Transport of Radionuclides to the Rio Grande

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Transport of Radionuclides to the Rio Grande

• Bruce Gallaher
• gallaher_at_lanl.gov
• Middle Rio Grande Water Quality Summit
• October 25, 2004

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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

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Monitoring Stations
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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

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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
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Cerro Grande Fire Accelerated Transport of
Radioactivity

• Fallout 137Cs and 90Sr in ash
• Old Manhattan Project 239Pu

Source Gallaher and Koch, 2004
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Trends in Cochiti Reservoir Sediments
Cesium-137
Plutonium-239,240
Background Limit
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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

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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.

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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 lt 1 rad/d
• Deleterious effects in aquatic populations not
  expected below this dose
• All results below the screening values

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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
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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

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