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Transport of Radionuclides to the Rio Grande

This document discusses the history of monitoring radioactivity in the Rio Grande and the sources of radioactivity in the river. It also examines the concentrations of radionuclides in the river and the potential human health risks associated with them. Additionally, it assesses the risks to aquatic organisms and provides an estimate of the radioactivity risk to these organisms. The document concludes that radionuclide concentrations in the Rio Grande are within acceptable levels for human health and below screening values for aquatic organisms.

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Transport of Radionuclides to the Rio Grande

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  1. Transport of Radionuclides to the Rio Grande Bruce Gallaher gallaher@lanl.gov Middle Rio Grande Water Quality Summit October 25, 2004 LA-UR-04-7342

  2. LANL Monitoring History • Regular LANL testing of Rio Grande sediments started in 1970s • Emphasis on radioactivity • Longer-lived isotopes (241Am,137Cs, 238Pu, 239Pu, 90Sr, Uranium) • Less water column testing • Complemented by fish testing LA-UR-04-7342

  3. Monitoring Stations LA-UR-04-7342

  4. Sources of Radioactivity in Rio Grande • World-wide fallout • Natural uranium • Old Manhattan Project Site (mostly 239Pu) • Traced 40+ km from site into Rio Grande and Cochiti Reservoir LA-UR-04-7342

  5. Concentrations in Rio Grande Influenced Largely by Sediment Loads Flow diagram for the annual budget for suspended sediment in the northern and middle Rio Grande Source: Graf 1994 LA-UR-04-7342

  6. Cerro Grande Fire Accelerated Transport of Radioactivity • Fallout 137Cs and 90Sr in ash • Old Manhattan Project 239Pu Source: Gallaher and Koch, 2004 LA-UR-04-7342

  7. Trends in Cochiti Reservoir Sediments Cesium-137 Plutonium-239,240 Background Limit LA-UR-04-7342

  8. Human Health Risks • Three separate teams assessed combined risks to post-fire users of Rio Grande • Over 100 chemicals and radioactive substances studied • Drinking water and eating fish primary exposure (137Cs, RDX, benzo(a)pryene) • Conclusions • Risks within EPA acceptable levels • Below international radiological dose guides • Not significantly higher than pre-fire risk levels LA-UR-04-7342

  9. Risks to Aquatic Organisms • No known detailed studies of radiological impacts on Rio Grande aquatic populations • We can estimate risks • Screening values • Whole effluent toxicity tests • Fish tissue analyses • NMED/FWS Intensive Surveys, etc. LA-UR-04-7342

  10. Estimate Radioactivity Risk To Aquatic Organisms • We assembled concentration data for 9 key radionuclides for Rio water and sediment • 25 to 60 results for each radionuclide since 1990 • Compared data to DOE screen values • DOE Biota Concentration Guides (DOE-STD-1153-2002) • Based on dose exposure of < 1 rad/d • Deleterious effects in aquatic populations not expected below this dose • All results below the screening values LA-UR-04-7342

  11. Whole Effluent Toxicity Testing • No tests on Rio Grande waters • LANL/NMED tested Los Alamos surface waters for one year after fire • No acute toxicity • Two of 15 samples showed chronic toxicity (ash-ladened samples.) Daphnia Fat head minnow LA-UR-04-7342

  12. Summary • Probably already have seen highest concentrations in Rio Grande • Long-term radionuclide concentrations in Rio Grande should stabilize near or slightly above fallout or natural levels • For human health, rad concentrations within EPA acceptable levels • For aquatic organisms, rad concentrations below DOE screening values • No tests of rad toxicity in Rio Grande on aquatics LA-UR-04-7342

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