eCFR Subpart AAAA 
[ecfr.gov]
This subpart applies to:
- Small municipal waste combustion (MWC) units that commence construction after Aug 30, 1999.
- Small MWC units that commence modification or reconstruction after June 6, 2001.
A small MWC unit has the capacity to combust at least 35 tons per day but no more than 250 tons per day of municipal solid waste or refuse-derived fuel.
Physical or operational changes made to an existing MWC unit primarily to comply with NSPS BBBB do not qualify as modifications or reconstruction.
Not subject to this subpart*:
- Small MWC units that combust less than 11 tons/day;
- Qualifying small power production facilities (per Section 3(17)(C) of the Federal Power Act, 16 USC 796(17)(C));
- Qualifying cogeneration facilities (per Section 3(18)(B) of the Federal Power Act, 16 USC 796(18)(B));
- MWC units that combust only tires;
- Hazardous waste combustion units with a permit under Section 3005 of the Solid Waste Disposal Act;
- Materials recovery units;
- Co-fired combustors;
- Plastics/rubber recycling units;
- Units that combust fuels made from products of plastics/rubber recycling plants;
- Cement kilns
Partially Exempt*:
- Air curtain incinerators that combust 100% yard waste.
*These facilities must still comply with certain requirements (per 40 CFR 60.1020). Please see the rule text for full details.