Author Archives: Charles Paradis

Faculty Article on Tracers-Based Separation of Advection and Dispersion

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Dr. Paradis and Rakiba Sultana (PhD Candidate) published a Geoscience Faculty Article titled, Tracer-based Separation of Advection and Dispersion from Breakthrough Curves.  The article describes a method to remove advection and dispersion from the breakthrough curve of a potentially reactive solute to visualize and quantify reactivity, all without the need to solve the advection-dispersion-reaction equation or transform true concentrations.  The article can be found here: https://dc.uwm.edu/geosci_facart/28/

Breakthrough curve of manganese showing measured concentration (msd ─■─), expected concentration from advection and dispersion only (adv ─□─) via Equation (1), injection concentration (inj —), and background concentration (bkg ─)

New Publication in Special Issue of Weathering of Mine Wastes

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Two cross-hole tracer tests and one infiltration tracer test were completed at a former uranium mill site in Grand Junction, Colorado. Reactive transport modeling was completed to derive physical and geochemical parameters. The observed data from saturated zone cross-hole tracer testing was adequately simulated using PHT-USG (reactive transport model) and PEST++ (calibration routine) with reasonable estimates of hydraulic conductivity, dispersion, effective porosity, cation exchange, calcite saturation index, and uranium sorption potential. The use of multiple layering in one cross-hole model was able to capture hydraulic conductivity variations with depth, which produced a double hump in the tracer concentrations. The complete article can be downloaded here: https://www.mdpi.com/2075-163X/13/7/947

100-series well constructions with injection and pumping pattern in relation to hydrogeology and solid-phase uranium concentrations. Red shading indicates depths with solid-phase uranium concentrations that are above background. Depths are to scale with two times horizontal exaggeration. Well 0105 is beyond the plane of the page (Figure 2). Arrows indicate flow directions.

 

New Publication on Alkalinity Enhanced Uranium Flushing

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Dr. Martin Dangelmayr (post-doc) and Cullen Meurer (former master’s student) published a cutting-edge technical article titled, Desorption and co-dissolution of uranium-bearing solids during alkalinity enhanced flushing of contaminated sediments, in the journal Groundwater Monitoring and Remediation.  The results of this research showed that alkalinity enhanced flushing of uranium could be employed as a viable remediation scheme if calcite precipitation could be minimized in a field application.

New Publication on Modeling Uranium Transport Parameters

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A new research article titled, Single-Well Push–Pull Tracer Test Analyses to Determine Aquifer Reactive Transport Parameters at a Former Uranium Mill Site (Grand Junction, Colorado), was recently published in the scientific journal Minerals.  This research used PHREEQC (geochemistry), PHT-USG (flow and transport), and PEST (calibration) to understand the importance of cation exchange, sorption, and gypsum dissolution on the fate and transport of uranium at a former mill tailings site.

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Figure 9. Model fit for uranium in all PPT wells, with and without gypsum addition for wells 0120 and 0121. Phases are: (1) traced river water injection, (2) untraced river water injection (chase), (3) drift phase, and (4) pumping phase. Posted values are the GC_s uranium sorption parameter values (moles/kg-water) for the upper and lower sensitivity testing (gray dashed curve) and the calibrated value from Table 4 (solid blue curve). GC_s values in bold italics indicate the authors’ picks for the best final values.

New Publication on Uranium Mobility

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A field tracer study was just published in the Journal of Contaminant Hydrology, titled, “Elucidating mobilization mechanisms of uranium during recharge of river water to contaminated groundwater“.  This publication was based on the master’s thesis of Kendyl Hoss (link to the Hoss thesis HERE).  This publication demonstrated that solid-phase uranium, in equilibrium with aqueous-phase uranium, may not be readily mobilized when recharged with uranium-free water, i.e., concentration-dependent uranium desorption and/or dissolution may be a very slow process; this has implications on the time it may take for uranium to flush from a contaminated site.

Pre-test isoconcentration profile map of uranium (mg/kg) on aquifer sediments (5% nitric acid leached) above and below baseflow water table (≈ 4.5 ft bgs, ≈ 1.4 m bgs) along A to A’ transect (Fig. 4), bgs = below ground surface, distance from A to A’ is 20 ft (6.1 m), depth is 13 ft (4.0 m).

Master’s Research Assistant Position in Contaminant Hydrogeology

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The Paradis Lab at UW-Milwaukee has a fully funded, two-year, master’s research assistant position beginning in the spring of 2023.  This position is funded by the NSF with an annual stipend of $26,180 and includes a tuition waiver, health benefits, and supplemental dental and/or vision insurance; additional financial support may be available via Department awards and University fellowships.  This position aims to elucidate the biogeochemical reactions that are likely responsible for mobilizing uranium under oxygen- and carbonate-rich conditions in groundwater.

This position will primarily require computational modeling of previously collected field experimental data and may include designing and conducting new laboratory experiments; field-based research will likely be minimal.  Strong applicants will hold a bachelor’s degree in geology with coursework that includes one year each of calculus, physics, and chemistry, one summer of field-based training in geology, and at least one course each in hydrogeology and computer programming.  Exceptional applicants will also have field- and lab-based research experience in contaminant hydrogeology and groundwater flow/contaminant transport modeling with computer programs such as MODFLOW, MT3D, PHREEQC, and PEST.

Interested applicants should write a one-page cover letter (pdf) that answers the following three questions: 1) How are you qualified for this position? 2) Why do you want this position? and 3) What will you do with your master’s degree? to Dr. Charles J. Paradis at paradisc@uwm.edu with the subject heading as follows: “MS App U-Mobility Last Name First Initial”.

Post-doc Publishes on Uranium Sorption to Rocks in Negev Desert, Israel

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Dr. Martin Dangelmayr’s research on uranium sorption to four different types of rocks (organic-rich phosphorite, a bituminous marl, a chalk, and a sandstone) in the Negev Desert in Israel was recently published in Minerals (link to open source). These rocks are being considered as potential hosts for spent nuclear fuel, thus their sorption capacity for uranium is very important.