The U.S. Environmental Protection Agency has filed a court brief defending a cap on the amount of emissions new power plants can produce.

"EPA reasonably exercised expert judgment in concluding that the best system of emission reduction for newly constructed steam generating units includes the use of a highly efficient boiler implementing partial CCS," said the document filed on Dec. 14 in the U.S. Court of Appeals for the District of Columbia Circuit. "The record amply supports EPA's conclusion that partial CCS is adequately demonstrated," it continued, citing cases such as that of Saskatchewan's Boundary Dam which it said has implemented full CCS at commercial scale.

The case stems from arguments made by North Dakota that the 1,400 pounds of carbon dioxide per megawatt-hour on a gross output basis standard set by the EPA for new, reconstructed, and modified fossil fuel plants is unachievable. The state argued that the Clean Power Plan cannot exist without this new source rule.

A number of other coal states including West Virginia and Kentucky have challenged the rule, as well as companies like Murray Energy Corp., Peabody Energy Corp. and several utilities.

Murray spokesperson Gary Broadbent told S&P Global Market Intelligence that the company would respond "in due course" to the filing. "This is another attempt by the Obama EPA to justify this illegal regulation," he said.

Oral arguments in the case are scheduled to be heard by a three-judge panel on April 17, 2017.