; and (ii) the term leak is defined to mean an instrument reading of not less than 50 parts per billion above background concentrations. (C) Maximum achievable control technology standards for covered facilities Not later than 1 year after the date of enactment of this Act, the Administrator shall— (i) promulgate a final rule modifying subpart YY of part 63 of title 40, Code of Federal Regulations, to ensure that— (I) the generic maximum achievable control technology standards described in that subpart— (aa) require no detectable emissions of hazardous air pollutants, unless the Administrator— (AA) determines that the maximum degree of reduction in emissions of hazardous air pollutants achievable pursuant to section 112(d)(2) of the Clean Air Act ( 42 U.S.C. 7412(d)(2) ) justifies higher limits; and (BB) publishes the determination under subitem (AA) and the proposed higher limits in a rulemaking; (bb) ensure an ample margin of safety to protect public health and prevent an adverse environmental effect; and (cc) prevent adverse cumulative effects to fetal health, the health of children, and the health of vulnerable subpopulations; and (II) the term no detectable emissions , as required under subclause (I)(aa), is defined to mean an instrument reading of less than 50 parts per billion above background concentrations; and (ii) in promulgating the final rule pursuant to clause (i), take into consideration— (I) the effects and risks of exposure from cumulative sources of hazardous air pollutants under the subpart modified under that clause