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Science for Watershed Decisions on Abandoned Mine Lands: Review of Preliminary Results, Denver, Colorado, February 4-5, 1998

Seasonal Fluctuations of Discharge and Dissolved Constituents from Selected Abandoned Mines in the Upper Animas River Watershed, Colorado

By Winfield G. Wright,¹ Kenneth J. Leib,² and M. Alisa Mast³

Water draining from two abandoned mines—the Evelyn and Forest Queen—in the upper Animas River watershed was sampled monthly during 1996-97 to determine the ranges of discharge and dissolved-constituent concentrations for remedial-design parameters and to describe the effects of snowmelt runoff on discharge from the mines. The discharge from the Evelyn Mine ranged from 0.01 to 0.03 cubic feet per second; there were no appreciable increases in discharge from the mine during the snowmelt-runoff period in 1997. However, concentrations of dissolved aluminum, iron, manganese, sulfate, and zinc in drainage from the Evelyn Mine increased during snowmelt runoff. This trend may indicate that the collapsed mine entrance at the Evelyn Mine possibly is controlling the discharge from the mine or that there is only a small amount of snowmelt-runoff infiltration into the abandoned-mine workings through fractures in bedrock that could increase the oxidation of sulfide minerals but not significantly increase the discharge. The Forest Queen Mine had a greater relative discharge (0.02 to 0.08 cubic feet per second), and the higher discharge correlates with the snowmelt-runoff period. Dissolved-constituent concentrations decreased slightly with increased discharge; however, dissolved-constituent loads more than doubled from the mine. Notably, the pH values from the Forest Queen Mine decreased from about 4.7 to 3.7 during the snowmelt runoff. Data collected from these two mines illustrate the hydrogeochemical variability of water discharging from abandoned mines and indicate that not all mines respond the same to recharge events.

¹U.S. Geological Survey, P.O. Box 3367, Durango, CO 81302 (wgwright@usgs.gov)

²U.S. Geological Survey, P.O. Box 3367, Durango, CO 81302 (kjleib@usgs.gov)

³U.S. Geological Survey, MS 415, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (mamast@usgs.gov)

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