California’s Air Resources Board downshifted this month by offering contractors “relief.” The regulatory board says it will delay enforcement of its emissions regulations—which were set to go into effect on March 1—for existing off-road diesel machinery until it receives a waiver from the U.S. Environmental Protection Agency. Construction lobbyists say the move is counterproductive to their recommendation to fully delay the rules for two more years. “CARB’s offer to not enforce the off-road regulation—a rule that it cannot fully enforce without a waiver from the federal EPA—as ‘relief’ is disingenuous at best,” says Mike Lewis, senior vice president of the
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.