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

Theory and(or) Reality: Analysis of Sulfate Mass-balance at Summitville, Colorado Poses Process Questions About the Estimation of Metal Loadings

By Kenneth E. Bencala and Roderick F. Ortiz

This report is available in pdf format : Bencala.pdf 187KB

ABSTRACT

Characterization of in-stream metal loading from acid mine drainage includes identification of location, discharge, and solute concentrations of inflows to the stream. In using the tracer injection and synoptic sampling method we recognize that drainage from a mine site enters a stream through distributed, dispersed, and ill-defined inflows. The veracity of the method relies upon implicit assumptions related to catchment hydrology, stream hydraulics, and chemical reactivity. As a practical examination of methodology, we analyzed the ambient sulfate data collected during a metal loading characterization of the inactive mine site at Summitville, Colorado. This analysis may be thought of as a 'successive mass-balance comparison.' The results lead us to pose the following issues which can be addressed in further study at acid mine drainage sites:

1. Catchment hydrology: Will extensive chemical sampling in the near-stream zone of the catchment characterize the connections between the stream and its catchment?
2. Stream hydraulics: Will the in-stream water be 'well-mixed' in the complex physical and chemical environments typical of acid mine drainage?
3. Chemical reactivity: Will the amount of sulfate removal be sufficiently slight for this constituent to be useful as an operational ambient tracer?

Although each issue is framed as a methodological issue, resolving each requires study at the process scale. Resolving each of these issues would enhance the degree of process interpretation in the characterization of metal loading using the tracer injection and synoptic sampling method.