Structural Constraints for Proposed Fort Hancock Low-Level Radioactive Waste Disposal Site (NTP-S34), Southern Hudspeth County, Texas: ABSTRACT

Abstract

Structural complexities reduce the homogeneity necessary for a site characterization model to an unacceptable level for performance assessment for radioactive waste disposal sites. The proposed site lies between the northern, stable Diablo platform and the southern, mobile Mesozoic Chihuahua tectonic belt. Structural movement along this interface has been active for the past 14,000 years. In addition, the area lies along the northern margin of the Permian Marfa basin and the northeastern margin of the deeply faulted Hueco bolson segment of the late Cenozoic Rio Grande rift system. Recent seismic activity with extensive surface rupture in Quitman Canyon (30 mi southeast of the site) is also documented from the 1931 Valentine, Texas, earthquake (6.4 Richter scale). The site is underlain by either a thrust fault or the complex terminus of a Mesozoic thrust fault. This fault is a segment of the continuous thrust sheet extending from exposures in the Sierra Blanc area, 30 mi east (Devil Ridge fault), to the El Paso area west (Rio Grande fault). This segment of the Devil Ridge-Rio Grande thrust is documented by the Haymond Krupp No. 1 Thaxton wildcat drilled at Campogrande Mountain immediately south of the site. The recent rift fault scarp (Campo Grande)more » immediately south of the Thaxton well has a 17-mi surface trace and is, no doubt, related to the subsurface Clint fault to the west in the El Paso area. An additional complexity is the presence of a monoclinal flexure with a minimum of 900 ft of surface relief (2 mi northeast of NTP-S34). A 4.5-mi, east-west, down-to-the-south normal fault occurs near the top of the monocline with a small associated graben. These complexities seriously compromise the proposed Fort Hancock site.« less