This technical report presents these assessments of long-term repository performance. It describes the models that the Agency developed specifically for this project, reviews the various assumptions made, and identifies the data used in these models. In general a relatively simple analytical methodology was formulated that should tend to overestimate the long-term risks from geologic repositories. Because much of this methodology is new, and because these risk assessments are a key part of our rulemaking, the Agency is publishing this as a draft report. During the public comment period on 40 CFR 191, a Subcommittee of the Agency's Science Advisory Board will conduct an independent technical review of our risk assessments (48 FR 509). All meetings of this Subcommittee will be announced in the Federal Register and will be open to the public.