Geochemical & Descriptive Data for Sedimentary Aquifer Materials, Southwestern Idaho
Methods
IDEQ has begun to delineate areas in Idaho called "Arsenic Areas of Concern" to help prioritize attention and resources in areas where arsenic is considered to be most critical to human health. This study focused on the area in southwestern Idaho designated by IDEQ as the "Arsenic Area of Concern—Canyon" and nearby areas.
Silicic volcanic rocks and fine-grained sediments deposited in lacustrine (lake) environments are two lithologies that are known to be associated with high-arsenic waters in the Western United States (Welch and others, 2000). High concentrations (>10 ug/L) of arsenic in ground water in southwestern Idaho are associated with outcrops of the Miocene-Pliocene lakebed deposits of the Glenns Ferry Formation.
It is believed that most domestic and drinking water wells in southwestern Idaho penetrate this formation at depth (Neely, 2002). Samples of aquifer materials in the form of drill cuttings, primarily unconsolidated sands, silts, and clays, from the Glenns Ferry Formation in southwestern Idaho were obtained from various sources. Samples were examined with a binocular microscope and their mineralogy and other notable features were described. Selected samples were analyzed geochemically to determine the concentrations of arsenic and other elements in the aquifer materials.
