THE DIRT: 30-year Water Quality Trends show improvements are being made
Water quality data was collected throughout the Bunker Hill Superfund Site before remediation work began, giving a reference point to compare data as work is completed. The United States Geological Survey (USGS) recently studied data going back 30 years to determine if water quality has improved after decades of remedial work.
Data from 1990 to 2018 indicate there is a dramatic downward trend in dissolved zinc concentration and loads throughout the South Fork Coeur d’Alene (SFCDA) River and Main Coeur d’Alene (CDA) River to the Spokane River. The total lead concentrations and loads also decreased at Pinehurst and Spokane River locations, but at Harrison, data indicates there may be a slight increase. Overall, total lead concentrations and loads have decreased 25-75% over this period except for loads at Harrison.
The USGS observed a sharp decrease in dissolved zinc concentrations and loads during the first part of the 30-year trend but that decrease flattened out over time. Similarly, total lead initially trended downward at most of the locations sampled with the exception of Harrison where an increase was observed from 1999-2009 and a flat trend in more recent years.
Previous work indicated that most of the dissolved zinc is coming from the SFCDA River from sources such as groundwater from the Central Impoundment Area. The majority of particulate lead is coming from the main stem of the CDA River where contaminated sediment that has been transported downstream from historic mining activity and deposited throughout the Basin continues to enter the waterway.
From 2003 to 2018, the SFCDA River remained the main source of dissolved zinc. Also, similar amounts of zinc entered and exited Lake Coeur d’Alene most years. Lead is a different story, with the majority still coming from the main stem of the CDA River including the lateral lakes, wetlands, and floodplains. Upward or flat trends are seen at Harrison as much lead is still in the system. Only limited remedial activities have occurred on the mainstem CDA River to date, so lead loads have not decreased.
These trends show water quality improvements have been made through remediation work and the Central Treatment Plant upgrades. This study provides evidence that remediation work is improving water quality and also points to areas that still need attention.
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 Corporation, and the Idaho Department of Environmental Quality.
