Water Table Configuration and Aquifer Tailings Distribution, Coeur d'Alene Valley, Idaho

The Coeur d'Alene District has ranked high in the production of lead, zinc, silver, and antimony for the past 80 years. The published literature indicates that mining practices in the district historically have had a significant impact on the environment. Past practices have left extensive deposits of old tailings which have been reworked by man and streams, especially in the valley of the south fork of the Coeur d'Alene River. These old tailings as well as tailings from some present operations represent a potential source of pollution for ground water. In order to gain greater insight into this potential source, the distribution of alluvium, tailings, and mixed tailings and alluvium was mapped using air photos and field observations. Seismic refraction and electrical resistivity depth soundings were utilized to interpret the thickness of the valley floor fill, which constitutes the aquifer supplying many of the wells in the area. A water-table map was prepared from water-level measurements at 88 locations. Ground-water was sampled at 49 locations, and the samples were analyzed for pH, electrical conductivity, calcium, cadmium, copper, iron, potassium, magnesium, manganese, sodium, lead, antimony, and zinc. The valley fill was found to thicken westward from 30 feet near Wallace to 414 feet near Rose Lake. The water-table map indicates that the main stem of the Coeur d'Alene River is gaining water from the groundwater system. Additional water-level measurements are needed east of Kingston before it can be determined whether the south fork is gaining or losing. High heavy-metal concentrations in the valley of the south fork can be correlated with geochemical anomalies, jig tailings deposits, tailings ponds, and metal processing plants. Low pH, high conductivity, and high concentrations of cadmium, antimony, zinc, and several other ions were noted in industrial wells adjacent to the Bunker Hill tailings pond near Smeltervill