The occurrence and persistence of trace elements in groundwater associated with uranium mining are a concern throughout the United States and the globe.  Using published geochemical data from the National Uranium Resource Evaluation (NURE) and USGS National Water Information System (NWIS) databases, the mobility of uranium, arsenic, molybdenum, and selenium were evaluated in groundwater in the alluvium/Beaumont, Chicot and Evangeline Aquifers along the Texas Gulf Coast.  Geochemical data for 2,093 (NURE) and 689 (NWIS) samples were analyzed in a geographic information system (GIS) based on what are referred to in this study as environmental criteria (EC).  EC were determined using Eh and pH ranges for each sample (e.g., reduced and pH 6.5 – 8.5) that can help predict possible element mobility in groundwater and surface water.  Eight EC categories with differing Eh and pH ranges were evaluated.  Twelve-digit hydrologic unit code (HUC) boundaries were used in GIS as analysis areas to determine the most commonly occurring EC category (statistical mode) in each HUC. Resulting maps identify areas having varying potential element mobility and can be evaluated using physical, chemical, and thermodynamic principles associated with geochemical barriers in mining and non-mining environments. Statistical distributions of empirical element concentrations were created for each EC and compared to laboratory reporting levels to identify the mobility of elements.  Uranium is most mobile under oxidizing conditions and pH greater than 6.5 and also mobile under reducing conditions and circumneutral pH.  Arsenic and selenium are mobile across most of the EC categories and molybdenum is predominantly mobile under oxidizing conditions.  Spatial comparisons of EC categories with transmissivity, infiltration, percent sand, depositional environments, and total dissolved solids provide more detailed understanding of the potential for the constituents of concern to occur and persist along the Texas Gulf Coast.  This methodology provides a systematic approach for identifying areas where groundwater near mining may be susceptible to element mobility and may be informative in other locations.

Geochemical and geological assessment of areas susceptible to occurrence and persistence of uranium, arsenic, molybdenum, and selenium related to mining in the Texas Gulf Coast

2019 Spring National Meeting

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