Savannah River Site Health Effects Subcommittee (SRSHES) Meeting

Meeting Minutes
March 13, 2003

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Mr. Vernon McDougall, Project Manager of the CDC contract for the SRS dose reconstruction, reported on the change in work scope and ATL’s progress to date. ATL is an environmental health and safety consulting firm located in Maryland. The company has been operating for eight years and serves several government clients, including CDC, DOE, Nuclear Regulatory Commission, Occupational Safety and Health Administration, and U.S. Environmental Protection Agency (EPA). ATL’s areas of expertise include environmental science, health physics, nuclear safety, occupational safety and health, modeling and scientific computing.

ATL was awarded the dose reconstruction contract in August 2002 and submitted the draft protocol to CDC the following month. In October 2002-February 2003, ATL attended a meeting and participated on several conference calls with CDC to revise drafts of the protocol in response to CDC’s changing needs. Since October 2002, ATL has been intensively focusing on the data analysis, modeling and computer programming. In the original scope of work, ATL was contracted to conduct screening based on the International Atomic Energy Association (IAEA) Safety Series No. 19 that provides a screening model for dose reconstructions. The endpoint from the model would be screening-level dose estimates for receptors in scenarios approved by SRSHES.

In October 2002, CDC changed the scope of work and required ATL to develop detailed release, transport and exposure models. The revised task would result in endpoints of dose and cancer risks for target organs and the whole body. The new scope of work also called for a statistical analysis of uncertainty effects. The modifications increased the size of the study and affected the philosophy of the overall project because the screening would have produced conservative results and erred on the side of overestimating dose. The revised scope of work is designed to provide realistic dose and risk estimates and will also evaluate uncertainties, particularly in parameter values. ATL realizes that the new tasks will result in several practical issues.

Realistic models are more difficult to properly apply. Additional research and computer programming will be needed to justify ~260 variables. The amount of data generated will be extensive. The statistical analysis of uncertainties will increase the size and scope of the project for computer analysts. Scenario locations recommended by SRSHES during the September 2002 meeting were reviewed by ATL. The Scenario Workgroup was commended for clearly describing each scenario. ATL made every effort to honor SRSHES’s recommendations while managing a tremendous amount of data, but some scenarios were modified. To determine the process by which meteorological conditions in the SRS area influence the migration of contaminants off-site, ATL will use 16-directional models that result in 22.5-degree arcs for exposures.

For the air exposure pathway, ATL determined that SRSHES did not recommend a family for the Williston, South Carolina area. This location is directly downwind from the site and had clear exposures. Meteorological data collected over the past 20 years showing wind rose in the Williston area were the justification for this determination. Based on this finding, CDC suggested that air exposures for the rural family in Clark Hill Lake be combined with and moved to Augusta, Georgia. With this change, ATL would be able to include an additional rural family in Williston, South Carolina. SRSHES also had not identified a location for the migrant family scenario. ATL suggested to CDC that this family be placed in New Ellenton, South Carolina as an additional receptor in the wind rose area.

In examining the home, school and church, ATL selected the home as the location for the air exposure pathway in five of the six scenarios. This approach was not taken with the rural family because the home was located in Gerard, South Carolina, but the school was located in Waynesboro, South Carolina. In this scenario, the school was selected as the location for the air exposure pathway. To further justify locations for the air exposure pathway, ATL used meteorological data to calculate relative air concentrations and deposition rates at ten miles from the site in several sectors.

For the milk exposure pathway, ATL proposed that the dairy location for the urban family scenario be moved from Aiken, South Carolina to New Ellenton. The plausibility of the revised air and milk exposure pathways was supported by the county Farm Bureau. Another major change was the number of scenarios proposed. SRSHES recommended 20 receptor locations, but ATL determined that some areas are similar in terms of distance from the site. To simplify the analysis, ATL proposes to use no more than ten air release locations. This strategy will reduce the number of computer runs by ~66%. Even with this streamlined approach, however, 24-hour/day computer modeling for 60 days will still be needed.

Mr. Norman Eisenberg, Senior Advisor of the CDC contract, reported on ATL’s technical approach and upcoming activities in the dose reconstruction project. ATL will base releases on the Phase II report; incorporate scenarios developed by the Scenario Workgroup; apply generic environmental models; calculate endpoints of dose, risk and organ doses as needed; use SRS-specific characteristics to revise established models; review many exposure and source locations for each receptor; and evaluate quantitative and qualitative aspects of uncertainties associated with dose and risk. The technical approach is designed to limit the number of apparent source and receptor locations to ten while still obtaining representative doses.

ATL’s overall approach to dose calculations is based on an existing risk assessment model. Variables that will be incorporated into the calculation include release, transport, exposure and consequence assessments. The model is designed to determine the amount of a contaminant released by a source; the volume of concentrations in the environment; levels of exposure to persons by ingestion, inhalation or direct contact; the time history of the release; and risks to persons based on an individual dose.

ATL will perform the risk assessment model for each exposure location and source. Federal Radiation Guidance 13 (FRG 13) will be used to qualify risk, such as probability of cancer incidence or cancer death. These figures are the most recently approved data from EPA. To address uncertainties, ATL will input releases and other variables in the risk assessment model, including uptake of radionuclides by breathing rate, vegetation and water consumption levels, and the impact of age on radiation sensitivity and consumption level. These calculations will generate both dose and risk.

Ms. Kato was not confident ATL will be able to produce realistic dose and risk estimates, particularly in light of uncertainties and other flaws in currently available data. She pointed out that results may be associated with plus or minus orders of magnitude in some cases. She asked ATL to provide SRSHES with a clear justification of all values selected. Ms. Kato also requested a clear distinction of the selection process, i.e., values based on CDC decisions versus those limited by current technologies. Mr. Eisenberg explained that estimating dose and risks in the revised scope of work will most likely generate much higher results than actual exposures. Uncertainties in releases and other parameters incorporated into dose models will be analyzed. CDC is interested in basing decisions on assessments that are as realistic as possible.

Mr. Eisenberg agreed with Ms. Kato’s observation that the figures will represent plus or minus orders of magnitude in some instances. In an effort to address this issue, ATL will conduct a point estimate evaluation of doses and risks for all persons in each scenario. All values selected will be clearly justified, but a distribution of point estimates for important variables will be established to represent uncertainties. However, the basis for distributions will also be provided to the extent possible. Mr. Lockridge requested that criteria for eliminating a particular radionuclide or pathway also be provided to SRSHES.

Mr. McDougall clarified that ATL is extensively relying on the Phase II report. Any radionuclide that was released based on these data will not be eliminated. ATL’s computer models are primarily designed for regulatory purposes, were developed with conservative values, and contain ~260 variables that affect dose and risk. With the revised scope of work, ATL will need to adjust these values and describe the rationale for each variable. Dr. Lee’s interpretation of the changed scope of work was that ATL will not conduct screening, but will immediately progress to estimating doses. The screening process was included in the project to focus SRSHES’s efforts and more effectively use resources to identify pathways and radionuclides that are most important to dose. Overlooking this step in the process may result in ATL analyzing pathways and radionuclides of least concern. Dr. Lee asked CDC to describe the rationale for eliminating screening from the contract.

Mr. Devitt added that CDC never informed SRSHES of ATL’s revised scope of work prior to distributing the briefing books. He was extremely unhappy about CDC’s lack of communication with a group that was established to provide advice and guidance. Mr. McDougall confirmed that CDC’s revised scope of work charges ATL with eliminating the screening process and advancing to the endpoint phase of the project. He pointed out that the revised tasks will result in the same results as the original scope of work. The change is merely CDC’s effort to streamline the overall project.

Mr. Charles Wood, the CDC Project Officer of the ATL contract, mentioned that calculations will be performed for scenarios approved by SRSHES. Consensus recommendations by SRSHES on these issues were forwarded to CDC and extensively discussed by RSB and ATL staff. Ms. Kato noted that SRSHES reached consensus on the scenarios, but ATL’s revised scope of work to eliminate screening was not a formal recommendation. Dr. Lee agreed with ATL’s justification to change the scenarios because receptors will now be more evenly distributed. However, she emphasized the need to continue to develop the scenarios from a historical perspective. For example, SRSHES suggested Aiken as the dairy location because cows may have been in the area in the early 1960s when the majority of iodine releases occurred.

Mr. Cliff Blackman, of the Georgia Department of Natural Resources, proposed that the Shells Bluff area along Georgia Highway 80 be considered as the location for the air exposure pathway for the rural family instead of Waynesboro. He indicated that Shells Bluff would have had the largest population of maximally exposed persons. Ms. Kato recommended that the water family scenario be moved to the Martin-Millette area since ATL’s data show greater surface water concentrations at this location. Mr. McDougall confirmed that ATL will take both these suggestions under advisement.

Mr. Devitt inquired about consistency between ATL’s modeling of air concentrations and deposition rates versus monitoring data collected by Georgia, South Carolina and SRS prior to the site being established. He mentioned that calculations can differ by several orders of magnitude depending on variables incorporated into a model. Mr. McDougall noted that ATL’s calculations were compared to existing water data, but an evaluation of air data has not yet been conducted. He emphasized that modeling is the only feasible approach in the project because some levels of exposure are too low in the environment to be measured. ATL’s modeling was found to be consistent with existing water data.

Dr. Lee questioned whether the proposed methodology will allow ATL to simultaneously input several release points into the risk assessment model. For example, SRS had five different releases at one time from five reactors. Mr. Eisenberg replied that the model allows for a finite number of releases in a single computer run. Ms. Guess specified that screening could have been used as a basis of comparison to existing modeling data. She agreed with Mr. Devitt that calculations can be influenced by variables incorporated into a model. The potential for uncertainties is minimized if models are compared to hard data.

Mr. Eisenberg addressed concerns raised by SRSHES members about the decision to eliminate a formal screening process from the dose reconstruction project. The objective of screening as outlined in the original scope of work was to reduce the number of radionuclides. The final outcome of the project will not be compromised with the revised tasks because ATL will perform calculations extremely similar to those that would have been conducted in the screening process. Under the modified scope of work, ATL will still review all releases to identify the most significant and least important pathways and radionuclides.

Another flaw in a formal screening approach is extreme assumptions. Some insignificant problems would be magnified, while important releases would be minimized. ATL’s new technical approach is sound and will provide a more balanced perspective of realistic dose and risk at SRS. For example, ATL will use the actual distance between the source and receptor rather than IAEA assumptions. Mr. Eisenberg suggested that after base case computer runs have been generated, ATL and SRSHES collectively review the results and determine if some pathways can be removed. Ms. Kato pointed out that doses are cumulative. ATL’s technical approach does not account for spikes in releases that occurred at certain times and in particular locations.

Mr. Eisenberg mentioned that ATL has considered the same limitation in its technical approach. Acute short-term releases are included in meteorological data and annual releases ATL will use to estimate doses, but the spikes are averaged over one year and will not be precisely reflected. ATL plans to conduct separate studies to calculate acute short-term releases, but the extent of this activity will depend on CDC. Despite this limitation in the modeling, doses of persons in scenarios will still be calculated throughout the entire life span. The inability to calculate doses due to the lack of available solid data on exact times releases occurred presents another problem with including peaks in the models.

Dr. Lee was concerned that ATL’s efforts to limit the number of source and receptor locations to ten may exclude impacted populations in the SRS area. This approach may cause frustration among certain members of the affected public whose doses will not be calculated. Mr. McDougall conveyed that CDC informed ATL of resource, budget and time constraints associated with completing the dose reconstruction project. Reducing the number of sources and receptors from 20 to 10 is ATL’s effort to perform the tasks within this framework. Dr. Umansky indicated that variability and assumptions may cause ATL to establish an extremely low probability value to generate significant findings. Mr. Eisenberg clarified that the level of confidence cannot be quantified in light of qualitative uncertainties. Instead of establishing a probability value, ATL will make these types of estimates based on judgment.

Mr. Hills inquired if actual off-site persons will be screened if the dose reconstruction identifies air, water, milk or vegetation pathways that resulted in heavier exposures, particularly areas with more cancer morbidity or mortality. Ms. Guess raised the possibility of randomly screening persons in the 50-mile SRS area created by SRSHES. This approach would serve to validate ATL’s calculations and produce actual data. Mr. Eisenberg replied that ATL is contracted to complete only those tasks outlined in the contract; screening has been eliminated from the project. CDC will then decide whether to undertake a more rigorous dose reconstruction study to determine whether SRS caused health problems in the area. However, he acknowledged the difficulty in randomly screening actual persons due to unknown sources and variations in dose history for each individual.

Mr. Eisenberg continued describing ATL’s technical approach by outlining additional assumptions and underlying factors that will be considered in the dose calculations. Radionuclides transported by air, surface water and food chains will be included. Existing computer codes will be realistically adapted and used to implement models. Figures for variables as close as possible to actual conditions in the SRS area will be selected. Uncertainties associated with realistic values will be considered when important variables are identified. If ATL is unable to select solid figures, conservative values will be chosen. The potential for total dose buildup in soil concentrations and other factors will be used to account for variability in annual releases.

Dose-significant characteristics will be modeled for each scenario, such as socioeconomic, living and working conditions of persons. Risks and doses will be estimated by radionuclide, year, receptor, pathway and other factors. This type of aggregate approach will allow ATL to understand the occurrence and importance of the dose and identify flaws in data, models or computer codes. After dose estimates are calculated with a best case calculation and randomly selected variables from distributions to represent uncertainties, sensitivity, uncertainty and auxiliary analyses will be performed. Ratios of doses from each radionuclide will be taken from the total dose. This calculation will identify radionuclides with the largest contributions to total dose that result in health effects. The model will also characterize environmental pathways that are most effective in transporting radionuclides to receptors.

ATL will use these data to evaluate factors, identify important stochastic variables, quantify dose and risk uncertainties, and understand technical issues. For example, sensitivity, uncertainty and auxiliary analyses could hypothetically determine that cesium-137 contributes 47% of the total dose; dose is most sensitive to uptake of cesium-137 by fish; and large acute releases may require a separate study. ATL will review the hypothetical findings to identify the most important results. In another calculation, ATL will define the mean value and confidence limits of dose and other outputs. To date, ATL has formulated a technical approach; evaluated and encoded release data; analyzed transport assessment issues; interpreted scenarios for calculation; and developed a quality assurance process for all aspects of the study.

ATL has initiated computerized analyses with the GENII version 2 code, other software and additional programs to specify the transport of radionuclides in the environment and exposure variables of persons. The computation size for the study is extremely large with >300 million data points: 39 years; 30 radionuclides released by air and water pathways; four exposure pathways from inhalation, ingestion, immersion and ground play; ten transport pathways from air, water and several food chains; 25 receptors; ten release points; and 30 exposure locations. The extraordinary task of computing, managing and analyzing a tremendous amount of data is further incentive for ATL to limit the number of receptor locations and release points to ten while still preserving the integrity of the dose calculations.

ATL selected GENII as the computer code for the study because it uses FRG 13 procedures and risk factors and is based on computer codes established >20 years. GENII is a complex system developed by Pacific Northwest Laboratory for EPA. In each step of the modeling process, ATL will need to specify variables that will impact outcomes. The variables will be thoroughly analyzed to identify the best values that represent practices and conditions at SRS. ATL has identified four major technical issues that will need to be addressed during the study. First, the model should be simplified, tractable and representative of actual doses. This problem can be resolved by combining air and water release points and merging exposure locations.

For example, the F & H combined stack could be merged with another point source for air releases, while streams and diffuse sources onsite could be combined for surface water releases. Second, completion of the release database identified several outstanding issues in the Risk Assessment Corporation (RAC) Phase II report. Zeroes associated with some releases could have represented missing data. Unspecified alpha and beta releases were not included. Releases were specified by element in some cases rather than by isotopic partitioning. ATL resolved these problems by adding source terms for unspecified alpha and beta releases; adding to or deleting from isotopes listed in the Phase II report; and partitioning some radionuclide releases into one isotope. For example, cesium-134 and -137 will be modeled as cesium-137 since this isotope results in a higher dose.

Third, environmental holdup of releases are difficult to model because the environment may store contaminants, liquid pathway releases and air releases in contaminated soil. Exposures may persist for years after the release that caused environmental concentrations. As a result, doses based on year of release may be incorrect. Seepage basins may delay exposures and releases from previously contaminated sediments and biota may also be delayed as well. ATL is making efforts to resolve these problems by developing a source term that can be divided by the flow in the Savannah River. A similar calculation would be made for Lower Three Runs Creek. Site releases will be used as the sole basis for doses from air and water pathways.

Doses from global fallout or other sources as well as residual SRS concentrations from natural radioactivity will not be considered. GENII does not account for environmental holdup of releases. ATL will perform auxiliary analyses to determine if the computer code should be modified or whether environmental holdup of releases actually needs to be modeled. Fourth, GENII may not precisely reflect acute versus average releases. For next steps, ATL will complete the computer analysis and programming, including the post-processor, statistical analysis, tests and evaluation of codes, and production runs. The data will then be analyzed and interpreted.

To support the main computation, ATL will perform auxiliary analyses for air dispersion, surface water transport and soil buildup. All findings will be compiled in a draft report. Throughout the project, ATL will be committed to generating a product of high technical quality; responding to questions, concerns and recommendations raised by CDC and SRSHES; and striving for results that will be useful to the community in understanding risks.

Mr. Lockridge asked if ATL’s uncertainty analysis will identify limitations in the computer code, such as an inability of GENII to address resuspension of particulate soil matter. He advised ATL to clearly outline flaws in the computer code to ensure this issue is transparent to the public. Mr. Eisenberg confirmed that GENII has the capacity to address resuspension doses, but the code does not automatically track deposition in the soil from earlier years. ATL identified this flaw early in the study and is considering the possibility of slightly modifying the computer code. However, this undertaking may be an ineffective use of time and effort since the total dose is only changed by 10% with resuspension. Mr. Eisenberg confirmed that the rationale for using GENII and the methodology for applying the computer code in dose calculations will be fully described in ATL’s report.

Dr. Crawford suggested that an individual drinking from the river below the Lower Three Runs Creek confluence be included in the water family scenario. Both Dr. Lee and Mr. Lockridge expressed concerns with ATL’s proposal to merge air and water release points. This approach may result in less information than is published in SRS Annual Environmental Reports. Mr. McDougall acknowledged that some RSB staff have expressed the same concern. To address this issue, ATL is currently conducting a separate study that should be completed by March 31, 2003. ATL will then submit a proposal to CDC outlining the process and rationale to combine air and water release points and potential impacts of this merger on SRS.

Ms. Drye asked if the results from ATL’s dose reconstruction project will be usable. Mr. Eisenberg replied that inherent assumptions, uncertainties in releases and other limitations may decrease the utility of the study in some instances. Nevertheless, the project will still reflect a state-of-the-art assessment of doses received from the site over the 39-year time period. Mr. Jeffrey Newman, of the Westinghouse Savannah River Company (WSRC) reported that the organization incorporated KDs into the GENII code using defaults, the published literature and SRS-specific data. He encouraged ATL to review WSRC’s model.

Dr. Lee expressed an interest in reviewing parameters ATL will incorporate into its models. She reported that CDC previously charged SRSHES with compiling SRS-specific variables, such as a greater level of fish consumption compared to other areas. Dr. Wilson inquired about the time frame for ATL to complete the project. Mr. McDougall replied that due to the revised scope of work, the study will not be completed in August 2003 as originally projected. ATL anticipates that an additional four to five months will be needed. Mr. Eisenberg agreed with Ms. Kato’s suggestion for SRSHES to list topics that should be covered in ATL’s status report at the next meeting. Dr. Bustos recessed the meeting for a break from 2:45 p.m.-2:55 p.m.

Before introducing the next agenda item, Dr. Bustos yielded the floor to an invited guest. Ms. Felicia Brown is a Community Program Manager in the South Carolina Department of Health and Environmental Control (SCDHEC). She was informed by Ms. Kim Newell, the SRSHES liaison representing SCDHEC, about the Epidemiological Data Workgroup’s request for technical assistance from an environmental epidemiologist. The staff member who filled this position retired from SCDHEC; the position is not expected to be refilled in the near future due to budget cuts. However, Ms. Brown offered to facilitate an SCDHEC epidemiologist attending a future SRSHES meeting.