National Academy of Sciences Revisiting Lake Coeur d’Alene Water Quality

The Idaho Department of Environmental Quality (IDEQ) and Kootenai County are cosponsoring an $800 thousand, 18-month study examining water quality conditions in Coeur d’Alene Lake. The National Academy of Sciences, Engineering and Medicine (NAS) will conduct the study with support from The Coeur d’Alene Tribe (CDA Tribe) and the Environmental Protection Agency.

This study further examines decades long concerns regarding the effect of historical mining activities in the Silver Valley contaminating millions of tons of lake sediments with metals such as zinc, arsenic, cadmium, and lead. While these metals are currently bound to sediments at the bottom of the Lake, the heart of federal, state, tribal and local concerns are these metals being released into the water column. Such an outcome would trigger an ecological, economic, and cultural disaster.

Metals concentration in the Lake has declined due to regulations implemented in the 1970s after the Clean Water Act was enacted by Congress. Data, however, collected by the CDA Tribe and IDEQ as part of implementing a collaborative Coeur d’Alene Lake Management Plan that began in 2009 indicate concerning trends.

At issue is if development, land use changes and other dynamics may influence the release of metals currently bound to lake sediments via sediment runoff from the landscape. Of particular concern is the effect of increased nutrient loading, e.g. phosphorus and nitrogen. Under these conditions, the water chemistry of changing oxygen levels from hypoxic conditions (low in dissolved oxygen) to anoxic conditions (no oxygen) would lead to release of metals.

The National Academies defines their scope of work as:

• Evaluate current water quality data from the Lake, lower rivers and lateral lakes with a focus on
• observed trends in nutrient loading and metals concentrations, while also considering how
• changes in temperature or precipitation could affect those trends.
• Consider the impacts of current summertime anoxia on the fate of the metals and nutrients.
• Consider whether reduced levels of zinc entering the lake as a result of the upgrade to the
• Central Treatment Plant and other upstream activities are removing an important control on
• algal growth.
• Discuss whether metals currently found in lake sediments will be released into the Lake if current trends continue. If sufficient data are not available to result in a high level of confidence in their conclusions, the NAS will identify the additional data that are required to achieve an appropriate level of confidence.
• Discuss the relevance of metals release in the lake to human and ecological health.

The NAS initiated meetings in December and project releasing a report in the summer of 2022.