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
Application of the Solute-Transport Models OTIS and OTEQ and Implications
for Remediation in a Watershed Affected by Acid Mine Drainage, Cement Creek,
Animas River Basin, Colorado
By Katherine Walton-Day, Robert L. Runkel,
Briant A. Kimball, and Kenneth E. Bencala
ABSTRACT
The solute-transport model OTIS and the reactive solute-transport model OTEQ
were used to simulate geochemical conditions in Cement Creek, a tributary to
the Animas River in southwestern Colorado. Results with OTIS indicated that
removal of iron and zinc is required to simulate observed stream conditions
on September 20, 1996. Two remediation scenarios that depicted remediation of
lesser and greater amounts of zinc from Prospect and Ohio Gulches and the May
Day Dump indicated that these actions would reduce zinc concentrations at the
mouth of Cement Creek by 7 percent and 13 percent, respectively. OTIS simulations do not account for the effects of changing stream pH on metal concentrations. OTEQ is used to quantify these effects. Preliminary OTEQ simulations indicated that precipitation of ferrihydrite improved the agreement between simulated and observed pH in the mixing zone of Illinois Gulch and Cement Creek. However, observed zinc removal in this zone was not successfully simulated due to the
spatial nature of the mixing process and lack of data about the identity and
thermodynamic properties of precipitates forming in the mixing zone. Use of
OTEQ to simulate remediation requires a better understanding of the processes
that occur in streams affected by acid mine drainage.
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