Document GkJggk6azzMdyOK6yv1Ez7VN

The particulate matter continuous emissions monitors (PM CEMS) required by the Rule at Big Stone arc not reliable at Big Stone's low levels of PM. The lack of reliable monitoring causes the technology to implement the standard to be unavailable on or after the compliance date. Aside from accuracy, it is highly uncertain whether CEMS can be installed and correlated by the compliance deadline. Big Stone has achieved low emitting ECili (LEE) status under the current MATS Rule, and the plant currently uses periodic stack testing as its compliance measure. In addition, granting the exemption would avoid PM CEMS installation costs to the tune of 5400,000, if EPA were to reconsider the MATS RTR and provide relief from the PM CEMS monitoring requirements. Background A. About Big Stone Otter Tail co-owns the Big Stone Plant, an approximate 475 MW coal-fired electrical generating unit (EGU) located near Big Stone City, South Dakota. Big Stone has one unit that combusts subbituminous coal, which has been providing reliable, economical, and environmentally responsible power since 1975. Big Stone generates electricity to support the Midcontinent Independent System Operator (MISO) and the Southwest Power Pool (SPP) portions of our national electrical grid. The station is equipped with efficient and cost-effective environmental controls, including a state-of-the-art fabric filter baghouse for PM control installed in 2016. Big Stone is subject to the MATS RTR requirements. B. MATS RTR and Presidential Exemption Section 112(i)(4) 1. The NIATS RTR EPA promulgated MATS under CAA Section 112 which regulates hazardous air pollutant (I IAP) emissions. Congress defines EPA's scope of review for the RTR under the CAA in Sections 112(d)(6) and 112(f)(2). CAA Section 112(d)(6) defines the technology review for air toxics standards such as MATS as follows: The Administrator shall review, and revise as necessary (taking into account developments in practices, processes, and control technologies), emission standards promulgated under this section no less often than every 8 years.' EPA originally finalized the RTR for MATS on May 22, 2020 (the 2020 MATS RTR).' In that rulemaking, EPA determined that the residual risks from coal-fired and oil-tired EGUs were acceptable and did not identify any new technologies to control I IAPs for these units. EPA finalized the RTR without any changes to emissions standards or work practices. When President Biden took office, he directed EPA to reconsider the 2020 MATS RTR. On May 7, 2024, EPA published the final MATS RTR. The MATS RTR lowers the PM emission standard from 0.030 lb/MMI3tu to 0.010 lb/MMBtu. The Rule also tightens the ' 42 U S.C. 7412(d)(6) 6 85 Fcd Rcg 31286 (May 22, 2020) 2 Sierra Club FOIA 2025-EPA-04883 ED_018388_00000190- 00002 SC_EVERSPLIT0005957