Refineries are required to blend biofuels such as ethanol into the nation's fuel each year, at a level set by the Renewable Fuels Standard. The administration came under fire last fall when it considered rolling back the RFS; Trump ultimately caved and kept the RFS steady after Republican Sen. Chuck Grassley of Iowa, who chairs the Senate Judiciary Committee, threatened to hold up court nominees.
In past administrations EPA has issued between six and eight waivers per year to small refineries for whom RFS compliance would be a financial hardship, but the unprecedented expansion has triggered outrage from biofuels advocates. "Brooke Coleman, head of the Advanced Biofuels Business Council, said he was concerned EPA’s [Scott] Pruitt was using the waivers to gut a program he dislikes," Renshaw and Prentice report. Grassley said the move raises legal questions.
The move triggered a dramatic drop in U.S. renewable fuel credits, which fell as low as 29 cents each on Wednesday, the first time they've fallen below 30 cents since September 2015.