Biomedical subjects

James W Jawitz

Publications and source records attributed to James W Jawitz.

4 recordsLinked to original sources

PubMed2006

DNAPL source depletion: linking architecture and flux response.

The relationship between dense non-aqueous phase liquid (DNAPL) mass reduction and contaminant mass flux was investigated experimentally in four model source zones. The flow cell design for the experiments featured a segmented extraction well that allowed for analysis of spatially resolved flux information. This flux information was coupled with image analysis of the NAPL spatial distribution to investigate the relationship between flux and the up-gradient NAPL architecture. Results indicate that in the systems studied, the relationship between DNAPL mass reduction and contaminant mass flux was primarily controlled by the NAPL architecture. A specific definition of NAPL architecture was employed where the source zone is resolved into a collection of streamtubes with spatial variability in NAPL saturation along each streamtube integrated and transformed into an effective NAPL content for each streamtube. The distribution of NAPL contents among the streamtubes (NAPL architecture) controlled dissolution dynamics. Two simplified models, a streamtube model and an effective Damkohler number model, were investigated for their ability to simulate dissolution dynamics.

Kinetics↗

PubMed2004

Controlled release, blind test of DNAPL remediation by ethanol flushing.

A dense nonaqueous phase liquid (DNAPL) source zone was established within a sheet-pile isolated cell through a controlled release of perchloroethylene (PCE) to evaluate DNAPL remediation by in-situ cosolvent flushing. Ethanol was used as the cosolvent, and the main remedial mechanism was enhanced dissolution based on the phase behavior of the water-ethanol-PCE system. Based on the knowledge of the actual PCE volume introduced into the cell, it was estimated that 83 L of PCE were present at the start of the test. Over a 40-day period, 64% of the PCE was removed by flushing the cell with an alcohol solution of approximately 70% ethanol and 30% water. High removal efficiencies at the end of the test indicated that more PCE could have been removed had it been possible to continue the demonstration. The ethanol solution extracted from the cell was recycled during the test using activated carbon and air stripping treatment. Both of these treatment processes were successful in removing PCE for recycling purposes, with minimal impact on the ethanol content in the treated fluids. Results from pre- and post-flushing partitioning tracer tests overestimated the treatment performance. However, both of these tracer tests missed significant amounts of the PCE present, likely due to inaccessibility of the PCE. The tracer results suggest that some PCE was inaccessible to the ethanol solution which led to the inefficient PCE removal rates observed. The flux-averaged aqueous PCE concentrations measured in the post-flushing tracer test were reduced by a factor of 3 to 4 in the extraction wells that showed the highest PCE removal compared to those concentrations in the pre-flushing tracer test.

Environmental Pollutants↗

PubMed2003

Rate-limited solubilization of multicomponent nonaqueous-phase liquids by flushing with cosolvents and surfactants: modeling data from laboratory and field experiments.

The impact of rate-limited mass transfer on in-situ cosolvent and single-phase microemulsion flushing for the solubilization of multicomponent nonaqueous-phase liquids (NAPLs) was investigated. Laboratory and field data from both cosolvent and microemulsion flushing studies were modeled using a one-dimensional flow, enhanced-dissolution code. Transport of the flushing agents was described with a one-dimensional advection-dispersion model; more complex heterogeneities encountered at the field scale were characterized using the superposition of two solute transport equations. Cosolvent and microemulsion flushing solubilize NAPLs by different mechanisms. The modeling results presented here show that nonequilibrium effects influence both of these processes differently. Solubilization of individual constituents by cosolvents was limited by the rate of diffusion or transport of the component through the organic phase, while the rate-limiting step for microemulsification was independent of the NAPL constituent and was likely external to the organic phase. These data indicate that by accounting for field-scale hydrodynamic variability, laboratory-measured nonequilibrium parameters may be used to accurately predict field-scale nonequilibrium NAPL solubilization. Finally, the effects of field-scale media heterogeneity are likely to dominate those of weakly rate-limited dissolution, and accurate characterization of the former may be sufficient for adequate prediction of field-scale NAPL solubilization.

Diffusion↗

PubMed2002

Controlled release, blind tests of DNAPL characterization using partitioning tracers.

The partitioning tracer technique for dense nonaqueous phase liquid (DNAPL) characterization was evaluated in an isolated test cell, in which controlled releases of perchloroethylene (PCE) had occurred. Four partitioning tracer tests were conducted, two using an inverted, double five-spot pumping pattern, and two using vertical circulation wells. Two of the four tests were conducted prior to remedial activities, and two were conducted after. Each test was conducted as a "blind test" where researchers conducting the partitioning tracer tests had no knowledge of the volume, method of release, nor resulting spatial distribution of DNAPL. Multiple partitioning tracers were used in each test, and the DNAPL volume estimates varied significantly within each test based on the different partitioning tracers. The tracers with large partitioning coefficients generally predicted a smaller volume of PCE than that expected based on the actual release volume. However, these predictions were made for low DNAPL saturations (average saturation was approximately 0.003), under conditions near the limits of the method's application. Furthermore, there were several factors that may have hindered prediction accuracy, including tracer degradation and remedial fluid interference.

Alcohols↗