Hydrology of sealing a repository in saturated tuff
In the hydrologic modeling studies it was assumed that the repositories were located in volcanic tuff such as is found in Yucca Mountain at the Nevada Test Site. This modeling study dealt only with repositories in saturated rock and investigated the effects on groundwater flow once drifts and shafts are filled with materials of various permeability. Temperature effects were not examined. Modeling was limited to two dimensions, necessitating simplifying assumptions in some cases. Groundwater flow for the drift model was assumed to be due primarily to a hydraulic head gradient caused by a dipping water table similar to that found in the Yucca Mountain region. In the shaft model a vertical pressure gradient was assumed so that comparisons of sealing designs could be made. Results indicated that observable deviations in the groundwater flow near a repository would occur unless the drifts and shafts were backfilled to a permeability approaching that of the native rock. A series of low permeability blocks in the drifts showed promise in reducing these deviations in groundwater flow, as long as the spacing between blocks remained relatively short (<10 m). Sealing only the intersections of drifts proved ineffective. The preferred orientation for the repository appeared to be one with the emplacement drifts perpendicular to the dominant flow direction. This orientation allowed less water to flow past the waste, and the access drifts could be used to provide a path of least resistance to draw more water away from the emplacement drifts. The most effective measure to prevent large flow rates through vertical shafts was to backfill the shaft to a permeability approaching that of the undisturbed rock. Bulkheads placed in the shaft had little influence on the flow. The effects of a highly permeable disturbed zone 1.37 m in thickness produced by drilling the shaft were also studied.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 59495
- Report Number(s):
- SAND-83-0280; ON: DE83015633
- Resource Relation:
- Other Information: PBD: Mar 1983
- Country of Publication:
- United States
- Language:
- English
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