On August 3, 2015 the Environmental Protection Agency (EPA) signed the final version of a new rule titled Carbon Pollution Emission Guidelines for Existing Stationary Sources: Electric Utility Generating Units, also known as the Clean Power Plan (CPP). It is expected that the final rule will be published in the Federal Register by the end of October, therefore, the effective date of the final rule will likely be the end of December 2015.

The CPP establishes Carbon Dioxide (CO2) emission performance rates representing the best system of emission reduction (BSER) for two subcategories of existing fossil fuel-fired electric generating units (EGUs):  steam generating units and stationary combustion turbines. In order to accomplish meeting the CO2 performance rates the CPP establishes state specific goals reflecting the CO2 performance rates and requires the implementation of state plans that establish emission standards or other measures to implement the CO2 emission performance rates.

EPA determined that the BSER for reducing CO2 emissions was a combination of measures including increasing the operational efficiency of existing coal-fired steam EGUs, substituting increased generation at existing natural gas combined cycle units for generation at existing steam EGUs, substituting generation from low- and zero-carbon generating capacity for generation at existing fossil fuel-fired EGUs, and increasing demand side energy efficiency to reduce the amount of fossil fuel-fired generation.

The CPP provides guidelines for the development, submittal, and implementation of state specific plans that establish standards of performance or other measures to achieve CO2 interim and final performance goals. A fact sheet provided by the EPA that discusses Illinois' CO2 emission goals can be found here. States can choose between two plan types to achieve their goals, either a rate-based state goal measured in pounds per megawatt hour (lb/MWhr) or a mass-based state goal measured in total short tons of CO2. Measures implemented by the state can include renewable energy standards and programs to improve residential energy efficiency, which are not federally enforceable, and can also include federally enforceable source-specific limits. States can also participate in market-based emissions trading programs to meet emissions goals. States must submit a final plan to EPA by September 6, 2016 or may be granted an extension to submit the final plan by September 6, 2018.

On August 3, 2015, Illinois Environmental Protection Agency Director Lisa Bonnett issued the following statement regarding the Clean Power Plan:

"Illinois is evaluating the final rule. Illinois' priority will be to ensure that our energy sector has the flexibility needed to meet the emission reduction limits under the Clean Power Plan, while providing residents and businesses with reliable and affordable electricity. Illinois is fortunate in that we have tremendous energy diversity, and we will want to leverage our strengths."