Mercury Concentration and Speciation in Sediments Throughout the Watershed Affected by Black Butte Mine in Oregon
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Date
2018-06
Authors
Cleveland, Rachael
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Abstract
The history of mining in Oregon has left a legacy of contaminated and abandoned sites
that threatens environmental and human health. The goal of this research is to better understand
mercury (Hg) cycling within an Oregon watershed that is being contaminated by an abandoned
mine. The chosen site is the Superfund site at Black Butte Mine, where contaminated sediment
has washed down a series of streams that drain into Cottage Grove Reservoir. The specific
objectives of this work are to determine how Hg sediment concentrations and forms (reactivity)
change from the mine site to the reservoir and how these factors change within the different areas
of the reservoir. Sediment sampling was conducted at the Black Butte Mine site, along drainage
creeks and streams, and throughout the Cottage Grove Reservoir. Sediment composites were
collected and used for total Hg and speciation analysis. The concentrations of mercury decreased
with distance from the mine site to the reservoir. Mercury in sediment was found in
progressively more reactive forms from the mine site to the reservoir. Within the reservoir,
reactivity of Hg was higher in the floodplains that experience seasonal variations than the
permanently inundated areas. The creek immediately adjacent to the mine site posed the most
dangers to human and environmental health in terms of total Hg. Above the mine tailings and at
the reservoir, conditions are supporting the transformation of inorganic Hg to organic Hg. This
information, particularly the forms of mercury found, has significant implications for Hg
bioaccumulation and the resulting safety of humans and species that live within the watershed.
Data gaps in the US Environmental Protection Agency and Oregon Department of
Environmental Quality's previous work on mercury analysis have been filled, which will inform
future work at this site and allow them to target areas of most concern. A new site of organic
mercury transformation has been identified, and future work can address this site. Additionally,
mercury cycling in sediment is now better understood at this site, which will inform future
research looking at mercury cycling at the watershed scale.
Description
33 pages
Keywords
Black Butte Mine, Mercury -- Oregon, Environmental health