Supplemental arsenic data for selected streams in the Missouri River basin, Montana, 1987

Geothermal waters within Yellowstone National Park contribute arsenic to the Madison River. Concentrations ranging from 200 to 300 micrograms per liter in the Madison River near the park boundary are diluted downstream by tributary inflows to the Madison and Missouri Rivers. However, significant amount of arsenic are present in the water of the Missouri River as it enter Fort Peck Lake. A monitoring network of 24 stations was operated during 1985 and 1986 in the upper Missouri River basin to measure arsenic concentrations and arsenic discharges. Additional monitoring at nine stations was conducted during March to July 1987 to supplement the data base. This report presents data acquired from the 1987 monitoring period. (USGS)