When a Permit requires the installation and certification of a total hydrocarbons (THC) continuous emissions monitoring system (CEMS), and also requires the establishment of the THC CEMS allowable by correlation during the stack test, the question has arisen as to which of these operations should be completed first, since they are closely linked and dependent on one another.

Since the THC CEMS needs to be providing valid data during the stack test in order to perform the correlation, it should be certified prior to conducting the stack test in which the THC allowable will be established. Assuming that the THC analyzer passes the 7-day calibration drift (CD) as well as the relative accuracy (RA) portion of the Performance Specification Test (PST) using the average reference method (RM) value in the denominator of the RA equation (Equation 2-6 of Performance Specification 2, incorporated by reference into Performance Specification 8 for THC analyzers), then the CEMS is certified and may be used to correlate the CEMS readings to the destruction and removal efficiency (DRE) results during the stack test to arrive at the THC allowable, as outlined in Technical Manual 1005, Appendix D.

However, if the THC CEMS does not pass the RA acceptance criteria using the RM value in the denominator, then the facility has two options:

1. Repeat the PST and pass as detailed above prior to the stack test.

2. Conduct the CEMS correlation test during the stack test at risk, and the subsequent THC limit established in this correlation test would then be used in the denominator of the RA equation. As long as the RA passes in this scenario, the THC CEMS is certified and the THC allowable is established. If the THC CEMS still cannot pass the RA criteria, then the THC CEMS is not certified and the THC allowable that was established is not valid. A PST of the CEMS consisting of a 7-day CD and RA determination must be repeated, as well as the establishment of the THC allowable. A full DRE stack test need not be repeated; as long as the operating conditions during the correlation retest are similar to that of the DRE test, then inlet and outlet flows from the original test can be used with newly measured inlet and outlet reference method concentrations. The correlation retesting can also be done in conjunction with the new PST by making three of the RA runs 1-hour in duration instead of 21-minutes in duration.

Questions on these procedures should be directed to the Emission Measurement Section.