Nearly half of existing coal- and oil-fired powerplants may need pollution-control upgrades under a newly proposed Environmental Protection Agency rule that sets the first national standard for mercury, arsenic, nickel and other pollutants. The proposed rule was released on March 16 in response to a court-ordered deadline that was set following a case brought by several environmental groups. A final rule is required by November. EPA estimates that coal-fired plants produce 99% of mercury emissions and that existing technology could prevent 91% of mercury in coal from being released. EPA expects the rule, when final, to encourage the 44% of
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.