Passive Treatment Opportunities in a Drastically Disturbed Watershed: Reversing the Irreversible?

Abstract

Like many large abandoned mining areas, the Tri-State Mining District of the central US is plagued by numerous environmental problems, including contaminated soils, tailings, waste rock, and water, with subsequent detrimental impacts to human and ecological health. In one of the major basins of the district, the Tar Creek watershed, impacts to surface waters were once deemed to be due to "irreversible man-made damages", resulting in minimal effort to address environmental risk from these legacy mine waters over the past 30 years. However, recent watershed-scale environmental monitoring studies, along with completion and evaluation of a full-scale passive treatment demonstration project, indicate that this may no longer be the case. Evaluation of artesian discharges indicates significant evolution of mine pool water quality (e.g., decreased metal concentrations, increased pH and alkalinity) since first flush. In-stream water quality, although still not meeting designated beneficial uses, has also changed. Substantial surface water degradation due to waste rock and tailings runoff and leachate is still problematic, but large-scale land reclamation (including wholesale removal and underground injection) is ongoing. Conceptual designs for watershed-scale passive treatment implementation have been developed and indicate that both artesian mine discharges and remaining runoff/leachate waters may be treatable in a cost-effective and sustainable manner. Recent voluntary relocation efforts, resulting in the dissolution of historic mining communities, provide opportunities for watershed-scale remediation and restoration. However, long-term operation and maintenance obligations for the proposed passive systems, incorporating the cultural and social needs of Native American tribes, requires sustained commitment of technical and financial resources. Promising initial results, coupled with results from other ongoing remediation efforts, warrant further exploration and reevaluation of previous administrative decisions.

Assessment of Bed Hydraulics and Metal Loadings in a Passive Vertical Flow Bioreactor in Commerce, Oklahoma

“…The branched flow is then recombined into a final polishing pond (C6). The system has been in operation since 2008 and has regularly met its treatment objectives, based on chemical analysis of the PTS outflow (Nairn et al ).…”

“…According to Nairn et al (), most of the treatment is accomplished in the system up to and including ponds C3S and C3N. The aerobic reactions and metal precipitation in ponds 1 and C2S and C2N occur quite uniformly, based on visual inspection of suspended solids and bed sediments, which are bright orange and characteristic of iron oxides and oxyhydroxides.…”