Rocky Flats Soil Action Level Project

The Citizen’s Advisory Board at Rocky Flats selected RAC to derive soil action levels to be used as the basis for cleanup and decommissioning of the Rocky Flats Plant near Denver, Colorado. Over a period of 18 months in 1998 and 1999, RAC worked with the Radionuclide Soil Action Level Oversight Panel, which consisted of a mix of technical specialists and individuals with no technical experience drawn from public interest groups, local governments, and the general public. These panel members from a cross section of the community had considerable experience in Rocky Flats issues and were tasked with developing recommendations for soil cleanup.

Ultimately, these recommendations were used as the basis for cleanup at the site. Working with local citizens during the process helped the Department of Energy, the Environmental Protection Agency, and the Colorado Department of Public Health and Environment reach a unified approach to cleanup at the site, which has now been completed. The work was supported by the Rocky Flats Citizen’s Advisory Board.

RAC developed seven realistic scenarios, which served as guides to a range of possible profiles of people who may have been in the area. Working with the panel, RAC considered a number of key factors in the scientific calculation of the radionuclide soil action level (RSAL), including the impact of a fire on the area after cleanup, identifying the limiting scenario, and longevity of institutional controls.

The significant findings from this work included setting the RSAL for plutonium at 10 pCi/gram (370 Bq/kg) and for uranium at 20 pCi/gram (740 Bq/kg). RAC calculated the time of maximum dose for decision making purposes as 2000, the year following the RSAL calculations. The cost of cleanup and the impact of the actual cleanup phase on local residents were not taken into account. This was a public study and the oversight panel’s role was critical and unique in setting a technically-based soil action level.



Till, J.E., G. G. Killough, K. R. Meyer, J. W. Aanenson, and A.S. Rood. 2000. Calculating Soil Action Levels And Uncertainties for Decision-Making During Cleanup of Contaminated Sites. Proc of International Radiation Protection Association. IRPA-10 Plenary Session, PS-2-3, Hiroshima. May.

E. Till, G. G. Killough, K. R. Meyer, J. W. Aanenson, and A.S. Rood. 2004. “Technical Basis and Public Process for Deriving Cleanup Levels at Rocky Flats. Proc. Workshop on Solutions to Security Concerns about Radioactive Legacy of the Cold War that Remain in Urban Environments. International Institute for Applied System Analysis at Vanderbilt University. Nashville, TN. November 14-16, 2004

Assessment of Cerro Grande Fire

Following the Cerro Grande Fire in northern New Mexico in May 2000, the New Mexico Environment Department contracted RAC to perform an independent analysis of the health risks to the public from the fire burning within the boundary of the Los Alamos National Laboratory (LANL) in areas known or suspected to be contaminated with radionuclides and chemicals. The fire, which burned about 45,000 acres over 16 days, released chemicals and radionuclides from the burning and heating of material located in vegetation and soils across the LANL facility and the surrounding area. The work was performed in an open environment so different organizations and members of the public could provide input to and comments on the work as it progressed.

The findings from this work established that the primary health risk during the fire were associated with breathing material released into the air. RAC estimated the risk of cancer from breathing any LANL-derived chemical or radioactive material that may have been carried in the smoke plume to be less than 1 chance in 10 million. Potential exposure in the surrounding communities to LANL-derived chemicals that are not carcinogenic were about 10 times lower than acceptable intakes established by the U.S. Environmental Protection Agency.

Some evidence suggests that some adverse health effects did result from breathing high concentrations of particulate matter in the smoke. Such exposure are associated with any forest fire. Because vegetation was destroyed, the storm water flow through the canyons increased, carrying greater amounts of soil, sediment, and ash from the impacted areas.

Fact Sheet: Releases to Air
Fact Sheet: Releases to Surface Water
Summary Report

(Adobe PDFs)


Grogan, H.A., J.W. Aanenson, P.D. McGavran, K.R. Meyer, S.S. Mohler, H.J. Mohler, J.R. Rocco, and L.H. Wilson, and J.E. Till. 2006. “Applied Modeling of the Cerro Grande Fire at Los Alamos: An Independent Analysis of Exposure, Health Risk, and Communication with the Public.” In Applied Modelling and Computations in Nuclear Science, Oxford University Press. ACS Symposium Series 945. Edited by T.M. Semkow, S. Pommé, S.M. Jerome, and D.J. Strome. American Chemical Society, Washington, DC.


Calculated concentrations of PM10 (particulate matter

Uravan Historical Dose Reconstruction

Union Carbide Corporation and Umetco Minerals Corporation engaged RAC to conduct a historical dose reconstruction of the Uravan milling site, which was located in a narrow canyon formed by the San Miguel River in western Colorado. RAC reconstructed emissions and ambient environmental concentrations of uranium decay series radionuclides from the site for the 49-year period of mill operations from 1936 to 1984. For the work, RAC reviewed numerous documents, visited the site, collected site-specific meteorological data, used independent soil sampling analyses to validate the atmospheric release and deposition model predictions, and conducted interviews with past and current employees. The model results were combined with residence history and lifestyle activity information to estimate radiation doses to former residents of Uravan.

The primary exposure pathway for Uravan residents was breathing air containing uranium and its decay products. The highest air concentrations in the town occurred in the late 1930s through the early 1940s, with lesser concentrations occurring from the mid-1950s through 1980. The complex terrain influenced plume dispersion and tended to result in higher concentrations in housing blocks located downwind (northwest) of the mill facilities than those located upwind (southeast). The salt roaster process and yellowcake dryer were the primary effluent sources for uranium isotopes. It was determined that by 2005 approximately 60% of the deposited uranium had leached from the surface soil.

The town of Uravan no longer exists, having closed in 1986. All the buildings were demolished after closure, except for the Boarding House and the Community Building, which are preserved in a historic district, and the area was remediated by Union Carbide and Umetco.



Rood, A.S., P.G. Voillequé, S.K. Rope, H.A. Grogan, and J.E. Till, 2008. “Reconstruction of Atmospheric Concentrations and Deposition of Uranium and Decay Products Released from the Former Uranium Mill at Uravan Colorado USA.” Journal of Environmental Radioactivity, 99: 1258–1278.


Apollo Historical Dose Reconstruction

For this ongoing project about the former nuclear fuel processing facility located in Apollo, Pennsylvania, RAC has reconstructed uranium emissions to air during its years of operation (July 1957 – April 1983). To this end, RAC reviewed more than 2.5 million pages of historical records relating to the operation of the Apollo facility. The uranium release estimates were coupled with atmospheric dispersion and transport model calculations to establish the time history of ambient air concentrations in the region. These data are then combined with the residence history of an individual to provide organ-specific dose estimates associated with facility emissions. The dose calculations account for age at exposure and gender.

Breathing air was the primary pathway of exposure to uranium emissions for residents of the area. The doses received in all cases were small.

Fernald Dosimetry Reconstruction Project

The Centers for Disease Control and Prevention contracted Risk Assessment Corporation to estimate the doses and risks to the public from radioactive materials released from the Fernald Feed Materials Production Center (FMPC) during its 38 years of operations, from 1951 through 1988. The FMPC is located near Fernald, Ohio, about 15 miles northwest of Cincinnati, Ohio, and processed uranium compounds for nuclear weapons production, as well as some uranium ore and thorium. Some waste materials with high radium content from processes in the early 1950s were stored in silos on the site. RAC’s work was reviewed

by the National Academy of Sciences. When the work was completed in 1999, the citizens around Fernald and the organizations responsible for operation of the facility had a much clearer understanding of the health risks that may have been received by the public from releases during its operation.

Significant findings from this work showed that uranium and radon and its decay products were the most important radioactive materials released from the site for off-site residents. Breathing air was the major pathway of exposure, and inhalation of the radon decay products from the silos contributed most of the radiation dose to off-site residents.

Fernald Task 6 Report



Till, J.E., G.G. Killough, K.R. Meyer, W.S. Sinclair, P.G. Voillequé, S.K. Rope, and M.J. Case. 2000. “The Fernald Dosimetry Reconstruction Project.” Technology, Vol. 7 pp270-295.

Meyer, K.R., P.G. Voillequé, D.W. Schmidt, S.K. Rope, G.G. Killough, B. Shleien, R.E. Moore, M.J. Case, and J.E. Till. 1996. “Overview of the Fernald Dosimetry Reconstruction Project and source term estimates for 1951-1988.” Health Physics. 71(4):425-37.

Rocky Flats Historical Public Exposures Project

RAC was contracted by the Colorado Department of Public Health and Environment (CDPHE) to estimate the increased cancer risk to residents of the surrounding communities during the former Rocky Flats Nuclear Weapons Plant’s operation from releases that were carried off-site and led to exposure of the public. The plant, located northwest of Denver, Colorado, operated from 1952 to 1989 and produced nuclear weapons triggers, called pits, from plutonium. RAC performed

Phase II of the Historical Public Exposures Study on the Rocky Flats Site. This work was supported by the CDPHE and overseen by a Panel of technical and non-technical individuals representing scientists and community members. By the study’s end, RAC had produced 20 technical reports documenting releases to the environment from the facility, the transport of these materials in the environment, and health risk to people who may have been exposed.

The findings from this work show that people who lived near the facility were exposed to plutonium mainly through inhalation during routine operations, from a major fire in 1957, and from plutonium resuspended from contaminated soil from an outdoor drum storage area, called the 903 Area. RAC developed a model to calculate ambient air concentrations, surface deposition, and lifetime carcinogenic risk with uncertainty from plutonium released to the air from the Rocky

Flats Plant. The model integrated airborne release estimates and atmospheric dispersion and deposition calculations from 37 years of routine plant operations and episodic releases. Five atmospheric transport models were evaluated for use in the study. Results were presented for five exposure scenarios that were location-independent. Carbon tetrachloride was found to be the chemical that presented the highest risk to the public.


Summary Report
Review of Routine Releases of Plutonium
(Adobe PDFs)



Till, J.E., A.S. Rood, P.G. Voillequé, P.D. McGavran, K.R. Meyer, H.G. Grogan, W.K. Sinclair, J.W. Aanenson, H.R. Meyer, S.K. Rope, and M.J. Case. 2002. “Risk to the Public from Historical Releases of Radionuclides and Chemicals at the Rocky Flats Nuclear Weapons Plant.” Journal of Exposure. Analysis and Epidemiology, Vol. 12 (5) pp355-372.

Rood, A.S., H.A. Grogan, and J.E. Till. 2002. “A Model for A Comprehensive Assessment of Exposure and Lifetime Cancer Incidence Risk from Plutonium released from the Rocky Flats Plant, 1953-1989.” Health Physics, Vol. 82 (2) pp 182-212.

Rood, A.S., P.D. McGavran, J.W. Aanenson, and J.E. Till. 2001. “Stochastic Estimates of Exposure and Cancer Risk from Carbon Tetrachloride Released to the Air from the Rocky Flats Plant.” Risk Analysis, Vol. 21 (4) pp 675-695.

McGavran, P.D., A.S. Rood., and J.E. Till. 1999. “Chronic Beryllium Disease and Cancer Risk Estimates with Uncertainty for Beryllium Released to the Air from the Rocky Flats Plant.” Environmental Health Perspectives. Vol. 107 (9): 731-744.

Rood, A.S., G.G. Killough, and J.E. Till. 1999. “Evaluation of Atmospheric Transport Models for Use in Phase II of the Historical Public Exposures Studies at the Rocky Flats Plant.” Risk Analysis, Vol. 19 (4): 559-576, Neeses, SC, 29107.


Atomic Veterans Study

Cancer Mortality among Military Participants at U.S. Nuclear Weapons Tests

More than 200,000 military personnel participated in U.S. atmospheric nuclear weapons tests from 1945 until the Limited Nuclear Test Ban Treaty in 1963.

RAC is part of a team of scientists working with Vanderbilt University on a five-year study to quantify the lifetime risk of cancer among 125,000 U.S. atomic veterans. These service personnel participated at one or more of the 230 aboveground atmospheric nuclear weapons tests at the Nevada Test Site or the Pacific Proving Ground between 1946 and 1958. The study is taking advantage of detailed radiation dose and veteran data already developed by the Department of Defense over the past 30 years that has recently been digitized and made available to researchers. RAC is providing the dose estimates with uncertainties for individual atomic veterans that will be used by the epidemiologists on the team in this follow-up study. Funding for the study is provided by the National Institutes of Health.

Significant findings from this work to date have included:

  • Development of a methodology for characterizing detailed exposure scenarios for individual veterans as opposed to groups of veterans evaluated as a whole. This methodology has provided a significant contribution to our understanding of the unique exposure circumstances encountered by these veterans and the likelihood that any individual participated in activities that resulted in exposure.
  • Bias and error in previously reported dose estimates have been carefully identified and quantified.
  • Individual dosimetry with associated uncertainties has been provided by RAC at a level of detail never before available for this group of nuclear test participants.


Till, J.E., H.L. Beck, J.W. Aanenson, H.A. Grogan, H.J. Mohler, S.S. Mohler, P.G. Voillequé. 2014. Military Participants at U.S. Atmospheric Nuclear Weapons Testing-Methodology for Estimating Dose and Uncertainty. Radiat Res. 181, 471 – 484.

Art Rood selected to be a member of ICRP Task Group 98

Art Rood selected to be a member of ICRP Task Group 98

Mr. Art Rood was invited to be a full member of ICRP Task Group 98, Application of the Commission’s Recommendations to exposures resulting from contaminated sites from past industrial, military, and nuclear activities. The mandate of the task group is to develop a report that describes and clarifies the application of the Commission’s Recommendations on radiological protection of workers, the public, and environment to exposures resulting from sites contaminated due to past industrial, military and nuclear activities.

RAC awarded NRC contract to present training courses to agency personnel

RAC has been awarded a contract with the Nuclear Regulatory Commission to present up to five training courses from 2015 through 2019 to agency personnel on the topic of “Environmental Risk Assessment Analysis.” RAC’s lectures, discussions, and demonstrations for these courses will be designed to allow participants to use the acquired knowledge for performance evaluations of licensee environmental assessments and to perform environmental impact reviews, inspect licensee programs, and manage environmental projects. RAC presented a similar course for NRC personnel in 2009.

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