INVITED TALK: From Research To Remediation: Some Applications Of Hydrogeochemical Research To Mine Site Remediation
Nordstrom, D. Kirk 1
1 U.S. Geological Survey, Boulder, CO
Research in chemistry, geochemistry, and hydrogeochemistry has been applied successfully to identify the geochemical processes that produce acid rock drainage and determine its fate, and to understand remediation scenarios. When iron in acid drainage fully oxidizes, does the pH always decrease? No, it can increase and chemistry and microbiology are keys to understanding the answer (1). What conditions cause efflorescent salts to form at mine sites? Water, drawn by capillary forces, evaporates to dryness and the efflorescent salts are left. In acid sulfate environments these salts usually form from waters of negative pH and very high metal concentrations (2). Can pH be negative? Not only can it be theoretically, but such low pH waters actually exist at Iron Mountain (2,3). Is mine plugging a reasonable option for treating acid mine drainage flowing from a portal? Probably not, unless you wish to increase the cost and complexity of the problem. Iron Mountain, California and Summitville, Colorado are good examples to prove that point (2). If several alternative remedial options are available with estimates for each of the decrease in loading, can the resultant improvement in stream water quality be predicted? Yes, by applying carefully controlled steady-injection tracer tests combined with synoptic sampling (4). Can ground-water quality before mining be estimated after mining has begun? The Questa project, New Mexico, is one of the first successful examples of this analysis.
(1) Nordstrom, D.K. Modeling low-temperature geochemical processes: in Drever, J.I., vol. ed., Vol. 5, Surface and Ground Water, Weathering and Soils, Treatise on Geochemistry, Holland, H.D. and Turekian, K.K., ex. eds., Elsevier, Amsterdam, 37-72, 2004.
(2) Nordstrom, D.K. and Alpers, C. N. Proc. Nat’l. Acad. Sci. 96, (1999), 3455.
(3) Nordstrom, D.K., Alpers, C.N., Ptacek, C.J. and Blowes, D.W. Envir. Sci. Tech. 34, (2000) 254.
(4) Ball, J.W., Runkel, R.L., and Nordstrom, D.K. Chap. 3, In Environmental Sciences and Environmental Computing. Vol. II, P. Zanetti (ed.), the EnviroComp Institute, 2004, (http://www.envirocomp.org).