5.11 ANTICIPATED HEALTH EFFECTS
This section describes the anticipated risk to human health for each of the EIS alternatives. The categories of anticipated risk presented were 1) remediation risk resulting from routine remediation activities, such as retrieving waste from tanks and waste treatment operations; 2) post-remediation risk, such as the risk resulting from residual contamination remaining after the completion of remediation activities; and 3) post-remediation risk resulting from human intrusion directly into the residual tank waste remaining after remediation.
Carcinogenic and noncarcinogenic adverse health effects on humans from exposure to radioactive and toxicological contaminants associated with each of these categories of risk were evaluated for each alternative. He alth effects from accidents are described in Section 5.12 and ecological risk effects are described in Section 5.4.6.
The No Action, Long-Term Management, In Situ Fill and Cap, and In Situ Vitrification tank waste alternatives each would result in less than one occupational latent cancer fatality, and cancer risk from chemical exposures for workers would range from 9.84E-07 to 1.95E-07 . During tank waste remediation activities, all of the alternatives involving waste retrieval would result in a similar number of latent cancer fatalities to involved and noninvolved workers (two to four according to the alternative) and similar levels of cancer risk from chemical exposure from 2.52E-06 to 8.22E-07. These health effects would be the result of the large number of tank waste remediation workers for the ex situ alternatives and retrieval, treatment, and handling of the waste. All of the capsule alternatives would result in less than one occupational latent cancer fatality from radiological exposures during remediation. All of the tank waste or capsule alternatives would result in less than one latent cancer fatality and cancer risk of less than 3.35E-06 to the general public during remedial activities.
After remediation was completed, there would be no potential for occupational health risk ; however, migration of residual tank waste and contaminants disposed of onsite in LAW vaults could pose risk to future Hanford Site users. The greatest health risk to future Site users would result from alternatives that would leave all of the waste untreated in the tanks (No Action, Long-Term Management, and In Situ Fill and Cap alternatives) or large amounts of untreated waste in the tanks (Ex Situ/In Situ Combination 1 and 2 alternatives ). All of these alternatives would pose similar risk with peak years of risk occurring from 300 to 2,500 years in the future. All of the ex situ alternatives would pose similar lower incremental lifetime cancer risk and hazard indices. Peak years of risk would occur from 5,000 to 10,000 years in the future. Future Site users that intruded into the waste remaining in the tanks would be exposed to substantial risk of a latent cancer fatality under all alternatives that leave more than 1 percent of the waste in the tanks (a probability of 1 in 100 and 3,000) compared to all of the ex situ alternatives (a probability of 1 in 11,700).
Radiation Effects
The effects of radiation emitted during disintegration (decay) of a radioactive substance depend on the kind of radiation (alpha and beta particles, and gamma and x-rays) and the total amount of radiation energy absorbed by the body. This absorbed energy is referred to as the absorbed dose. The absorbed dose, when multiplied by certain quality factors that take into account different sensitivities of various tissues, is referred to as the effective dose equivalent, or simply dose. The common unit of effective dose equivalent is the rem (1 rem equals 1,000 mrem). The total dose received by the exposed population is measured in person-rem. For example, if 1,000 people each received a dose of 0.3 rem (300 mrem), the collective dose would be 1,000 persons 0.3 rem (300 mrem) = 300 person-rem. Alternatively, the same collective dose (300 person-rem) would result from 10,000 people, each of whom received a dose of 0.03 rem (30 mrem) (10,000 0.03 = 300 person-rem).
An individual could be exposed to ionizing radiation externally (from a radioactive source outside the body) and internally (from ingesting or inhaling radioactive material). The external dose is different from the internal dose. It is estimated that the average individual in the United States receives a dose of about 0.3 rem (300 mrem) per year from natural sources of radiation. For perspective, a modern chest x-ray results in an approximate dose of 0.008 rem (8 mrem), while a diagnostic hip x-ray results in an approximate dose of 0.083 rem (83 mrem). A person must receive an acute (short-term) dose of approximately 600 rem (600,000 mrem) before there is a high probability of near-term death. Radiation also can cause a variety of ill-health effects in people. The consequence of environmental and occupational radiation exposure is the induction of latent cancer fatalities. This effect is referred to as latent cancer fatalities because the cancer may take many years to develop and for death to occur.
The factor that this EIS used to relate a dose to its effect was 0.0004 latent cancer fatalities per person-rem for a Site worker and 0.0005 latent cancer fatalities per person-rem for individuals among the general population. The general population latent cancer fatalities factor is slightly higher due to the presence of individuals in the general public that may be more sensitive to radiation than workers (e.g., infants). The concept of calculating latent cancer fatalities can be demonstrated by estimating the effects of natural radiation exposure on an individual. For example, the number of cancer fatalities corresponding to an individual's exposure over a (presumed) 70-year lifetime with a natural radiation dose of 0.3 rem (300 mrem) per year is as follows:
1 person 0.3 rem (300 mrem)/year 70 years 0.0005 latent cancer fatalities/person-rem = 0.0105 latent cancer fatalities.
This should be interpreted in a statistical sense; that is, the estimated effect of background radiation exposure on an exposed individual would produce a 1.05 percent chance that the individual might incur a latent cancer caused by the exposure. In other words, about 1.05 percent of the population is estimated to die of cancer induced by the radiation background.
Uncertainty in Risk Assessments
Human health risk assessment results are conditional estimates dependent on the assumptions that must be made to account for uncertainties of biological processes or a lack of information on source data, transport, or receptor behavior. Therefore, in evaluating risk estimates, it is important to recognize the uncertainties involved in the analysis to place the risk estimates in proper perspective. The uncertainties associated with the TWRS EIS risk estimates are quantitative where many parameters are involved in the models used in the analysis and qualitative for certain risk, such as worker risk based on the historical statistics or actuarial data. Volume Three, Appendix D presents some parameter uncertainties associated with remediation risk (Section D.4.16 ), anticipated post-remediation risk (Section D.5.17 ), ecological risk (Section D.6.5), and intruder risk (Section D.7.5), which are briefly discussed as follows. A detailed discussion of the uncertainties associated with the risk assessment is presented in Volume Five, Appendix K.
To estimate risk, information must be available on dose-response relationships, which defines the biological response from exposure to a contaminant. Although human epidemiological data are used for developing radiation and nonradiological chemical dose-response models, this information also is developed in laboratory tests using animals exposed to relatively high doses. Therefore, uncertainty is inherent in dose-response relationships, including extrapolating from effects in animals at high doses to potential effects in humans that most often are exposed at much lower doses.
Another important component of risk assessment is estimating exposure concentration. Uncertainties associated with this component of the analysis included estimating releases of contaminants from emission sources to different environmental media such as the groundwater, soil, air, and surface water, the transport and transformation of contaminants in these media, and the pathway, frequency, and duration by which humans contact the contaminants.
The risk associated with the potential release of radionuclides or chemicals to ambient environmental media during routine operations was estimated using models. The risk estimates determined by these models have a greater uncertainty than those based on the historical or actual data. However, it is reasonable to assume that potential releases would occur on a routine basis over the operational lifetime of the facility. The risk estimates for post-remediation and intruder scenarios were associated with more uncertainty than facility routine operation risk and involved uncertainties associated with the hypothetical land use and intrusion in addition to modeling. Finally, the maximally-exposed individual risk estimates generally involved a greater level of uncertainty than population risk estimates.
5.11.1 Remediation Risk
Radiological and chemical risk from remediation activities for each alternative was evaluated for Hanford Site workers involved in remediation activities; Hanford Site workers not involved in remediation activities (noninvolved workers); the general public; and a maximally-exposed individual from the workers, noninvolved workers, and general public. A maximally- exposed individual is an individual who is assumed to receive the highest possible exposure.
A more detailed description of the methodology and assumptions used in the assessment of human health risk is contained in Volume Three, Appendix D.
5.11.1.1 Comparison of Radiological Consequences from Remediation Operations
Table 5.11.1 summarizes latent cancer fatality risk for each alternative. Details of the risk calculation methodology are presented in Volume Three, Appendix D. Factors that were incorporated into the analysis included differences in the dose-to-risk conversion factor between workers and noninvolved workers and the general population; extent of exposure in each category; and the number of workers involved in each alternative.
The worker dose would result from occupational exposure to radiation. The historical dose to a Hanford Site tank farm worker has been 14 mrem/year. This same dose was assumed for radiation workers during construction of the transfer lines, retrieval system tie-ins, and tank farm confinement facilities, and during tank farm operations, monitoring, maintenance, and closure activities. A dose of 200 mrem/year was assumed for personnel operating evaporators, retrieval facilities, separation and treatment facilities (both in situ and ex situ), and for processing the capsules. The dose of 200 mrem/year was the average whole body deep exposure to operational personnel at the PUREX Plant facility in 1986 (WHC 1995g and Jacobs 1996). An average dose of 200 mrem/year was assumed for the capsule alternatives.
The maximally-exposed individual worker dose is based on a Hanford Site maintenance and operations contractor administrative control level of 500 mrem/year (HSRCM 1994). Because each alternative consists of several operations, the duration of exposure for the maximally-exposed individual was assumed to be equivalent to the duration of the operation requiring the greatest amount of time.
The potential exposure to the noninvolved worker was based on inhaling respirable radiological contaminants, which would be released to the atmosphere (at ground level or through an elevated stack) from remediation activities during each year of operation. The noninvolved worker population was assumed to occupy the area from the Hanford Site boundary to within 100 m (330 ft) of the point of release. The maximally-exposed individual was also assumed to be within 100 m (330 ft) from the point of release for ground releases and between 200 and 800 m (600 and 2,600 ft) from the point of release for elevated releases.
The potential exposure to the general public would result from exposure from air emissions released to the environment during remediation activities, and transported offsite by atmospheric dispersion during each year of operation. Routes of exposure would be from inhaling gaseous and particulate emissions; ingesting vegetables, meats, and milk products contaminated by airborne deposition; and receiving external exposure from submersion in contaminated airborne plumes. The general public population was assumed to occupy the area extending from the Hanford Site boundary (Volume Three, Section D.2.2.3) to an 80-km (50-mi) radius from the release point, centered in the 200 Areas. A reduced Site boundary was assumed for risk assessment and excluded areas that are likely to be released by DOE in the near future. Volume Three, Section D.2.2.3 defines the adjusted Site boundary. The maximally-exposed individual was assumed to live on the Hanford Site boundary and raise and consume all of their own food.
In the case of an exposed population, risk is expressed as the expected increase in latent cancer fatalities in the population at risk over the duration of the proposed alternative. For the maximally- exposed individual, it is expressed as the increased probability of dying from cancer as a result of the exposure over the duration of the alternative.
The results of the health risk calculations for the tank waste alternatives are presented in Table 5.11.1. The greatest risk to workers would result from the Phased Implementation alternative ( 3.27 latent cancer fatalities to the worker population as a result of remediation). Risk to the worker population was of similar magnitude for all ex situ alternatives (e.g., 1.96 latent cancer fatalities for Ex Situ No Separations, 2.02 latent cancer fatalities for the Ex Situ/In Situ Combination 1 and 2 alternatives , and 3.12 latent cancer fatalities for Ex Situ Intermediate Separations). This is a result of the large number of tank farm radiation workers that would be involved with these alternatives (e.g., 53,500 person-years for Ex Situ Extensive Separations; 58,500 person-years for Ex Situ Intermediate Separations; 45,000 person-years for Ex Situ/In Situ Combination 1 and 2; 36,700 person-years for Ex Situ No Separations; and 58,500 person-years for Phased Implementation).
For the noninvolved worker population, the greatest risk would be from the Phased Implementation alternative (e.g., 9.04E-04 latent cancer fatalities). The risk from other ex situ alternatives are essentially the same but slightly lower than the Phased Implementation alternative. The risks from Ex Situ Intermediate Separations, Ex Situ No Separations, and Ex Situ Extensive Separations alternatives are 7.92E-04, 8.28E-04, and 7.24E-04 latent cancer fatalities, respectively. All of these risks are extremely low. These risks result primarily from onsite transportation of waste and separation and treatment operations.
For the general public population, no latent cancer fatalities would be expected under any of the tank waste alternatives. The calculations for the cesium and strontium capsule alternatives show there would be no expected latent cancer fatalities under any of the alternatives for remediation workers, noninvolved Hanford Site workers, or the general public population.
5.11.1.2 Comparison of Nonradiological Chemical Consequences from Remediation Operations
The chemical hazard evaluation estimated inhalation intakes for identified chemical emissions and evaluated potential Incremental Lifetime Cancer Risk (ILCR) and noncarcinogenic health hazards using chemical-specific cancer slope factors and reference doses, respectively. Although the cesium and strontium capsules contain chloride, fluoride, and the decay products barium-137 and zirconium-90, no emissions of these chemicals would be associated with any of the capsule alternatives. Consequently, chemical risks were not evaluated for the capsule alternatives. The detailed methodology for estimating chemical intakes and subsequent cancer risk and noncancerous hazards are presented in Volume Three, Appendix D. The key assumptions, methodology overview, and risk assessment results are summarized in the following text.
During remediation activities, routine chemical emissions from the tank farm were based on calculations using tank farm emissions data (Jacobs 1996). Operational emissions from the tank farms, such as would occur while retrieving waste from tanks and gravel-filling the tanks, were based on the tank farm emissions data and appropriate scaling for potential increased emission rates.
The hazard index approach conservatively assumed that the noncarcinogenic health effects would be additive for all chemicals (i.e., all chemicals would have the same mechanism of action and affect the same target organ). The hazard index represents the summation of hazards evaluated. A hazard index greater than or equal to 1.0 (unity) would be indicative of potential adverse health effects in the population of concern from exposure to multiple chemicals. Conversely, a hazard index less than 1.0 would suggest that no adverse health effects would be expected.
All carcinogenic risks were assumed to be additive. Consequently, the total ILCR would represent the summation of individual chemical cancer risks, from each emission source, for each alternative analyzed. Regulatory agencies have defined an acceptable level of risk to be between 1 in 10,000 (1.0E-04) and 1 in 1,000,000 (1.0E-06), with 1.0E-06 being the point of departure and referred to as de minimis (below which there is no concern) risk. For the purpose of this EIS, a risk below 1.0E-06 was considered low, and a risk greater than 1.0E-04 was considered high.
Tables 5.11.2 and 5.11.3 summarize the noncarcinogenic health hazards and carcinogenic risks associated with air emissions for each alternative. As shown by the results in Table 5.11.2, the hazard indices for the maximally-exposed individual worker, maximally-exposed individual noninvolved worker, and maximally-exposed individual general public were well below the benchmark value of 1.0 for all alternatives. Therefore, none of the proposed remediation alternatives would be expected to result in adverse health effects from air emissions.
As shown by the results in Table 5.11.3, ILCR for the maximally-exposed individual general public would be well below 1.0E-06 for all remediation alternatives. For the maximally-exposed individual non-involved worker, estimated ILCRs were slightly greater than 1.0E-06 for the Ex Situ Intermediate Separations (1. 09 E-06), Ex Situ/In Situ Extensive Separations (1.01E-06), Ex Situ/In Situ Combination 1 and 2 (1. 09 E-06), and Phased Implementation (1. 09 E-06) alternatives. For these alternatives, the majority of the overall risk (approximately 73 percent of the overall risk) was attributable to emissions released during tank waste retrieval operations. For the maximally-exposed individual involved worker, estimated ILCRs were just above 1.0E-06 for the Ex Situ Intermediate Separations (2.5 1 E-06), Ex Situ No Separations (1.9 0 E-06), Ex Situ Extensive Separations (2.3 3 E-06), Ex Situ/In Situ Combination 1 and 2 (2.5 2 E-06), and Phased Implementation (2.5 1 E-06) alternatives. For these alternatives, the majority of the overall cancer risk (between 70 and 73 percent of the overall risk) was attributable to emissions released during tank waste retrieval operations.
Table 5.11.2 Comparison of Nonradiological Chemical Hazards from Remediation Operations
Table 5.11.3 Comparison of Nonradiological Chemical Cancer Risks from Remediation Operations
5.11.2 Post-Remediation Risk
5.11.2.1 Methodology
This section describes the potential risks to human health after all remediation activities were completed. Post-remediation human health risks were calculated for two types of health effects: the potential for ILCR and toxic effects. The ILCR was expressed as the increased probability of an individual developing cancer from exposure to radioactive or nonradioactive carcinogenic chemicals. The ILCR rate was approximately one and one-half times higher than the latent cancer fatality risk discussed in Section 5.11.1. There is no universally accepted standard for the level of risk that is considered acceptable. For known or suspected carcinogens, acceptable exposure levels suggested by Federal (55 FR 8666 and 40 CFR 300) and State (WAC 173-340) standards generally are those that represent an ILCR in the range between 1.0E-04 and 1.0E-06, which indicates a probability of 1 in 10,000 to 1 in 1,000,000, respectively. An ILCR of 1.0 means that an individual's lifetime probability of developing cancer approaches 100 percent. For the purposes of this EIS, a risk of less than 1.0E-06 (1 in 1,000,000) was considered low. A risk greater than 1.0E-04 (1 in 10,000) was considered high.
Noncarcinogenic chemicals were evaluated in terms of a hazard index, which is the ratio of chemical intake to a reference dose below which no adverse health effects would be expected. For a hazard index less than 1.0, no adverse health effects would be expected. For a hazard index greater than 1.0, adverse health effects would be expected. A health effect could be fatal or it could be a minor temporary effect on the human body, depending on the specific chemical and amount of exposure involved.
Three key factors were involved in calculating potential risks: the source term, transport, and exposure. The source term is the amount and type of contaminant that may be released to the environment. For example, under the No Action (Tank Waste) alternative the source term would be the entire contents of the tanks that could be released over time into the groundwater. The source terms of the alternatives would vary because of the differences in the quantity, form, or manner of containment of the waste left onsite. The source term for each alternative is described in Volume Three, Appendix D and summarized in Section 5.11.2.2.
Transport refers to movement of the contaminants in the environment from the source (e.g., tanks) to the receptor, which is the person who might be exposed to the contaminant. Following loss of institutional controls (assumed to be 100 years), the tank contents would be released to the subsurface soils and be available for transport to groundwater from infiltration of rainwater and percolation through the soil column. Based on the existing depth of the tanks, resulting soil contamination would be below the maximum depth of soil likely to be contacted by all potential receptors, with the exception of the intruder scenario. Consequently, the soil medium was not evaluated as a post-remediation transport mechanism for any of the alternatives. Because tank waste would be released to the subsurface, no contaminants would be transported into the air, and this medium was not evaluated for any of the alternatives. Also, for this EIS, post remediation impacts for all tank waste alternatives except No Action and Long-Term Management included a closure scenario (closure as a landfill) that included covering the tank farms and LAW vaults with a Hanford Barrier. Therefore, groundwater would be the only post-remediation transport mechanism for all the alternatives.
Under all of the alternatives, any waste that would be disposed of offsite would not be of concern for exposure at the Hanford Site. Any waste that remained on the Hanford Site would have a potential to cause exposure to people in the surrounding community. Onsite waste, under all of the alternatives, would be in a waste tank, a LAW vault, or drywells (cesium and strontium capsules). The potential transport of waste from the tanks or the vaults could result from leaks that might occur during retrieval. Another mechanism would be precipitation filtering through the Hanford Barriers placed over the tanks and vaults, into the underlying vadose zone, and then into the groundwater aquifer. This process can be extremely slow because of the low precipitation rates for the Hanford Site, the ability of the Hanford Barrier to retard water movement, the slow rate that some contaminants would be leached by water, and the slow rate that the contaminated water would move through the vadose zone into the groundwater aquifer. Once in the groundwater, the contaminants would move relatively quickly to the Columbia River, where they would discharge as springs along the river bank or seep directly into the river. Once in the surface water, contaminants would be rapidly diluted by mixing with the river flow. The total process can be extremely slow, taking hundreds or thousands of years from the initiation of the leak, depending on the alternative. Groundwater migration with subsequent discharge to the Columbia River would be the only pathway for migration of contaminants that would occur after remediation was complete for any of the alternatives. A detailed description and computer modeling of the groundwater transport pathway for each alternative is contained in Volume Four, Appendix F and summarized in Section 5.2.
Because the groundwater pathway can take hundreds or thousands of years to result in exposures, and because contaminants in the waste are persistent (i.e., remain in the environment for a long time), risk must be calculated for a number of extended time periods. This shows how potential risk may increase or decrease over time as contaminants move through the groundwater and as radioactive decay changes the characteristics of the contaminants. To show these changes, risks were calculated for five time periods: 300, 500, 2,500, 5,000, and 10,000 years from the present.
The risks described in this section are the incremental risks for the TWRS alternatives only, and do not take into account soil and groundwater below the tank farms and other portions of the Hanford Site that currently are contaminated with a wide variety of radiological and chemical contaminants.
Exposure was the third factor involved in calculating potential risk. Exposure involves the pathway, duration, and intensity of potential exposure from contaminants that have been transported into and through the groundwater. The type and amount of exposure would be dependent on future potential land uses. Five exposure scenarios were modeled: Native American , residential farmer, industrial worker, recreational land user, and recreational shoreline user of the Hanford Reach along the Columbia River. These exposure scenarios were considered likely post-remediation future uses of the land on and adjacent to the Hanford Site and represented a range of land uses that aided in comparison of the impacts of alternatives. The potential risk for each of these future uses would be different because each scenario would involve different levels of consumption and contact with contaminated groundwater or surface water contaminated by discharge of groundwater. Future Site uses will be the subject of analysis in the Hanford Remedial Action EIS, which is being prepared by DOE.
The Native American scenario represented exposures to a Native American who engaged in both traditional lifestyle activities (e.g., hunting, fishing, and using a sweat lodge) and contemporary lifestyle activities (e.g., irrigated farming). Exposure pathways included those defined for the residential farmer scenario plus additional pathways unique to the Native American subsistence lifestyle (such as sweat lodge use). The exposures were assumed to be continuous for 365 days per year over a 70-year lifetime. The scenario used native food ingestion rates. By incorporating subsistence lifestyle activities and native food ingestion rates, this scenario resulted in exposures that would be approximately five times higher than the exposures for the residential farmer scenario.
The residential farmer scenario represented use of the land for residential and agricultural production. This scenario involved a person living on the Hanford Site, drinking water pumped from the groundwater, and producing and consuming animal, vegetable, and fruit products irrigated with groundwater. The exposures were assumed to be continuous and included occasional surface water recreational activities and surface water sediment contact.
The industrial worker scenario involved exposures to workers who lived outside of the Hanford Site but worked in a commercial or industrial setting on the Hanford Site for 20 years. The scenario involved consuming water pumped from the groundwater and indoor activities, although some outdoor activities also were included. These exposures would not be continuous because the worker was assumed to go to a home outside the Hanford Site at the end of the 8-hour work day. The scenario was intended to represent nonremediation workers who would wear no protective clothing.
The recreational land user was a random Sitewide land user. This scenario involved exposure to contamination from recreational camping, hiking, and other land-based recreational activities. These exposures would not be continuous, but rather were assumed to occur for 14 days per year for 30 years. There would be no groundwater or surface water pathway for the recreational land user, thus there were no risks for this exposure scenario under any of the TWRS alternatives. This scenario is not described further in this analysis.
The recreational shoreline user scenario involved exposure to contamination in the groundwater and Columbia River and along its shoreline from recreational swimming, boating, and other shoreline activities. The scenario involved mainly outdoor activities. These exposures would not be continuous, but rather were assumed to occur for 14 days per year for 30 years.
The exposure parameters (e.g., amount of water consumed) for each of these exposure scenarios are shown in Volume Three, Appendix D. The residential farmer, industrial worker, and recreational user exposure scenarios were consistent with the Hanford Site Risk Assessment Methodology, which is the Site-approved method for calculating risks (DOE 1995c). For the first time, DOE has included a Native American exposure scenario in an analysis of potential long-term health effects. This scenario was developed from the Columbia River Comprehensive Impact Assessment (Napier et al. 1996), which was modified at the request of and in consultation with the potentially affected Tribes. This scenario is in its initial stages of development and has not received a complete review by the scientific community, nor has it been approved by the potentially affected Tribes. Therefore, this scenario should be considered preliminary and may have more uncertainty associated with it than the other scenarios. However, the scenario does provide a bounding assessment of the potential health effects to a Native American who might inhabit the Site in the future and engage in both subsistence lifestyle activities (e.g., hunting, fishing, and using sweat lodges) and contemporary lifestyle activities (e.g., irrigated farming). Volume Three, Appendix D contains a detailed description of the methodology and assumptions used to develop the risk calculations.
5.11.2.2 Risk Assessment Results
Summary
Table 5.11.4 shows the maximum calculated potential ILCR from both radiological and carcinogenic chemicals and the noncarcinogenic chemical hazard for each tank waste alternative. The ILCR data shown in Table 5.11.4 are plotted graphically for the Native American, residential farmer, industrial worker , and recreational shoreline user scenarios in Figures 5.11.1 through 5.11. 4 . Risk distribution contour maps for the residential farmer at the time of maximum risk for each alternative are shown in Figures 5.11.5 through 5.11.14. Similar figures showing risk distributions for the other exposure scenarios are presented in Volume Three, Appendix D.
Potential risks were not shown for the recreational land user because this exposure would involve no consumption of groundwater and no contact with the Columbia River. Therefore, there would be no pathway for potential exposure, and there would be no post-remediation risks associated with this scenario.
In general, the results showed the following ranking of the tank waste alternatives from greatest risk to lowest risk, although the order would change somewhat over the 10,000-year period addressed in this analysis:
- No Action;
- Long-Term Management;
- In Situ Fill and Cap;
- Ex Situ/In Situ Combination 2;
- Ex Situ/In Situ Combination 1 ;
- Ex Situ Intermediate Separations;
- Phased Implementation;
- Ex Situ Extensive Separations;
- Ex Situ No Separations; and
- In Situ Vitrification.
All of the ex situ alternatives, except the Ex Situ/In Situ Combination 1 and 2 alternatives , would result in similar risk levels. This is because most of the risk would result from contaminants leached from the 1 percent residual waste that would be left in the tanks after waste retrieval under these alternatives. The risk from the 1 percent residuals in the tanks generally would be 100 or more times greater than the risk from contaminants leached from the LAW vaultsalthough this would vary somewhat at different time periods.
An assessment was prepared of the total latent cancer incidence and fatalities that could occur over 10,000 years for each of the exposure scenarios: Native American , residential farmer, industrial worker, and recreational shoreline use. Table 5.11.5 presents the potential total cancer incidence and fatalities for each alternative over the entire 10,000-year period. The methodology and detailed analysis are presented in Volume Three, Appendix D, Section D.5.15.1. The uncertainties associated with these calculations are high; however, these calculations provide an estimate of possible impacts under one set of future use assumptions and help to compare the long-term risks among the alternatives. These calculations were based on assumptions and represent one set among many possible sets of scenarios representing long-term risk.
Figure 5.11.1 Post-Remediation Risk to the Native American for All Tank Waste Alternatives
Figure 5.11.2 Post-Remediation Risk to the Residential Farmer for All Tank Waste Alternatives
Figure 5.11.3 Post-Remediation Risk to the Industrial Worker for All Tank Waste Alternatives
Table 5.11.4 Summary of Bounding Case Incremental Lifetime Cancer Risks and Hazard Indices
Table 5.11.4 Summary of Bounding Case Incremental Lifetime Cancer Risks and Hazard Indices (cont'd)
The integrated post-remediation health effects over 10,000 years from the present for the downriver population on the Columbia River for an estimated population of 500,000 were calculated for each alternative. Table 5.11.6 presents the total fatalities, population dose, and maximum incremental dose for each alternative.
As discussed earlier in this section, the post-remediation risk calculations contained a number of conservative assumptions designed to ensure that the results would provide an upper bound of the long-term risk associated with the TWRS alternatives. For comparison purposes, a nominal case was also evaluated. The nominal case was based on average rather than conservative assumptions. Evaluation methods for the nominal case were identical to the bounding case. Tables 5.11.7 and 5.11.8 present the risk range for the bounding and nominal cases. Risk range refers to the difference between the risk values for the bounding case and the corresponding values for the nominal case.
Table 5.11.7 shows the maximum calculated values for ILCR and noncarcinogenic chemical hazard for the bounding and nominal cases. Values shown are the highest values calculated for each exposure scenario and time period under each alternative. The risk range can be determined by comparing values for the bounding case with the corresponding values for the nominal case. For example, under the bounding case for the No Action (Tank Waste) alternative, the post-remediation risk to the residential farmer at 300 years was calculated to be 4.58E-01; the corresponding risk for the nominal case was calculated to be 1.92E-01 (Table 5.11.7).
Table 5.11.8 shows the total post-remediation cancer incidence calculated over a 10,000 year period for the bounding and nominal cases. The risk range can be determined in the same manner as for the maximum risk range. For example, under the bounding case for the No Action (Tank Waste) alternative, the total cancer incidence for the residential farmer over 10,000 years was calculated to be 759; the corresponding cancer incidence for the nominal case was calculated to be 626 (Table 5.11.8).
No Action Alternative (Tank Waste)
The source term under this alternative would be the entire inventory of the tank waste. After the 100-year administrative control period, the tank tops would collapse, and without a Hanford Barrier, precipitation would move through the waste relatively fast, leaching contaminants into the underlying vadose zone and groundwater. The groundwater would rapidly transport contaminants to the Columbia River. The fastest moving contaminants would reach the groundwater aquifer in approximately 140 years after 100 years of administrative control. Within 300 years the ILCR for the Native American, residential farmer , and industrial worker scenarios would be greater than 1.0E-01 (high risk), and the hazard indices would be greater than 1.0 for all the scenarios, indicating that toxic effects would occur. Within 300 years, the ILCR for the recreational shoreline user would be greater than 1.0E-02 (high risk). The ILCR slowly would decrease over time but would be high for at least 10,000 years for the Native American scenario and at least 2,500 years for the residential farmer scenario.
Long-Term Management Alternative
Under this alternative, the source of contamination would be the entire inventory of the tank waste. This would be the same source as under the No Action (Tank Waste) alternative; however, 1 percent of the current DST inventory would remain in the original DSTs as residual waste and the other 99 percent would be contained in replacement DSTs. As in the No Action alternative, the tank tops would collapse after the administrative control period; however, this collapse would take longer to occur because of the replacement DSTs. As previously described, without a Hanford Barrier, contamination would rapidly leach from the tanks and would reach the groundwater in approximately 140 years after 100 years of administrative control.
Within 300 years, the ILCR would exceed 1.0E-01 (high risk) for the Native American, residential farmer, and industrial worker scenarios and 1.0E-02 (high risk) for the recreational shoreline user. The hazard indices would be greater than 1.0 for all the scenarios, indicating that toxic effects would occur. The ILCR would decrease over time at a somewhat more rapid rate than for the No Action alternative but would remain high for at least 10,000 years for the Native American scenario and at least 2,500 years for the residential farmer scenario.
In Situ Fill and Cap Alternative
The source for contamination under this alternative would be the entire inventory of the tank waste. This would be the same source as under the Long-Term Management alternative; however, there would be a Hanford Barrier over the tanks to retard infiltration under this alternative. Water from precipitation would move slowly through the Hanford Barrier and leach contaminants from the unstabilized waste. Contaminants would not reach the groundwater until approximately 2,300 years from the present. The ILCR would be less than 1.0E-06 (low risk) for all receptors until after 2,500 years. At 5,000 years, potential risks would exceed 1.0E-01 (high risk) for the Native American , 1.0E-02 (high risk) for the residential farmer, 1.0E-03 (high risk) for the industrial worker, and 1.0E-04 (high risk) for the recreational shoreline user. The hazard indices would approach or reach 1.0, indicating that toxic effects would be expected.
In Situ Vitrification Alternative
The source term under this alternative would be the entire inventory of the tank waste. This would be the same waste inventory as under the No Action (Tank Waste) alternative ; however, the waste would be in an immobilized (vitrified) form, and there would be a low-permeability Hanford Barrier over the tanks to retard infiltration of precipitation. Water from precipitation would move slowly through the Hanford Barrier and leach contaminants from the vitrified waste. Contaminants would not reach the groundwater aquifer for approximately 2,350 years , and the ILCR would be less than 1.00-06 (low risk) for all receptors until after 2,500 years.
At 5,000 and 10,000 years, the ILCR would exceed 1.0E-04 (high risk) for the Native American scenario and be between 1.0E-06 (low risk) and 1.0E-04 for the residential farmer, industrial worker, and recreational shoreline user scenarios. The hazard indices would be less than 1.0 for all exposure scenarios and all time periods, indicating that no toxic effects would occur.
Ex Situ Intermediate Separations Alternative
There would be two sources for contamination under this alternative. One source term would be the 1 percent of the current tank waste that would remain in the tanks as residual waste. The other source would be the vitrified waste in the LAW vaults. Both sources would be covered with a Hanford Barrier. While water from precipitation would move slowly through the Hanford Barrier and through the tanks as previously described, the volume of contaminants available to be leached would be only 1 percent of the current tank volume; therefore , the levels of contamination in the groundwater would be reduced substantially. Water from precipitation also would move slowly through the Hanford Barrier and through the LAW vaults, slowly leaching contaminants in the vitrified waste into the groundwater aquifer. The groundwater contamination from the 1 percent residual waste in the tanks would be approximately 100 times or more greater than the contaminants from the LAW vaults, although this would vary somewhat at different time periods. Contaminants would not reach the groundwater until approximately 1,100 years from the present.
The ILCR would be less than or near 1.0E-06 (low risk) until after 2,500 years for all but the Native American scenario. Potential risks for the Native American scenario would exceed 1.0E-04 (high risk) at 2,500 years and would remain above 1.0E-04 through the 10,000-year time period. At 5,000 years, the hazard index would exceed 1.0 for the Native American, indicating that toxic effects would be expected. For the residential farmer and industrial worker scenarios, the ILCR would exceed 1.0E-04 at 5,000 years and be between 1.0E-06 and 1.0E-04 at 10,000 years. The hazards index for the residential farmer would exceed 1.0 at 5,000 years, indicating that toxic effects would be expected. The hazard index for the industrial worker would not exceed 1.0 for any time period. For the recreational shoreline user scenario, the ILCR would only exceed 1.0E-06 (but be below 1.0E-04) at the 5,000-year time period, and the hazard index would be below 1.0. The ILCR from the 1 percent residuals in the tanks would be approximately 100 times greater than the ILCR from the LAW vaults.
Ex Situ No Separations Alternative
Under this alternative, the source would be the same as under the Ex Situ Intermediate Separations alternative except there would be no LAW vaults because all waste retrieved would be disposed of at the potential geologic repository. The source for this alternative would be the 1 percent of the current tank waste that would remain in the tanks as residual waste. As described previously, water from precipitation would move slowly through the Hanford Barrier and leach the residuals into the aquifer within approximately 1,100 years from the present. The risks and hazards associated with this alternative would be nearly identical to the Ex Situ Intermediate Separations alternative because the risks from the 1 percent residuals would be 100 times greater than from the LAW vaults, and they overshadow the ILCR from the LAW vaults. The absence of LAW vaults under this alternative would have little impact on risks. Hazard indices would approach or reach 1.0 at 5,000 years for the Native American and residential farmer, indicating that toxic effects would be expected.
Ex Situ Extensive Separations Alternative
Under this alternative, the sources would be the same as under the Ex Situ Intermediate Separations alternative except that the LAW vaults would contain approximately 100 to 1,000 times lower concentrations of technetium-99 and uranium (total). However, because the ILCR from the 1 percent residuals would be 100 times greater than the LAW vaults in the Ex Situ Intermediate Separations alternative, the reduction in the technetium-99 and uranium (total) would have little e ffect on overall ILCR. Therefore, the ILCR and hazard indices for this alternative essentially would be the same as the Ex Situ Intermediate Separations and Ex Situ No Separations alternatives.
Ex Situ/In Situ Combination 1 Alternative
Under this alternative, approximately one-half of the tank waste by volume would be remediated using the In Situ Fill and Cap alternative and the other half would be remediated under the Ex Situ Intermediate Separations alternative. By selecting the appropriate tanks for retrieval, approximately 90 percent of the largest contributors to groundwater risk (technetium-99, iodine-129, carbon-14, and uranium) would be retrieved, vitrified, and disposed of in the HLW, which would be sent to the potential geologic repository. Both the tanks and the LAW vaults would be covered with a Hanford Barrier, and water from precipitation would leach the contaminants as previously described. Contaminants would not reach the groundwater for approximately 500 years. At 2,500 years, the ILCR would exceed 1.0E-04 (high risk) for the Native American scenario but would be less than or near 1.0E-06 (low risk) for the other scenarios. At 5,000 years, the ILCR would exceed 1.0E-03 for the Native American, residential farmer, and industrial worker, and be between 1.0E-06 and 1.0E-04 for the recreational shoreline user. Potential risks would decrease over time but would remain above 1.0E-04 for the native American and residential farmer at the 10,000-year period, and between 1.0E-06 and 1.0E-04 for the industrial worker and recreational shoreline user. Hazard indices would exceed 1.0 only for the Native American and residential farmer at 5,000 and 10,000 years, indicating that toxic effects would be expected at these time periods.
Ex Situ/In Situ Combination 2 Alternative
The Ex Situ/In Situ Combination 2 alternative would use modified tank selection criteria to provide for ex situ treatment of the largest contributors to groundwater risk while limiting the volume of waste to be processed. Under this variation, approximately 25 tanks instead of 177 tanks would be retrieved and remediated using the Ex Situ Intermediate Separations alternative, while the remaining tanks would be remediated under the In Situ Fill and Cap alternative. As for the Ex Situ/In Situ Combination 1 alternative, the tanks and LAW vaults would be covered with a Hanford Barrier and contaminants would not reach groundwater for approximately 500 years. The ILCR would be less than or near 1.0E-06 (low risk) until after 2,500 years. Potential risks at 5,000 and 10,000 years would be higher than for Ex Situ/In Situ Combination 1 alternative because a greater volume of unstabilized tank waste would be available to leach into the groundwater. The ILCR would exceed 1.0E-04 for all scenarios at 5,000 years and remain above 1.0E-04 for all but the recreational shoreline user through the 10,000-year period. Hazard indices would exceed 1.0 only for the Native American and residential farmer at 5,000 and 10,000 years, indicating that toxic effects would be expected at these time periods.
Phased Implementation Alternative
There would be two sources for contamination under this alternative. One source term would be the 1 percent of the current tank waste that would remain in the tanks as residual waste. The other source would be the vitrified waste in the LAW vaults. Both sources would be covered with a Hanford Barrier. While water from precipitation would move slowly through the Hanford Barrier and through the tanks as previously described, the volume of contaminants available to be leached would be only 1 percent of the current tank volume; therefore, the levels of contamination in the groundwater would be reduced substantially. Water from precipitation also would move slowly through the Hanford Barrier and through the LAW vaults, slowly leaching contaminants in the vitrified waste into the groundwater aquifer. The groundwater contamination from the 1 percent residual waste in the tanks would be approximately 100 times or more greater than the contaminants from the LAW vaults, although this would vary somewhat at different time periods. Contaminants would not reach the groundwater until approximately 1,100 years from the present. At 2,500 years, the ILCR would exceed 1.0E-04 (high risk) for the Native American scenario but would be less than or near 1.E-06 (low risk) for the other scenarios. At 5,000 years, the ILCR would exceed 1.0E-04 for the Native American, residential farmer, and industrial worker, and be between 1.0E-06 and 1.0E-04 for the recreational shoreline user. Potential risks would decrease over time but would remain above 1.0E-04 for the Native American at the 10,000-year period and between 1.0E-06 and 1.0E-04 for the residential farmer and the industrial worker. Hazard indices would exceed 1.0 only for the Native American and residential farmer at 5,000 years, indicating that toxic effects would be expected. The ILCR from the 1 percent residuals in the tanks would be approximately 100 times greater than the ILCR from the LAW vaults.
Capsule Alternatives
All of the cesium and strontium capsule alternatives, except Onsite Disposal, would involve removing all of the cesium and strontium from the Hanford Site, and therefore would not result in any post-remediation risks. Under the Onsite Disposal alternative, the cesium and strontium would decay into their stable progeny before the steel canisters corroded and allowed the release of cesium and strontium, which could move through the vadose zone (Section 5.2). Cesium and strontium, with half-lives of only 30.2 and 28.6 years, respectively, would decay into their stable progeny, barium-137 and zirconium-90. As described in Volume Four, Appendix F, it would take approximately 600 years to transport the cesium and strontium to the groundwater. After this time period, there would be small amounts of cesium and strontium remaining, and no measurable amount would reach the groundwater. Barium and zirconium, the progeny, eventually would reach the groundwater in concentrations so low that they would represent a negligible risk. Therefore, none of the capsule alternatives would result in any substantial post-remediation risks.
5.11.3 Post-Remediation Intruder Scenario
An intruder scenario analysis is presented in Volume Three, Appendix D. The increased cancer incidence risk and increased latent cancer fatality risk for the alternatives are calculated in Volume Three, Appendix D, Section D.7.0, Tables D.7.4.1 and D.7.4.2. The intrusion was a postulated well drilling scenario on the Hanford Site after the assumed loss of institutional control 100 years from the present. The exposure to the well driller who would drive a 30-cm (0.98-ft)-diameter well through the onsite waste and would bring the waste to the surface was calculated. Exposure to a post-drilling resident also was calculated. The post-drilling resident was assumed to have a vegetable garden in the exhumed waste that supplied 25 percent of this individual's vegetable intake.
The greatest risk would come from the No Action, Long-Term Management and In Situ Fill and Cap tank waste alternatives, in which the entire nonimmobilized inventory of waste would remain in the tanks. For each of these three alternatives, the probability of a cancer incidence was calculated to be 1.02E-02 (1 in 100) for the driller and 5.07E-02 (1 in 20) for the post-drilling resident. The probability of a latent cancer fatality was calculated to be 8.52E-03 (1 in 100) for the driller and 4.23E-02 (1 in 24 ) for the post-drilling resident.
The Ex Situ/In Situ Combination 1 alternative would have the next highest risk with a probability of a cancer incidence of 1.47E-03 (1 in 700) for the driller and 7.94E-03 (1 in 125) for the post-drilling resident. The probability of a latent cancer fatality was calculated to be 1.23E-03 (1 in 800) for the driller and 6.62E-03 (1 in 150) for the post-drilling resident. The Ex Situ/In Situ Combination 2 alternative would have the next highest risk with a cancer incidence probability of 7.26E-04 (1 in 4,000) for the driller and 3.04E-03 (1 in 328) for the post-drilling resident. The probability of a latent cancer fatality was calculated to be 6.05E-04 (1 in 1,500) for the driller and 2.53E-03 (1 in 400) for the post-drilling resident. These risks would be lower than the risks for the Ex Situ/In Situ Combination 1 alternative because waste would be retrieved from a greater number of DSTs. The Ex Situ/In Situ Combination 2 alternative would be similar to the In Situ Vitrification alternative, which would have a probability of a cancer incidence of 3.79E-04 (1 in 2,600) for the driller and 2.54E-03 (1 in 400) for the post-drilling resident. The probability of a latent cancer fatality was calculated to be 3.16E-04 (1 in 3,000) for the driller and 2.04E-03 (1 in 500) for the post-drilling resident.
The lowest risk would come from the Ex Situ Intermediate Separations, Ex Situ No Separations, Ex Situ Extensive Separations, and Phased Implementation alternatives in which 99 percent of the inventory of waste would be removed from the tanks. For each of these four alternatives, the probability of a cancer incidence was calculated to be 1.02E-04 (1 in 10,000) for the driller and 5.07E-04 (1 in 2,000) for the post-drilling resident. The probability of a latent cancer fatality was calculated to be 8.52E-05 (1 in 11,700) for the driller and 4.23E-04 (1 in 2,400) for the post-drilling resident.
The only increased risk from the capsule alternatives would come from the Onsite Disposal alternative. Under the other alternatives, cesium and strontium would be removed from the Hanford Site. The probability of a cancer incidence and latent cancer fatality for both the driller and the post-drilling resident was calculated to be 1.0.
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