Laboratory reports latest stormwater results

Contact: David Lyons, davidlyons@lanl.gov, (505) 665-9198 (00-122)

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LOS ALAMOS, N.M., Sept. 11, 2000 -- Officials at the U.S. Department of Energy's Los Alamos National Laboratory today reported a broad set of stormwater sampling results from summer storms. The results are from two independent laboratories that analyzed stormwater samples collected in June, July and August from runoff generated by storms on and around the Pajarito Plateau, much of which was burned in the Cerro Grande Fire.

These results will be discussed at Friday's regularly scheduled public meeting of the Laboratory and DOE Emergency Rehabilitation Team.

Bruce Gallaher, of the Laboratory's Water Quality and Hydrology Group said that the most significant results are the presence of cyanide in stormwater running onto Laboratory property and heightened levels of fallout radionuclides measured in stormwater sediments. Cyanide and fallout radionuclides have been measured in several storms this summer, but primarily from storms that were centered on highly burned areas and created relatively high flows of water.

Results from some stormwater flows also show elevated levels of metals and common minerals that appear to be from natural sources. The Laboratory continues to receive and analyze these results.

Gallaher said that the presence of cyanide upstream from the Laboratory is most likely the result of fire retardants used in fighting the Cerro Grande Fire. Some of the fire retardants contain cyanide compounds, such as potassium ferrocyanide. The compound is added to the slurry to prevent caking or hardening of the slurry and to protect the tanks on slurry bombers from corrosion. Cyanide has never been used in any significant quantities in Laboratory research or operations.

Laboratory scientists measured cyanide levels in the stormwater runoff as great as five times the New Mexico surface water standard for fisheries. Scientists from the New Mexico Flood Risk Assessment Team, a multi-agency organization led by the New Mexico Department of Health with participation from the Laboratory, plan to evaluate the cyanide readings from a human health standpoint. However, Laboratory officials currently believe that there are no long-term consequences from the cyanide because of the short duration of these storm events and the significant dilution that occurs when stormwater reaches the Rio Grande.

The New Mexico surface water standard for fisheries, a measure of toxicity for fish, is 22 micrograms of cyanide per liter of water. During one storm in Pajarito Canyon, Laboratory scientists collected samples that indicated cyanide levels of 110 micrograms per liter.

In addition to cyanide flowing onto Laboratory property, Gallaher said that his team recorded increased concentrations of radionuclides from worldwide fallout (fallout is the result of atmospheric testing of nuclear weapons conducted during the '50s and '60s) in stormwater sediment, as compared to pre-fire measurements from numerous locations in Northern New Mexico. The increased concentrations were recorded primarily in large storms, such as the June 28 and July 9 storms, that hit a broad swath of the watersheds above the Laboratory.

Fallout radionuclides measured in the suspended sediment found in stormwater were significantly higher than pre-fire levels. Cesium-137 was measured five to 20 times pre-fire levels, plutonium was five to 10 times higher and strontium-90 was two to three times higher. Laboratory scientists recorded the heightened levels in stormwater coming onto and crossing the Laboratory.

"We're continuing to study these results, but we believe that the increases in fallout radionuclides are the result of the fire," Gallaher said. "The results indicate that the fire caused the transfer and concentration of these radionuclides from the forest canopy and in the forest litter to the ashy layer of the burned surface soil."

Gallaher added that this phenomenon has been observed in other locations outside New Mexico that experienced forest fires. The post-fire concentrations of cesium-137 slightly exceed screening action limits for residential use, typically by a factor of 2 or less. Through its role in the FRAT, the Laboratory plans to continue to evaluate the results for potential long-term health effects.

Gallaher said that he and his team have been able to draw some general conclusions based on the results that they have received to date:

For small runoff events, the overall levels of total (gross) alpha and beta radiation levels appear to be comparable to data collected before the fire. Small amounts of Laboratory contaminants are seen in these samples, but they were also seen in pre-fire samples.

Larger storms cause significant changes in the quality of the runoff. These changes are the direct result of the fire. Large storms often drain the heavily burned areas and carry large quantities of black ash and sediment. In a filled stormwater sample container, 25 percent or more of the volume is typically sediment.

The levels of radioactive substances dissolved in stormwater are comparable to or slightly elevated above pre-fire levels in runoff. Dissolved gross alpha and beta levels were found to be below the U.S. Environmental Protection Agency Maximum Contaminant Limits for drinking water systems.

Approximately 90 percent of the radioactivity in an unfiltered stormwater sample from a large storm is associated with the sediment and ash carried by the flood flows. The main sources of radioactivity are naturally occurring radioactive substances in the sediment and ash, such as potassium-40, radon and uranium.

Additional information on stormwater runoff results, as well as data tables, can be found on the Environment, Safety and Health Web site at http://www.esh.lanl.gov/~esh18/teams/CGFire/index.html.

More news releases from the Environment, Safety and Health (ESH) Division