The purpose of this ListServ (Advisory) is to clarify some of the language in Technical Manual 1005 (TM1005) regarding unit operation and CEMS downtime. This is not a change to the existing requirements nor does it supersede any Federal rule or regulation.

TM1005 states that, "CEMS must provide a minimum of seventy-five (75) percent [45 minutes] of the one-minute data averages for each one hour (60 minute) clock period." (IV.B.4.b)

TM1005 further states that, "For any one hour (60 minute) period where less than forty-five (45) minutes of CEMS/COMS data is provided for any analyzer, the entire sixty (60) minute period is considered downtime for that analyzer and shall be included in the quarterly EEMPR as downtime." (IV.B.4.c)

TM1005 additionally states, "Downtime includes those periods where the CEMS or COMS are not providing compliance emission data while the process is in operation. It also includes periods of Quality Assurance (QA) and Preventive Maintenance (PM) procedures and CEMS calibration (if calibration period exceeds 15 minutes in any one hour). All downtime is to be recorded on the quarterly EEMPR form." (IV.B.4.f).

Questions have arisen for partial operating hours and the accrual of downtime. Per IV.B.4.f, downtime is not accrued when the source is not operating. The 45 minutes of CEMS/COMS data required per clock hour stated in IV.B.4.c is for 60 minutes of source operation in that hour. The overriding requirement is for 75% of one-minute data for the operating minutes in each hour. Accordingly, for clock hours when the unit operates less than 60 minutes, IV.B.4.c is clarified to mean the CEMS must be collecting valid data for 75% of the operating minutes, where fractional minutes are rounded down to the nearest full minute. Consistent with IV.B.4.c, when this criterion is not met, all operating minutes in the hour will be considered downtime.

Lastly, consistent with our 8/26/21 Listserv, a valid compliance hour requires 45 minutes of operation. CEMS/COMS data must be collected for downtime purposes as detailed above, regardless of whether a clock hour is a valid compliance hour or not.