The U.S. Environmental Protection Agency has re-opened the door for developing a standard for perchlorate in drinking water. Perchlorate is a naturally occurring substance and also a man-made chemical used as an oxidizer in rocket fuel and fireworks. In October 2008, EPA published a preliminary determination not to regulate the substance. But the agency said on Aug. 5 it wanted to reassess perchlorate’s impact on public health. In large doses, it can affect the thyroid gland. Alan Roberson, the American Water Works Association’s director of security and regulatory affairs, says a drinking-water standard for perchlorate probably would require utilities to
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.