Insights gained from stable isotopes and environmental tracers in this study allow a conceptual model to be built that provides information pertinent to groundwater mixing and transport, sulfide oxidation mechanisms, and timeframes of remediation. This conceptual model of the site (not to scale) is based on hydrologic and geochemical data.
Isotopic and environmental tracers for improved understanding of geochemical and hydrologic processes occurring near flooded mine workings
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By Colorado Water Science Center
August 24, 2023
Draining mine tunnels contribute metals and acidity to streams throughout the western United States. One remediation strategy that is increasing in usage is the emplacement of hydraulic bulkheads to impound water within the subsurface. Potential secondary effects of bulkhead usage are difficult to quantify however because of the inherent complexity of most mountain hydrologic systems.
In cooperation with the U.S. Environmental Protection Agency (EPA), the U.S. Geological Survey (USGS) is working to investigate processes controlling groundwater flow and acid mine drainage (AMD) geochemistry in several locations with hydraulic bulkheading. This research assists in understanding the potential efficacy of the bulkhead remediation strategy at other locations within the western United States.
In order to gain understanding of the hydrologic and geochemical processes occurring in the subsurface, the USGS collects water-quality data from draining mines, groundwater wells, and springs. A comprehensive suite of water-quality parameters is utilized including trace metals, rare earth elements (REE), stable isotopes, tritium, carbon-14, and noble gases. These water-quality data are paired with hydrologic evaluation of the groundwater-flow regime to quantify hydrological and geochemical processes affecting water quality in flooded mine workings, which can inform remedial decisions.
Results
Results from the Captain Jack mine site, located west of Boulder, Colorado, indicated that the groundwater system is disconnected and that the water within the mine workings has very little connection to the groundwater in the adjacent bedrock. Extremely high hydraulic gradients are maintained between the bedrock and mine groundwaters, even when water is impounded within the mine workings (see figure below).
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Based on stable isotopes and groundwater age indicators it appears that old groundwater sustains high metal concentrations flowing into the impounded mine water and that sulfide oxidation (the process that generates AMD) can still occur when the workings are flooded (see figure below).
Sources/Usage: Public Domain. View Media Details
Related Links
EPA Superfund Site: Captain Jack Mill, Ward, CO - https://cumulis.epa.gov/supercpad/cursites/csitinfo.cfm?id=0800892
Geochemistry, mineralogy, and acid-generating behaviour of efflorescent sulphate salts in underground mines in Nevada, USA - https://doi.org/10.1144/geochem2018-074
Conceptual model of groundwater site
Insights gained from stable isotopes and environmental tracers in this study allow a conceptual model to be built that provides information pertinent to groundwater mixing and transport, sulfide oxidation mechanisms, and timeframes of remediation. This conceptual model of the site (not to scale) is based on hydrologic and geochemical data.
Vertical and horizontal gradients in groundwater level elevations
Groundwater level elevations within the mine workings (indicated by the red dotted lines) and within crystalline bedrock outside the mine workings (indicated by the blue dotted lines) are substantially different from one another.
Groundwater level elevations within the mine workings (indicated by the red dotted lines) and within crystalline bedrock outside the mine workings (indicated by the blue dotted lines) are substantially different from one another.
Captain Jack Superfund Site, Boulder County, Colorado
The Captain Jack site is located in mountainous terrain northwest of Boulder, Colorado. Here the terrain is visible behind an old train track leading into a mine adit.
Location: Captain Jack Superfund site, Boulder County, Colorado
The Captain Jack site is located in mountainous terrain northwest of Boulder, Colorado. Here the terrain is visible behind an old train track leading into a mine adit.
Location: Captain Jack Superfund site, Boulder County, Colorado
Calcite Precipitation at Captain Jack Superfund Site, Boulder County, CO
Interactions between water and minerals in the subsurface (including efflorescent sulfate salts and calcite such as this sample from the Big Five adit) are a primary control on water quality in mining environments. Research is evaluating the importance of these minerals in generating acid mine drainage.
Interactions between water and minerals in the subsurface (including efflorescent sulfate salts and calcite such as this sample from the Big Five adit) are a primary control on water quality in mining environments. Research is evaluating the importance of these minerals in generating acid mine drainage.
Draining mine tunnels contribute metals and acidity to streams throughout the western United States. One remediation strategy that is increasing in usage is the emplacement of hydraulic bulkheads to impound water within the subsurface. Potential secondary effects of bulkhead usage are difficult to quantify however because of the inherent complexity of most mountain hydrologic systems.
In cooperation with the U.S. Environmental Protection Agency (EPA), the U.S. Geological Survey (USGS) is working to investigate processes controlling groundwater flow and acid mine drainage (AMD) geochemistry in several locations with hydraulic bulkheading. This research assists in understanding the potential efficacy of the bulkhead remediation strategy at other locations within the western United States.
In order to gain understanding of the hydrologic and geochemical processes occurring in the subsurface, the USGS collects water-quality data from draining mines, groundwater wells, and springs. A comprehensive suite of water-quality parameters is utilized including trace metals, rare earth elements (REE), stable isotopes, tritium, carbon-14, and noble gases. These water-quality data are paired with hydrologic evaluation of the groundwater-flow regime to quantify hydrological and geochemical processes affecting water quality in flooded mine workings, which can inform remedial decisions.
Results
Results from the Captain Jack mine site, located west of Boulder, Colorado, indicated that the groundwater system is disconnected and that the water within the mine workings has very little connection to the groundwater in the adjacent bedrock. Extremely high hydraulic gradients are maintained between the bedrock and mine groundwaters, even when water is impounded within the mine workings (see figure below).
Sources/Usage: Public Domain. View Media Details
Based on stable isotopes and groundwater age indicators it appears that old groundwater sustains high metal concentrations flowing into the impounded mine water and that sulfide oxidation (the process that generates AMD) can still occur when the workings are flooded (see figure below).
Sources/Usage: Public Domain. View Media Details
Related Links
EPA Superfund Site: Captain Jack Mill, Ward, CO - https://cumulis.epa.gov/supercpad/cursites/csitinfo.cfm?id=0800892
Geochemistry, mineralogy, and acid-generating behaviour of efflorescent sulphate salts in underground mines in Nevada, USA - https://doi.org/10.1144/geochem2018-074
Conceptual model of groundwater site
Insights gained from stable isotopes and environmental tracers in this study allow a conceptual model to be built that provides information pertinent to groundwater mixing and transport, sulfide oxidation mechanisms, and timeframes of remediation. This conceptual model of the site (not to scale) is based on hydrologic and geochemical data.
Insights gained from stable isotopes and environmental tracers in this study allow a conceptual model to be built that provides information pertinent to groundwater mixing and transport, sulfide oxidation mechanisms, and timeframes of remediation. This conceptual model of the site (not to scale) is based on hydrologic and geochemical data.
Vertical and horizontal gradients in groundwater level elevations
Groundwater level elevations within the mine workings (indicated by the red dotted lines) and within crystalline bedrock outside the mine workings (indicated by the blue dotted lines) are substantially different from one another.
Groundwater level elevations within the mine workings (indicated by the red dotted lines) and within crystalline bedrock outside the mine workings (indicated by the blue dotted lines) are substantially different from one another.
Captain Jack Superfund Site, Boulder County, Colorado
The Captain Jack site is located in mountainous terrain northwest of Boulder, Colorado. Here the terrain is visible behind an old train track leading into a mine adit.
Location: Captain Jack Superfund site, Boulder County, Colorado
The Captain Jack site is located in mountainous terrain northwest of Boulder, Colorado. Here the terrain is visible behind an old train track leading into a mine adit.
Location: Captain Jack Superfund site, Boulder County, Colorado
Calcite Precipitation at Captain Jack Superfund Site, Boulder County, CO
Interactions between water and minerals in the subsurface (including efflorescent sulfate salts and calcite such as this sample from the Big Five adit) are a primary control on water quality in mining environments. Research is evaluating the importance of these minerals in generating acid mine drainage.
Interactions between water and minerals in the subsurface (including efflorescent sulfate salts and calcite such as this sample from the Big Five adit) are a primary control on water quality in mining environments. Research is evaluating the importance of these minerals in generating acid mine drainage.