D.5.0 ANTICIPATED POST-REMEDIATION RISK
This section presents the results of the assessment of anticipated post-remediation risk for each of the TWRS EIS alternatives. Post-remediation risk is the risk to a future land user from exposure to residual contamination after the TWRS mission has been completed. Anticipated risk was evaluated for five exposure scenarios: 1) the Native American; 2 ) the residential farmer; 3 ) the industrial worker; 4 ) the recreational shoreline user; and 5 ) the recreational land user. These scenarios were selected to represent a range of possible land uses that could occur at the Hanford Site in the future.
The risk presented in this section was evaluated using the modular risk assessment methodology described in Section D.2.1. The modular approach separates the four basic components of the risk assessment process (i.e., source, transport, exposure, and risk) into discrete modules that can be assessed independently and then combined.
The following sections discuss the source, transport, exposure, and risk modules developed for each of the TWRS EIS alternatives. Due to their length, the support ing tables and graphs are presented at the end of this section.
D.5.1 NO ACTION ALTERNATIVE (TANK WASTE) (BASELINE RISK ASSESSMENT)
This section presents the anticipated post-remediation risk associated with the No Action alternative for tank waste. Post remediation for this alternative refers to risk remaining after tank farm operational activities and 100 years institutional controls (40 CFR 191) are discontinued.
D.5.1.1 Source
Post-remediation contamination sources under the No Action alternative would consist of the current inventories in the SSTs , DSTs , and MUSTs (Jacobs 1996). Additional discussion of contaminant source inventories is provided in Volume Two, Appendix A.
D.5.1.2 Transport
Post remediation contaminant releases would be from the tanks to the soil. Contaminants released to the soil would migrate to groundwater in proportion to their ionic mobility. Air emissions from all sources were assumed to be zero. Thus, groundwater transport (i.e., transport in the vadose zone and aquifer) was the only transport pathway considered for this assessment. The point concentrations used for the risk calculations (i.e., future concentrations at a given receptor originating from a particular source) were generated through groundwater transport modeling and are discussed briefly in the following text. A detailed discussion of groundwater modeling is provided in Volume Four, Appendix F.
Groundwater modeling predicts that contaminants released from the tanks would be present in groundwater beneath the Hanford Site for all periods of interest [i.e., 300, 500, 2,000, 5,000, and 10,000 years from the present (40 CFR 191)]. Calculated groundwater contaminant concentrations and spatial distributions are discussed in Volume Four, Appendix F.
Example point concentrations for one constituent (I-129) are displayed in Table D.5.1.1. The table shows calculated groundwater concentrations by grid cell for the periods of interest. Similar data have been tabulated for the other constituents calculated to reach groundwater but are not presented here in the interest of brevity.
Contaminated groundwater would eventually discharge to the Columbia River where it would be rapidly diluted by mixing with the river flow. The contaminant mass entering the river would cause the recreational shoreline user to receive small exposures from surface water activities. To evaluate an upper bound for these exposures, conservative surface water concentrations were calculated for five mobile constituents of concern (C-14, I-129, Tc-99, U-238, and nitrate) by applying a dilution factor to the maximum calculated groundwater concentration given in Volume Four, Appendix F for each constituent in each time period. The resultant river water concentrations were then conservatively assumed to be present uniformly in the surface water used by the recreational shoreline user.
The dilution factor was determined by using results from the surface water impacts analysis described in Section 5.2.2. In that analysis, a mixing calculation indicated that the concentration of nitrate in the Columbia River would reach a maximum of 0.177 mg/L under the Long-Term Management alternative at 300 years from 1995. This concentration (0.177 mg/L) is approximately 0.12 mg/L above the river's 0.05 mg/L background nitrate concentration and resulted from the discharge of groundwater with a maximum calculated nitrate concentration of 1.05E+03 mg/L. Using these results, the ratio of surface water concentration (0.177-0.05=0.127 mg/L) to groundwater concentration (1.05E+03 mg/L) yields a dilution factor for nitrate of 0.127/1.05E+03=1.21E-04. For the risk analysis, the maximum calculated groundwater concentrations for the constituents of concern were multiplied by the dilution factor to produce maximum surface water concentrations. Applying the nitrate dilution factor to the other four constituents is considered appropriate because these constituents have approximately the same groundwater mobility (i.e., the same Kd) as nitrate.
D.5.1.3 Exposure
Exposure is quantified using a URF. A URF is the risk associated with exposure to a unit concentration of a given contaminant under one of five exposure scenarios (i.e., Native American, residential farmer, industrial, recreational shoreline user, and recreational land user). URFs were developed for the appropriate exposure pathway (i.e., ingestion, inhalation, and direct contact) for each applicable exposure scenario. URFs are discussed and presented in Section D.2.1.3.
Exposure would occur as the result of direct or indirect exposure to groundwater and, for the recreational shoreline user, to surface water. The recreational land user scenario assumes no use of groundwater; thus there is no complete exposure pathway. Therefore, there is no risk associated with this scenario and it is not discussed further. Because the Native American, residential farmer, industrial, and recreational shoreline user scenarios included groundwater use, these receptors have complete exposure pathways and receive direct exposure. These receptors would have the potential to receive indirect exposures through the pathways shown in Section D.2.1.3.
D.5.1.4 Risk
The anticipated risk to a receptor within a grid cell was calculated as the product of the point concentration and the URF (Section D.2.1.4). The risk module calculates risk for each exposure scenario, source, and period of interest across all grid cells on the Hanford Site. To visually display the anticipated risk, GIS software was used to generate contour maps illustrating potential risk to a receptor at various locations across the Hanford Site. Each area defined by contour lines represents a zone with a discrete value of risk. Risk from radionuclides and carcinogenic chemicals was combined and presented on one set of maps. HIs from noncarcinogenic chemicals are presented on a separate set of maps.
For radionuclides and carcinogenic chemicals, the risk is defined as the increased probability that an individual at any location along a contour line would develop cancer under the defined conditions of the exposure scenario. Human health risk is defined in terms of the incremental lifetime cancer risk (ILCR). Although there is no universally accepted standard for the level of risk considered acceptable, for purposes of this analysis risk of 1.00E-06 (one in one million) is considered to be low and risk greater than 1.00E-04 (one in ten thousand) is considered high. An ILCR of 1 means that an individual's lifetime probability of developing cancer approaches 100 percent.
For noncarcinogenic chemicals, the HI is the ratio of chemical intake to a reference dose below which no toxic effects are expected. Where the HI is less than 1.0, no toxic effects are expected. Where it is greater than 1, toxic effects are expected. Contour maps for the HI are constructed in the same way as for the cancer risk.
On certain contour maps, white areas with risk values less than the minimum value contoured (i.e., less than 1.0E-06) appear as "holes" in the risk distributions. One such set of "holes" trending in a northwest-to- southeast direction north of the 200 Areas represents areas where basalt occurs above the water table, preventing the influx of contaminated water into these areas. Another such set underlying the 200 West Area represent s conditions of groundwater mounding created by liquid discharges from Hanford Site facilities. The roughness associated with the contour lines is a function of the resolution of the analysis (i.e., 1 by 1 km [0.6 by 0.6 mi] grid size).
The risk calculation for the No Action alternative combines the risk contributed by the SSTs and DSTs into a single risk value for each grid cell. Risk calculations were performed for all five periods of interest. Risk contour maps are presented for all scenarios and time periods except in cases where the maximum combined risk from radionuclides and carcinogenic chemicals is below 1.00E-06, or the maximum hazard from noncarcinogenic chemicals is less than an HI of 1.0. No maps are presented in these latter cases.
Contour maps depicting the risk from radionuclides and carcinogenic chemicals in tank waste are presented in Figures D.5.1.1 to D.5.1.5 for the Native American scenario, Figures D.5.1.6 to D.5.1. 9 for the residential farmer scenario , Figures D.5.1.10 to D.5.1. 13 for the industrial worker scenario , and Figures D.5.1.14 to D.5.1. 16 for the recreational shoreline user scenario. Contour maps depicting the HI from noncarcinogenic chemicals in tank waste are presented in Figures D.5.1.17 to D.5.1.19 for the Native American scenario, Figures D.5.1. 20 to D.5.1. 22 for the residential farmer scenario , and Figure D.5.1. 23 for the industrial worker scenario. No HI maps are presented for the recreational shoreline user scenario because the maximum HI did not exceed 1.0.
Note that the contour maps depicting risk (ILCR) to the recreational shoreline user include a contribution from C-14, I-129, Tc-99, and U-238 in surface water. A summary of the surface water contributions for the recreational shoreline user scenario is shown in Table D.5.1.2 for each alternative and time period. These contributions are quite small and in the case of the residential farmer scenario would be even smaller because the residential farmer scenario involves substantially less surface water activity. For this reason, surface water contributions for the residential farmer scenario are disregarded for this and all other TWRS alternatives. For the Native American scenario, surface water pathways are integrated into the groundwater pathways for all alternatives.
Table D.5.1.2 Risk for Recreational Shoreline User from Surface Water
D.5.2 LONG-TERM MANAGEMENT ALTERNATIVE
This section presents the anticipated post-remediation risk associated with the Long-Term Management alternative for tank waste. Post remediation for this alternative refers to the risk remaining after operation of the tank farms (i.e., institutional controls) is discontinued (assumed to be 100 years from 1995 for the purpose of this EIS). Over the 100-year period, the SSTs would continue to be stabilized and isolated to prevent liquid infiltration and the DSTs would undergo two tanking campaigns.
D.5.2.1 Source
Under the Long-Term Management alternative, the post-remediation source for SSTs would consist of the current SST farms. The source for the DSTs would consist of the current DST farms (containing 1 percent residual) and the replacement DST farms (containing the remaining 99 percent of the inventory) (WHC 1995g and Jacobs 1996). Additional discussion of source inventories is provided in Volume Four, Appendix F.
D.5.2.2 Transport
Post-remediation contaminant releases would be to the soil below the tanks. Contaminants released to the soil would migrate to groundwater in proportion to their ionic mobility. Groundwater modeling predicts that contaminants released from the tanks would be present in groundwater beneath the Hanford Site for all periods of interest (i.e. 300, 500, 2,000, 5,000, and 10,000 years from the present). Calculated groundwater contaminant concentrations and distributions are discussed in Volume Four, Appendix F.
To evaluate surface water exposures for the recreational shoreline user scenario, surface water concentrations resulting from groundwater discharge to the Columbia River were conservatively calculated using a dilution factor approach as described for the No Action alternative in Section D.5.1.2.
D.5.2.3 Exposure
Exposure for the Long-Term Management alternative was analyzed using the same URF methods and factors used for the No Action alternative (Section D.5.1.3). URFs are presented in Section D.2.1.3.
D.5.2.4 Risk
Risk for the Long-Term Management alternative is calculated using the same approach used for the No Action alternative (Section D.5.1.4). The risk calculation combines the risk contributed by the SSTs, original DSTs, and the replacement DST groups into a single risk value for each grid cell.
Contour maps depicting the risk from radionuclides and carcinogenic chemicals in tank waste are presented in Figures D.5.2.1 to D.5.2.5 for the Native American scenario, Figures D.5.2.6 to D.5.2. 9 for the residential farmer scenario , Figures D.5.2.10 to D.5.2. 13 for the industrial scenario , and Figures D.5.2.14 to D.5.2. 16 for the recreational shoreline user scenario. Contour maps depicting the HI from noncarcinogenic chemicals in tank waste are presented in Figures D.5.2.17 to D.5.2.19 for the Native American scenario, Figures D.5.2. 20 to D.5.2.22 for the residential farmer scenario, and Figure D.5.2. 23 for the industrial scenario. No HI maps are presented for the recreational shoreline user scenario because the maximum HI did not exceed 1.0.
D.5.3 IN SITU FILL AND CAP ALTERNATIVE
This section presents the anticipated post-remediation risk associated with the In Situ Fill and Cap alternative. Implementing this alternative would involve leaving radioactive waste in the existing tanks. DST liquid would be pumped to the evaporator and the concentrated waste returned to the DST Farms. The tanks would then be filled with gravel and capped with Hanford Barriers (WHC 1995f and Jacobs 1996).
D.5.3.1 Source
Post-remediation contamination sources under this alternative would consist of the current tank inventory as described in Volume Four, Appendix F.
D.5.3.2 Transport
Transport for the In Situ Fill and Cap alternative was analyzed using the same approach used for the No Action alternative (Section D.5.1.2) except that under the In Situ Fill and Cap alternative a Hanford Barrier would be placed over the tanks to reduce the infiltration of precipitation. This barrier would slow the process of leaching contaminants from the waste.
Groundwater modeling predicts that contaminants released from the fill and cap residuals would not reach groundwater during the first 500 years. Point concentrations are therefore zero for all constituents for the 300- and 500-year periods. During the latter three periods of interest (i.e., 2,500, 5,000, and 10,000 years from the present), modeling predicts that contaminants released from the in situ fill and cap residuals would be present in groundwater. Predicated groundwater contaminant concentrations and distributions during each time period are discussed in Volume Four, Appendix F.
To evaluate surface water exposures for the recreational shoreline user scenario, surface water concentrations resulting from groundwater discharge to the Columbia River were conservatively calculated using a dilution factor approach as described for the No Action alternative in Section D.5.1.2.
D.5.3.3 Exposure
Exposure for the In Situ Fill and Cap alternative was analyzed using the same URF methods and factors as used for the No Action alternative (Section D.5.1.3). URFs are presented in Section D.2.1.3.
D.5.3.4 Risk
Risk for the In Situ Fill and Cap alternative was calculated using the same approach as used for the No Action alternative (Section D.5.1.4). Because all tank constituents are calculated to have groundwater concentrations of zero within all cells for the 300- and 500-year periods, no risk calculations were performed for those periods.
Contour maps depicting the risk from radionuclides and carcinogenic chemicals for the In Situ Fill and Cap alternative are presented in Figures D.5.3.1 and D.5.3.2 for the Native American scenario; Figures D.5.3. 3 and D.5.3.4 for the residential farmer scenario; Figures D.5.3.5 and D.5.3. 6 for the industrial worker scenario; and Figures D.5.3. 7 and D.5.3. 8 for the recreational shoreline user scenario. Contour maps depicting the HI from noncarcinogenic chemicals are presented in Figures D.5.3.9 and D.5.3.10 for the Native American scenario, and Figures D.5.3. 11 and D.5.3. 12 for the residential farmer scenario. No HI maps are presented for the industrial worker or recreational shoreline user scenario s because the maximum HI from noncarcinogenic chemicals does not exceed 1.0.
D.5.4 IN SITU VITRIFICATION ALTERNATIVE
This section presents the anticipated post-remediation risk associated with the In Situ Vitrification alternative. This alternative would involve melting the tank waste and tanks into a glass monolith. Implementing this alternative would involve 1) sending all pumpable liquid from the DSTs to the evaporator for removing excess water; 2) constructing tank farm confinement facilities; 3) filling tank voids with Hanford Site sand; 4) vitrifying, using joule heating, to melt the tank waste and tanks in place into a single block of glass; and 5) installing Hanford Barriers over the vitrified site.
D.5.4.1 Source
Post-remediation contamination sources under the In Situ Vitrification alternative would consist of the current tank inventory (minus volatiles) but in a vitrified form that would release contaminants very slowly (WHC 1995f and Jacobs 1996). Additional discussion of contaminant source inventories is provided in Volume Four, Appendix F.
D.5.4.2 Transport
Post-remediation contaminant releases would be to the soil below the vitrified tanks. Contaminants released to the soil would migrate to groundwater in proportion to their ionic mobility. Groundwater modeling predicts that contaminants released from the vitrified tanks would not reach groundwater during the first 500 years. Point concentrations are therefore zero for all constituents for the first two periods of interest (i.e., 300 and 500 years from the present). During the latter three periods of interest (i.e., 2,500, 5,000, and 10,000 years from the present), modeling predicts that contaminants released would be present in groundwater. Predicated groundwater contaminant concentrations and distributions are discussed in Volume Four, Appendix F.
To evaluate surface water exposures for the recreational shoreline user scenario, surface water concentrations resulting from groundwater discharge to the Columbia River were conservatively calculated using a dilution factor approach as described for the No Action alternative in Section D.5.1.2.
D.5.4.3 Exposure
Exposure for the In Situ Vitrification alternative was analyzed using the same URF methods and factors used for the No Action alternative (Section D.5.1.3). URFs are presented in Section D.2.1.3.
D.5.4.4 Risk
The risk is calculated using the same approach used for the No Action alternative (Section D.5.1.4). Because all constituents in the vitrified tanks are calculated to have groundwater concentrations of zero within all cells for the 300- and 500-year periods, no risk calculations were performed for those periods.
Contour maps depicting the risk from radionuclides and carcinogenic chemicals in the vitrified tanks are presented in Figures D.5.4.1 and D.5.4.2 for the Native American scenario, Figures D.5.4.3 and D.5.4. 4 for the residential farmer scenario , and Figures D.5.4.5 and D.5.4.6 for the industrial worker scenario . The maximum risk (ILCR) from radionuclides and carcinogenic chemicals did not exceed 1.00E-06 for the recreational shoreline user scenario; therefore , no risk contour maps are presented. The maximum HI from noncarcinogenic chemicals did not exceed 1.0 for any scenario or time period; therefore, no maps are presented for the HI.
D.5.5 EX SITU INTERMEDIATE SEPARATIONS ALTERNATIVE
This section presents the anticipated post-remediation risk associated with the Ex Situ Intermediate Separations alternative. Implementing this alternative would involve retrieving tank waste, separating the HLW and LAW fractions, treating/immobilizing both fractions by converting them to glass, and disposing of the final glass waste forms. The vitrified LAW would be disposed of in onsite vaults. The vitrified HLW would be shipped to the proposed national HLW repository.
D.5.5.1 Source
Post-remediation contamination sources under the Ex Situ Intermediate Separations alternative would consist of tank residuals and the LAW disposal vaults. Tank waste retrieval efficiency is assumed to be 99 percent (WHC 1995f and Jacobs 1996). The contaminant inventory in tank residuals was therefore assumed to be 1 percent of the current inventory discussed in Volume Two, Appendix A. The LAW vaults would contain the contaminant inventory remaining in the LAW fractions following pretreatment and vitrification. Additional discussion of the inventory for the LAW vaults is presented in Volume Four, Appendix F.
D.5.5.2 Transport
Post-remediation contaminant releases were assumed to be to the soil below the tanks and the LAW vaults. Contaminants released to the soil would migrate to groundwater in proportion to their ionic mobility.
Groundwater modeling predicts that contaminants released from tank residuals would not reach groundwater during the first 500 years. Point concentrations are therefore zero for all constituents at periods of 300 and 500 years. During the latter three periods of interest (i.e., 2,500, 5,000, and 10,000 years from the present), modeling predicts that contaminants released from tank residuals would be present in groundwater beneath the Hanford Site.
Groundwater modeling predicts that contaminants leached from the LAW vaults would not reach groundwater during the first 2,500 years. Point concentrations are therefore zero for all constituents at periods of 300, 500, and 2,500 years. During the latter two periods of interest (i.e., 5,000 and 10,000 years from the present), modeling predicts that contaminants released from the LAW vaults would be present in groundwater beneath the Hanford Site. Calculated groundwater contaminant concentrations and distributions are discussed in Volume Four, Appendix F.
To evaluate surface water exposures for the recreational shoreline user scenario, surface water concentrations resulting from groundwater discharge to the Columbia River were conservatively calculated using a dilution factor approach, as described for the No Action alternative in Section D.5.1.2.
D.5.5.3 Exposure
Exposure for the Ex Situ Intermediate Separations alternative was analyzed using the same URF methods and factors used for the No Action alternative (Section D.5.1.3). URFs are presented in Section D.2.1.3.
D.5.5.4 Risk
Risk for the Ex Situ Intermediate Separations alternative is calculated using the same approach used for the No Action alternative (Section D.5.1.4). Risk calculations were performed separately for the tank residuals, LAW vaults, and residuals and vaults combined.
Contaminants released from tank residuals are calculated to have groundwater concentrations of zero in all cells at periods of 300 and 500 years from the present. Risk calculations were therefore performed only for periods 2,500, 5,000, and 10,000 years from the present. Contour maps depicting the risk from radionuclides and carcinogenic chemicals in tank residuals are presented in Figures D.5.5.1 and D.5.5.2 for the Native American scenario, Figures D.5.5. 3 and D.5.5.4 for the residential farmer scenario, Figures D.5.5. 5 and D.5.5. 6 for the industrial scenario, and Figure D.5.5. 7 for the recreational shoreline user scenario. Maps depicting the HI from noncarcinogenic chemicals in tank residuals are presented in Figures D.5.5.8 for the Native American scenario and Figure D.5.5. 9 for the residential farmer scenario. No HI maps are presented for the industrial or recreational shoreline user scenarios because the maximum HI did not exceed 1.0 for either scenario.
Contaminants released from LAW vaults are calculated to have groundwater concentrations of zero in all cells at periods of 300, 500, and 2,500 years from the present. Risk calculations were therefore performed only for periods of 5,000 and 10,000 years from the present. Contour maps depicting the risk from radionuclides and carcinogenic chemicals in LAW vaults are presented in Figures D.5.5.10 and D.5.5.11 for the Native American scenario, Figures D.5.5. 12 and D.5.5.13 for the residential farmer scenario, and in Figure s D.5.5.14 and D.5.5.15 for the industrial scenario. No risk maps are presented for the recreational shoreline user scenario because the maximum risk (ILCR) from radionuclides and carcinogenic chemicals in LAW vaults did not exceed 1.00E-06. No HI maps are presented because the maximum HI from noncarcinogenic chemicals in the LAW vaults did not exceed 1.0 for any scenario.
Risk calculations for the combined tank residuals and LAW vaults were performed only for periods of 2,500, 5,000, and 10,000 years from the present (contaminants would not reach groundwater during the 300- and 500-year periods). Contour maps depicting the combined risk from radionuclides and carcinogenic chemicals in tank residuals and LAW vaults are presented in Figures D.5.5.16 to D.5.5.18 for the Native American scenario, Figures D.5.5. 19 to D.5.5.21 for the residential farmer scenario, Figures D.5.5. 22 to D.5.5. 24 for the industrial scenario, and Figure D.5.5. 25 for the recreational shoreline user scenario. Maps depicting the combined HI from noncarcinogenic chemicals in tank residuals and LAW vaults are presented in Figure D.5.5.26 for the Native American scenario and Figure D.5.5.27 for the residential farmer scenario. No HI maps are presented for the industrial scenario or recreational shoreline user scenario because the maximum combined HI did not exceed 1.0 for either scenario.
D.5.6 EX SITU NO SEPARATIONS ALTERNATIVE
This section presents the anticipated post-remediation risk associated with the Ex Situ No Separations alternative. Under this alternative, tank waste would be retrieved and vitrified or calcined. The retrieved waste would not be separated into HLW and LAW waste streams. Waste from SSTs and DSTs would be blended as necessary and vitrified into a HLW glass or calcined and put into canisters. The HLW glass or the calcined waste would be shipped offsite to the proposed national HLW repository (WHC 1995c and Jacobs 1996).
D.5.6.1 Source
Post-remediation contamination sources under the Ex Situ No Separations alternative would consist of tank residuals. Since tank waste retrieval would be conducted in the same manner as for the Ex Situ Intermediate Separations alternative (i.e., 99 percent retrieval efficiency), the contaminant inventory in the tank residuals would be the same.
D.5.6.2 Transport
Because the contaminant inventory in tank residuals was the same as for the Ex Situ Intermediate Separations alternative, a separate groundwater transport modeling analysis was not required. Modeling results for the Ex Situ No Separations alternative would be the same as the results for the tank residuals for the Ex Situ Intermediate Separations alternative (Section D.5.5.2).
D.5.6.3 Exposure
Because the contaminant inventory in the tank residuals would be the same as for the Ex Situ Intermediate Separations alternative, exposures would be the same.
D.5.6.4 Risk
Risk and HI contours for the tank residuals in the Ex Situ No Separations alternative would be the same as for the tank residuals in the Ex Situ Intermediate Separations alternative (Section D.5.5.4, Figures D.5.5.1 to D.5.5.9 ).
D.5.7 EX SITU EXTENSIVE SEPARATIONS ALTERNATIVE
This section presents the anticipated post-remediation risk associated with the Ex Situ Extensive Separations alternative. This alternative would involve implementing the same basic operations described for the Ex Situ Intermediate Separations alternative but would involve conducting a more complex waste separation operation. Fifteen processing systems (12 more than for the Ex Situ Intermediate Separations alternative) would be used to reduce the volume of HLW and to reduce the amount of radioactive contaminants in the LAW (WHC 1995e and Jacobs 1996).
D.5.7.1 Source
Post-remediation contamination sources under the Ex Situ Separations alternative would consist of tank residuals and LAW vaults. Because tank waste retrieval would be conducted in the same manner as for the Ex Situ Intermediate Separations alternative (i.e., 99 percent retrieval efficiency), the contaminant inventory in the tank residuals would be the same. As in the Ex Situ Intermediate Separations alternative, the LAW vaults would contain the contaminant inventory remaining in the LAW following separation and treatment. Additional discussion of the inventory for the LAW vaults is presented in Volume Four, Appendix F.
D.5.7.2 Transport
Because the contaminant inventory in tank residuals would be the same as for the Ex Situ Intermediate Separations alternative, a separate groundwater transport modeling analysis was not required. Modeling results for tank residuals for the Ex Situ Intermediate Separations alternative (Section D.5.5.2) apply to the Ex Situ Extensive Separations alternative as well.
Groundwater modeling predicts that contaminants leached from the LAW vaults would not reach groundwater during the first 2,500 years. Point concentrations are therefore zero for all constituents at periods of 300, 500, and 2,500 years. During the latter two periods of interest (i.e., 5,000 and 10,000 years from the present), modeling predicts that contaminants released from the LAW vaults would be present in groundwater beneath the Hanford Site. Calculated groundwater contaminant concentrations and distributions are discussed in Volume Four, Appendix F.
To evaluate surface water exposures for the recreational shoreline user scenario, surface water concentrations resulting from groundwater discharge to the Columbia River were conservatively calculated using a dilution factor approach as described for the No Action alternative in Section D.5.1.2.
D.5.7.3 Exposure
Because the contaminant inventory in tank residuals would be the same as for the Ex Situ Intermediate Separations Alternative, exposure would be the same. Exposures for the LAW vaults were analyzed using the same URF methods and factors used for the No Action alternative (Section D.5.1.3). URFs are presented in Section D.2.1.3.
D.5.7.4 Risk
As in the Ex Situ Intermediate Separations alternative, risk calculations were performed separately for tank residuals, LAW vaults, and residuals and vaults combined.
Risk for the tank residuals in the Ex Situ Extensive Separations alternative would be the same as for the tank residuals in the Ex Situ Intermediate Separations alternative (Section D.5.5.4, Figure D.5.5.1 to D.5.5.9 ).
Because constituents released from LAW vaults would not reach groundwater for 2,500 years, risk calculations were performed only for periods of 5,000 and 10,000 years. Contour maps depicting the risk from radionuclides and carcinogenic chemicals in LAW vaults are presented in Figures D.5.7.1 and D.5.7.2 for the Native American scenario , Figures D.5.7.3 and D.5.7.4 for the residential farmer scenario , and Figure D.5.7.5 for the industrial scenario. No risk maps are presented for the recreational shoreline user scenario because the maximum risk (ILCR) from radionuclides and carcinogenic chemicals in LAW vaults did not exceed 1.00E-06. No HI maps are presented because the maximum HI from noncarcinogenic chemicals in LAW vaults did not exceed 1.0 for any scenario.
Although the risk for tank residuals would be the same as for the Ex Situ Intermediate Separations alternative, the risk for LAW vaults would be different; therefore, the combined risk from residuals and vaults would be different. Risk calculations for the combined tank residuals and LAW vaults were performed only for periods of 2,500, 5,000, and 10,000 years from the present (contaminants would not reach groundwater during the 300- and 500-year periods). Contour maps depicting the combined risk from radionuclides and carcinogenic chemicals in tank residuals and LAW vaults are presented in Figures D.5.7.6 and D.5.7.7 for the Native American scenario, Figures D.5.7. 8 and D.5.7.9 for the residential farmer scenario, Figures D.5.7. 10 and D.5.7. 11 for the industrial scenario, and Figure D.5.7. 12 for the recreational shoreline user scenario. Map s depicting the combined HI from noncarcinogenic chemicals in tank residual s and LAW vaults are presented in Figure D.5.7.13 for the Native American scenario and Figure D.5.7.14 for the residential farmer scenario . No HI maps are presented for the industrial or recreational shoreline user scenarios because the maximum combined HI did not exceed 1.0 for either scenario.
D.5.8 EX SITU/IN SITU COMBINATION 1 ALTERNATIVE
This section presents the anticipated post-remediation risk associated with the Ex Situ/In Situ Combination 1 alternative for tank waste. This alternative would involve a combination of the Ex Situ Intermediate Separations alternative (Section D.5.5) and the In Situ Fill and Cap alternative (Section D.5.3). Tanks with the highest content of mobile constituents of concern (i.e., uranium isotopes, Tc-99, I-129, and C-14) would be remediated in accordance with the Ex Situ Intermediate Separations alternative. Tanks with a low content of these constituents would be remediated in accordance with the In Situ Fill and Cap alternative.
This EIS examines a tank selection process based on recovering 90 percent of the constituents that contribute to post-remediation risk. Implementing this process would remove approximately 50 percent of the tank waste by volume and result in ex situ remediation of approximately 70 of the 177 tanks; the remaining tanks (approximately 107) would be remediated as described under the In Situ Fill and Cap alternative. Further details of the tank selection process are provided in Volume Two, Appendix B.
D.5.8.1 Source
For the ex situ portion of this alternative, post-remediation contamination sources would be the same type but of lesser quantity than those described in Section D.5.5.1 for the Ex Situ Intermediate Separations alternative (i.e., tank residuals and LAW disposal vaults). For the in situ portion, post- remediation sources would be the same type but of lesser quantity than those described in Section D.5.3.1 for the In Situ Fill and Cap alternative (i.e., tank residuals). Additional discussion of contaminant source inventories is provided in Volume Four, Appendix F.
D.5.8.2 Transport
Post-remediation contaminant releases would be to the soil below the tanks and LAW vaults. Contaminants released to the soil would migrate to groundwater in proportion to their ionic mobility.
Groundwater modeling predicts that contaminants released from the tank residuals (both ex situ and in situ) would not reach groundwater during the first 500 years. Point concentrations are therefore zero for all constituents at periods of 300 and 500 years. During the latter three periods of interest (i.e., 2,500, 5,000, and 10,000 years from the present) modeling predicts that contaminants released from tank residuals would be present in groundwater beneath the Hanford Site.
Groundwater modeling predicts that contaminants leached from the LAW vaults would not reach groundwater during the first 2,500 years. Point concentrations are therefore zero for all constituents at periods of 300, 500, and 2,500 years. During the latter two periods of interest (i.e., 5,000 and 10,000 years from the present), modeling predicts that contaminants released from the LAW vaults would be present in groundwater beneath the Hanford Site. Calculated groundwater contaminant concentrations and distributions are discussed in Volume Four, Appendix F.
To evaluate surface water exposures for the recreational shoreline user scenario, surface water concentrations resulting from groundwater discharge to the Columbia River were conservatively calculated using a dilution factor approach as described for the No Action alternative in Section D.5.1.2.
D.5.8.3 Exposure
Exposures for the Ex Situ/In Situ Combination 1 alternative were analyzed using the same URF methods and factors as used for the No Action alternative (Section D.5.1.3). URFs are presented in Section D.2.1.3.
D.5.8.4 Risk
Risk for the Ex Situ/In Situ Combination 1 alternative is calculated using the same approach used for the No Action alternative (Section D.5.1.4). Risk calculations were performed separately for the tank residuals (both ex situ and in situ), LAW vaults, and residuals and vaults combined.
Contaminants released from the ex situ tank residuals are calculated to have groundwater concentrations of zero in all cells at periods of 300 and 500 years from the present. Risk calculations were therefore performed only for periods of 2,500, 5,000, and 10,000 years from the present. Contour maps depicting risk from radionuclides and carcinogenic chemicals in ex situ residuals are presented in Figures D.5.8.1 and D.5.8.2 for the Native American scenario, Figures D.5.8. 3 and D.5.8.4 for the residential farmer scenario, and Figures D.5.8. 5 and D.5.8. 6 for the industrial scenario. No risk maps are presented for the recreational shoreline user scenario because the maximum risk (ILCR) did not exceed 1.00E-06. A map depicting the HI from noncarcinogenic chemicals in ex situ tank residuals is presented in Figure D.5.8. 7 for the Native American scenario. No HI maps are presented for the residential farmer, industrial, or recreational shoreline user scenarios because the maximum HI did not exceed 1.0 for these scenario s .
Contaminants released from the in situ tank residuals are calculated to have groundwater concentrations of zero in all cells at periods of 300 and 500 years from the present. Risk calculations were therefore performed only for periods of 2,500, 5,000, and 10,000 years from the present. Contour maps depicting the risk from radionuclides and carcinogenic chemicals in the in situ tank residuals are presented in Figures D.5.8.8 and D.5.8.9 for the Native American scenario, Figures D.5.8. 10 and D.5.8. 11 for the residential farmer scenario, Figures D.5.8. 12 and D.5.8. 13 for the industrial scenario, and Figures D.5.8. 14 and D.5.8. 15 for the recreational shoreline user scenario. Maps depicting the HI from noncarcinogenic chemicals in the in situ tank residuals are presented in Figures D.5.8.16 and D.5.8.17 for the Native American scenario and Figures D.5.8.18 and D.5.8. 19 for the residential farmer scenario. No HI maps are presented for the industrial or recreational shoreline user scenarios because the maximum HI did not exceed 1.0 for either scenario.
Contaminants released from LAW vaults are calculated to have groundwater concentrations of zero in all cells at periods of 300, 500, and 2,500 years from the present. Risk calculations were therefore performed only for periods of 5,000 and 10,000 years from the present. Contour maps depicting the risk from radionuclides and carcinogenic chemicals in LAW vaults are presented in Figures D.5.8.20 and D.5.8.21 for the Native American scenario, Figures D.5.8. 22 and D.5.8.23 for the residential farmer scenario, and Figures D.5.8.24 and D.5.8.25 for the industrial scenario . No risk maps are presented for the recreational shoreline user scenario because the maximum risk (ILCR) did not exceed 1.00E-06. No HI maps are presented because the maximum HI from noncarcinogenic chemicals in the LAW vaults did not exceed 1.0 for any scenario.
Risk calculations for the tank residuals (ex situ and in situ) in combination with the LAW vaults were performed only for periods of 2,500, 5,000, and 10,000 years from the present (contaminants would not reach groundwater during the 300- and 500-year periods). Contour maps depicting the combined risk from radionuclides and carcinogenic chemicals in tank residuals (ex situ and in situ) and LAW vaults are presented in Figures D.5.8.26 to D.5.8.28 for the Native American scenario, Figures D.5.8.29 to D.5.8. 31 for the residential farmer scenario, Figures D.5.8. 32 to D.5.8. 34 for the industrial scenario, and Figures D.5.8. 35 and D.5.8. 36 for the recreational shoreline user scenario. Maps depicting the combined HI from noncarcinogenic chemicals in tank residuals (ex situ and in situ) and LAW vaults are presented in Figures D.5.8.37 and D.5.8.38 for the Native American scenario and Figures D.5.8. 39 and D.5.8. 40 for the residential farmer scenario. No HI maps are presented for the industrial or recreational shoreline user scenarios because the maximum combined HI did not exceed 1.0 for either scenario.
D.5.9 EX SITU/IN SITU COMBINATION 2 ALTERNATIVE
This section presents the anticipated post-remediation risk associated with the Ex Situ/In Situ Combination 2 alternative for tank waste. This variation of the Ex Situ/In Situ Combination 1 alternative would use modified tank selection criteria to provide for ex situ treatment of the largest contributors to long-term risk (i.e., uranium isotopes, Tc-99, I-129, and C-14) while limiting the volume of waste to be processed. Under this variation, approximately 25 tanks instead of 70 tanks would be remediated as described for the Ex Situ Intermediate Separations alternative, while the remaining tanks would be remediated as described for the In Situ Fill and Cap alternative. Further details of the tank selection process are provided in Volume Two, Appendix B.
D.5.9.1 Source
Post-remediation contamination sources for the ex situ portion of this alternative would be of the same type as those described for the Ex Situ/In Situ Combination 1 alternative (i.e., tank residuals and LAW vaults). However, under this alternative these sources would contain less contamination because less waste would be retrieved. Post-remediation sources for the in situ portion of this alternative would also be of the same type as those described for the Ex Situ/In Situ Combination 1 alternative (i.e., tank residuals). However, under this alternative these sources would contain more contamination because more waste would be left in place.
D.5.9.2 Transport
Post-remediation contamination releases would be to the soil below the tanks and LAW vaults. Contaminants released to the soil would migrate to groundwater in proportion to their ionic mobility.
Groundwater modeling calculates that contaminants released from the tank residuals (both ex situ and in situ) would not reach groundwater during the first 500 years. Point concentrations are therefore zero for all constituents at periods of 300 and 500 years. During the latter three periods of interest (i.e., 2,500, 5,000, and 10,000 years from the present), modeling calculates that contaminants released from tank residuals would be present in groundwater beneath the Hanford Site.
Groundwater modeling calculates that contaminants leached from the LAW vaults would not reach groundwater during the first 2,500 years. Point concentrations are therefore zero for all constituents at periods of 300, 500, and 2,500 years. During the latter two periods of interest (i.e., 5,000 and 10,000 years from the present), modeling calculates that contaminants released from the LAW vaults would be present in groundwater beneath the Hanford Site. Calculated groundwater contaminant concentrations and distributions are discussed in Volume Four, Appendix F.
To evaluate surface water exposures for the recreational shoreline user scenario, surface water concentrations resulting from groundwater discharge to the Columbia River were conservatively calculated using a dilution factor approach as described for the No Action alternative in Section D.5.1.2.
D.5.9.3 Exposure
Exposures for the Ex Situ/In Situ Combination 2 alternative were analyzed using the same URF methods and factors as used for the No Action alternative (Section D.5.1.3). URFs are presented in Section D.2.1.3.
D.5.9.4 Risk
Risk for the Ex Situ/In Situ Combination 2 alternative is calculated using the same approach used for the No Action alternative (Section D.5.1.4). Risk calculations were performed separately for the tank residuals (both ex situ and in situ), LAW vaults, and residuals and vaults combined.
Contaminants released from the ex situ tank residuals are calculated to have groundwater concentrations of zero in all cells at periods of 300 and 500 years from the present. Risk calculations were therefore performed only for periods of 2,500, 5,000, and 10,000 years from the present. Contour maps depicting risk from radionuclides and carcinogenic chemicals in ex situ residuals are presented in Figures D.5.9.1 and D.5.9.2 for the Native American scenario, Figures D.5.9.3 and D.5.9.4 for the residential farmer scenario, and Figure D.5.9.5 for the industrial scenario. No risk maps are presented for the recreational shoreline user scenario because the maximum risk (ILCR) did not exceed 1.00E-06. No HI maps are presented because the maximum HI did not exceed 1.0 for any scenario.
Contaminants released from the in situ tank residuals are calculated to have groundwater concentrations of zero in all cells at periods of 300 and 500 years from the present. Risk calculations were therefore performed only for periods of 2,500, 5,000, and 10,000 years from the present. Contour maps depicting risk from radionuclides and carcinogenic chemicals in the in situ residuals are presented in Figures D.5.9.6 and D.5.9.7 for the Native American scenario, Figures D.5.9.8 and D.5.9.9 for the residential farmer scenario, Figures D.5.9.10 and D.5.9.11 for the industrial scenario, and Figures D.5.9.12 and D.5.9.13 for the recreational shoreline user scenario. Maps depicting the HI from noncarcinogenic chemicals in the in situ tank residuals are presented in Figures D.5.9.14 and D.5.9.15 for the Native American scenario and Figures D.5.9.16 and D.5.9.17 for the residential farmer scenario. No HI maps are presented for the industrial or recreational shoreline user scenarios because the maximum HI did not exceed 1.0 for either scenario.
Contaminants released from the LAW vaults are calculated to have groundwater concentrations of zero in all cells at periods of 300, 500, and 2,500 years from the present. Risk calculations were therefore performed only for periods of 5,000 and 10,000 years from the present. Contour maps depicting risk from radionuclides and carcinogenic chemicals in LAW vaults are presented in Figures D.5.9.18 and D.5.9.19 for the Native American scenario, Figures D.5.9.20 and D.5.9.21 for the residential farmer scenario, and Figures D.5.9.22 and D.5.9.23 for the industrial scenario. No risk maps are presented for the recreational shoreline user scenarios because the maximum risk (ILCR) did not exceed 1.00E-06. No HI maps are presented because the maximum HI from noncarcinogenic chemicals in the LAW vaults did not exceed 1.0 for any scenario.
Risk calculations for the tank residuals (ex situ and in situ) in combination with the LAW vaults were performed only for periods of 2,500, 5,000, and 10,000 years from the present (contaminants would not reach groundwater during the 300- and 500-year periods). Contour maps depicting the combined risk from radionuclides and carcinogenic chemicals in tank residuals (ex situ and in situ) and LAW vaults are presented in Figures D.5.9.24 to D.5.9.26 for the Native American scenario, Figures D.5.9.27 to D.5.9.29 for the residential farmer scenario, Figures D.5.9.30 and D.5.9.31 for the industrial scenario, and Figures D.5.9.32 and D.5.9.33 for the recreational shoreline user scenario. Maps depicting the combined HI from noncarcinogenic chemicals in tank residuals (ex situ and in situ) and LAW vaults are presented in Figures D.5.9.34 and D.5.9.35 for the Native American scenario and Figures D.5.9.36 and D.5.9.37 for the residential farmer scenario. No HI maps are presented for the industrial or recreational shoreline user scenarios because the maximum HI did not exceed 1.0 for either scenario.
D.5. 10 PHASED IMPLEMENTATION ALTERNATIVE
This section presents the anticipated post-remediation risk associated with the Total alternative. Implementing this alternative would involve retrieving tank waste, separating the HLW and LAW fractions, treating/immobilizing both fractions by converting them to glass, and disposing of the final glass waste forms. The vitrified LAW would be disposed of in onsite vaults. The vitrified HLW would be shipped to the proposed national HLW repository.
D.5. 10 .1 Source
Post-remediation contamination sources under the Total alternative would consist of tank residual s and the LAW disposal vaults. Tank waste retrieval efficiency is assumed to be 99 percent (WHC 1995f and Jacobs 1996). The contaminant inventory in tank residuals was therefore assumed to be 1 percent of the current inventory discussed in Volume Two, Appendix A. The LAW vaults would contain the contaminant inventory remaining in the LAW fractions following pretreatment and vitrification. Additional discussion of the inventory for the LAW vaults is presented in Appendix F.
D.5. 10 .2 Transport
Post-remediation contaminant releases were assumed to be to the soil below the tanks and the LAW vaults. Contaminants released to the soil would migrate to groundwater in proportion to their ionic mobility.
Groundwater modeling predicts that contaminants released from tank residuals would not reach groundwater during the first 500 years. Point concentrations are therefore zero for all constituents at periods of 300 and 500 years. During the latter three periods of interest (i.e., 2,500, 5,000, and 10,000 years from the present), modeling predicts that contaminants released from tank residuals would be present in groundwater beneath the Hanford Site.
Groundwater modeling predicts that contaminants leached from the LAW vaults would not reach groundwater during the first 2,500 years. Point concentrations are therefore zero for all constituents at periods of 300, 500, and 2,500 years. During the latter two periods of interest (i.e., 5,000 and 10,000 years from the present), modeling predicts that contaminants released from the LAW vaults would be present in groundwater beneath the Hanford Site.
D.5. 10 .3 Exposure
Exposure for the Total alternative was analyzed using the same URF methods and factors used for the No Action alternative (Section D.5.1.3). URFs are presented in Section D.2.1.3.
D.5. 10 .4 Risk
Risk for the Total alternative is calculated using the same approach used for the No Action alternative (Section D.5.1.4). Risk calculations were performed separately for the tank residuals, LAW vaults , and residuals and vaults combined.
Contaminants released from tank residuals are calculated to have groundwater concentrations of zero in all cells at periods of 300 and 500 years from the present. Risk calculations were therefore performed only for periods 2,500, 5,000, and 10,000 years from the present. Contour maps depicting the risk from radionuclides and carcinogenic chemicals in tank residuals are presented in Figures D.5.10.1 and D.5.10.2 for the Native American scenario, Figures D.5. 10.3 and D.5.10.4 for the residential farmer scenario, Figures D.5. 10.5 and D.5. 10.6 for the industrial scenario, and Figure D.5. 10.7 for the recreational shoreline user scenario. M aps depicting the HI from noncarcinogenic chemicals in tank residuals are presented in Figure D.5.10.8 for the Native American scenario and Figure D.5. 10.9 for the residential farmer scenario. No HI maps are presented for the industrial or recreational shoreline user scenario because the maximum HI did not exceed 1.0 for either scenario.
Contaminants released from LAW vaults are calculated to have groundwater concentrations of zero in all cells at periods of 300, 500, and 2,500 years from the present. Risk calculations were therefore performed only for periods of 5,000 and 10,000 years from the present. Contour maps depicting the risk from radionuclides and carcinogenic chemicals in LAW vaults are presented in Figures D.5.10.10 and D.5.10.11 for the Native American scenario, Figures D.5. 10.12 and D.5.10.13 for the residential farmer scenario, and Figure s D.5.10.14 and D.5.10.15 for the industrial scenario. No risk maps are presented for the recreational shoreline user scenario because the maximum risk (ILCR) from radionuclides and carcinogenic chemicals in LAW vaults did not exceed 1.00E-06. No HI maps are presented because the maximum HI from noncarcinogenic chemicals in the LAW vaults did not exceed 1.0 for any scenario.
Risk calculations for the combined tank residuals and LAW vaults were performed only for periods of 2,500, 5,000, and 10,000 years from the present (contaminants would not reach groundwater during the 300- and 500-years periods). Contour maps depicting the combined risk from radionuclides and carcinogenic chemicals in tanks residuals and LAW vaults are presented in Figures D.5.10.16 to D.5.10.18 for the Native American scenario, Figures D.5. 10.19 to D.5.10.21 for the residential farmer scenario, Figures D.5. 10.22 to D.5. 10.24 for the industrial scenario, and Figure D.5. 10.25 for the recreational shoreline user scenario. M aps depicting the combined HI from noncarcinogenic chemicals in tank residuals and LAW vaults are presented in Figure D.5.10.26 for the Native American scenario and Figure D.5. 10.27 for the residential farmer scenario. No HI maps are presented for the industrial scenario or recreational shoreline user because the maximum combined HI did not exceed 1.0 for either scenario.
D.5. 11 NO ACTION ALTERNATIVE (CAPSULES)
Post-remediation is not included in this alternative. This alternative does not remediate the waste. After 10 years, a remediation decision would be made (Jacobs 1996).
D.5. 12 CAPSULES ONSITE DISPOSAL ALTERNATIVE
This section presents the anticipated post-remediation risk associated with the Onsite Disposal alternative for the capsules. Implementing this alternative would involve retrieving capsules from WESF, placing capsules in Overpack canisters, and transferring the canisters to an onsite drywell disposal facility where they would be stored indefinitely (WHC 1995h and Jacobs 1996).
D.5. 12 .1 Source
The inventory of cesium and strontium in drywell disposal would be the same as the cesium and strontium inventory given in Section D.2.1.1.2.
The radioisotopes Cs-137 and Sr-90 (half lives of 30.2 and 28.6 years, respectively) will eventually decay to their stable progeny (Ba-137 and Zr-90, respectively). Groundwater transport modeling for tank waste indicates that neither Cs-137, Sr-90, nor their progeny would reach groundwater before 1,200 years (Volume Four, Appendix F), and the Cs-137 and Sr-90 would have nearly completely decayed to their stable progeny products within this time period. Therefore, only minute quantities of Cs-137 and Sr-90 would reach the groundwater.
The Cs-137 and Sr-90 daughter products (elements Ba-137 and Zr-90) are not carcinogenic, but are known to cause toxic effects at intakes greater than their respective reference doses. A rigorous groundwater transport analysis would only be needed if the estimated concentration of these stable daughters in groundwater resulted in intakes that exceed the reference doses within the 10,000-year period of interest. The following calculations show that intakes based on estimated future aquifer concentrations would be at least one order of magnitude below the reference doses. In this calculation, it was conservatively assumed that the mass of the stable daughters in the aquifer would be equal to the current mass of the parent radionuclides.
| Cs-137 Case | ||
| Data | ||
| Current Cs-137 inventory | = | 5.30E+07 Ci |
| Cs-137 specific activity | = | 8.70E+01 Ci/g |
| Standard human weight | = | 70 kg |
| Standard human consumption | = | 2 L/day |
| = | 2,000 cm3/day | |
| Aquifer volume | = | 1,000 m · 1,000 m · 10 m |
| 1.00E+07 m3 | ||
| 1.00E+13 cm3 (assumed) | ||
| Calculation | ||
| Total mass of Ba-137 | = | 5.30E+07 Ci ÷ 8.7E+01 Ci/g |
| = | 6.10E+05 g | |
| Ba-137 concentration in aquifer | = | 6.10E+05 g ÷ 1.0E+13 cm3 |
| = | 6.10E-08 g/cm3 | |
| Intake for standard human | = | 2.00E+03 cm3/day · 6.1E-08 g/cm3 ÷ 70 kg |
| = | 1.80E-06 g/kg/day | |
| = | 1.80E-03 mg/kg/day | |
Conclusion
The reference dose for Ba-137 ingestion from HEAST (EPA 1993) is 3.50E-02 mg/kg/day. Comparing the calculated intake to the reference dose indicates that there would be no expected toxic effects from Ba-137 (i.e., 1.80E-03 mg/kg/day is less than 3.50E-02 mg/kg/day).
| Sr-90 Case | ||
| Data | ||
| Current Sr-90 inventory | = | 2.30E+07 Ci |
| Sr-90 specific activity | = | 1.40E+02 Ci/g |
| Standard human weight | = | 70 kg |
| Standard human consumption | = | 2 L/day |
| = | 2,000 cm3/day | |
| Aquifer volume | = | 1,000 m · 1,000 m · 10 m |
| 1.00E+07 m3 | ||
| 1.00E+13 cm3 (assumed) | ||
| Calculation | ||
| Total mass of Z r-90 | = | 2.30E+07 Ci ÷ 1.4E+02 Ci/g |
| = | 1.70E+05 grams | |
| Z r-90 concentration in aquifer | = | 1.70E+05 grams ÷ 1.0E+13 cm3 |
| = | 1.70E-08 g/cm3 | |
| Intake for standard human | = | 2.00E+03 cm3/day · 1.7E-08 g/cm3 ÷ 70 kg |
| = | 4.80E-07 g/kg/day | |
| = | 4.80E-04 mg/kg/day | |
Conclusion
The reference dose for Zr-90 ingestion from HEAST (EPA 1993) is 7.00E-02 mg/kg/day. Comparing the calculated intake to the reference dose indicates that there would be no expected toxic effects from Z r-90 (i.e., 4.80E-04 mg/kg/day is less than 7.00E-02 mg/kg/day).
Because there would be no exposure under this alternative, there would be no anticipated risk associated with the Cs and Sr capsules under the Onsite Disposal alternative.
D.5. 13 OVERPACK AND SHIP ALTERNATIVE
Implementing this alternative would involve retrieving capsules from WESF, placing capsules in overpack canisters, and transporting the canisters offsite for disposal in a geologic repository (WHC 1995b and Jacobs 1996). Because all the capsules would be removed from the Hanford Site, there would be no post-remediation risk.
D.5. 14 CAPSULES VITRIFY WITH TANK WASTE ALTERNATIVE
Implementing this alternative would involve 1) retrieving capsules from WESF; 2) decladding the capsules and removing their contents; 3) combining the cesium and strontium with HLW from the SSTs and DSTs; 4) vitrifying the HLW into a glass; 5) placing the HLW glass into onsite interim storage; and 6) transporting the HLW glass offsite for disposal in a geologic repository (WHC 1995h and Jacobs 1996). Because all the capsule contents would be removed from the Hanford Site as part of the HLW glass , there would be no post-remediation risk.
D.5. 15 TOTAL HEALTH IMPACTS
D.5. 15 .1 Total Health Impacts for Hanford Site Users
This section discusses the calculation of the total or integrated post-remediation risk over the 10,000-year period of interest. This risk has been calculated for each alternative and for four types of receptors: the Native American, the residential farmer, the industrial worker, and the recreational shoreline user. The exposure scenarios are described in Section D.2.1.3 and assume a hypothetical post-remediation use scenario under which onsite controls are not maintained.
The total risk is expressed as the total cancer incidence and cancer fatalities over the 10,000-year period for each receptor group. It is calculated by multiplying the ILCR for each receptor group (as presented in Figures D.5.1.1 through D.5. 10.27 ) by the population for that group. Note that the risk contours shown in Figures D.5.1.1 through D.5. 10.27 give the ILCR for an individual. For example, an isopleth with a value of 1.0E-03 indicates that an individual located along that contour line has a 0.001 chance of developing cancer, or that one person out of 1,000 will develop cancer. By making assumptions regarding populations, individual risks are used to calculate total risks, which indicate the number of individuals in each receptor group that may contract cancer or die from cancer over the 10,000-year period of interest.
The method used to calculate total risk uses the areas described by the individual risk contours shown in Figures D.5.1.1 through D.5.10.27 . These areas were calculated using computer contouring software for periods of 300, 500, 2,500, 5,000, and 10,000 years from the present for each receptor and alternative. The number of individuals exposed in each contour area during each time interval was calculated using assumed values for population density or total population and the duration of active land use for each receptor group. The corresponding cancer incidence and cancer fatalities were obtained by multiplying the number of exposed individuals by the risk value (ILCR) for the given contour area. The total risk for each receptor is the sum of all the cancer incidences and fatalities for each contour area during each time interval.
Assumptions were made for such factors as the duration of exposure, the population affected, and the lifespan or duration of active use for a generation.
For the Native American scenario, the following assumptions were used.
- The duration of each generation is 70 years of continuous occupancy.
- The population density is 1.91 persons/km2. This value is based on an assumed population of 1,500 individuals occupying 785 km2 (303 mi2) of the total area of the Hanford Site. This value is similar to the population density of the Umatilla Indian Reservation, which is 2.08 persons/km2 based on information presented in the Comprehensive Plan of the Confederated Tribes of the Umatilla Indian Reservation (CTUIR 1995).
Consequently, the number of Native Americans at any given time is 1,500 (1.91 · 785). During a 10,000-year time span, there would be 143 generations (10,000 ÷ 70), or a total of 2.1E+05 (143 · 1,500) receptors for the Native American scenario.
For the residential farmer scenario, the following assumptions were used.
- The d uration of each generation is 70 years of continuous farming.
- The p opulation density is 4.97 persons/km2 (WSDFM 1994). This population density is similar to the present (1990's) farming area surrounding the Site.
- Farming will occupy 785 km2 (303 mi2) of the total area of the Hanford Site.
Consequently, the number of farming individuals at any given time is 3,900 (4.97 · 785). During a 10,000-year time span, there would be 143 generations (10,000 ÷ 70), or a total of 5.6E+05 (143 · 3,900) receptors for the residential farmer scenario.
For the industrial worker scenario, the following assumptions were used.
- A workforce of 2,200 would occupy the Site. Previous estimates have indicated a large industrial complex at the Site would have a workforce of 1,700 (TRIDEC 1993).
- The d uration of each worker's employment would be 30 continuous years; 30 years is assumed to be one generation or occupation period for the industrial worker.
- The c alculated worker population would remain constant as a function of time.
- The worker population would not be uniformly distributed throughout the Site as for the Native American and residential farmer scenarios. Instead, the workers would occupy an industrial complex assumed to be located in the risk contour area with the highest probability of occurrence. Probability of occurrence for this assessment was calculated by dividing the areas for the individual contours by the total area of 785 km2 (303 mi2).
During a 10,000-year period, the net result would be 333 generations (10,000 ÷ 30) of industrial workers or a total population of 7.3E+05 receptors (333 · 2,200).
For the recreational shoreline user scenario, the following assumptions were used.
- The duration of active use of the area for recreation is 30 years per person (DOE 1995c), usage is for 14 days per year, and 30 years is assumed to be one recreational generation.
- During the period of interest there would be 40,000 one-day visits to the shoreline (NPS 1994). This would be equivalent to 2,857 visits of 14 days per visit. For use in calculations, it is assumed that 1,950 visits of 14 days each that result in exposure would occur in shoreline areas.
Consequently, during a 10,000-year period there would be 333 generations (10,000 ÷ 30), or a total of 6.5E+05 receptors (333 · 1,950) for the recreational shoreline scenario.
The results of calculating total or integrated risk for the Native American, residential farmer, industrial worker, and recreational shoreline user for all alternatives are shown in Table D.5. 15 .1. This table shows the total calculated cancer incidence and cancer fatalities for each group of receptors and for each alternative over the entire 10,000 years.
Example Calculation for Total Risk
Given a set of risk contours at 500 years, the total risk to the residential farmer based on 2 risk contours with areas of 47 km2 (18 mi2) and 64 km2 (24 mi2) and ILCR values of 0.05 and 0.001, respectively, is calculated as follows.
The risk contours at 500 years must be used to represent the next 2,000 years of exposure because the next risk contour available is for 2,500 years from the present time. During this 2,000-year period there will be 28.57 generations of residential farmers (2,000 ÷ 70) occupying the land with a population density of 4.97 persons per km2. The cancer incidence, R(1), over this period for the 47 km2 area with an ILCR of 0.05 is:
R(1) = 47 · 4.97 · 28.57 · 0.05 = 333.7 cancer incidences
The cancer fatalities corresponding to this cancer incidence are 333.7 ÷ 1.2 = 278 fatalities. This conversion is based on the ratio of the dose to risk conversion factors for cancer incidence and cancer fatalities (6.0E-04 ÷ 5.0E-04 = 1.2) given in the ICRP (ICRP 1991).
Using the same method, the cancer incidence, R(2), over this period for the 64 km2 (24 mi2) area with an ILCR of 0.001 is:
R(2) = 64 · 4.97 · 28.57 · 0.001 = 9.0 cancer incidences.
The corresponding cancer fatalities are 9.0 ÷ 1.2 = 7.6 fatalities.
The total risk is the sum of R(1) and R(2), that is:
R(total) = R(1) + R(2) = 333.7 + 9.0 = 342.7 = 343 cancer incidences.
The corresponding cancer fatalities are 343 ÷ 1.2 = 285.6 = 286 fatalities.
The above total risk is calculated by assuming that the two isopleths with risk levels of 0.05 and 0.001 have the same risk magnitude for the entire 2,000 year duration of the calculation. In reality, as time increases, the risk level decreases because of radioactive decay and the transport and dilution of contaminants in the aquifer. To make the adjustment for this , it is assumed that one-half of the risk level at the start of the period would be the risk for the entire duration. Therefore, the total cancer incidence would be one-half of 343, or 172, and the total cancer fatalities would be one-half of 286, or 143.
A high degree of uncertainty is associated with calculating cancer incidence and cancer fatalities over 10,000 years. Changes in population density, climate, use restrictions, and many other factors can affect these calculations. Therefore, the total cancer incidence and cancer fatalities should be considered rough approximations only and have been rounded to one significant digit in the text and Summary of this EIS.
D.5. 15 .2 Total Health Impacts Along the Columbia River
Different contaminants will enter the groundwater and reach the Columbia River at varying times in the future. The contaminants time of first arrival at the Columbia River, the time that peak concentration is reached, and the time of final arrival of a contaminant are dependent not only on the transport properties of the contaminant, but also on the alternative under consideration. Transport of contaminants through the groundwater is described in detail in Volume Four, Appendix F. A summary of first arrival times, times of peak concentration, and times of final arrival is shown in Table D.5. 15 .2 for C-14, I-129, Tc-99, U-238, and Np-237. This table also shows the total inventory in curies for each radionuclide, taking into account radioactive decay from the present until the time of peak concentration.
Total cancer fatalities are calculated using factors that relate the number of fatal cancers to the curies of each contaminant that is released to the river. These factors are calculated by using a computer program for calculating population dose integrated over 10,000 years, which estimates the time integral of collective dose over a period of up to 10,000 years for time variant radionuclide releases to surface waters, such as rivers (DOE 1987).
For long-term releases of radionuclides to the Columbia River, estimated downriver population totals are needed. For purposes of the TWRS EIS it is assumed that the potentially affected downriver population is 500,000, a number that has been used previously (DOE 1987).
A summary of the calculation results for total fatalities, population dose in person-rem, and the maximum incremental dose in mrem is shown in Table D.5. 15 .3.
D.5.16 RISK RANGE
The post-remediation risk calculations presented in Section D.5.0 contain a number of conservative assumptions designed to ensure that the results provide an upper bound of the long-term risk associated with the TWRS alternatives. For comparison purposes, a nominal case has also been evaluated. The nominal case is based on most likely rather than conservative assumptions. Evaluation methods for the nominal case were identical to the bounding case. This section presents 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.
D.5.16.1 Maximum Risk Range
Tables D.5.16.1 and D.5.16.2 show the maximum calculated values for ILCR and noncarcinogenic chemical hazard for the bounding case and nominal case, respectively. Values shown on these tables are the highest values calculated for each exposure scenario and time period under each alternative. The risk range can be determined by comparing values on the bounding case table with their corresponding values on the nominal case table. For example, under the bounding case the post-remediation risk to the residential farmer at 300 years for the No Action alternative is calculated to be 4.58E-01 (Table D.5.16.1). Under the nominal case, this risk is calculated to be 1.92E-01. (Table D.5.16.2).
Table D.5.16.1 Summary of Bounding Case Maximum Incremental Lifetime Cancer Risk and Hazard Indicies
Table D.5.16.2 Summary of Nominal Case Maximum Incremental Lifetime Cancer Risk and Hazard Indicies
D.5.16.2 Total Health Impacts Range
Table D.5.16.3 shows the total post-remediation cancer incidence and fatalities calculated over a 10,000-year period for the nominal case. The corresponding values for the bounding case are shown in Table D.5.15.1. The risk range can be determined in the same manner as discussed above for the maximum risk range. For example, under the bounding case for the No Action alternative, the total cancer incidence for the residential farmer over 10,000 years is calculated to be 759 (Table D.5.15.1). Under the nominal case, the corresponding cancer incidence is calculated to be 626 (Table D.5.16.3).
D.5.17 UNCERTAINTY
The uncertainty analyses for post-remediation risk assessment are based on the HSRAM uncertainty analysis. The carcinogenic and noncarcinogenic risk presented in the post-remediation risk evaluation are estimates given multiple assumptions about exposures, toxicity, and other variables. The uncertainties are inherent (e.g., toxicity values, default exposure parameters) or specific (e.g., data evaluation, contaminant identification) in the risk assessment process. Specific considerations in evaluating uncertainty are Site-specific factors, exposure assessment factors, toxicity assessment factors, and risk characterization factors . A detailed discussion of uncertainty in the post-remediation risk assessment is provided in Volume Five, Appendix K.
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