PURPOSE: This rule establishes requirements for emission units emitting sulfur dioxide (SO2). These requirements maintain existing SO2 regulatory requirements previously found in 10 CSR 10-6.260 that were in place prior to the establishment of the June 22, 2010, one (1)-hour SO2 National Ambient Air Quality Standards (NAAQS). The rule consolidates, streamlines, and updates existing regulatory requirements in accordance with 536.175, RSMo.

PUBLISHER’S NOTE: The secretary of state has determined that publication of the entire text of the material that is incorporated by reference as a portion of this rule would be unduly cumbersome or expensive. This material as incorporated by reference in this rule shall be maintained by the agency at its headquarters and shall be made available to the public for inspection and copying at no more than the actual cost of reproduction. This note applies only to the reference material. The entire text of the rule is printed here.

1. (1) Applicability. This rule applies to owners and operators of indirect heating sources that emit sulfur dioxide (SO2) and have a total capacity greater than three hundred fifty thousand British thermal units (350,000 Btus) per hour actual heat input. The following exceptions apply to any source not listed in Table I of this rule. Upon request of the director, owners or operators must furnish the director information to confirm that an exception criterion is met:

   1. (A) Individual units fueled exclusively with natural gas (as defined in 40 CFR 72.2), liquefied petroleum gas as defined by American Society for Testing and Materials (ASTM) International, ultra-low sulfur distillate fuel oil with a maximum fuel sulfur content of fifteen (15) ppm, or any combination of these fuels, and this exception is determined by complying with the recordkeeping requirements in subsection (4)(C) of this rule;
   2. (B) Individual indirect heating units with a rated capacity less than or equal to three hundred fifty thousand British thermal units (350,000 Btus) per hour actual heat input; or

   3. (C) Individual units subject to a more restrictive SO2 emission limit or more restrictive fuel sulfur content limit under—

      1. 1. 10 CSR 10-6.070; or
      2. 2. Missouri’s federally approved state implementation

plan.

1. (2) Definitions.

   1. (A) Indirect heating source—A source operation in which fuel is burned for the primary purpose of producing steam, hot water, or hot air, or other indirect heating of liquids, gases, or solids where, in the course of doing so, the products of combustion do not come into direct contact with process materials.
   2. (B) Stationary source—Any building, structure, facility, or installation which emits or may emit any air pollutant subject to regulation under the Clean Air Act. Building, structure, facility, or installation includes all pollutant emitting activities that are located on one (1) or more contiguous or adjacent properties and are under common control of the same person(s).
   3. (C) Definitions of certain terms specified in this rule, other than those defined in section (2) of this rule, may be found in 10 CSR 10-6.020.

2. (3) General Provisions.

   1. (A) SO2 Emission Limits. Owners or operators of sources and/or units listed in Table I of this rule must limit their SO2 emissions as specified. Table I—Sources subject to SO2 emission limits

      Emission Limit per Source (Pounds SO2 per Million

      Source Btus Actual Averaging

      Source ID Heat Input)a Time

   New Madrid Power Plant – Marston 1430004 10.0 3 hours Thomas Hill Energy Center Power Division – Thomas Hill 1750001 8.0 3 hours University of Missouri (MU) – Columbia Power Plant 0190004 8.0 3 hours Doe Run Company – Buick Resource 1-hour test Recycling 8,650 pounds repeated 3 Facility 0930009 times SO2 /hr Ameren Missouri – Labadie Energy Daily average, Centerb 0710003 4.8 00:01 to 24:00 0.12 Evergy Inc. excluding – Hawthorn periods of Generating startup and 30-day rolling Stationc 0950022 shutdownd average

   a Applies to indirect heating units only and applies to such units individually. b Applies to Boilers 1, 2, 3, and 4 only and individually. c Applies to Boiler 5A only. d Natural gas shall be used for startup of Hawthorn Boiler 5A. During startup, once the unit converts to firing coal, the dry scrubber shall be started appropriately to comply with relevant standard applicable during normal operation. During shutdown, the dry scrubber shall be operated after cessation of coal being fed in the unit for as long as possible thereafter considering operational and safety concerns.

   1. (B) Owners or operators of indirect heating sources with a total capacity, excluding exempt units, greater than three hundred fifty thousand British thermal units (350,000 Btus) per hour actual heat input must limit their SO2 emissions as follows:

      1. 1. For sources located in Missouri, other than in Franklin,

Jefferson, St. Louis, St. Charles Counties, or City of St. Louis, no more than eight pounds (8 lbs.) of SO2 per million Btus actual heat input averaged on any consecutive three- (3-) hour time period unless that source is listed in Table I of this rule; and

1. 2. For sources located in Franklin, Jefferson, St. Louis, St.

Charles Counties, or City of St. Louis, no more than two and three-tenths pounds (2.3 lbs.) of SO2 per million Btus actual heat input averaged on any consecutive three- (3-) hour time period unless—

1. A. The source is listed in Table I of this rule; or
2. B. The source has a total rated capacity of less than two

thousand (2,000) million Btus per hour and then the following restrictions apply.

1. (I) During the months of October, November,

December, January, February, and March of every year, no person shall burn or permit the burning of any coal containing more than two percent (2%) sulfur or of any fuel oil containing more than two percent (2%) sulfur. Otherwise, no person shall burn or permit the burning of any coal or fuel oil containing more than four percent (4%) sulfur.

1. (II) Part (3)(B)2.B.(I) of this rule does not apply to any

source if it can be shown that emissions of SO2 from the source into the atmosphere will not exceed two and three-tenths pounds (2.3 lbs.) per million Btus actual heat input to the source.

1. (C) Compliance Determination. Compliance must be determined as follows:

   1. 1. For sources and/or units listed in Table I of this rule

already subject to an SO2 Continuous Emission Monitoring System (CEMS) requirement, SO2 CEMS data—

1. A. SO2 CEMS are not required for the following cases:

   1. (I) Units fueled exclusively by natural gas and not

using any secondary fuel; or

1. (II) Units fueled by natural gas and only using fuel

oil for less than forty-eight (48) hours annually and only for qualifying situations (e.g., testing, maintenance, or operator training). The forty-eight- (48-) hour annual limit for the use of fuel oil as a secondary fuel does not include qualifying curtailment events and compliance must be demonstrated using paragraph (3)(C)2. of this rule; and

1. B. SO2 CEMS must follow the requirements in subsection

(5)(C) of this rule; and

1. 2. For sources subject to subsection (3)(B) of this rule and

for sources listed in Table I of this rule not required to use SO2 CEMS for compliance—

1. A. Fuel delivery records;
2. B. Fuel sampling and analysis;
3. C. Performance tests;
4. D. Continuous emission monitoring; or
5. E. Other compliance methods approved by the staff

director and the U.S. Environmental Protection Agency and incorporated into the state implementation plan.

1. (4) Reporting and Recordkeeping.

   1. (A) Owners or operators of all sources subject to any requirements in section (3) of this rule must—

      1. 1. Report any excess emissions other than startup,

shutdown, and malfunction excess emissions already required to be reported under 10 CSR 10-6.050 to the staff director for each calendar quarter within thirty (30) days following the end of the quarter. In all cases, the notification must be a written report and include, at a minimum, the following:

1. A. Name and location of source;
2. B. Name and telephone number of person responsible

for the source;

1. C. Identity and description of the equipment involved;
2. D. Time and duration of the period of SO2 excess

emissions;

1. E. Type of activity;
2. F. Estimate of the magnitude of the SO2 excess emissions

expressed in the units of the applicable emission control regulation and the operating data and calculations used in estimating the magnitude;

1. G. Measures taken to mitigate the extent and duration of

the SO2 excess emissions; and

1. H. Measures taken to remedy the situation which caused

the SO2 excess emissions and the measures taken or planned to prevent the recurrence of these situations;

1. 2. Maintain a record of any applicable data, calculations,

results, records, and reports from any SO2 emissions performance test, SO2 continuous emission monitoring, fuel deliveries, and/or fuel sampling tests that are necessary to determine compliance with the requirements of this rule; and

1. 3. Maintain a record of any applicable SO2 monitoring

data, performance evaluations, calibration checks, monitoring system and device performance tests, and any adjustments and maintenance performed on these systems or devices.

1. (B) Owners or operators of sources using fuel delivery records for compliance must also maintain the fuel supplier certification information to certify all fuel deliveries. Bills of lading and/or other fuel delivery documentation containing the following information for all fuel purchases or deliveries are deemed acceptable to comply with the requirements of this rule:

   1. 1. The name, address, and contact information of the fuel

supplier;

1. 2. The type of fuel (bituminous or sub-bituminous coal,

diesel, #2 fuel oil, etc.);

1. 3. The moisture content of the coal (if applicable);
2. 4. The sulfur content or maximum sulfur content expressed

in percent sulfur by weight or in ppm sulfur; and

1. 5. The heating value of the fuel.
2. (C) Owners or operators of sources meeting an exemption listed in subsection (1)(A) of this rule must maintain documentation of all fuels combusted in the unit(s) exempted by subsection (1)(A) and documentation demonstrating these fuels meet the exemption criteria in subsection (1)(A). Documentation demonstrating the fuels meet the exemption criteria can include but is not limited to fuel contracts that specify the maximum allowable sulfur content of all fuels combusted in the exempt unit(s).
3. (D) All required reports and records must be retained on-site for a minimum of five (5) years and made available within five

1. (5) business days upon written or electronic request by the director.

   1. (E) Owners or operators of sources subject to this rule must furnish the director all data necessary to determine compliance status.

2. (5) Test Methods.

   1. (A) Owners or operators of sources using performance tests to demonstrate compliance with this rule must use one (1) or more of the following 40 CFR 60 test methods as specified in 10 CSR 10-6.030(22):

      1. 1. Method 1: Sample and velocity traverses for stationary

sources;

1. 2. Method 2: Determination of stack gas velocity and

volumetric flow rate (Type S pitot tube);

1. 3. Method 3: Gas analysis for the determination of dry

molecular weight;

1. 4. Method 4: Determination of moisture content in stack

gases;

1. 5. Method 6: Determination of Sulfur Dioxide Emissions

from Stationary Sources;

1. 6. Method 6A: Determination of Sulfur Dioxide, Moisture,

and Carbon Dioxide from Fuel Combustion Sources;

1. 7. Method 6B: Determination of Sulfur Dioxide and Carbon

Dioxide Daily Average Emissions from Fossil Fuel Combustion Sources;

1. 8. Method 6C: Determination of Sulfur Dioxide Emissions

from Stationary Sources (Instrumental Analyzer Procedure); and

1. 9. Method 8: Determination of sulfuric acid mist and sulfur

dioxide emissions from stationary sources.

1. (B) For owners or operators of sources using performance tests to demonstrate compliance with this rule, the heating value of the fuel must be determined as specified in 10 CSR 10-6.040. The actual heat input must be determined by multiplying the heating value of the fuel by the amount of fuel burned during the source test period.

2. (C) Owners or operators of sources using SO2 CEMS for demonstrating compliance with this rule must—

   1. 1. If SO2 CEMS is already used to satisfy other requirements

(other than only to demonstrate compliance with this rule), continue to follow all correlating SO2 CEMS requirements; or

1. 2. If SO2 CEMS is used only to demonstrate compliance with

this rule, the SO2 CEMS and any necessary auxiliary monitoring equipment must follow the requirements in 40 CFR 75 and/or 40 CFR 60, Appendices B and F. 40 CFR 75 promulgated as of June 30, 2018, hereby incorporated by reference in this rule, as published by the Office of the Federal Register. Copies can be obtained from the U.S. Publishing Office Bookstore, 710 N. Capitol Street NW, Washington, DC 20401. This rule does not incorporate any subsequent amendments or additions. 40 CFR 60, Appendices B and F are as specified in 10 CSR 10-6.030(22).

1. (D) Owners or operators of secondary lead smelters must operate an SO2 CEMS as follows:

   1. 1. The SO2 CEMS must be certified by the owner or operator

in accordance with 40 CFR 60 Appendix B, Performance Specification 2 and Section 60.13 as specified in 10 CSR 10- 6.030(22) as is pertinent to SO2 continuous emission monitors as adopted by reference in 10 CSR 10-6.070; and

1. 2. The span of SO2 continuous emission monitors must

be set at an SO2 concentration of one-fifth percent (0.20%) by volume.

1. (E) Owners or operators of sources using fuel sampling to demonstrate compliance with this rule must use fuel sampling and analysis to determine sulfur weight percent, or equivalent, of fuel(s) used to operate fuel emission sources and/or units regulated by this rule in accordance with 10 CSR 10-6.040.
2. (F) Owners or operators of sources may use an alternative test method that provides results at least the same accuracy and precision as the replaced method, and is approved in advance by the staff director, the EPA, and incorporated into the state implementation plan.

AUTHORITY: section 643.050, RSMo Supp. 2024.* Original rule filed April 10, 2015, effective Nov. 30, 2015. Amended: Filed June 21, 2018, effective March 30, 2019. Amended: Filed Sept. 20, 2024, effective May 30, 2025. *Original authority: 643.050, RSMo 1965, amended 1972, 1992, 1993, 1995, 2011, 2022.