Engineering topics

Parker, Jack C.

Publications and source records attributed to Parker, Jack C..

4 records

DOE OSTI2018

Improved Method for Estimating Reaction Rates During Push‐Pull Tests

Abstract The breakthrough curve obtained from a single‐well push‐pull test can be adjusted to account for dilution of the injection fluid in the aquifer fluid. The dilution‐adjusted breakthrough curve can be analyzed to estimate the reaction rate of a solute. The conventional dilution‐adjusted method assumes that the ratios of the concentrations of the nonreactive and reactive solutes in the injection fluid vs. the aquifer fluid are equal. If this assumption is invalid, the conventional method will generate inaccurate breakthrough curves and may lead to erroneous conclusions regarding the reactivity of a solute. In this study, a new method that generates a dilution‐adjusted breakthrough curve was theoretically developed to account for any possible combination of nonreactive and reactive solute concentrations in the injection and aquifer fluids. The newly developed method was applied to a field‐based data set and was shown to generate more accurate dilution‐adjusted breakthrough curves. The improved dilution‐adjusted method presented here is simple, makes no assumptions regarding the concentrations of the nonreactive and reactive solutes in the injection and aquifer fluids, and easily allows for estimating reaction rates during push‐pull tests.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

Fate and transport of uranium (VI) in weathered saprolite

We conducted batch and column experiments to investigate sorption and transport of uranium (U) in the presence of saprolite derived from interbedded shale, limestone, and sandstone sequences. Sorption kinetics were measured at two initial concentrations (C0; 1, 10 mM) and three soil:solution ratios (Rs/w; 0.005, 0.25, 2 kg/L) at pH 4.5 (pH of the saprolite). The rate of U loss from solution (mmole/L/h) increased with increasing Rs/w. Uranium sorption exhibited a fast phase with 80% sorption in the first eight hours for all C0 and Rs/w values and a slow phase during which the reaction slowly approached (pseudo) equilibrium over the next seven days. The pH-dependency of U sorption was apparent in pH sorption edges. U(VI) sorption increased over the pH range 4e6, then decreased sharply at pH > 7.5. U(VI) sorption edges were well described by a surface complexation model using calibrated parameters and the reaction network proposed by Waite et al. (1994). Sorption isotherms measured using the same Rs/w and pH values showed a solids concentration effect where U(VI) sorption capacity and affinity decreased with increasing solids concentration. Moreover, this effect may have been due to either particle aggregation or competition between U(VI) and exchangeable cations for sorption sites. The surface complexation model with calibrated parameters was able to predict the general sorption behavior relatively well, but failed to reproduce solid concentration effects, implying the importance of appropriate design if batch experiments are to be utilized for dynamic systems. Transport of U(VI) through the packed column was significantly retarded. We also conducted transport simulations using the reactive transport model HydroGeoChem (HGC) v5.0 that incorporated the surface complexation reaction network used to model the batch data. Model parameters reported by Waite et al. (1994) provided a better prediction of U transport than optimized parameters derived from our sorption edges. The results presented in this study highlight the challenges in defining appropriate conditions for batch-type experiments used to extrapolate parameters for transport models, and also underline a gap in our ability to transfer batch results to transport simulations.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2013

U(VI) bioreduction with emulsified vegetable oil as the electron donor-- Microcosm tests and model development

Microcosm tests were conducted to study U(VI) bioreduction in contaminated sediments with emulsified vegetable oil (EVO) as the electron donor. In the microcosms, EVO was degraded by indigenous microorganisms and stimulated Fe, U, and sulfate bioreduction, and methanogenesis. Removal of aqueous U occurred concurrently with sulfate reduction, with more reduction of total U in the case of higher initial sulfate concentrations. X-ray absorption near-edge spectroscopy (XANES) analysis confirmed U(VI) reduction to U(IV). As the acetate concentration peaked in 10~20 days in oleate microcosms, the maximum was reached in 100~120 days in the EVO microcosms, indicating that EVO hydrolysis was rate-limiting. The acetate accumulation was sustained over 50 days longer in the oleate and EVO than in the ethanol microcosms, suggesting that acetate-utilizing methanogenesis was slower in the cases of oleate and EVO. Both slow hydrolysis and methanogenesis could contribute to potential sustained bioreduction in field application. Biogeochemical models were developed to couple degradation of EVO, production and oxidation of long-chain fatty acids, glycerol, acetate, and hydrogen, reduction of Fe(III), U(VI) and sulfate, and methanogenesis with growth and decay of microbial functional groups. The models were used to simulate the coupled processes in a field test in a companion article.

Tang, Guoping↗

DOE OSTI2012

A Microsoft Excel Program for Two-Well Tracer Test Data Analysis

Two-well tracer tests are often conducted to investigate subsurface solute transport in the field. Analyzing breakthrough curves in the extraction and monitoring wells using numerical methods is nontrivial due to highly nonuniform flow conditions. We extended, and implemented analytical solutions for the convection-dispersion equation for an injection-extraction well-duplet in a homogeneous confined aquifer under steady state conditions. Functions were provided to calculate the concentrations in the extraction and monitoring wells at any location due to a step or pulse injection. Type curves for a step injection were compared with those calculated by numerically integrating the solution for a pulse injection. The results from the two approaches are similar when the dispersivity is small. As the dispersivity increases, the latter was found to be more accurate but requires more computing time. The code was verified by comparing the results with published type curves and applied to analyze data from the literature. It can be used as a first approximation for two-well tracer test data analysis, and to check accuracy of numerical solutions. The code and example files are publically-available.

54 ENVIRONMENTAL SCIENCES↗