Hydrogeochemical and mineralogical factors influencing uranium in background area groundwater wells: Grants, New Mexico

• Main Authors: Shannon Ulrich, Jeffrey Gillow, Shawn Roberts, Gregory Byer, Julie Sueker, Kathryn Farris
• Format: Article
• Language: English
• Published: Elsevier 2019-12-01
• Series: Journal of Hydrology: Regional Studies
• Online Access: http://www.sciencedirect.com/science/article/pii/S221458181930134X

Study region: Lower San Mateo Creek Basin (SMCB), New Mexico Study focus: Groundwater in the alluvial aquifer of the lower SMCB has a high concentration of total dissolved solids, alkalinity, and dissolved uranium at concentrations above USEPA limits; the source of the water quality was investigated through evaluation of geology, mineralogy, and geochemistry of sediments and groundwater. Surface-expressing bedrock in the larger Basin is dominated by uranium-bearing units such as the Morrison Formation and Dakota Sandstone; erosion of these units contributed sediment to Quaternary alluvium valley fill in the Basin with heterogeneous distribution of uranium. The potential for uranium-bearing alluvial fill to affect the groundwater quality was investigated upgradient of the Grants Reclamation Project (GRP), a former uranium milling facility in the lower SMCB, by hydrogeochemical and geophysical methods. New hydrological insights for the region: Uranium is primarily associated with fine-grained materials (clay/silt) and is labile depending upon sediment geochemical conditions. Natural occurrence of uranium minerals in SMCB alluvial sediments here results in concentrations in groundwater greater than the USEPA water quality standards; as such, site-specific standards are established and supported by the findings of this work. Regional groundwater systems, derived from weathered mineralized bedrock, require careful evaluation of water quality to understand background conditions; uranium in groundwater results from hydrogeochemical processes at the interface of fine and coarse grained sediments within the aquifer. Keywords: Grants mineral belt, San Mateo Creek Basin, Eroded sandstone bedrock, Alluvial aquifer, Uranium, Lithologic analysis