Two senators from big coal-producing states are trying to thwart plans to mothball a coal-fired power plant that heats the U.S. Capitol and replace it with a system that uses cleaner natural gas and fuel oil. Capitol architect Alan Hantman had proposed the upgrade to the plant, which is among the most polluting facilities in Washington, D.C. But Sens. Robert Byrd (D-W.Va.) and Mitch McConnell (R-Ky.) sent a letter to Hantmann last month protesting the plan to eliminate the use of coal; the architect’s office is now reexamining its proposal.