Document x57dBoyX09BKqj7eRV5QjoDQQ

letter responds to EPA's invitation. EPA also announced on its wcbsite the availability of exemptions and directed requests for exemption be submitted by March 3 1.111 Accordingly, Otter Tail and the Co-owners are seeking a two-year exemption from the MATS RTR standards at Big Stone, due to technological unavailability related to PM CEMS requirements and the time and cost necessary to meet the requirements. Section III explains that the technology required to meet the Rule's that PM standard is not available because of the infeasibility of CF,MS as the compliance measure. Section IV finds that it is in the national security interest to issue an exemption from compliance with the MATS RTR for Big Stone. III. PM CELAIS Are Not Technologically Able to Assure Compliance with the Revised PM Standard The MATS RTR requires the installation of PM CEMS to demonstrate compliance with the revised 0.010 lb/MMBtu PM standard. Big Stone has easily achieved I.F.F. status under the current MATS rule and currently complies with MATS using periodic PM stack testing. PM CEMS are not installed on its unit. For the reasons identified below, CEMS arc not a technology that is available due to inaccuracies and correlation challenges at low PM levels. The accuracy of PM CEMS at low PM omissions levels is not proven. PM CEMS do not directly measure PM emissions. In other words, the instrument (foes not measure the mass of PM and the volume of flue gas from which that mass of PM was sampled. Instead, commercially available PM CEMS measure some property (i.o., light scatter or beta attenuation) that must be correlated to actual stack PM measurements. [I At lower emissions levels, PM CEMS have not been demonstrated to have the sensitivity needed to accurately account for lower emissions levels. Technological feasibility has not been proven at low PM emissions levels.'' Duo to the indirect measurements, PM CEMS correlation testing must ensure the measurements are true to the actual PM emission rates. '3 PS-1 1 correlation testing requires PM spiking to create a correlation curve. EPA requires that PM CEMS undergo the certification testing outlined in Performance Specification 11 - Specifications and Test Procedures for Particulate Matter Continuous Emissions Monitoring Systems at Stationary Sources.14 This procedure requires sources to test emissions at three levels to create a correlation curve: (1) 0 to 50% of the maximum particulate matter concentration, (2) 25 to 75% of the maximum particulate matter concentration, and (3) 50 to 100% of the maximum particulate matter concentration. If sources cannot vary PM omissions through process operations or by varying 11' https: cpa. ,ovStationai-v-sourcos-air-pollution 'clean-air-act-section-112-presidential-exemption- information. -1Fhe EPA statement at 88 Fcd. Rcg. at 24872, that a beta gauge "detector measures the amount of radiation emitted by the sample" is catcgorically incorrect and illustrative of several uninformcd statements (c.g., cost cstimatcs) about P\1 CEMS in the preamble to the proposed rulc. I ' See Con/mews EPA 's I'mposed Ride. NESIIAP Coal- and red Ideuiriu 1-1 iy learn General g Umis Revielt r,J fl+r Residual Risk and li ,uhnoIogy Review, Docket No EPA-I IQ-OAR-2018-0794-5994, at 22 (Junc 28, 2023) (PCiEN Comments) (citing and attaching Ralph I. Roberson, Weal Coninienis r)n EPA 's !'..,posed Ride fercury and A ir Sirmriarris Risk and li,uhnologr Review, at 3 (2023) (PM CEMS Technical \lerno)) '3 Id https:, www cpa.gov'sitcsidefaultitilcs12019-06,doeumentsiricrformanec sriccitication 11.ridf 4 Sierra Club FOIA 2025-EPA-04883 ED_018388_00000190-00004 SC_EVERSPLIT0005959