; and (ii) the list of unregulated contaminants to be monitored under section 1445(a)(2)(B)(i), in accordance with such section. (D) Monitoring When establishing monitoring requirements for public water systems as part of a national primary drinking water regulation under subparagraph (A) or subparagraph (G)(ii), the Administrator shall tailor the monitoring requirements for public water systems that do not detect or are reliably and consistently below the maximum contaminant level (as defined in section 1418(b)(2)(B)) for the perfluoroalkyl or polyfluoroalkyl substance or class of perfluoroalkyl or polyfluoroalkyl substances subject to the national primary drinking water regulation. (E) Health protection The national primary drinking water regulation promulgated under subparagraph (A) shall be protective of the health of subpopulations at greater risk, as described in section 1458. (F) Health risk reduction and cost analysis In meeting the requirements of paragraph (3)(C), the Administrator may rely on information available to the Administrator with respect to one or more specific perfluoroalkyl or polyfluoroalkyl substances to extrapolate reasoned conclusions regarding the health risks and effects of a class of perfluoroalkyl or polyfluoroalkyl substances of which the specific perfluoroalkyl or polyfluoroalkyl substances are a part. (G) Regulation of additional substances (i) Determination The Administrator shall make a determination under paragraph (1)(A), using the criteria described in clauses (i) through (iii) of that paragraph, whether to include a perfluoroalkyl or polyfluoroalkyl substance or class of perfluoroalkyl or polyfluoroalkyl substances (other than those perfluoroalkyl and polyfluoroalkyl substances listed under clauses (i) through (vi) of subparagraph (A) of this paragraph) in the national primary drinking water regulation under such subparagraph (A) not later than 18 months after the later of— (I) the date on which the perfluoroalkyl or polyfluoroalkyl substance or class of perfluoroalkyl or