LINKING ABANDONED MINE REMEDIATION TO ENVIRONMENTAL GEOCHEMISTRY, AQUATIC RECOVERY, AND THE VALUE OF RECREATIONAL ANGLING IN CENTRAL COLORADO

Remediation of abandoned mine sites typically aims to restore impaired water, soil, and sediment quality to concentrations that are in compliance with regulatory guidelines. A consequence of remediation is the restoration of numerous ecosystem services – final ecosystem outputs that benefit people. This study evaluated approaches for the valuation of ecosystem services affected by mine remediation. The California Gulch (Leadville district) and Eagle Mine (Gilman district) Superfund sites in central Colorado were chosen due to the availability of geochemical, biologic, and economic data for their respective watersheds. In these watersheds, one ecosystem service endpoint that links the natural and social science models for the purpose of ecosystem service valuation is the brown trout population for recreational angling.

In both districts, mining of carbonate-hosted Pb-Zn-Ag deposits resulted in waste rock and mill tailings disposed on the surface. The water-quality issues have largely been addressed through source control – removal and disposal of solid mine waste, or active treatment of effluent from mine tunnels. Most of the remedial activities in both watersheds were completed between 2000 and 2001. Downstream exceedances of water-quality criteria for aquatic life protection in both watersheds before remediation and during recovery have been dominated by Zn (68 to 80 %), Cd (10 to 20 %), and Cu (10 %). The reductions of contaminants due to remediation have resulted in increases in the abundance of aquatic macroinvertebrates and fish. The growth in trout populations has been modeled using the logistic function, which uses a starting population, a growth rate, and a carrying capacity as inputs. Specific sites that fall significantly below the predicted populations typically have residual, ongoing environmental issues such as fluvial tailings or seepage of leachate from waste piles.

Ecosystem service valuation is used to estimate the change in net economic value of the increased trout population to recreational anglers. The technique of benefit transfer is employed to apply value estimates for brown trout angling, from the literature, to the two sites in question.The resulting value estimate for the recovery in brown trout population is significantly below the amount expended on remediation.