|
Conclusions
<br />The use of leaching tests like the 5-minute USGS field leach test are very effective in providing
<br />geochemical data to investigators. Data produced from these tests aid in predicting the geochemical
<br />characteristics of runoff from historical mine-waste piles. Leachate geochemical data can be used to
<br />fingerprint individual historical mine-wastes, that is, to establish the unique leachate geochemical signature
<br />for a mine-waste pile. When used as an assessment tool on a number of mine-waste piles, geochemical
<br />fingerprints from individual mine-waste can be compared to the geochemical signature of other piles. These
<br />comparisons allow an investigator to identify the worst point-source contributors to stream-water-quality
<br />degradation. Comparison of the leachate geochemical fingerprints from the 13 mine-wastes included in this
<br />study revealed significant differences in the geochemical characteristics from mine-wastes located in
<br />adjacent basins.
<br />I found that it is also effective to look at changes in leachate geochemistry over time. Comparison
<br />of changes in leachate geochemistry after the 5-minute leach test (simulated cloudburst) to those produced
<br />from the longer term 18-hour leach test showed that not all leachates behave in a similar manner, even
<br />though they were derived from mine-waste piles located relatively close together. Whereas comparative
<br />time trends for all 13 sites for pH, specific conductance, and sulfate correlated well, major- and trace-
<br />element concentration changed, sometimes dramatically, as the leachate pH went up or down over time.
<br />Leachate time trends showed that some wastes are net acid producing, while others are net acid consuming
<br />over time. It was interesting to note that, even though pH went up over time in leachates from the Santiago
<br />and Waldorf mine-wastes, these two wastes produced some of the most potentially toxic leachate
<br />geochemical profiles of all the sites studied.
<br />Finally, the use of leaching tests in conjunction with ranking protocols like those presented here is
<br />a very useful tool in showing which mine-wastes have the most potential to produce toxic runoff. Use of a
<br />consistent ranking criteria for basin-to-basin comparison can reveal which drainage basins contain mine-
<br />waste piles having the most impact on tributary river systems, as well as which individual mine-waste piles
<br />may be the greatest contributors as point-source inputs for water-quality problems. Examples of the use of
<br />relative ranking schemes given in this paper show that, according to the leachate geochemical data from the
<br />mine-wastes included in this study and the criteria used for this investigation, the mine-waste piles with the
<br />most toxic geochemical profiles were produced from mines in the Leavenworth drainage basin (Waldorf
<br />and Santiago mines); whereas mine-waste piles located in the Deer Creek drainage basin generally had less
<br />potential for producing highly toxic leachates.
<br />References
<br />du Bray, Edward A., 1995, Preliminary compilation of descriptive geoenvironmental mineral deposit models: U.S.
<br />Geological Survey Open-File Report 95-0831.
<br />Fey, D.L., Church, S.E., Unruh, D.M., and Bove, D.J., 2002, Water and sediment study of the Snake River watershed,
<br />Colorado: U.S. Geological Survey Open-File Report 02-0330.
<br />Hageman, Philip L., 2002, Mercury in water by flow injection-cold vapor-atomic fluorescence spectrometry, in Taggart,
<br />Analytical methods for chemical analysis of geologic and other materials: U.S. Geological Survey Open-File
<br />Report 02-0223.
<br />Hageman, Philip L., and Briggs, Paul H., 2000, A simple field leach for rapid screening and qualitative characterization of
<br />mine-waste material on abandoned mine lands, in ICARD 2000: Proceedings from the Fifth International
<br />Conference on Acid Rock Drainage, Denver, Colorado, May 21-24, 2000: Society for Mining, Metallurgy,
<br />and Exploration, Inc., p. 1463-1475.
<br />Hageman_SIR_2508.doc 10 7/21/2004 2:50 PM
|