Arsenic and chloride data for five stream sites in the Madison River drainage, Montana, 1988

Enriched geothermal waters in Yellowstone National Park contribute large quantities of arsenic to the Madison River. Because arsenic may be acutely or chronically toxic to humans when ingested, it is of concern in the upper Missouri River basin where the water is used for domestic purposes. In passage of water downstream, concentrations of arsenic in the Madison and Missouri Rivers are diluted by tributary inflows. However, insufficient information existed to describe concentrations during runoff at specific locations. As a result, a monitoring network was established to better define arsenic concentrations during the 1988 peak runoff and during periods prior to and following the runoff. In addition to arsenic, samples were analyzed for chloride because of its association with geothermal water and specific conductance because it is a surrogate measure of dissolved-solids concentration. This report presents data acquired during 1988 at five sampling stations in the Madison River drainage. (USGS)