Prior to the availability and operation of continuous emissions monitoring (CEM) systems, and subsequent to the baseline emissions testing under N.H. Rev. Stat. § 125-O:14, II, stack tests or another methodology approved by the department shall be conducted twice per year to determine mercury emissions levels from the affected sources. Any stack tests performed shall employ a federally recognized and approved methodology, proposed by the owner and employing a test protocol approved by the department. When a federal performance specification takes effect, and a mercury CEM system capable of meeting the federal specifications becomes available, a mercury CEM system, approved by the department, shall be installed at Merrimack Units 1 and 2 and at other affected sources as deemed appropriate by the department.