This report presents a strategy for sealing exploratory boreholes associated with the Yucca Mountain Site Characterization Project. Over 500existing and proposed boreholes have been considered in the development of this strategy, ranging from shallow (penetrating into alluvium only) to deep (penetrating into the groundwater table). Among the comprehensive list of recommendations are the following: Those boreholes within the potential repository boundary and penetrating through the potential repository horizon are the most significant boreholes from a perfonnance standpoint and should be sealed. Shallow boreholes are comparatively insignificant ,andrequire only nominal sealing. The primary areas in which to place seals are away from high-temperature zones at a distance from the potential repository horizon in the Paintbrush nonwelded tuff and the upper portion of the Topopah Spring Member and in the tuffaceous beds of the Calico Hills Unit. Seals should be placed prior to waste emplacement.Performance goals for borehole seals both above and below the potential repository are proposed. Detailed construction information on the boreholes that could be used for future design specifications is provided along with a description of the environmental setting, i.e., the geology, hydrology, and the in situ and thermal stress states. A borehole classification scheme based on the condition of the borehole wall in different tuffaceous units is also proposed. In addition, calculations are presented to assess the significance of the boreholes acting ,as preferential pathways for the release of radionuclides.Design calculations are presented to answer the concerns of when, where, and how to seal. As part of the strategy development, available technologies to seal exploratory boreholes (including casing removal, borehole wall reconditioning, and seal emplacement) are reviewed. It is recommended that the surface-based site characterization program maintain exploration boreholes with casing so that seals can be placed at selected sealing locations, that grout not be introduced at sealing locations, and that work plans for drilling additional boreholes be developed that address sealing issues. Borehole-specific sealing plans should also be developed. _3__TIONOF THIS DOOU ' IMIT,

Subsidence effects at the WIPP site were estimated using numerical methods as well as the influence function method and NCB method because a single Universally accepted method is not available for salt. The use of parallel methods and the agreement between their results gnxtly enhanced the confidence in the analysis because the prediction would not depend on the assumptions inherent in a single method. ~~Les effets d'affaissement a site WIPP etaient estimk en utilisant les m6thodes num6riques et aussi avec la m6thode de fonction d'influence et la mCthode de NCB. Ceci est A cause de non-existence d'une seule m6thode acceptable universale pour le sel. L'utilisation des m6thodes en paralleles et l'accord entre leurs resultats augmentent la cogidence des resultats obtenue parceque la prediction ne depend pas sur les suppositions hherentes d'une seule m6thode.