Amendments promote Douglas-fir survival on Formosa Mine tailings

While mining provides valuable metals and minerals to meet societal demands, it can cause environmental contamination from unstable mining residuals (tailings). Tailings are often acidic, laden with heavy metals, and lacking adequate nutrients and physical conditions for plant growth, precluding the establishment of plant cover to reduce the offsite movement of mining wastes. This paper describes a case study for the Formosa Mine in Douglas County, Oregon where tailings were amended with a mixture of lime, biosolids, biochar and microbial inoculum to facilitate establishment of Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco) seedlings. Results show that the tailings pH increased, and Douglas-fir seedlings survived and grew with these amendments. After two years, pH did, however, decrease again in select downslope locations, and was associated with an increase tree mortality, with approximately a quarter of the seedlings dying. This suggests amendments will likely need to be reapplied once every year or two, particularly in areas receiving inputs from upslope tailings, until the site is completely reforested. This study not only provides a prescription for addition of biochar and other amendments to enhance plant growth for revegetation purposes in low pH metal-contaminated mine tailings it also demonstrates a method to address similar problems at other mine sites. The product will describe to the Regions and Program Offices a literature review, review of previous site amendment applications, and conduct a case study around a specific site.    The first objective would be to review scientific and Superfund literature where soil amendment practices have been used to remediate soils, sediment, and waste rock (spoil).  Geochemical characteristics of the media (soil, sediment, spoil), contaminant, and amendment will be cataloged along with all experimental outcomes.  This exercise will be used to identify key parameters that would be useful for amendment selection. The second objective will be to revisit sites that have been previously remediated using amendments and evaluate the status to determine if the amendment is still effective and if identified variables were key predictors of success.  The third portion of the product would use the Coeur d’Alene River Basin (CRB) in Idaho, OU3 for the Bunker Hill Superfund Site, as a case study site for verifying identified key parameters and potentially determining additional ones for amendment selection.

Impact/Purpose

Past mining activities in the United States have left a legacy of heavy metal contaminated soils, which need to be cleaned up to allow for healthy plants on the site, and to prevent water and soil pollution. The EPA has regulatory authority, especially under Comprehensive Environmental Response, Compensation, and Liability Act (Superfund) to oversee cleanup of these sites; and responsibility to regions, states and local communities under the Office of Research and Development’s Safe and Healthy Community Research Program to develop new techniques to assist in this cleanup. Of special concern to EPA’s Region 10 is the Formosa mine superfund site in south-central Oregon, which has a large area of mine tailings where it is difficult to establish vegetation. This research was designed to determine if a newly developed technique, addition of biochar to tailings, could assist revegetation efforts. Results show that the tailings pH increased, and Douglas-fir seedlings survived and grew with these amendments. After two years, pH did, however, decrease again in select downslope locations, and was associated with an increase tree mortality, with approximately a quarter of the seedlings dying. This suggests amendments will likely need to be reapplied once every year or two, particularly in areas receiving inputs from upslope tailings, until the site is completely reforested. This study not only provides a prescription for addition of biochar and other amendments to enhance plant growth for revegetation purposes in low pH metal-contaminated mine tailings it also demonstrates a method to address similar problems at other mine sites.

Citation

Johnson, M., D. Olszyk, M. Bollman, Marj Storm, R. Coulombe, M. Nash, V. Manning, K. Trippe, D. Watts, AND J. Novak. Amendments promote Douglas-fir survival on Formosa Mine tailings. American Society of Agronomy, MADISON, WI, 53(5):553-561, (2024). [DOI: 10.1002/jeq2.20587]

DOI: Amendments promote Douglas-fir survival on Formosa Mine tailings