Flow and transport in unsaturated fractured rock: Effects of multiscale heterogeneity of hydrogeologic properties
The heterogeneity of hydrogeologic properties at different scales may have different effects on flow and transport processes in a subsurface system. A model for the unsaturated zone of Yucca Mountain, Nevada, is developed to represent complex heterogeneity at two different scales: (1) layer scale corresponding to geologic layering and (2) local scale. The layer-scale hydrogeologic properties are obtained using inverse modeling, based on the available measurements collected from the Yucca Mountain site. Calibration results show a significant lateral and vertical variability in matrix and fracture properties. Hydrogeologic property distributions in a two-dimensional, vertical cross section of the site are generated by combining the average layer-scale matrix and fracture properties with local-scale perturbations generated using a stochastic simulation method. The unsaturated water flow and conservative (nonsorbing) tracer transport through the cross section are simulated for different sets of matrix and fracture property fields. Comparison of simulation results indicates that the local-scale heterogeneity of matrix and fracture properties has a considerable effect on unsaturated flow processes, leading to fast flow paths in fractures and the matrix. These paths shorten the travel time of a conservative tracer from the source (repository) horizon in the unsaturated zone to the water table for small fractions of total released tracer mass. As a result, the local-scale heterogeneity also has a noticeable effect on global tracer transport processes, characterized by an average breakthrough curve at the water table, especially at the early arrival time of tracer mass. However, the effect is not significant at the later time after 20 percent tracer mass reaches the water table. The simulation results also verify that matrix diffusion plays an important role in overall solute transport processes in the unsaturated zone at Yucca Mountain.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Office of Civilian Radioactive Waste Management. Yucca Mountain Site Characterization Office (US)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 807412
- Report Number(s):
- LBNL-50503; JCOHE6; R&D Project: 80NB7A; B& R 820101000; TRN: US0301822
- Journal Information:
- Journal of Contaminant Hydrology, Vol. 60, Issue 1-2; Other Information: Journal Publication Date: January 2003; PBD: 9 Jul 2002; ISSN 0169-7722
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
CALIBRATION
CROSS SECTIONS
DIFFUSION
FRACTURE PROPERTIES
FRACTURES
NEVADA
SIMULATION
SOLUTES
TRANSPORT
WATER
WATER TABLES
YUCCA MOUNTAIN
HETEROGENEITY FLOW AND TRANSPORT FRACTURES AND MATRIX DUAL-PERMEABILITY MEDIA UNSATURATED ZONE YUCCA MOUNTAIN