An Aerial Radiological Survey of the Yucca Mountain Project Proposed Land Withdrawal and Adjacent Areas

An aerial radiological survey of the Yucca Mountain Project (YMP) proposed land withdrawal was conducted from January to April 2006, and encompassed a total area of approximately 284 square miles (73,556 hectares). The aerial radiological survey was conducted to provide a sound technical basis and rigorous statistical approach for determining the potential presence of radiological contaminants in the Yucca Mountain proposed Land withdrawal area. The survey site included land areas currently managed by the Bureau of Land Management, the U.S. Air Force as part of the Nevada Test and Training Range or the U.S. Department of Energy (DOE), National Nuclear Security Administration Nevada Site Office (NNSA/NSO) as part of the Nevada Test Site (NTS). The survey was flown at an approximate ground speed of 70 knots (36 meters per second), at a nominal altitude of 150 ft (46 m) above ground level, along a set of parallel flight lines spaced 250 ft (76 m) apart. The flight lines were oriented in a north-south trajectory. The survey was conducted by the DOE NNSA/NSO Remote Sensing Laboratory-Nellis, which is located in Las Vegas, Nevada. The aerial survey was conducted at the request of the DOE Office of Civilian Radioactive Waste Management. The primary contaminant of concern was identified by YMP personnel as cesium-137 ({sup 137}Cs). Due to the proposed land withdrawal area's proximity to the historical Nuclear Rocket Development Station (NRDS) facilities located on the NTS, the aerial survey system required sufficient sensitivity to discriminate between dispersed but elevated {sup 137}Cs levels from those normally encountered from worldwide fallout. As part of that process, the survey also measured and mapped the exposure-rate levels that currently existed within the survey area. The inferred aerial exposure rates of the natural terrestrial background radiation varied from less than 3 to 22 microroentgens per hour. This range of exposure rates was primarily due to the surface geological features within the survey area. The survey area has extensive areas of desert valleys, mountain ranges, extinct volcanic cones, and old lava flows. With the exception of five areas identified within the NRDS boundaries (discussed later in this report), there were no areas within the survey that exceeded aerial survey minimum detectable concentration levels of 0.4 through 0.7 picocuries per gram (pCi/g). The {sup 137}Cs levels do not exceed typical worldwide fallout levels for the continental United States