The Milltown Reservoir Sediments site is located in Missoula County, Montana. The site is adjacent to the Milltown Dam where the Big Blackfoot River joins the Clark Fork River. Constructed in 1906, this hydroelectric dam formed a reservoir that trapped sediments from mining, milling, and smelting operations in the upper Clark Fork Valley. During the years since construction, the reservoir storage has been almost totally filled with arsenic contaminated sediments. In May, 1981, Milltown's four community water supply wells were found to be contaminated with arsenic and other heavy metals. The highest arsenic levels measured have been between 0.54 to 0.90 milligrams per liter (mg/l). The selected remedial alternative consists of: construction of a new well from a hydraulically separate aquifer; construction of a new distribution system; flushing the plumbing system of each house to remove suspended materials from the water system and plumbing and testing the water quality in each house to assure that the arsenic standard has been met. The capital cost for the selected alternative is estimated to be $262,714 and annual O&M costs are $4,238.

"04/14/84." "PB85-214070." "EPA/ROD/R08-84/001." "Office of Emergency and Remedial Response."