Except for adjustments of the performance standard on a case-by-case basis under KRS 224.20-144, the performance standard that shall be established for existing gas-fired electric generating units shall be based on the following:
(1) The best system of emission reduction which has been adequately demonstrated for gas-fired electric generating units subject to the performance standard. Best system of emission reduction shall take into account the cost of:
(a) Achieving the emission reduction;
(b) Impacting non-air-quality health and the environment; and (c) Maintaining energy requirements needed to serve the load of the electric generating unit;
(2) Reductions in emissions of carbon dioxide that can reasonably be achieved through measures undertaken at each gas-fired electric generating unit; and (3) Efficiency and other measures that can be undertaken at the unit to reduce carbon dioxide emissions from the unit without switching from natural gas to other fuels that emit less carbon dioxide than natural gas or by limiting the utilization of the electric generating unit.