The history of the Coeur d’Alene Basin is rooted in the relationship of its inhabitants to Coeur d’Alene Lake, its tributaries, and rivers. The lake has sustained its inhabitants from time immemorial and has been influenced by the land use activities of these inhabitants. The challenge today is to ensure that land use activity is managed in ways that will protect the lake’s water quality.
From the late 1880’s to the early 1980s, the “Silver Valley” was the country’s largest producer of silver, lead, zinc, and other metals. The mining and ore-processing methods used to extract silver, lead, zinc, and other metals produced large quantities of waste material containing toxic hazardous substances such as cadmium, lead, and zinc. Much of this material was discharged directly to, or washed into the South Fork of the Coeur d’Alene River and its tributaries. In 1983, the US EPA listed the Bunker Hill Mining and Metallurgical Complex on the National Priorities List under CERCLA, often referred to as the Superfund process. This site is in the heart of the Silver Valley and the Coeur d’Alene Lake basin.
As much as 83 million tons of particulate and dissolved metals from mining-related activities have been deposited into the lake since the 19th century. High flows moving through the Coeur d’Alene Basin every spring continue to deliver historic mining waste materials, sediment, and nutrients to Coeur d’Alene Lake. Lakebed sediments are highly contaminated with antimony, arsenic, lead, cadmium, zinc, copper, silver, and mercury throughout much of the lake (National Academy of Science).
EPA issued its interim Record of Decision in 2002 to identify actions for cleanup in the Bunker Hill Superfund Site. It didn’t include remedial actions for Coeur d’Alene Lake. They deferred the decision of whether to select remedial actions for the lake, anticipating the Lake Management Plan. EPA concluded that an effective lake management plan outside of the CERCLA process would reduce riverine inputs of nutrients and metals that continue to contribute to contamination of the lake and Spokane River. Other human activities around the basin, such as logging, farming, and home building, contribute sediments and nutrients (phosphorus and nitrogen) into the lake, often as a result of natural events such as snow, rain, and floods. In more recent years, tourism has gained momentum in the Coeur d’Alene area. While it is vital to the local economy, it also brings more pressure to our water resources. Dissolved oxygen approaches zero in summer months in deeper southern waters. Deeper waters in the northern end of the lake generally remain above 6 mg/L. The relationship between the metals in lakebed sediments and dissolved oxygen is significant. As nutrient enrichment causes oxygen levels to drop below 6 mg/l, the potential for metals to be released and remobilized from the lakebed increases. This is what we are managing for.