2025 AIChE Annual Meeting
(21c) Modeling Hydraulic and Contaminant Transport in the Evangeline Aquifer with Modflow-Usg and Phreeqc
In-situ recovery (ISR) was introduced to the uranium mining industry in the 1970s as an alternative to the traditional large-area surface disruption method known as open-pit mining. As of the late 1990s, ISR has been the only method of uranium recovery in Texas. In-situ recovery involves the injection of local groundwater mixed with an acid/base solution below ground several hundred feet into an unconsolidated sandstone uranium-hosted geological formation to produce redox reactions to drive uranium dissolution and mobilization in the ore body. Due to the nature of the chemical interactions occurring within an aquifer, it is imperative to understand the movement and transformational behavior of the possible contaminants in groundwater for hydraulic site control and remediation efforts for ISR operations. This study will focus on the Kingsville Dome (KVD) uranium mining site in Kleberg County, southwest of Corpus Christi. The (KVD) has been in on and off operations between 1988 through 2009. In 2013, the (KVD) entered the restoration phase, and then in 2020, it entered standby and still is today. The KVD’s uranium is hosted in sandstone within the Goliad geological formation located in the Gulf Coast Aquifer. The Gulf Coast Aquifer is a major Texas aquifer consisting of three aquifers: the Chicot Aquifer, the Evangeline Aquifer, and the Jasper Aquifer. The KVD mining depths fall within the Evangeline aquifer. The Evangeline Aquifer is the most productive water-bearing hydrological unit within the Gulf Coast Aquifer, which spans a little over 50 Texas counties and is used for agriculture, domestic and industrial uses. The KVD was owned and operated by Uranium Resources Inc. until Encore Energy purchased it in 2023. This paper will utilize up-to-date and site-specific data available/acquired to create a fate and transport model coupled with a reactive transport model using the software programs MODFLOW-USG for groundwater flow modeling and PHREEQC for geochemical reactive transport simulations. The model initially shows that downgradient contamination mobility within the Evangeline aquifer strongly correlates with redox conditions, ion exchange behavior, and injection and extraction rates. This model will aim to predict changes in groundwater quality from various ISR restoration scenarios. Future models using a similar type of software should be able to test remediation scenarios adequately using various injection fluids. With the re-emergence of the need for domestic uranium production, understanding geochemical changes down-gradient of uranium in situ recovery sites is crucial for evaluating potential impacts on surrounding groundwater quality and flow, which is vital for various stakeholders.