U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 1 of 3--Contamination From Hard-Rock Mining, Water-Resources Investigation Report 99-4018A

Colloid Formation and the Transport of Aluminum and Iron in the Animas River Near Silverton, Colorado

By Laurence E. Schemel, Briant A. Kimball and Kenneth E. Bencala

This report is available in pdf format : schemel1.pdf 62KB

ABSTRACT

Flows and concentrations of dissolved and colloidal aluminum (Al) and iron (Fe) were measured in the upper Animas River to identify sources of colloids and quantify their transport. Colloidal Al and Fe are important in this reach of the river near Silverton, Colorado, because of effects on river bed habitat, macroinvertebrates, and fish. The largest sources of Al and Fe to the river were Cement Creek (42 percent of the total load) and Mineral Creek (56 percent of the total load). Acidic inflow from Cement Creek (pH 3.8) supplied dissolved Al that formed colloids as it was neutralized upon mixing in the Animas River. The Al supplied by Mineral Creek was colloidal, and nearly all of the Al in the Animas River was colloidal. Both creeks supplied Fe in dissolved and colloidal form. Some colloidal Fe formed in the mixing zone downstream of Cement Creek, and colloidal Fe continued to form downstream in the river as dissolved Fe was oxidized. Although colloidal Al and Fe accumulated on the river bed, transports measured in this 2.5 km reach of the river showed that losses of Al and Fe from the water column as a result of colloid formation were less than 10 percent of the total transport.