Originally completed in 2007, Unit 12 is currently a simple cycle natural gas fired combustion turbine with a capacity of approximately 143 megawatts. The conversion to combined cycle operation will include the installation of a heat recovery steam generator, steam turbine generator, auxiliary boiler and cooling tower. This highly efficient configuration will allow for the recapture of excess heat from the existing unit to produce approximately 100 megawatts of additional power generation.

Burns & McDonnell will serve as engineering, procurement and construction contractor for the expansion. At peak construction, the project will employ approximately 140-150 workers.

Upon completion of the combined cycle project in 2016, the three most senior generators at Riverton, Units 7, 8 and 9, will be retired. Units 7 and 8 historically operated utilizing coal fuel, but were transitioned to natural gas operation in 2012. After more than 100 years, this transition brought to a close the coal generation era at Riverton.

According to Blake Mertens, vice president of energy supply, "The new plant configuration at Riverton ensures we continue to provide safe, reliable energy to our customers with least-cost resources while significantly lowering emissions when compared to coal-fired generation. While this ends the coal era at Riverton, this investment will extend the life of the plant and continue to afford jobs in the community of Riverton."