SIOUX FALLS, S.D. (AP) — Past fireworks displays at Mount Rushmore National Memorial are the likely source of a pollutant found in water within the site in western South Dakota, according to a government report released Monday. "The lack of alternative perchlorate sources in the area, such as a military site or agricultural land with applied fertilizers, and the presence of firework debris suggest that past fireworks are the perchlorate source," Galen Hoogestraat, a USGS scientist and the lead author of the report said in a statement. High concentrations of perchlorate in drinking water can affect the human thyroid gland, but Dr.