Potential Airborne Releases and Deposition of Radionuclides from the Santa Susana Field Laboratory during the Woolsey Fire.

ABSTRACT: The Santa Susana Field Laboratory (SSFL), located in southern California, is a former research facility, and past activities have resulted in residual radioactive contamination in Area IV of the Site. The Woolsey Fire burned across the site, including some of the contaminated areas, on 8-11 November 2018. Atmospheric transport modeling was performed to determine where the smoke plume went while the fire burned across the SSFL and the deposition footprint of particulates in downwind communities. Any radionuclides on vegetation and in surface soil released by the fire were assumed to follow particulate matter transport path and deposition. The predicted deposition footprint was used to guide confirmatory soil sampling at 16 locations including background. Highest offsite deposition was determined to be northeast of the Oak Park community, which is located about 6 km southwest of SSFL. Depth-profile sampling was used to evaluate whether radionuclides of SSFL origin were potentially emitted and deposited during the Woolsey Fire. If radionuclides had been deposited from the Woolsey Fire at sufficient concentrations, then they would be detected in the surface layer and would be expected to be higher within the plume footprint than outside it. An upper bound estimate of the hypothetical effective dose to a person in Oak Park based on measured radionuclide concentrations in soil and vegetation on the SSFL was less than 0.0002 mSv. The occurrence of naturally occurring radionuclides at concentrations above the established background for the SSFL was attributed to natural variability in geologic formations and not SSFL. No anthropogenic radionuclides were measured at levels above those expected from global fallout. The soil sampling confirmed that no detectable levels of SSFL-derived radionuclides migrated from SSFL at the locations sampled because of the Woolsey Fire or from past operations of the SSFL.

Dosimetry associated with veterans who participated in nuclear weapons testing.

BACKGROUND: This article summarizes the methodology, results, and challenges of the reconstruction of red bone marrow and male breast doses for a 1982-person sub-cohort of ∼114,270 U.S. military veterans who participated in eight atmospheric nuclear weapons tests between 1945 and 1962. These doses are being used in an epidemiological investigation of leukemia and male breast cancer as part of a study of one million U.S. persons to investigate risk from chronic low-dose radiation exposure. METHODS: Previous doses to these veterans had been estimated for compensation and tended to be biased high but newly available documentation made calculating individual doses and uncertainties using detailed exposure scenarios for each veteran possible. The techniques outlined in this report detail the methodology for developing individual scenarios and accounting for bias and uncertainty in dose based on the assumptions made about exposure. RESULTS: Doses to the atomic veterans in this sub-cohort were relatively low, with about two-thirds receiving red bone marrow doses <5 mGy and only four individuals receiving a red bone marrow dose >50 mGy. The average red bone marrow dose for members of the sub-cohort was 5.9 mGy. Doses to male breast were approximately 20% higher than red bone marrow doses. DISCUSSION AND CHALLENGES: Relatively low uncertainty was achieved as a result of our methodology for reconstructing exposures based on knowledge of the individual veterans' locations and activities from military records. Challenges did arise from use of military records to determine probability of participation in specific activities but accounted for in estimates of uncertainty.

Asbestos exposure and mesothelioma mortality among atomic veterans.

BACKGROUND: The United States (U.S.) conducted 230 above-ground atmospheric nuclear weapons tests between 1945 and 1962 involving over 250,000 military personnel. This is the first quantitative assessment of asbestos-related mesothelioma, including cancers of the pleura and peritoneum, among military personnel who participated in above-ground nuclear weapons testing. METHODS: Approximately 114,000 atomic veterans were selected for an epidemiological study because they were in one of eight series of weapons tests that were associated with somewhat higher personnel exposures than the other tests and because they have been previously studied. We were able to categorize specific jobs into potential for asbestos exposure based on a detailed database of the military activities of the atomic veterans. Standardized mortality ratios (SMR) were calculated by service, rank (officer/enlisted) and ratings (occupation code and work location aboard ship) after 65 years of follow-up. RESULTS: Mesothelioma deaths were significantly increased overall (SMR 1.56; 95% CI 1.32-1.82; n = 153). This increase was seen only among those serving in the PPG (SMR 1.97; 95% CI 1.65-2.34; n = 134), enlisted men (SMR 1.81; 95% CI 1.53-2.13; n = 145), and the 70,309 navy personnel (SMR 2.15; 95% CI 1.80-2.56; n = 130). No increased mortality rates were seen among the other services: army (SMR 0.45), air force (SMR 0.85), or marines (SMR 0.75). Job categories with the highest potential for asbestos exposure (machinist's mates, boiler technicians, water tender, pipe fitters, and fireman) had an of SMR 6.47. Job categories with lower potential (SMR =1.35) or no potential (SMR =1.28) for asbestos exposure had non-significantly elevated mesothelioma mortality. CONCLUSIONS: The large excess of mesothelioma deaths seen among atomic veterans was explained by asbestos exposure among enlisted naval personnel. The sources of exposure were determined to be on navy ships in areas (or with materials) with known asbestos content. No excess of mesothelioma was observed in other services or among naval personnel with minimal exposure to asbestos in this low-dose radiation exposed cohort.

Analysis of Environmental Data to Support Quantification of Historical Releases from a Former Uranium Processing Facility in Apollo, Pennsylvania.

ABSTRACT: This paper describes how environmental measurement data were used to help quantify the spatial impact and behavior of uranium released to the environment from a uranium manufacturing facility in Apollo, PA. The Apollo facility released enriched uranium to the environment while it operated between 1957 and 1983. Historical monitoring data generated by the site, along with other independent data sources, provided a long-term record documenting the presence and behavior of uranium in the local environment. This record of evidence, together with reconstructed estimates of facility releases, has been used to estimate environmental concentrations during facility operations and potential exposures to members of the public. Historical environmental measurement data were also used to confirm predictions of deposition and concentrations in air. The data are used here to derive atmospheric deposition velocities for the uranium emissions. Based on the spatial pattern of measurements and calculated deposition velocities around the facility, the released material contained larger particles that deposited close to the facility, and the released material remains largely in the surface layers of the soil, indicating limited downward mobility. Evidence of measurable impacts was determined to extend a relatively short distance (<500 m) from the facility. The soil data collected around Apollo are also compared to findings related to uranium mobility at another facility where uranium was released to the environment, and similar behavior was observed at both sites.

Reconstruction of Enriched Uranium Released to Air from the Former Apollo Facility, Apollo, Pennsylvania.

ABSTRACT: The former Apollo facility converted enriched uranium hexafluoride into uranium oxide for shipment to nuclear fuel fabrication plants from 1957 to 1983. This paper describes quantification of the source term from the Apollo facility in terms of quantities of uranium released, particle size, and solubility characteristics. Releases occurred through stacks, rooftop vents, and an incinerator that operated from 1964 to 1969. Incidental and accidental releases are addressed as part of this analysis. Atmospheric releases of uranium from plant operations were estimated from stack sampling and production records. Roof vents, both filtered and unfiltered, were the major emission points from the plant. The total estimated release of uranium activity (including 234U, 235U, and 238U) to the air was 28 GBq. Measurements by others found that the releases were primarily associated with large particles and that their solubility was variable but generally low (Class Y). The release estimates presented here and those findings were incorporated into a sophisticated atmospheric transport model to estimate atmospheric concentrations and soil contamination levels due to the releases and to reconstruct historical doses to individuals that lived in the vicinity of the former Apollo facility.

Reconstruction of atmospheric concentrations of enriched uranium from the former Apollo facility, Apollo, Pennsylvania, USA.

The former Apollo facility in western Pennsylvania converted enriched uranium hexafluoride into uranium oxide for shipment to nuclear fuel fabrication plants from 1957 to 1983. Atmospheric releases of uranium from plant operations were estimated from stack sampling and production records. Releases occurred through stacks, rooftop vents, and an incinerator that operated from 1964 to 1969. Roof vents that exhausted workplace air was the major emission source from the plant. Total estimated release of uranium activity (including 234U, 235U, and 238U) to the air was 27.9 GBq. Atmospheric transport modeling was performed using a complex terrain model because the plant was located in an incised river valley. Almost two years of meteorological data were collected from a nearby 10-m tower, along with sounding from a collocated sodar. Light mean wind speed (1.56 m s-1) and predominately stable atmospheric conditions frequently resulted in poor dispersion conditions in the facility environs. Environmental sampling included continuous air monitoring data and depth profiles of uranium in soil that was deposited from airborne releases. Soil measurements exhibited a sharp drop-off in uranium concentrations with distance from the facility, indicating that large non-inhalable particles were emitted to the atmosphere. Large particles (~15-25 µm aerodynamic equivalent diameter) accounted for 17.5% of the total emissions. Soil measurements were used for model calibration and validation, while air measurements were used to evaluate model performance. Air concentrations were generally over-predicted for locations near the facility but showed only a slight positive bias for locations north of the facility. Predicted uranium activity air concentrations from Apollo sources averaged over 34 years were about three times greater than the background gross alpha activity value of 81 µBq m-3 in a ~0.5 km2 region surrounding the Apollo facility. The contribution of Apollo uranium to the gross alpha air concentration would have been negligible several kilometers from the facility.

Use of Routine Environmental Monitoring Data to Establish a Dose-based Compliance System for a Low-level Radioactive Waste Disposal Site.

A dose-based compliance methodology was developed for Waste Control Specialists, LLC, low-level radioactive waste facility in Andrews, Texas, that allows routine environmental measurement data to be evaluated not only at the end of a year to determine regulatory compliance, but also throughout the year as new data become available, providing a continuous assessment of the facility. The first step in the methodology is a screening step to determine the potential presence of site emissions in the environment, and screening levels are established for each environmental media sampled. The screening accounts for spatial variations observed in background for soil and temporal fluctuations observed in background for air. For groundwater, the natural activity concentrations in groundwater wells at the facility are highly variable, and therefore the methodology uses ratios for screening levels. The methodology compares the ratio of gross alpha to U + U to identify potentially abnormal alpha activity and the ratio of U to U to identify the potential presence of depleted uranium. Compliance evaluation is conducted for any samples that fail the screening step. Compliance evaluation uses the radionuclide-specific measurements to first determine (1) if the dose exceeds the background dose and if so, (2) the dose consequences, so that the appropriate investigation or action occurs. The compliance evaluation is applied to all environmental samples throughout the year and on an annual basis to determine regulatory compliance. The methodology is implemented in a cloud-based software application that is also made accessible to the regulator. The benefits of the methodology over the existing system are presented.

Red Bone Marrow and Male Breast Doses for a Cohort of Atomic Veterans.

Both red bone marrow and male breast doses with associated uncertainty have been reconstructed for a 1,982-person subset of a cohort of 114, 270 military personnel (referred to as "atomic veterans") who participated in U.S. atmospheric nuclear weapons testing from 1945 to 1962. The methods used to calculate these doses and corresponding uncertainty have been reported in detail by Till et al. in an earlier publication. In this current article we report the final results of those calculations. These doses are being used in a case-cohort design epidemiological investigation of leukemia and male breast cancer. This cohort of atomic veterans is one component in a broader-scope study of approximately one million U.S. persons designed to investigate risk from chronic low-dose radiation exposure. Doses to the atomic veterans in this sub-cohort were relatively low, with approximately two-thirds receiving red bone marrow doses <5 mGy and only four individuals receiving a red bone marrow dose >50 mGy. The average red bone marrow dose for members of the sub-cohort was 5.9 mGy. Doses to male breast were approximately 20% higher than red bone marrow doses. The uncertainty in the estimated doses was relatively low, considering relevant personnel dosimetry was available for only about 25% of the subjects, and most of the doses were reconstructed from film badges worn by co-workers or from the individual's military record and military unit activities. The average coefficient of variation for the individual dose estimates was approximately 0.5, comparable to the uncertainty in doses estimated for the Japanese A-bomb survivors. Although the reconstructed red bone marrow doses were about 36% lower on average than the conservative doses previously estimated by the military for compensation, the overall correlation was quite good, suggesting that the estimates of doses from external exposure by the military for all ∼115,000 cohort members could be adjusted appropriately and used in further epidemiological analyses.

Military participants at U.S. Atmospheric nuclear weapons testing--methodology for estimating dose and uncertainty.

Methods were developed to calculate individual estimates of exposure and dose with associated uncertainties for a sub-cohort (1,857) of 115,329 military veterans who participated in at least one of seven series of atmospheric nuclear weapons tests or the TRINITY shot carried out by the United States. The tests were conducted at the Pacific Proving Grounds and the Nevada Test Site. Dose estimates to specific organs will be used in an epidemiological study to investigate leukemia and male breast cancer. Previous doses had been estimated for the purpose of compensation and were generally high-sided to favor the veteran's claim for compensation in accordance with public law. Recent efforts by the U.S. Department of Defense (DOD) to digitize the historical records supporting the veterans' compensation assessments make it possible to calculate doses and associated uncertainties. Our approach builds upon available film badge dosimetry and other measurement data recorded at the time of the tests and incorporates detailed scenarios of exposure for each veteran based on personal, unit, and other available historical records. Film badge results were available for approximately 25% of the individuals, and these results assisted greatly in reconstructing doses to unbadged persons and in developing distributions of dose among military units. This article presents the methodology developed to estimate doses for selected cancer cases and a 1% random sample of the total cohort of veterans under study.

An integrated approach to data management, risk assessment, and decision making.

This paper describes a methodology called Risk Analysis, Communication, Evaluation, and Reduction (RACER) that converts environmental data directly to human health risk to enhance decision making and communication. The methodology was developed and implemented following the Cerro Grande fire in New Mexico that burned approximately 7,500 acres of Los Alamos National Laboratory in May 2000. The absence of a coordinated and comprehensive approach to managing and understanding environmental data was a major weakness in the responding agencies' ability to make and communicate decisions. RACER consists of three basic elements: managing information, converting information to knowledge, and communicating knowledge to decision makers and stakeholders. Data are maintained in a web-accessible database that accepts data as they are validated and uploaded. The user can select data for evaluation and convert them to knowledge using human health risk as a benchmark for ranking radionuclides, chemicals, pathways, or other criteria needed to make decisions. Knowledge about risk is communicated using graphic and tabular formats. The process is transparent, flexible, and rapid, which enhances credibility and trust among decision makers and stakeholders. The fundamental principles used in RACER can be applied anywhere radionuclides or chemicals are present in the environment.

RACER: dynamic use of environmental measurement data for decision making and communication.

To facilitate access to and use of environmental measurement data, Risk Assessment Corporation has developed a data management system as part of its Risk Analysis, Communication, Evaluation, and Reduction process. The concepts of data consistency are not new, but many data management applications are developed around managing the entire data life cycle, rather than on using the data to reach meaningful conclusions. The RACER process is specifically focused on the efficient use of available data to promote sound decision making. The RACER data management system provides a means of understanding trends in data, comparing data to frequently referenced comparison values, and organizing environmental measurement data for use by other components of the RACER process that evaluate human health impacts. Data transfers to the system can be automated to occur frequently for facilities collecting large volumes of data to achieve a dynamic point of access to measurement data that reflects the most recently available information. Because the RACER process is designed around the most common uses of data, its utility spans a broad range of potential applications, from routine monitoring and reporting to emergency response decision making based on potential human health impacts. Because it is portable and flexible, the elements of the system can be used in any situation where there is a need to efficiently access and interpret environmental measurement data. Its output and functions are equally relevant for small datasets with hundreds of measurements or large and complex datasets with millions of measurements.

Application of NCRP air screening factors for evaluating both routine and episodic radionuclide releases to the atmosphere.

Two separate methods were used to identify the most important historic airborne releases of radionuclides at the Idaho National Engineering and Environmental Laboratory (INEEL) with regard to potential human health impact. Both routine and episodic releases were evaluated. Although not specifically intended for an initial screening or ranking evaluation, particularly for episodic releases, the National Council on Radiation Protection and Measurements (NCRP) screening method was shown to be a valid method for providing a measure of the relative importance of both routine and episodic radionuclide releases, based on comparisons with the Radiological Safety Analysis Code (RSAC). For the work at the INEEL, a relative ranking procedure was used to identify the most important releases because a screening criterion (e.g., dose or risk value) against which the potential health impacts of the releases could be measured was not established. In addition, a precedent for a screening-level evaluation of episodic releases is lacking at this time. As a result, a ranking procedure was considered necessary because it was not clear that the NCRP method would provide screening-level dose estimates for episodic releases that could be defensibly compared to a screening criterion. To evaluate the NCRP method at the INEEL, routine operational releases were evaluated and ranked separately from episodic, or acute, releases because different assumptions and approaches were required to assess their potential importance. Based on comparisons with the RSAC method, the NCRP method may slightly underpredict the ingestion dose for episodic releases; however, using the NCRP screening method to identify the relative importance of release events, radionuclides, years, and facilities was shown to be valid and defensible for both routine and episodic releases. Because of the NCRP method's simplicity and relative ease of application, it provides a cost-effective and scientifically defensible way to make decisions and set priorities about decisions and directions in risk assessment.

Risks to the public from historical releases of radionuclides and chemicals at the Rocky Flats Environmental Technology Site.

This paper summarizes the methods and results of estimating risks of cancer incidence resulting from plutonium, carbon tetrachloride, and beryllium releases from operations at the Rocky Flats Environmental Technology Site, near Denver, Colorado, from 1953 through 1989. The key findings 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. Results were presented for five exposure scenarios that were location-independent. Individuals described by the laborer scenario received the highest risk of all scenarios considered. Upper bound (95th percentile) incremental lifetime cancer incidence risks for the laborer scenario were in about the 10(-4) range (1 chance in 10,000) for developing cancer from Rocky Flats plutonium releases during a lifetime. At the 5th percentile level, the maximum cancer risk was about 10(-7) (1 chance in 10 million) for developing cancer during a lifetime. Estimated cancer risks at the 95th percentile level are within the range of for acceptable risks established by the US Environmental Protection Agency of 10(-6) to 10(-4). Carbon tetrachloride was found to be the chemical that presented the highest risk to the public. The 5th and 95th percentile risk values for exposure to carbon tetrachloride were 9.2x10(-7) and 2.5x10(-5), respectively.