ABSTRACT
The Elizabeth Mine, located in South Strafford, Vermont, is one of the oldest and largest hard-rock former metal-sulfide mining sites in New England. The site has been listed on the National Priority List by the United States Environmental Protection Agency (USEPA) and investigations are underway at the site to determine the environmental impact of tailings and waste rock on the surrounding area and downstream receiving waters. This paper presents a preliminary-level ecological risk assessment approach in planning and evaluation to support an early cleanup action. Extensive sampling of surface water, sediments, ground water and soils was conducted to establish the spatial and temporal pattern of contamination in different media. A screening level ecological risk assessment was conducted to identify exposure pathways and contaminants that pose significant risks to ecological receptors. Chemical-specific hazard quotients (HQs) and hazard indices (HIs) were found to be elevated in the immediate vicinity of the source areas, in the Ompompanoosuc River and two affected tributaries. Multiple lines of evidence were used in the evaluation, including surface water and sediment chemistry, surface water and sediment toxicity tests, benthic organism studies, and fish population studies. The measurement endpoints included sediment and water toxicity testing for the site and reference areas, and analyses of composition and structure of the benthic and fish communities in affected sites and selected reference areas. Each line of evidence, independently and in conjunction, confirmed that the site contamination has resulted in significant detrimental effects on ecological receptors. A decrease in chemical concentrations in surface water with distance downstream is correlated with ecosystem recovery, with site-related impacts observed several miles downstream of the source areas. The ecological risk evaluation is critical at a site where the risk basis will be ecological impact rather than human health. The use of ecological risk as a basis for a Non-Time-Critical Removal Action (NTCRA) is not common in the Superfund program. A NTCRA, however, can be an effective way to accomplish rapid risk reduction (ecological or human health). A NTCRA can be implemented at the same time as the Remedial Investigation/Feasibility Study (RI/FS) allowing for prompt risk reduction for the more obvious site hazards while the comprehensive investigation is completed.
