Microbiological characteristics of pristine and contaminated deep vadose sediments from an arid region

The unsaturated (vadose) zone in arid and semiarid regions can be >100 m thick and may receive little or no moisture recharge from the surface. The microbiological properties of the vadose zone are of interest because of the potential for microorganisms to impact the fate and transport of contaminants in these environments. At numerous sites in the western United States, large volumes of wastewater or process water have been disposed of directly to the surface or shallow subsurface and have subsequently migrated through the vadose zone to the groundwater. The purpose of this study was to determine and compare the microbial properties of pristine and impacted vadose zone sediments. Vadose zone sediments from depths ranging from 24 to 90 m were obtained from 3 boreholes drilled on the Hanford site in south‐central Washington State. One borehole was located in a pristine area and the other two were located in areas where wastewater had been disposed of directly to the surface and near subsurface. An open‐flo...