Publications

Scenario developments is part of the iterative performance assessment (PA) process for the Waste Isolation Pilot Plant (WIPP). Scenario development for the WIPP has been the subject of intense external review, and is certain to be the subject of continued scrutiny as the project proceeds toward regulatory compliance. The principal means of increasing confidence is this aspect of the PA will be through the use of a systematic and thorough procedure toward developing the scenarios and conceptual models on which the assessment is to be based. Early and ongoing interaction with project reviewers can assist with confidence building. Quality of argument and clarity of presentation in PA will be of key concern. Appropriate tools are required for documenting and tracking assumptions, through a single assessment phase, and between iterative assessment phases. Risks associated with future human actions are of particular concern to the WIPP project, and international consensus on the principles for incorporation of future human actions in assessments would be valuable.

The United States Department of Energy (DOE) is developing the Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico for the disposal of transuranic wastes generated by defense programs. Applicable regulations (40 CFR 191) require the DOE to evaluate disposal-system performance for 10,000 yr. Climatic changes may affect performance by altering groundwater flow. Paleoclimatic data from southeastern New Mexico and the surrounding area indicate that the wettest and coolest Quaternary climate at the site can be represented by that at the last glacial maximum, when mean annual precipitation was approximately twice that of the present. The hottest and driest climates have been similar to that of the present. The regularity of global glacial cycles during the late Pleistocene confirms that the climate of the last glacial maximum is suitable for use as a cooler and wetter bound for variability during the next 10,000 yr. Climate variability is incorporated into groundwater-flow modeling for WIPP PA by causing hydraulic head in a portion of the model-domain boundary to rise to the ground surface with hypothetical increases in precipitation during the next 10,000 yr. Variability in modeled disposal-system performance introduced by allowing head values to vary over this range is insignificant compared to variability resulting from other causes, including incomplete understanding of transport processes. Preliminary performance assessments suggest that climate variability will not affect regulatory compliance.