In a settlement with the U.S. Environmental Protection Agency, the Tennessee Valley Authority has agreed to shut some coal-fired generating units and install new or upgraded pollution-control equipment on others to cut air-pollution emissions at 11 of its powerplants. The pollution-control improvements will cost an estimated $3 billion to $5 billion. Under the settlement, announced on April 14, TVA will shut 18 of its generating units, which equal about 16% of its coal-fired electric power capacity. EPA says the measures will cut TVA nitrogen-oxide emissions by 69% and sulfur-dioxide emissions by 67%, compared with 2008 levels. The settlement addresses alleged
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.