104 STAT. 2614 PUBLIC LAW 101-549—NOV. 15, 1990 that listed for any type of utility boiler if the Administrator finds that the maximum listed rate for that boiler type cannot be achieved using low NO, burner technology. The maximum allowable emission rates are as follows: "(A) for tangentially fired boilers, 0.45 Ib/mmBtu; "(B) for dry bottom wall-fired boilers (other than units apply- ing cell burner technology), 0.50 Ib/mmBtu. After January 1, 1995, it shall be unlawful for any unit that is an affected unit on that date and is of the type listed in this paragraph to emit nitrogen oxides in excess of the emission rates set by the Administrator pursuant to this paragraph. Regulations. "(2) Not later than January 1, 1997, the Administrator shall, by regulation, establish allowable emission limitations on a Ib/mmBtu, annual average basis, for nitrogen oxides for the following types of utility boilers: "(A) wet bottom wall-fired boilers; "(B) cyclones; "(C) units applying cell burner technology; "(D) all other types of utility boilers. The Administrator shall base such rates on the degree of reduction achievable through the retrofit application of the best system of continuous emission reduction, taking into account available technology, costs and energy and environmental impacts; and which is comparable to the costs of nitrogen oxides controls set pursuant to subsection (b)(D- Not later than January 1, 1997, the Administrator may revise the applicable emission limitations for tangentially fired and dry bottom, wall-fired boilers (other than cell burners) to be more stringent if the Administrator determines that more effective low NOx burner technology is available: Provided, That, no unit that is an affected unit pursuant to section 404 and that is subject to the requirements of subsection (b)(1), shall be subject to the revised emission limitations, if any. "(c) REVISED PERFORMANCE STANDARDS. —(1) Not later than January 1, 1993, the Administrator shall propose revised standards of performance to section 111 for nitrogen oxides emissions from fossilfuel fired steam generating units, including both electric utility and nonutility units. Not later than January 1, 1994, the Administrator shall promulgate such revised standards of performance. Such revised standards of performance shall reflect improvements in methods for the reduction of emissions of oxides of nitrogen. "(d) ALTERNATIVE EMISSION LIMITATIONS.—The permitting authority shall, upon request of an owner or operator of a unit subject to this section, authorize an emission limitation less stringent than the applicable limitation established under subsection (b)(1) or (b)(2) upon a determination that— "(1) a unit subject to subsection (b)(l) cannot meet the applicable limitation using low NO^ burner technology; or (2) a unit subject to subsection (b)(2) cannot meet the applicable rate using the technology on which the Administrator based the applicable emission limitation. Regulations. The permitting authority shall base such determination upon a showing satisfactory to the permitting authority, in accordance with regulations established by the Administrator not later than eighteen months after enactment of the Clean Air Act Amendments of 1990, that the owner or operator— "(1) has properly installed appropriate control equipment designed to meet the applicable emission rate;
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