Today, the U.S. Environmental Protection Agency (EPA) released revised underground injection control (UIC) program permitting guidance for wells that use diesel fuels during hydraulic fracturing activities. EPA developed the guidance to clarify how companies can comply with a law passed by Congress in 2005, which exempted hydraulic fracturing operations from the requirement to obtain a UIC permit, except in cases where diesel fuel is used as a fracturing fluid. EPA is issuing the guidance alongside an interpretive memorandum, which clarifies that class II UIC requirements apply to hydraulic fracturing activities using diesel fuels, and defines the statutory term diesel fuel by reference to five chemical abstract services registry numbers.