Wednesday, April 14, 2010: 4:00 p.m.
Continental A (Westin Tabor Center, Denver)
Elevated concentrations of uranium and arsenic are found in groundwaters on the eastern side of Espaņola Basin in northern New Mexico. Between Santa Fe and Nambe, a distance of about 25 miles, over half of the domestic wells have uranium concentrations exceeding EPA's maximum contaminant level (MCL) of 30 ppb uranium. The Espaņola Basin includes the watershed of the Rio Grande and is part of the Rio Grande Rift. In June 2009, we sampled over 500 domestic wells on the eastern side of the Espaņola Basin. Groundwater samples were analyzed at Los Alamos National Laboratory for major cations, anions, trace elements, and stable isotopes of hydrogen and oxygen. Results were analyzed using GIS, geochemical modeling and data analysis. Along the presumed flow path, east to west, total dissolved solids (TDS), uranium, and bicarbonate concentrations are low in the Sangre de Cristo Mountains, significantly higher in the foothills, and then gradually become lower approaching the Rio Grande. Mixing models support several sources of water in the Espaņola Basin containing variable concentrations of arsenic and uranium. Previous work on Chimayo Geyser, located north of Santa Fe in the foothills of the Sangre de Cristo Mountains, found high concentrations of dissolved carbon dioxide (Keating et al., 2009). The geyser is on the Chimayo Fault, a deep tectonic rift fault that trends north south for approximately 100 miles through the foothills of the Sangre de Cristo. We hypothesize that the carbon dioxide is widespread through the Chimayo Fault having implications for metal mobility, mixing, and the observed high TDS and uranium in the Sangre de Cristo foothills.
(Keating, E., Fessenden, J., Kanjorski, N., Koning, D., Rajesh, P., 2009, The impact of CO2 on shallow groundwater chemistry: observations at a natural analog site and implications for carbon sequestration, Environmental Earth Sciences, doi: 10.1007/s12665-009-0192-4.)