility Limited Potential Emissions (without fugitive emissions)

178.66 170.22 166.31 7.17 100.74 112.94 160,679 49.35 5.33

(Nickel) 19.37

Total Facility Projected Actual Emissions**

2,467.5 826.39 209.45 5.13 41.27 49.05 * 41.99 *

*Not reported in Minnesota emission inventory. ** Actual emissions are estimated for the first‐time invoice that is required for facilities obtaining an initial Part 70 operating permit.

Table 3. Facility Classification

Classification Major Synthetic minor/area Minor/Area New Source Review X Part 70 X Part 63 X

2. Regulatory and/or Statutory Basis

2.1 New Source Review (NSR) The facility is a non‐major source under New Source Review regulations. As the facility is not one of the source categories listed in 40 CFR § 52.21(b)(1)(iii), fugitive emissions are excluded in determining whether the facility is a major stationary source. The facility’s potential emissions are displayed in Table 2 which includes a distinction for emissions that are considered fugitive. As fugitive emissions are not considered in this determination, all regulated air pollutants are less than the major source thresholds for NSR, i.e., 250 tons per year of any regulated NSR pollutant (40 CFR § 52.21(b)(1)). In addition, PolyMet accepted limits on its emissions and operations in order to avoid major source classification under NSR. Therefore, the facility is not considered a new major source for NSR. Restrictions on emissions and operations that limit annual emissions from the facility below NSR major source thresholds are referred to as synthetic minor limitations and can take a number of forms, such as process throughput limits, emissions rate or concentration limits, vehicle miles traveled limits, and control efficiency requirements. The effect of these limits and their sum over the entire facility results in the total facility limited potential emissions found in Table 2. Details about the emissions calculations and how they sum to the results in Table 2 can be found in Attachment 1 to this TSD. Synthetic minor emission limits, process throughput restrictions, and control efficiency requirements are found in the permit based on which equipment is covered by the particular limit. For example, a pound per hour emission rate or grams per dry standard cubic meter concentration limit on exhaust gases from a point source will be found at the stack level, or STRU, where those emissions vent to the atmosphere. A process throughput limitation would be found at the equipment level (EQUI) or fugitive source (FUIGI) where the material is processed. Finally, a control efficiency requirement will be found at the treatment, or TREA, level of the permit where the emissions are controlled. While most of these limits are contained in the permit at


the individual source where they are generated, emitted, or controlled, some limits that apply to a group of items or apply to many of the same type of item will be located in the permit at a component group, or COMG, to which the affected items are a member of the group. Each synthetic minor NSR limitation is cited as “Title I Condition: Avoid major source under 40 CFR 52.21(b)(1)(i) and Minn. R. 7007.3000” to delineate purpose and authority for the limit. With regards to greenhouse gas emissions, the Supreme Court of the United States, on June 23, 2014, ruled that the Clean Air Act neither compels nor permits the United States Environmental Protection Agency (EPA) to adopt an interpretation of the Clean Air Act requiring a stationary source of pollution to obtain a (Prevention of Significant Deterioration) PSD or Title V permit on the sole basis of its potential greenhouse gas (GHG) emissions. However, EPA reasonably interpreted the Clean Air Act to require sources that would need permits based on their emissions of conventional pollutants to comply with Best Available Control Technology (BACT) requirements for greenhouse gases. As the operations proposed by the Permittee are below all NSR major source thresholds for conventional pollutants, the facility is currently not required to obtain a PSD permit for its GHG emissions.

2.2 Part 70 Permit Program The facility is a major source under the Part 70 operating permit program.

2.3 New Source Performance Standards (NSPS) Portions of the operations described in this permit action are subject to the following requirements:

40 CFR pt. 60, subp. Dc, Standards of Performance for Small Industrial, Commercial, and Institutional Steam Generating Units.

40 CFR pt. 60, subp. LL, Standards of Performance for Metallic Mineral Processing Plants.

40 CFR pt. 60, subp. OOO, Standards of Performance for Nonmetallic Mineral Processing Plants.

40 CFR pt. 60, subp. IIII, Standards of Performance for Stationary Spark Ignition Internal Combustion Engines.

2.3.1 40 CFR pt. 60, subp. Dc ‐ Standards of Performance for Small Industrial, Commercial, and

Institutional Steam Generating Units 40 CFR pt. 60, subp. Dc applies to steam generating units that have a maximum design heat input capacity of 29 megawatts (100 MMBtu/hr) or less, but greater than or equal to 2.9 megawatts (10 MMBtu/hr), that commence construction, modification, or reconstruction after June 9, 1989. Steam generating units are defined as, “a device that combusts any fuel and produces steam or heats water or heats any heat transfer medium. This term includes any duct burner that combusts fuel and is part of a combined cycle system. This term does not include process heaters as defined in this subpart.” PolyMet operates one boiler (EQUI 118: Autoclave Startup Boiler) that is subject to 40 CFR pt. 60, subp. Dc. EQUI 118 has a maximum heat input capacity of 50 MMBtu/hr and can only combust natural gas. There are no emission standards applicable to EQUI 118, but the facility must keep records of fuel type and usage each calendar month.

2.3.2 40 CFR pt. 60, subp. LL ‐ Standards of Performance for Metallic Mineral Processing Plants 40 CFR pt. 60, subp. LL applies to affected facilities, as identified in 40 CFR § 60.380(a), in metallic mineral processing plants that commence construction or modification after August 24, 1982. Affected facilities include each crusher and screen in open‐pit mines; each crusher, screen, bucket elevator, conveyor belt transfer point, thermal dryer, product packaging station, storage bin, enclosed storage area, truck loading station, truck unloading station, railcar loading station, and railcar


unloading station at the mill or concentrator. Metallic mineral processing plants are any combination of equipment that produces metallic mineral concentrates from ore, as defined in 40 CFR § 60.381. As PolyMet processes ore to produce a metallic mineral concentrate, the facility meets the definition of a metallic mineral processing plant. As the facility meets this definition, the ore processing and production equipment at the facility are subject to the requirements of 40 CFR pt. 60, subp. LL. The ore processing and production equipment consist of the following affected facilities: EQUI 32, EQUIs 55‐56, EQUI 97, EQUI 101, EQUIs 104‐106, EQUI 628, and EQUIs 644‐648. As each of these emission units will commence construction after August 24, 1982, each emission unit is subject to the requirements of 40 CFR pt. 60, subp. LL. Regarding the existing ore processing and production equipment at the PolyMet facility, 40 CFR pt. 60, subp. LL applies to existing equipment that commences modification or reconstruction after August 24, 1982. A modification is defined in 40 CFR § 60.2 as any physical change in, or change in the method of operation of, an existing facility which increases the amount of any air pollutant (to which a standard applies) emitted into the atmosphere by that facility or which results in the emission of any air pollutant (to which a standard applies) into the atmosphere not previously emitted. Reconstruction is defined in 40 CFR § 60.15 as the replacement of components of an existing facility to such an extent that the fixed capital cost of the new components exceeds 50 percent of the fixed capital cost that would be required to construct a comparable entirely new facility; and it is technologically and economically feasible to meet the applicable standards set forth in 40 CFR pt. 60. 40 CFR § 60.383 contains further directions for reconstruction specifying the cost of replacement of ore‐contact surfaces (crushing surfaces; screen meshes, bars, and plates; conveyor belts; elevator buckets; and pan feeders) on processing equipment shall not be considered in calculating either the “fixed capital cost of the new components” or the “fixed capital cost that would be required to construct a comparable new facility” under 40 CFR § 60.15. While this equipment was constructed prior to August 24, 1982, PolyMet has identified that the cost to restart some of the equipment may be close to or over the 50% reconstruction threshold. As a result, PolyMet decided to accept applicability of 40 CFR pt. 60, subp. LL requirements for the existing ore processing and production equipment. The affected sources include EQUIs 1‐31, EQUIs 33‐54, and EQUIs 57‐92. As each of these emission units will commence reconstruction after August 24, 1982, each emission unit is subject to the requirements of 40 CFR pt. 60, subp. LL. 2.3.3 40 CFR pt. 60, subp. OOO ‐ Standards of Performance for Nonmetallic Mineral Processing Plants 40 CFR pt. 60, subp. OOO applies to affected facilities, as identified in 40 CFR § 60.670(a)(1), in fixed or portable nonmetallic mineral processing plants that commence construction, modification, or reconstruction after August 31, 1983. Affected facilities include each crusher, grinding mill, screening operation, bucket elevator, belt conveyor, bagging operation, storage bin, enclosed truck or railcar loading station. Nonmetallic mineral processing plants are any combination of equipment that is used to crush or grind any nonmetallic minerals, as defined in 40 CFR § 60.671. Nonmetallic mineral processing plants are any combination of equipment that is used to crush or grind any nonmetallic minerals, as defined in 40 CFR § 60.671, which includes crushed and broken stone and limestone. As PolyMet operates equipment for the purposes of processing rock for construction (the portable crushing plant) and limestone handling, the affected facilities are subject to the requirements of 40 CFR pt. 60, subp. OOO. The portable crushing plant and limestone receiving, crushing, and handling equipment consist of the following affected facilities: EQUIs 135‐145, FUGI 24, FUGIs 37‐48, and FUGIs


50‐54. As each of these emission units will commence construction after August 31, 1983, each emission unit is subject to the requirements of 40 CFR pt. 60, subp. OOO. Additionally, bentonite is defined as a nonmetallic mineral in 40 CFR § 60.671 that is subject to the requirements of 40 CFR pt. 60, subp. OOO. Although crushing or grinding of bentonite is not performed at PolyMet, the facility already meets the definition of a nonmetallic mineral processing plant for the purposes of 40 CFR pt. 60, subp. OOO. Therefore, the affected facilities as identified in 40 CFR § 60.670(a)(1) on the bentonite material handling operations are possibly subject to the requirements of 40 CFR pt. 60, subp. OOO. However, the bentonite material handling operations (FUGI 6) are truck loading and unloading operations that are a part of construction of the tailings basin. As truck unloading is not an affected facility and the loading operations are not enclosed, FUGI 6 does not qualify as an affected facility under 40 CFR pt. 60, subp. OOO. As none of the bentonite handling operations qualify as affected facilities, FUGI 6 is not subject to the requirements of 40 CFR pt. 60, subp. OOO.

2.3.4 40 CFR pt. 60, subp. IIII ‐ Standards of Performance for Stationary Compression Ignition Internal Combustion Engines 40 CFR pt. 60, subp. IIII applies to stationary compression ignition internal combustion engines that were manufactured after April 1, 2006 and commenced construction, modification, or reconstruction after July 11, 2005. PolyMet operates four stationary internal combustion engines that are subject to 40 CFR pt. 60, subp. IIII: EQUI 188, EQUI 190, EQUI 192, and EQUI 194. EQUI 188 and EQUI 190 are fire pump engines with an engine displacement of less than 30 liters per cylinder and are subject to the emission limits as required by 40 CFR § 60.4205(c). EQUI 192 and EQUI 194 are 2007 model year and later emergency stationary engines with an engine displacement of less than 30 liters per cylinder that are not fire pump engines. These two engines are subject to the emission limits as required by 40 CFR § 60.4205(b). Regarding the existing backup generators (EQU 184 and EQUI 186) at the PolyMet facility, 40 CFR pt. 60, subp. IIII does not apply. Because this equipment was manufactured prior to April 1, 2006, the existing backup generators (EQU 184 and EQUI 186) are not subject to the requirements of 40 CFR pt. 60, subp. IIII. In addition, this equipment was never removed from the existing location and, as a result, are not subject to the deadlines in 40 CFR § 60.4208 for importing or installing stationary internal combustion engines produced in previous model years. Regarding the generator used to move electrical equipment (EQUI 196) at the PolyMet facility, 40 CFR pt. 60, subp. IIII does not apply. Because this equipment is mounted on either a trailer or pickup, it does not meet the definition of a stationary internal combustion engine. 40 CFR pt. 60, subp. IIII applies to stationary compression ignition internal combustion engines as defined in 40 CFR § 60.4219. A stationary internal combustion engine is defined as, “any internal combustion engine, except combustion turbines, that converts heat energy into mechanical work and is not mobile. Stationary internal combustion engines differ from mobile internal combustion engines in that a stationary internal combustion engine is not a nonroad engine as defined at 40 CFR § 1068.30 (excluding paragraph (2)(ii) of that definition), and is not used to propel a motor vehicle, aircraft, or a vehicle used solely for competition.” PolyMet operates EQUI 196 and several diesel and gasoline powered portable pumps that are moved to a different location at the facility at least once every 12 months, as well as several engines used to


propel motor vehicles. These types of operations meet the definition of a nonroad engine in 40 CFR § 1068.30 and therefore are not subject to the requirements of either 40 CFR pt. 60, subp. IIII. Regarding 40 CFR pt. 60, subp. IIII, the U.S. Court of Appeals for the District of Columbia Circuit issued a decision on May 1, 2015 that vacated the provisions of 40 CFR § 60.4211(f)(2) which allow operation of an emergency generator without emission controls for up to 100 hours per year as part of an emergency demand‐response program.

On July 21, 2015 the court amended the May 1, 2015 decision to specify that the decision would vacate only those portions of the regulations addressed to emergency demand response [40 CFR § 60.4211(f)(2)(ii)‐(iii)], and would leave in effect the provisions that allow emergency engines to operate for maintenance checks and readiness testing [40 CFR § 60.4211(f)(2)(i)].

On August 14, 2015, the court granted EPA’s July 15, 2015 motion to stay issuance of the court’s mandate until May 1, 2016. Therefore, all provisions of 40 CFR § 60.4211(f)(2) remained valid and in effect until revised by EPA or until May 1, 2016, whichever was earlier.

However, as EPA did not revise the challenged rules under 40 CFR pt. 60, subp. IIII before May 1, 2016, the court issued its amended judgment that vacated the provisions of 40 CFR § 60.4211(f)(2)(ii)‐(iii) on May 4, 2016. With the issuance of the court’s mandate, these provisions have no legal effect.

EPA also issued guidance, on April 15, 2016, on how the EPA intends to implement regulatory requirements in 40 CFR pt. 60, subp. IIII as a result of the vacatur. It is EPA’s view that this change means that an engine may not operate in circumstances described in the vacated provisions for any number of hours per year unless it is in compliance with the emissions standards and other applicable requirements for a non‐emergency engine.

2.4 Part 61 National Emission Standards for Hazardous Air Pollutants (NESHAP)

Portions of the operations described in this permit action are subject to the requirements of 40 CFR pt. 61, subp. M, National Emissions Standard for Asbestos. 2.4.1 40 CFR pt. 61, subp. M ‐ National Emission Standard for Asbestos

40 CFR pt. 61, subp. M applies to sources specified in 40 CFR §§ 61.142 through 61.151, 61.154, and 61.155. These sources include asbestos mills; roadways; manufacturing; demolition and renovation; spraying; fabricating; insulating materials; waste disposal for asbestos mills; waste disposal for manufacturing, fabricating, demolition, renovation, and spraying operations; inactive waste disposal sites for asbestos mills and manufacturing and fabricating operations; active waste disposal sites; and operations that convert asbestos‐containing waste material into nonasbestos (asbestos‐free) material. The PolyMet facility will utilize existing buildings that are known to contain asbestos containing materials. Any demolition or renovation activities at the existing structures that affect certain quantities of asbestos containing material are subject to the requirements of 40 CFR pt. 61, subp. M, specifically, 40 CFR § 61.145. This section specifies notification requirements and procedures for asbestos emissions control during the demolition or renovation activities.

2.5 Part 63 National Emission Standards for Hazardous Air Pollutants (NESHAP) The facility has accepted limits on HAP emissions such that it is an area source under 40 CFR pt. 63. Thus, no major source NESHAPs apply. Each limit implemented to maintain the facility as a synthetic minor source under 40 CFR pt. 63 are cited as “Title I Condition: Avoid major source under 40 CFR 63.2” to delineate purpose and authority for the limit. Portions of the operations described in this permit action are subject to the following requirements:


40 CFR pt. 63, subp. ZZZZ ‐ National Emissions Standards for Hazardous Air Pollutants for Stationary Reciprocating Internal Combustion Engines.

40 CFR pt. 63, subp. CCCCCC ‐ National Emissions Standards for Hazardous Air Pollutants for Source Category: Gasoline Dispensing Facilities.

2.5.1 40 CFR pt. 63, subp. ZZZZ ‐ National Emissions Standards for Hazardous Air Pollutants for Stationary

Reciprocating Internal Combustion Engines 40 CFR pt. 63, subp. ZZZZ applies to affected sources, as identified in 40 CFR § 63.6590, which include any existing, new, or reconstructed stationary reciprocating internal combustion engine located at a major or area source of HAP emissions. PolyMet operates six stationary internal combustion engines at its facility that are subject to 40 CFR pt. 63, subp. ZZZZ: EQUI 184, EQUI 186, EQUI 188, EQUI 190, EQUI 192, and EQUI 194. Regarding EQUI 184 and EQUI 186, each engine qualifies as an existing affected source as defined in 40 CFR § 63.6590(a)(1)(iii) because they were constructed before June 12, 2006. Under 40 CFR 63. 6603(a), because each engine is an existing stationary engine located at an area source of HAPs, each engine must meet the requirements of Table 2d of 40 CFR pt. 63, subp. ZZZZ. Regarding EQUI 188, EQUI 190, EQUI 192, and EQUI 194, each engine qualifies as a new affected source as defined in 40 CFR § 63.6590(a)(2)(iii) because they will be constructed after June 12, 2006. In addition, each engine qualifies as a new emergency stationary internal combustion engine that meets the criteria in 40 CFR § 63.6590(c)(1). Under 40 CFR 63. 6590(c)(1), because each engine is a new stationary engine located at an area source of HAPs, each engine must meet the requirements of 40 CFR pt. 63, subp. ZZZZ by meeting the requirements of 40 CFR pt. 60, subp. IIII. No further requirements of 40 CFR pt. 63, subp. ZZZZ apply to each engine. However, each engine must meet the definition of an emergency stationary reciprocating internal combustion engine in 40 CFR § 63.6675, which includes operating according to the provisions specified in 40 CFR § 63.6640(f). Regarding the generator used to move electrical equipment (EQUI 196) at the PolyMet facility, 40 CFR pt. 63, subp. ZZZZ does not apply. Because this equipment is mounted on either a trailer or pickup, it does not meet the definition of a stationary internal combustion engine. 40 CFR pt. 63, subp. ZZZZ applies to affected sources, as identified in 40 CFR § 63.6590, which include any existing, new, or reconstructed stationary reciprocating internal combustion engine located at an area source of HAP emissions. A stationary reciprocating internal combustion engine is defined as, “Any reciprocating internal combustion engine which uses reciprocating motion to convert heat energy into mechanical work and which is not mobile. Stationary RICE differ from mobile RICE in that a stationary RICE is not a non‐road engine as defined at 40 CFR § 1068.30, and is not used to propel a motor vehicle or a vehicle used solely for competition.” PolyMet operates EQUI 196 and several diesel and gasoline powered portable pumps that are moved to a different location at the facility at least once every 12 months, as well as several engines used to propel motor vehicles. These types of operations meet the definition of a nonroad engine in 40 CFR § 1068.30 and therefore are not subject to the requirements of either 40 CFR pt. 63, subp. ZZZZ. Regarding 40 CFR pt. 63, subp. ZZZZ, the U.S. Court of Appeals for the District of Columbia Circuit issued a decision on May 1, 2015, that vacated the provisions of 40 CFR § 63.6640(f)(2) which allow operation of an emergency generator without emission controls for up to 100 hours per year as part of an emergency demand‐response program.


On July 21, 2015 the court amended the May 1, 2015 decision to specify that the decision would vacate only those portions of the regulations addressed to emergency demand response [40 CFR § 63.6640(f)(2)(ii)‐(iii)], and would leave in effect the provisions that allow emergency engines to operate for maintenance checks and readiness testing [40 CFR § 63.6640(f)(2)(i)].

On August 14, 2015, the court granted EPA’s July 15, 2015 motion to stay issuance of the court’s mandate until May 1, 2016. Therefore, all provisions of 40 CFR § 63.6640(f)(2) remained valid and in effect until revised by EPA or until May 1, 2016, whichever was earlier.

However, as EPA did not revise the challenged rules under 40 CFR pt. 60, subp. IIII before May 1, 2016, the court issued its amended judgment that vacated the provisions of 40 CFR § 63.6640(f)(2)(ii)‐(iii) on May 4, 2016. With the issuance of the court’s mandate, these provisions have no legal effect.

EPA also issued guidance, on April 15, 2016, on how the EPA intends to implement regulatory requirements in 40 CFR pt. 63, subp. ZZZZ as a result of the vacatur. It is EPA’s view that this change means that an engine may not operate in circumstances described in the vacated provisions for any number of hours per year unless it is in compliance with the emissions standards and other applicable requirements for a non‐emergency engine.

2.5.2 40 CFR pt. 63, subp. CCCCCC ‐ National Emission Standards for Hazardous Air Pollutants for Source

Category: Gasoline Dispensing Facilities 40 CFR pt. 63, subp. CCCCCC applies to affected sources, identified in 40 CFR § 63.11111, as each gasoline dispensing facility located at an area source of HAP emissions including each gasoline storage tank and gasoline cargo tank during delivery of product to a gasoline dispensing facility. PolyMet operates two gasoline storage tanks at its facility that are subject to 40 CFR pt. 63, subp. CCCCCC: EQUI 631 and EQUI 632. Each storage tank has an anticipated monthly throughput of less than 10,000 gallons of gasoline and as a result must comply with the requirements of 40 CFR § 63.11116.

2.6 Compliance Assurance Monitoring (CAM) The table below lists the sources (and their respective pollutants) at the facility which are subject to CAM, whether the source is a large pollutant specific emission unit (PSEU) for the pollutant, and the monitoring for the applicable pollutants. However, the Permittee is not required to submit the monitoring plan required under 40 CFR § 64.4 at this time. CAM submittals are required for other PSEUs under 40 CFR § 64.5(a)(2) as part of an application for the reissuance of a Part 70 permit. Therefore, CAM submittals for the emission units authorized in this permit action were not required to be submitted with the application. The Permittee is required to submit the monitoring plan required under 40 CFR § 64.4 with their next application for permit renewal.

Table 4. CAM Summary

Unit Control

CAM Applicability

(Large or Other) Pollutant Monitoring EQUI 1

North 60" Crusher TREA 1

(Fabric Filter) Other

PM, PM10, PM2.5

To be determined

EQUI 2 South 60" Crusher

TREA 2 (Fabric Filter)

Other PM, PM10, PM2.5

To be determined

EQUI 3 North distribution Box



To be determined


Unit Control

CAM Applicability


North 36" Crusher 1 TREA 3


PM, PM10, PM2.5

To be determined

EQUI 5 North 36" Crusher 2



To be determined




To be determined




To be determined

EQUI 8 South Distribution Box



To be determined

EQUI 9 South 36" Crusher 1



To be determined




To be determined




To be determined




To be determined

EQUI 13 North 36" Conveyor Feed Chute to

Conveyor 1A #1



To be determined


Conveyor 1A #2



To be determined


Conveyor 1B #1



To be determined


Conveyor 1B #2



To be determined

EQUI 17 South36" Conveyor Feed Chute to

Conveyor 1A #1



To be determined


Conveyor 1A #2



To be determined


Conveyor 1B #1



To be determined


Conveyor 1B #2



To be determined

EQUI 21 South Pan Conveyor #1



To be determined




To be determined




To be determined




To be determined


Unit Control

CAM Applicability


North Pan Conveyor #1 TREA 10


PM, PM10, PM2.5

To be determined

EQUI 26 North Pan Conveyor #2



To be determined




To be determined




To be determined

EQUI 29 Drive House 1 East Transfer



To be determined

EQUI 30 Drive House 1 West Transfer



To be determined

EQUI 32 Conveyor Transfer Chute ‐ 2A and 2B to

4B/4A (Fine Crusher Building)



To be determined

EQUI 33 West Coarse Ore Bin



To be determined

EQUI 49 North Transfer Point



To be determined

EQUI 50 South Transfer Point



To be determined

EQUI 53 Fine Ore Storage ‐ North

TREAs 23‐30 (Fabric Filters)


To be determined

EQUI 54 Fine Ore Storage ‐ South

TREAs 31‐34 (Fabric Filters)


To be determined

EQUI 57 Fine Ore Feeders ‐ North 1



To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined


Unit Control

CAM Applicability


Fine Ore Feeders ‐ North 13 TREA 39


PM, PM10, PM2.5

To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined

EQUI 81 Fine Ore Feeders ‐ South 1



To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined




To be determined


Unit Control

CAM Applicability


Autoclave vent (1 unit) and Emergency Pressure Relief Vent

TREAs 51 & 52 (Wet Scrubbers)

Other PM, PM10, PM2.5, SAM

To be determined

EQUI 109 Autoclave Flash Vessels (1 unit)

TREAs 51 & 52 (Wet Scrubbers)

Other PM, PM10, PM2.5, SAM

To be determined

EQUI 135 Limestone Railcar Dump



To be determined

EQUI 136 Limestone hopper to conveyor



To be determined

For large pollutant specific emission units, records of the monitored parameter must be made at a minimum of 4 times per hour, or once every 15 minutes. For other PSEUs (not large), records must be made at a minimum of once per 24 hours.

2.7 Environmental Review and Air Emissions Risk Analysis (AERA) 2.7.1 Environmental Review

The facility was required to prepare and complete an Environmental Impact Statement (EIS) as the proposed PolyMet operations meet the mandatory threshold for an EIS in Minn. R. 4410.4400, subp. 8(B) & (C). The Minnesota Department of Natural Resources (MNDNR), U.S. Forest Service (USFS), and U.S. Army Corps of Engineers (USACE) jointly prepared an EIS to evaluate the project in accordance with the National Environmental Policy Act (NEPA; 42 U.S.C. §§ 4321‐4347) and the Minnesota Environmental Policy Act (MEPA; Minn. Stat. ch. 116D). The environmental review process described the potential environmental effects of the project, examined potential alternatives to the project as proposed, and identified how effects can be avoided or mitigated. The environmental impact statement underwent multiple opportunities for public review comment. A scoping Environmental Assessment Worksheet (EAW) was prepared for the project and informed the Final Scoping Decision Document (FSDD), which identified topics to be carried forward and analyzed in the EIS. The notice of the availability of the scoping EAW was published in the Environmental Quality Board Monitor on June 6, 2005 and requested comments on the scoping EAW. A public meeting for the scoping process was held on June 29, 2005, in Hoyt Lakes, Minnesota. The MNDNR, USFS, and USACE issued the FSDD on October 25, 2005. Subsequently, an EIS Preparation Notice summarizing the FSDD was published in the Environmental Quality Board Monitor on April 24, 2006. To obtain additional assistance and expertise in the EIS preparation, the MNDNR entered into a State of Minnesota Interagency Agreement with the MPCA and the Minnesota Department of Health (MDH) on April 6, and April 10, 2006, respectively. Both agencies would review and assist in the development of a Draft EIS and Final EIS. MPCA would participate as necessary in any public information meeting. The notice of the availability of the Draft EIS was published in the Environmental Quality Board Monitor on November 2, 2009, and requested comments on the Draft EIS. Two public meetings for the Draft EIS were held; one on December 9, 2009, in Aurora, Minnesota; and one on December 10, 2009, in Blaine, Minnesota. The MNDNR, USFS, and USACE prepared a Supplemental Draft EIS based on EPA’s review of the Draft EIS; the addition of the USFS Land Exchange with PolyMet; and the project changes identified by PolyMet, the Draft EIS, and comments submitted on the Draft EIS.


The notice of the availability of the Supplemental Draft EIS was published in the Environmental Quality Board Monitor on December 9, 2013, and requested comments on the Supplemental Draft EIS. Three public meetings for the Supplemental Draft EIS were held; one on January 16, 2014, in Duluth, Minnesota; one on January 22, 2014, in Aurora, Minnesota; and one on January 28, 2014, in St. Paul, Minnesota. The MNDNR, USFS, and USACE reviewed and consider substantive public comments received during the notice period and subsequently prepared a Final EIS. The notice of the availability of the Final EIS was published in the Environmental Quality Board Monitor on November 9, 2015, and requested comments on the Final EIS. The MNDNR considered the Final EIS and all timely, substantive comments. On March 3, 2016, the state environmental review process concluded when the DNR determined that the Final EIS for the proposed NorthMet Mining Project and Land Exchange was adequate. Additional information about the Final EIS and DNR’s adequacy decision are available on the MNDNR’s website. Regarding the federal environmental review process, portions are still ongoing. On January 9, 2017, the U.S. Forest Service signed the Final Record of Decision authorizing a land exchange with PolyMet Mining, Inc. The land exchange has not occurred. The U.S. Army Corps of Engineers EIS process concludes when it makes its decision on whether to issue a permit for wetland impacts, called a Section 404 permit. At time of this draft document, that decision is still pending. Information from the Final EIS is used by the MPCA in conjunction with the permit application to inform the permit. The Final EIS identified several commitments specific to the air quality permitting process that were addressed as part of the Air Emissions Permit. These mitigation commitments resulted in unique conditions as part of this permit and include the topics identified below. Additional discussion regarding each of the topic areas is available in the section(s) identified for each area.

Class I area visibility impacts (Section 3.3 ‐ Class I Dispersion Modeling).

Fugitive emissions at the Mine Site and Plant Site, specifically: o Maintaining a fugitive emissions control plan (Section 3.6 ‐ Fugitive Emission Control Plans). o An ambient monitoring plan to monitor fugitive emissions of PM10 at the Mine Site (Section

3.7 ‐ Special Purpose Monitoring Plan).

Additional control of mineral fibers (Section 3.8 ‐ Amphibole Mineral Fibers).

Mercury Emissions (Section 3.9 ‐ Minnesota Mercury Total Maximum Daily Load (TMDL) Study). Other identified commitments, specific to the air quality permitting process, were more generic. These included commitments from various comments and responses on plans/materials that informed the EIS, but were not included as part of the EIS. These commitments generally included further discussion during permitting on the topics identified below. Additional discussion regarding each of the topic areas is available in the section(s) identified for each area.

Applicable rules and regulations (Section 2.9 ‐ Regulatory Overview).

Emission calculations (Section 3.1 ‐ Calculation of Potential to Emit).

Additional modeling performed for permitting, specifically: o Class II Dispersion Modeling (Section 3.2 ‐ Class II Dispersion Modeling). o Class I Dispersion Modeling (Section 3.3 ‐ Class I Dispersion Modeling). o Health Risk Assessment Modeling (Section 3.4 ‐ Air Emissions Risk Analysis (AERA) Modeling)

Operating, monitoring, recordkeeping, and reporting requirements (Section 3.10 ‐ Monitoring)


2.7.2 Air Emissions Risk Analysis (AERA) Conducting an Air Emission Risk Analysis (AERA) is one way the MPCA works to protect the environment and enhance human health. The AERA process evaluates and quantifies the potential human health risks due to the air pollution emitted by a proposed project. Screening tools, computer models and inhalation health benchmarks assess the potential cancer and non‐cancer health risks of a project’s air emissions. To assess the potential cumulative risks of a project in a community, the MPCA considers nearby facilities, background contamination, and local land use activities, such as the farming or fishing occurring in an area. Further contextual information, such as the locations of nearby schools and hospitals, is collected to identify potential routes of exposure and sensitive populations. The results from a risk analysis describe the potential risks posed to the individuals that would experience the highest level of exposure and incorporates the MPCA Environmental Justice Policy. The results of the analysis are referenced in the MPCA environmental review process to determine a project’s potential for significant environmental impact and to inform alternative proposals. Information from AERAs may also be employed to determine air permitting limits or monitoring requirements for facilities. An AERA is required when an EIS is required by Minn. R. 4410.4400 and the project increases air emissions of a single pollutant (excluding greenhouse gases) by 250 tons per year or more after the use of control equipment. As a result, an AERA was completed for the PolyMet EIS and updated and verified as part of preparing Air Emissions Permit 13700345‐101. There were multiple iterations of the AERA to adjust for changes in modeling guidance and true‐up emissions scenarios. The AERA Modeling Report contains the forms and memos documenting technical decisions and submittals and is included as Attachment 10. The documents are in chronological order according to submission date, but are not completely comprehensive due to the size and complexity of the submittals. The first document in the AERA Modeling Report is the MPCA summary of the AERA. Additional discussion regarding the AERA is available in Section 3.4.

2.8 Minnesota State Rules Portions of the facility are subject to the following Minnesota Standards of Performance:

Minn. R. 7011.0110 Emission Standards for Visible Air Contaminants

Minn. R. 7011.0150 Control of Fugitive Particulate Matter

Minn. R. 7011.0515 Standards of Performance for New Indirect Heating Equipment

Minn. R. 7011.0570 Standards of Performance for Small Industrial‐Commercial‐Institutional Steam Generating Units

Minn. R. 7011.0710 Standards of Performance for Pre‐1969 Industrial Process Equipment

Minn. R. 7011.0715 Standards of Performance for Post‐1969 Industrial Process Equipment

Minn. R. 7011.2300 Standards of Performance for Stationary Internal Combustion Engines

Minn. R. 7011.2305 Standards of Performance for Stationary Compression Ignition Internal Combustion Engines

Minn. R. 7011.2700 Standards of Performance for New Metallic Mineral Processing Plants

Minn. R. 7011.3350 Standards of Performance for New Nonmetallic Mineral Processing Plants

Minn. R. 7011.7185 National Emission Standards for Hazardous Air Pollutants for Source Category: Gasoline Dispensing Facilities


Minn. R. 7011.8150 National Emission Standards for Hazardous Air Pollutants for Stationary Reciprocating Internal Combustion Engines

Minn. R. 7011.9920 National Emission Standard for Asbestos

2.9 Regulatory Overview The table below provides an overview of the applicable regulations that apply to operations authorized by this permit action.

Table 5. Regulatory Overview of Facility

Subject item* Applicable regulations Rationale

TFAC 1 Air Quality Total Facility

40 CFR pt. 61, subp. M National Emission Standards for Asbestos. The facility will utilize existing buildings that are known to contain asbestos containing materials. Any demolition or renovation activities at the existing structures that affect certain quantities of asbestos containing material are subject to the requirements of 40 CFR pt. 61, subp. M, specifically, 40 CFR § 61.145.

40 CFR pt. 1068 General Compliance Provisions for Highway, Stationary, and Nonroad Programs. The permit contains monitoring and recordkeeping requirements established by 40 CFR pt. 1068 to identify which engines operated at the facility qualify as nonroad engines and not stationary engines.

40 CFR pt. 68 Risk Management Plan. The facility is required to submit a risk management plan to EPA under 40 CFR pt. 68 as the facility will use liquid sulfur dioxide in the hydrometallurgical process above the quantity of 5,000 pounds.

Minn. R. 7011.0150 Fugitive Dust Control Plan. The facility is required to comply with a Fugitive Emission Control Plan. This plan identifies all fugitive emission sources, primary and contingent control measures, operating practices, and record keeping.

Title I Condition: Avoid major source under 40 CFR 52.21(b)(1)(i)

Prevention of Significant Deterioration. The permit contains an operational limit on the amount of ore throughput at the facility that was used in determining emissions from facility operations, reducing emissions below PSD major source thresholds.

Minn. R. 7007.0800, subp. 2(A) & (B), Minn. R. 7009.0020‐0090, Minn. Stat. 116.07, subd. 4a(a)

National Ambient Air Quality Standards. The facility completed air dispersion modeling to show modeled compliance with the PM10, PM2.5, NO2, and SO2 NAAQS and MAAQS. The permit contains an operational limit on the amount of ore throughput at the facility that was used in determining emissions from facility operations for modeling purposes. In addition, the facility is required to maintain an ambient air boundary control strategy and remodel for the NAAQS under certain circumstances described within the permit.

Minn. R. 7007.0800, subp. 2(B), Minn. R. 7007.0800, subp. 3, Minn. Stat. 116.07, subd. 4a(a)

Mobile Source Requirements. The modeling performed by the facility in support of its visibility demonstration for Class I areas included emissions from mobile sources at the facility. Mobile source emission rates used in the visibility impacts analysis were calculated based on assumptions of vehicle type, quantity, availability and utilization. The permit contains language limiting the emissions from the mobile sources to their modeled values.



Minn. R. 7007.0800, subp. 2(B), Minn. R. 7007.0800, subp. 3, Minn. Stat. 116.07, subd. 4a(a)

Air Emissions Risk Analysis (AERA) Re‐calculation. The facility was required to complete an AERA as an Environmental Impact Statement was required under Minn. R. 4410.4400. The facility is required to recalculate the AERA under certain circumstances described within the permit. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.

Minn. R. 7007.0800, subp. 2(B), Minn. R. 7007.0800, subp. 4(D), Minn. R. 7007.0800, subp. 16(J), Minn. Stat. 116.07, subd. 4a(a)

Fiber Monitoring Plan. The permit requires the facility to continue fiber monitoring in order to quantify the concentration of fibers in ambient air. At the time of this permit action, it remains unknown if the operations at this facility will impact the concentration of fibers in the ambient air in the City of Hoyt Lakes.

Minn. R. 7007.0800, subp. 2(A), Minn. R. 7007.0800, subp. 4(D)

Special Purpose Monitoring Plan. The facility is required to use air quality monitoring equipment to monitor emission of PM10 as part of an ongoing evaluation of the effectiveness of the fugitive emissions control plan.

COMG 1 Limestone Preparation Building ‐ NSPS Subpart OOO Affected Facilities

40 CFR pt. 60, subp. OOO, Minn. R. 7011.3350

Standards of Performance for Nonmetallic Mineral Processing Plants. This group is comprised of emission units that all meet the meet the definition of a “conveying system” in 40 CFR § 60.671 and are all affected facilities under 40 CFR pt. 60, subp. OOO. This group contains emission limits that apply to the combined emissions of the group members. Limits set for opacity of emission from building openings. The affected facilities contained within this group are enclosed in a building and the Permittee has chosen to comply with the applicable building emission limits as allowed by the standard.

COMG 2 Portable Crushing Plant


Prevention of Significant Deterioration. The permit contains operational limits and emission limits to reduce PM, PM10, and PM2.5 emissions below PSD major source thresholds. The permit allows PolyMet the flexibility to add, replace, and/or modify equipment in this group under the PM10 and PM2.5 (PreCap) emission limits.


Ambient Air Quality Standards. The permit contains PM10 and PM2.5 emission limits resulting from dispersion modeling to ensure emissions do not cause a violation of the NAAQS.

COMG 3 HEPA Filter Requirements

Minn. R. 7007.0800, subp. 14, Minn. R. 7007.0800, subp. 2(B), Minn. Stat. 116.07, subd. 4a(a)

Minnesota Rules. The permit contains requirements on the operation of control equipment. The operation of the control equipment is not necessary in order for the process to meet applicable emissions limits. The operation of this piece of control equipment is for purposes of fiber emissions mitigation identified as a commitment during the environmental review process for Air Emissions Permit No. 13700345‐101. PolyMet may replace a HEPA filter listed in COMG 3 if the new HEPA filter complies with all other requirements of COMG 3.

COMG 4 Area 2 Space

Minn. R. 7005.0100, subp. 35a, Minn. R. 7007.0800, subp. 2(A)

Minnesota Rules. The permit contains restrictions on the types of fuel used in the combustion units.



Heaters Minn. R. 7011.0515 Standards of Performance for New Indirect Heating Equipment. Limits set for PM and opacity.

Minn. R. 7011.0610 Standards of Performance for Fossil‐Fuel‐Burning Direct Heating Equipment. Limits set for PM and opacity.

COMG 5 Area 1 Space Heaters



Minn. R. 7011.0515 Standards of Performance for New Indirect Heating Equipment. Limits set for PM and opacity.


COMG 6 MSFMF Space Heaters





COMG 7 WWTS Space Heaters


Minnesota Rules. The permit contains restrictions on the types of fuel used in the combustion units. It also specifies that these units must have a low NOX design.



COMG 8 Fine Crusher Space Heaters





COMG 9 Concentrator Building Space Heaters





COMG 10 Hydromet Building Space Heaters







COMG 11 Reagent Building Space Heaters





COMG 12 Limestone Preparation Building Space Heaters’





COMG 13 Coarse Crusher Building Space Heaters





COMG 14 Drive House Space Heaters





COMG 15 Flotation Addition Space Heaters





COMG 16 Concentrate Dewatering Building Space Heaters





COMG 17 Concentrate Loadout Building Space Heaters







COMG 18 Rebuild Shop Space Heaters





COMG 19 Main Warehouse Space Heaters





COMG 20 General Shops Space Heaters





COMG 21 Warehouse Electrical Space Heaters





COMG 22 Rubber Shop Space Heaters





COMG 23 Lube House Space Heaters







EQUI 1 North 60” Crusher


Prevention of Significant Deterioration. The permit contains requirements to operate and maintain control equipment and emission limits to reduce PM, PM10, and PM2.5 emissions below PSD major source thresholds. The emission unit has a total enclosure for capture. The permit specifies that new, replaced, or modified control equipment must meet the current control equipment requirements.

Title I Condition: Avoid major source under 40 CFR 63.2

National Emission Standards for Hazardous Air Pollutants. The permit contains requirements to operate and maintain control equipment to reduce HAP emissions below NESHAP major source thresholds. The emission unit has a total enclosure for capture. The permit specifies that new, replaced, or modified control equipment must meet the current control equipment requirements.



40 CFR pt. 60, subp. LL, Minn. R. 7011.2700

Standards of Performance for Metallic Mineral Processing Plants. This unit meets the definition of a “crusher” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. subp. LL. Limits set for PM from stack emissions and opacity from stack and process fugitive emissions.

EQUI 2 South 60” Crusher











EQUI 3 North Distribution Box







EQUI 4 North 36” Crusher 1


















EQUI 9 South 36” Crusher 1






























EQUI 13 North 36" Conveyor Feed Chute to Conveyor 1A #1
















EQUI 15 North 36" Conveyor Feed Chute to Conveyor 1B #1
















EQUI 17 South 36" Conveyor Feed Chute to Conveyor 1A #1
















EQUI 19 South 36" Conveyor Feed Chute to Conveyor 1B #1





















40 CFR pt. 60, subp. LL Standards of Performance for Metallic Mineral Processing Plants. This unit meets the definition of a “conveyor belt transfer point” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. subp. LL. Limits set for PM from stack emissions and opacity from stack and process fugitive emissions.





























EQUI 31 2A Tipper Car










EQUI 32 Conveyor Transfer Chute ‐ 2A and 2B to 4B/4A (Fine Crusher Building)








EQUI 33 West Coarse Ore Bins







40 CFR pt. 60, subp. LL Standards of Performance for Metallic Mineral Processing Plants. This unit meets the definition of a “storage bin” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. subp. LL. Limits set for PM from stack emissions and opacity from stack and process fugitive emissions.



EQUI 34 Fine Crushing ‐ East 1 ‐ 7' Standard





40 CFR pt. 60, subp. LL Standards of Performance for Metallic Mineral Processing Plants. This unit meets the definition of a “crusher” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. subp. LL. Limits set for PM from stack emissions and opacity from stack and process fugitive emissions.

EQUI 35 Fine Crushing ‐ East 1 ‐ Screen 1





40 CFR pt. 60, subp. LL Standards of Performance for Metallic Mineral Processing Plants. This unit meets the definition of a “screen” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. subp. LL. Limits set for PM from stack emissions and opacity from stack and process fugitive emissions.









EQUI 37 Fine Crushing ‐ East 1 ‐ 7' Shorthead 1












EQUI 39 Fine Crushing ‐ West 1 ‐ 7' Standard








EQUI 40 Fine Crushing ‐ West 1 ‐ Screen 1














EQUI 42 Fine Crushing ‐ West 1 ‐ 7' Shorthead 1




















Standards of Performance for Metallic Mineral Processing Plants. This unit meets the definition of a “conveyor belt transfer point” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. subp. LL. Limits set for PM from stack emissions and opacity from stack and process fugitive emissions.










EQUI 51 5N Tripper Car











EQUI 52 5S Tripper Car

















Standards of Performance for Metallic Mineral Processing Plants. This unit meets the definition of a “storage bin” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. subp. LL. Limits set for PM from stack emissions and opacity from stack and process fugitive emissions.











Standards of Performance for Metallic Mineral Processing Plants. This unit meets the definition of a “storage bin” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. subp. LL. Limits set for PM from stack emissions and opacity from stack and process fugitive emissions.

EQUI 55 Conv. Trans. Collection Belt to Transfer Belt







EQUI 56 Conv. Trans. Transfer Belt to SAG Feed Belt



















EQUI 93 Sag Mill (wet process)

Minn. R. 7011.0715 Standards of Performance for post‐1969 Industrial Process Equipment. Equipment for which there is no other promulgated performance standard is subject to the opacity and PM limits in this rule. Construction of the unit was on or after July 9, 1969.

EQUI 94 Ball Mill (wet process)


EQUI 95 Rougher Flotation




EQUI 96 Scavenger Flotation


EQUI 97 Rougher Regrind


Standards of Performance for Metallic Mineral Processing Plants. This unit meets the definition of a “crusher” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. subp. LL. Limit set for opacity from process fugitive emissions.

EQUI 98 Scavenger Regrind


EQUI 99 Flotation Cleaner 1




EQUI 101 Rougher (Cu/Ni) Conc Fine Grinding


Standards of Performance for Metallic Mineral Processing Plants. This unit meets the definition of a “crusher” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. subp. LL. Limit set for opacity from process fugitive emissions.

EQUI 102 Separation Flotation


EQUI 103 Scavenger (Ni) Conc Fine Grinding


EQUI 104 Concentrate Storage Area #1










Standards of Performance for Metallic Mineral Processing Plants. This emission unit meets the definition of an “enclosed storage area” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. 60, subp. LL. Limits set for PM from stack emissions and opacity from stack and process fugitive emissions.









Standards of Performance for Metallic Mineral Processing Plants. This emission unit meets the definition of an “enclosed storage area” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. 60, subp. LL. Limits set for PM from stack emissions and opacity from stack and process fugitive emissions.

EQUI 106 Railcar Loading ‐ Copper Concentrate








Standards of Performance for Metallic Mineral Processing Plants. This emission unit meets the definition of a “railcar loading station” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. 60, subp. LL. Limits set for PM from stack emissions and opacity from stack and process fugitive emissions.



EQUI 107 Railcar Loading ‐ Nickel Concentrate








EQUI 108 Autoclave vent (1 unit) and Emergency Pressure Relief Vent


Prevention of Significant Deterioration. The permit contains requirements to operate and maintain control equipment and emission limits to reduce PM, PM10, PM2.5, and Sulfuric Acid Mist emissions below PSD major source thresholds. The emission unit has a total enclosure for capture. The permit specifies that new, replaced, or modified control equipment must meet the current control equipment requirements.






Prevention of Significant Deterioration. The permit contains requirements to operate and maintain control equipment and emission limits to reduce PM, PM10, PM2.5, and Sulfuric Acid Mist emissions below PSD major source thresholds. The emission unit has a total enclosure for capture. The permit specifies that new, replaced, or modified control equipment must meet the current control equipment requirements.






EQUI 110 AuPGM Precipitation Tanks






EQUI 111 Iron and Aluminum Precipitation Tanks (3)






EQUI 112 CuS Cementation Tank N2 Vent








EQUI 113 MHP Stage 1 Tank Vent






EQUI 114 2nd Stage Hydroxide Precipitation


EQUI 115 Hydroxide Product Storage and Handling


EQUI 116 Hydroxide Bagging


EQUI 117 Oxygen Plant Adsorber Regeneration Heater






EQUI 118 Autoclave Startup Boiler (Natural Gas)



40 CFR pt. 60, subp. Dc, Minn. R. 7011.0570

Standards of Performance for Small Industrial‐Commercial‐Institutional Steam Generating Units. This unit is a 50 MMBtu/hr steam generating unit constructed after June 9, 1989 that burns only natural gas. It meets the criteria for an affected facility under 40 CFR § 60.40c(a). There are no emission limits that apply, only recordkeeping requirements for fuel usage.

Minn. R. 7007.0800, subp. 2(B), Minn. Stat. 116.07, subd. 4a(a)

Air Emissions Risk Analysis (AERA) Re‐calculation. The permit contains requirements for PolyMet to submit an updated AERA if the hourly natural gas fuel usage rate exceeds the value used to determine emissions from this unit. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.

EQUI 120 Flotation Flocculant Silo Feeder (Magnafloc 10)


EQUI 121 Flotation Flocculant Silo (Magnafloc 10)




EQUI 123 Acid Flocculant Silo Feeder


EQUI 124 Acid Flocculant Silo


Prevention of Significant Deterioration. The permit contains requirements to operate and maintain control equipment and an operational limit on process throughput to reduce PM, PM10, and PM2.5 emissions below PSD major source thresholds. The emission unit has a total enclosure for capture. The permit specifies that new, replaced, or modified control equipment must meet the current control equipment requirements.


Ambient Air Quality Standards. The permit contains an operational limit on process throughput used to determine PM10 and PM2.5 emissions that were used in dispersion modeling to ensure emissions do not cause a violation of the NAAQS.




EQUI 125 Acid Flocculant to Mix Tank (Magnafloc 351)


EQUI 126 Xanthate Collector Mix Tank (w/baghouse)






EQUI 127 NaHS Mix Tank/Storage Tank






EQUI 128 MgO to Mix Tank


EQUI 129 Coagulant to Mix Tank




EQUI 130 Frother Mix Tank


EQUI 131 Copper Sulfate Mix Tank


EQUI 132 Lime Conveyor


EQUI 133 Lime Slaker (w/scrubber)






EQUI 134 Plant Lime Silo












Standards of Performance for Nonmetallic Mineral Processing Plants. This emission unit meets the definition of an “enclosed truck or railcar loading station” in 40 CFR § 60.671 and is an affected facility under 40 CFR pt. 60, subp. OOO. Limits set for PM.

EQUI 136 Limestone Hopper to Conveyor




Standards of Performance for Nonmetallic Mineral Processing Plants. This emission unit meets the definition of a “belt conveyor” in 40 CFR § 60.671 and is an affected facility under 40 CFR pt. 60, subp. OOO. Limits set for PM.

EQUI 137 Limestone Conveyor to Stacker Conveyor


Prevention of Significant Deterioration. The permit contains an operational limit on process throughput to reduce PM, PM10, and PM2.5 emissions below PSD major source thresholds.




Standards of Performance for Nonmetallic Mineral Processing Plants. This emission unit meets the definition of a “belt conveyor” in 40 CFR § 60.671 and is an affected facility under 40 CFR pt. 60, subp. OOO. Limits set for opacity.

EQUI 138 Limestone Reclaim Chute (to tunnel conveyor)







EQUI 139 Limestone Reclaim Feeder to Conveyor









EQUI 140 Limestone Tunnel Conveyor to Bunker





EQUI 141 Limestone Bunker to crusher feed conveyor (enclosed)





EQUI 142 Limestone Crusher Feed Conveyor Discharged (enclosed)





EQUI 143 Limestone Crusher for stack emissions






Standards of Performance for Nonmetallic Mineral Processing Plants. This emission unit meets the definition of a “crusher” in 40 CFR § 60.671 and is an affected facility under 40 CFR pt. 60, subp. OOO. Limits set for PM.

EQUI 144 Limestone Crusher





to Conveyor Minn. R. 7007.0800, subp. 2(A) & (B), Minn. R. 7009.0020‐0090, Minn. Stat. 116.07, subd. 4a(a)


EQUI 145 Limestone Conveyor to Mix Tank





EQUI 146 Carboxymethylcellulose Mix Tank


EQUI 147 MSFMF Lime Silo






EQUI 148 MSFMF Lime Transfer to Tank






EQUI 149 Liquid SO2 Unloading


Ambient Air Quality Standards. The permit contains an operational limit on process throughput used to determine SO2 emissions that were used in dispersion modeling to ensure emissions do not cause a violation of the NAAQS.




EQUI 150 Limestone Reclaim Pocket Dump






EQUI 151 Oxygen Plant Cooling Tower


EQUI 172 Administration Building New Boiler




EQUI 184 Existing Backup Generator 1


Ambient Air Quality Standards. The permit contains best management practices that PolyMet accepted to exclude the generator from the dispersion modeling demonstration per the most recent version of the MPCA Air Dispersion Modeling Practices Manual.

40 CFR pt. 63, subp. ZZZZ, Minn. R. 7011.8150

National Emissions Standards for Hazardous Air Pollutants for Stationary Reciprocating Internal Combustion Engines. The engine is located at an area source of HAPs and was constructed before June 12, 2006. Therefore, it is an existing affected source under 40 CFR § 63.6590(a)(1)(iii).

Minn. R. 7011.2300 Standards of Performance for Stationary Internal Combustion Engines. Limits set for SO2 and opacity.






40 CFR pt. 63, subp. ZZZZ, Minn. R. 7011.8150

National Emissions Standards for Hazardous Air Pollutants for Stationary Reciprocating Internal Combustion Engines. The engine is located at an area source of HAPs and was constructed before June 12, 2006. Therefore, it is an existing affected source under 40 CFR § 63.6590(a)(1)(iii).






EQUI 188 Fire Pump #1



40 CFR pt. 63, subp. ZZZZ

National Emissions Standards for Hazardous Air Pollutants for Stationary Reciprocating Internal Combustion Engines. The engine is located at an area source of HAPs and will be constructed after June 12, 2006. Therefore, it is a new affected source under 40 CFR § 63.6590(a)(2)(iii). Under 40 CFR § 63.6590(c) the engine meets the requirements 40 CFR pt. 63, subp. ZZZZ by meeting the requirements of 40 CFR pt. 60, subp. IIII and no further requirements apply under 40 CFR pt. 63, subp. ZZZZ.

40 CFR pt. 60, subp. IIII Standards of Performance for Stationary Compression Ignition Internal Combustion Engines. This engine is a fire pump with a commenced construction date after July 11, 2005, a manufacture date after July 1, 2006, and a displacement less than 30 liters per cylinder.









40 CFR pt. 60, subp. IIII Standards of Performance for Stationary Compression Ignition Internal Combustion Engines. This engine is a fire pump with a commenced construction date after July 11, 2005, a manufacture date after July 1, 2006, and a displacement less than 30 liters per cylinder.






EQUI 192 Plant Site WWTS Back‐up Generator





40 CFR pt. 60, subp. IIII Standards of Performance for Stationary Compression Ignition Internal Combustion Engines. This engine is a 1496 horsepower non‐fire pump emergency engine with a commenced construction date after July 11, 2005, a manufacture date after April 1, 2006, and a displacement less than 10 liters per cylinder.




EQUI 194 MSFMF Back Up Generator





40 CFR pt. 60, subp. IIII Standards of Performance for Stationary Compression Ignition Internal Combustion Engines. This engine is a 748 horsepower non‐fire pump emergency engine with a commenced construction date after July 11, 2005, a manufacture date after April 1, 2006, and a displacement less than 10 liters per cylinder.






EQUI 196 Generator to Move Electrical Equipment








EQUI 628 AuPGM Concentrate Packaging


Standards of Performance for Metallic Mineral Processing Plants. This unit meets the definition of a “product packaging station” in 40 CFR § 60.381 and is an affected facility under 40 CFR pt. subp. LL. Limits set on opacity of process fugitive emissions.

EQUI 629 WWTS Calcite Handling






EQUI 630 WWTS Degasifier


EQUI 631 Gasoline Tank

40 CFR pt. 63, subp. CCCCCC, Minn. R. 7011.7185

National Emission Standards for Hazardous Air Pollutants for Source Category: Gasoline Dispensing Facilities. The facility is an area source of HAPs with a gasoline dispensing facility with a monthly throughput less than 10,000 gallons.



40 CFR pt. 63, subp. CCCCCC, Minn. R. 7011.7185

National Emission Standards for Hazardous Air Pollutants for Source Category: Gasoline Dispensing Facilities. The facility is an area source of HAPs with a gasoline dispensing facility with a monthly throughput less than 10,000 gallons.




EQUI 633 Frother (MIBC) Tank


EQUI 634 Frother (DF 250) Tank


EQUI 635 Fuel Oil Tank




EQUI 637 Sulfuric Acid Tank


Ambient Air Quality Standards. The permit contains an operational limit on process throughput used to determine SO2 emissions that were used in dispersion modeling to ensure emissions do not cause a violation of the NAAQS.


EQUI 638 Hydrochloric Acid Tank








EQUI 642 Caustic Tank






EQUI 644 PC Transfer Point #1


Prevention of Significant Deterioration. The permit contains requirements to operate and maintain control equipment to reduce PM, PM10, and PM2.5 emissions below PSD major source thresholds. The emission unit has a total enclosure for capture. The permit specifies that new, replaced, or modified control equipment must meet the current control equipment requirements.





EQUI 645 Pebble Crusher






























EQUI 649 WWTP Lime Silo








EQUI 650 WWTS Lime Transfer to Mix Tank






EQUI 651 WWTS Other Dry Material Handling






FUGI 1

Unpaved Roads, Dunka Rd.


Ambient Air Quality Standards. The permit contains limits on VMTs resulting from dispersion modeling to ensure emissions do not cause a violation of the NAAQS.

Minn. R. 7011.0110 Emission Standards for Visible Air Contaminants. Limits set for opacity.

FUGI 2

Mine Site Fueling Facility Circle


FUGI 4

Limestone Stacker Conveyor to Stockpile




FUGI 5

Tailings Basin Construction






FUGI 6

Tailings Basin Bentonite Handling


FUGI 7

Tailings Basin Bentonite Hauling


FUGI 8

Tailings Basin – Light Trucks




FUGI 9

Tailings Basin Wind Erosion


FUGI 10

Mine Site Surface Overburden, Truck Load


FUGI 11

Mine Site Surface Overburden, Truck Unload – reclaim area


FUGI 12

Mine Site Surface Overburden, Truck Unload – stockpile/storage pile/East Pit


Ambient Air Quality Standards. The permit contains an operational limit on operating hours during certain months used to determine PM10 and PM2.5 emissions that were used in dispersion modeling to ensure emissions do not cause a violation of the NAAQS.


FUGI 13

Mine Site Surface Overburden, Truck Reload


Ambient Air Quality Standards. The permit contains an operational limit on operating hours during certain months used to determine PM10 and PM2.5 emissions that were used in dispersion modeling to ensure emissions do not cause a violation of the NAAQS.




FUGI 14

Mine Site Waste Rock Truck Load


Air Emissions Risk Analysis (AERA) Re‐calculation. The permit contains requirements for PolyMet to calculate revised emission rates of Arsenic, Cobalt, and Nickel if the quantity of material handled by this source exceeds the projected maximum value for the current Mine Year of operations. The permit requires PolyMet to submit an updated AERA if those calculations show a pollutant exceeds the maximum hourly rate modeled. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.


FUGI 15

Mine Site Waste Rock Truck Unload


Air Emissions Risk Analysis (AERA) Re‐calculation. The permit contains requirements for PolyMet to calculated revised emission rates of Arsenic, Cobalt, and Nickel if the quantity of material handled by this source exceeds the projected maximum value for the current Mine Year of operations. The permit requires PolyMet to submit an updated AERA if those calculations show a pollutant exceeds the maximum hourly rate modeled. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.


FUGI 16

Mine Site Ore, Truck Load




FUGI 17

Mine Site Ore, Truck Unload ‐ Rail Transfer Hopper


FUGI 18

Mine Site Ore, Railcar Load




FUGI 19

Mine Site Ore Load/Unload – Surge Pile


FUGI 20

Mine Site Stockpile Reclaim Truck Load


FUGI 21

Mine Site Stockpile Reclaim Truck Unload




FUGI 22

Mine Site Surface Overburden, Screen #1




Ambient Air Quality Standards. The permit contains an operational limit on process throughput and operating hours during certain months used to determine PM10 and PM2.5 emissions that were used in dispersion modeling to ensure emissions do not cause a violation of the NAAQS.


FUGI 23

Mine Site Surface Overburden, Screen #1 Discharge






FUGI 24

Mine Site Portable Crushing Plant ‐ Crusher 1


Standards of Performance for Nonmetallic Mineral Processing Plants. This emission unit meets the definition of a “crusher” in 40 CFR § 60.671 and is an affected facility under 40 CFR pt. 60, subp. OOO. Limits set for opacity.

FUGI 25

Mine Site Blast Hole Drilling




FUGI 26

Mine Haul Roads




Air Emissions Risk Analysis (AERA) Re‐calculation. The permit contains requirements for PolyMet to submit an updated AERA if the daily VMTs exceed the value used to determine emissions from this source. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.


FUGI 27

Mine Site Cat 1 Stockpile Wind Erosion


FUGI 28

Mine Site Cat 2/3 Waste Rock Stockpile Wind Erosion


FUGI 29

Mine Site Cat 4 Waste Rock Stockpile Wind Erosion


FUGI 30

Mine Site Ore Surge Pile Wind Erosion


FUGI 31

Mine Site Overburden Storage Pile Wind Erosion


FUGI 32

Mine Site Portable Crushing Plant ‐ non‐NSPS ‐ Truck Load 1


FUGI 33

Mine Site Surface





Overburden, Screen #2




FUGI 34







FUGI 35

Mine Site Surface Overburden, Screen #3






FUGI 36







FUGI 37




FUGI 38






FUGI 39




FUGI 40

Mine Site Portable Crushing Plant ‐ Screen 1


Standards of Performance for Nonmetallic Mineral Processing Plants. This emission unit meets the definition of a “screening operation” in 40 CFR § 60.671 and is an affected facility under 40 CFR pt. 60, subp. OOO. Limits set for opacity.

FUGI 41




FUGI 42




FUGI 43




FUGI 44

Mine Site Portable Crushing Plant ‐ Transfer Point 1


Standards of Performance for Nonmetallic Mineral Processing Plants. This emission unit meets the definition of a “transfer point” in 40 CFR § 60.671 and is an affected facility under 40 CFR pt. 60, subp. OOO. Limits set for opacity.

FUGI 45




FUGI 46




FUGI 47




FUGI 48






FUGI 49

Mine Site Portable Crushing Plant ‐ Non‐NSPS ‐ Transfer to Stockpile 1


FUGI 50




FUGI 51




FUGI 52




FUGI 53




FUGI 54




FUGI 55

Mine Site Portable Crushing Plant ‐ Non‐NSPS ‐ Transfer to Stockpile 2


FUGI 56

Mine Site Portable Crushing Plant ‐ Non‐NSPS ‐ Truck Load 2


STRU 3 North 60 Distribution Box & 36" Crushers Stack


Prevention of Significant Deterioration. The permit contains emission limits to reduce PM, PM10, and PM2.5 emissions below PSD major source thresholds.





STRU 4 South 60 Distribution Box & 36" Crushers Stack





STRU 5 North 36" Pan Feeders to Conveyor 1A Stack





STRU 6 North 36" Pan Feeders to Conveyor 1B Stack





STRU 7 South 36" Pan Feeders to Conveyor 1A Stack





STRU 8 South 36" Pan Feeders to Conveyor 1B & South Pan Feeder Stack





STRU 9 North Pan Feeder





Stack Minn. R. 7007.0800, subp. 2(A) & (B), Minn. R. 7009.0020‐0090, Minn. Stat. 116.07, subd. 4a(a)


STRU 14 East Fine Crushing (1) Stack





STRU 15 West Fine Crushing (1‐2) & Transfer Points Stack





STRU 19 Conveyor Transfer Chute & Fine Ore Feeders North 1‐2 Stack





STRU 20 Fine Ore Feeders North 3‐5 Stack










STRU 22 Fine Ore Feeders





North 9‐11 Stack Minn. R. 7007.0800, subp. 2(A) & (B), Minn. R. 7009.0020‐0090, Minn. Stat. 116.07, subd. 4a(a)






















STRU 27 Fine Ore Feeders South 1‐3 Stack





STRU 28 Fine Ore Feeders





South 4‐6 Stack Minn. R. 7007.0800, subp. 2(A) & (B), Minn. R. 7009.0020‐0090, Minn. Stat. 116.07, subd. 4a(a)












STRU 35 Autoclave Scrubber Stack


Prevention of Significant Deterioration. The permit contains emission limits to reduce PM, PM10, PM2.5, and sulfuric acid mist emissions below PSD major source thresholds.


National Emission Standards for Hazardous Air Pollutants. The permit contains emission limits to reduce nickel emissions (as a surrogate for all metal HAP emissions) and hydrochloric acid emissions below NESHAP major source thresholds.


Ambient Air Quality Standards. The permit contains PM10, PM2.5, and SO2 emission limits resulting from dispersion modeling to ensure emissions do not cause a violation of the NAAQS.


Air Emissions Risk Analysis (AERA) Re‐calculation. The permit contains hydrogen sulfide (H2S) emission limits resulting from AERA modeling. In addition, the permit contains requirements for PolyMet to conduct a performance test for emissions of Arsenic, Nickel, and NOX if the Permittee modifies either EQUI 108 or EQUI 109 by increasing the maximum operating capacity of either of the emission units. The permit requires PolyMet to submit an updated AERA if those performance tests show a revised emission rate exceeds the maximum hourly rate modeled. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.



Minn. R. 7007.0502 Mercury Emissions. The provisions in Minn. R. 7007.0502 apply to “existing mercury emission sources” and aim to limit statewide mercury emissions below 789 pounds per year from existing facilities. Even though PolyMet has potential mercury emissions greater than three pounds per year, is not subject to the rule because it is a new facility. The permit contains requirements for PolyMet to implement mercury reduction measures in accordance with the December 6, 2012 Guidelines for New and Modified Mercury Air Emission Sources. This is to ensure that the mercury increases from PolyMet do not impede the statewide mercury total maximum daily reduction goals under Minn. R. 7007.0502. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.

STRU 37 Plant Scrubber Stack


Prevention of Significant Deterioration. The permit contains emission limits to reduce PM, PM10, PM2.5, and sulfuric acid mist emissions below PSD major source thresholds.


Ambient Air Quality Standards. The permit contains PM10, PM2.5, and SO2 emission limits resulting from dispersion modeling to ensure emissions do not cause a violation of the NAAQS.


Air Emissions Risk Analysis (AERA). The permit contains hydrogen sulfide (H2S) emission limits resulting from AERA modeling. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.

STRU 43 Limestone Unloading Baghouse Stack





STRU 107 Pebble Crusher Stack







TREA 1 Fabric Filter ‐ Baghouse ‐ North 60" Crushers


Prevention of Significant Deterioration. The permit contains requirements to operate and maintain control equipment, control efficiency limits, and operational parameter limits to reduce PM, PM10, and PM2.5 emissions below PSD major source thresholds. The control equipment has a total enclosure for capture. The permit specifies that new, replaced, or modified control equipment must meet the current control equipment requirements.


National Emission Standards for Hazardous Air Pollutants. The permit contains requirements to operate and maintain control equipment, control efficiency limits, and operational parameter limits to reduce HAP emissions below NESHAP major source thresholds. The control equipment has a total enclosure for capture. The permit specifies that new, replaced, or modified control equipment must meet the current control equipment requirements.

TREA 2 Fabric Filter ‐ Baghouse ‐ South 60" Crushers





TREA 3 Fabric Filter ‐ Cartridge Filter ‐ North 36" Crushers







TREA 4 Fabric Filter ‐ Cartridge Filter ‐ South 36" Crushers





TREA 5 Fabric Filter ‐ Cartridge Filter ‐ North 36" Conveyor Feed Chutes to Conveyor 1A





TREA 6 Fabric Filter ‐ Cartridge Filter ‐ North 36" Conveyor Feed Chutes to Conveyor 1B







TREA 7 Fabric Filter ‐ Cartridge Filter ‐ South 36" Conveyor Feed Chutes to Conveyor 1A





TREA 8 Fabric Filter ‐ Cartridge Filter ‐ South 36" Conveyor Feed Chutes to Conveyor 1B





TREA 9 Fabric Filter ‐ Cartridge Filter ‐ South Pan Conveyors







TREA 10 Fabric Filter ‐ Cartridge Filter ‐ North Pan Conveyors





TREA 11 Fabric Filter ‐ Cartridge Filter ‐ Drive House 1 East Transfer





TREA 12 Fabric Filter ‐ Cartridge Filter ‐ Drive House 1 West Transfer







TREA 13 Fabric Filter ‐ Cartridge Filter ‐ Conveyor Transfer Chute





TREA 14 Fabric Filter ‐ Cartridge Filter ‐ 2A Tripper Car





TREA 15 Fabric Filter ‐ Cartridge Filter ‐ West Coarse Ore Bins







TREA 16 Fabric Filter ‐ Cartridge Filter ‐ Fine Crushing ‐ East 1





TREA 17 Fabric Filter ‐ Cartridge Filter ‐ Fine Crushing ‐ West 1












TREA 19 Fabric Filter ‐ Cartridge Filter ‐ North Transfer Point





TREA 20 Fabric Filter ‐ Cartridge Filter ‐ South Transfer Point





TREA 21 Fabric Filter ‐ Cartridge Filter ‐ 5N Tripper Car







TREA 22 Fabric Filter ‐ Cartridge Filter ‐ 5S Tripper Car





TREA 23 Fabric Filter ‐ Cartridge Filter ‐ Fine Ore Storage ‐ North












TREA 31 Fabric Filter ‐ Cartridge Filter ‐ Fine Ore Storage ‐ South






















TREA 35 Fabric Filter ‐ Cartridge Filter ‐ Conv. Trans. Collection Belt to SAG Feed Belt, Fine Ore Feeders North 1 & 2





TREA 36 Fabric Filter ‐ Cartridge Filter ‐ Fine Ore Feeders North 3, 4, & 5

















TREA 42 Fabric Filter ‐ Cartridge Filter ‐ Fine Ore Feeders North 21, 22, 23, & 24







TREA 43 Fabric Filter ‐ Cartridge Filter ‐ Fine Ore Feeders South 1, 2, & 3






















TREA 47 Fabric Filter ‐ TBD ‐ Concentrate Storage Area #1












TREA 49 Fabric Filter ‐ TBD ‐ Railcar Loading ‐ Copper Concentrate





TREA 50 Fabric Filter ‐ TBD ‐ Railcar Loading ‐ Nickel Concentrate





TREA 51 Wet Scrubber ‐ Autoclave vent and Emergency Pressure Relief Vent, Flash Vessels


Prevention of Significant Deterioration. The permit contains requirements to operate and maintain control equipment, control efficiency limits, and operational parameter limits to reduce PM, PM10, PM2.5, and sulfuric acid mist emissions below PSD major source thresholds. The control equipment has a total enclosure for capture. The permit specifies that new, replaced, or modified control equipment must meet the current control equipment requirements.






Air Emissions Risk Analysis (AERA). The permit contains requirements to operate and maintain control equipment, control efficiency limits, and operational parameter limits to reduce emissions of hydrogen sulfide (H2S). This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.

Minn. R. 7007.0800, subp. 14, Minn. R. 7007.0800, subp. 2(A) & (B)

Minnesota Rules. The permit contains requirements to operate and maintain control equipment, control efficiency limits, and operational parameter limits to reduce emissions of SO2.

Minn. R. 7007.0502 Mercury Emissions. The permit contains requirements to operate and maintain control equipment, control efficiency limits, and operational parameter limits to reduce emissions of mercury in accordance with the December 6, 2012 Guidelines for New and Modified Mercury Air Emission Sources. This is to ensure that the mercury increases from PolyMet do not impede the statewide mercury total maximum daily reduction goals under Minn. R. 7007.0502. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.

TREA 52 Wet Scrubber ‐ Autoclave vent and Emergency Pressure Relief Vent, Flash Vessels, Iron and Aluminum Precipitation Tanks











Minn. R. 7007.0502 Mercury Emissions. The permit contains requirements to operate and maintain control equipment, control efficiency limits, and operational parameter limits to reduce emissions of mercury in accordance with the December 6, 2012 Guidelines for New and Modified Mercury Air Emission Sources. This is to ensure that the mercury increases from PolyMet do not impede the statewide mercury total maximum daily reduction goals under Minn. R. 7007.0502. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.

TREA 53 Wet Scrubber ‐ AuPGM Precipitation Tanks, CuS Cementation Tank N2 Vent, MHP Stage 1 Tank Vent, NaHS Mix Tank/Storage Tank







TREA 54 Fabric Filter ‐ TBD ‐ Flotation Flocculant Silo



TREA 55 Fabric Filter ‐ TBD ‐ Acid Flocculant Silo





TREA 56 Fabric Filter ‐ TBD ‐ Xanthate Collector Mix Tank (w/baghouse)



TREA 57 Wet Scrubber ‐ Lime Slaker (w/scrubber)



TREA 58 Fabric Filter ‐ TBD ‐ Plant Lime Silo



TREA 59 Fabric Filter ‐ TBD ‐ Limestone Railcar Dump, Limestone Hopper to Conveyor



40 CFR pt. 60, subp. OOO

Standards of Performance for Nonmetallic Mineral Processing Plants. The permit contains requirements to operate and maintain a bag leak detector under 40 CFR § 60.674(d)(1)‐(3) in lieu of conducting Method 22 visual emission tests under 40 CFR § 60.674(c).

TREA 60 Fabric Filter ‐ TBD ‐ Limestone Crusher



40 CFR pt. 60, subp. OOO

Standards of Performance for Nonmetallic Mineral Processing Plants. The permit contains requirements to operate and maintain a bag leak detector under 40 CFR § 60.674(d)(1)‐(3) in lieu of conducting Method 22 visual emission tests under 40 CFR § 60.674(c).



TREA 61 Fabric Filter ‐ TBD ‐ MSFMF Lime Silo



TREA 91 Fabric Filter ‐ Cartridge Filter ‐ Pebble Crusher





TREA 92 Fabric Filter ‐ TBD ‐ WWTS Lime Silo



*Location of the requirement in the permit (e.g., EQUI 1, STRU 2, etc.).

The language 'This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act' refers to permit requirements that are established only under state law and are not established under or required by the federal Clean Air Act. The language is to clarify the distinction between permit conditions that are required by federal law and those that are required only under state law. State law‐only requirements are not enforceable by the EPA or by citizens under the federal Clean Air Act, but are fully enforceable by the MPCA and citizens under provisions of state law.


3. Technical information 3.1 Calculations of Potential to Emit (PTE)

This section of the TSD provides a detailed explanation of emission calculations for PolyMet operations. PolyMet intends to operate mining and ore processing equipment in addition to auxiliary support equipment throughout the facility. The facility is designed to process an average of 32,000 tons of ore per day (11,680,000 tons per year). This design basis is a fundamental assumption underlying the calculations of potential emissions. Air pollution control equipment, including fabric filters, wet scrubbers, and fugitive emission control methods are used to reduce emissions of pollutants identified with each controlled emission source. Generally, emission calculations have been developed based on material throughputs; applicable performance standards; site‐specific sampling data, pilot‐test data, restrictions, and assumptions; information contained within EPA’s document, “AIRS Facility Subsystem Source Classification Codes and Emission Factor Listing for Criteria Air Pollutants”; and information contained within EPA’s document, “AP‐42: Compilation of Air Emission Factors”. Speciation of particulate emissions performed by PolyMet was based on interpretation of pilot plant data, site‐specific overburden sampling, drill core analysis of waste rock and ore zones, and other sampling work in the region. The emission sources at the Mine Site are mostly fugitive in nature, meaning the emissions occur outdoors and are not routed to a stack or vent. Fugitive sources are commonly associated with open‐pit mining operations. Point sources at the Mine Site are limited to a lime silo and associated mixing equipment, space heaters, and emergency and other low utilization generators. Emissions from the Mine Site will primarily consist of fugitive emissions from the sources identified below:

Unpaved roads (which includes mine roads, the Dunka Road, and other access roads).

Material handling operations (which includes loading and unloading haul trucks with overburden, waste rock, and ore, as well as loading railcars with ore).

Crushing and screening operations (which includes processing of overburden and other approved rock for use in the road construction, dam construction, berm construction, blast hole stemming, and railroad ballast. Ore is not crushed at the Mine Site.

Blast hole drilling. The majority of emission sources at the Plant Site will be point sources. These sources will include:

The crushing and concentration operations, including operations from the ore railcar dumping, through the crushing and grinding, to flotation (where the valuable minerals are concentrated) and including equipment that transports flotation concentrate either to be further processed within the Hydrometallurgical Plant or to be stored and shipped off‐site.

The autoclave, where the valuable metals will be leached from the nickel concentrate using pressure oxidation and related equipment.

The hydrometallurgical process tanks, which will include the processes used to separate and recover the valuable metals from the autoclave leach solution.

Handling sources for process consumables, which will include the handling, transfer, and storage of the additives used in flotation, the autoclave, and the hydrometallurgical process tanks

Combustion sources and fuel tanks, which will include boilers, heaters, emergency diesel engines, and fuel tanks for diesel and gasoline.


The main sources of fugitive emission at the Plant Site will be limestone handling, traffic on unpaved roads, flotation tailings basin and hydrometallurgical residue facility construction, and wind erosion at the flotations tailing basin. Attachment 1 to this TSD contains Form GI‐07, which summarizes the PTE of the Facility, and detailed spreadsheets and supporting information prepared by the MPCA and the Permittee. 3.1.1 Mine Site Material Handling Emissions

Emissions from these operations consist primarily of PM, PM10, and PM2.5 emissions with smaller emissions of metal HAPs. Loading railcars with ore and loading and unloading haul trucks with overburden, waste rock, and ore will generate fugitive emissions. AP‐42 Section 13.2.4, Aggregate Handling and Storage Piles, was used to calculate emissions from drop operations from material handling operations except for emissions at the rail transfer hopper where the operations are shielded from the wind, so non‐wind speed dependent factors from AP‐42 were used. This section relates wind speed and the moisture content of the material being handled to emissions in lb/ton of material handled.

3.1.2 Mine Site Crushing and Screening Emissions Emissions from these operations consist primarily of PM, PM10, and PM2.5 emissions with smaller emissions of metal HAPs. Overburden may be screened to separate larger rocks from soil and gravel. The different fractions can be stockpiled separately and used for construction or reclamation purposes. Typically, the natural moisture content of the overburden will prevent significant particulate from becoming airborne, but water sprays may be used if dry conditions occur. A portable crushing and screening plant also will be operated at the Mine Site to generate materials for construction purposes. The plant will reduce the size of large rocks from the overburden or crush other rock approved for construction purposes. The rock will be crushed to produce materials suitable for construction activities at the Mine Site, for use in blast hole stemming, and for use as railroad ballast. AP‐42 Section 13.2.4, Aggregate Handling and Storage Piles, was used to calculate emissions from the screen discharge for the overburden screens and the loading of crushed rock into trucks at the portable crushing plant. Emission factors from AP‐42 Section 11.19.2, Crushed Stone Processing and Pulverized Mineral Processing were used to calculate emissions from the portable crushing plant, including crushing, screening and associated material transfers.

3.1.3 Blast Hole Drilling Emissions Emissions from these operations consist primarily of PM, PM10, and PM2.5 emissions with smaller emissions of metal HAPs. Blast holes will be drilled in both waste rock and ore for the placement of explosives. Drill rigs will inject water down the drill hole, which will minimize particulate generation. Emissions from blast hole drilling were estimated with an emission factor from AP‐42, Section 11.9, Western Surface Coal Mining. This section includes an emission factor for drilling expressed in pounds of Total Suspended Particulates (TSP) per hole drilled. PM10 and PM2.5 were conservatively assumed to be equal to TSP


emissions. This emission factor is for western surface coal mining, but the emissions for the type of mining associated with PolyMet operations should be equivalent.

3.1.4 Crushing, Concentrating, and Flotation Emissions Emissions from these operations consist primarily of PM, PM10, and PM2.5 emissions with smaller emissions of metal HAPs. PolyMet plans to reactivate the first two crushing stages of the former LTVSMC Plant with conveying and storage equipment. PolyMet plans to install a new SAG Mill and Ball Mill to replace the tertiary and quaternary crushing stages. Emissions from these crushing operations are based on a performance specification for the fabric filters that will be installed in the crushing plant. This specification and an associated design airflow rate for each operation was used to determine potential emissions. As these emission rates were used as part of several analyses, the permit contains a requirement that the Permittee must conduct performance testing to verify the calculated emission rate. The flotation process is a wet process, but additives are used which may cause emissions of VOCs. The frothers, methyl isobutyl carbinol and Dowfroth 250, contain VOCs. Carbon disulfide is a potential decomposition product of the xanthate collector. Emission calculations for the flotation process use data from sampling conducted during a flotation pilot study. Copper flotation concentrate will always be produced as a salable product. Nickel flotation concentrate can also be sold as a finished product or it can report to the hydrometallurgical plant for further processing. The handling and storage of flotation concentrate is not expected to produce emissions as this material is a damp filter cake. However, the emission calculations and modeling assume that direct ventilation and dust collectors will be installed to handle flotation cake air streams. Flotation concentrate will be stored in an enclosed building and loaded into railcars with a front‐end loader or similar piece of equipment. The concentrate will be shipped via covered railcars with the covers secured in place prior to the railcar leaving the loading area. The emission estimates for the flotation concentrate storage and railcar loading are based on a performance specification for the fabric filters that will be installed on these operations. As these emission rates were used as part of several analyses, the permit contains a requirement that the Permittee must conduct performance testing to verify the calculated emission rate.

3.1.5 Autoclave Emissions Emissions from these operations consist primarily of PM, PM10, PM2.5, SO2, sulfuric acid mist, NOX, carbon monoxide, VOCs, hydrogen disulfide, carbon disulfide, and reduced sulfur compounds. An autoclave will be installed to further process the nickel flotation concentrate. In the autoclave, pressure oxidation will be conducted in the presence of chloride to leach the valuable minerals in the concentrate into solution where they can be recovered. A flash vessel associated with the autoclave will be used to bring the autoclave discharge solution down to atmospheric pressure. PolyMet performed sampling on pilot‐test autoclave operations at three different points in the development of this project in years 2000, 2005, and 2009. The concentrations in both the air and condenser underflow streams were measured to quantify controlled and uncontrolled emissions. The test results of the observed pollutants were scaled up from the averaged emission rates collected


during the 2005 pilot scale test operations and used to estimate commercial‐plant‐scale pollutant emissions. Emissions from the autoclave vent and flash vessel will be controlled by a venturi scrubber and packed bed scrubber in series. As these emission rates were used as part of several analyses, the permit contains a requirement that the Permittee must conduct performance testing to verify the calculated emission rate.

3.1.6 Hydrometallurgical Process Tank Emissions Emissions from these operations consist primarily of SO2, sulfuric acid mist, and hydrogen disulfide. The hydrometallurgical process tanks will include various steps designed to extract residual copper from the concentrate, produce a gold/platinum group metals concentrate, and precipitate nickel and cobalt as a hydroxide precipitate. Many of these tanks will have the potential to emit sulfuric acid mist and sulfur dioxide. At this point in the process, the sulfur in the leach solution will have been oxidized to sulfuric acid, so reduced sulfur compounds are not expected to be emitted as a result of the handling and processing of this solution. However, the sodium hydrosulfide used in the process can break down to form hydrogen sulfide. Liquid sulfur dioxide will also be added to the process for iron reduction. The tanks will be covered and vented to a scrubbing system. Caustic will be added to the scrubber liquor to promote the removal of SO2 and hydrogen sulfide from the exhaust stream.

3.1.7 Process Consumables Handling, Storage, and Processing Emissions Process consumables delivered in solid form, as well as process consumables that are volatile or that can decompose to form volatile compounds, can generate emissions during storage and handling. Emissions from process consumables handling, storage, and processing operations (including flocculants, frothers, lime, limestone, and other additives) were calculated using emission factors from AIRS 3‐05‐011‐09 (March 1990) and AP‐42 Section 11.19.2, Crushed Stone Processing and Pulverized Mineral Processing. The emission estimates for some process lime handling sources are based on a performance specification for the fabric filters that will be installed on these operations. As these emission rates were used as part of several analyses, the permit contains a requirement that the Permittee must conduct performance testing to verify the calculated emission rate.

3.1.8 Unpaved Road Emissions Haul roads will be constructed at the Mine Site for transportation of waste rock, ore, and overburden to the appropriate location. In addition to traffic from the haul trucks, there also will be a small amount of light truck traffic on the mine roads. A small fuel tanker also will be used to refuel the diesel‐powered tracked equipment. The mine haul roads will change somewhat during the mine operation due to changing configurations of the mine pits and stockpiles. Initially, waste rock will be stockpiled. After Mine Year 11, mining will cease in the East Pit and the majority of waste rock will be backfilled into that pit. After Mine Year 14, mining will cease in the Central Pit and it too will be available for the in‐pit backfill of waste rock. During the in‐pit disposal phase, the temporary waste rock stockpiles will be relocated to the mined out pits for permanent placement. The changes to the mining operation over time will affect the traffic patterns at the Mine Site and the location of emission generating activities, so the worst‐case year for each operating mode was evaluated in the emission calculations and air dispersion modeling. The worst‐case years used for modeling, based on Haul Truck vehicle miles travelled, were Mine Year 8 for the stockpile phase and Mine Year 13 for the in‐pit phase. Emissions from the material hauling operations are generated by haul trucks travelling on unpaved roads. Emissions generated from unpaved roads at the facility were calculated using the information


present in AP‐42 Section 13.2.2, Unpaved Roads. Emissions data was calculated using Equation 1a in the section in combination with the traffic expected for the facility. This includes information for average vehicle weight, silt content of the road, and vehicle miles traveled to generate emission rates.

3.1.9 Wind Erosion Emissions Emissions generated by wind erosion of stockpiles and the exposed beaches at the tailings basin were calculated using information from AP‐42 Section 13.2.5, Industrial Wind Erosion. Emission rates in this section are based on information such as wind speed, how often the material is disturbed/moved, and the type/size of material in the exposed area. This information was used to generate an emission factor, and then combined with the size of the exposed area to calculate an emission rate for each stockpile and the mine strip. Based on this calculation procedure, wind erosion is not predicted to occur at the Mine Site or limestone stockpiles, but will occur under certain conditions at the tailings basin.

3.1.10 Internal Combustion Engine Emission Calculations Emissions from combustion operations included in this permit action include internal combustion engines used for backup power and emergencies located around the facility. An engine will also be located at the Mine Site to move large electrically powered equipment when that equipment is being relocated at the Mine Site. This unit is not an emergency engine, but it has limited utilization and mining operations will be curtailed when it is in use. Emissions from the internal combustion engines were calculated based on the maximum design fuel input and emission factors in AP‐42 Section 3.3, Gasoline and Diesel Industrial Engines. For the emergency engines, hours of operation for calculating annual potential emissions are identified as 500 hours per year as each engine qualifies as an emergency generator under the U.S. EPA memorandum entitled “Calculating Potential to Emit (PTE) for Emergency Generators”, dated September 6, 1995. The permit contains a requirement that the Permittee must maintain documentation supporting this designation to allow use of the hours of operation limit in calculating annual potential emissions.

3.1.11 Space Heater Emissions Emissions from combustion operations included in this permit action include space heaters in multiple buildings located around the facility. Emissions generated from natural gas space heating at the facility were calculated using the information present in AP‐42 Section 1.4, Natural Gas Combustion and information provided by potential space heater vendors. Natural gas space heaters will be of low‐NOX design. Emissions generated from propane‐fired space heating at the facility were calculated using the information present in AP‐42 Section 1.5, Liquefied Petroleum Gas Combustion.

3.1.12 Actual Emissions Actual emissions are estimated for the first‐time invoice that is required for facilities obtaining an initial Part 70 operating permit. Projected actual emissions were calculated using the same emission factors that were used in determining the potential emissions from all operations at the facility. In determining the projected actual emissions from the facility operations, the Permittee used expected hours of operation and material throughput to estimate emissions from the material handling operations at the facility. In estimating actual emissions from unpaved roads and stockpiles, the calculated potential emissions were used in addition to an agreed annual control efficiency that can be assumed for following the actions described in the facility’s fugitive dust control plan.


This control efficiency was developed by a workgroup consisting of the MPCA, taconite industry, and consultant members that reviewed existing literature and surveyed other state agencies and mining industries. The workgroup agreed to a tiered approach to establish control efficiencies to allow facilities flexibility in the level of effort in the fugitive control plan and the corresponding control efficiency received for those actions. The workgroup defined three tiers of plans which provided increasing control efficiency for fugitive emissions from haul truck roads among other fugitive sources. The fugitive dust control plans submitted by PolyMet meet the requirements of the Level III‐A Plan, described in the workgroup document, which provides for a 80% daily control efficiency for fugitive emissions. In addition, the provisions of the Mine Site fugitive dust control plan regarding Mine Haul Roads (FUGI 26) meet the requirements of the Level III‐B Plan, described in the workgroup document, which provides for greater than 80% daily control efficiency for fugitive emissions. The daily control efficiency used for segments of the Mine Haul Roads (FUGI 26) was 80% for haul road segments within the open pits and 90% for haul road segments not within the open pits. The MPCA fugitive emissions workgroup document is available as Attachment 6 to this TSD.

3.2 Class II Dispersion Modeling The facility completed air dispersion modeling to show modeled compliance with the PM10, PM2.5, NO2, and SO2 National Ambient Air Quality Standards (NAAQS) and Minnesota Ambient Air Quality Standards (MAAQS). This modeling demonstration included nearby sources and background concentrations of the respective pollutants to model the cumulative effects and determine modeled compliance. The modeling was performed using the American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) platform. The table below shows the predicted impacts and modeled concentrations of these pollutants in comparison to the NAAQS and MAAQS.

Table 6. Class II Modeling ‐ Predicted Impacts and Modeled Concentrations

Pollutant Averaging Period

NAAQS (µg/m3)

MAAQS (µg/m3)

Modeled Impact (µg/m3)

Percent of NAAQS (%)

Percent of MAAQS (%)

PM10 24‐hour 150 150 134.4 89.6 89.6

PM2.5 24‐hour 35.0 35.0 31.4 89.7 89.7

PM2.5 Annual 12.0 12.0 11.1 92.5 92.5

NO2 1‐hour 188 188 107.1 57.0 57.0

SO2 1‐hour 196 197 89.7 45.7 45.5

The Permittee assumed certain worst case emission rates when the modeling was conducted, so these have been incorporated as permits limits in the permit. Limits included in the permit as a result of air dispersion modeling to show compliance with the NAAQS and MAAQS in Class II areas are cited as “Minn. R. 7007.0800, subp. 2(A) & (B), Minn. R. 7009.0020‐0090, Minn. Stat. 116.07, subd. 4a(a)” to identify purpose and authority for the limit. In addition, per MPCA practice, a table of the modeled parameters has been added to the permit as an appendix. Other than the specific operating restrictions mentioned above, the parameters listed in Appendix D of the permit describe the operation of the facility at maximum capacity. In other words, the flow rates and temperatures listed in Appendix D represent the minimum parameters at the maximum emission rates. The MPCA does not require any specific compliance demonstration with these parameters because they are worst‐case conditions. Listing the parameters in the permit appendix provides a benchmark for determining if and when additional modeling is required. The MPCA review of the results of the Class II modeling submittal is available as Attachment 7 to this TSD.


3.2.1 Mine Site Phased Operations The Permittee identified that there will be two unique, main phases of mining operations that occur at the Mine Site of the facility. These phases are identified as the “Temporary Stockpile Phase” (Phase 1) and the “In‐pit Disposal / Stockpile Reclamation Phase” (Phase 2). The Permittee indicated that the change in mine operating phases is scheduled to occur approximately in Year 11 of mine operation. In this year, the East Pit will be mined out. At this point, newly mined waste rock will be placed in the East Pit and rock from the temporary stockpiles will begin to be relocated to the East Pit. The Permittee evaluated emissions from operations that would occur during each phase to determine the worst case emissions and determined the maximum emission rate occurred during Year 8 for Phase 1 and Year 13 for Phase 2. These two years were subsequently modeled using the parameters identified in Appendix D of this permit to show compliance with the NAAQS and MAAQS for each phase of mining operations.

3.2.2 Ambient Air Boundary Control Strategy The NAAQS and MAAQS applies to areas designated as “ambient air.” The federal definition of ambient air is identified at 40 CFR § 50.1(e) as “that portion of the atmosphere, external to buildings, to which the general public have access.” Additionally, Minnesota regulates “ambient air” by prohibiting emissions as identified in Minn. R. 7009.0020 which states, “no person shall emit any pollutant in such an amount or in such a manner as to cause or contribute to a violation of any Minnesota ambient air quality standard under part 7009.0080 beyond the person’s property line… [except in places where] the general public has access to the person’s property or portion thereof… the general public shall not include employees, trespassers, or other categories of persons who have been directly authorized by the property owner to enter or remain on the property for a limited period of time and for a specific purpose.” As described earlier in Section 3.2, the facility completed air dispersion modeling to show modeled compliance with the PM10, PM2.5, NO2, and SO2 NAAQS and MAAQS. For the modeling demonstration, PolyMet delineated where their controlled access ended and ambient air began by an “effective fenceline” encompassing the facility and Mine Site. To establish this effective fenceline, PolyMet performed an assessment of its ability to limit access for the area identified as under their control. The air dispersion modeling was reviewed and approved by the MPCA and demonstrates that PolyMet will comply with the applicable NAAQS and MAAQS for the area outside of their effective fenceline. Appendix C to this permit defines the effective fenceline while permit conditions at the Total Facility (TFAC) level identify measures that will be used to secure the boundary and control access as well as the associated monitoring, recordkeeping, and reporting. The effective fenceline control measures include use of fencing, locked or monitored gates or barriers at access points, security patrols, and remote monitoring. PolyMet will use signage to discourage public access (i.e., “no trespassing”); however, the MPCA does not consider this practice a stand‐alone control measure. A detailed explanation of the effective fenceline, complete with aerial images and proposed measures to control access within the effective fenceline can be found in the Ambient Air Boundary Control Plan, included as Attachment 8 to this TSD. The facility is required to begin controlling access prior to blasting of waste rock or ore, but no later than the initial startup of Mine Site Blast Hole Drilling (FUGI 25), whichever is earlier. In addition, if PolyMet makes a change that affects modeled compliance with the NAAQS or MAAQS resulting in a change to the effective fenceline, the permit requires that the Ambient Air Boundary Control Plan be updated to reflect the modification.


3.2.3 Paved Road Exclusion Paved roads were not included in the modeling analysis consistent with the guidance in the May 16, 2011 MPCA memo titled, "Air Quality Policy on Paved Roads and Fugitive Particulate Matter". The policy memo advises that if the predicted ambient impacts (including background) are less than 95% of the NAAQS or MAAQS and the facility maintains an appropriate and enforceable fugitive dust control plan, fugitive dust from paved roads need not be included in the modeling. The Permittee is required to maintain and comply with a fugitive emissions control plan (identified in Appendix B of this permit).

3.2.4 Intermittent Emission Sources PolyMet will have seven internal combustion engines that will be used intermittently for backup power generation (EQUIs 184, 186, 192, and 194), to move large electrically powered mining equipment (EQUI 196), or as a fire pump as part of a fire sprinkler system’s water supply (EQUIs 188 and 190). For emission sources such as these, questions have been raised about how to model intermittent emissions, particularly for compliance with short‐term ambient air quality standards (e.g., the one‐hour standards for SO2 and NO2, and to a lesser degree, the 24‐hour standards for PM10 and PM2.5). The MPCA has coordinated existing permitting practice with modeling intermittent emissions and used the following approach to determine when to include sources with intermittent emissions as well as how to model them. This approach is identified in the MPCA’s Air Dispersion Modeling Practices Manual (October 2017 Version). An excerpt of this approach is identified below:

By default, emergency generators complying with existing permit conditions that embody Best Management Practices (BMPs) need not be modeled.

One possible exception to this is large generators (greater than 500 hp) and/or generators located near an ambient boundary; the MPCA air quality permitting program will inform you of the need to model such units on a case‐by‐case basis. Because of this, the modeling protocol should identify the size and location of emergency generators that will not be modeled.

Emergency generators are generators that operate primarily during emergencies and during maintenance and testing periods. Emergency generators cannot be used for peak shaving or operate to generate income for a facility to supply power to an electric grid, or otherwise supply power as part of a financial arrangement with another entity. However, an emergency generator may be operated during periods in which the Regional Transmission Organization (in this case, the Midwest ISO) has determined there are emergency conditions that could lead to a potential electrical blackout, such as unusually low frequency, equipment overload, capacity or energy deficiency, or unacceptable voltage level.

Consistent with this approach the facility’s emergency and other intermittently operated engines were not included in the modeling. These engines are intermittent sources located away from the fenceline of the facility and have adopted best management practices. The best management practices are included as permit requirements at each engine (EQUIs 184, 186, 188, 190, 192, 194, and 196).

3.2.5 Particulate Deposition Characteristics AERMOD provides for two methods to simulate wet and dry deposition of particulate emissions. Method 1 is used when a significant fraction (greater than about 10 percent) of the total particulate mass has a diameter of 10 micrometers or larger, or when the particle size distribution is known. The particle size distribution must be known reasonably well in order to use Method 1. Method 2 may be used when the particle size distribution is not well known and when a small fraction (less than 10 percent of the mass) is in particles with a diameter of 10 micrometers or larger. Method 2


incorporates conservative assumptions about project materials in the absence of site‐specific data. The use of either approach requires MPCA approval as part of the modeling protocol review process. As part of the modeling performed to demonstrate modeled compliance with the PM10 NAAQS and MAAQS, the facility used AERMOD’s Method 1 to account for PM10 plume depletion. The facility used this option for fugitive emission sources at the facility. Fugitive emission sources at the Mine Site include: truck loading and unloading operations; material handling sources; blast hole drilling; unpaved roads; and portable crushing/screening equipment. Fugitive emission sources at the Plant Site include: tailings basin wind erosion; tailings basin unpaved roads; tailings basin material handling sources; unpaved access roads; and outdoor limestone handling equipment. Method 1 input variables include: particle diameter; mass fraction; and particle density. The plume depletion parameters source‐specific to account for the differences in particle characteristic among sources. The Method 1 particle diameter represents the mass‐mean particle diameter for the particles within the size category of interest. PolyMet calculated the particle diameter based on the AP‐42 emission factor equations used in the emission inventory to estimate PM2.5 and PM10 emissions. Two AP‐42 equations (Unpaved Roads AP‐42 13.2.2.2‐2, and Aggregate Handling AP‐42 13.2.4) were used to develop the representative size categories. The mass mean particle diameter is calculated as an average of the AP‐42 size category and the next lowest category based on the volume of a spherical particle at each of the size categories and shown in the table below. For the PM2.5 size category, a minimum diameter of 1 micrometer was assumed as representative of the smallest mechanically‐generated particulate.

Table 7. Calculation of Mass‐Mean Particle Diameter Source Parameter Particle Size Category

Material Handling

Diameter (µm) 1 2.5 5 10

Volume (µm3) [1] 0.5 8.2 65.4 523.6

Average Particle Volume (µm3) [2]

n/a 4.4 36.8 294.5

Particle Diameter for Average Volume (µm) [3]

n/a 2.03 4.13 8.25

Haul Roads and Other Sources

Diameter (µm) 1 2.5 5 10

Volume (µm3) [1] 0.5 8.2 n/a 523.6

Average Particle Volume (µm3) [2]

n/a 4.4 n/a 265.9

Particle Diameter for Average Volume (µm) [3]

n/a 2.03 n/a 7.98

[1] Calculated as Volume = 4/3*pi*(diameter/2)3 [2] Calculated as Average Volume = (size category volume + next lowest size category volume)/2 [3] Calculated as Particle Diameter = 2*(3/4/pi*Average Volume)1/3

The mass fraction within each size category was also determined from the respective AP‐42 emission factor equation as shown in the table below.


Table 8. Calculation of Mass Fraction in Size Category Source Parameter Particle Size Category

Material Handling Size Category (µm) 2.5 5 10

Particle Size Multiplier (k) [1] 0.053 0.2 0.35

Particle Size Fraction (of largest category) [2] 0.15 0.57 1

Mass Fraction in category [4] 0.15 0.42 0.43

Haul Roads Size Category (µm) 2.5 5 10

Particle Size Multiplier (k) [1] 0.15 n/a 1.5

Particle Size Fraction (of largest category) [2] 0.1 n/a 1

Mass Fraction in category [4] 0.1 n/a 0.9

Screening Size Category (µm) 2.5 5 10

Emission Factor (lb/ton) [3] 0.00005 n/a 0.00074



Crushing Size Category (µm) 2.5 5 10

Emission Factor (lb/ton) [3] 0.0001 n/a 0.00054



[1] As identified in respective AP‐42 equations (AP‐42 13.2.2.2‐2 and AP‐42 13.2.4) [2] Calculated as Particle Size Fraction = k value / largest k value [3] Calculated as Particle Size Fraction = emission factor value / largest emission factor value [4] Calculated as Category Mass Fraction = size fraction ‐ next lowest size fraction

The particle density data used for each material type was determined based on multiple sources; however, the only site‐specific particle input parameter was density data. Ore density was determined as part of the pilot plant work with results that ranged from 2.98 g/cm3 to 3.02 g/cm3 and averaged 3.0 g/cm3. Waste rock density was determined in the mine plan for the facility as 2.45 tons/yd3 (2.9 g/cm3). Overburden density was obtained from lab results included as part of a geotechnical data package with results that averaged 2.7 g/cm3 and a range of results for overburden within the region PolyMet operates with results that ranged from 2.6 g/cm3 to 2.75 g/cm3 and averaged 2.7 g/cm3. LTVSMC tailings density was obtained from lab results included as part of a geotechnical data package with results that averaged 2.9 g/cm3. The density of tailings generated by PolyMet mining operations was obtained from lab results included as part of a geotechnical data package with results that averaged 3.0 g/cm3. The material processed in the portable crushing and screening equipment will be either waste rock or overburden. The particle density for overburden of 2.7 g/cm3 was used for these operations. The road surface, which will be reflected in the dust generated from traffic on unpaved roads, may be composed of several materials including waste rock, overburden, or LTVSMC tailings. The lowest density for overburden of 2.7 g/cm3 was used for these operations. Fugitive material handling sources are part of the limestone system at the Plant Site. A density of 2.6 g/cm3 to 2.75 g/cm3 was obtained from a safety data sheet from a potential supplier, and a density of 2.7 g/cm3 was used for these operations. Lime handling at the wastewater treatment operations was also included as part of the Method 1 deposition option. A density of 3.37 g/cm3 was obtained from a safety data sheet from a potential supplier and was used for these operations. The NAAQS modeling results are below the applicable PM10 ambient standards; however, modeling refinement and related assumptions are relatively high for this project in comparison to other modeling analyses. The ambient monitoring plan to monitor fugitive emissions of PM10 at the Mine Site (see Section 3.7 ‐ Special Purpose Monitoring Plan) can be used to verify if the modeling results


are representative or conservative. The prevailing winds and the modeled results show the highest model results to occur to the southeast of the equalization basins where PM10 monitors will be installed and operated. The purpose of the monitoring equipment is to confirm the effectiveness of the fugitive emission control measures. The Special Purpose Monitoring Plan requires the Permittee to conduct a root cause analyses when certain action levels are triggered. If the root cause evaluation does not identify corrective actions that return monitor results below action levels, the modeling assumptions, including the AERMOD Method 1 input assumptions can be further evaluated.

3.2.6 Class II Remodeling Requirements In order to continue to protect ambient standards after a permit issuance, the MPCA may require that future changes to a modeled parameter trigger remodeling or an equivalent or better dispersion (EBD) analysis. The MPCA evaluates what remodeling requirements should result from a modeling analysis on a case‐by‐case basis based. This evaluation depends on the type of modeling conducted, how close the modeled ambient concentration is to the relevant standard, how likely the source is to make changes that would increase the PTE of the pollutant(s) modeled, how well the operating assumptions and emission estimates in the model resemble how the facility operates, etc. In order to protect the NAAQs and MAAQS, the MPCA may require a facility to perform remodeling or an EBD analysis when the facility proposes a change to a modeled parameter. Based on the results of the modeling analysis performed for this permit action, the permit contains requirements directing PolyMet to remodel under the following circumstances:

Remodel for the PM10 NAAQS and MAAQS for changes that will result in an emission rate increase greater than or equal to 0.855 pounds PM10 per hour.

Remodel for the PM2.5 NAAQS and MAAQS for changes that will result in an emission rate increase greater than or equal to 0.571 pounds PM2.5 per hour.

Remodel for the PM10, PM2.5, NO2, and SO2 NAAQS and MAAQS after startup of mining and processing operations if there are any changes/additions to the modeled parameters identified in Appendix D of the permit.

Remodel for the PM10, PM2.5, NO2, and SO2 NAAQS and MAAQS after beginning operations in the hydrometallurgical plant if there are any changes/additions to the modeled parameters identified in Appendix D of the permit.

Regarding the PM10 and PM2.5 standards, the MPCA included remodeling requirements for when the facility makes changes that result in an increase in emissions above a certain threshold. Regarding the NO2 and SO2 standards, the MPCA included remodeling requirements to capture any changes to modeled parameters after milestones in facility operations (after startup of mining and processing operations, and after beginning operations in the hydrometallurgical plant). There are different remodeling triggers for these pollutants based on the results of the modeling analysis as displayed in Table 6. The facility is required to remodel for changes that involve emission increases of PM10 or PM2.5, but not for changes that involve emission increases of NO2 or SO2 based on the proximity to the standards as displayed in Table 6 (~90% for the PM10 and PM2.5 standards versus ~57% for the NO2 standard and ~45% for the SO2 standard). The MPCA decided to include remodeling requirements for changes that involve emission increases of PM10 or PM2.5 because the facility has greater emissions of PM10 and PM2.5 compared to emissions of NO2 and SO2 and the modeling analysis showed results closer in proximity to the standards for PM10 and PM2.5. Regarding the PM10 and PM2.5 standards, the thresholds for emission rate increases (0.855 pounds PM10 per hour and 0.571 pounds PM2.5 per hour) were selected as they represent the thresholds for


insignificant modifications as found in Minn. R. 7007.1250. While Minn. R. 7007.1250 does not contain a threshold for emissions of PM2.5, the threshold identified in the permit was chosen by following the same manner used to establish the pollutant thresholds in Minn. R. 7007.1250. These thresholds were originally established as 25% of the significant emission rate threshold, converted to a pound per hour rate assuming continuous operation year‐round, for the PSD program. For PM2.5, the PSD significant emission rate is 10 tons per year. See the example calculation below:

10 . 18760

20001

25%0.571 .

Regarding the NO2 and SO2 standards, the MPCA included remodeling requirements to capture any changes when the facility is constructed compared to the initial facility design (see modeled parameters listed in Appendix D). The remodeling requirements direct the facility to perform a modeling analysis at two points in time:

180 days after startup of mining and processing operations, defined in the permit as the initial startup date of the primary crushers (EQUI 1 or EQUI 2), whichever is earlier.

180 days after beginning operations in the hydrometallurgical plant, defined in the permit as the initial startup date of the autoclave (EQUI 108).

These remodeling requirements are required only if, at the respective trigger dates, there are changes made to any modeled parameter or emission rate documented in Appendix D of the permit, or if there are any additions to the information in Appendix D that were not previously modeled. The facility is also required to remodel for changes that affect PM10 or PM2.5 when the facility is constructed compared to the initial facility design under the same circumstances.

3.3 Class I Dispersion Modeling Generally, Class I dispersion modeling is performed when a facility is required to perform modeling as part of the (Prevention of Significant Deterioration) PSD program. Facilities performing this modeling must show they will not adversely affect any Class I areas. Whether a project needs to perform this analysis depends on the size of the facility/project and how close it is to the Class I areas. Class I areas in Minnesota include the Boundary Waters Canoe Area Wilderness and Voyagers National Park. Other nearby Class I Areas includes Rainbow Lake Wilderness in Wisconsin and Isle Royale National Park in Michigan. Class I areas are of special national or regional scenic, recreational, natural, or historic value for which the PSD regulations provide special protection. Under the Clean Air Act, the FLM and the Federal official with direct responsibility for management of Federal Class I parks and wilderness areas (i.e., Park Superintendent, Refuge Manager, Forest Supervisor) is charged with the affirmative responsibility to protect that area’s unique attributes, expressed generically as air quality related values (AQRVs). The permitting authority, MPCA, is responsible for administering the PSD program and ensuring that the NAAQS and increments are protected within the state. PolyMet completed Class I dispersion modeling, as part of a mitigation commitment made during the environmental review process, to show the emissions from the proposed PolyMet operations will not adversely impact any Class I areas. The original evaluation was completed as part of the environmental review process, and updated and verified as part of preparing Air Emissions Permit 13700345‐101. The Class I dispersion modeling was performed using the proposed mining and processing operations identified as part of this permit action.


Similar to the modeling performed to demonstrate compliance with the NAAQS and MAAQS, the Permittee assumed certain worst case emission rates when the modeling was conducted, so these have been incorporated as permits limits in the permit. Operating restrictions specific to the Class I modeling performed were also incorporated as permit limits in the permit. The MPCA review of the results of the Class I modeling submittal is available as Attachment 9 to this TSD.

3.3.1 Class I Increment Analysis

A Class I increment analysis is required when the modeled Class I area impacts of the facility’s emissions alone are above the Significant Impact Levels (SILs). Modeling of the PolyMet facility showed that its impacts were above the 24‐hour PM10 SIL in the Boundary Waters Canoe Area Wilderness. Therefore, an analysis of the cumulative impact from all sources of PM10 (past and present, increases and decreases) on the Class I areas was prepared. The table below shows the modeling results from the analysis performed by PolyMet that indicate the facility was below the Class I SILs for PM10 (annual averaging period), NO2 (annual averaging period), and SO2 (3‐hour, 24‐hour, and annual averaging periods). No further analysis was required for these Class I increments. The PM10 (24‐hour averaging period) Class I SIL modeling results indicate that cumulative increment modeling is required for said pollutant and averaging period.

Table 9. Class I Modeling ‐ Predicted Impacts and Modeled Concentrations


PSD Class I Increment (µg/m3)

Significant Impact Level

(µg/m3)

Modeled Results

Boundary Waters

Canoe Area (µg/m3)

Voyageurs National Park

(µg/m3)

Isle Royale National Park

(µg/m3)

Rainbow Lakes Area Wilderness (µg/m3)

PM10 24‐hour 8 0.3 0.290 0.130 0.029 0.028

PM10 Annual 4 0.2 0.021 0.005 0.001 0.002

NO2 Annual 2.5 0.1 0.008 0.002 0.000 0.001

SO2 3‐hour 25 1 0.106 0.020 0.002 0.004

SO2 24‐hour 5 0.2 0.027 0.005 0.001 0.001

SO2 Annual 2 0.1 0.001 0.000 0.000 0.000

The emission inventory for the PolyMet increment analysis included modifications to existing sources, new facilities that have been permitted or submitted permit applications prior to PolyMet, and increases in actual emissions from existing facilities. Additional details of each are presented in the permit application. The maximum cumulative modeled concentration for the areas that exceeded the 24‐hour PM10 SIL are shown in the table below. Overall, the modeling analysis indicates that the emissions associated with the PolyMet facility will not deteriorate the air quality significantly in the Class I areas, because all modeled concentrations are below the Class I increment. The increment modeling results indicate that there is remaining increment to allow for future growth. Considering both increment consuming emission increases and increment expanding emission decreases, the maximum modeled increase in concentration of PM10 is 1.95 µg/m3 in the Boundary Waters Canoe Area Wilderness and 1.20 µg/m3 in Voyagers National Park. This increase is below the increment standard of 8 µg/m3 for Class I areas.


Table 10. Cumulative 24‐Hour PM10 Increment Modeling


PSD Class I Increment (µg/m3)

Modeled Results

Boundary Waters Canoe Area

(µg/m3)


(µg/m3)

PM10 24‐hour 8 1.95 1.20

3.3.2 Acid Deposition Impacts Analysis

Class I dispersion modeling for Class I air quality related values (AQRVs) is typically required when the facility is within 300 kilometers of a Class I area. A portion of the modeling analysis is an evaluation of the potential impacts of SO2 and NOX emissions to species (flora and fauna) and ecosystems (terrestrial and aquatic). The potential impacts associated with the PolyMet project were evaluated based on the methodology outlined in the U.S. Forest Service publication1, “Screening Procedures to Evaluate Effects of Air Pollution on Eastern Wildernesses Cited as Class I Air Quality Areas” and the National Park Service publication2 “Federal Land Managers’ Interagency Guidance for Nitrogen and Sulfur Deposition Analyses”. Four Class I areas were included in the deposition analysis for PolyMet: the Boundary Waters Canoe Area Wilderness (located 34 km from the PolyMet facility), Voyageurs National Park (82 km), Rainbow Lake Wilderness (142 km), and Isle Royale National Park (218 km). The table below compares the sum of background SO2 concentrations plus modeled ambient air SO2 concentrations resulting from the project emissions at the four Class I areas. In evaluating potential adverse effects to flora and fauna, lichen species are generally used as a threshold indicator of potential air pollution damage because they are especially susceptible to air pollution and show adverse effects before other plant species and animal species. If pollutant concentrations are sufficiently low that no damage occurs to native lichens, then it can reasonably be concluded that all other flora and fauna species are protected. The most sensitive lichen species are only present when annual average SO2 concentrations are less than 40 μg/m3. As can be seen in the table, all estimated SO2 ambient air concentrations are below 40 μg/m3. The Federal Land Managers have set a screening level concentration referred to as the “Green Line Concentration”. All modeled concentrations are also below the “Green Line Concentration” of 5 μg/m3, indicating that there should be no adverse effects from the project emissions on flora or fauna in the Class I areas.

1 U.S. Environmental Protection Agency Office of Air Quality Planning and Standards. Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary Report and Recommendations for Modeling Long Range Transport Impacts. December 1998. EPA‐454/R‐98‐019. 2 National Park Service U.S. Department of the Interior. Federal Land Managers’ Interagency Guidance for Nitrogen and Sulfur Deposition Analyses (Natural Resource Report NPS/NRSS/ARD/NRR—2011/ 465). November 2011.


Table 11. Screening Analysis for Effects on Flora and Fauna from SO2 Total Annual Average Ambient Air Concentrations

Location

Background Air Concentration

(µg/m3)

Modeled Project Contribution

(µg/m3)

Total Projected Air Concentration

(µg/m3)

Green Line Concentration

(µg/m3)

Boundary Waters Canoe Area Wilderness

1.2 0.001 1.2 5


0.7 0.000 0.7 5


2.0 0.000 2.0 5

Rainbow Lake Wilderness

1.6 0.000 1.6 5

Adverse effects to terrestrial and aquatic ecosystems are evaluated using the deposition analysis thresholds (DATs) to evaluate if the incremental impact of the PolyMet operations for deposition is acceptable. DATs have been developed by the FLMs to evaluate the contribution of additional nitrogen or sulfur to deposition within Class I areas. The DATs are intended to distinguish where deposition increases may result in potentially adverse ecosystem stresses, as well as where the deposition increases are likely to have a negligible impact on AQRVs. Adverse effects to terrestrial and aquatic ecosystems are evaluated slightly differently by the National Park Service and the U.S. Forest Service. comparison for the U.S. Forest Service sites, Boundary Waters Canoe Area Wilderness and Rainbow Lake Wilderness area, should be made between the column titled “Total Concentration or Deposition” and the column titled “Green Line Value or Deposition Analysis Threshold”. Comparison for the National Park Service sites, Voyageurs National Park and Isle Royale National Park should be made between the column titled “Model Air Concentration or Calculated Project‐ Related Deposition” and “Green Line Value or Deposition Analysis Threshold”. PolyMet‐related ambient air concentrations and deposition values for potential terrestrial impacts were estimated using the CALPUFF modeling system and results are presented in the table below. The pollutant values required for the terrestrial impacts evaluation are the PolyMet‐related nitrogen and sulfur deposition and SO2 ambient air concentrations. The SO2 and NOX emissions from the project are not expected to have an adverse effect on terrestrial ecosystems in the Class I areas.

Table 12. Screening Analysis for Potential Terrestrial Impacts

Location Pollutant Background

Data

Model Air Concentration or Calculated Project‐Related Deposition

Total Concentration or Deposition

Green Line Value or

Deposition Analysis Threshold


Annual Average SO2 (μg/m3) 1.2 0.001 1.2 5 μg/m3

3‐Hour Max SO2 (μg/m3) 10.8 0.105 10.9 100 μg/m3

Total Sulfur (kg/ha/yr) 2.85 0.001 2.9 0.01 kg/ha/yr

Total Nitrogen (kg/ha/yr) 4.75 0.008 4.8 0.01 kg/ha/yr







Location Pollutant Background

Data

Model Air Concentration or Calculated Project‐Related Deposition

Total Concentration or Deposition

Green Line Value or




3‐Hour Max SO2 (μg/m3) 18 0.002 18 100 μg/m3








PolyMet‐related deposition values for potential aquatic impacts were estimated using the CALPUFF modeling system and results are presented in the table below. The pollutant values required for the terrestrial impacts evaluation are the PolyMet‐related nitrogen and sulfur deposition. The SO2 and NOX emissions from the project are not expected to have an adverse effect on aquatic ecosystems in the Class I areas.

Table 13. Screening Analysis for Potential Aquatic Effects

Location Pollutant

Background Deposition (kg/ha/yr)

Estimated Project‐Related Deposition

(kg/ha/yr)

Total Deposition (kg/ha/yr)


(kg/ha/yr)


Total Sulfur 2.85 0.001 2.85 0.01

Total Nitrogen 3.80 0.008 3.81 0.01


Total Sulfur 1.84 0.000 1.84 0.01

Total Nitrogen 3.87 0.001 3.87 0.01


Total Sulfur 2.15 0.000 2.15 0.01

Total Nitrogen 3.85 0.000 3.85 0.01


Total Sulfur 2.98 0.000 2.98 0.01

Total Nitrogen 4.16 0.000 4.16 0.01

3.3.3 Visibility Impacts Analysis

Class I dispersion modeling for Class I air quality related values (AQRVs) is typically required when the facility is within 300 kilometers of a Class I area. One AQRV is visibility. Whether a project needs to perform a visibility analysis depends on the size of the facility/project and how close it is to the Class I areas. The potential visibility impacts associated with the PolyMet project were evaluated based on currently accepted guidance from the Federal Land Managers (FLMs). The FLMs are charged with direct responsibility for management of Class I areas. Potential changes in the visibility were expressed in terms of a light extinction coefficient (bext). Three Class I areas were included in the visibility analysis for PolyMet: the Boundary Waters Canoe Area Wilderness (located 34 km from the PolyMet facility), Voyageurs National Park (82 km), and Isle Royale National Park (218 km). The Rainbow Lake Wilderness Areas in Wisconsin does not have an AQRV for visibility. The Boundary Waters Canoe Area Wilderness falls under the jurisdiction of the U.S. Department of Agriculture (U.S. Forest Service) whereas the national parks fall under the jurisdiction of the U.S. Department of the Interior (National


Park Service and U.S. Fish and Wildlife Service). Visibility has not been established as an AQRV for the Rainbow Lakes Wilderness, so visibility impacts were not modeled for that area. Modeling results for visibility impacts compared to a baseline of the existing facility are presented in the table below for the three years modeled. The listed values are indicated by year due to pairing of emissions in time and space. When compared to pristine conditions, the Project has no days with a change in extinction greater than 5% at Voyageurs or Isle Royale. Using current modeling guidance (FLAG 2010 ‐ Method 8), the 98th percentile day impacts have a change in extinction of less than 5% change at BWCAW and 5 total days greater than 5%. These visibility modeling results meet the current FLM criteria for demonstrating no adverse impacts.

Table 14. Class I Modeling ‐ Visibility Impacts Analysis Results

Location Parameter

Year

2002 2003 2004


Maximum Δbext (%) 7.89 5.61 6.17

8th highest Δbext (%) 4.63 3.65 4.13

Days with Δbext ≥ 5% 5 4 3



Maximum Δbext (%) 1.45 2.71 2.27

8th highest Δbext (%) 0.96 1.01 1.09




Maximum Δbext (%) 0.8 0.55 0.7

8th highest Δbext (%) 0.39 0.18 0.26



The results presented above are inclusive of a number of measures PolyMet has proposed to mitigate the potential impacts to visibility in Class I areas from the proposed project. These measures include; limiting the emissions from mobile sources; upgrading the insulation in the existing Crusher and Concentrator buildings; utilize low‐NOX space heating equipment; use of Tier IV certified engines for any mining fleet equipment; use of efficient gen‐set locomotives; reducing dust collector exhaust for heating demand reductions; use of pollution control equipment; and use of fuel in their mobile equipment with a sulfur content not to exceed 15ppm. Permit requirements which result from the Class I visibility mitigation measures are cited as “Minn. R. 7007.0800, subp. 2(B), Minn. R. 7007.0800, subp. 3, Minn. Stat. 116.07, subd. 4a(a)” to denote purpose and authority.

3.3.4 Mobile Source Tailpipe Emissions The modeling performed by PolyMet in support of its visibility demonstration included emissions from mobile sources at the facility. Mobile source emission rates used in the visibility impacts analysis were calculated based on assumptions of vehicle type, quantity, availability and utilization. The permit contains language limiting the emissions from the mobile sources to their modeled values. The mobile sources include:

Locomotives (electric gen‐set locomotive and switcher locomotive);

Mine Fleet Mobile Sources (haul trucks, front‐end loaders, sand and water trucks, blast hole drills, dozers, integrated tool handlers, and backhoes); and

Tailings Basin Construction Mobile Sources (haul trucks, excavators, dozers, graders, and compactors).


There are three numerical emission limits for each category of mobile sources; one limit on PM10 emissions from that category, calculated and averaged on a daily basis; one limit on NOX emissions from that category, calculated and averaged on a daily basis; and one limit on SO2 emissions from that category, calculated and averaged on a daily basis. Compliance with the limits will be demonstrated through a mine management system that will monitor and record fuel use rates or, depending on the particular tracking package installed on the vehicle, hours of operation for each mine fleet mobile source. In accordance with Appendix F of the air emission permit, the mobile source fuel use or hours of operation data are processed using site specific fuel use rates and established emission factors specific to the size and type of each engine in order to determine emissions of each pollutant from each vehicle, summed and averaged on a daily basis. Vehicle operations data and emissions calculations are to be kept onsite and available for inspection while any deviations are required to be included in the semiannual deviations report. In order to substantiate continued compliance with the EPA tiered vehicle emission standards for each vehicle, the Permittee must certify that the equipment is operated and maintained in compliance with the manufacturers recommended maintenance procedures, practices and schedules. Similarly, in order to authenticate the vehicle emissions data, the Permittee must follow a site specific monitoring plan that details ongoing operation and maintenance procedures, ongoing data quality assurance procedures, and ongoing recordkeeping and reporting procedures. Additionally, operational restrictions on diesel fuel use and sulfur content of the fuel will remain in place to provide reasonable assurance that the mine fleet emission limit will be met. Therefore, the restrictions implemented on the mine fleet provide reasonable assurance that the facility will be incompliance with the Class I visibility mitigation. Appendix E to this permit contains the calculation methodology used in demonstrating compliance with the mobile source emission limit requirements established by Air Emissions Permit 13700345‐101 used to model potential impacts visibility in Class I areas. Emission source assumptions used to model potential impacts to visibility in Class I areas are enforced through the air emission permit. Specifically, the permit establishes limits on emissions of NOX, SO2, and PM10 from the Mining Vehicles Tailpipe Emissions, Tailings Basin Construction Vehicle Tailpipe Emissions, and Locomotive Emissions.

3.4 Air Emissions Risk Analysis (AERA) Modeling

The Clean Air Act requires the EPA to regulate the emissions of 187 specific air toxics, also referred to as Hazardous Air Pollutants (HAPs). Instead of promulgating ambient air quality standards for these pollutants, the EPA regulates HAPs through National Emission Standards for Hazardous Air Pollutants (NESHAPs). In Minnesota, potential health effects from air toxics are further reviewed using the AERA process and accompanying risk screening tools. These tools are routinely updated to ensure the most current toxicity and air modeling information is used to assess the potential for adverse health impacts. Upon completion of an AERA, quantitative risk results are compared to the following facility risk guidelines developed in collaboration with MDH and consistent with EPA guidance.

Total facility cancer risk below or at: one in 100,000 (1E‐05).

Total facility hazard index below or at: one. The facility is located in Northern Minnesota, in the Iron Range that is zoned for Mineral Mining and Industrial use. The AERA addressed four hypothetical exposure scenarios: an acute (maximum hour) along the owned property boundary, an offsite worker (maximum annual‐with nonresident worker related exposure assumptions) along the owned boundary, a hypothetical resident along the Mineral Mining/Industrial Boundary, and a resident who also eats a large portion of home grown vegetables and


meats (called the farmer scenario) along the Mineral Mining/Industrial Boundary. The AERA receptors for these scenarios are based on where it is reasonable for people to be and or live. The locations where a trespasser could potentially access the property were also assessed for the acute risk scenario since the owned and controlled area are not fenced. The AERA was performed using the proposed mining and processing operations identified as part of this permit action. The original AERA evaluation was completed as part of the environmental review process, and updated and verified as part of preparing Air Emissions Permit 13700345‐101. Similar to the modeling performed to demonstrate compliance with the NAAQS and MAAQS, the Permittee assumed certain worst case emission rates when the modeling was conducted, so these have been incorporated as permits limits in the permit. Operating restrictions specific to the AERA modeling performed were also incorporated as permit limits in the permit. The AERA Modeling Report contains the forms and memos documenting technical decisions and submittals and is included as Attachment 10. The documents are in chronological order according to submission date, but are not completely comprehensive due to the size and complexity of the submittals. The first document in the AERA Modeling Report is the MPCA summary of the AERA. 3.4.1 Air Emissions Risk Analysis (AERA) Recalculation

The highest air toxic contributions to risk estimates are particulate metal emissions from the open pits; diesel tailpipe emissions of PAHs and dioxins from mining vehicles; and, hourly emissions of metals (arsenic, nickel) and nitrogen dioxide from the proposed processing plant. The AERA results are at facility risk guideline levels when rounded, however modeling refinement and related AERA assumptions are relatively high for this project in comparison to other AERA analyses. As a result, technical staff recommended that an AERA recalculation be performed under certain circumstances. Therefore, the air permit requires an AERA recalculation under the following circumstances:

Process throughput increases for open pit material handling operations (FUGI 14, FUGI 15, FUGI 16, or FUGI 21).

Vehicle miles traveled increase for Mine Site Haul Roads (FUGI 26).

Mining vehicle fuel use increases (as identified at the TFAC level).

Performance testing is required for the Autoclave stack (STRU 35) in the proposed processing plant to measure the hourly emission rate of arsenic, nickel, and nitrogen dioxide. The AERA is required to be recalculated if the performance tests result in an emission rate above the original rate used in the AERA.

Hourly recordkeeping of fuel usage is required for the Autoclave Startup Boiler (EQUI 118) in the proposed processing plant. The AERA is required to be recalculated if the hourly fuel usage rate exceeds the original rate used in the AERA.

The pit locations are shifted toward the site boundaries. Additional discussion regarding the AERA recalculation requirements is available in Tables 5 and 13.

3.5 Cross Media Analysis

A cross‐media analysis was conducted by PolyMet to address potential water quality concerns from dust deposition from the facility operations. This analysis included air modeling of potential facility‐generated dust particles, an evaluation of the potential for release of sulfate and metals from oxidation of the deposited dust, and the resulting potential for impact on the quality of downgradient waters. The MPCA’s conclusions and recommendations following review of the Cross‐media Analysis did not result in any additional requirements in Air Emissions Permit 13700345‐101.


3.6 Fugitive Emission Control Plans Appendix B to Air Emissions Permit 13700345‐101 identifies two fugitive emission control plans; the first encompasses fugitive emission sources at the Plant Site while the second covers fugitive emission sources at the Mine Site. The fugitive emission control plans address operating practices that PolyMet will use to control fugitive dust emissions. Significant sources of fugitive dust emissions include mine haul roads, service roads, material handling and processing operations, and the tailings basin. The fugitive emission control plans detail daily visible emissions checks on all active haul roads, unpaved service roads, material loading, material unloading, material processing, stockpiles, the tailings basin, tailings basin access roads, and tailings basin construction activities. Reported fugitive dust emissions will be investigated and evaluated for appropriate corrective action. The observation of visible emissions does not, in and of itself, demonstrate noncompliance with any applicable requirement but is a signal to trigger investigation and, if necessary, reasonable and appropriate corrective action. PolyMet will maintain records of daily visible emissions observations, haul road water applications, dust suppressant application, road maintenance, vehicle miles traveled per type of vehicle, meteorological conditions, material throughput, drilling activities, tailings basin surveys, mulching and seeding activities, and reports of tailings basin deposition areas and reduction efforts. The records of daily visible emissions observations will include any investigation and corrective actions completed for observations that conclude attention is required and the weather conditions present at the time of the observation. In non‐freezing conditions, dust from unpaved roads will be controlled by water application or chemical dust suppressants as required by weather, traffic, and road conditions. PolyMet will maintain adequate watering capabilities to control dust during typical conditions and use MPCA‐approved dust suppressants as a backup to watering when conditions warrant. PolyMet will also grade the road surface and, as required, add crushed and screened rock to maintain the road surface and control fugitive dust emissions. Finally, traffic may be routed around dusty road sections. In freezing conditions, dust from unpaved roads will be controlled by application of salts (sodium chloride, calcium chloride, and magnesium chloride), snow, and under some conditions, light applications of water. Unpaved roads will be maintained as necessary and new road material will be applied as needed. Contracted portable crushing and screening will be employed at the Mine Site to prepare approved material for various construction uses including road surfacing, blast hole stemming, and railroad ballast. The majority of the portable crushing and screening equipment is subject to 40 CFR pt. 60, subp. OOO, Standards of Performance for Non‐metallic Mineral Processing Plants, including all crushers, screens, and most material transfer points. Best management practices will be used to minimize material transfer point drop distances while water sprays will be the primary control measure. When water sprays are not practical due to weather conditions, chemical dust suppressants will be used as needed, or operations may temporarily cease if primary control measures do not adequately reduce fugitive emissions. Fugitive emissions suppression practices for the floatation tailings basin, or FTB, will include a combination of operational techniques and mitigation measures. Tailings are spigotted from the outside edges of the FTB across the beach area to the pond. Medium and coarse tailings are retained on the beach area while the finest tailings are deposited in the pond. Tailings will also be deposited sub‐aqueously by use of a tremi diffuser. The first several years of tailings deposition and LTV Steel Mining Company (LTVSMC) tailings movement will take place around the current Cell 2E. The FTB design includes a single large cell after a splitter dike between


Cell 2E and 1E is inundated. While the maximum beach length of the current operational plan will be approximately 29,800 feet, only a limited portion of the basin will be active as the tailings will be spigotted from piping located around the basin. Inactive areas will be reclaimed as conditions allow, resulting in a subset, approximately 5% or 1,500 feet, of the total beach potentially subject to wind erosion. LTVSMC tailings will be used for dam construction. Tailings are excavated, loaded onto trucks, and unloaded in the construction area. In addition to the LTVSMC tailings, off‐site borrow material will be used for construction of buttresses and if the supply of LTVSMC tailings is not sufficient, off‐site construction material will also be used to construct the FTB dams. FTB dam construction will only occur during warmer months and during dam construction, the exterior face of the dams will be amended with a bentonite layer. Fugitive emissions from these material handling operations will be mitigated by minimizing drop distances, water application, and cessation of activities if primary controls are not sufficient to reduce fugitive emissions. Daily visible emission checks will be made on the tailings basin. If visible emissions are observed during the visible emission check or are reported by an equipment operator or employee, PolyMet will investigate the condition and implement appropriate corrective actions above the routine mitigation measures described below, to address the visible emissions. The observation of visible emissions does not, in and of itself, demonstrate noncompliance with any applicable requirement but is a signal to trigger investigation and, if necessary, reasonable and appropriate corrective action. During freezing months (typically late November through early April), freshly deposited tailings freeze and are covered with snow which minimizes dust emissions. Road plowing and general traffic are limited to active areas during the cold weather months. During nonfreezing months water elevation in the basin is maintained to provide maximum inundated coverage for interior slopes and beaches while preserving a safe freeboard from the top of the perimeter dam and the water line. Moisture is maintained in active areas of the FTB from wet tailings deposition, precipitation, and by capillary action (near the pond). As safe access allows, application of water or/and dust suppressant, mulching, and/or seeding for permanent cover will be used to control fugitive dust emissions from exposed beach areas.

3.7 Special Purpose Monitoring Plan PolyMet will operate numerous sources of particulate matter. In order to manage these emissions, PolyMet will utilize a fugitive emissions control plan as described in the previous section. The plan describes the actions, monitoring, and recordkeeping that PolyMet will take in order to reduce these emissions. Part of this plan involves the use of air quality monitoring equipment. The purpose of the monitoring equipment is to provide near‐real‐time feedback to the facility operators regarding the effectiveness of their emission control measures. If monitored levels reach certain pre‐determined levels, then PolyMet must take certain prescribed actions. If these levels are repeatedly reached, then PolyMet must perform a root cause analysis to determine why this has happened, and what it will do to ensure it does not happen in the future. These may involve changes to the fugitive emissions control plan. The facility’s special purpose monitoring plan is included as Attachment 11 to this TSD. The permit conditions at the Total Facility (TFAC) level identify the monitoring locations, monitor specifications, sampling frequency, and monitor operating procedures as well as the associated monitoring, recordkeeping, and reporting.


3.7.1 Monitor Placement and Selection At least two monitors and one meteorological station will be used: one monitor will be located on the north side of PolyMet’s mining area, and the second monitor will be located on the southern end of PolyMet’s mining area. The location selections were informed by historical wind data and predictive modeling data. For specific locations, please see Attachment 11 to this TSD. To ensure that the monitoring data is reliable, PolyMet will use EPA‐certified Federal Equivalent Method (FEM) monitors. This type of monitor is routinely used for air quality monitoring; in this application, the monitors will be placed near particulate emitting activities and processes. This siting is expected to yield a greater amount of information about the emitting processes than if the monitors were located outside the effective fenceline of the facility. PolyMet will begin operating the monitors prior to the start of any mining operations, and will continue operating the monitors until the MPCA issues a permit that allows PolyMet to cease operation of the monitors. The monitors will collect PM10 every hour, 24 hours per day, seven days per week; the exception to this is for audits, maintenance, and malfunctions. The PM10 size fraction was selected because it is believed to best represent the effectiveness of the fugitive emission controls, and this size fraction typically remains airborne longer than total suspended particulates. The meteorological station will collect wind speed, direction, temperature, pressure, and precipitation data. This information will be used to help identify those sources that may be responsible for the measured emission levels. This data, in turn, will inform a course of action so that the facility can improve their control strategy for those sources.

3.7.2 Action Levels This permit action includes three separate action levels. The action levels are staggered so that as the measured concentration rises, the facility must take increasingly complex responses to identify and remedy the issue. The first action level is set at 105 µg/m3, which is the predicted concentration at the selected southern location. If this value is exceeded over any three consecutive hours, then the facility must take action. The second action level is set at 150 µg/m3, which coincides with the current ambient air standard for PM10. If this value is exceeded over any single hour, then the facility must take action. The third action level is also set at 150 µg/m3. However, if this value is exceeded over a 24‐hour period, then the facility must notify the MPCA, take action, and perform a root cause analysis. This monitor is placed within the effective fenceline so while exceedance of these action levels does trigger a response, it is not a violation of the NAAQS. Furthermore, if any of the action levels are exceeded eight or more times in a 12‐month period, then PolyMet must perform a root cause analysis and identify additional measures that must be added to its fugitive emissions control plan. This analysis is separately performed for four types of processes: drilling and blasting; truck unloading and loading at the Mine Site; mine haul roads and mine service roads; and mine site portable crushing and screening equipment. This analysis will also be performed when the action levels were exceeded, but were unable to be attributed to a particular process.

3.7.3 Reporting and Review PolyMet will submit two reports every year with information about these monitors. The report will include all of the raw data and summary of the data. The MPCA will periodically audit the performance of the monitors in accordance with the USEPA Quality Assurance Handbook for Air Pollution Measurement Systems. Additional information about the special purpose monitoring plan is available in Attachment 11 to this TSD.


3.8 Amphibole Mineral Fibers

PolyMet proposes to mine and process ore from the geologic formation known as the Duluth Complex located in Northeast Minnesota. This geologic formation is known to contain a group of minerals called amphiboles. Amphibole minerals are a type of naturally occurring metamorphic mineral that can be found in two different crystalline structures: the asbestiform and non‐asbestiform types. Asbestiform‐type amphibole minerals are composed of long, thick, flexible fibrils that separate along grain boundaries. Conversely, the crystalline structure of non‐asbestiform amphiboles do not form this way, but can take on the form of blockier ‘cleavage fragments’ when liberated from ore through various mining processes, such as blasting, crushing, concentrating, and handling of the ore. Studies of fibers in the Duluth Complex, confirmed by analysis undertaken for the PolyMet project, confirm that nearly all of the amphibole minerals in the Duluth Complex (and the ore, tailings, and process water at the PolyMet site) are expected to be of the non‐asbestiform variety, with asbestiform amphibole minerals comprising less than 0.1 ppm by weight of mineralized ore (MEQB 1979)3 (SGS 2004)4. When ore containing amphibole minerals of either the asbestiform or non‐asbestiform type is crushed as part of the mining process, particles that fit the Minnesota definition of a ‘fiber’ can be generated and emitted into the surrounding air. Minnesota Fibers (“fibers”) are defined in the Minnesota Department of Health Methods 851 and 852 as any amphibole or chrysotile mineral particle with a 3:1 or greater aspect ratio (length to width). The negative effects on human health from inhalation exposure to asbestiform amphibole mineral fibers is well documented. These effects include an increased risk of developing lung cancer and mesothelioma. There is currently ongoing debate about whether exposure to inhalable non‐asbestiform amphibole fibers, such as cleavage fragments, has any negative impacts on respiratory health. Non‐asbestiform amphibole fibers is the type of amphibole that is expected to be found in the ore that PolyMet will process. The 2015 Final EIS for the NorthMet Mining and Land Exchange recognizes that there is an uncertain level of potential health risk presented by these non‐asbestiform fibers and focuses on minimizing the potential release of airborne fibers and monitoring their concentration in the ambient air. For these reasons, MPCA is exercising its discretionary authority under Minn. Stat. 116.07, subd. 4a(a) to incorporate into this permit requirements to prevent and minimize the emissions of fibers and for monitoring their concentrations in the ambient air. PolyMet has operated an ambient fiber monitor located at the City of Hoyt Lakes Wastewater Treatment Plant since May 2008. The purpose of this monitoring work has been to establish baseline ambient fiber concentrations located near the residential population closest to the facility. Monitoring samples are sent to a third party laboratory for identification and quantification of fibers using the Minnesota Department of Health (MDH) transmission electron microscopy (TEM) Method 852 ‐ Analysis for Mineral Fibers in Air. The MPCA used monitoring data from May 12, 2008, through December 30, 2014, to calculate 365‐day rolling averages for fiber concentrations. These rolling averages for fiber concentrations (amphibole plus chrysotile) in Hoyt Lakes ranged between 230 fibers/m3 to 650 fibers/m3 over this sampling period. For comparison, fiber monitoring from 2006 to 2016 at two other sites in northeastern Minnesota has produced 365‐day rolling averages between roughly 500 fibers/m3 and 2500 fibers/m3 (Beaver Bay) and between roughly 700 fibers/m3 and 3000 fibers/m3 (Silver Bay).

3 Minnesota Environmental Quality Board. 1979. “The Minnesota Regional Copper‐Nickel Study (1976‐1979).” Executive Summary 1. St. Paul, Minnesota: Minnesota Environmental Quality Board. 4 SGS. 2004. “Flotation Pilot Plant Products Environmental Investigation and Testing.” SGS Lakefield Research Limited.


3.8.1 Permit Conditions to Minimize and Monitor Fiber Concentrations The size of fibers places them in same size fraction as fine particulate matter, which are particles less than 2.5 micrometers in aerodynamic diameter (PM2.5). Data identified in the 2007 Mineral Fibers Report, developed by Barr Engineering for the EIS, found that 95% of mineral fibers identified in the tests samples were 3 micrometers or smaller in aerodynamic diameter, with most being less than 2 micrometers in aerodynamic diameter. Therefore, it is anticipated that minimizing fine particulate matter emissions from the facility will also minimize fiber emissions. The PM2.5 ambient air quality modeling results can be used as a surrogate for dispersion of ambient fibers. The modeling results indicated that concentrations of fine particulates would decrease rapidly with distance from the source, and the highest potential concentrations of fibers would occur at or very close to the facility. Therefore, it is anticipated that concentrations of fibers would decrease in the same way. Any potential impacts of fiber emissions are anticipated to be minimized based on the use of fine particulate controls similar to best available control technology, the implementation of a fugitive emission control plan, and the distance of the facility to nearby populations. As a result, this permit requires the following:

Installation and operation of fine particulate control technologies similar to Best Available Control Technology (BACT) on ore crushing and concentrating operations to minimize fugitive particulate emissions.

Implementation of a fugitive emission control (FEC) plan at the Mine and Plant Sites to reduce fugitive emissions and respond to observed fugitive emissions in an effective manner.

Ambient fiber monitoring to measure ambient fiber concentrations in the nearest residential population, the City of Hoyt Lakes to determine if fiber concentrations change as a result of the facility’s operations.

3.8.2 Inclusion of Particulate Controls Similar to Best Available Control Technology

The facility’s emissions are below the thresholds that would make the source subject to the federal Prevention of Significant Deterioration (PSD) program. Therefore, the facility is not required to perform a top‐down BACT analysis as set forth in the PSD regulations and the facility is not subject to other applicable requirements that would require imposition of emission limits. However, the facility conducted a technology review to identify fine particulate controls for point sources in the ore crushing and concentrating portions of the project that are similar to BACT. These point sources include ore processing operations, such as course and fine crushing and concentration, and the material handling sources associated with these activities. MPCA has reviewed PolyMet’s technology review and concurs with the level of control proposed for point sources of PM2.5. Due to the similar size of fine particulates and fibers, the installation and operation of fine particulate controls are expected to reduce the potential emission of fibers consistent with BACT‐level controls for PM2.5. Specifically, the following types of fine particulate controls were selected from the analysis:

Fabric filter (baghouse or cartridge) dust collectors on crushing and concentrating sources. These controls will be applied to all emission sources within the coarse crushing, drive house material handling, fine crushers, and concentrator operations.

Exhaust air from the dust collectors may be internally recirculated in certain buildings to reduce heating demand. The reduced heating demand results in lower combustion pollutant emissions from heating sources. When internally venting the fabric filter control equipment, exhaust air from these crusher/concentrator sources, High‐Efficiency Particulate Air (HEPA) filters will be used. This is done as an additional measure of controlling particulate matter within closed building spaces.


The inclusion of fine particulate controls as permit conditions for controlling fiber emissions is a state‐only requirement that MPCA is requiring pursuant to Minnesota Rule 7007.0800, subp. 2(B). To ensure the controls perform as expected, parametric monitoring of point source controls is required as outlined in Section 3.9 Monitoring. Future permit modifications that would affect these control measures must take into account how the modification would also impact the control of fiber emissions.

3.8.3 Amphibole Mineral Fibers and Fugitive Dust Controls

Any fugitive dust that is generated from Duluth Complex rock has the potential to contain fibers. Processing of the mined ore does not begin until the ore arrives at the Plant Site by rail. Therefore, it is not expected that ore handling operations at the Mine Site will result in a significant source of fiber emissions. Potential sources of fugitive fiber emissions at the Plant Site include the flotation tailings basin, flotation tailings basin construction and maintenance activities, and handling of tailings in the existing LTV Steel Mining Company (LTVSMC) tailings basin. Fibers may also be generated and emitted from activities associated with construction, maintenance, and use of unpaved roads that utilize waste rock as a component of their construction. However, the potential for emission of fibers from these sources is expected to be low because these roads will be constructed of waste rock and overburden material that is expected to contain few amphibole minerals. To prevent and minimize fugitive dust, the permit requires that PolyMet maintain an MPCA approved fugitive emission control plan that covers activities at both the Mine Site and the Plant Site. It is expected that the control measures that prevent and minimize fugitive dust emissions will also prevent and minimize fiber emissions. The FEC plan outlines the procedures to prevent and minimize the release of fugitive dust emissions from identified sources. The facility’s fugitive dust control plans are included as part of the permit in Appendix B. These procedures include the practices to control emissions, performance monitoring, best management practices, and recordkeeping requirements for potential fugitive sources at both the Plant and Mine Sites. Requiring the FEC plan as a permit condition for the purpose of controlling fiber emissions is a state‐only requirement.

3.8.4 Ambient Fiber Monitoring Requirements

The permit requires the Permittee to continue fiber monitoring in order to quantify the concentration of fibers in ambient air. Fiber monitoring is required to be conducted at the City of Hoyt Lakes Waste Water Treatment Facility. This monitoring will provide data that can be used to determine whether the concentration of fibers in ambient air changes as a result of the facility’s operation. PolyMet will be required to start fiber monitoring within 15 days of initial startup of the crushing and concentrating operations, defined in the permit as the initial startup date of the primary crushers (EQUI 1 or EQUI 2), whichever is earlier. Monitoring is required to be conducted according to an MPCA approved ambient fiber sampling plan at a sampling frequency of at least one 96‐hour sample every 12 calendar‐days. Fiber monitoring shall follow the 12‐day schedule for sample collection in the annual Sampling Schedule Calendar available on the EPA website or equivalent. After the samples are collected from the monitor, they are sent to an MPCA approved laboratory for analysis within 60 calendar‐days. This laboratory will use the MDH TEM Method 852 ‐ Analysis for Mineral Fibers in Air to identify fibers based on mineralogy and aspect ratio and will quantify their concentration over the sampling period. In order to ensure that fiber monitoring returns data of high quality, the facility is required to develop and maintain an MPCA approved ambient fiber monitoring plan. Any substantive or material change to this plan must first be approved by the MPCA. The facility’s ambient fiber monitoring plan is


included as Attachment 12 to this TSD. The permit conditions at the Total Facility (TFAC) level identify the monitoring locations, monitor specifications, sampling frequency, and monitor operating procedures as well as the associated monitoring, recordkeeping, and reporting. These measures are state‐only requirements and are not enforceable by the EPA Administrator and citizens under the Clean Air Act. At the time of this permit action, it remains unknown if the operations at this facility will impact the concentration of fibers in the ambient air in the City of Hoyt Lakes. The permit requirement for fiber monitoring is intended to provide data that could allow for an analysis of whether ambient concentrations of fibers may have changed from the baseline, and whether they are attributable to the project’s emissions.

3.9 Minnesota Mercury Total Maximum Daily Load (TMDL) Study

The U.S. Environmental Protection Agency approved Minnesota's Statewide Mercury Total Maximum Daily Load study in March 2007. The long‐term goal of the mercury TMDL is for fish toxicity levels to meet water quality standards; the approach for Minnesota’s share is mass reductions from state mercury air emission sources to reach a statewide emissions rate of 789 pounds per year. The MPCA adopted the TMDL goal into state rules in 2013 at Minn. R. 7007.0502, subp. 1. To achieve the TMDL emissions goal, an implementation plan was completed by stakeholders in 2009. The Mercury TMDL Implementation Plan includes guidelines for new mercury air emission sources and modifications to existing sources that result in increased mercury emissions. The application of the Guidelines for New and Modified Mercury Emissions Sources5 (“Guidelines”) is to ensure that mercury emission increases due to a new or modified mercury emission source will not jeopardize the state‐wide reduction goal needed to meet water quality standards. PolyMet Mining Company’s (PolyMet) proposed copper/nickel mining project is a new project, and has potential mercury emissions under this permit that exceed 3 pounds per year, making the project subject to the Guidelines. The MPCA has determined that with the conditions of this permit, the project will not impede TMDL reduction goals:

The project will not impede the progress of any of the “sector” mercury emission goals. Minnesota’s inventory of mercury emissions has been characterized by the MPCA by grouping emission facilities into three sectors: emissions incidental to energy production, purposeful use, or mining. The mining sector goal was established specifically for the ferrous mining operations, e.g. taconite mining. The PolyMet project is the first proposed non‐ferrous mine in the state. Because there were no existing non‐ferrous sources in the state at the time that the TMDL was finalized, there was no non‐ferrous sector emission reduction goal established.

The PolyMet project will not impede progress towards the overall TMDL reduction goals. The most recent assessment of statewide mercury emissions show that overall mercury emission reductions are permanent and occurring ahead of schedule. o Significant progress in the electric generation sector has resulted in mercury emission reductions in

advance of what was anticipated by the TMDL, due to state mercury reduction statutes, new federal mercury control standards for electricity utility and industrial coal‐fired boilers, and shifting electricity generation to renewable and natural gas sources. When the Mercury TMDL Implementation Plan was complete in 2009, it was projected that electric utilities would emit 1661

5 https://www.pca.state.mn.us/sites/default/files/wq‐iw4‐01s.pdf


pounds of mercury in 2010. Actual mercury emissions in 2010 were less than half of that projection (800.9 pounds). The interim 2018 goal for the utilities sector is 355 pounds of mercury emissions per year; MPCA projects that 2018 emissions will be less than 170 pounds.

o The taconite sector, another large mercury emitting sector in the state, has successfully piloted mercury controls on a small scale and are required by Minnesota rule to submit reduction plans by December 2018 to achieve the sector reduction goal by 2025.

o Emissions from the products sector has remained stable, or is growing primarily due to legacy use of mercury. Mercury continues to be released from municipal solid waste, and will until the disposal of products that contain mercury ceases, like fluorescent lamps. Releases from the use of dental amalgam will fall after 2025 when the long term outcome of improved dental care begins to affect emissions of mercury from cremation.

The magnitude of mercury emissions from this project is small: permitted total project potential emissions are 4.6 pounds; actual emissions will be less, reflective of actual operating hours and operating conditions.

PolyMet will have emission controls in place. This permit contains mercury emission limits and appropriate monitoring, recordkeeping and reporting as identified in Table 15.

3.9.1 Guideline #1 ‐ Employ Best Mercury Controls Available

The mercury emissions sources for the proposed project include the Autoclave (EQUI 108) and Autoclave Flash Vessels (EQUI 109) and fuel usage processes. Nearly all of the mercury emissions from PolyMet operations are emitted from the autoclave. The potential to emit of mercury for this project is 4.1 pounds per year. Due to the high moisture content of the autoclave exhaust, dry controls such as baghouses and fabric filters are technically infeasible. For this reason, the MPCA has determined that the two‐stage mercury control, a venturi scrubber (TREA 51) followed by a packed bed wet scrubber (TREA 52), is the best mercury controls available for this activity. In the United States, all gold mining applications use venturi scrubbers so selection of a venturi scrubber is consistent with non‐ferrous industry practices. The venturi scrubber removes particle bound and oxidized mercury. A packed bed wet scrubber will remove residual oxidized mercury. The two‐stage mercury control system is expected to achieve 25% control for elemental mercury and 90% control for particle bound and oxidized mercury. The scrubber effluent is recycled within the hydrometallurgical process to conserve water. Water and waste solids discharged from the process which may contain mercury are sent to the Hydrometallurgical Residue Facility. The Residue Management Plan details how solid residues from the hydrometallurgical plant, which may contain mercury, will be safely managed and remain isolated from further transport to the environment. The remaining mercury emissions from PolyMet operations are emitted from fuel‐burning operations. PolyMet will use gaseous fuels for space heating equipment and the small amount of process fuel usage. It is estimated that the permitted potential emissions from fuel will be 0.5 pounds per year. Gaseous fuels have the lowest mercury content of fossil fuels available for use in space heating, and are considered clean fuels. Use of gaseous fuels represents the best mercury control technically feasible for fuel combustion.

3.9.2 Guideline #2 ‐ Complete Environmental Review PolyMet completed environmental review as required by Minnesota rules and federal regulations. Cumulative mercury deposition modeling was conducted by PolyMet and submitted in January 2012 and approved by the cooperating agencies and the MPCA in August 2012. The mercury deposition modeling was conducted using the MPCA Mercury Risk Estimation Method (MMREM) based analysis. This analysis was a local mercury deposition health assessment and was completed only for the Plant


Site, since the Plant Site has the majority of mercury emissions. The MMREM work was not updated as part of the permit drafting processing for Air Emissions Permit 13700345‐101, since the anticipated mercury emissions did not change. The local mercury deposition health assessment, calculated through the MMREM spreadsheet, does not make an adjustment for increased sulfur loadings from site emissions. An additional analysis was conducted by PolyMet to assess whether an increased level of sulfur deposition/emissions could increase the methylation of existing mercury. A discussion of this analysis is included in Section 3.5 (Cross Media Analysis).

3.9.3 Guideline #3 ‐ Provide Emission Estimates to MPCA for Inclusion in an Enforceable Document and a Determination by the MPCA of Whether the Project Will Impede TMDL Reduction Goals. This permit contains requirements to limit mercury emissions from the Autoclave operations. The permit contains enforceable mercury limit, conditions to ensure that the control equipment is properly run and maintained, recordkeeping, and routine compliance demonstrations. The compliance demonstration requirements will ensure the mercury limit is met on an ongoing basis as well as provide information about actual emissions. As discussed above, with the conditions of this permit, the MPCA has determined that this project will not impede achieving TMDL reduction goals. As a result of this determination guidelines #4 and #5, which speak to the development of mitigation or offsets of mercury emissions, are not applicable to this project.

3.10 Monitoring In accordance with the Clean Air Act, it is the responsibility of the owner or operator of a facility to have sufficient knowledge of the facility to certify that the facility is in compliance with all applicable requirements. In evaluating the monitoring included in the permit, the MPCA considered the following:

the likelihood of the facility violating the applicable requirements;

whether add‐on controls are necessary to meet the emission limits;

the variability of emissions over time;

the type of monitoring, process, maintenance, or control equipment data already available for the emission unit;

the technical and economic feasibility of possible periodic monitoring methods; and

the kind of monitoring found on similar units elsewhere. The table below summarizes the monitoring requirements.


Table 15. Monitoring

Subject Item* Requirement (basis) What is the monitoring? Why is this monitoring adequate?

TFAC 1 Air Quality Total Facility

Process Throughput ≤ 11,680,000 tons per year (limit to avoid PSD; NAAQS modeling)

Monthly recordkeeping; Monthly monitoring; Monthly calculations

The permittee is required to monitor and record the monthly material throughput and perform monthly calculations of the 12‐month rolling sum of material throughput to show that the material usage does not exceed the operational limit. These requirements are sufficient to have a reasonable assurance of compliance.

Electric Gen‐Set Locomotive and Switcher Locomotive: NMHC+NOx ≤ 2.98 g/bhp‐hr PM ≤ 0.15 g/bhp‐hr NOX ≤ 166.20 lb/day PM10 ≤ 6.69 lb/day SO2 ≤ 0.31 lb/day Operating Hours ≤ 10 hours per day (from 6:00am to 6:00pm), for 10 hours total, during each calendar day of the following months: April ‐ November. (Class I Visibility)

Certified engine, daily monitoring, recordkeeping, emissions calculations

The Permittee is required to purchase an engine certified to the Tier 3 engine standards. The permit contains requirements documenting the calculation method and frequency of calculations to demonstrate compliance with the emission limits. The permittee is required to calculate emissions in accordance to Appendix E based on daily operating records. The permittee is required to monitor and record the daily startup and shutdown time and the number of hours operated for this source to show that the hours operated does not exceed the operational limit. These requirements are sufficient to have a reasonable assurance of compliance.



Mine Fleet Mobile Sources: PM, variable depending on horsepower NOX, variable depending on horsepower CO, variable depending on horsepower NMHC, variable depending on horsepower NOX ≤ 852.98 lb/day PM10 ≤ 8.21 lb/day SO2 ≤ 2.21 lb/day Operating Hours ≤ 10 hours per day (from 6:00am to 6:00pm), for 10 hours total, during each calendar day of the following months: April ‐ November. (Class I Visibility)





Tailings Basin Construction Mobile Sources: PM, variable depending on horsepower NOX, variable depending on horsepower CO, variable depending on horsepower NMHC, variable depending on horsepower NOX ≤ 521.36 lb/day PM10 ≤ 5.01 lb/day SO2 ≤ 1.20 lb/day Operating Hours ≤ 10 hours per day (from 6:00am to 6:00pm), for 10 hours total, only during each calendar day of the months of April ‐ November. (Class I Visibility)



COMG 1 Limestone Preparation Building ‐ NSPS Subpart OOO Affected Facilities

PM ≤ 0.032 g/dscm (0.014 gr/dscf) for stack emissions Opacity ≤ 7% for building openings (NSPS subp. OOO)

Control equipment O&M; Performance testing; Visible emissions checks

The Permittee is required to operate and maintain the control equipment any time the emission unit is in operation and conduct performance testing to measure PM emissions and opacity from building openings as specified in the NSPS requirements. These requirements are sufficient to have a reasonable assurance of compliance. The permit also contains requirements to conduct daily visual emissions checks on the sources in this group. These requirements are found in the EQUI 140, EQUI 141, EQUI 142, EQUI 144, and EQUI 145 sections of the permit.



COMG 2 Portable Crushing Plant

PM ≤ 4.24 lb/hr PM ≤ 5.30 tpy PM10 ≤ 1.77 lb/hr PM10 ≤ 2.22 tpy PM2.5 ≤ 0.253 lb/hr PM2.5 ≤ 0.316 tpy (limit to avoid PSD)

Emissions calculations

The permittee will demonstrate compliance by calculating emissions with equations in the COMG 2 section of the permit. These equations use conservative estimates for the PM, PM10, and PM2.5 emission factors and are a conservative estimate of the actual emissions from the portable crushing plant.

PM10 ≤ 1.77 lb/hr PM10 ≤ 2.22 tpy PM2.5 ≤ 0.253 lb/hr PM2.5 ≤ 0.316 tpy Operating Hours ≤ 12 hours/day (from 6:00 am to 6:00 pm) during each calendar day of the months of November ‐ April. There is no restriction on hours of operation for these operations during other months. (limit to avoid PSD; NAAQS modeling)

Emissions calculations; recordkeeping

The permittee will demonstrate compliance by calculating emissions with equations in the COMG 2 section of the permit. These equations use conservative estimates for the PM10 and PM2.5 emission factors and are a conservative estimate of the actual emissions from the portable crushing plant. PolyMet is able to use daily operational records to show the startup and shutdown time and the number of hours operated each for each unit in COMG 2.

COMG 3 HEPA Filter Requirements

No applicable control efficiencies Pressure drop: 0.5 ≤ ΔP ≤ 10.0 inches (Minn. R. 7007.0800, subps. 2 & 14)

Control equipment O&M; Daily pressure drop, inspections

Monitoring based on the Minnesota Performance Standard for Control Equipment is adequate to have a reasonable assurance of compliance. The operation of this piece of control equipment is for purposes of fiber emissions mitigation identified as a commitment during the environmental review process for Air Emissions Permit No. 13700345‐101. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.


PM ≤ 0.4 lb/MMBtu Opacity ≤ 20%, with exceptions (Minn. R. 7011.0515)

Recordkeeping: fuel records

These requirements apply individually to all indirect‐fired space heaters listed in this group. These units use natural gas and propane; therefore, the likelihood of violating either of the emission limits is very small. PolyMet can demonstrate that these units will continue to operate such that emissions are well below the emission limits by only burning natural gas or propane.



PM, variable depending on airflow Opacity ≤ 20%, with exceptions (Minn. R. 7011.0610)


These requirements apply individually to all direct‐fired space heaters listed in this group. These units use natural gas and propane; therefore, the likelihood of violating either of the emission limits is very small. PolyMet can demonstrate that these units will continue to operate such that emissions are well below the emission limits by only burning natural gas or propane.








COMG 6 MSFMF Space Heaters







COMG 7 WWTS Space Heaters



These requirements apply individually to all indirect‐fired space heaters listed in this group. These units use only natural gas; therefore, the likelihood of violating either of the emission limits is very small. PolyMet can demonstrate that these units will continue to operate such that emissions are well below the emission limits by only burning natural gas.





These requirements apply individually to all direct‐fired space heaters listed in this group. These units use only natural gas; therefore, the likelihood of violating either of the emission limits is very small. PolyMet can demonstrate that these units will continue to operate such that emissions are well below the emission limits by only burning natural gas.

COMG 8 Fine Crusher Space Heaters







COMG 9 Concentrator Building Space Heaters







COMG 10 Hydromet Building Space Heaters









COMG 11 Reagent Building Space Heaters







COMG 12 Limestone Preparation Building Space Heaters







COMG 13 Coarse Crusher Building Space Heaters









COMG 14 Drive House Space Heaters







COMG 15 Flotation Addition Space Heaters







COMG 16 Concentrate Dewatering Building Space Heaters









COMG 17 Concentrate Loadout Building Space Heaters







COMG 18 Rebuild Shop Space Heaters







COMG 19 Main Warehouse Space Heaters









COMG 20 General Shops Space Heaters







COMG 21 Warehouse Electrical Space Heaters







COMG 22 Rubber Shop Space Heaters









COMG 23 Lube House Space Heaters







EQUI 1 North 60” Crusher

PM ≤ 0.05 g/dscm (0.022 gr/dscf) for stack emissions Opacity ≤ 7% for stack emissions Opacity ≤ 10% for process fugitive emissions (NSPS subp. LL)

Control equipment O&M; Performance testing

The Permittee is required to operate and maintain the control equipment any time the emission unit is in operation and conduct performance testing to measure PM emissions and opacity as specified in the NSPS requirements. These requirements are sufficient to have a reasonable assurance of compliance.

PM ≤ 3.41 lb/hr PM10 ≤ 3.41 lb/hr PM2.5 ≤ 3.41 lb/hr (limit to avoid PSD)

Performance testing; Control equipment O&M

The Permittee is required to conduct performance testing for PM, PM10, and PM2.5 emissions and operate and maintain the control equipment any time the emission unit is in operation. These requirements are sufficient to have a reasonable assurance of compliance.

PM10 ≤ 3.41 lb/hr PM2.5 ≤ 3.41 lb/hr (NAAQS modeling)


The Permittee is required to conduct performance testing for PM10 and PM2.5 emissions and operate and maintain the control equipment any time the emission unit is in operation. These requirements are sufficient to have a reasonable assurance of compliance.



EQUI 2 South 60” Crusher










EQUI 3 North Distribution Box


























EQUI 31 2A Tipper Car












EQUI 32 Conveyor Transfer Chute ‐ 2A and 2B to 4B/4A (Fine Crusher Building)










EQUI 33 West Coarse Ore Bins












EQUI 34 Fine Crushing ‐ East 1 ‐ 7' Standard
























EQUI 51 5N Tripper Car












EQUI 52 5S Tripper Car
































EQUI 55 Conv. Trans. Collection Belt to Transfer Belt




EQUI 56 Conv. Trans. Transfer Belt to SAG Feed Belt










EQUI 93 Sag Mill (wet process)

PM, variable depending on airflow Opacity ≤ 20%. (Minn. R. 7011.0715)

None For these units, based on EPA published emissions factors, it is highly unlikely that they could violate the applicable requirement. In addition, these units are typically operated and vented inside a building, so testing for PM or opacity is not feasible.

EQUI 94 Ball Mill (wet process)



EQUI 95 Rougher Flotation



EQUI 96 Scavenger Flotation



EQUI 97 Rougher Regrind

Opacity ≤ 10% for process fugitive emissions. (NSPS subp. LL)

Performance testing

The Permittee is required to conduct performance testing to measure opacity as specified in the NSPS requirements. These requirements are sufficient to have a reasonable assurance of compliance.

EQUI 98 Scavenger Regrind











EQUI 101 Rougher (Cu/Ni) Conc Fine Grinding


Performance testing


EQUI 102 Separation Flotation



EQUI 103 Scavenger (Ni) Conc Fine Grinding

























EQUI 106 Railcar Loading ‐ Copper Concentrate












EQUI 107 Railcar Loading ‐ Nickel Concentrate

PM, variable depending on airflow Opacity ≤ 20% (Minn. R. 7011.0715)


The Permittee is required to conduct performance testing for PM emissions and operate and maintain the control equipment any time the emission unit is in operation. As this emission unit meets the requirements of Minn. R. 7011.0715, subp. 3, in addition to the control equipment operation, it is highly unlikely that the unit could violate the applicable requirement.







EQUI 108 Autoclave vent (1 unit) and Emergency Pressure Relief Vent








EQUI 110 AuPGM Precipitation Tanks






EQUI 111 Iron and Aluminum Precipitation Tanks (3)




EQUI 112 CuS Cementation Tank N2 Vent




EQUI 113 MHP Stage 1 Tank Vent




EQUI 114 2nd Stage Hydrogen Precipitation



EQUI 115 Hydroxide Product Storage and Handling



EQUI 116 Hydroxide Bagging



EQUI 117 Oxygen Plant Adsorber Regeneration Heater



This units use only natural gas; therefore, the likelihood of violating either of the emission limits is very small. PolyMet can demonstrate that these units will continue to operate such that emissions are well below the emission limits by only burning natural gas.



EQUI 118 Autoclave Startup Boiler (Natural Gas)

No applicable limits (NSPS subp. Dc)


There are no applicable limits required by the NSPS, only recordkeeping of fuel usage. The Permittee is required to keep monthly records of natural gas combusted.

EQUI 120 Flotation Flocculant Silo Feeder (Magnafloc 10)



EQUI 121 Flotation Flocculant Silo (Magnafloc 10)




EQUI 123 Acid Flocculant Silo Feeder



EQUI 124 Acid Flocculant Silo


Control equipment O&M

The Permittee is required to operate and maintain the control equipment any time the emission unit is in operation. As this emission unit meets the requirements of Minn. R. 7011.0715, subp. 3, in addition to the control equipment operation, it is highly unlikely that the unit could violate the applicable requirement.

Process Throughput ≤ 105.8 tons per day (limit to avoid PSD; NAAQS modeling)

Recordkeeping; Daily monitoring

The permittee is required to monitor and record the daily throughput of material handling to show that the material usage does not exceed the operational limit. These requirements are sufficient to have a reasonable assurance of compliance.

EQUI 125 Acid Flocculant to Mix Tank (Magnafloc 351)





EQUI 126 Xanthate Collector Mix Tank (w/baghouse)








Performance testing


EQUI 127 NaHS Mix Tank/Storage Tank




EQUI 128 MgO to Mix Tank



EQUI 129 Coagulant to Mix Tank



EQUI 130 Frother Mix Tank



EQUI 131 Copper Sulfate Mix Tank





EQUI 132 Lime Conveyor



EQUI 133 Lime Slaker (w/scrubber)










EQUI 134 Plant Lime Silo




Process Throughput ≤ 104.4 tons per day (limit to avoid PSD; NAAQS modeling)




PM ≤ 0.032 g/dscm (0.014 gr/dscf) (NSPS subp. OOO)


The Permittee is required to operate and maintain the control equipment any time the emission unit is in operation and conduct performance testing to measure PM emissions as specified in the NSPS requirements. These requirements are sufficient to have a reasonable assurance of compliance.



EQUI 136 Limestone Hopper to Conveyor




EQUI 137 Limestone Conveyor to Stacker Conveyor

Opacity ≤ 7% (NSPS subp. OOO)

Performance testing; Fugitive emission control plan; Visible emissions checks

The Permittee is required to conduct performance testing to measure opacity as specified in the NSPS requirements. These requirements are sufficient to have a reasonable assurance of compliance. The permit also contains requirements to maintain and comply with a fugitive emissions control plan and conduct daily visual emissions checks on this source. These requirements are sufficient to have a reasonable assurance of compliance.

Process Throughput ≤ 3125 tons per day Process Throughput ≤ 281,250 tons per year (limit to avoid PSD; NAAQS modeling)

Recordkeeping; Daily monitoring; Monthly calculations

The permittee is required to monitor and record the daily throughput of material handling and perform monthly calculations of the 12‐month rolling sum of material handled to show that the material usage does not exceed the operational limit. These requirements are sufficient to have a reasonable assurance of compliance.

EQUI 138 Limestone Reclaim Chute (to tunnel conveyor)







EQUI 139 Limestone Reclaim Feeder to Conveyor









EQUI 140 Limestone Tunnel Conveyor to Bunker




EQUI 141 Limestone Bunker to crusher feed conveyor (enclosed)




EQUI 142 Limestone Crusher Feed Conveyor Discharged (enclosed)




EQUI 143 Limestone Crusher for stack emissions




PM ≤ 0.0826 lb/hr PM10 ≤ 0.0826 lb/hr PM2.5 ≤ 0.0826 lb/hr PM2.5 ≤ 0.0265 lb/hr (24‐hour average) (limit to avoid PSD)



PM10 ≤ 0.0826 lb/hr PM2.5 ≤ 0.0826 lb/hr PM2.5 ≤ 0.0265 lb/hr (24‐hour average) (NAAQS modeling)





EQUI 144 Limestone Crusher to Conveyor




EQUI 145 Limestone Conveyor to Mix Tank




EQUI 146 Carboxymethylcellulose Mix Tank



EQUI 147 MSFMF Lime Silo




Process Throughput ≤ 240 tons per day (limit to avoid PSD; NAAQS modeling)



EQUI 148 MSFMF Lime Transfer to Tank


Fugitive emission control plan; Visible emissions checks

For these units, based on EPA published emissions factors, it is highly unlikely that they could violate the applicable requirement. The permit also contains requirements to maintain and comply with a fugitive emissions control plan and conduct daily visual emissions checks on this source. These requirements are sufficient to have a reasonable assurance of compliance.






EQUI 149 Liquid SO2 Unloading



Process Throughput ≤ 159.68 tons per hour of liquid SO2 and less than one fill per hour Process Throughput ≤ 4362 tons per year of liquid SO2 (NAAQS modeling)



EQUI 150 Limestone Reclaim Pocket Dump


Fugitive emission control plan; Visible emissions checks

For these units, based on EPA published emissions factors, it is highly unlikely that they could violate the applicable requirement. The permit also contains requirements to maintain and comply with a fugitive emissions control plan and conduct daily visual emissions checks on this source. These requirements are sufficient to have a reasonable assurance of compliance.




EQUI 151 Oxygen Plant Cooling Tower


None For these units, based on EPA published emissions factors, it is highly unlikely that they could violate the applicable requirement.

EQUI 172 Administration Building New Boiler



This unit uses natural gas only by design; therefore, the likelihood of violating either of the emission limits is very small. PolyMet can demonstrate that this unit will continue to operate such that emissions are well below the emission limits by only burning natural gas.


Opacity: ≤ 20% SO2 ≤ 0.50 lb/MMBtu SO2 ≤ 0.0015 lb/MMBtu (Minn. R. 7011.2300)

Recordkeeping: Monthly fuel usage records, fuel purchase records and certification

PolyMet can demonstrate that the emission limits will be met by maintaining records of the fuel type burned and a certification from the fuel supplier that the sulfur content does not exceed 15 ppm maximum per gallon. In addition, this unit is not reasonably expected to emit pollution in excess of the opacity limit.








PM ≤ 0.22 g/hp‐hr NMHC+NOx ≤ 3.0 g/hp‐hr Sulfur content ≤ 15 ppm (NSPS subp. IIII; NESHAP Subp. ZZZZ)

O&M Plan; Recordkeeping; Non‐resettable hour meter

The Permittee is required to purchase an engine certified to the emission standards established by the NSPS requirements. The engine must be installed, configured, and operated according to the manufacturer’s specifications and as specified in the NSPS requirements. These requirements are sufficient to have a reasonable assurance of compliance. In addition, the permittee is required to keep records of fuel type burned and a certification from the fuel supplier that the sulfur content does not exceed 15 ppm maximum per gallon.





PM ≤ 0.22 g/hp‐hr NMHC+NOx ≤ 3.0 g/hp‐hr Sulfur content ≤ 15 ppm (NSPS subp. IIII; NESHAP Subp. ZZZZ)








EQUI 192 Plant Site WWTS Back‐up Generator

PM ≤ 0.20 g/hp‐hr NMHC+NOx ≤ 6.4 g/hp‐hr CO ≤ 3.5 g/hp‐hr Sulfur content ≤ 15 ppm (NSPS subp. IIII; NESHAP Subp. ZZZZ)






EQUI 194 MSFMF Back Up Generator

PM ≤ 0.20 g/hp‐hr NMHC+NOx ≤ 6.4 g/hp‐hr CO ≤ 3.5 g/hp‐hr Sulfur content ≤ 15 ppm (NSPS subp. IIII; NESHAP Subp. ZZZZ)






EQUI 196 Generator to Move Electrical Equipment

Operating Hours ≤ 500 hours/year

(limit to avoid PSD)

Recordkeeping; Non‐resettable hour meter; Monthly Calculations

The Permittee is required to keep records of the operating hours through the use of a non‐resettable hour meter and perform monthly calculations of hours operated. These requirements are sufficient to have a reasonable assurance of compliance.






EQUI 628 AuPGM Concentrate Packaging


Performance testing


EQUI 629 WWTS Calcite Handling

Process Throughput ≤ 20 tons per day. (limit to avoid PSD; NAAQS modeling)

Recordkeeping: daily monitoring

The permit requires daily material throughput monitoring to show that the material usage does not exceed the operational limit.



EQUI 630 WWTS Degasifier




No applicable limit (NESHAP subp. CCCCCC)

Recordkeeping of practices

There are no applicable limits required by the NESHAP, only best management practices. The Permittee is required to keep records of malfunctions and actions taken during malfunctions to minimize emissions.




No applicable limit (NESHAP subp. CCCCCC)

Recordkeeping of practices

There are no applicable limits required by the NESHAP, only best management practices. The Permittee is required to keep records of malfunctions and actions taken during malfunctions to minimize emissions.



EQUI 633 Frother (MIBC) Tank





EQUI 634 Frother (DF 250) Tank









EQUI 637 Sulfuric Acid Tank

Process Throughput ≤ 16.1 tons per hour of liquid SO2 and less than one fill per hour. Process Throughput ≤ 193.1 tons per year of liquid SO2. (NAAQS modeling)



















EQUI 642 Caustic Tank










EQUI 645 Pebble Crusher


















EQUI 649 WWTP Lime Silo







EQUI 650 WWTS Lime Transfer to Mix Tank





Visible emissions checks

For these units, based on EPA published emissions factors, it is highly unlikely that they could violate the applicable requirement. The permit also contains requirements to conduct daily visual emissions checks on this source. These requirements are sufficient to have a reasonable assurance of compliance.

EQUI 651 WWTS Other Dry Material Handling

Process Throughput ≤ 400 pounds per day (limit to avoid PSD; NAAQS modeling)






Visible emissions checks

For these units, based on EPA published emissions factors, it is highly unlikely that they could violate the applicable requirement. The permit also contains requirements to conduct daily visual emissions checks on this source. These requirements are sufficient to have a reasonable assurance of compliance.

FUGI 1 Unpaved Roads, Dunka Rd.

"Light‐ and Medium‐Duty Vehicle" VMT ≤ 367 miles/day (calendar month average) (NAAQS Modeling)


The permittee is required to monitor and record the monthly vehicle miles traveled (VMTs) for each type of vehicle and perform monthly calculations of total VMTs to show that the VMTs do not exceed the operational limit. These requirements are sufficient to have a reasonable assurance of compliance.

Opacity ≤ 20% (Minn. R. 7011.0110)

Fugitive emission control plan; Daily visible emission checks

The Permittee is required to maintain and comply with a fugitive emission control plan to prevent the discharge of visible fugitive emissions from becoming airborne. In addition to procedures identified in the fugitive emission control plan, daily visible emission checks provide a reasonable assurance of compliance.

FUGI 2 Mine Site Fueling Facility Circle

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 4 Limestone Stacker Conveyor to Stockpile

Process Throughput ≤ 3125 tons per day Process Throughput ≤ 281,250 tons per year (NAAQS modeling)



Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 5 Tailings Basin Construction

“Tailings Haul Truck” VMT ≤ 9427 miles/day (NAAQS Modeling)


The permittee is required to monitor and record the daily vehicle miles traveled (VMTs) for each type of vehicle to show that the VMTs do not exceed the operational limit. These requirements are sufficient to have a reasonable assurance of compliance.



Operating Hours ≤ 12 hours/day, 6:00am‐6:00pm, only during each calendar day of the months of April ‐ October. (NAAQS Modeling)


The permittee is required to monitor and record the daily startup and shutdown time and the number of hours operated for this source to show that the hours operated does not exceed the operational limit. These requirements are sufficient to have a reasonable assurance of compliance.

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 6 Tailings Basin Bentonite Handling

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 7 Tailings Basin Bentonite Hauling

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 8 Tailings Basin – Light Trucks

“Light‐Duty” VMT ≤ 1516 miles/day (calendar month average) (NAAQS Modeling)



Opacity ≤ 20% (Minn. R. 7011.0110)





FUGI 9 Tailings Basin Wind Erosion

Opacity ≤ 20% (Minn. R. 7011.0110)


The Permittee is required to maintain and comply with a fugitive emission control plan to prevent the discharge of visible fugitive emissions from becoming airborne. Fugitive emission control activities such as mulching, seeding, tailings basin surveys, and reports of deposition areas and reduction efforts are required to be kept by the Permittee. In addition to procedures identified in the fugitive emission control plan and required recordkeeping, daily visible emission checks provide a reasonable assurance of compliance.

FUGI 10 Mine Site Surface Overburden, Truck Load

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 11 Mine Site Surface Overburden, Truck Unload – reclaim area

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 12 Mine Site Surface Overburden, Truck Unload – stockpile/storage pile/East Pit

Opacity ≤ 20% (Minn. R. 7011.0110)



Operating Hours ≤ 12 hours/day, 6:00am‐6:00pm, only during each calendar day of the months of November ‐ April. There is no restriction on hours of operation during the May ‐ October. (NAAQS Modeling)





FUGI 13 Mine Site Surface Overburden, Truck Reload

Opacity ≤ 20% (Minn. R. 7011.0110)






FUGI 14 Mine Site Waste Rock Truck Load

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 15 Mine Site Waste Rock Truck Unload

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 16 Mine Site Ore, Truck Load

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 17 Mine Site Ore, Truck Unload ‐ Rail Transfer Hopper

Opacity ≤ 20% (Minn. R. 7011.0110)





FUGI 18 Mine Site Ore, Railcar Load

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 19 Mine Site Ore Load/Unload – Surge Pile

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 20 Mine Site Stockpile Reclaim Truck Load

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 21 Mine Site Stockpile Reclaim Truck Unload

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 22 Mine Site Surface Overburden, Screen #1

Process Throughput ≤ 12000 tons/day of surface overburden screened Process Throughput ≤ 1,000,000 tons/yr of of surface overburden screened (Limits to avoid PSD; NAAQS Modeling)








Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 23 Mine Site Surface Overburden, Screen #1 Discharge







Opacity ≤ 20% (Minn. R. 7011.0110)





FUGI 24 Mine Site Portable Crushing Plant ‐ Crusher 1



The Permittee is required to operate and maintain a wet suppression system any time the emission unit is in operation and conduct performance testing to measure opacity as specified in the NSPS requirements. Monthly inspections are required to check proper water flow. The Permittee is also required to maintain and comply with a fugitive emission control plan to prevent the discharge of visible fugitive emissions from becoming airborne. In addition to procedures identified in the fugitive emission control plan, daily visible emission checks provide a reasonable assurance of compliance. See COMG 2 for visible emission check requirements.

FUGI 25 Mine Site Blast Hole Drilling

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 26 Mine Haul Roads

Effective until “Mine Year 11 Transition” date: "Mine Site Haul Truck" VMT ≤ 2746 miles/day (NAAQS Modeling)


The permittee is required to monitor and record the daily vehicle miles traveled (VMTs) for each type of vehicle to show that the VMTs do not exceed the operational limit. In addition, the Permittee is required to notify the MPCA of the date of the “Mine Year 11 Transition” that signal the change in applicable requirements. These requirements are sufficient to have a reasonable assurance of compliance.

Effective until “Mine Year 11 Transition” date: "Mine Site Haul Truck" VMT ≤ 2735 miles/day (NAAQS Modeling)


The permittee is required to monitor and record the daily vehicle miles traveled (VMTs) for each type of vehicle to show that the VMTs do not exceed the operational limit. In addition, the Permittee is required to notify the MPCA of the date of the “Mine Year 11 Transition” that signal the change in applicable requirements. These requirements are sufficient to have a reasonable assurance of compliance.

"Light‐ and Medium‐Duty Vehicle" VMT ≤ 367 miles/day (calendar month average) (NAAQS Modeling)





Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 27 Mine Site Cat 1 Stockpile Wind Erosion

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 28 Mine Site Cat 2/3 Waste Rock Stockpile Wind Erosion

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 29 Mine Site Cat 4 Waste Rock Stockpile Wind Erosion

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 30 Mine Site Ore Surge Pile Wind Erosion

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 31 Mine Site Overburden Storage Pile Wind Erosion

Opacity ≤ 20% (Minn. R. 7011.0110)





FUGI 32 Mine Site Portable Crushing Plant ‐ non‐NSPS ‐ Truck Load 1

Opacity ≤ 20% (Minn. R. 7011.0110)


The Permittee is required to maintain and comply with a fugitive emission control plan to prevent the discharge of visible fugitive emissions from becoming airborne. In addition to procedures identified in the fugitive emission control plan, daily visible emission checks provide a reasonable assurance of compliance. See COMG 2 for visible emission check requirements.








Opacity ≤ 20% (Minn. R. 7011.0110)












Opacity ≤ 20% (Minn. R. 7011.0110)










Opacity ≤ 20% (Minn. R. 7011.0110)












Opacity ≤ 20% (Minn. R. 7011.0110)

















FUGI 40 Mine Site Portable Crushing Plant ‐ Screen 1






FUGI 44 Mine Site Portable Crushing Plant ‐ Transfer Point 1






















FUGI 49 Mine Site Portable Crushing Plant ‐ Non‐NSPS ‐ Transfer to Stockpile 1

Opacity ≤ 20% (Minn. R. 7011.0110)













FUGI 55 Mine Site Portable Crushing Plant ‐ Non‐NSPS ‐ Transfer to Stockpile 2

Opacity ≤ 20% (Minn. R. 7011.0110)



FUGI 56 Mine Site Portable Crushing Plant ‐ Non‐NSPS ‐ Truck Load 2

Opacity ≤ 20% (Minn. R. 7011.0110)



STRU 3 North 60 Distribution Box & 36" Crushers Stack









STRU 4 South 60 Distribution Box & 36" Crushers Stack







STRU 5 North 36" Pan Feeders to Conveyor 1A Stack







STRU 6 North 36" Pan Feeders to Conveyor 1B Stack







STRU 7 South 36" Pan Feeders to Conveyor 1A Stack









STRU 8 South 36" Pan Feeders to Conveyor 1B & South Pan Feeder Stack







STRU 9 North Pan Feeder Stack







STRU 14 East Fine Crushing (1) Stack







STRU 15 West Fine Crushing (1‐2) & Transfer Points Stack









STRU 19 Conveyor Transfer Chute & Fine Ore Feeders North 1‐2 Stack






























STRU 35 Autoclave Scrubber Stack

PM ≤ 8.66 lb/hr PM10 ≤ 8.66 lb/hr PM2.5 ≤ 8.66 lb/hr SAM ≤ 0.984 lb/hr (limit to avoid PSD)


The Permittee is required to conduct performance testing for PM, PM10, PM2.5, and sulfuric acid mist emissions and operate and maintain the control equipment any time the emission unit is in operation. These requirements are sufficient to have a reasonable assurance of compliance.

HCl ≤ 0.116 lb/hr Nickel ≤ 1.00 lb/hr (limit to avoid major NESHAP)


The Permittee is required to conduct performance testing for nickel (as a surrogate for all metal HAPs) and hydrochloric acid emissions and operate and maintain the control equipment any time the emission unit is in operation. These requirements are sufficient to have a reasonable assurance of compliance.

PM10 ≤ 8.66 lb/hr PM2.5 ≤ 8.66 lb/hr SO2 ≤ 0.236 lb/hr (NAAQS modeling)


The Permittee is required to conduct performance testing for PM10, PM2.5, and SO2 emissions and operate and maintain the control equipment any time the emission unit is in operation. These requirements are sufficient to have a reasonable assurance of compliance.

Hydrogen Sulfide (H2S) ≤ 0.366 lb/hr


The Permittee is required to conduct performance testing for H2S emissions and operate and maintain the control equipment any time the emission unit is in operation. These requirements are sufficient to have a reasonable assurance of compliance. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.

Mercury ≤ 4.10 lb/hr Performance testing; Control equipment O&M; Monthly calculations

The Permittee is required to conduct performance testing for mercury emissions and operate and maintain the control equipment any time the emission unit is in operation. In addition, the Permittee is required to perform monthly calculation to show that the emission limit has not been exceeded. These requirements are sufficient to have a reasonable assurance of compliance.

STRU 37 Plant Scrubber Stack

PM ≤ 0.139 lb/hr PM10 ≤ 0.139 lb/hr PM2.5 ≤ 0.139 lb/hr SAM ≤ 0.139 lb/hr (limit to avoid PSD)


The Permittee is required to conduct performance testing for PM, PM10, PM2.5, and sulfuric acid mist emissions and operate and maintain the control equipment any time the emission unit is in operation. These requirements are sufficient to have a reasonable assurance of compliance.



PM10 ≤ 0.139 lb/hr PM2.5 ≤ 0.139 lb/hr SO2 ≤ 0.439 lb/hr (NAAQS modeling)


The Permittee is required to conduct performance testing for PM10, PM2.5, and SO2 emissions and operate and maintain the control equipment any time the emission unit is in operation. These requirements are sufficient to have a reasonable assurance of compliance.

Hydrogen Sulfide (H2S) ≤ 0.0630 lb/hr


The Permittee is required to conduct performance testing for H2S emissions and operate and maintain the control equipment any time the emission unit is in operation. These requirements are sufficient to have a reasonable assurance of compliance. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.

STRU 43 Limestone Unloading Baghouse Stack

PM ≤ 1.03 lb/hr PM10 ≤ 1.03 lb/hr PM2.5 ≤ 1.03 lb/hr PM2.5 ≤ 0.0189 lb/hr (24‐hour average) (limit to avoid PSD)



PM10 ≤ 1.03 lb/hr PM2.5 ≤ 1.03 lb/hr PM2.5 ≤ 0.0189 lb/hr (24‐hour average) (NAAQS modeling)



STRU 107 Pebble Crusher Stack










PM/PM10/PM2.5 control efficiency of 99%/99%/99% Pressure drop: 1.0 ≤ ΔP ≤ 10.0 inches (limit to avoid PSD)

Control equipment O&M; Bag leak detectors; Daily pressure drop recordkeeping

The Permittee is required to operate and maintain the control equipment any time the emission unit is in operation, monitor and record the pressure drop across the fabric filter, and operate and maintain a bag leak detector at all times the fabric filter is in operation. These requirements are sufficient to have a reasonable assurance of compliance.

Metal HAPs control efficiency of 99% Pressure drop: 1.0 ≤ ΔP ≤ 10.0 inches (limit to avoid major NESHAP)










TREA 3 Fabric Filter ‐ Cartridge Filter ‐ North 36" Crushers







TREA 4 Fabric Filter ‐ Cartridge Filter ‐ South 36" Crushers









TREA 5 Fabric Filter ‐ Cartridge Filter ‐ North 36" Conveyor Feed Chutes to Conveyor 1A







TREA 6 Fabric Filter ‐ Cartridge Filter ‐ North 36" Conveyor Feed Chutes to Conveyor 1B







TREA 7 Fabric Filter ‐ Cartridge Filter ‐ South 36" Conveyor Feed Chutes to Conveyor 1A









TREA 8 Fabric Filter ‐ Cartridge Filter ‐ South 36" Conveyor Feed Chutes to Conveyor 1B







TREA 9 Fabric Filter ‐ Cartridge Filter ‐ South Pan Conveyors







TREA 10 Fabric Filter ‐ Cartridge Filter ‐ North Pan Conveyors







TREA 11 Fabric Filter ‐ Cartridge Filter ‐ Drive House 1 East Transfer









TREA 12 Fabric Filter ‐ Cartridge Filter ‐ Drive House 1 West Transfer







TREA 13 Fabric Filter ‐ Cartridge Filter ‐ Conveyor Transfer Chute







TREA 14 Fabric Filter ‐ Cartridge Filter ‐ 2A Tripper Car









TREA 15 Fabric Filter ‐ Cartridge Filter ‐ West Coarse Ore Bins







TREA 16 Fabric Filter ‐ Cartridge Filter ‐ Fine Crushing ‐ East 1























TREA 19 Fabric Filter ‐ Cartridge Filter ‐ North Transfer Point







TREA 20 Fabric Filter ‐ Cartridge Filter ‐ South Transfer Point







TREA 21 Fabric Filter ‐ Cartridge Filter ‐ 5N Tripper Car









TREA 22 Fabric Filter ‐ Cartridge Filter ‐ 5S Tripper Car












































TREA 35 Fabric Filter ‐ Cartridge Filter ‐ Conv. Trans. Collection Belt to SAG Feed Belt, Fine Ore Feeders North 1 & 2


























TREA 42 Fabric Filter ‐ Cartridge Filter ‐ Fine Ore Feeders North 21, 22, 23, & 24














Control equipment O&M; Visible emission checks; Daily pressure drop recordkeeping

The Permittee is required to operate and maintain the control equipment any time the emission unit is in operation, monitor and record the pressure drop across the fabric filter, and perform daily visible emission checks. These requirements are sufficient to have a reasonable assurance of compliance.











TREA 49 Fabric Filter ‐ TBD ‐ Railcar Loading ‐ Copper Concentrate









TREA 50 Fabric Filter ‐ TBD ‐ Railcar Loading ‐ Nickel Concentrate







TREA 51 Wet Scrubber ‐ Autoclave vent and Emergency Pressure Relief Vent, Flash Vessels

PM/PM10/PM2.5 control efficiency of 99.06%/99.06%/99.06% SAM control efficiency of 99% Pressure drop: 10.0 ≤ ΔP ≤ 70.0 inches Water flow rate ≥ 40.0 gallons per minute. (limit to avoid PSD)

Control equipment O&M; Daily pressure drop and water flow rate recordkeeping

The Permittee is required to operate and maintain the control equipment any time the emission unit is in operation, monitor and record the pressure drop across the wet scrubber, and monitor and record the water flow rate. These requirements are sufficient to have a reasonable assurance of compliance.

Metal HAPs control efficiency of 99.06% HCl control efficiency of 99% Pressure drop: 10.0 ≤ ΔP ≤ 70.0 inches Water flow rate ≥ 40.0 gallons per minute. (limit to avoid major NESHAP)



SO2 control efficiency of 90% Pressure drop: 10.0 ≤ ΔP ≤ 70.0 inches Water flow rate ≥ 40.0 gallons per minute. (NAAQS Modeling)





Hydrogen Sulfide (H2S) control efficiency of 70% (Minn. R. 7007.0800, subp. 2(B), Minn. R. 7007.0800, subp. 14, Minn. Stat. 116.07, subd. 4a(a))


The Permittee is required to operate and maintain the control equipment any time the emission unit is in operation, monitor and record the pressure drop across the wet scrubber, and monitor and record the water flow rate. These requirements are sufficient to have a reasonable assurance of compliance. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.

Mercury control efficiency of 25.75% (Minn. R. 7007.0502)



TREA 52 Wet Scrubber ‐ Autoclave vent and Emergency Pressure Relief Vent, Flash Vessels, Iron and Aluminum Precipitation Tanks

PM/PM10/PM2.5 control efficiency of 99.06%/99.06%/99.06% SAM control efficiency of 99% Pressure drop: 1.0 ≤ ΔP ≤ 10.0 inches Water flow rate ≥ 40.0 gallons per minute. Liquid pH: 5.0 ≤ pH ≤ 6.0 (limit to avoid PSD)

Control equipment O&M; Daily pressure drop, water flow rate, and pH recordkeeping

The Permittee is required to operate and maintain the control equipment any time the emission unit is in operation, monitor and record the pressure drop across the wet scrubber, monitor and record the water flow rate, and monitor and record the scrubber liquid pH. These requirements are sufficient to have a reasonable assurance of compliance.

Metal HAPs control efficiency of 99.06% HCl control efficiency of 99% Pressure drop: 1.0 ≤ ΔP ≤ 10.0 inches Water flow rate ≥ 40.0 gallons per minute Liquid pH: 5.0 ≤ pH ≤ 6.0 (limit to avoid major NESHAP)





SO2 control efficiency of 90% Pressure drop: 1.0 ≤ ΔP ≤ 10.0 inches Water flow rate ≥ 40.0 gallons per minute. Liquid pH: 5.0 ≤ pH ≤ 6.0 (NAAQS Modeling)





The Permittee is required to operate and maintain the control equipment any time the emission unit is in operation, monitor and record the pressure drop across the wet scrubber, monitor and record the water flow rate, and monitor and record the scrubber liquid pH. These requirements are sufficient to have a reasonable assurance of compliance. This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act.

Mercury control efficiency of 25.75% (Minn. R. 7007.0502)





TREA 53 Wet Scrubber ‐ AuPGM Precipitation Tanks, CuS Cementation Tank N2 Vent, MHP Stage 1 Tank Vent, NaHS Mix Tank/Storage Tank

PM/PM10/PM2.5 control efficiency of 99%/99%/99% SAM control efficiency of 99% Pressure drop: 1.0 ≤ ΔP ≤ 10.0 inches Water flow rate ≥ 40.0 gallons per minute. Liquid pH: 5.0 ≤ pH ≤ 6.0 (limit to avoid PSD)



SO2 control efficiency of 90% Pressure drop: 1.0 ≤ ΔP ≤ 10.0 inches Water flow rate ≥ 40.0 gallons per minute. Liquid pH: 5.0 ≤ pH ≤ 6.0 (NAAQS Modeling)






TREA 54 Fabric Filter ‐ TBD ‐ Flotation Flocculant Silo






TREA 55 Fabric Filter ‐ TBD ‐ Acid Flocculant Silo




TREA 56 Fabric Filter ‐ TBD ‐ Xanthate Collector Mix Tank (w/baghouse)




TREA 57 Wet Scrubber ‐ Lime Slaker (w/scrubber)

PM/PM10/PM2.5 control efficiency of 99%/99%/99% Pressure drop: 10.0 ≤ ΔP ≤ 70.0 inches Water flow rate ≥ 1.0 gallons per minute. (limit to avoid PSD)



TREA 58 Fabric Filter ‐ TBD ‐ Plant Lime Silo




TREA 59 Fabric Filter ‐ TBD ‐ Limestone Railcar Dump, Limestone Hopper to Conveyor




Operational requirements (NSPS Limit)

Control equipment O&M; Bag leak detectors; Inspections

The Permittee is required to maintain and operate a bag leak detection system to measure particulate matter loadings for the fabric filter. Monitoring includes developing an operation and maintenance plan and performing inspections as specified in the NSPS requirements to ensure the emission units controlled by the fabric filters meets the NSPS requirements. These requirements are sufficient to have a reasonable assurance of compliance.



TREA 60 Fabric Filter ‐ TBD ‐ Limestone Crusher




TREA 61 Fabric Filter ‐ TBD ‐ MSFMF Lime Silo




TREA 91 Fabric Filter ‐ Cartridge Filter ‐ Pebble Crusher







TREA 92 Fabric Filter ‐ TBD ‐ WWTS Lime Silo







*Location of the requirement in the permit (e.g., EQUI 1, STRU 2, etc.).

The language 'This is a state‐only requirement and is not enforceable by the U.S. Environmental Protection Agency (EPA) Administrator and citizens under the Clean Air Act' refers to permit requirements that are established only under state law and are not established under or required by the federal Clean Air Act. The language is to clarify the distinction between permit conditions that are required by federal law and those that are required only under state law. State law‐only requirements are not enforceable by the EPA or by


citizens under the federal Clean Air Act, but are fully enforceable by the MPCA and citizens under provisions of state law.

3.11 Insignificant Activities Poly Met Mining, Inc. has several operations, which are classified as insignificant activities under the MPCA’s permitting rules. These are listed in Appendix A to the permit. The permit is required to include periodic monitoring for all emissions units, including insignificant activities, per EPA guidance. The insignificant activities at this Facility are only subject to general applicable requirements. Using the criteria outlined earlier in this TSD, the following table documents the justification why no additional periodic monitoring is necessary for the current insignificant activities.

Table 16. Insignificant Activities

Insignificant activity

General applicable emission limit Discussion

Emissions from a laboratory, as defined in Minn. R. 7007.1300, subp. 3(G)

PM, variable depending on airflow Opacity ≤ 20% (Minn. R. 7011. 0715)

PolyMet Mining, Inc. has and utilizes laboratories to conduct routine analysis of solids and liquids for metals, sulfur, and general chemistry parameters. These are very small, intermittent, bench‐top operations that typically do not even have any emissions. It is highly unlikely that they could violate the applicable requirement. [Minn. R. 7007.1300, subp. 3(G)]

Brazing, soldering or welding equipment


PolyMet Mining, Inc. has and operates welding equipment for maintenance and repair of process equipment and vehicles. For these units, based on EPA published emissions factors, it is highly unlikely that they could violate the applicable requirement. In addition, these units are typically operated and vented inside a building, so testing for PM or opacity is not feasible.

[Minn. R. 7007.1300, subp. 3(H)(3)]

Infrequent use of spray paint equipment for routine housekeeping or plant upkeep activities not associated with primary production processes at the stationary source


PolyMet Mining, Inc. uses spray paint equipment for plant upkeep.

While spray equipment will have the potential to emit particulate matter, these particular activities are those not associated with production, so they would be infrequent and usually occur outdoors. For these units, based on EPA published emissions factors, it is highly unlikely that they could violate the applicable requirement.

[Minn. R. 7007.1300, subp. 3(K)]

Equipment venting PM/PM10 inside a building, provided that emissions from the equipment are: a). filtered through an air cleaning system; and b). vented inside of the building 100% of the time


PolyMet Mining, Inc. has and operates wood and metal shops with dedicated ventilation to a dust collector that vents into the building.

For these units, based on EPA published emissions factors, it is highly unlikely that they could violate the applicable requirement. In addition, these units are typically operated and vented inside a building, so testing for PM or opacity is not feasible.

[Minn. R. 7008.4110]


3.12 Permit Organization

In general, the permit meets the MPCA Tempo Guidance for ordering and grouping of requirements as well as the use of appendices. One area that deviates from the guidance is in the use of groups where the requirements in the group apply to the members of the group individually. This was done in order to shorten the permit and where no testing or tracking specific to a unit is in the permit (thereby reducing the likelihood that there where will be further unit‐specific requirements later). In this permit, federal requirements from NESHAPs and NSPS are included in two different formats. The requirements for 40 CFR pt. 60, subps. Dc, LL, OOO, and IIII and 40 CFR pt. 63, subps. ZZZZ and CCCCCC are incorporated into the permit as individual permit requirements, which has historically been MPCA’s standard practice. However, the requirements for the associated General Provisions in 40 CFR pt. 60, subp. A and 40 CFR pt. 63, subp. A are included in a different way. For the applicable portions of the associated general provisions, a requirement in Section 5 of the permit lists the citations of all of the applicable parts of the standard along with a reference to the permit appendix where the full text of the standard is included. 40 CFR pt. 60, subp. A and 40 CFR pt. 63, subp. A are included in Appendices E and F, respectively.

3.13 Comments Received This section will be completed upon conclusion of the public notice and EPA review periods. Public Notice Period: [start date] ‐ [end date] Public Informational Meeting: February 7, 2018 (Aurora, Minnesota) Public Informational Meeting: February 8, 2018 (Duluth, Minnesota) EPA Review Period: [start date] ‐ [end date]

4. Permit Fee Assessment This permit action is the issuance of a first‐time individual Part 70 permit based on an application received on August 24, 2016. Therefore, application fees and additional point fees apply under Minn. R. 7002.0016 and 7002.0019. This action includes refined dispersion modeling to show compliance with the NAAQS. The MPCA charges an additional 15 points for refined modeling regardless of the number of pollutants modeled or the programs modeled for. The MPCA charges an additional 10 points for each federal standard incorporated into the permit. This permit action includes the incorporation of four NSPSs (40 CFR pt. 60, subps. Dc, LL, OOO, and IIII), one Part 61 NESHAP (40 CFR pt. 61, subp. M), and two Part 63 NESHAPs (40 CFR pt. 63, subps. ZZZZ and CCCCCC). The MPCA also charges additional points for limits that PolyMet assumed to avoid certain programs. The permit incorporates limits to avoid major source classification under PSD and part 63 NESHAP for an additional 10 points for each program. Finally, the MPCA assesses 15 additional points for conducting the AERA. Attachment 4 to this TSD contains the MPCA’s assessment of Application and Additional Points used to determine the permit application fee for this permit action as required by Minn. R. 7002.0019.


5. Conclusion Based on the information provided by PolyMet Mining, Inc. the MPCA has reasonable assurance that the proposed operation of the emission facility, as described in the Air Emission Permit No. 13700345‐101 and this TSD, will not cause or contribute to a violation of applicable federal regulations and Minnesota Rules. Staff members on permit team: Hassan Bouchareb (permit engineer) Sarah Seelen (peer reviewer) Leslie Frederickson (legal review)

Steven Palzkill (enforcement) Andy Place (compliance) Marc Severin (compliance) Lisa Fay (environmental review) Jim Sullivan (air modeling) Kristie Ellickson (AERA modeling) Joe Handtmann (permit writing assistant) Beckie Olson (permit writing assistant) Laurie O’Brien (administrative support)

TEMPO360 Activities: Part 70 Permit (IND20160002) Attachments: 1. PTE Summary Calculation Spreadsheets

2. Subject Item Inventory 3. Facility Requirements Report 4. Points Calculator 5. PolyMet Process Flow Diagram 6. MPCA Fugitive Emissions Memo 7. Class II Modeling Report 8. Class II Ambient Air Boundary Control Plan 9. Class I Modeling Report 10. AERA Modeling Report 11. Special Purpose Monitoring Plan 12. Ambient Fiber Monitoring Plan

for draft air emission permit no. 13700345 101

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