Processes Controlling Fate and Transport of Metals Associated with Legacy Mining

Science Center Objects

The project goal is to investigate best approaches to integrating conceptual, (bio)geochemical, hydrological, and toxicological models to improve prediction of metal mobility and remediation at legacy mine land (LML) sites.

Science Issue and Relevance

Management of legacy mine lands is an important ongoing issue for the Federal government, as the majority of affected lands and waters are on or bordered by Federally managed lands, including Bureau of Land Management (BLM), U.S. Forest Service (USFS), and National Park Service (NPS), and often require taxpayer money to remediate and restore. Legacy management issues, such as scaling in acid mine drainage impacted pipelines, waste containment failures, and effects of extreme events  (storms, flooding, drought, fire), cost site managers hundreds of thousands of dollars each year.

Processes controlling metals at legacy mine sites

Process-based understanding of metal fate and transport in the environment is needed to effectively clean up legacy mine land sites. Metal mobility in affected environments depends on the:

  1. mineralogy of mineral source,
  2. abundance and concentrations of metals,
  3. reactivity (redox, water-rock, biological), and
  4. hydrology of system.

Furthering the knowledge of the processes governing these influences will benefit cleanup efforts.

Geochemical modeling: Knowledge Gaps

  • Geochemical modeling of metal mobility and transport at mine sites is often conducted with a limited data and process-level understanding (i.e., large gaps or assumptions in the conceptual model), which increases the uncertainty of model results and limits the usefulness of a quantitative model for site management
  • Hydrological, geochemical, and toxicological models are often developed separately and inherently lack the interrelated connections observed in environmental systems.

Methods to Address Issue

Our project uses detailed mechanistic information derived from laboratory and field studies to integrate conceptual, geochemical, microbiological, hydrological, and bioavailability models and to test model performance against field conditions. Our approach is to holistically connect mineralogy, water chemistry, microbiology, bioavailability, and hydrology through geochemical modeling.

Our project has integrated tasks, combining laboratory-derived, process-level knowledge with field-based, site-specific data to develop scientifically rigorous conceptual and quantitative geochemical models for legacy mine land sites. The geochemical
model will also be developed with hydrological and bioavailability models to demonstrate the advantage of a cohesive approach.

Linking Coupled Biogeochemical Processes and Geochemical Modeling - fundamental biogeochemical processes will be studied in both the laboratory and the field, with the goal of developing and improving approaches to geochemical modeling for legacy mine land site management. Work continues field and laboratory studies linked to the development of geochemical models at Iron Mountain Mine (near Redding, CA) and Leviathan Mine (in CA near Reno, NV). Both are EPA Superfund sites with extensive previous and ongoing research activities. Continued work at these sites will challenge and improve developed models. We will also develop biogeochemical models for sites impacted by natural sulfide weathering and/or moderately impacted by mining.

Iron Oxide Mineralogy and Controls on Metal Mobility - we will address a fundamental knowledge gap in our understanding of metal mobility in mine drainage. Specifically, iron oxides are a critical sink for metals in mine drainage, yet the fundamental controls of their formation, stability, and fate of associated metals are not well understood. Constraining the geochemistry of iron oxides will improve modeling of the long-term fate of mineral precipitates and associated metals for legacy mine land site waste management as well as potential metal recovery efforts.

MiniSippers-Analytical and Field-based Methods - the accuracy and predictive capability of geochemical models are often limited by the low temporal resolution of the water quality data inputs. MiniSippers are automated water samplers that collect, filter and preserve samples at predetermined time intervals. We will deploy MiniSippers at field study sites to automatically collect high temporal resolution water samples. MiniSippers can collect ~250 water samples with daily or sub-daily sampling resolution and run for 12 months. We will continue to develop and deploy novel field-based sampling techniques designed for reliable, high-resolution water sampling of mine-impacted waters.

Geochemical and Environmental Impacts Mapping -  integrate relevant USGS rock, water, soil, and USGS/other agency groundwater data with geologic and hydrologic data to address environmental and mineral assessment issues on a broad regional scale. 

Integrated Studies of the Mobility and Bioaccessibility of Mississippi-valley Type (MVT) Elements: conduct regionally focused (county level) research on the biotic and human health impacts of major and trace elements to fully characterize the pathways linking natural and mining-related elemental sources and biotic receptors.

 

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