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Site Characterization Process

The Department of Energy's (DOE's) 1988 Site Characterization Plan for Yucca Mountain established the initial basis for the many engineering and scientific investigations of the site. It has been conducting site characterization to gather enough information about the Yucca Mountain site to evaluate the waste isolation capabilities. In 1991, the State of Nevada granted the DOE the permits necessary to proceed with certain site characterization activities. These activities included excavating test pits and trenches, drilling bore holes, and monitoring ground water.

In September 1994, the DOE began excavation of the exploratory studies facility using a tunnel boring machine. The initial design called for a continuous tunnel 7.6 meters (25 feet) in diameter. The tunnel was completed in April 1997. The tunnel begins at the North Portal and extends to the northwest approximately 2000 meters (1.24 miles). The tunnel then transitions into an approximately 60 degree turn to the south. The section from the North Portal to the 60 degree turn is known as the North Ramp. The turn from the North Ramp leads to a main tunnel 300 meters (984 feet) below the surface. The main tunnel has a north-south alignment and extends south approximately 3000 meters (1.86 miles). The main tunnel ends in a 90 degree turn. From this turn the tunnel travels east about 1300 meters (0.8 miles) and emerges at the South Portal. The tunnel machine has bored through a series of geologic features including a structural feature known as the Bow Ridge Fault. Within the tunnel are seven testing alcoves and four test niches that are being used to investigate the hydrologic, hydrochemical, and thermomechanical properties of the rocks underlying Yucca Mountain.

In December 1997, the DOE began excavation of a smaller exploratory tunnel (5.5 meters/18 feet) across the main tunnel. This smaller tunnel is known as the "east-west" or "cross" drift and runs almost perpendicular to the North Ramp. The "cross" drift begins to the west of the Bow Ridge Fault and crosses over and above the north-south main tunnel. It is about 2600 meters (1.6 miles) long and ends near the Solitario Canyon Fault. The "cross" drift will also contain instrumentation for scientific tests and should provide additional data on the sub-surface geology of Yucca Mountain to the west of the main tunnel. The layout of both the Exploratory Studies Facility and the Cross Drift can be viewed.

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Thursday, June 12, 2008