The Clark Fork and Blackfoot rivers flowed unimpeded on March 28 for the first time in more than 100 years following demolition of Milltown Dam and powerhouse near Missoula, Mont. Removal was done under a $100-million agreement with the U.S. Environmental Protection Agency funded mostly by Atlantic Richfield Co., Los Angeles. The project was part of a 120-mile-long Superfund site because of mining sediment that built up behind the dam, producing an arsenic-laden plume that contaminated groundwater and area wells. Envirocon Inc., Missoula, oversaw most work.