Geotechnical Field Measurements for Evaluation of the WIPP Site

Since 1974 the northern Delaware Basin of New Mexico has been the focus of intensive geotechnical investigations in the Department of Energy (DOE) program to site and develop a geologic facility to demonstrate the safe disposal of defense transuranic (TRU) waste. This facility, the Waste Isolation Pilot Plant (WIPP), is now proposed for a location 25 miles east of Carlsbad, New Mexico. The waste will be placed in rooms excavated in the salt beds of the Salado formation 2150 feet below the land surface. To ascertain whether the geology and hydrology of the site and region are acceptable has required extensive drilling and surface based geologic mapping and geophysical exploration. Geophysical surveys, epecially seismic and gravity, have proven useful in mapping subsurface structures in the site area. Long-term safety considerations prevent drilling deep holes (i.e., through the salt) in the immediate repository area, but holes up to 4000 feet deep have been drilled to confirm the geophysical interpretations, to obtain samples for analysis and to allow determination of hydrologic parameters in the potential aquifers above the salt beds. Seventy-four exploratory holes have been drilled for a total of more than 103,000 feet, of which 32,000 feet were cored. More than 30 of these holes have been used to obtain hydrologic data. This paper will focus on two particular aspects of the WIPP site investigations in order to illustrate the methods and techniques by which data were obtained for analysis and evaluation.