Persistent Science Challenges in Legacy Mine Land Site Management
The objective of this project is to provide targeted research results to benefit cooperators managing legacy mine land sites in the western U.S. by addressing three persistent scientific challenges: (1) determining the contribution of mining-related metal sources to water quality degradation when substantial natural background metal sources are also present; (2) adequately characterizing key processes controlling the storage and transport of metals in and on solid phases; and (3) obtaining sufficient information on the deeper mountain-block groundwater flow and metal transport system to determine whether and where to install structural bulkheads in draining mine tunnels.
Science Issue and Relevance
Considerable progress has been made in the restoration of legacy mine land (LML) sites in the western U.S., yet many sites continue to negatively impact stream ecosystems and water resources. In some cases, the primary impediments to additional reclamation work are financial or regulatory, but in many others the challenges are mainly scientific such that it remains unclear how to prioritize and best implement additional work. Development and improvement of site assessment methods and process-level understanding are needed to overcome these scientific challenges and advance remediation efforts at LML sites.
Methods to Address Issue
The project includes five Tasks that focus on different legacy mine land site characterization challenges and/or study locations.
Task 1: Natural background metal sources in mountain headwaters
Task 1 addresses uncertainties in natural background metal contributions that complicate remedial decisions in mountain headwaters. Work consists primarily of a site investigation in the East Mancos watershed, Colorado, aimed at distinguishing mining-related metal sources from co-located apparent natural background sources through the application and further development of a new bank-specific stream mass loading characterization method developed under a prior project. Work also includes the establishment of a natural acid-rock drainage monitoring network within the Colorado Mineral Belt to better assess and understand the extent and causes of recent increases in stream metal concentrations in mineralized watersheds apparently tied to climate warming.
Task 2: Metal(loid) mobility and sequestration involving solid phases
Task 2 addresses challenges related to currently inadequate characterization and understanding of metal(loid) mobility and sequestration involving solid phases at many LML sites. Work mainly includes site studies at Tomichi Creek, Colorado, and the Iron Mountain Mine, California, along with laboratory studies, aimed at developing: (a) new approaches for sediment collection and characterization to quantify the residence and movement of sediment-bound metal(loid)s under different hydrological conditions; and (b) new process-level understanding of metal(loid) attenuation in solid-phases and bioavailability/bioaccessibility that can be applied to geochemical models and inform remediation strategies.
Task 3: Mountain-block groundwater flow and metal transport
Task 3 addresses challenges presented by uncertainties in deeper mountain-block groundwater flow and metal transport systems. Work involves a site investigation at the Perigo Mine in the Colorado Front Range where bulkhead installation is being considered to control mine-tunnel drainage. Two deep bedrock boreholes are being drilled to enable the application and further developed of an integrated discrete-depth hydrologic, geophysical, and geochemical data collection approach recently developed under a prior project. Results will be combined with those from surface geophysical surveys and novel hydrogeophysical monitoring studies to provide key information on the groundwater flow and metal transport system at various depths in the vicinity of the mine tunnel.
Task 4: Idaho Cobalt Mineral Belt (CMB) studies supporting mine waste reclamation
Task 5: Idaho Cobalt Belt Structural Controls
Tasks 4 and 5 involve studies in the Idaho Cobalt Belt that integrate aspects of all three of the scientific challenges addressed in Tasks 1-3. Task 4 work aims to evaluate the effectiveness of mine site remediation in Panther Creek and its tributaries, investigating physical and biogeochemical processes affecting the mobilization of trace metals from mine wastes relative to background geologic sources. A central focus is determining the impact of the 2022 Moose Fire on trace metal mobility from mine wastes. Task 5 work involves geologic mapping and a detailed Pb-isotopic study within the Idaho Cobalt Belt to provide more information on mineralization, geologically-controlled groundwater flow pathways, and background As, Co, and Cu concentrations within the Panther Creek watershed and surrounding region.
The objective of this project is to provide targeted research results to benefit cooperators managing legacy mine land sites in the western U.S. by addressing three persistent scientific challenges: (1) determining the contribution of mining-related metal sources to water quality degradation when substantial natural background metal sources are also present; (2) adequately characterizing key processes controlling the storage and transport of metals in and on solid phases; and (3) obtaining sufficient information on the deeper mountain-block groundwater flow and metal transport system to determine whether and where to install structural bulkheads in draining mine tunnels.
Science Issue and Relevance
Considerable progress has been made in the restoration of legacy mine land (LML) sites in the western U.S., yet many sites continue to negatively impact stream ecosystems and water resources. In some cases, the primary impediments to additional reclamation work are financial or regulatory, but in many others the challenges are mainly scientific such that it remains unclear how to prioritize and best implement additional work. Development and improvement of site assessment methods and process-level understanding are needed to overcome these scientific challenges and advance remediation efforts at LML sites.
Methods to Address Issue
The project includes five Tasks that focus on different legacy mine land site characterization challenges and/or study locations.
Task 1: Natural background metal sources in mountain headwaters
Task 1 addresses uncertainties in natural background metal contributions that complicate remedial decisions in mountain headwaters. Work consists primarily of a site investigation in the East Mancos watershed, Colorado, aimed at distinguishing mining-related metal sources from co-located apparent natural background sources through the application and further development of a new bank-specific stream mass loading characterization method developed under a prior project. Work also includes the establishment of a natural acid-rock drainage monitoring network within the Colorado Mineral Belt to better assess and understand the extent and causes of recent increases in stream metal concentrations in mineralized watersheds apparently tied to climate warming.
Task 2: Metal(loid) mobility and sequestration involving solid phases
Task 2 addresses challenges related to currently inadequate characterization and understanding of metal(loid) mobility and sequestration involving solid phases at many LML sites. Work mainly includes site studies at Tomichi Creek, Colorado, and the Iron Mountain Mine, California, along with laboratory studies, aimed at developing: (a) new approaches for sediment collection and characterization to quantify the residence and movement of sediment-bound metal(loid)s under different hydrological conditions; and (b) new process-level understanding of metal(loid) attenuation in solid-phases and bioavailability/bioaccessibility that can be applied to geochemical models and inform remediation strategies.
Task 3: Mountain-block groundwater flow and metal transport
Task 3 addresses challenges presented by uncertainties in deeper mountain-block groundwater flow and metal transport systems. Work involves a site investigation at the Perigo Mine in the Colorado Front Range where bulkhead installation is being considered to control mine-tunnel drainage. Two deep bedrock boreholes are being drilled to enable the application and further developed of an integrated discrete-depth hydrologic, geophysical, and geochemical data collection approach recently developed under a prior project. Results will be combined with those from surface geophysical surveys and novel hydrogeophysical monitoring studies to provide key information on the groundwater flow and metal transport system at various depths in the vicinity of the mine tunnel.
Task 4: Idaho Cobalt Mineral Belt (CMB) studies supporting mine waste reclamation
Task 5: Idaho Cobalt Belt Structural Controls
Tasks 4 and 5 involve studies in the Idaho Cobalt Belt that integrate aspects of all three of the scientific challenges addressed in Tasks 1-3. Task 4 work aims to evaluate the effectiveness of mine site remediation in Panther Creek and its tributaries, investigating physical and biogeochemical processes affecting the mobilization of trace metals from mine wastes relative to background geologic sources. A central focus is determining the impact of the 2022 Moose Fire on trace metal mobility from mine wastes. Task 5 work involves geologic mapping and a detailed Pb-isotopic study within the Idaho Cobalt Belt to provide more information on mineralization, geologically-controlled groundwater flow pathways, and background As, Co, and Cu concentrations within the Panther Creek watershed and surrounding region.