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(109) Ecological effects characterization for multiple contaminants in a perennially flowing canyon on a semi-arid plateau. Tardiff, Mark1, Hickmott, Donald2, Reneau, Steven2, Soholt, Lars2, 1 2 ABSTRACT- One mission of Los Alamos National Laboratory has been to develop explosives formulations, cast and machine explosive charges, and assemble and test explosive components for the United States nuclear weapons program. Historically, effluents containing high explosives, barium and other heavy metals from a machining facility were discharged to Cañon de Valle. These wastewaters were discharged to the canyon for forty years at rates of one to ten million gallons per year making up as much as half of the canyon flow. Effluent discharges to the canyon were discontinued in 1996. Cañon de Valle has a perennial interrupted stream that supports grass and herbaceous ground cover and a multi-layer canopy of conifers, oak and aspen. There is an active nesting site for the Mexican spotted owl, a United States listed threatened species, within foraging range of the contaminated area. An ecological effects characterization is being conducted to evaluate the consequences of the residual legacy contaminant inventory in the canyon. An overview of contaminant distributions in the soils, sediment, surface water and alluvial water will be presented. The screening ecological risk assessment included eleven measurement endpoints and twenty-three contaminants of potential ecological concern. Toxicity reference values were not available for all combinations of endpoints and contaminants. The results of the screening assessment and the approach to problem formulation that reduced the contaminants of concern to six will be described. The assessment endpoints for the baseline ecological risk assessment are the Mexican spotted owl and the biotic structure and complexity associated with flowing water in the canyon. The lines of evidence for the baseline assessment are the body burdens of contaminants in prey species for the owl and population estimates for small mammals. The study design and rationale for the biota sampling to support the baseline ecological risk assessment will also be presented. Key words: site-specific risk assessment, complex mixtures, threatened and endangered species, biota sampling |
