Preliminary evaluation of the Eagle Flat region, as designated by the Texas Legislature, indicates several areas that may have geologic and hydrologic conditions favorable for further evaluation as potential siting areas for the Texas low-level radioactive waste repository. This determination is based on a review of available data regarding surface drainage, thickness and character of alluvial fill, depth to groundwater, and apparent presence or absence of such features as late Cenozoic faults, fissures, known natural resources, and evidence of erosion. Some general siting areas have been identified that contain several sections that appear to have favorable characteristics. Examples of apparently favorable general siting areas are east of Yucca Mesa, south of Eagle Flat Mountain, and north of Little Hills. Our preliminary assessment is that, of the three areas cited above, the Yucca Mesa location should be given priority consideration. Initial flooding and drainage analysis indicates that the Yucca Mesa site includes sufficient surface areas unaffected by flooding. There are no known fissures or late Cenozoic faults. Depth to groundwater may be in excess of 500 ft, and the water quality may be poor. Shallow alluvium may be somewhat finer grained than at other settings, and the surface appears to be relatively stable and devoid of major incision by existing drainages. Although each of these characteristics needs to be investigated by further work, the most critical unanswered question is the thickness of alluvial fill. Available gravity data, including recent work by The University of Texas at El Paso, indicates that 100 ft or more of alluvial fill may be present in the area. Other areas may be present that are of equal or similar merit, but the preliminary analysis and available information suggest that the Yucca Mesa location apparently has the most favorable characteristics of those general siting areas identified currently. Smaller potential siting areas, generally about 400 to 800 acres in size, also may exist locally throughout the region where alluvial fill may be of sufficient thickness and drainage characteristics may be appropriate. These smaller potential siting areas would require additional site-specific evaluation of surface drainage characteristics before drill testing could be recommended. Any potential siting area is unique and would require site-specific evaluation activities to assess its suitability for characterization.Bureau of Economic Geolog
