The Warm Springs Ponds were built to treat the toxic flows of Silver Bow Creek at the headwaters of the Clark Fork River, and over the years have become a popular recreational area, known for birdwatching and a trophy trout fishery.
The three man-made Warm Springs Ponds cover 2,400 acres at the confluence of Silver Bow, Mill, Willow, and Warm Springs creeks, the headwaters of the Clark Fork River. The ponds were built in 1911 to trap mining tailings before they entered the Clark Fork River. Lime is added at the inlet of the ponds to precipitate the metal out of the water and into the bottom sediments. The ponds contain an estimated 19 million cubic yards of sediments, tailings, and heavy metal sludge, with more than 20 contaminants like arsenic, copper, cadmium, lead and zinc.
An investigation of the ponds was completed in 1989. Public comments were extensive and led to a decision to expedite certain cleanup plans in a portion of the area, the Mill-Willow Bypass. The bypass contained approximately 200,000 cubic yards of tailings and contaminated soils that were a principal cause of fish kills. In 1990 and 1991, the tailings and contaminated soils were excavated and consolidated in Pond 3. Groundwater interception trenches were installed to divert ground water to Pond 3 for treatment. The PRPs designed the selected remedy in late 1991, and began cleanup activities in mid 1992; construction was completed in 1995. EPA's five year review of the remedy in 2000 concluded that although Warm Springs Ponds (the focus of the review) has not always performed as dictated by the ROD, the remedial action has been protective of human health and the environment.
Treatment for metals removal has been good, though the ponds release arsenic during part of the year. A CFRTAC review of the 2005 performance data of the Warm Springs Ponds found that the they chronically discharge high levels of arsenic into the Clark Fork River. Arsenic is toxic to humans and has been found to cause cancer in relatively low concentrations, the ponds are designed to treat copper and other metals.
Uncertainty surrounds the ultimate fate of the Warm Springs Ponds and Wildlife Management Area that covers about 4100 acres at the headwaters of the Clark Fork River. One central question is whether the ponds will remain intact (wet closure) or be drained and filled in with dirt (dry closure). Although it's early in the process, agencies disagree whether wet closure or dry closure is a better solution. Also unknown is how long they'll be needed. After the risk of mining contamination from Silver Bow Creek is reduced it is unknown how long the ponds will be needed to provide safety to the water entering the Clark Fork River with estimates ranging from five to 40 years or more.
Decisions on future ownership and operation of the ponds are also uncertain. The area provides habitat for many kinds of ducks and geese, birds of prey and other birds as well as big game like deer, elk, moose, antelope and bear. The ponds also provide a home for many trout and other aquatic wildlife. Currently MFWP manages the fish and wildlife resources of the area and is working on a lease agreement with ARCO.
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