Heavy Metals in the Flood Plain Deposits Along the Upper Clark Fork River

Concentrations of copper, arsenic and cadmium in sediments and soils deposited on the flood plain of the upper Clark Fork River drainage were determined to be one to two orders of magnitude greater than in soils from typical noncontaminated systems. Aerial deposition of metal particulates during the period of smelting activities (1884-1980) has contributed approximately 2% of the excess copper, 9% of the excess arsenic, and 30% of the excess cadmium in the riparian zone of a ranch on the flood plain at Deer Lodge; the remaining 98% excess copper, 91% excess arsenic and 70% excess cadmium in the riparian zone was deposited by the river transporting contaminated sediments originating from upstream mining and smelting activities. Metal concentrations in contaminated sediments did not decrease with distance downstream from the source areas at Anaconda and Butte.