Baseline Ecological Effects Characterization for Terrestrial Receptors in a Semi-Arid Canyon with Perennial Flow. M. F. Tardiff, K. D. Bennett, and D. D. Hickmott, Neptune and Company, Los Alamos National Laboratory
One mission of Los Alamos National Laboratory has been to develop and test explosive components for the United States nuclear weapons program. Historically, effluents from a machining facility containing high explosives and barium 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’s 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. A baseline 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 refinement of preliminary contaminants of concern for the terrestrial resources reduced the contaminants of concern to four metals and two high explosives. The assessment endpoints selected in the problem formulation are the Mexican spotted owl and the biotic structure and complexity of the terrestrial, riparian and aquatic environments associated with flowing water in the canyon. The terrestrial lines of evidence for the baseline assessment are the body burdens of contaminants in prey species for the owl and population characteristics for small mammals. The measurement endpoint rationale, small mammal study design, and the first set of field study results will be presented.
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