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D.1.0 INTRODUCTION

This appendix describes the analysis of anticipated risk for the Tank Waste Remediation System (TWRS) Environmental Impact Statement (EIS). Risk is defined as the number or degree of human health or ecological effects from exposure to radiation and chemicals resulting from TWRS activities during and after remediation. The mission of TWRS is to manage and dispose of TWRS waste, including current and future tank waste, associated inactive miscellaneous underground storage tanks (IMUSTs), and cesium (Cs) and strontium (Sr) capsules in an environmentally sound, safe, secure, and cost-effective manner. Sections D.1.0 through D.5.0 of this appendix address the methodology and results of the human health risk assessment. Section D.6.0 presents the methodology and results of the ecological risk assessment. Section D.7.0 presents the methodology and results of the assessment of risks from inadvertent human intrusion into the residual waste after remedial actions are complete. This EIS analyzes the following alternatives for remediation, which are discussed in Volume Two, Appendix B:

• Tank Waste
  • No Action alternative (Tank Waste)
  • Long-Term Management alternative
  • In Situ Fill and Cap alternative
  • In Situ Vitrification alternative
  • Ex Situ Intermediate Separations alternative
  • Ex Situ No Separations alternative
  • Ex Situ Extensive Separations alternative
  • Ex Situ/In Situ Combination 1 alternative
  • - Ex Situ/In Situ Combination 2 alternative
  • Phased Implementation alternative
• Capsule
  • No Action alternative (Capsules)
  • Onsite Disposal alternative
  • Overpack and Ship alternative
  • Vitrify with Tank Waste alternative.

The scope of the risk assessment includes risk associated with conditions during and after the remedial actions. The assessment evaluates three primary types of risk: 1) risk associated with baseline conditions (No Action alternative); 2) risk associated with the TWRS EIS remedial action alternatives; and 3) risk associated with residual (post-remediation) contamination.

Baseline risk is the risk to a land user in the absence of remedial actions. Depending on the land-use scenario, the receptor for baseline conditions may be exposed to contaminated media through one or more pathways. For purposes of this assessment, the No Action alternatives (Tank Waste and Capsules) are considered the baseline.

Remedial action risk is separated into risk from routine operations and risk from accidents. Risk from routine operations is addressed in this appendix and consists of the risk to TWRS workers, noninvolved workers on the Hanford Site, and the general public resulting from remediation associated with the remedial action alternatives. Risk from accidents is addressed in Volume Four, Appendix E.

Post-remediation risk is the risk resulting from residual contamination remaining onsite after remediation is completed. The receptors and potential exposure pathways for post-remediation risk are based on land use and are identical to those used for baseline risk.

Table D.1.0.1 shows the three primary categories of risk along with key assumptions used in the analysis.

Table D.1.0.1 Primary Risk Types and Risk Assessment Assumptions

The objective of this risk assessment is to support the analysis of environmental consequences by providing estimates of the following:

• Noncarcinogenic toxic effects, expressed as a hazard index (HI), attributable to each EIS alternative. The hazard index is a comparison of the estimated exposure to a chemical threshold value below which no toxic effects are expected;
• Latent cancer fatalities (LCFs) and incremental lifetime cancer risks (ILCRs) attributable to each alternative from routine operations during remedial actions. LCFs are the increases in number of cancer fatalities resulting from exposure to potential radiological carcinogens. ILCRs are the increased probability of developing cancer as a result of exposure to chemical carcinogens;
• Incremental lifetime cancer incidence attributable to post-remediation conditions for each alternative and subalternative. Incremental lifetime cancer incidence is the increased probability of an individual developing cancer over a lifetime (70 years) from exposure to potential carcinogens (both radiological and chemical);
• Risk to ecological receptors for all alternatives; and
• Carcinogenic effects attributable to each alternative from inadvertent human intrusion into residual contamination following completion of remedial actions.