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The objective of these tests was to investigate the hydrological properties important to repository performance:
The lower lithophysal unit has many fractures that are less than 1 meter in length, and lithophysal cavities ranging in size from 15 to 100 cm. Both the fracture and lithophysal cavity size and spacing vary significantly along the 5-meter drift walls over an 800-meter stretch within the same unit. Therefore the tests were conducted in 20-m-long boreholes at regularly spaced locations along the drift irrespective of (and unbiased to) specific features from fractures and lithophysal cavities.
A systematic approach was taken in order to gain an understanding of the "average" and the "statistical distribution" of the hydrological characteristics for the spatially heterogeneous unit.
Two criteria governed the design of the equipment system: automation and mobility. Because the field-scale measurements involving liquid flow in unsaturated rocks require continuous testing for periods of weeks to months, the control of test equipment was fully automated to allow the equipment system to be operated remotely with no human presence at the field site. The second criterion of mobility was achieved by designing all equipment needed for the systematic characterization as a complete unit to fit on flatbed rail carts. This design allowed the equipment system to be efficiently transported from one test station to another along the tunnel for testing in the regularly spaced low-angle boreholes.
Hydrologic characterization of the lower lithophysal zone of the Topopah Spring welded tuff zone (Tptpll) was performed in the ECRB Cross-Drift, using the systematic approach of testing at regular intervals. Analyses of data from several sets of tests were performed in 10 zones, using four low-angle boreholes. The results indicated that:
The systematic-testing data set was used for calibration of drift seepage models.