Geochemical and Descriptive Data for Sedimentary Aquifer Materials in Southwestern Idaho

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Status: Completed

Introduction

Elevated arsenic concentrations in ground water in Idaho have been reported in several recent studies (Howarth, 1995; Welch and others, 1999, 2000; Neely, 2002). The issue of arsenic in drinking water in Idaho—particularly in southern and southwestern Idaho&mash;recently has taken on increased urgency because the newly established U.S. Environmental Protection Agency (EPA) maximum contaminant level (MCL) of 10 micrograms per liter (ug/L), lowered from 50 ug/L, has drastically increased the number of domestic and public-supply wells that will not meet the 2006 MCL compliance deadline.

Statewide, arsenic concentrations exceeded the new MCL in at least one sample from about 15 percent of the tested wells. In southwestern Idaho, arsenic concentrations exceeded the new MCL in more than 40 percent of tested wells (Neely, 2002). The cost of removing dissolved arsenic from drinking water is expected to be high and probably will not be a viable alternative for most water users and providers in the near future.