AMBIENT RADIONUCLIDES IN SURFACE WATERS OF THE UPPER ROANOKE RIVER BASIN OF VIRGINIA

In response to concerns over the potential development of uranium deposits in the headwaters of the Upper Roanoke River Basin—the source of drinking water for numerous communities downstream—the U.S. Geological Survey sampled at eight sites along Whitethorn Creek, the Banister and Roanoke Rivers and Lake Gaston in December 2011 and August 2012 to represent water-quality conditions at high and low flows, respectively. These analytical results provide a range of baseline ambient radionuclide data in order to evaluate changes should uranium deposits be developed in the future. Water samples were analyzed for isotopes of uranium (²³⁴U, ²³⁵U, and ²³⁸U), thorium (²²⁸Th, ²³⁰Th, and ²³²Th), radium (²²³Ra, ²²⁴Ra, ²²⁶Ra, and ²²⁸Ra), and radon (²²²Rn) as well as major dissolved inorganic and trace metals. In addition, gross alpha and gross beta (72-hour and 30-day) radioactivities were determined at each site and field properties (water temperature, specific conductance, pH, dissolved oxygen, and alkalinity) were measured.

Dissolved natural uranium concentrations were below 0.1 microgram per liter and generally increased as values of specific conductance, total dissolved solids, and alkalinity increased. Radionuclides and gross alpha and beta activities were either not detected or at levels well below established drinking water standards at all sampling sites. Analytical results for the radionuclides were consistently higher for the Roanoke (Staunton) River at Randolph site than those for the sites in the basins draining the Coles Hill uranium deposit. The gross alpha and beta activities indicate that surface waters in the Upper Roanoke River Basin are dominated by radionuclides with relatively short half-lives. Although U- and Ra-isotopes were detected at seven sites, the results between the 2011 and 2012 sampling runs were rarely consistent. The U- and Ra-isotopes were detected above Kerr Reservoir, but were not detected at the site on the Roanoke River below the reservoir.