Fernald Environmental Management Project Research Articles

Estimating the spatial-temporal distribution of Radon releases from the K-65 silos

This study investigates the spatial and temporal distribution of Radon at the Department of Energy's (DOE) Fernald Environmental Management Project (FEMP), in southwest Ohio in 1999. It employs the United States Environmental Protection Agency's (EPA) Industrial Source Complex Short Term 3 (ISCST3) dispersion model, existing monitoring data and Geographic Information Systems (GIS) as tools to develop an integrated radiological monitoring, assessment and protection technique. This study develops a three-stage hybrid model that takes advantage of both spatial interpolation and dispersion modelling. Specifically the model involves the initial estimation of source emission rates, estimation of Radon concentration at sampling locations, and interpolation of the estimates at discrete locations to generate a continuous surface. Arcview GIS is used to simulate 'pollution hotspot' maps and digital surfaces from ISCST3 estimations. Multiple digital, vector pollution contour, raster grid surfaces and hard copy pollution thematic maps can now be generated for FEMP and vicinity.

Atmospheric aerosol measurements of 238U and 232Th at Fernald, Ohio, and implications on inhalation dose calculations.

Measurements of the aerosol size distribution of 238U and 232Th at the U.S. Department of Energy's Fernald Environmental Management Project site were made to improve the inhalation dose calculations to off-site individuals. For approximately 1 y an 8-stage cascade impactor was co-located with a high volume sampler and operated at the Fernald Environmental Management Project site to collect aerosol samples. During most of the year, the site was dominated by giant particles with more than 70% of the mass of 238U above 15 microm. The seasonal average of the activity median aerodynamic diameter, based on the impactor samples, which excluded particles >15 microm, for both uranium and thorium was approximately 6.5 microm. These numbers reflect the activities at the site and the domination of the resuspension processes. During most sampling periods the size distribution was bimodal. Thorium concentrations were comparable to the uranium concentrations during the late spring and summer period and decreased to approximately 25% of the 238U concentration in the late summer. Fernald Environmental Management Project is required to calculate the maximum allowable dose from airborne emissions, excluding radon, to meet NESHAP compliance. These calculations assume an AMAD of 1 microm. We found that if you combine size distribution information with the latest ICRP 66 lung model you reduce the estimated dose by a factor of 7. Inclusion of the size distribution of radionuclides at any sampling site would substantially improve the dose estimates to the population.

Solubility of airborne uranium compounds at the Fernald Environmental Management Project.

The in vitro solubility of airborne uranium dusts collected at a former uranium processing facility now undergoing safe shutdown, decontamination, and dismantling was evaluated by immersing air filters from high volume samplers in simulated lung fluid and measuring the 238U in sequential dissolution fractions using specific radiochemical analysis for uranium. X rays and photons from the decay of uranium and thorium remaining on the filter after each dissolution period were also directly measured using a planar germanium detector as a means for rapidly evaluating the solubility of the uranium-bearing dusts. Results of these analyses demonstrate that two distinct types of uranium-bearing dusts were collected on the filters depending upon the location of the air samplers. The first material exhibited a dissolution half-time much less than 1 d and was most likely UO3. The dissolution rate of the second material, which was most likely U3O8, exhibited two components. Approximately one-third of this material dissolved with a half time much less than 1 d. The remaining two-thirds of the material dissolved with half times between 230 +/- 16 d and 1,350 +/- 202 d. The dissolution rates for uranium determined by radiochemical analysis and by gamma spectrometry were similar. However, gamma spectrometry analysis suggested a difference between the half times of 238U and its initial decay product 234Th, which may have important implications for in vivo monitoring of uranium.

Uranium Solubility of Carbonate-Rich Uranium-Contaminated Soils

A 300 d solubility study involving two carbonate-rich, uranium-contaminated soils from the Department of Energy's Fernald Environmental Management Project site was conducted to predict the behavior of uranium during on-site remediation of these soils. Geochemical modeling was performed on the aqueous species dissolved from these soils following the solubility measurements to predict the on-site uranium leaching and transport potential. Results showed that the soluble levels of the major components (total uranium, calcium, magnesium, and carbonate) increased continually for the first 4 weeks. After the first 4 weeks, these components either reached a steady-state or continued to increase linearly throughout the study. Soluble uranium levels of both soils and their correlation with alkalinity was strongly mediated by the source term of the contamination. Geochemical modeling predicted and anion exchange experiments confirmed that uranyl-carbonate complexes were the most stable and abundant complexes. Further modeling showed that uranium solubility in these soils and in onsite groundwater wells is controlled by UO2(H2PO4)2, but is also mediated by complexation with carbonate and the oxidation state of the uranium. For assessing the risk related to off-site transport of uranium, it should be recognized that the solubility of uranium-bearing minerals is the critical factor in controlling uranium solubility of these soils rather than sorption/desorption processes as measured by the uranium distribution coefficient (Kd) in these soils.

Carbonate Leaching of Uranium from Contaminated Soils

Uranium (U) was successfully removed from contaminated soils from the Fernald Environmental Management Project (FEMP) site near Fernald, Ohio. The laboratory column leach process, referred to as the simulated heap leach process, using 0.5 M sodium bicarbonate as the dominant reagent, was able to achieve uranium removals of 75−90%, corresponding approximately to the percentage of uranium in the oxidized state. Parametric optimization studies are reported. The dissolution of uranium took place in two stages: a rapid desorption associated with soil surfaces and a slow step associated with diffusion of uranium toward solid surfaces. In addition, use of the oxidizing agent, sodium peroxide, improved uranium removal due to oxidation of U(IV), enhancing the solubility of the uranium. The results suggest that the process will be effective for field scale remediation of uranium-contaminated soils because of the efficiency, mild complexing agent employed, lack of prescreening of the soil and the simple equipment n...

Characterization and solubility measurements of uranium-contaminated soils to support risk assessment.

Remediation of uranium-contaminated soils is considered a high priority by the U.S. Department of Energy because these soils, if left untreated, represent a hazard to the environment and human health. Because the risk to human health is a function of the solubility of uranium in the soils, the objectives of this work are to measure the uranium solubility of two contaminated soils, before and after remedial treatment, and determine the health risk associated with these soils. Two carbonate-rich, uranium-contaminated soils from the U.S. Department of Energy Fernald Environmental Management Project facility near Cincinnati, Ohio, as well as two nearby background soils were characterized and their uranium solubility measured in a 75-d solubility experiment using acid rain, groundwater, lung serum, and stomach acid simulants. Results show that the soluble uranium levels of each soil by each simulant are greatly influenced by their contamination source term. Risk calculations and biokinetic modeling based on the solubility data show that the risks from the soil ingestion and groundwater ingestion pathways are the predominant contributors to the total carcinogenic risk, whereas the risk from the soil inhalation pathway is the smallest contributor to this risk. However, kidney toxicity was the greater health concern of the Fernald Environmental Management Project soils, primarily from undiluted ingestion of the groundwater solution following contact with the contaminated soils. Sensitivity analyses indicate that uranium solubility is a key parameter in defining kidney toxicity; therefore, without proper consideration of the solubility of radionuclides/metals in untreated and treated soils, important factors may be overlooked which may result in soil cleanup goals or limits which are not protective of human health and the environment. We recommend that characterization and measurement of target radionuclides/metals solubilities should also be required by the regulatory community to support the establishment of scientifically-sound, site-specific, soil cleanup goals or limits.

Indicator Geostatistical Analysis of Sand Interconnections Within a Till

AbstractAt the Fernald Environmental Management Project (FEMP) site in southwestern Ohio, sand and gravel lenses within till provide potential pathways for the flow of contamination into the underlying aquifer. These high‐permeability lenses account for 22% of the volume of the till, have a complex arrangement, and are smaller in scale than the site. Even the relatively dense subsurface sampling program at the FEMP site is not adequate to determine facies interconnections with certainty. To delineate probable facies boundaries, a binary indicator random variable was used to represent the presence of high or low‐permeability sediment. The 800 available lithologic logs that penetrate the till were coded with the binary system at 2 ft (0.6 m) intervals yielding 15,829 observations. These data were used to compute the declustered mean of indicator values in horizontal intervals, giving an estimate of the proportion of high‐permeability sediment in each vertical zone. The areal correlation in specific zones was examined through indicator variograms, which had pronounced anisotropy. Three‐dimensional indicator point kriging was used to produce maps of the probability of existence of high‐permeability sediment. These maps were used in a preliminary analysis of sand body interconnectedness. Results indicate that portions of sand bodies are interconnected through the entire interval studied and that the areal extent of vertical interconnection is up to 1000 ft.

Uranium Contamination in the Great Miami Aquifer at the Fernald Environmental Management Project, Fernald, Ohio

AbstractGround‐water investigations at a former U.S. Department of Energy nuclear weapons complex near Fernald, in southwestern Ohio, included the delineation of uranium contamination above the USEPA proposed drinking water standard of 20 μg/l. Contamination occurs in a buried valley and has migrated > 1.5 km south‐southeast of the facility boundary. Flooring of the plume(s) appears to be > 32 m below the water table of the Great Miami Aquifer. U6+ predominates in the modeled U‐O2‐CO2‐H2O system and U retardation decreases at depth. U234/U238 disequilibria analyses complement hydrogeologic studies which suggest that U leakage through the clayey till cap is less significant than the predominant transport pathway of infiltration via drainage channels incised into the aquifer.

Statistical Analysis of Real-Time, Environmental Radon Monitoring Results At the Fernald Environmental Management Project

A comprehensive real-time, environmental radon monitoring program is being conducted at the Fernald Environmental Management Project, where a large quantity of radium-bearing residues have been stored in two covered earth-bermed silos. Statistical analyses of radon measurement results were conducted to determine what impact, if any, radon emitted by the radium bearing materials contained in the silos has on the ambient radon concentration at the Fernald Environmental Management Project site. The distribution that best describes the outdoor radon monitoring data was determined before statistical analyses were conducted. Random effects associated with the selection of radon monitoring locations were accommodated by using nested and nested factorial classification models. The Fernald Environmental Management Project site was divided into four general areas according to their characteristics and functions: 1) the silo area, where the radium-bearing waste is stored; 2) the production/administration area; 3) the perimeter area, or fence-line, of the Fernald Environmental Management Project site; and 4) a background area, located approximately 13 km from the Fernald Environmental Management Project site, representing the naturally-occurring radon concentration. A total of 15 continuous, hourly readout radon monitors were installed in these 4 areas to measure the outdoor radon concentration. Measurement results from each individual monitor were found to be log-normally distributed. A series of contrast tests, which take random effects into account, were performed to compare the radon concentration between different areas of the site. These comparisons demonstrate that the radon concentrations in the production/administration area and the perimeter area are statistically equal to the natural background, whereas the silo area is significantly higher than background. The study also showed that the radon concentration in the silo area was significantly reduced after a sealant barrier was applied to the contents of the silos.

USDOE remediation site case study

The uranium concentration ranges of important pathway matrices for the United States are compared with off- and on-site ranges at the Fernald Environmental Management Project (FEMP). Empirically established uranium uptake factors for humans are linked with the National Council on Radiation Protection and Measurements (NCRP) recommendations on limits for exposure of the public to ionizing radiation. The maximum effective dose equivalent (EDE) to the local population is derived from the USDOE interim drinking water guideline and consideration of the inhalation and ingestion pathways for diet and local soils. The maximum effective dose equivalent estimates calculated for the inhalation and ingestion of uranium from local sources in the environs of the FEMP would be considered negligible under the individual risk level (NIRL) concept developed by the NCRP. However, empirical site data and risk modeling based on these data are necessary to meet USDOE mission objectives at FEMP and other remediation sites.

Micro‐Purge Low‐Flow Sampling of Uranium‐Contaminated Ground Water at the Fernald Environmental Management Project

AbstractEfforts to sample representative, undisturbed distributions of uranium in ground water beneath the Fernald Environmemal Management Project (FEMP) prompted the application of a novel technique that is less invasive in the monitoring well. Recent studies (Kearl et al. 1992; Barcelona et al. 1994) indicate that representative samples can and should be collected without prior well volume exchange purging or borehole evacuation. Field experiments conducted at the FMMP demonstrate that under specific sampling conditions in a welldefined hydrogeologic system, representative ground water samples for a monitoring program can be obtained without removing the conventional three well volumes from the well. The assumption is made that indicator parameter equilibration may not be necessary to determine when to collect representative samples at the P'liMP. Preliminary results obtained from the field experiment suggest that this may be true. The technique employs low purge rates (< 1 L/min) with dedicated bladder pumps with inlets located in the screened interval of the well, while not disturbing the stagnant water column above the screened interval. If adopted, this technique, termed micro‐purge low‐flow sampling, will produce representative ground water samples, significantly reduce sampling costs, and minimize; waste water over the monitoring life cycle at the FEMP. This technique is well suited for sites that have been fully characterized and are undergoing long‐term monitoring.

Pilot study risk assessment for selected problems at three U.S. Department of Energy facilities

Objective and realistic human health risk assessments were performed for environmental problems at the Savannah River Site (SRS), the Fernald Environmental Management Project (FEMP), and the Nevada Test Site (NTS). At the SRS, cancer mortality risks were analyzed for projected public exposures to 3H and 137Cs released into the Savannah River. For annual human exposures to SRS tritium in Savannah River water, calculated incremental individual lifetime risks in two human receptor populations were small (8×10 −7; upper 95 percentile point of the distribution). The 95th percentile point of the distribution for incremental individual lifetime risks from one year's exposure to 137Cs is less than 10 −8. No deaths are expected in either population as a result of exposures to tritium or cesium released to the Savannah River from the SRS. Routine releases of radon and radon progeny from the K-65 silos at FEMP resulted in individual lifetime risks greater than 1×10 −4 only for onsite workers and fenceline residents. Population risks were less than 1.0 for all identified receptor populations. Assessment of risks from exposure to uranium in ground water released by the FEMP predicted no toxic effects for human receptors. All estimated cancer risks were small. The largest predicted individual lifetime risk was for a well close to the facility (1.3×10 −5). For the various above-ground shot sites at the NTS, the highest predicted lifetime cancer risks are for a resident farmer, assuming a loss of institutional control, and exceed 1×10 −4 at the 95th cumulative percentile level. At 50 000 and 100 000 y in the future, the predicted cancer risks are all below 10 −6. In the assessment of exposure to radionuclides in ground water at the NTS, for an individual onsite near the site boundary, the geometric mean of the maximum potential excess lifetime risk of cancer mortality for an individual is 7×10 −3. For an individual using water offsite, the geometric mean of the maximum potential excess lifetime risk of cancer mortality is 7×10 −7.