Evolution of the unsaturated zone testing at Yucca Mountain

Area of Science:

• Geology
• Hydrogeology
• Environmental Science

Background:

• Yucca Mountain site evaluation has transitioned from surface investigations to underground drift testing.
• Characterization efforts address key issues within the unsaturated zone (UZ).

Purpose of the Study:

• To summarize the evolution of site characterization activities and prominent issues concerning the unsaturated zone (UZ) at Yucca Mountain.
• To highlight lessons learned from underground testing for future process quantification.

Main Methods:

• Evolved data collection from mapping faults and fractures to estimating percolation and quantifying seepage.
• Conducted fracture-matrix interaction, matrix diffusion, and thermal tests at various scales.
• Evaluated tuff interfaces and local faults in different geological units.

Main Results:

• Demonstrated evolution in data collection from qualitative mapping to quantitative seepage measurements.
• Quantified fracture-matrix interaction and matrix diffusion effects.
• Measured water mobilization and moisture redistribution during thermal tests.

Conclusions:

• Underground testing has refined understanding of hydrological processes in the unsaturated zone.
• Further quantification is needed for migration through the drift shadow zone and liquid flow through faults.