Document e7JnNDx6eqxbndXBD5p7NkaVp

This means that the valid correlations currently established for the Unit 1 and Unit 2 PM CEMS would no longer be acceptable with the lower emissions limit, and new PM GEMS correlations would have to be developed meeting the more restrictive requirements. In public comments on the proposed MATS rule amendment, many commenters questioned the feasibility of obtaining valid PM correlations following PS-11 under the proposed lower PM emissions standard. EPA's response was to increase the volume of PM required to be collected during a test run from 1 dscm to 4 dscm. While this change may improve the poor accuracy of the empirical PM results at the lowest PM emission rates, it will also increase each test run duration from 1 hour to 3 hours. This means that a periodic PM correlation or RCA test that currently takes days will, under the new PM standard, instead take weeks. The longer duration of an already difficult test will increase the potential for test protocol upsets, personnel fatigue, and equipment failures, and will diminishGVEA's ability to dispatch its generating resources in accordance with electrical demand, maintenance and economic needs. Extending the duration of these already cumbersome periodic tests will result in an even greater cost to GVEA's member-owners and even more disruption to power plant operations. Based on GVEA's experience, it is not technically feasible to consistently complete an adequate number of valid test runs of the proposed duration to maintain compliance with the performance standard. If EPA elects to lower the PM emission standard, GVEA believes it should first a practical correlation method that is feasible at the lower emission limit, so regulated facilities can affordably and reasonably certify and maintain compliant PM CEMS. Please see the following attachments for additional information and technical issues previously provided to EPA regarding 40 CFR 63 Subpart UUUUU: Attachment 1: Comments provided by GVEA, Docket ID No. EPA-11Q-OAR-2018-0794, 88 FR 24854, June 23 2023 Attachment 2: Comments provided by GVEA, Docket ID No. EPA-11Q-OAR-2018-0794, April 17, 2019 Attachment 3: Technical Comments on EPA's Proposed Rulc: Mercury and Air Toxics Standards Risks and Technology Review PM CEMS, RI.R Consulting, I.I.C, June 16, 2023 3. Technical Infeasibility for the Mercury Standard GVEA does not believe it is technically feasible to achieve the amended mercury emissions standard at Healy Unit 1 and Unit 2 by July 6, 2027. Adapting specialized equipment to function in a coal-Fired power plant in Healy, Alaska, takes more time than it would in the lower 48 states, and maintaining that equipment takes more time than one might expect as well. Healy Unit 2 has a carbon injection system for mercury control and a mercury sorbent trap monitoring system (STMS) for monitoring. The STMS system does not provide real-time emission information because the emissions levels represented by a given trap set are not known until the traps arc transported from Healy, Alaska to the lab in Ohio, analyzed, and the results reported back to GVEA. The sorbent trap analysis takes about two to three weeks to complete. As a result, GVEA is not equipped to identify rising mercury emissions levels if they occur (due to natural variability in coal mercury content) and therefore cannot actively manage the carbon injection system in response to such events to avoid an exceedance. GVEA suffered an exceedance of the mercury emissions limit on Unit 2 in 2020 due to an anomalous spike in coal mercury content, and was unaware of the exceedance until the STMS analytical results were received 17 days after the event began. In response to the 2020 mercury exceedance event, GVEA procured a mercury process monitor for f scaly Unit 2. The monitor is not approved by EPA to act as a compliance demonstration instrument, but rather serves as an on-site, real-time mercury emissions analyzer with which a facility can respond to changes in mercury levels by actively adjusting the mercury control system. GVEA has been working on installation of the mercury process monitor since 2021. The installation was initially delayed because transport, personnel, and travel were thwarted by the Covid-19 pandemic. Since 2022, the delays have been largely attributable to challenges more typical of the Healy Power Plant's remote subarctic setting. In order to accommodate the seasonal extreme temperatures that can drop below negative 40 degrees Fahrenheit, GVEA has worked extensively with the vendor to develop a custom sample line bundle that will maintain a specific gas temperature alumg a sample path starling at the hot sampling point in the stack, crossing an elevated outdoor catwalk, and then passimg into the warm power plant to the mercury analyzer unit. The first two attempts at this custom sample line have failed, necessitating painstaking removal, packaging, and transport of the large umbilical bundle and associated parts back to the vendor for evaluation. Currently, GVEA's installation of a non-regulatory mercury process monitor has taken four years and as of March 2025 is not yet complete. Once the process monitor is consistently operational, the next steps GVEA anticipates needing to complete in order to meet the new MATS mercury emission limit will include installation, Sierra Club FOIA 2025-EPA-04883 ED_018388_00000056-00004 SC_EVERSPLIT0005599