Q84. For a unit that is not required to use Tier 4 (CEMS monitoring), which tier is required if you receive HHV with some coal shipments, but not every coal shipment?

A84. If the unit is less than or equal to 250 mmBtu/hr, since you do not obtain HHV at the minimum frequency specified in §98.34(a), you may use Tier 1 to calculate CO2 mass emissions.  You would also be able to use Tier 1 if the unit is greater than 250 mmBtu/hr and the fuel provided less than 10 percent of the annual heat input for the unit (see §98.33(b)(1)(viii)).  However, if the unit is greater than 250 mmBtu/hr and the coal provides 10 percent or more of the unit’s annual fuel input, then you must ensure that the carbon content of each shipment is determined and use Tier 3.  However, if multiple deliveries of a particular type of fuel are received from the same supply source in a given calendar month, the deliveries for that month may be considered, collectively, to comprise a fuel lot, requiring only one representative sample, subject to the following conditions: (1) For coal, the “type” of fuel means the rank of the coal ( i.e., anthracite, bituminous, sub-bituminous, or lignite), (2) The owner or operator shall document in the monitoring plan under § 98.3(g)(5) how the monthly sampling of each type of fuel is performed.  (See § 98.34(b)(3)(ii)(B)).

Where the HHV or carbon content for a fuel lot is missing, determine a substitute value by calculating the arithmetic average of the quality-assured HHVs or carbon contents for the fuel lots delivered immediately before and immediately after the fuel lot for which the HHV or carbon content is missing. If the “after” value has not been obtained by the time that the GHG emissions report is due, you may use the “before” value for missing data substitution or the best available estimate of the HHV or carbon content of the fuel lot. If no quality-assured data are available for the fuel lot delivered prior to that for which the HHV or carbon content is missing, the substitute data value shall be the first quality-assured value obtained from a subsequent fuel delivery. (See §98.35(b)(1).)