Q280. I have a landfill gas powered engine located at a landfill that must report under subpart HH. Under which subpart am I required to report combustion emissions for the engine? What about for a flare located at the landfill?

A280.  For stationary combustion units that operate only on landfill gas and that are located at landfills, CO2 and N2O emissions must be reported under subpart C. Although subpart C provides a calculation methodology for CH4 emissions, CH4 emissions from landfill gas units located at landfills are already calculated and reported under subpart HH. For these units, no CH4 emissions need to be reported in subpart C since they are already included in subpart HH. Also note that not all destruction devices as defined in subpart HH are considered stationary combustion units in subpart C. If a destruction device required to report CH4 emissions in subpart HH is considered a flare according to the definition of flare provided in 40 CFR 98.6, you would not need to calculate CO2 and N2O emissions for the flare in subpart C. The same principle applies to other units exempted from subpart C in 40 CFR 98.30(b).