Preliminary evaluation of hydrogeology and ground-water quality in valley sediments in the vicinity of Killarney Lake, Kootenai County, Idaho

Ground water near Killarney Lake in the Coeur d'Alene River Valley, Idaho, contains arsenic, cadmium, lead, and zinc in concentrations that would make it unsuitable for a potable (drinking water) supply. Dissolved arsenic in one well was more than six times higher than the U.S. Environmental Protection Agency' s maximum contaminant level. However, ground water discharging to the Coeur d'Alene River in the area probably has minimal effects on river water quality because of poor transmissive characteristics of the fine-grained valley sediments. Hydraulic conduc- tivity values are between 1.0 x 100 and 6.3 x 100 feet per day, calculated from slug-test data from three of the six monitoring wells installed for this study; the ground-water-flow gradient is 0.0015 or less, determined from the water-level contour map; and the valley sediments are about 400 feet thick. Although the sediments near Killarney Lake do not transmit large quantifies of water, coarser grained sediments upstream from Killarney Lake. Because sediments along the Coeur d'Alene River are contaminated downstream from the South Fork Coeur d'Alene River near Enaville, where mining wastes were discharged for more than 100 years, it is possible that ground water near Cataldo could contribute significant quantities of contaminants to the Coeur d'Alene River.