Stream water quality improvements after installation of a passive treatment system

Abstract

Perennial borehole discharges have flowed unabated from abandoned lead-zinc mines in the Tri-State Mining District for 30 years and considerably degraded the physical, chemical, and biological integrity of a first-order tributary to Tar Creek in Ottawa County in northeastern Oklahoma. Water quality has been monitored at the discharges and the receiving tributary monthly since fall 2004. Construction of a large multi-cell passive treatment system was completed in late 2008. Prior to construction of the treatment system, metals loads immediately downstream from the confluence of the discharges and tributary were 163 kg Fe/d, 20 kg Zn/d, 52 g Cd/d, and 106 g Pb/d. In the first year of operation, the passive treatment system has been successful at removing Cd, Pb, and As to below detection limits and Fe and Zn to <1 mg/L. These changes have resulted in substantial decreases in in-stream loading to 23 kg Fe/d, 6 kg Zn/d, 12 g Cd/d, and Pb to below detection limits. Mining influences, upstream of this confluence, continue to degrade water quality. However, the passive treatment system has resulted in significant decreases in metal mass loadings. Copyright © (2010) by the American Society of Mining and Reclamation.