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.