Rocky Mountain Section - 64th Annual Meeting (9–11 May 2012)

Paper No. 5
Presentation Time: 2:30 PM


BRYAN, Charles R.1, SIEGEL, Malcolm2, VINSON, David S.3, RAANAN-KIPERWAS, Hadas4, VENGOSH, Avner5 and DWYER, Gary5, (1)Sandia National Laboratories, Albuquerque, NM 87185, (2)School of Medicine, University of New Mexico, Albuquerque, NM 87131, (3)Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721, (4)Wetlands Division, U.S. EPA, Washington, DC 20460, (5)Division of Earth & Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC 27708,

Elevated Ra activities and U concentrations occur in some New Mexico groundwaters, and represent health hazards as Ra can be a significant contributor to the total radioactivity, and U is a nephrotoxin. Data are presented here from three contrasting sites in bedrock aquifers: (1) Wells sampled in Permian sandstones near Glorieta have elevated U (8.5 to 24.2 µg/L) and in one case, elevated Ra (up to >14 pCi/L); (2) a deep well near the Zuni Mountains has highly elevated Ra (>20 pCi/L) and low U; and (3) wells sampled near Laguna Pueblo, in the Jackpile and Brushy Basin Members of the Morrison Formation (units hosting roll-front U deposits nearby), are reducing and have low U and Ra.

Trends in Ra isotope ratios (224Ra/228Ra and 228Ra/226Ra) provide insights into the sources and mobility of U and Ra in these wells, and can influence decisions about water treatment vs. obtaining alternative water sources to meet drinking water standards. The Glorieta waters are oxic, with variable 228Ra/226Ra values, indicating a variable degree of U enrichment in the aquifer sandstones, while 224Ra/228Ra ratios close to one suggest that Ra is labile, sorbing and desorbing rapidly relative to the half-life of 224Ra (3.6 days). In reducing groundwaters near the Zuni Mountains, U concentrations are low. Ra is low in one well but highly elevated in a nearby well, and 228Ra/226Ra values are very low (<0.25), implying enrichment of U in the aquifer sediments. Although U concentrations were low in reducing groundwaters from the Laguna area, low 228Ra/226Ra values (<0.4) suggest enrichment of U relative to Th in the clastic sedimentary aquifer units. 224Ra/228Ra values are variable but overall close to 1. This study used an innovative low-cost method for 226Ra analyses. Radium was concentrated onto Mn oxide coated fibers and counted via decay products after a 20 day incubation period using an inexpensive radon-in-air detector. This technique could be used for low-cost long-term monitoring of water sources or pilot tests for radium treatment.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

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