The Amargosa Desert Research Site (ADRS), in the northern Mojave Desert, is about 20 km east of Death Valley National Park. Recognizing the paucity of information on unsaturated-zone hydrology in arid regions, the USGS, in 1983, established the ADRS through agreements with the Bureau of Land Management (BLM) and the State of Nevada. The ADRS serves as a field laboratory for the study of arid-land processes. The ADRS includes two field study areas: a 16-ha area adjacent to a waste-burial facility 17 km south of Beatty and 0.1-ha area about 3 km south of the waste facility.
The Beatty facility was the first commercially operated low-level radioactive waste site in the United States. Burial-trench construction entailed excavation of native soil, emplacement of waste, and backfilling with previously stockpiled soil. The surfaces of completed burial trenches and perimeter areas were kept free of vegetation. Upon closure of the low-level radioactive waste facility, the radioactive-waste trench area was capped with a minimum 2-m thick cover of stockpiled soil. In addition to the burial of low-level radioactive waste (1962-92), the facility is used to dispose of hazardous chemical waste (1970 to present). Lining of low-level radioactive waste trenches was not required; lining of chemical waste trenches was required beginning in 1988.
The northern Mojave Desert is one of the driest regions in the United States. Annual precipitation at the ADRS averages 112 mm (1981-2005) and has ranged from 3.5 mm during 2002 to 225 mm during 1983 (Johnson and others, 2007). About 70 percent of the precipitation is associated with frontal systems during October through April. Snow, however, is rare. Summer rainfall occurs predominantly during localized, short-duration, convective storms. Annual potential (pan) evaporation is about 1900 mm (Nichols, 1987). Monthly mean air temperatures range from 3°C during December to 33°C during July (Andraski and others, 1995).
The study area is about 845 m above sea level. Vegetation in the area is sparse; creosote bush [Larrea tridentata (DC.) Cov.], an evergreen shrub, is the dominant species. Soils and sediments are typically coarse textured and highly stratified (Andraski, 1991, 1996). Sediments in the area are largely unconsolidated fluvial and alluvial fan deposits that are at least 170 m thick (Nichols, 1987). The water table in the area ranges from about 85 to 115 m below land surface (Fischer, 1992).
An infrastructure that can support field research of processes that control water, gas, and chemical movement at the ADRS has evolved over more than two decades of USGS work at the site. The USGS-Nevada Water Science Center maintains field areas and experimental sites established to represent undisturbed- and disturbed-surface conditions. Meteorological data are collected by an automated weather station (e.g., Johnson and others, 2007). An instrument shaft was designed and installed (1983) to facilitate emplacement and maintenance of electronically based measurement devices in the upper 13 m of the unsaturated zone beneath an undisturbed, vegetated area (Morgan and Fischer, 1984; Fischer, 1992).
Three disturbed sites established in 1987 allow study of arid-site processes under simulated solid-LLRW-burial and nonvegetated-surface conditions (Andraski, 1996, 1997). Thermocouple psychrometers are used to measure subsurface water potentials and temperatures and a neutron-moisture probe is used to measure water content to a maximum depth of 33 m.
Telecommunication systems are used for remote retrieval of data from dataloggers at the 16-ha research area. Arrays of soil-gas probes and plant-sample sites allow for periodic collection and analysis of the chemical composition of unsaturated zone air and plant water. In addition, deep test holes drilled at the two field study areas have been used for measurements of water potential, temperature, and air pressure, and for collection of soil gas samples throughout the thick unsaturated zone (Fischer, 1992; Prudic and Striegl, 1995; Andraski and Prudic, 1997; Prudic and others, 1999; Andraski, 2005).