THE DIRT: The Central Treatment Plant’s upgrades are making an impact!

There are many clean-up actions and remedies currently taking place in the Bunker Hill Superfund Site that are intended to improve the water quality of the South Fork of the Coeur d’Alene River. These remedies often take time before their effectiveness is quantified and determined. Recent studies have shown that some of these remedies are making great improvements.

The Central Treatment Plant (CTP) that is located near the Central Impoundment Area (CIA) in Kellogg was upgraded and completed in 2021 to treat groundwater and mine water waste. The CTP upgrades were necessary to treat and meet current, more stringent discharge requirements. The design included a groundwater collection system that consists of a soil bentonite cutoff wall between the CIA and Interstate 90 that blocks contaminated groundwater flow to the river. The contaminated groundwater is pumped back to the CTP where it is treated and discharged back into the SFCDA following current water quality standards. The CTP was also designed to treat Acid Mine Drainage, which is acidic and laden with metals, that continually flows out of the Bunker Hill Mine.

The United States Geological Survey (USGS) did a seepage study to help understand the impacts of the upgrades at the CTP to surface water. They utilized data collected in 2017 which was before the upgrades were made. They sampled again in 2022 to look at differences after completing the remediation. A seepage study measures the amount of water at two points and subtracts the upstream from the downstream to get the specific portion coming into or out of the river. They must also factor in inputs and outputs, like tributaries coming in or anything exiting out.

The USGS’s comparison study showed a significant reduction in contaminants of concern. Their study showed an 86% reduction in zinc, an 81% reduction in cadmium, and an 88% reduction in phosphorus.

Field observations also support this data regarding phosphorus – in 2022, there was a lot less algae in the stream which correlates with the reduced phosphorus loading. Also in 2022, the left riverbank near the seeps was noticeably drier than in 2017 which supports the bentonite wall is cutting off groundwater to this area. All of this is considered a success story with lower trace metals and nutrient loads reaching the CDA River and eventually CDA Lake.

The Dirt is a series of informative articles focused on all aspects of cleanup efforts associated with the Bunker Hill Superfund Site. Our goal is to promote community awareness of contamination issues, to provide tools for protecting public health, and to keep the community informed of current and future cleanup projects. The Dirt is a group of committed and local experts from multiple agencies including the Basin Environmental Improvement Project Commission, Panhandle Health District, Shoshone County, Silver Valley Economic Development Committee, and the Idaho Department of Environmental Quality.