40 CFR 61.122 - Emission standard.
Emissions of polonium-210 to the ambient air from all calciners and nodulizing kilns at an elemental phosphorus plant shall not exceed a total of 2 curies a year; except that compliance with this standard may be conclusively shown if the elemental phosphorus plant:
(a) Installs a Hydro-Sonic ® Tandem Nozzle Fixed Throat Free-Jet Scrubber System including four scrubber units,
(b) All four scrubber units are operated continuously with a minimum average over any 6-hour period of 40 inches (water column) of pressure drop across each scrubber during calcining of phosphate shale,
(c) The system is used to scrub emissions from all calciners and/or nodulizing kilns at the plant, and
(d) Total emissions of polonium-210 from the plant do not exceed 4.5 curies per year.